| Abstrakt: |
AbstractLife history characteristics (age, growth, survival, and maturity) were compared between the deepwater “humper” and shallow-water “lean” forms of lake trout Salvelinus namaycushin Lake Mistassini, Quebec, to determine whether the two morphotypes may represent resource polymorphism. Lake trout were sampled using graded-mesh (range = 51–114 mm stretch) gill nets set in deep and shallow waters. Humpers were typically caught in deep waters (>50 m) and averaged 474 mm TL (range = 389–616 mm) and 852 g in weight (range = 470–1,710 g), whereas leans were typically caught in shallow waters (<50 m) and averaged 525 mm TL (range = 301–865 mm) and 1,210 g in weight (range = 200–6,500 g). Humpers and leans did not differ in weight–length relationships and grew slimmer with length over a common TL range (389–616 mm). Average age of humpers was 27 years (range = 13–49 years); average age of leans was 21 years (range = 6–42 years). The two forms did not differ in total annual mortality (A) of fish older than 17 years, the first age beyond which numbers declined with age for both morphs (A= 5.1%; 95% confidence interval = 2.4–7.8%). Humpers grew slower (annual growth rate ω= 53 mm/year) than leans (ω= 68 mm/year) and to a shorter mean asymptotic length (L∞= 514 mm) than leans (L∞= 605 mm). Mature humpers (mean TL = 475 mm, SE = 9.0; N= 58) were shorter on average than mature leans (mean TL = 539 mm, SE = 8.5; N= 65); mature humpers (mean age = 27 years, SE = 1.0; N= 56) were also older on average than mature leans (mean age = 23 years, SE = 0.98; N= 61). We conclude that lean and humper forms of lake trout in Lake Mistassini differed in age, growth, and maturity; this is consistent with the resource polymorphism that has been observed for other lake trout populations and other char species.Received June 24, 2011; accepted July 2, 2012 |
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