PARENT SESSION
Oral Session #43: Fish: Ecology and Conservation.
Presiding: B. Harvey
Tuesday, August 6. 1:00 PM to 4:45 PM. Cochise Meeting Room, TCC.
Bioenergetic explanations for sexually dimorphic walleye growth: the influences of sex-specific reproductive and activity costs.
SASS, GREG*,1, KITCHELL, JAMES1, 1 Center for Limnology, Madison, Wisconsin
ABSTRACT- Walleye, Stizostedion vitreum, growth in the lakes of northern Wisconsin is sexually dimorphic; female walleye grow larger and faster than males. We used bioenergetics modeling to test eight scenarios for their potential to explain the observed differences in growth between sexes. Specifically, we examined the influence of: (1) feeding rates; (2) growth efficiency; (3) diet composition; (4) age at maturity; (5) less than annual spawning by females; (6) male fasting during spawning; (7) a combination of 5 and 6; and (8) overall reproductive and activity costs. Differences in feeding rates, growth efficiency, diet, and age at maturity were unlikely explanations for sexually dimorphic growth. Increased energy allocation to somatic tissue growth as a result of females not spawning each year explained some of the observed differences in growth. Reabsorption of the gonads or lack of spawning by mature females has been observed in several walleye populations, which provides empirical support to this mechanism. Lower feeding rates by male walleye and increased activity costs during spawning could account for the remaining differences observed in growth. Once mature, male walleye spawning behavior may result in increased energy expenditure and lower feeding rates than females. The combined effects of females not spawning every year and fishery selection pressure for smaller males may have implications for the management of the joint tribal and recreational fishery in northern Wisconsin.
KEY WORDS: Bioenergetics modeling, walleye, spawning behavior, sexually dimorphic growth