Sex and Year Comparisons of Lake Superior Pink Salmon ( Oncorhynchus Gorbuscha) Adipose Fins

Abstract

The adipose fins of pink salmon ( Oncorhynchus gorbuscha Walbaum) from the Carp River, a southeastern Lake Superior tributary, are sexually dimorphic. The adipose fins of males are consistently longer than those of females for all sizes of fish measured, despite sex and year differences in fish size. Greater relative adipose fin size in males may help reduce caudal peduncle wear resulting from agonistic interactions among competing males on the spawning grounds. Differences in relative adipose fin size between years were not found, consistent with the lack of segregation between even- and odd-year stocks which characterizes Great Lakes populations. Adipose fin size increased in a positive allometric fashion with increasing fish length in both sexes. Compared to British Columbia pink salmon, adipose fin sizes are less distinct sexually but similarly variable. This finding holds promise for use as a technique for sexing older Great Lakes pinks externally, and hence may have management implications.