J. zyxwvutsrqponm Appl. Ichthyol. zyxwvutsrqpon 14 (1998), zyxwvutsrqp 23-30 ISSN 0175-8659 zyxwvutsrq 0 1998 Blackwell Wissenschafts-Verlag, Berlin zyxwvutsrqpo Rereiired: zyxw Fehruarj' 21. zy 1997 Arcepfed: December. 15. 1997 Aspects of the culture-basedfishery of the shortfinned eel, Anguiffa australis, in western Victoria, Australia Bradley W. Skehan and Sena S. De Silva School of Ecology and Environmen~, Deakin University, PO Box 423 Warrnambool. Victoria 3280, Australia Summary The Victorian eel fishery is based primarily on the shortfinned eel, Anguilla australis, and is essentially a culture-based fishery. 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. In the present study commercial catch, effort and stocking data for 17 culture lakes in western Victoria (37"26'-38"15'S, 142"13'-144"06'E) were consulted with the view to improving the selection and management of culture lakes and their eel fishery. The database was used to explore the development of various yield-predictive models, incorporating different mor- phometric data of the lakes and fishery data, and combinations thereof. Models depicting curvilinear relationships between the annual mean fish yield per hectare of several lakes and their catchment area: shoreline development (DJ ratio (where DL = sf2JlIA and A = lake surface area in km2and s = shore- line length in km), and mean water surface area were the most valid statistically. While fish yield was most strongly correlated with surface area, other factors such as lake fertility may have had an important contribution. The effectiveness of the stocking program was investigated using time-lapse analysis which was also used to estimate when elvers and larger 'restock' fish appear in the commercial catches. Whereas 'restock' eels entered at 1-5 years after stocking, elvers entered after 8-1 3 years. The mean yield per hectare was linearly related to the stocking rate of 'restock' eels. The preliminary results of elver stockings caution that a re-evaluation of this program may be necessary. Introduction The Australian eel fishery currently accounts for about 500 tonnes (t) per year, based on three Anguillid species (Stewart 1993). The fishery, however, is mainly concentrated in the east- ern States, primarily in Victoria which contributes about 350 t to the fishery. The Victorian eel fishery is based largely on the shortfinned eel, Anguilla australis Richardson 1841, and the fishery is essentially culture-based. This fishery adopts two stra- tegies: stocking of glass eel and elvers caught during their migration into inland waters, and restocking/releasing of smal- ler size young eels, which are caught from various waters and often in poor condition. By and large the annual stocking of glass eels and elvers into designated inland water bodies is the predominant component of this culture-based fishery. Overall, there is very little known on the biology (Beumer 1979; Sloane 1984a,b,c), culture and the fishery of Australian shortfinned eel and/or the Australian freshwater eel fishery in general. Hall et al. (1990) presented an overview of the Victorian eel fishery, but culture-based aspects of the fishery were not fully dealt with. McHugh (1996) studied the feeding ecology and growth of eels in west Victorian culture lakes with a view to improving the selection of water bodies for the extensive grow-out of eels. De Silva et al. (I 997) evaluated the changes in fatty acid profile in relation to development of young shortfin eel. With the decline in glass eel and elver resources globally, and the consequent increase in world demand of this resource for intensive culture purposes, particularly by some Asian countries such as China, Japan, Korea and Taiwan, the need has arisen to examine the long-term viability of the existing strategies of the inland eel fishery in Victoria (Ingram and Gooley 1996). It is believed that a more rational use of the stocking material is needed to keep the Australian eel fishery viable, and indeed make maximal and sustainable use of Australian glass eel and elver resources. Also, emphasis on local eel culture is expected to increase in the future, in response to concerns that wild stocks can no longer sustain further increases in fishing pressure (Stewart 1993; Ingram and Gooley 1996). Yield prediction is basic to inland fisheries management irres- pective of whether a fishery is dependent on natural stocking and/or stock enhancement. Yield prediction employing various morphoedaphic properties (Rawson 1952, 1995; Ryder 1965; Oglesby 1977), stocking densities (Wijeyaratne and Costa 198 I; De Silva et al. 1992) and catch and effort data (De Silva et al. 1991) have been realized for several tropical and north tem- perate lakes and reservoirs as useful tools for the management of their fisheries. Lorenzen (1995), on the other hand, con- sidered the population dynamics of culture-based fisheries and developed suitable models for their management. In the present paper the eel fishery in 17 inland water bodies in Victoria, Australia (37"26'-38"15'S, 142"13'-144"06'E) are examined, and attempts are made to develop yield-predictive models incorporating morphometric features of the lakes, such as water surface area, catchment or watershed area, and shore line development and stocking strategies of culture lakes for the Australian shortfinned eel, Anguilla australis. The research is expected to contribute to an improved selection and man- agement strategy of culture lakes in western Victoria, and pro- vide new direction for the Victorian eel fishery. Furthermore, as yield prediction for Australian inland waters is still in its infancy, this research will provide supporting evidence that yield prediction is equally applicable to temperate waters in the Southern Hemisphere. U S Copyright Clearance Center Code Statement 0 1 75-8659/98/ 1 40 1-0023$14.00/0