Seasonal Natural and Fishing Mortality of Striped Bass in a Southeastern Reservoir

Abstract

Reliable estimates of natural and fishing mortality are important for management of exploited fish populations, but these components of the total mortality rate can be difficult to determine by traditional fisheries methods. We used telemetry data to determine seasonal instantaneous fishing (F) and natural mortality (M) rates of subadult and adult striped bass Morone saxatilis in Badin Lake, North Carolina. Our analyses were based on the fates of 64 fish implanted with sonic transmitters and released and tracked for 2 years. Natural mortality was low and constant during the course of the study (M ± SE = 0.10 ± 0.01) and was similar to estimates for other reservoir populations of striped bass. A natural mortality rate of 0.09–0.16 may be a reasonable approximation for populations across the southeastern United States. Fishing mortality varied seasonally and was highest in the spring and summer of 2002 and the summer and fall of 2003; annual fishing mortality (F ± SE) was 0.65 ± 0.08 in 2002 and 0.77 ± 0.08 in 2003. Due to these high harvest rates, estimated annual survival rates were low for the Badin Lake population (47% in 2002; 42% in 2003). Results of a yield-per-recruit model suggest that harvest of older, larger individuals can be increased in Badin Lake with a decrease in fishing mortality or a moderate increase in the minimum size limit, even when the effect of catch-and-release mortality of fish below the size limit is considered. Our results also indicate important considerations for researchers using this method in the future, including the need to estimate downstream emigration and delay the inclusion of newly tagged fish in analysis to avoid biasing estimates of fishing mortality.