© Baker, J.L. (2009) Marine Species of Conservation Concern in South Australia Full citation Baker, J.L. (2009) Marine Species of Conservation Concern in South Australia: Volume 1 - Bony and Cartilaginous Fishes. Report for the South Australian Working Group for Marine Species of Conservation Concern. J. Baker (consultant); Science and Conservation Division, and Coast and Marine Conservation branches of S.A. Department for Environment and Heritage (DEH); Marine and Coastal Community Network of S.A. (MCCN), and Threatened Species Network (TSN). Web version published by Reef Watch, South Australia.

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Short-finned Eel / Southern Shortfin Eel / Shortfin Eel / Silver Eel

Family Name:	Anguillidae
Scientific Name:	Anguilla australis australis Richardson, 1841
Recommended Status:	South Australia: Rare (A,Di,ii); South-eastern Australia: Near Threatened
Rationale:  Anguilla australis australis is of conservation concern, due to (i) narrow habitat range within a key part of the life cycle: i.e. the species is dependent for part of its life upon a small number of estuaries and lowland rivers, particularly in cool temperate regions, and impacts upon the quality of critical habitat may affect this species; (ii) slow growth rate; (iii) late sexual maturity, particularly for females (iv) relatively long-lived (more than 30 years) and complex life cycle, involving extensive migration, and (iv) erratic and variable recruitment over space and time. These characteristics make populations intrinsically vulnerable to population decline, and susceptible to over-exploitation. In South Australia, there are few recent records, with most of those from the lower South-East. In South Australia, this species has a limited area of available habitat in coastal wetland systems, and the quality and quantity of critical estuarine and riverine habitat has declined in South Australia during the past few decades. Eel fisheries in western Victoria may also impact upon the South Australian population, but movement patterns into South Australia, and natural abundances over space and time, are not well known. In south-eastern Australia, this species is fully fished, but in some areas (e.g. Victoria) there are numerous management actions in place to ensure that wild populations are not over-harvested. Despite management controls, Short-finned Eel populations, which naturally change over time due to variable recruitment, face a number of on-going threats, including long-term impacts. Examples include: reduced river flows over space and time (from both environmentally-determined and anthropogenic reasons); interrupted migration to passage upstream (e.g. due to the effects of weirs, reservoirs, barrages, dams and floodgates); significant loss of habitat in lakes, rivers, streams and estuaries (including degradation of water quality and loss of submerged aquatic macrophytes); acidification of rivers, and also increasing incidence of acid sulphate soils (which can adversely affect recruitment, behaviour, and demography of particularly susceptible species, such as A. australis australis); increased susceptibility to mass die-off events (due to drought, and consequent increased temperature, salinity and pH in critical habitats); possibility for infection of wild eels populations with diseases that affect cultured eels; and possible population impacts (such as alteration of migration patterns) due to the long-term effects of global warming. Some of the aforementioned impacts may adversely affect population numbers, migration, recruitment strength, and growth rates, which can impact upon populations of this relatively long-lived species, in future decades. There is a need for long term, cautious, co-operative management (of both eel fishing and impacts on critical habitats) across southern Australia, to protect Short-finned Eel populations from decline over space and time.

Page Contents

Current Conservation Status

In New Zealand, an ecological ranking of fished species included Anguilla australis as category “E” (i.e. to be avoided by consumers), due to its long life span and delayed age at maturity; the lack of current or reference biomass estimates; the unknown sustainability of current catch levels, and the lack of a management plan (Weeber and Szabo, 2005).

A conservation assessment in N.S.W. recommended that the species be listed as Lower Risk – Least Concern under the international IUCN Red List (Morris et al., 2001). It is considered to be uncommon, and possibly declining in the Sydney region (ANGFA NSW, 2003), and northern New South Wales (e.g. Harris and Gehrke, 1997, cited by Morris et al., 2001).

The species is considered rare in the Murray-Darling Basin system (Murray Darling Basin Authority, 2009).

The species is considered rare in South Australia (Native Fish Australia, 2002). The National Parks and Wildlife Council and Department for Environment and Heritage (2003) and Hammer et al. (2007) recommended that the species be listed as Rare, under a schedule of the National Parks and Wildlife Act 1972. Criteria for listing were RA bd(ii) in 2003 (National Parks and Wildlife Council and Department for Environment and Heritage, 2003) and RA d(ii) in 2007 (Hammer et al., 2007).

Distribution

Global

This species is found in Australia, New Zealand (including Chatham and Stewart Island) and the south-western Pacific, including New Caledonia, Norfolk Island and Lord Howe Island, Fiji, Samoa and Philippines (Gomon, in Gomon et al., 1994; Beumer, 1996; Inland Fisheries Service of Tasmania, 2000; Native Fish Australia, 2002; NIWA, 2003; Froese and Pauly, 2009 and references therein).

Southern Australia

The Short-finned Eel is naturally found in parts of south-east Queensland, New South Wales, and throughout rivers and estuaries in Victoria, South Australia and Tasmania (Pollard et al., 1980). The species has been translocated into Western Australia.

Large quantities of glass eels of this species have been collected from central and southern Queensland (B. Pease, pers. comm., 2000, cited by Morris et al., 2001).

The Short-finned Eel has been recorded from the Snowy River system (McKinnon et al., 2000).

The species is common and widespread in Victoria south of the Great Dividing Range; particularly in many southern Victorian lakes and rivers (Gippland area), and occurs occasionally in northern streams draining into the Murray River (DPI Victoria, 1998b, 2005h). This species also occurs in catchments that drain into Port Phillip Bay (including some metropolitan rivers – e.g. Coleman and Amenta, 2002), and also in coastal rivers in western Victoria.

The species is known from coastal and lowland rivers, streams and estuaries in Tasmania and Bass Strait (Beumer, 1996; Edgar et al., 1999). Examples include estuaries on King, Flinders and Vansittart islands; also the Leven River in northern Tasmania (Pinto, 2002); Tamar River (as far up as Cataract Gorge) (Hydro Tasmania, 2003) and its tributaries (e.g. North Esk River - Horner, 2003); Emu River upstream of Burnie (Krasnicki, 2001); Tomahawk and Boobyalla river catchment (Davies and Warfe, 2002), and small creeks, rivers and estuaries in north-eastern and eastern Tasmania, such as Cox’s Creek and Cox’s Rivulet (Davies and Cook, 2006) and the Little Swanport River catchment (Harvey et al., 2006). This species has been re-stocked into areas where its former distribution has been disrupted by dams, such as upstream of the Trevallyn Dam (Davies and Cook, 2003). In western Tasmania, this species has been recorded from areas such as Macquarie Harbour (O’Connor et al., 1996). In southern Tasmania, A. australis australis has been recorded rarely in the Derwent and Huon estuaries (Edgar et al., 1999), and downstream of natural barriers (falls, chutes, rapids) in the Warra catchment area in southern Tasmania (Davies et al., 2001). There are records from the North West Bay River, which is bounded by the Derwent River catchment to the North, the Huon River catchment to the West, the Browns River catchment to the East and small coastal catchments to the south (Krasnicki and Graham, 2001). Anguilla australis australis is also reported from inland lakes (e.g. Lakes Crescent and Sorell – Hardy, 2003). The species is also known from the Port Davey / Bathurst Harbour region in southern Tasmania (Johnston, 1882 and/or Edgar 1991, cited by RPDC, 2002).

South Australia

South Australia is the western end of the geographic range (Gomon, in Gomon et al., 1994).

Examples of locations in South Australia where the species may have been previously recorded include the following (NB: old records from SA Museum have not been verified): various parts of the south-east of S.A. (see below) (Hammer, 2002; Hammer et al., 2007); Kangaroo Island (e.g. records from South West River, Eleanor River, and Wilson River during the 1980s, and Stun’sail Boom River in 2005); various parts of the Murray (e.g. Barmera), and Lower Murray (such as sites between Blanchetown and Mannum; Devon Downs; Mypolonga; Milang); the Bremer River / Langhorne Creek area (1980s) (Gomon, in Gomon et al. 1994; Higham et al., 2005; Hammer et al., 2007; South Australian Museum records, cited in OZCAM database, 2009).

In lower south-eastern South Australia, the species has been recorded in higher numbers than areas further north-west (Hammer, 2002). During 2001-02, the species was recorded at the following locations: Hammerhead Pond (8 specimens), Piccaninnie Ponds (highest number in that survey: 30 specimens), Piccaninnie Outlet Drain, Ewens Ponds, and two sites in the Eight Mile Creek drainage area (Hammer, 2002). During a pilot study of fish movement in lower south-eastern South Australia, a single eel elver was recorded (Hammer, 2008, cited by M. Hammer, Aquasave, pers. comm., 2009).

In recent years, there have been isolated records from the Adelaide region, such as Salisbury wetlands (Waterwatch record, 2005) and the Onkaparinga River (SARDI Aquatic Sciences data, 2006), but it is not known if these are natural occurrences, or translocations (Hammer et al., 2007). During a survey of fishes in the eastern Mt Lofty Ranges, this species was not recorded (Hammer, 2004).

Habitat

Anguilla australis australis has both freshwater and marine stages to its life cycle. In southern Australia, the species occurs in a variety of habitats during different stages of the life cycle, with examples including coastal rivers and streams, creeks, lakes and swamps, to estuaries and the open sea (Cadwallader and Backhouse, 1983, cited by Morris et al., 2001; Inland Fisheries Service of Tasmania, 2000).

Short-finned Eels can survive environmental hazards such as high water temperatures or low dissolved oxygen concentrations, hence the species can live in habitats where other species cannot survive (NIWA, 2003).

When in the fresh water phases, this species prefers low-lying swampy streams and lagoons. Although it occurs in a wide variety of habitats, it is essentially a still-water species, and spends most of its life cycle in fresh water, migrating downstream to spawn at sea when sexually mature (McDowall and Beumer, 1980; DPI Victoria, 1998b). Still water habitats include coastal swamps, lagoons, farm dams and river back eddies. They will also migrate overland to reach remote waterways (Seafood Industry of Victoria, 2004).

In Tasmania, Harvey et al. (2006) reported that A. australis australis prefers to inhabit still waters in areas of slow silty habitat.

In a study of lowland streams in New Zealand, Glova et al. (1998) reported that A. australis australis was found in pool, run, and riffle sites from the tidal area to upper reaches. During an experiment to determine cover preference, Glova (2002) reported that juvenile eels (100mm – 199mm) released into channels with various cover types (cobbles, macrophytes, woody debris, pipes), preferentially chose cobbles, irrespective of density of eels per area. Koehn et al. (1994, cited by Davies, 2005) observed selection by Short-finned Eels of woody debris in Victorian streams, with a strong preference for log-jams, and younger eels selected fine substrates (sand, gravel and pebbles). Cover is a major determinant of eel abundance within stream reaches, provided by woody debris, marginal vegetation, undercut banks or bank-side grasses (Glova et al., 1998, Koehn et al., 1994, Jellyman and Sykes, 2003). The last of these authors observed nocturnal movement of A. australis in two New Zealand streams, and eel movement was almost exclusively associated with the river bank, and few cross-channel movements were recorded. Short-finned Eels were most commonly found in runs (rather than riffles) (Jellyman and Sykes, 2003). In another New Zealand study, A. australis individuals in a shallow lake were recorded in various habitats types near the lake edge (raupo, aquatic macrophyte, reed, willow, exposed clay, and mud), and the smaller eels (less than 35cm) were more closely associated with the marginal habitat, rather than the deep waters away from the lake shore (Chisnall, 1996).

Studies in south-eastern Australia have shown that glass eels at the estuarine / freshwater interface, may prefer seagrass / macrophytes or rocks / cobbles in which to hide during the day (Silberschneider, 2005).

The Glass Eels (an immature stage) may occur in Zostera seagrass (Sloane, 1984b), and on the ebb tide in estuaries, glass eels seek shelter in mud or vegetation (Cadwallader and Backhouse, 1983, cited by Koehn and O’Connor, 2002).

The Yellow or Brown Eels (an immature feeding stage) are found in both still and moving waters (Potter, 1980), but show a preference for slow, silty stream habitat, with older eels found well inland, in coastal drainages (Sloane, 1984d; Koehn and O'Connor, unpubl. data, Arthur Rylah Institute for Environmental Research, cited by Koehn and O’Connor, 2002). Some individuals spend several years, or even all their feeding life, in upper estuarine areas (Sloane 1984c, cited by Koehn and O’Connor, 2002).

In South Australia, A. australis australis is known from estuarine creeks in the lower South East (Hammer, 2002), and also the Murray River, and creeks and irrigation drains in Murray River tributaries; and creeks and rivers on northern Kangaroo Island (S.A. museum records 1973, 1990, 1996 and undated, and see Distribution notes cited above).

In New Zealand, Short-finned Eels are found at lower elevations and not as far inland as Long-finned Eels A. reinhardtii, but they are still able to climb large obstacles such as waterfalls when they are young. They are often very numerous in lowland lakes, wetlands, and streams (NIWA, 2003). The species has also been found in New Zealand mangroves (Morrisey et al., 2007), and more rarely, in estuarine and coastal seagrass beds (Schwarz et al., 2006).

During a study across a range of rivers in the south and north islands of New Zealand, Jowett and Richardson (1995) observed that optimum depths for A. australis australis were less than 10 cm. The eels do not show a preference for particular water velocities, but are less abundant at velocities > 1.0 m/s and show a preference for fine substrates (sands and gravels). Short-fin eels do not significantly change their habitat selection for depth and velocity during floods (Jowett and Richardson, 1995, cited by Davies, 2005).

Uncommonly, Short-finned Eels have been recorded in mangrove habitats in south-eastern Australia (e.g. Hindell and Jenkins, 2004; Smith and Hindell, 2005).

Previously, this species has been recorded in abundance in prawn farming ponds at Port Stephens in New South Wales (Maguire and Bell, 1982).

Notes on Biology and Behaviour

Age and Growth

Maximum length and weight are about 1.1 - 1.2m and 6.8kg respectively (DPI Victoria, 2005h), but eels of this species are usually smaller (40-60cm). More commonly, adult females are between 52cm and 110 cm, weighing from ~ 300g to more than 3 kg (12-25 years of age) (Beumer, 1983, cited by Koehn and O’Connor, 2002); males are commonly 37 - 55 cm long and ~ 90g to 260g in weight (7 - 15 years of age) (Beumer, 1983, cited by Koehn and O’Connor, 2002). Mean age of adult eels is around 22 years, and the range of age on downstream migration has been cited as 9-41 years in New Zealand (Boubée, undated) or 18 to about 30 years in southern Australia (Sloane, 1984e, cited by Koehn and O’Connor, 2002). The species is commonly reported to live to 32 years (Kailola et al., 1993), but there are reports from New Zealand of A. australis eels up to 41 years (Boubée, 2006). Mature migrating adults in Victoria vary from 6 to about 24 years of age (DPI Victoria, 1998b).

Growth rates are apparently faster in still or slow-flowing waters (Pollard et al., 1980, cited by Morris et al., 2001).

Graynoth and Jellyman (2002) showed that growth rate changes over time due to food supply (or lack thereof).

Diet and Feeding Behaviour

Eels are primarily carnivorous, but can also be opportunistic omnivores. They eat at night, and adult eels are known to eat fish of various types, worms, insects, small crustaceans, molluscs and water plants (Cadwallader and Backhouse, 1983; DPI Victoria, 1998b). A study in New Zealand reported differences in prey preference and feeding pattern according to size of Short-finned Eel, and the smallest eels (80–100mm total length, TL) preferentially consumed ostracods (Crustacea) and larvae of Chironomidae (Diptera) and Psilochorema sp. (free-living Trichoptera); medium-sized eels (101–199mm TL) preferred larvae of Chironomidae, and Costachorema sp., Hydrobiosis sp. and Psilochorema sp.; and large eels (200–300mm TL) preferred ostracods, Psilochorema sp. and Hudsonema amabilis (cased Trichoptera) (Sagar and Glova, 1998). Differences in the timing of feeding between the three size classes of eel are explained in terms of microhabitat use; differences in diet are explained in terms of prey size, and are also related to eel size (Sagar and Glova, 1998).

In New Zealand, one study showed that this species fed mainly on crustaceans such as the crab Helice crassa, and shrimp Palaemon affinis, along with some amphipod species. Larger eels (>350mm) also feed on small fish, e.g. the Exquisite Goby Favonigobius exquisitus (Morrisey et al., 2007).

Feeding appears to follow a seasonal pattern, being most intense at night in shoreline shallows, during spring and summer (DPI Victoria, 1998b, 2005h).

Eels do not eat when they are hibernating. There are records of eels going without food for up to 10 months (DPI Victoria, 1998b).

Behaviour

Short-finned Eels have nocturnal and cryptic habits, but may be seen moving into shallow areas at dusk to feed (Inland Fisheries Service of Tasmania, 2000).

Feeding eels are believed to occupy a definite home range (Inland Fisheries Service of Tasmania, 2000). Studies of tagged eels indicate that maturing adults in fresh water establish home ranges of about 400m (DPI Victoria, 1998b, 2005h).

Short-finned Eels can also hibernate or enter a period of dormancy over winter due to low temperatures (e.g. if temperature falls below 10oC) (DPI Victoria, 1998b, 2005h). They have also been known to bury themselves in damp mud when the water dries up (Inland Fisheries Service of Tasmania, 2000).

A study in New Zealand of radio-tagged A. australis australis eels in two streams, showed that movements of eels commenced at dusk and continued throughout the night. Eel movement was almost exclusively bank-side, and seldom cross-channel; eels also showed considerable fidelity to a particular bank (Jellyman and Sykes, 2003). Boubee et al. (2001, cited by Davies, 2005) observed downstream migrations of adult short-fin eels in New Zealand, which occurred on a few nights each autumn. Migrations began when water temperatures declined and ceased when temperatures fell below about 11ºC. A rise in stream flow was a key factor required to initiate migration events (Sloane, 1984e; Boubee et al., 2001; Sloane, pers. obs., cited by Davies, 2005).

There may be some sexual segregation by habitat in Short-finned Eel populations (e.g. Sloane, 1984e; Murray-Darling Basin Commission, undated). According to Beumer (1987, cited by Koehn and O’Connor, 2002), most eels that migrate upstream into freshwater (see Notes on the Life Stages below) mature into females; some Glass Eels and Yellow or Brown Elvers remain in estuaries and lower reaches of streams, and most of these mature into males.

Reproduction

The species spends most of its life cycle in fresh-water, and migrates downstream to spawn at sea when sexually mature (DPI Victoria, 2005h). Generally, mature adults migrate from ages 6 to at least 24. In some areas, adults may remain in fresh-waters for 20 years or more before migrating to the sea to breed and then die (Murray-Darling Basin Commission, undated).

Males mature between 8 and 12 years old (possibly up to 14), and females from 10 years (or older) to at least 20 (possibly to 24) years old, during migration to spawning grounds (Beumer 1987, cited by Koehn and O’Connor, 2002; Murray-Darling Basin Commission, undated).

At the Clyde River in Tasmania (Sloane, 1984e), a study of the downstream migration of maturing A. australis australis, showed that 5.2 tonnes of migrating eels entered a trap from November to April, with 53% of the catch taken during January. Of the 190 eels examined, only a single male specimen was found. Female A. australis australis migrated downstream at a mean length of 94.5 cm, a mean weight of 1700g and a mean age of 22.1 years (range 18-30 years). There was a significant positive correlation between catch and water temperature, temperatures above 12ºC being associated with eel migration (Sloane, 1984e).

When mature, male and female silver eels (i.e. the adult stage of Short-finned Eel) migrate to the mouths of streams to commence their spawning migration to the Coral Sea (Beumer, 1987, cited by Koehn and O’Connor, 2002). In some areas, sea migrations peak during summer to autumn (Merrick and Schmida, 1984). In Victorian rivers for example, mature adults leave estuarine areas from December to February (Tunbridge, 1988, cited by Koehn and O’Connor, 2002). The eels probably do not eat during the spawning migration (Merrick and Schmida, 1984, cited by Koehn and O’Connor, 2002).

The spawning area is in the Coral Sea (McDowall and Beumer, 1980; Beumer and Harrington 1980, Beumer, 1983), probably near New Caledonia (DPI, Victoria, 1998b; McKinnon et al., 2002), but precise spawning locations are not well known. Apparently, this is the sole spawning site for all Australian and New Zealand freshwater eels, with some eels having to travel in excess of 3,000 kilometres to get there (DPI Victoria, 2005h).

Spawning occurs in depths greater than 200m – 350m (Beumer, 1983, Beumer and Harrington, 1980, cited by Koehn and O’Connor, 2002; DPI Victoria, 2005h). Females from 520 to 930mm long have been found to contain between 0.46 and 3.06 million eggs (Cadwallader and Backhouse, 1983, cited by Morris et al., 2001).

Mature eels are believed to die after spawning (Inland Fisheries Service of Tasmania 2000; Native Fish Australia 2002).

In southern Australia, recruitment is highly variable west of about Melbourne area (Gooley, 1999, cited by M. Hammer, Aquasave, pers. comm., 2009).

Notes on the Life Stages

The eggs are pelagic, and following hatching (about 2 days), the leptocephali (transparent, leaf-shaped larvae) feed on microscopic plankton and grow, and are passively carried from the spawning grounds toward the eastern Australian coastline by the South Equatorial Current, and then along the coast by the East Australian Current (McKinnon et al., 2002). Via this process, they are deposited along the coastlines of eastern Australia, New Zealand, Lord Howe Island and Norfolk Island. Study of dispersal patterns, using otolith growth increments and microchemistry, has indicated that faster-growing and earlier-metamorphosed leptocephali recruit to northern Australia, and slow-growing and late-metamorphosed leptocephali recruit to southern Australia and New Zealand (Shiao et al., 2001). In addition, based on current direction and the similarity in age of leptocephali at metamorphosis, age at capture and the period between metamorphosis and estuarine arrival, New Zealand glass eels are unlikely to be transported across the Tasman Sea from southern Australia by the East Australian Current, and must reach their destination via a different route (Shiao et al., 2001).

The ability of eels to reach Victorian waters is believed to be dependent on the formation of relatively erratic eddy currents, which split off from the main east Australian current and transport the developing larvae through Bass Strait. These currents break down before they reach the mouth of the Murray River and this is reported to be why eels are naturally absent in the Murray River and its tributaries north of the Great Dividing Range. In years when these currents are strong, there is a mass arrival of glass eels along the Victorian coast, but in some years the currents are weak and very few glass eels arrive. The glass eels’ attraction to an estuary depends on their ability to detect freshwater flows from rivers. In years when river flows are low and estuaries may even be closed, recruitment of glass eels is correspondingly reduced, or may even be zero (DPI Victoria, 2005h).

The larvae metamorphose into transparent “glass eels” near the continental shelf, a process which takes 1 to 2 (or 3) years (Beumer, 1983 and 1987; Beumer and Harrington, 1980; McDowall and Beumer, 1980; Sloane, 1984b, all cited by Koehn and O’Connor, 2002); and tidal currents transport the glass eels, which are also actively swimming, toward and into embayments and estuaries at random (McKinnon et al., 2002; DPI Victoria, 2005h).

Attracted to freshwater outflows from coastal rivers, Short-finned Eels metamorphose into their typical cylindrical adult body shape (Pollard et al., 1980), which is accompanied by a reduction in width and length, loss of the teeth, and cessation of feeding for a short time (Cadwallader and Backhouse, 1983, cited by Morris et al., 2001).

Glass Eels (which have no pigmentation) are around 50-60mm long (McKinnon et al., 2002). This stage ceases feeding for a period, and moves into estuarine areas and the lower reaches of rivers (Beumer, 1983; Sloane, 1984b, DPI Victoria, 1998b).

Generally, this migration process into estuarine waters usually occurs from autumn to spring, particularly winter and early spring (Beumer and Harrington, 1980; Merrick and Schmida, 1984; Tunbridge, 1988, cited by Koehn and O’Connor, 2002; McKinnon et al., 2002; DPI Victoria, 2003b), but the migration may extend to the summer months in some areas (e.g. Tasmania) (Sloane, 1984b).

In New South Wales, glass eels enter estuaries from April through to September (B. Pease, pers. comm. 2000, cited by Morris et al., 2001). During a study in N.S.W. estuaries, Short-finned Eels showed a consistent and defined recruitment across all sites, with the peak recruitment season from April - August (Silberschneider, 2005). When glass eels enter estuaries their upstream migration is assisted by the night flood tide. During the ebb tide, glass eels burrow into the substrate and resurface at the next night flood tide. The eels do not select particular habitats at this time, and their location is mainly dictated by the tide. However, once glass eels reach the estuarine / freshwater interface, they may prefer more complex habitats such as seagrass / macrophytes or rocks / cobbles in which to hide during the day. At this interface, glass eels undergo a physiological change to adapt to a freshwater existence and this change may take up to a few weeks. During this time, glass eels commonly enter the water column during the night flood tide and may be able to locate more suitable habitats in which to hide during the day (Silberschneider, 2005).

Some glass eels will quickly pass through the estuary and migrate upstream and others will remain in the estuaries for some time (DPI Victoria, 2005h). At the time of entering estuaries, Short-finned Eels are at least 200 to 300 days old and 50-70mm long. They migrate to the upper reaches of estuaries by selectively using flood tides, and seek shelter in mud and amongst vegetation when not travelling. During this time they rapidly develop into fully pigmented elvers (Brown Elvers, the next stage in development), increase in size, grow new teeth, and acclimatise to lower salinity levels.

Glass Eels, and Yellow or Brown Elvers (the last two of which are immature feeding eels) may be found in the lower reaches of rivers / estuaries, buried in substrate, preceding their upstream migration into fresh-water, when they penetrate upper reaches of streams, creeks, and rivers, or move into lakes or swamps (Cairns, 1941; Sanders, 1973; McDowall and Beumer, 1980; Beumer and Harrington, 1980, Beumer, 1983; Beumer, 1987). Some elvers remain in an estuary until they mature, but most will migrate upstream in secondary migrations, known as 'eel fares', which involve glass eels and elvers of several age groups moving inland into rivers, creeks, lakes and swamps (DPI Victoria, 2005h). Brown Elvers persist in the bottom sediments of estuaries for several years before moving into fresh-water. The elvers hibernate in winter, when temperatures are low (Cairns, 1941, cited by Koehn and O’Connor, 2002). Further inland from the sea, the size and age of elvers increases; eels migrate further upstream for several years in succession (Sanders, 1973; Sloan, 1984c, cited by Koehn and O’Connor, 2002; Inland Fisheries Service of Tasmania, 2000; Native Fish Australia, 2002). Day length, increased water temperature, reduced river flow, and social interaction, all may contribute to initiating and controlling elver migrations; high stream flows and reduced water temperature inhibit migration (Sloane, 1984a, 1984c, cited by Koehn and O’Connor, 2002). According to Beumer (1987, cited by Koehn and O’Connor, 2002), most eels that migrate upstream into freshwater, mature into females; some Glass Eels and Yellow or Brown Elvers remain in estuaries and lower reaches of streams, and most of these mature into males. Yellow and Brown Elvers exhibit homing behaviour, and occupy a definitive home range (Beumer, 1979, cited by Koehn and O’Connor, 2002). For example, in one study, most tagged eels were recaptured within 400m of the release point, even after 21 months (Beumer, 1987, cited by Koehn and O’Connor, 2002). Upstream migrations of elvers in Victoria occurs from May in the east to October in the west (DPI Victoria, 1998b), but most authors report that the upstream migration occurs during various months of spring and/or summer, depending on the State and location (e.g. see Cairns, 1941; McDowall and Beumer, 1980, 1983; Sloane, 1984a, 1984c; Tunbridge, 1988). Movement upstream often occurs at night, after sunset, and the young eels remain close to the banks, avoiding fast flowing water (Beumer and Harrington, 1980; Sloane, 1984c; Beumer, 1987; DPI Victoria, 1988b). Upstream migration appears to be in response to a number of factors including falling salinity and rising water temperatures (DPI Victoria, 1998b). At a stream barrier such as a weir, dam or waterfall, Glass Eels and Brown Elvers may congregate. Eels of this age / size can move along the damp sides of a barrier; can move considerable distances over wet or damp ground, or through moss or algae; and are also capable of climbing damp, vertical, concrete dam walls (Cairns, 1941; Beumer and Harrington, 1980; Harris, 1984a; Sloan, 1984c; Beumer, 1987, cited by Koehn and O’Connor, 2002).

Mature males and females (“silver eels”) migrate downstream and congregate in estuaries and the mouths of streams, to commence the spawning migration in the sea (Cairns, 1941; Beumer, 1983, 1987; Sloane, 1984e, cited by Koehn and O’Connor, 2002). One study showed that the onset of downstream migration may be related to temperature (with a migration peak during high spring temperatures) and size of eels (Sloane, 1984e), and another study considered that the migration may be influenced by rainfall and associated water volume (Cadwallader and Backhouse, 1983). The migration of mature eels downstream and out to sea, has variously been reported to occur in spring, summer and autumn (Beumer, 1983, 1987; Sloan, 1984e; Tunbridge, 1988). Eels from Victoria may take 2 to 3 months to reach the spawning area in the Coral Sea (Beumer, 1983; Merrick and Schmida, 1984). At maturity, eels undergo a number of changes in preparation for the spawning migration. After a period of voracious feeding, and significant growth, their eyes become larger and their skin takes on a silvery appearance. Internally, their gonads begin to develop and their digestive system closes down and starts to degenerate. During this “silver eel” stage, they migrate back to the sea during late summer and autumn. They quickly move into deeper water and in total darkness swim north against the current to reach the Coral Sea. By the time they arrive, they have used up all their energy resources. The eels then spawn and die, and their young commence the cycle over again (DPI Victoria, 2005h).

Other Information

A study of the genetics of populations of Anguilla australis australis from six estuaries in eastern Australia and three estuaries in New Zealand, has indicated that populations of A. australis australis in eastern Australia and in New Zealand may be reproductively isolated from one another. During that study, genetic differentiation among populations of <i.>A. australis australis was 2-fold to 10-fold higher than that among populations of other temperate eels in the North Atlantic Ocean, suggesting that two groups of A. australis australis may reflect sub-species. Genetic isolation between Australian and New Zealand populations indicates that juveniles recruit independently into these two regions from geographically or temporally isolated spawning areas (Shen and Zheng, 2007).

Fisheries Information

General

The flesh of freshwater eels is considered to be excellent quality, and considered to be a delicacy in many parts of the world. Short-finned Eel is described as “good eating, particularly if smoked” and “easily taken on a baited hook, and providing good angling” (DPI Victoria, 1998b).

South-Eastern Australia – Commercial

Short-finned Eel forms the basis for a small but important commercial fishery, with most of the catch being exported overseas, as frozen product. In Australia, the species is most often smoked prior to eating (Gomon, in Gomon et al., 1994). In eastern Australian fisheries, the Short-finned Eel is more commercially important than the Long-finned Eel (DPI Victoria, 1998b). The species is commercially fished in New South Wales, Victoria and Tasmania (Inland Fisheries Service of Tasmania, 2000).

One example of the commercial fishing of Anguilla australis australis in Tasmania is the Lake Crescent eel fishery, which has existed since 1965 (Chilcott 1986, cited by Heffer, 2003). Previously, the eel fishery was restricted to the capture of downstream migrating eels with a trap installed at the Clyde River outflow. Upon the discovery of European carp (Cyprinus carpio) within the lake, fine (1.1 mm) mesh screens were installed at the Clyde River outflow preventing migration of eels down the river. Consequently, the fishery is now operated using fyke nets within the lake. An eel trap was also installed at the Lake Sorell gate to capture eels moving from Lake Sorell to Lake Crescent but cannot be used when water levels are low (Frijlink, 2000). Due to the lack of natural recruitment of eels to the system, the eel population in Clyde River and Lake Crescent is maintained by the stocking of elvers by the Inland Fisheries Service (Heffer, 2003), and by transfers (Davies et al., 2005).

Short-finned eels are the most abundant and fished eel species in Victoria, comprising up to 95% of the total annual catch (DPI Victoria, 2003a). The Victorian catch is approximately 80%t of the total annual catch of eels in Australia (and Australia's contribution to the world market is less than 1% of the world catch). Four of the life stages (leptocephali glass eels; pigmented elvers; yellow eels; silver eels) are commercially utilised in Victoria (Hall, et al. 1990, cited by DPI Victoria, 2003a), but a major component of the Victorian commercial eel fishery comprises adult eels at various stages of migration (DPI Victoria, 2002). Yellow and silver eels are commercially fished for domestic and export markets, and glass eels and pigmented elvers are used for stock enhancement and aquaculture (see below). A large component of the eel production is from stock enhancement, whereby elvers and undersized eels are stocked under specified licence conditions into selected lakes for extensive on-growing under natural conditions (DPI Victoria, 2003b). In Victoria, the commercial eel fishery extends across the coast of that State, and operates in estuarine and freshwater habitats including lakes, rivers, swamps and privately-owned dams. Production from the fishery has been generally declining over the last few years, predominantly due to prolonged drought conditions, with 86 tonnes of eels (2 species) caught in 2004/05 (McKinnon , 2006). Previously catches were up to 200 tonnes (DPI Victoria, 1998b), but are now less than 100t per annum (see below). The eel fishery has been relatively stable, in terms of production, over the last 2 decades; however the fishery is strongly affected by seasonal factors, and recent drought conditions have resulted in relatively low production of Short-finned Eel in successive years. A large component of eel production is from stock enhancement, whereby elvers and small or poorly conditioned “yellow” eels, or “snigs”, are stocked under specified licence conditions into selected Crown waters (mainly western Victorian lakes) and large private dams for extensive on-growing under natural conditions. Translocation of eels into and within Victoria is now undertaken according to translocation guidelines and protocols recently developed (McKinnon, 2006). In the past, substantial quantities of elvers have been sourced from the Trevallyn Tailrace (Tamar River) and Meadowbank Dam (Derwent River) in Tasmania for restocking into Victorian waters. This practice is expected to continue, according to appropriate translocation protocols, once stock-enhanced waters recover from drought conditions of the 1990s and early 2000s (McKinnon, 2006). In most years the commercial catch is roughly comprised of up to 40% stock-enhanced Short-finned Eel (about 40-50t per annum); however protracted drought conditions since 1994 have resulted in a significant decrease in both stock-enhanced, and wild Short-finned Eel production (McKinnon, 2006). The wild eels form the basis for a small but lucrative export industry. Short-finned eels are mainly exported to Europe as a snap-frozen product with about 5 percent being smoked for local consumption (Seafood Industry of Victoria, 2004). The wild Short-finned Eel component of the fishery is comprised largely of migrating adult eels. The reliance of the existing commercial eel fishery in Victoria on wild-caught adults is great, particularly during periods of drought when productivity from stock-enhanced waters is low (McKinnon, 2006). Eel fishing occurs from Mallacoota to Portland, but most of the fishing takes place in the lakes and wetlands of the Western District (DPI Victoria, 2005h). Of 48 major Victorian rivers, 21 are closed to commercial eel fishing (DPI Victoria, 2003b). Much of the production depends on the eel fishers translocating large numbers of small eels from waters where conditions for growth are poor, to more favourable areas where they can grow to reach commercial size and condition over a number of years (DPI Victoria, 2005h). Eel fishing occurs in estuarine and freshwater river reaches, and natural and artificial impoundments. During the early 2000s, there was a maximum of 18 transferable Eel Fishery Access Licences (EFAL) operating throughout Victoria, each allocated specific and non-specific Crown waters (plus private waters) in which to fish (DPI Victoria, 2003a). A small quantity of eel is also taken commercially in bay and inlet fisheries by haul seine operators. In the commercial eel fishery in Victoria, the species is taken in fyke nets, mainly at night, and there are strict specifications for the number permitted, and the operation of the nets. In addition to water allocation, the commercial fishery is also managed with limited entry and gear restrictions. The minimum legal length for eels is 30cm TL. The catch (in tonnes live weight) of Short-finned Eel in Victorian waters in recent years, is as follows:

Commercial Catch of Wild Short-finned Eel in Victorian Waters 1997 to 2007
Year	Catch (t)
1997/98	151
1998/99	92
1999/00	96
2000/01	127
2001/02	131
2002/03	78
2003/04	74
2004/05	60
2005/06	55
2006/07	49
(DNRE Victoria, 2002 - 2007)

The distribution of Short-finned Eel is well established in Victoria, and fishery-dependent catch returns are presently quantified by allocated water and/or stock-enhanced water fished, or more broadly by regions where unspecified Crown waters and private waters are fished (DPI Victoria, 2003b). In Victoria, commercial catch data for the fishery have been collected in detail since 1979 (DPI Victoria, 2003b). Productivity is highly susceptible to short term and seasonal environmental variations in temperature, salinity and river flow; hence the significant variation in total catch (Sloane, 1984c; DNRE Victoria, 2002, cited by DPI Victoria, 2003a).

Glass eels (5cm long), which travel up the rivers in south-eastern Australia, are harvested in small quantities (less than 200 kilograms per year), with special nets for a developing eel aquaculture industry (McKinnon et al., 2002). In Victoria, there is only a small number of farms producing eels intensively, but the possibility of more widespread intensive culturing of eels is being investigated (DPI Victoria, 2003a). Also in New South Wales, glass eels are exploited as seed stock for a growing eel aquaculture industry. Glass eels, elvers and small yellow eels are harvested from the wild for aquaculture, because there are few prospects for developing commercial scale artificial propagation techniques in the near future (N.S.W. Fisheries, 2003f). According to McKinnon et al. (2002), commercial quantities of glass eels can be harvested in a sustainable manner from rivers in eastern Australia. All States now have measures in place to prevent over-harvesting.

The species is listed as part of the bycatch in the Commonwealth-managed Coral Sea Fishery, and the South East Trawl fishery (SETF) component of the Southern and Eastern Scalefish and Shark Fisheries (SESSF) (Bromhead and Bolton, 2005). Bycatch appears to be very low in the SETF (e.g. in a sampling study during the early 2000s, the species was recorded in only 1 trawl shot, and 2kg were discarded, according to Wayte et al., 2004).

South-Eastern Australia - Recreational

Anguilla australis australis is taken by anglers in southern Australian States, and records are kept of maximum sizes caught (e.g. Australian Anglers Association, 2005; AAA Victorian Division, 2003).

In Victoria, recreational eel fishing is permitted in all Crown waters which are open to recreational angling, including waters which are stock enhanced by the commercial sector (DPI Victoria, 2003b). There is limited information on the level of recreational eel fishing in Victoria, but evidence suggests that the recreational take of Short-finned Eel is significant (DPI Victoria, 2003b).

Previously in South Australia, historical records indicate that anglers may have caught the species in the Murray River, and in dams and creeks associated with tributaries of the Murray River; and in rivers / creeks on Kangaroo Island (S.A. Museum records).

In an Australia-wide recreational fishing survey, anguillid eels were not distinguished from conger eels and other eels, and there are no publicly available, species-specific recreational catch estimates for Short-finned Eels. Total eel catches (all eel species) in Australia during the 2000 to 2001 period of the national survey, were reported to be about 170,654 individuals, comprising 7,766 from Queensland; 5,350 from New South Wales; 147,254 from Victoria; 8,239 from Tasmania; < 1,000 from South Australia; and 1,164 from Western Australia.

Other

Indigenous cultural fishing of Short-finned Eel also takes place in some parts of south-eastern Australia. For example, in Victoria, the main areas where such fishing is known to take place include the Hopkins River and Mount Emu Creek catchments, and other waters in the Hopkins Basin (DPI Victoria, 2002, 2003a). Stone eel traps are common and each year, different family groups harvest eels from specific traps. Eels form an integral part of the culture and tradition of the people of Framlingham, for example, and are recognised as a key theme in the Framlingham Aboriginal Trust Management Plan (DPI Victoria, 2002). According to Rolls (2006), archaeological evidence has shown that the Gunditjmara people in the western district of Victoria began work in about 6000BC to grow out Short-finned Eels. Before they began work, tidal Darlot Creek was fed by the Condah swamps, which were fed in turn from the overflow of Lake Condah. By a complex system of walls and trenches and dams, the people turned a big area into an eel farm, and held eels in there for up to 20 years. Builth (2005) further discusses the significance, in the culture of Gunditjmara, of raising, eating and trading Short-finned Eels.

In central and southern N.S.W., the Short-finned Eel is also recorded as a species targeted commercially in indigenous coastal fisheries (Schnierer and Faulkner, 2002, cited by Umwelt Australia, 2004).

Aquaculture and Stocking

Commercial producers in Victoria, Tasmania, New South Wales, and Queensland capture glass eels and elvers from the wild under permit (e.g. 50-200kg / State during the early 2000s). Small, but increasing, quantities of glass eels are being harvested from estuaries in New South Wales as seed stock for the Australian eel aquaculture industry (B. Pease, pers. comm. 2000, cited in Morris et al., 2001). The eels are used for commercial grow-out trials in intensive freshwater recirculation systems, and wild elvers and sub-adult eels are translocated from Victorian and Tasmanian coastal rivers to public and private lakes, swamps, wetlands and farm dams where they are left to grow (in “extensive” systems) to marketable size. The majority of production is from Victoria (Gooley and Gavine, 2003).

Historically, the Victorian eel industry has utilised the productive inland natural lake systems of that State for the extensive grow-out of Short-finned Eels. Crown waters in which stock enhancement occurs are fished by Eel Fishery Access Licence (EFAL) holders under an Aquaculture Licence (DPI Victoria, 2003b). Production is greatly affected by rainfall and Victoria’s drought periods (e.g. early 2000s), which significantly reduce the capacity to harvest from extensive culture waters. More recently, intensive eel aquaculture technology adapted from European recirculation systems has been adopted for the culture of Short-finned Eel (DNRE Victoria, 2004). The fishery is highly regulated and adopts two basic strategies: stocking of glass eel and elvers caught in estuarine waters during their inland migration, and stocking of undersized, juvenile fish which are in poor condition when caught from various inland waters. The latter group is popularly known as 'restock' fish (Skehan and De Silva, 1998). A time-lapse analysis study in Victoria estimated that 'restock' eels enter the commercial catches 1–5 years after stocking, but elvers enter after 8–13 years (Skehan and De Silva, 1998).

Vulnerable Population Characteristics and Threatening Processes

Anguilla australis australis is of conservation concern, due to (i) narrow habitat range within a key part of the life cycle: i.e. the species is dependent for part of its life upon a small number of estuaries, particularly in cool temperate regions, and impacts upon the quality of critical estuarine habitat may affect this species; (ii) slow growth rate; (iii) late sexual maturity, particularly for females (more than 10, and possibly up to 20+ years of age for females, and 8 to 12 years for males); (iv) relatively long-lived (more than 30 years) and complex life cycle, involving extensive migration, and (iv) erratic and variable recruitment; i.e. in years when currents are strong, there is a mass arrival of glass eels along the south-eastern Australian coast, but in some years the currents are weak and very few glass eels arrive (Inland Fisheries Service of Tasmania, 2000; DPI Victoria, 2005h). These characteristics make populations vulnerable to over-exploitation of sexually immature individuals, and it would be very easy for eel stocks to be overfished.

The species is considered to have a low resilience to exploitation, and very high vulnerability to fishing-induced population decline (Cheung et al., 2005, cited in Froese and Pauly, 2009). It is noted that globally, populations of other eel species with similar life histories to A. australis australis have crashed for reasons that are still uncertain (G. Edgar, TAFI, pers. comm., 2009). For example, European Eel Anguilla anguilla is now listed as critically endangered (IUCN Red List, 2009), due to sharp declines in recruitment, stock size and yield. Recruitment of the glass eel stage of Anguilla anguilla has declined significantly since 1980, and since 2000 has been at an historical low at just 1-5% of the pre-1980 levels.

A study of the abundance and distribution of the glass eel stage of the Short-finned Eel in south-eastern Australia (see McKinnon et al., 2002), showed that (i) the abundance of the glass eel stage varied widely between and within seasons over a wide geographical range, and (ii) the largest quantities of glass eels were consistently caught in one river in Queensland and another river in Victoria (McKinnon et al. 2002), indicating that eel productivity is inconsistent over the range of the species. This has implications for the commercial and recreational capture of this species, as some populations which are less abundant, may be more vulnerable to decline (due to fishing and other impacts) than are others.

Coastal access is important for species such as Short-finned Eel, due to this species having both fresh-water and marine stages to the life cycle (Hammer, 2002). Decline in water flow in estuaries across south-eastern Australia may adversely affect populations of this species. The attraction of Anguilla eels to an estuary depends on the ability of glass eels to detect freshwater flows from rivers. In years when river flows are low and estuaries may even be closed, recruitment of glass eels is correspondingly reduced or may be zero (DPI Victoria, 2005h).

In South Australia, this species has a limited area of available habitat in coastal wetland systems. According to Hammer (2002) there appears to be density differences in areas of south-eastern Australia with and without fishing pressure. Therefore, due to the combination of degradation of wetlands and estuaries in the South-East (see Hammer et al., 2007), possible local harvest (adults fished recreationally), and interstate harvest (glass eel fisheries in Victoria), the species is likely to have declined in South Australia on top of an already restricted range (Hammer, 2002; Hammer et al., 2007). However, the extent to which eel fisheries in western Victoria impact upon the South Australian population is uncertain, since movement patterns into South Australia, and natural abundances over space and time, are not well known.

The growth rate and recruitment strength in A. australis australis may vary over time (e.g. Graynoth and Jellyman, 2002), which can reduce commercial catches of migrating silver eels during the following decade; hence there is a need for cautious long-term management of eel fisheries that harvest wild eels.

In southern Australia, A. australis australis is considered to have suffered from the effects of weirs, which prevent or inhibit the freshwater migration phase of the life cycle (Inland Rivers Network, Nature Conservation Council of N.S.W., 1999). Bishop and Bell (1978, cited by Morris et al., 2001) suggested that the construction of dams and weirs on coastal streams has prevented or limited the upstream movements of elvers. Most eels have some ability to climb over or around weirs and dams, but structures that slow their upstream migrations increase the risk of predation and reduce the number of eels able to reach upstream habitats. High barriers would invariably lead to significant effects on eel stocks in the upstream reaches (Pollard et al., 1980; Gehrke et al., 2001). Obstructed migration also leads to large congregations of glass eels and elvers trapped at the bases of the obstructions, allowing heavy predation upon them by birds (Cadwallader and Backhouse, 1983) and other fishes (Morris et al., 2001). In Victoria, a large barrier found in the Plenty River system is the wall of Toorourrong Reservoir, which is located high in the catchment on the east branch of the river. Anguilla australis australis were previously reported to be common in the area (NRE reports, cited by Lieschke et al., 2000), but this structure appears to be restricting the upstream movement of migratory species such as Short-finned Eel (Raadik and Lieschke 1999, cited by Lieschke et al., 2000).

Periodic closure of the Murray Mouth, in addition to the long term changes to volume and flow rate that have occurred in the area, is likely to directly affect the life cycle of this species, and have long term implications for populations of this species (Higham et al., 2002). The current long-term closure could be devastating to this species in South Australia (M. Hammer, Aquasave, pers. comm., 2009).

Previously, the lack of effective fishways in the Murray-Darling river system has been implicated in the decline of native fish populations (Stuart et al., 2002). Fishways have been developed during the past decade to address this issue (see Management Notes).

In N.S.W., the species is considered Threatened, due to reduced distribution and abundance throughout the northern part of its range (Morris et al., 2001). For example, surveys conducted from 1960 to 1976 in northern New South Wales collected this species at only six sites (Llewellyn, 1983), and extensive surveys carried out from 1994 to 1996 collected only a single specimen from the north coast rivers of N.S.W. (Harris and Gehrke, 1997, cited by Morris et al., 2001). Floodgates in N.S.W. are also implicated in the decline of A. australis australis populations, due to the restrictions they impose on migration (N.S.W. Department of Primary Industries, 2007b).

In general, the main issue for freshwater fish species is habitat loss and modification. In South Australia for example, some of the concerns include the construction of dams, weirs, barrages (and drains) along watercourses, which changes the rate, volume and direction of water flow; restricts access of native fish species to existing habitat and new areas for colonisation, and also interrupts patterns of migration (e.g. during spawning). Widespread residential and/or agricultural development adversely affects the habitat of native freshwater fish, through water extraction and diversion, point source and diffuse source water pollution, and loss or degradation of essential habitat such as riparian vegetation (resulting in reduced habitat for feeding and sheltering; stream and river bank instability; changes to channel morphology; increased siltation, and reduced capacity of streams and channels to filter agricultural and urban pollutants). Further, the introduction of exotic fish has resulted in increased competition and predation for native river- and stream-dwelling species in S.A. (Urban Forest Biodiversity Program, undated).

In New Zealand brackish lakes, degradation of water quality and loss of submerged aquatic macrophytes (which results in change to the species composition of aquatic macro-invertebrate prey for eels) may have adversely affected the growth rate of A. australis australis over time (Kelly and Jellyman, 2007). Similar changes in lake quality may have occurred in south-eastern Australia during the past few decades.

Chronic drainage of acid sulphate soils may be a long-term impact on this species in some parts of south-eastern Australia. Drainage of acid sulphate soils may affect the recruitment, behaviour, and demography of particularly susceptible species, such as A. australis australis (Kroon et al., 2004).

Short-finned Eel is one of the estuarine species adversely affected during fish kills in modified estuaries (Australian Natural Resources Atlas, 2007). This species can also accumulate toxins from microalgae, during algal blooms (e.g. Dolamore, 2006).

In Tasmania, direct threats to populations include hydro-electricity dams and other large, in-stream barriers within migration paths (Inland Fisheries Service of Tasmania, 2000). The natural spawning migration of eels between lakes and the ocean is essential to sustain populations, and some of these (e.g. in Tasmania), now have to be artificially enhanced by translocating elvers. Other issues in Tasmania include river pollution (e.g. acidification) from mining activities. For example, there has been concern about impacts on the Short-finned Eel population in the King River, due to mining waste from previous activities at Mt Lyell.

Inadequately regulated fishing of wild populations is considered to be a threatening process in some areas (e.g. Tasmania – Inland Fisheries Service of Tasmania, 2000). In Victoria, evidence suggests that the “illegal commercial” take of eels may be considerable; however the exact quantities of eels taken illegally is difficult to determine (DPI Victoria, 2003b). There is reported to be “a huge unsatisfied world demand for glass eels for aquaculture, and without tight control, the Australian resource could be quickly stripped to satisfy European and Asian requirements” (DPI Victoria, 2005h).

In Victoria, in the two summers of 2004/05 and 2005/06, a number of fish kill events, primarily involving eels, occurred in water bodies across Victoria. Some of the greatest quantities of dead eels were observed in lakes which have been routinely stocked with eels as part of the commercial eel fishery (McKinnon, 2006). Leahy et al. (2007) reported the death of mass numbers of Anguilla australis australis and other fishes in 10 water bodies across Victoria (including three sub-catchments of the Yarra River, two freshwater lakes in the Greater Melbourne area, and two estuarine embayments). The common factor in all deaths was 10 years of drought, from 1997 onwards. The largest event occurred in lakes within Victoria’s Western District and constituted more than 95% of all eels that had died in the last two summers to 2007. At Lake Modewarre (where the pH was 10 in 2006) there were deaths in two separate seasons, totalling 50,000 eels. At Lake Bolac, approximately 5,000 eels died. EPA investigations indicated that multiple factors influenced by the persisting drought have led to the fish deaths. Monitoring of Lake Modewarre and Lake Bolac in the summer of 2005 and 2006 showed a common set of conditions that preceded the eel deaths, all related to 10 years of below-average rainfall. This included a 30 to 40 per cent rise in salinity for the three-to-six-week period preceding the deaths, alkaline pH (>8.5), and an air temperature of 35ºC or greater on the day of the deaths or the day before the deaths (Leahy et al. (2007). It is possible that prolonged drought conditions in future, across southern Australia, may increase the frequency of such episodes of mass eel deaths.

Long-term changes to lake salinity, due to diversion of freshwater inflow, may also adversely affect eel populations. For example, A. australis australis was previously the only fish species recorded in Lake Corangamite in Victoria, but the salinity level of this lake has now increased significantly in recent decades (Williams, 1995).

Research from New Zealand suggests that increased temperatures associated with global warming could adversely affect migration of Short-finned Eels. For example, experimental work has shown that the optimal upstream migration temperature for glass eels of Anguilla australis australis in the Tukituki River, Hawkes Bay is 16.5ºC and when the water temperature reaches 22ºC, migration is almost completely suppressed (data by August and Hicks, cited by Ryan and Ryan, 2006; August and Hicks, 2008).

It may be important to consider whether diseases that may affect cultured eels (such as epizootic hematopoietic necrosis) have opportunity to spread to wild eel populations and if so, preventative measures should be taken.

Research Notes

During the past two decades, much research has been undertaken on the various stages of the lifecycle (see Notes on Biology and Behaviour, above). More recently, collaborative work in the 4 eastern States has been undertaken on glass eel stocks (both Short-finned, and Long-finned A. reinhardtii), as part of the developing glass eel fishery for aquaculture (see McKinnon et al., 2002 and N.S.W. Fisheries, 2003f). Aspects of the research have included study of the seasons that the two species of glass eels move into rivers, and their relative abundance in the four eastern States; study of eel biology during the migration period; conditions that trigger movement into the rivers; quantification of fish bycatch in glass eel nets, and investigation of methods for reducing bycatch (McKinnon et al., 2002).

In New South Wales, a collaborative project between N.S.W. Fisheries and the University of Technology (Sydney), has employed collectors to assess habitat utilisation patterns of glass eels in Port Hacking, and to assess seasonal recruitment of glass eels along the entire N.S.W. coast, with a view to using the collectors for long-term monitoring of annual recruitment of glass eels in N.S.W. (N.S.W. Fisheries, 2003f). This work formed part of a project by V. Silberschneider, to determine the recruitment and age dynamics of Anguilla australis australis and A. reinhardtii glass eels in the estuaries of New South Wales. In that project, a sampling device (“an artificial habitat collector”) was developed and used to sample six estuaries on a monthly basis. Short-finned Eels showed a more consistent and defined recruitment across all sites than Long-finned Eels, and the peak recruitment season for A. australis australis was from April - August (Silberschneider, 2005).

A genetic differentiation test (using microsatellite loci) has been undertaken for populations of Anguilla australis australis from six estuaries in eastern Australia and three estuaries in New Zealand (Shen and Tzeng, 2007).

Research Recommendations

According to McKinnon (2006), despite continued fishing, some eels in western Victorian lakes may be several decades old, and have been unable to undertake spawning migrations due to the land-locked nature of these lakes. In Europe, it is thought that a related species of eel may make repeated attempts to reach the sea and that eels will revert to the yellow eel stage if they cannot do this (van den Thillart et al., 2005). It is not known whether eel age or level of sexual maturity may influence susceptibility to environmental stressors. A comprehensive study of the population biology of stocked eel populations in Victorian lakes has therefore been recommended (McKinnon, 2006).

The relationship between spawning stock and recruitment is poorly known, which makes it difficult to set meaningful management reference points in commercial fisheries. The majority of reference points require information on several population parameters including age structure, growth, natural mortality, spawning stock size and recruitment size. The limited knowledge of these parameters and of the population dynamics of Short-finned Eel is a significant impediment in the development of specific management reference points for eel (DPI Victoria, 2002). Also, there is little or no quantitative information on carrying capacity of habitat types for eels, or on the habitat variables which determine carrying capacity (DPI Victoria, 2002).

The relationship between eel populations in western Victoria and south-eastern South Australia should be investigated, particularly, the movement of eels from Victoria into South Australian waters, over space and time.

Management Recommendations

With an increasing number of obstructions to river flow, and diminishing habitat due to the clearing of natural vegetation, it is important to reduce eel mortality rates associated with obstructions to upstream movement. This is especially necessary where dams and weirs are located below prime eel habitat.

Improvements to fish passage, especially at sites which have barriers restricting movement of elvers and glass eels directly from marine to freshwater habitats, should have a positive effect on the recruitment levels of this species (Morris et al., 2001) (see Management Notes, below).

A comprehensive database of glass eel catch and effort should be maintained for all States in eastern Australia (McKinnon et al., 2002), as occurs in Victoria.

The commercial harvesting of glass eels and adult eels from the same rivers may require offsets in effort to manage the risk of overfishing in those rivers (DPI Victoria, 2002).

In Victoria, the wild fishery is considered to be fully exploited, and stock enhancement and aquaculture have been recommended as the best ways of increasing production (e.g. Skehan et al. 1998; DPI Victoria, 2003b).

Reintroduction of logs to rivers that have had such snags previously removed, may benefit eel populations. For example, in New South Wales, 436 logs were used to create 20 engineered log jams (ELJs) in a 1.1 km reach of the Williams River, a gravel-bed river that has been de-snagged and had most of its riparian vegetation removed over the last 200 years, In that river, a BACI (before, after, control, impact) experiment showed that the number of Long-finned Eels Anguilla reinhardtii in the test site (with logs) was three times higher than the number at the control site (no logs). The experiment was designed to test the effectiveness of reintroducing woody debris as a means of improving channel stability and recreating habitat diversity (Brooks et al., 2004).

Recommended measures to help elucidate and prevent future “fish kill” events that adversely affect eel populations include: monitoring (over 24 hour periods) of key water quality variables in affected and unaffected water bodies over summer at surface and at depth; collection of morphometric and histological data on eels in these water bodies, including live and dead eels during future fish kill events; undertaking survival and recovery trials with eels during future fish kill events; a population biology study of stock-enhanced eel lakes (e.g. in western Victoria); and determining the tolerance to the main environmental stressors over a wide size range, including glass eels, elvers, yellow eels and silver eels (McKinnon, 2006).

Management Notes

In Victoria, the commercial fishery is “input-managed”, with limited entry, gear restrictions and water allocation the main input restrictions. There is a restriction on the number of rivers open to eel fishing, and stock enhancement is encouraged in the fishery in appropriate waters (DPI Victoria, 2002). Fyke nets are the only gear permitted for use by eel fishery licence holders. A small quantity of eel is also taken commercially in bay and inlet fisheries by haul seine operators (McKinnon, 2006). In Victoria, entry to the fishery is reported to be tightly controlled, and the most productive waters have been allocated to individual fishers. This encourages each operator to fish their water conservatively and ensures that, if they exercise restraint, they will benefit from that allocation over the long term. In addition to this, there are many coastal streams that are closed to commercial eel fishing. Although this was done initially to ensure that platypus in these waters were not caught in nets, it also attempts to ensure that there is an unexploited area to provide spawning stock to return to the sea. The eel fishery management plan aims to protect natural eel populations in about 50% of major Victorian rivers (DPI Victoria, 2003b). Another management measure in Victoria has been to ban all commercial and recreational exploitation of eels that are less than 30cm long (DPI Victoria, 2005h).

In Victoria, there are reference points (target and/or limit), that trigger management actions, including a “biological bottom line” and/or a catch or effort upper limit beyond which the stock should not be taken (DPI Victoria, 2002) (but see Research Recommendations). During the early 2000s, a management plan for the eel fishery in Victoria recommended a precautionary trigger point be set at 20% reduction in catch, based on the mean catch for the preceding 3 years. Once the trigger point is reached for any component of the fishery, an immediate review of the fishery was recommended. Also, a blanket cap on effort applies to all licence holders. The management plan aims to refine the cap on effort with respect to determining the appropriate level of effort for individual waters fished (DPI Victoria, 2002).

In Victoria, a key objective of the eel fishery management plan is to promote and assist the use of sustainably harvested glass eel resources (i.e. stock enhancement), to contribute to a significant proportion of eel fishery production in Victoria (DPI Victoria, 2003b).

During the early 2000s, the Murray-Darling Basin Commission undertook a fishway construction program, to restore fish passage at locks and weirs along the Murray River between Lake Hume and the Goolwa barrages (Stuart et al., 2002). State agencies from Victoria, New South Wales and South Australia are collaborating, to develop up to 13 new fishways. The key research objectives include quantifying the contribution of the fishways toward improved fish passage and identifying changes to whole native fish communities. Pilot sampling to address these objectives commenced in September 2001 and initially involved field-testing a range of methods to develop a long-term experimental design. Data collected will be incorporated into the design of the new fishways, while also providing a baseline sample of current fish populations. Following construction, the performance of new fishways will be assessed, to ensure that future fishways work efficiently (Stuart et al., 2002). By the mid 2000s, 2 of the 13 fishways were up and running (at Locks 15 Euston and Lock 8 near the South Australian border), and upstream fishways were being constructed at weirs and locks 1 to 7, 9, 10 and 11. By 2008, 10 new fishways had been constructed (Murray-Darling Basin commission media release, June, 2008). Prototype fishways have also been constructed on the Barrages located between Lake Alexandrina and the Murray Mouth area in South Australia.

Spillways and bypasses have been trialled in New Zealand, to facilitate passage of eels that would otherwise be damaged by attempts (during migration) to pass through, under or over dams associated with hydroelectricity power production (e.g. Boubée, undated).

For recreational fishing of this species in Queensland, there is a 30cm minimum size, and a bag limit of 10 eels. In N.S.W., there is a size limit of 30cm, and a bag limit of 10 Short-finned Eels (N.S.W. Fisheries web site, May, 2009). The previous N.S.W. bag limit was 20 per day (N.S.W. Fisheries web site, 2003). In Tasmania, fishers must hold a current angling licence to fish A. australis australis by any method other than a bush pole (no licence is required if catching fish using a bush pole more than 1m long, without a reel and running line). In Victoria, there are fishing regulations (including minimum size of 30cm TL, and a daily bag limit of 10 eels) and recreational fishing licence requirements, and specifications by which the anglers may take Short-finned Eels (DPI Victoria, 1998b).

In Victoria, eel fishers have needed a Master Fisherman's Licence to catch and sell eels, since 1968. Those fishers who stock eels for extensive culture have required a permit since 1971. A licence holder is able to use up to 50 nets, and the licence is transferable. Since the introduction of the Fisheries Act 1995, eel fishers in Victoria now must hold an Eel Fishery Access Licence. Restrictions on eel fishing activities include the size of mesh used in a fyke net, and the maximum length of wing ends. No person other than a person operating under a commercial eel access licence can legally use or have a fyke net. There is a 30cm size limit for eels (Seafood Industry of Victoria, 2004).

In Tasmania, some attempts have been made to overcome barriers to eel migration. For example, in 1996, Hydro Tasmania installed an eel ladder on the Trevallyn Dam to provide passage for elvers.

Other Information

In recent years, a number of aquaculture research projects have been undertaken on the species, due to its aquaculture potential (e.g. De Silva et al., 2001; Ingram et al., 2001).

The Short-finned Eel occurs in a number of protected areas in New South Wales, including the State Forests of Watagon, Heaton, Ourimbah, McPherson, Putty, Pokolbin and Olney, and also Kosciusko National Park (Morris et al., 2001).

This species also occurs in Piccaninnie Ponds Conservation Park, Ewens Ponds Conservation Park, and Lower Lakes Ramsar site in South Australia (M. Hammer, Aquasave, pers. comm., 2009).

Support for S.A. Listing: Graham Edgar (University of Tasmania) and Barry Hutchins (ex-W.A. Museum).