Probability-Based Analysis of Pilot Whale-Pelagic Longline Interactions

We apply joint-probability analysis to evaluate the probabilities of interactions between pelagic longline gear (PLL) and pilot whales. The objectives of this study were to: (1) Investigate how pilot whales and Risso’s dolphins are interacting with pelagic longline gear during fishing and haulback; and (2) Characterize pilot whales’ and/or Risso’s dolphins’ social structure/behavior and/or habitat utilization in the Mid-Atlantic Bight region and how it may influence interactions with pelagic longline gear. Interaction probabilities were created using varying temporal and spatial parameters along with detailed gear information. From 2010 to 2012, temperature-depth recorders (TDRs) were deployed on commercial PLL gear (n=23, average soak duration 6 hours) and digital acoustic tags (DTags) were deployed on pilot whales (n=8, average tag duration 8 hours). TDR records were used to generate probabilities of gear depths at varying times and DTag records were used to create both habitat utilization envelopes and feeding probabilities varying across depths and times. The combination of these fine-scale pilot whale data (DTag and echolocation) and PLL gear depth distribution were used to evaluate the probabilities of interactions between PLL gear and pilot whales at varying temporal and horizontal-vertical spatial scales, as well as different feeding motivations. By creating a standard exportable methodology for assessing interaction probability bycatch reduction methodologies can be applied to specifically identified and thus targeted areas of high interaction probabilities.