Common Bottlenose dolphins (Tursiops truncates) in North Carolina are vulnerable to fisheries bycatch (fisheries interaction (FI)), particularly in gillnets. Although observed bycatch is relatively rare, stranding with evidence of FI is universal and can be used to evaluate relative levels of and influences on bycatch. Stranding from 1997 through 2012 had evidence of FI (N-191) but no evidence of human interaction (n-170). Research by National Marine Fisheries Services, which was carried out in a Generalized Linear Model in three periods (TP) showed that bycatch risk of older calves and subadults was 1.5 (summer) to 3.5 (spring) times greater than for an adult or young one-year-old. Therefore, young dolphins surviving past their first year face the risk of bycatch. Thus, the observer’s objective of the study was to examine quantitively whether there was a differential risk of bycatch by sex and age class controlled for variables previously demonstrated to have a significant effect on stranding: a marked reduction in spiny dogfish gillnetting effort, geographic area and season.
Common bottlenose dolphins (Tursiops truncates) are vulnerable to bycatch in a variety of fishing gear throughout their range. Circumstances around how a dolphin becomes entangled in gear are often a mystery as these events are rarely observed. Depredation has been documented for gill nets in North Carolina (NC), gillnets and trammel nets. Bottlenose dolphins also depredate trawlers and feed on discards or prey stirred up by or attracted to the gear. This depredation may be dangerous due to the risk of entanglement.
Bycatch of the coastal form of bottlenose dolphins has been documented along the mid-Atlantic coast of the US by fisheries observers and by stranding networks that recover stranded animals with gear attached or entanglement lessons. This bycatch is of concern for the conservation of local stocks, which is particularly acute in N.C. Understanding the exact nature of dolphin interaction with fisheries is difficult, but some factors can be examined that may offer clues regarding influences on the risk of bottlenose dolphins becoming entangled. In N.C., for example, stranded bottlenose dolphins with signs of FI have had a partial or seasonal component associated with coastal gillnet fisheries targeting partial species such as sport (leiostomes xanthurus) and spiny dogfish (Squalus acanthus).
The official observers (National Marine Fisheries Service) evaluated to determine their effect on a stranded dolphin being FI; season, area, habitat (coastal or estuary), sex, age class, and period. The variables season, space, and habitat were chosen by known spatiotemporal variation in fishing activities. They used the Generalized Linear Model (GLM) to determine the effect of possible predictor variables on the risk of stranding being FI vs. no (hereafter referred to as bycatch risk). The sample size did not allow for all variables to be examined simultaneously.
Their research indicated that, from 1997 through 2012. 1.368 bottlenose dolphins stranding were recovered in N.C. (Annual mean=85.5, SD=17.4). Of those, 60 %( n=821) were categorized as could not be determined (CBD) (Annual mean=513, SD=8.6). Of the remaining 547 stranding’s, 42 %( n=229) were categorised as FI (Annual mean=14.3, SD=7.1), 50 %( n=274) were categorized as NO for HI (annual mean=17.1, SD=2.0)
