Life history variables of resident Brown trout Salmo trutta L. in a coastal stream in northern Norway
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Abstract
This study focused on the population structure and life history of resident Brown trout in the lower parts of a coastal stream in northern Norway. An uneven age distribution was strongly evidenced by the low number of young fish. There was a high frequency of sexually mature males, while only a few females were sexually mature. Males mature sexually at ages between 2 - 8 years, compared with 4 - 5 years for females. Females had a significantly higher mortality rate than males, and were fewer in number amongst older fish. There were no differences between the sexes in growth rates or in the length/weight relationship. It is suggested that the low number of spawning females, as well as density-independent mortality in young stages caused by environmental catastrophes, are important factors affecting the present structure of the Brown trout population in the study area. The population is probably maintained by immigration of older specimens into the area.
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