Pelagic false killer whales (PFKW) are killed or seriously injured in the Hawai‘i-based deep-set longline fishery more than any other cetacean population, with bycatch regularly exceeding allowable levels. Knowledge of the movements and habitat use of this population is limited, but could inform efforts to mitigate bycatch. We use satellite tag data from five PFKW from three groups to assess longline fishery interactions and resource selection. In 2013, two whales (154d and 14d) were tagged in the Northwestern Hawaiian Islands, and a group of three (123d, 15d and 12d) off Hawai‘i Island. Tracks ranging from west of Midway to >1900km east of Hawai‘i Island were compared to 4182 set positions made by the Hawai‘i-based deep-set longline fleet during the tracking period. Information on longline effort from other countries was not available. In one case, three PFKW changed direction and rapidly approached a set from almost 100km when the vessel was hauling gear and remained within the area being fished during the following set, before moving away during the third set. On some occasions (n=3), PFKW potentially reacted to the gear haul, but either stopped short of approaching the set or quickly transited the area of the set without stopping. Other times (n=2), PFKW did not appear to react to sets that were within 30km. Resource selection analysis was conducted on the three PFKW with the longest independent tracks, using a switching state space model to determine representative daily positions. We assessed positions as a function of the nearest longline set, as well as 25 oceanographic, atmospheric and lunar variables. The best fit model was chlorophyll-a concentration, distance to the nearest longline set, and significant wave height. Understanding the behavior of PFKW in response to both longline vessels and the natural environment is vital for ongoing efforts aimed at reducing bycatch.
Citation:
Anderson, D., R. Baird, A. Bradford, D. Webster. 2017. Longline fishery interactions and resource selection of satellite-tagged pelagic false killer whales in the North Pacific. Abstract (Proceedings) 22nd Biennial on the Biology of Marine Mammals, Halifax, Nova Scotia, October 22-27, 2017.