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Long‐Term Changes in Brown Trout and Rainbow Trout Populations in Great Lake, Tasmania
Author(s) -
Davies P. E.,
Sloane R. D.
Publication year - 1988
Publication title -
north american journal of fisheries management
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.587
H-Index - 72
eISSN - 1548-8675
pISSN - 0275-5947
DOI - 10.1577/1548-8675(1988)008<0463:ltcibt>2.3.co;2
Subject(s) - brown trout , rainbow trout , salmo , fishery , trout , dominance (genetics) , fishing , catch and release , biology , geography , recreational fishing , fish <actinopterygii> , biochemistry , gene
Great Lake, central Tasmania, was first stocked with brown trout Salmo trutta in 1870 and with rainbow trout Oncorhynchus mykiss (formerly Salmo gairdnert ) in 1910; both species established self‐supporting populations. Angling statistics revealed a general decline in mean weight of both species from 1892 (brown trout) and 1912 (rainbow trout) to 1950. During 1950–1985, the annual mean size of trout in anglers' catch and spawning migrations stabilized; overall mean weights of brown trout and rainbow trout were, respectively, 1.2 and 1.0 kg in anglers' catch, and 1.4 and 1.5 kg in spawning migrations. Four stages were evident in the fishery: initial dominance of brown trout prior to 1920, rainbow trout dominance in anglers' catch and spawning migrations during 1920–1940, declining numbers of rainbow trout and mean weight in catch from 1940 to 1950, and equal representation of both species in angler catches with a predominance of brown trout in spawning migrations from 1950 to 1985. Various correlations between lake levels, the size of trout in angler catches and spawning migrations, and the species composition of catch and spawning migrations are explained in terms of inundation of new ground, location of feeding zones, and bias due to angling method. Mean weight of fish in the catch was inversely correlated with minimum lake depth during the period 1945 to 1985. Characteristics of the recreational fishery were evaluated from license form census data from 1945–1946 to 1957–1958 and from postal questionnaire returns for the 1985–1986 and 1986–1987 seasons for full‐season license holders. A significant decrease in catch per angler day since the 1945–1957 period has been accompanied by an increase in the total harvest, an increase in days fished per angler, and an increase in the number of anglers fishing the lake. These changes have not been accompanied by significant changes in the mean catch weights or the length‐frequencies in anglers' catches or in the spawning migrations of either trout species. Two management strategies, removal of spawning brown trout and stocking with juvenile rainbow trout, failed to significantly increase the proportion of rainbow trout in the catch or in the spawning migrations. Man‐made environmental changes and lake‐level fluctuations associated with management for hydroelectric power generation are considered the dominant influences on the dynamics of the trout populations in Great Lake.