Population dynamics of an exploited population of Orconectes virilis in Northwestern Ontario

Abstract

Exploitation of northern stocks of the crayfish Orconectes virilis (Hagen) produced significant alterations in several population parameters. High fishing efforts increased per capita fecundity, young-of-year (YOY) production, and age- and sex-specific growth, and altered mortality patterns. Climatic variation, measured as arbitrarily defined weather variables, did not influence life history parameters in the exploited population. However, short-term temperature fluctuations affected YOY production and future reproductive potential in the control lake. The control population in Shallow Lake exhibited strong density dependence in regulating both mortality and growth rates of pre-recruit age classes. Behavioural dominance by maturing males (age I-to-age II) effectively controlled juvenile life history parameters , i.e., egg-to-YOY and YOY-to-age I mortality and growth. As a result a dynamic oscillatory relationship existed between annual age I-to-age II male growth and female year-class strength, which in turn correlated with cohort egg production. Exploitation of Dock Lake's population broke down this process so that year-class strength directly correlated with annual growth but cohort egg production varied independently. The amount harvested, using passive fishing gear, proportionately increased with increases in nominal effort. However interactions between sampling intensity, duration of harvest and behavioural responses resulted in a upper limit to the percent of the exploitable stock that that could be removed by this fishery. Rlteration of life history parameters contributed to population resilience and stability as fishing pressure increased.