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

Abstract

Marine mammal depredation on fisheries (animals removing fish caught on fishing gear) is a worldwide issue involving socio-economic and ecological consequences. Longline fisheries are the most impacted by odontocete (toothed whales) depredation. While technological means have provided limited efficacy in reducing depredation, this study examined the fishing practices influencing both the proportion of depredated longline sets and the amount of fish removed by whales. We used an 8-year dataset from the Patagonian toothfish (Dissostichus eleginoides) longline fisheries operating in Crozet and Kerguelen Economic Exclusive Zones (EEZs) (South Indian Ocean) and GLMMs to investigate sperm whale (Physeter macrocephalus) depredation. Sperm whale depredation occurred on 61% of 5260 sets in Crozet and 41% of 16,902 sets in Kerguelen, and resulted in minimum estimated toothfish losses of 702 tons and 2649 tons, respectively, in the two areas. The probability of depredation decreased in winter months, increased with depth fished and decreased when vessels travelled over distances of >60 km from fishing grounds with encountering depredation. These findings suggest the natural spatio-temporal distribution of sperm whales and their ability to follow vessels over limited ranges influence the number of captured fish removals. The amount of depredated toothfish decreased with the speed at which longline sets were hauled and increased with the soaking time of sets suggesting that whales may depredate sets during both hauling and soaking operations. Together, these observations indicate that rates of depredation may be influenced by the conditions of fishing operations and could therefore be Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site.employed to implement strategies of avoidance in all fisheries facing similar depredation impacts.

Commercial fishing patterns influence odontocete whale-longline interactions in the Southern Ocean

“…In a recent study, Janc et al . 51 showed a drop in the probability of sperm whale interaction when vessels travelled over a range of 40 to 60 km between sets. While this distance is lower than the distance estimated for killer whale (100 km 50 ), it is likely that vessels are less incline to implement costly strategies of avoidance of sperm whales given the lower impact of that species on catch rates compared to that of killer whales 15,27 .…”

When large marine predators feed on fisheries catches: Global patterns of the depredation conflict and directions for coexistence

“…Cronin, Gerritsen, Reid, & Jessopp, 2016;Oksanen, Niemi, Ahola, & Kunnasranta, 2015;Stepanuk, Read, Baird, Webster, & Thorne, 2018;Straley et al, 2014;Thorne, Baird, Webster, Stepanuk, & Read, 2019). Move-on practices, although commonly used by fishers, were shown effective only when vessels travelled distances sufficiently large to reduce the chances of being actively followed by predators (Forney, Kobayashi, Johnston, Marchetti, & Marsik, 2011;Janc et al, 2018;Tixier et al, 2018;Tixier, Vacquie Garcia, Gasco, Duhamel, & Guinet, 2015). Adjustments in the way fishers used their gear to reduce opportunities for species to depredate, such as decreasing soaking time or increasing the hauling speed, proved also effective in both static net and longline fisheries (Cosgrove et al, 2013(Cosgrove et al, , 2015Janc et al, 2018;Tixier, Vacquie Garcia, et al, 2015).…”

Killer whale (Orcinus orca) interactions with blue-eye trevalla (Hyperoglyphe antarctica) longline fisheries

“…As shown in previous studies, the data on presence/absence of killer whale interaction were likely to be autocorrelated in time and in space over consecutive fishing operations ( Tixier et al, 2014a ; Tixier et al, 2014b ; Janc et al, 2018 ). To account for such autocorrelation, we included the presence/absence records of killer whales during the previous fishing day and the distance travelled by vessels between this previous day and the next, as an interaction structural term in the null model ( Data S1 ).…”