Abstract
Fine‐scale knowledge of spatiotemporal dynamics in cetacean distribution and abundance throughout the Western Antarctic Peninsula (WAP) is sparse yet essential for effective ecosystem‐based management (EBM). Cruise vessels were used as platforms of opportunity to collect data on the distribution and abundance of humpback whales (Megaptera novaeangliae) during the austral summer of 2019/2020 in a region that is also important for the Antarctic krill (Euphausia superba) fishery, to assess potential spatiotemporal interactions for future use in EBM. Data were analyzed using traditional design‐based line transect methodology and spatial density surface hurdle models fitted using a set of physical environmental covariates to estimate the abundance and distribution of whales in the area, and to describe their temporal dynamics. Our results indicate a rapid increase in humpback whale abundance in the Bransfield and Gerlache Straits through December, reaching a stable abundance by mid‐January. The distribution of humpback whales appeared to change from a patchier distribution in the northern Gerlache Strait to a significantly concentrated presence in the central Gerlache and southern Bransfield Straits, followed by a subsequent dispersion throughout the area. Abundance estimates agreed well with previous literature, increasing from approximately 7000 individuals in 2000 to a peak of 19,107 in 2020. Based on these estimates, we project a total krill consumption of between 1.4 and 3.7 million tons based on traditional and contemporary literature on per capita krill consumption of whales, respectively. When taken in the context of krill fishery catch data in the study area, we conclude that there is minimal spatiotemporal overlap between humpback whales and fishery activity during our study period of November–January. However, there is potential for significant interaction between the two later in the feeding season, but cetacean survey efforts need to be extended into late season in order to fully characterize this potential overlap.
Highlights
As a result of overexploitation, fishing has shifted focus to areas beyond national jurisdictions (Kawaguchi & Nicol, 2007; Nicol et al, 2012)
A complete list of all models run for the Density Surface Hurdle Models (DSHMs) along with deviance explained and ΔAIC is shown in Appendix S1: Tables S1 and S2 for PA and AB submodels, respectively
Our study demonstrates the utility of platforms of opportunity such as tourist vessels as a viable means to collect data in support of ecosystem-based management (EBM) in the Western Antarctic Peninsula (WAP) area
Summary
As a result of overexploitation, fishing has shifted focus to areas beyond national jurisdictions (Kawaguchi & Nicol, 2007; Nicol et al, 2012). Distance sampling is used to estimate a detection probability function that can be applied to estimate whale density (number km−2 or nm−2) and subsequently estimating the total abundance of whales in the area of interest by multiplying the density by the area The latter assumes that the survey covers representative areas of the entire region (Buckland et al, 2005) and is generally referred to as a “design-based” approach (Barry & Welsh, 2001). Optimal line-transect surveys typically use Research Vessels fitted with double sighting platforms, following predetermined systematic transects arranged across the study region to ensure unbiased sampling coverage (Buckland et al, 2005). Given the poor understanding of the spatiotemporal dynamics in humpback whale abundance and distribution in the WAP area, we used Antarctic cruise vessels as platforms of opportunity to undertake repeated line transect surveys of humpback whales across the Bransfield Strait to develop time-evolving abundance and distribution estimates throughout the summer season. We draw together our spatiotemporally resolved consumption estimates, with the assumption that whales migrate out of the area in the same way they arrived, into a conceptual model of the overlap in space and time between humpback whales, centrally foraging penguins, and the fishery
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