Research Document - 2011/128

Synthesis of biological and harvest information used to assess populations of northern form Dolly Varden (Salvelinus malma malma) in Canada. Part III: Comparison among populations

By C.P. Gallagher, M.-J. Roux, K.L. Howland, and R.F. Tallman

Abstract

Biological information of anadromous, resident and isolated life history types of northern form Dolly Varden (Salvelinus malma malma) collected from the Yukon and Northwest Territories are synthesized, with emphasis placed on populations of anadromous Dolly Varden from the Firth River/Joe Creek, Babbage River and Vittrekwa River. Data collected from all rivers (excluding the Vittrekwa due to low sample size) supporting anadromous populations which included the Big Fish and Rat rivers and the aforementioned systems were compared to elucidate effects of population decline on biological characteristics. Populations known to have experienced declines were compared with others that were believed to have experienced lower harvest rates for time periods when methodologically consistent biological information was available from all river systems (1986-88 and 1993-95). Data includes population sizes, length and age characteristics, growth, and reproduction. The synthesized information suggests some differences in biological characteristics among anadromous populations. Larger size and older ages were attained in the Firth River compared to other systems. Length characteristics between male and female spawners were similar in the Firth River and Joe Creek, however males attained larger sizes than females in the Babbage. There were some differences in age between sexes among years although the data were highly variable. Females and males within each system appeared to mature at similar ages. Females consistently outnumbered males among stocks. Among population comparisons demonstrated that Dolly Varden from the Firth River/Joe Creek and females from the Big Fish River appear to spawn annually upon reaching maturation, which is not the pattern observed in the Babbage and Rat rivers and in males from the Big Fish River. Additional comparisons revealed that declines in abundance appear to change the population demographics such as a decrease in the proportion of large size fish, lower growth rate, and a decrease in the proportion of spawning males. Relatively little information exists on resident and isolated Dolly Varden. These fish are smaller in size, have slower growth and do not attain similar maximal ages compared to anadromous Dolly Varden.

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