Monitoring warm‐water fish populations in north temperate regions: sampling considerations when using proportional stock density

Three lakes were repeatedly sampled at night using boat electric fishing, experimental gill netting, and fyke netting from May to November 1993 to evaluate the feasibility of using proportional stock density (PSD) to monitor warm‐water fish populations in Washington State, USA. Additionally, average night‐time boat electric fishing catch‐per‐effort of largemouth bass, Micropterus salmoides (Lacepéde), from 30 Washington lakes was also analysed to determine the amount of effort required to obtain adequate samples for precise PSD estimates. Temporal variations in PSD were not large enough to affect the management of warm‐water fish populations in the small Washington lakes studied. However, the considerable effort required to obtain precise PSD estimates may limit its usefulness for warm‐water fisheries surveys in the Pacific Northwest. On average, from three to 13 nights of electric fishing effort are needed to capture enough stock‐length largemouth bass for PSD estimates, depending on the precision desired (80–95%) and the location of the lake (eastern or western Washington). Catch of stock‐length fish can be maximized by using electric fishing for centrarchids and gill netting for yellow perch, Perca flavescens (Mitchill), in June or September. Adequate samples for precise PSD estimates can be difficult to obtain from Pacific Northwestern lakes, even when using recommended gear at optimum sampling times. Inability to capture an adequate sample size for precise PSD estimates may be responsible for some of the fluctuation in PSDs in some studies of warm‐water fish populations in northern areas. Managers in other northern climates may find that low sample size may account for large variations in PSDs reported.