Gulf of Alaska | Ecosystem Perspectives
Transition to pot fishing gear in the Gulf of Alaska sablefish fishery and implications for sperm whale depredation Presenter: Megan Williams , mwilliams@oceanconservancy.org, Ocean Conservancy
Daniel Goethel , daniel.goethel@noaa.gov, Alaska Fisheries Science Center Dana Hanselman , dana.hanselman@noaa.gov, Alaska Fisheries Science Center
Sperm whale ( Physeter macrocephalus ) depredation (whales removing or damaging sh caught on shing gear) in the Gulf of Alaska (GOA) can reduce sablefish ( Anoplopoma fimbria ) catch rates and increase uncertainty in survey- and fishery-derived estimates of sablefish abundance. To minimize fishery interactions with sperm whales, the North Pacific Fishery Management Council legalized longline pot fishing gear for sablefish in the Gulf of Alaska in 2017. This research employs a Generalized Additive Mixed Modeling approach to explore the potential impacts associated with the transition to pot fishing gear in the commercial sablefish fishery on: 1) the frequency of sperm whale depredation events, and 2) the effect of depredation on sablefish catch rates. The proportion of commercial fishery longline hook and line sets impacted by depredation increased from 2001-2021 across the GOA; however, the rate of increase varied regionally. The sperm whale depredation effect on sablefish catch rates for impacted sets also increased over time and was greatest in most GOA regions from 2016-2021 (42%-47% catch rate reductions 2016-2021). These results suggest that sperm whales may be increasing depredation pressure on remaining hook and line fishers and/or are becoming more efficient at removing sablefish from the longline gear. However, given the rapid displacement of hook and line gear with pot gear since 2017, the total number of depredation events have decreased; thus overall sablefish mortality due to whale depredation has also decreased. This research has implications for the sablefish stock assessment as well as for sablefish harvest strategies and highlights the important connections between management, marine mammal interactions and fishery participation.
Alaska Marine Science Symposium 2023 31
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