Southeast Alaska Sperm Whale Avoidance Project (SEASWAP): a successful collaboration among scientists and industry to study depredation in Alaskan waters

Abstract

In Alaskan waters, depredation on sablefish longline gear by sperm whales increases harvesting cost, negatively biases stock assessments, and presents a risk of entanglement for whales. The Southeast Alaska Sperm Whale Avoidance Project (SEASWAP), a collaborative effort involving industry, scientists, and managers, since 2003 has undertaken research to evaluate depredation with a goal of recommending measures to reduce interactions. Prior to 2003, little was known about sperm whale distribution and behaviour in the Gulf of Alaska (GOA). Although fishers were reporting increasing interactions, the level of depredation varied with no apparent predictor of occurrence across vessels. Between 2003 and 2007, fishers were provided with fishery logbooks and recorded information on whale behaviour, whale presence and absence, during the set, soak, and haul for 319 sets in the GOA. Data were evaluated for a vessel, area, and seasonal (month) effect in the presence and absence of sperm whales. Using catch per unit effort (cpue) as a metric, in kg/100 hooks, results indicated that depredation depended on both the vessel and the area. More whales associated with vessels from April to August. Sperm whales were also likely to be present when cpue was high, revealing that whales and fishers both knew the most productive fishing areas, but confounding the use of cpue as a metric for depredation. Using a Bayesian mark-recapture analysis and the sightings histories of photo-identified whales, an estimated Nˆ=135 (95% CI 124, 153) sperm whales were associating with vessels in 2014. A spatial model was fitted to 319 longline sets and quantified a 3% loss in cpue, comparable to other global studies on sperm whale depredation. Through all phases of SEASWAP, our understanding of depredation has gained significantly. This successful collaboration should be considered as a model to create partnerships and build collaborations between researchers and fisherpeople encountering marine mammal interactions with fishing gear.

How do fishing practices influence sperm whale (Physeter macrocephalus) depredation on demersal longline fisheries?

“…For example, sperm whales have been reported depredating on 18 to 25% of Patagonian toothfish longline sets in South Georgia (Moir Clark and Agnew, 2010; Purves et al, 2004;Söffker et al, 2015) and 35% of the sets in the Falklands (Goetz et al, 2011;Yates and Brickle, 2007). In Alaska, 10 to 35% of all longline sets were depredated by sperm whales on the sablefish fisheries (Hill et al, 1999;O'Connell et al, 2015;Peterson and Carothers, 2013;Straley et al, 2006Straley et al, , 2015Thode et al, 2015).…”

Evidence for dietary time series in layers of cetacean skin using stable carbon and nitrogen isotope ratios

“…Between 2003 and 2017 in the eastern GOA, skin from 28 free‐ranging male sperm whales was collected via biopsy in the same manner as the sample from experiment 1 (Table ). These samples were collected as part of the Southeast Alaska Sperm Whale Avoidance Project (SEASWAP, http://www.seaswap.info), which focuses on sperm whales that interact with longline fishing vessels in the eastern GOA, primarily targeting sablefish . From each of the samples a single column of skin was cut into subsamples corresponding to the three skin layers described above: “outer,” “middle,” and “inner,” parallel to the angle of the blubber–skin interface of each sample.…”

“…These samples were collected as part of the Southeast Alaska Sperm Whale Avoidance Project (SEASWAP, www.seaswap.info), which focuses on sperm whales that interact with longline fishing vessels in the eastern GOA, primarily targeting sablefish. 76,78 From each of the samples a single column of skin was cut into subsamples corresponding to the three skin layers described above: "outer," "middle," and "inner,"…”

“…While the current diet of sperm whales in the GOA is poorly understood, stomach content data from historical whaling show that they feed on a variety of deep‐sea fishes and squid . They are also known to remove sablefish ( Anoplopoma fimbria ) and halibut ( Hippoglossus stenolepis ) from commercial longline fishing gear in the GOA …”

“…61,[73][74][75] They are also known to remove sablefish (Anoplopoma fimbria) and halibut (Hippoglossus stenolepis) from commercial longline fishing gear in the GOA. [76][77][78][79] In this investigation, we aim to determine if layers of cetacean skin exhibit isotopically distinct signatures, which may be attributed to temporal shifts in diet. To address this objective we designed a pilot study consisting of two experiments.…”