Effects of commercial fishing regulations on stranding rates of bottlenose dolphin (Tursiops truncatus).

Fisheries management actions taken to protect one speciescan have unintended, and sometimes positive, consequences on other species. For example, regulatory measures to reduce fishing effort in the winter gillnet fishery for spiny dogfish (Squalus acanthias) off North Carolina (NC) also led to decreases in the number of bycaught bottlenosedolphins (Tursiops truncatus). This study found that a marked decrease in fishing effort for spiny dogfish inNC also corresponded with a marked decrease in winter stranding rates of bottlenose dolphins with entanglementlesions (P= 0.002). Furthermore, from 1997 through 2002, there was a significant positive correlation (r2 = 0.79;P= 0.0003) between seasonal bycatch estimates of bottlenose dolphins in gill nets and rates of stranded dolphinswith entanglement lesions. With this information, stranding thresholds were developed that would enable the detection of those increases in bycatch in near real-time. This approach is valuable because updated bycatch estimates from observer data usually have a time-lag of two or moreyears. Threshold values could be used to detect increases in stranding rates, triggering managers immediately to direct observer effort to areas of potentially high bycatch or to institute mitigation measures. Thus, observercoverage and stranding investigations can be used in concert for more effective fishery management.