Spatiotemporal Overlap of Baleen Whales and Krill Fisheries in the Western Antarctic Peninsula Region

Abstract

In Antarctica, abundant consumers rely on Antarctic krill for food, but krill are also the subject of a commercial fishery. The fishery overlaps in time and space with the foraging areas of these consumers, thus potential competition between krill fisheries and krill consumers is a major management concern. The fishery is managed by the Commission for the Conservation of Antarctic Marine Living Resources with an ecosystem approach, according to which fishing should not interfere with either the population growth of krill, or krill-dependent consumers. Krill catches have become increasingly spatially concentrated in a small number of hotspots, raising concerns about how local depletion of krill impacts consumers. Such concentrated fishing demonstrates that there is a mismatch between the spatial and temporal scale at which krill fisheries are currently managed, and that at which fisheries operate and consumers forage. Information on the seasonal dynamics of predator abundance and their foraging behaviour is fundamental to future precautionary management of the krill fishery. We analysed the spatiotemporal distribution of two major krill consumers – humpback and minke whales – and that of krill fishing, off the Western Antarctic Peninsula. We used whale tracking data (58 humpback whale tracks and 19 minke whale tracks) to develop spatial random forest models predicting the monthly distribution of whale foraging areas from January-July. Using these predictions, we calculated spatiotemporally-explicit geographic overlap between whales and fisheries, the latter represented by krill fishing effort and catch data. Over the krill fishing season, fishing effort and catch hotspots shifted to the southwest, into the Bransfield Strait where effort and catch was highest. Predicted humpback whale foraging areas increased in the Bransfield Strait over the same period, while predicted minke whale foraging areas showed an opposite trend. For both we predicted a whale-fishing interaction hotspot in the Bransfield Strait, strongest in April and May. Our results illustrate the fine spatial scale of likely interactions between baleen whales and the krill fishery, and their concentration over the season, underlining the need for fishery management more closely aligned to the spatiotemporal scale of likely predator-fishery interactions.

A surplus no more? Variation in krill availability impacts reproductive rates of Antarctic baleen whales

“…Our results add a critical new facet to a growing body of work regarding cetaceans and competition with the growing krill fishery (Reisinger et al, 2022). We suggest a need for immediate management actions to mitigate the negative impacts to both baleen whales and Antarctic krill stocks.…”

“…The Convention on the Conservation of Antarctic Marine Living Resources (CCAMLR) is responsible for the conservation and maintenance of ecosystem function, krill stocks, and commercial fishing, including implementing conservation measures defining and regulating the total allowable catch, spatial and temporal rules of the fishery, and monitoring of krill dependent species (CCAMLR, 2010(CCAMLR, , 2021. CCAMLR must utilize this along with other new knowledge on baleen whale foraging ecology and demography (i.e., Bierlich et al, 2022;Pallin, Bierlich, et al, 2022;Pallin, Botero-Acosta, et al, 2022;Reisinger et al, 2022), along with the impact that both We show significant variation in the pregnancy rates of humpback whales feeding along the WAP. Humpback whales are sentinel species of ecosystem health (Bengtson Nash et al, 2018).…”

“…Whales are ecosystem engineers that enhance local primary production, stabilizing their prey base (e.g., Savoca et al, 2021), so understanding the factors that affect their demography is critical to managing these whale stocks and, thus, their contributions to the ecosystem. Ideally, we could forecast periods when ecological conditions are favorable or not for whales and use this knowledge to implement targeted and dynamic management strategies to modify human activities, such as krill fishing, that competes for resources with predators like humpback whales (Reisinger et al, 2022).…”

Seasonal gain in body condition of foraging humpback whales along the Western Antarctic Peninsula

“…Furthermore, there is concern for 1) the impacts of increased tourism along the WAP and migration routes (Avila et al, 2020;Sprogis et al, 2020;Arranz et al, 2021;Cavanagh et al, 2021) and 2) the krill fishery in key foraging areas . The commercial krill fishery has negatively affected krill-eating penguin populations (Watters et al, 2020;Krüger et al, 2021;Reisinger et al, 2022), and recent changes in the fishery's operation places it in greater spatiotemporal overlap with foraging humpback whales around the WAP. Our work provides a foundational baseline for seasonal changes in body condition of this population, which can be used for monitoring any negative impacts from increasing environmental and anthropogenic stressors in the future and enact greater protective measures for humpback whales and other krill predators in the region.…”

“…The WAP region has experienced dramatic increases in tourism since the 1990s (Cavanagh et al, 2021;Johannessen et al, 2022) and recent evidence suggests vessel noise, including whale watching vessels, can cause disturbance to cetaceans (Sprogis et al, 2020;Arranz et al, 2021). Furthermore, the WAP region has experienced increased activities by the krill fishery, which overlap with key foraging areas for humpback whales (Nicol and Foster, 2016;Reisinger et al, 2022).…”