Community dynamics resulting from an experimental pulse fishery on the walleye (Stizostedion vitreum vitreum Mitchill) in Henderson Lake / by Brian D. Wisenden
Wisenden, Brian D.
SubjectWalleye (Fish) Ontario Henderson Lake
Population density, age structure, production and biomass of walleye, northern pike and white suckers
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Henderson Lake is a small 151 ha boreal percid lake approximately 128km northwest of Thunder Bay. A pulse fishery conducted from 1980 to 1982 inclusively, removed 3226 walleye reducing the stock to very low levels (Reid, 1985). The. current study had four objectives: first, to continue monitoring the population density, age structure, production and biomass of walleye, northern pike and white suckers; second, to collect comparative walleye age and growth data from a nearby control lake; thirdly, to investigate the feeding ecology of young of the year walleye as well as to discern any potential competitive interactions with the superabundant yellow perch population; and fourth, to review the community dynamics of Henderson Lake for signs of shifts in species abundance and growth in response to the walleye exploitation. These data provided interesting insights into the feasibility of a pulse fishery as an alternative walleye management strategy. Since 1980, the walleye decreased in mean age to maturity and increased in fecundity and growth (Reid, 1985) but unexpectedly, had five consecutive years of recruitment failure between 1980 and 1984. Normal walleye recruitment in the nearby Lanigon Lake suggests that the year class failures in Henderson Lake were not due to climatic factors. Possible causes include recruitment overfishing (Cushing, 1977) exacerbated by variable spring water thermal regimes. The stunted yellow perch population, the principal forage species, both increased in abundance and became further stunted in response to reduced walleye predation. Four years after removal stopped, northern pike aged four and older increased both in growth as well as fecundity. As recruitment increased growth of young pike stabilized. Pike production, biomass and turnover rates dramatically increased from 1982 to 1986. These changes were probably a delayed response to improved forage opportunities and decreased walleye abundance. No changes were observed in the sucker population in response to the walleye removal. The first evidence for walleye population recovery came with production of strong year classes in 1985 and 1986. Young of the year (YOY) walleye in Henderson Lake grew faster than any others reported in the literature with the exception of Lake Erie fish in 1959 (Parsons, 1972) . YOY walleye made regular crepuscular feeding forays into shallow water with peaks of activity at 21;20hr at a mean ambient light intensity of 2.76W/m^. Stomach contents revealed a diet of fish (94.68- 99.79% by weight) most of which were YOY yellow perch. Dietary overlap indices between YOY walleye and adult yellow perch in the length ranges of 91-131mm and 131-200mm (total length) indicated that perch were potential competitors with 10-41% and 10-33% dietary overlap, respectively. The recovery period for walleye must be reasonably brief if pulse fishing is to be a viable method of walleye management. Both the increase in perch abundance, and consequentially pike production, may delay reestablishment of walleye densities sufficient to support another pulse fishery. The variable spring thermal regime and short growing season imposed by the northtemperate climate of Henderson Lake delayed the responses in the percid community. Pulse fishing as an alternative management strategy must consider the possibility of recruitment failure, time lags in the community dynamics and interspecific suppression of the recovery process and even complete collapse.