H. Helminen et al., YEAR-CLASS FLUCTUATIONS OF VENDACE (COREGONUS-ALBULA) IN LAKE PYHAJARVI, SOUTHWEST FINLAND, DURING 1971-90, Canadian journal of fisheries and aquatic sciences, 50(5), 1993, pp. 925-931
Many recent studies have stressed density-dependent regulation mechani
sms in oscillating vendace (Coregonus albula) populations. Long-term s
tudies on the population dynamics of vendace have been hampered by the
difficulty of obtaining reliable estimates of year-class sizes. Data
collected from Lake Pyhajarvi (Southwest Finland) during 1971-91 allow
ed relatively accurate analysis of vendace abundance changes. in the w
inters of 1979-91, daily catch statistics were collected from professi
onal fishermen. Species, age, and size composition were analysed from
regular catch samples. We estimated the size of the vendace population
from the decrease in the CPUE during 10 winters. For the remaining 10
years, estimates were based on the relationship between the numbers o
f a year-class in autumn and mean individual growth rate. A 2-yr cycle
was the most conspicuous feature of the data implying density-depende
nt regulation. We suggest that in Lake Pyhajarvi the basic model produ
cing a persistent 2-yr cycle is the asymmetrical food competition betw
een age groups.