| dc.description.abstract | 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. | |
