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Fast‐start predator‐escape performance of mummichogs Fundulus heteroclitus was tested across field‐informed variation in temperature (24, 30 and 36°C) and salinity (2, 12 and 32 ppt). Performance was similar across temperatures and salinities when fish were allowed to acclimate to these conditions. However, when mummichogs experienced acute temperature changes, performance exhibited thermal dependence in two contrasting ways. Fast‐start turning rates and linear speeds varied directly with the temperature at which the manoeuvre was executed, but these aspects of performance varied inversely with acclimation temperature, with cool‐acclimated fish exhibiting faster starts across test temperatures. Temperature effects were consistent across salinities. These results suggest that while mummichogs increase performance with acute temperature increases, long‐term rises in sea temperature may cause these fish to become more susceptible to predation during abrupt cooling events, such as when storm events flood shallow water estuaries with cool rainwater.

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 6 SE ¼ 0.10 6 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 6 SE) was 0.65 6 0.08 in 2002 and 0.77 6 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. FIGURE 1.-Map of Badin Lake, North Carolina, where fishing and natural mortality rates of striped bass were assessed. 682 THOMPSON ET AL.

The traditional view of habitat requirements for inland striped bass Morone saxatilis suggests that these fish need dissolved oxygen (DO) levels above 2–3 mg/L and temperatures below 25°C to thrive. However, striped bass are found in reservoirs where hypolimnetic hypoxia forces them into warm temperatures (27–30°C) for much of the summer, and contrary to expectations, these populations do not consistently experience poor growth or mortality. We used telemetry of adult striped bass in Badin Lake, North Carolina, to characterize habitat selection by striped bass in systems with unsuitable summer habitat. As summer stratification developed, striped bass selected preferred temperatures of 20–23°C as long as the DO was at least 2 mg/L. Once hypoxia forced striped bass into warmer water, the fish concentrated at the top of the oxycline (defined as the depth just above the largest decline in DO occurring over a 1‐m change in depth), which was 1–2°C warmer but had greater DO levels (4–8 mg/L) than the coolest water, with DO of 2 mg/L. Striped bass remained at the top of the oxycline into the fall, even after deeper water with preferred temperatures and a DO level of 2 mg/L became available. We suggest that these patterns, supported by observations in the literature, represent summer habitat selection rules for striped bass in reservoirs where all oxygenated habitat exceeds temperatures traditionally considered suitable for striped bass. We also show that the depth distribution of Badin Lake striped bass in response to physical habitat constraints causes them to overlap spatially with warmwater prey inhabiting shallow, warmwater depths both in the summer and early fall. Badin Lake striped bass continue to feed and grow over the summer, providing evidence that the availability of adequate prey resources can offset the costs of poor summer habitat. Warm, productive reservoirs without permanent thermal refuges may therefore provide better habitat for maintaining quality growth and condition than those systems where occupation of cooler temperatures segregates striped bass from their prey.

An understanding of the spatial distribution of forage fish resources is required to make informed fishery management decisions. We used mobile hydroacoustics to assess the distribution and abundance of forage fish in Badin Lake, a reservoir in central North Carolina. By sampling a series of cross‐channel and longitudinal transects and analyzing the data using geostatistics, we characterized both large‐ and small‐scale spatial patterns in forage fish density. Forage fish were observed in higher densities in upstream regions of the reservoir and were seen only in surface waters during July 2000 owing to the existence of a strong thermo–oxycline and in two layers (surface and near bottom) during mixed conditions in December 2001. We observed differences in the scale of patchiness (200–700 m) in forage fish distribution depending on the region of the reservoir where sampling took place, and we infer that these patterns are governed by prevailing limnological conditions. Modeling the spatial variation in the acoustic data using geostatistics resulted in similar average densities (July 2000: 0.56 ± 0.28 (mean ± SD) fish/m2; December 2001: 0.57 ± 0.49 fish/m2) and improvements in the precision of abundance estimates based on approximated variance (July 2000: 7.05 × 106 ± 8.30 × 105 fish; December 2001: 7.07 × 106 ± 2.10 × 106 fish) when compared with arithmetic averaging and extrapolation (July 2000: 0.60 ± 0.61 fish/m2, 7.5 × 106 ± 4.61 × 106 fish; December 2001: 0.60 ± 0.69 fish/m2, 8.00 × 106 ± 6.34 × 106 fish). We found that sampling along longitudinal transects is a more efficient way to characterize the spatial patterns of forage fish distribution and to estimate systemwide abundance and biomass than using data collected with both a longitudinal and cross‐channel sampling design in this system.