| dc.description.abstract | Most studies of the walleye have been conducted on highly
exploited populations. Savanne Lake in northwestern Ontario, and
having an area of 364.29 ha, was exploited until 1969, whereupon
it was designated a fish sanctuary. Study was conducted during
the spring months of 1973, 1974 and 1976. Walleyes were marked
and recaptured in trapnets. Marking was accomplished by attaching
a Floy tag FTF69 under the second dorsal fin with monofilament
line. The 6th, 12th and second dorsal spines were clipped In the
springs of 1973, 1974 and 1976, respectively, for Schumacher-
Eschmeyer estimates. Schumacher-Eschmeyer spring population estimates
of 5211, 5184 and 5463 for the three study years represent
the spawning population most vulnerable to the gear.
The annual mortality rates were a high 8 to 85% for the component
of the population sampled and characteristically increased
with age over the three years of study.
Growth retardation was observed among tagged walleyes; some
of the walleyes neither grew in length nor laid down a new annulus
in each year of their life. These observations were attributed
to limited food supply and extensive handling, tagging and finclipping
of the fish over the study period.
No relationship was noted between year-class strength and
year-class growth. Walleyes showed similar annual percentage
increments in their growth during the three sampling years. Relative
growth of walleyes increased substantially by the end of the
first year, decreased sharply the second year and continued to
decrease at a lesser rate until, on the average, the fifth or
sixth year. After this, growth was very slow.
Annual biomass of 6.58 kg.ha[superscript 1] for 1973-74, 6.06 kg.ha[superscript 1] for 1974-75 and 2.64 kg.ha[superscript 1] for 1975-76 for age groups 7 and older was low. Production estimates of 1.0 kg.ha[superscript 1].yr[superscript 1] for 1973-74, 1.31 kg.ha[superscript 1].yr[superscript 1] for 1974-75 and 0.52 kg.ha[superscript 1].yr for 1975-76 for age groups 7 and older are likely values for a theoretical yield of 1.9 kg.ha[superscript 1].yr[superscript 1] based on the morphoedaphic
index (Ryder 1965) and support the 30 percent rule. The brood
stock production estimate of 1.85 kg.ha[superscript 1].yr[superscript 1] for fish of age 5.5 (weighted mean age to first maturity) and older, and representing
about 20% of the total walleye production in the lake,
relates closely to the theoretical yield of 1.9 kg.ha[superscript 1]..yr[superscript 1] based on the 30 percent rule.
The slow growth of the walleyes was attributable to chemical
characteristics typical of lakes in this region of the Canadian
Shield, as well as to their high density relative to the available
food. | |
