First observations of Weddell seals foraging in sponges in Erebus Bay, Antarctica

Abstract

Attaching cameras to marine mammals allows for first-hand observation of underwater behaviours that may otherwise go unseen. While studying the foraging behaviour of 26 lactating Weddell seals (Leptonychotes weddellii) in Erebus Bay during the austral spring of 2018 and 2019, we witnessed three adults and one pup investigating the cavities of Rossellidae glass sponges, with one seal visibly chewing when she removed her head from the sponge. To our knowledge, this is the first report of such behaviour. While the prey item was not identifiable, some Trematomus fish (a known Weddell seal prey) use glass sponges for shelter and in which to lay their eggs. Three of the four sponge foraging observations occurred around 13:00 (NZDT). Two of the three sponge foraging adults had higher-than-average reproductive rates, and the greatest number of previous pups of any seal in our study population, each having ten pups in 12 years. This is far higher than the study population average of three previous pups (± 2.6 SD). This novel foraging strategy may have evolved in response to changes in prey availability, and could offer an evolutionary advantage to some individuals that exploit prey resources that others may not. Our observations offer new insight into the foraging behaviours of one of the world’s most studied marine mammals. Further research on the social aspects of Weddell seal behaviour may increase our understanding of the extent and mechanisms of behavioural transfer between conspecifics. Research into the specific foraging behaviour of especially successful or experienced breeders is also warranted.

Beneath the Antarctic sea‐ice: Fine‐scale analysis of Weddell seal (Leptonychotes weddellii) behavior and predator–prey interactions, using micro‐sonar data in Terre Adélie

“…), that is, to estimate the energy budget of lactating females, or to assess foraging success. These analyses could use hydrophones, that record swallow and breathing sounds or video cameras with light (Foster‐Dyer et al., 2023 ). For example, Foster‐Dyer et al.…”

“…For example, Foster‐Dyer et al. also combined information on the prey species, obtained through video cameras, and the seals' demographic descriptors (breeding history and pup age) to examine foraging behavior (Foster‐Dyer et al., 2023 ).…”

“…Anticipating the very high energetic demand from their pup, they accumulate body reserves during gestation. Although most phocid seals are believed to fast during lactation (capital breeding strategy), the length of Weddell seals' lactation period and their high requirement of absolute energetic transfer suggest females must forage during lactation, to cover at least part of their need (Costa, 1991 ; Foster‐Dyer et al., 2023 ; Hindell et al., 2020 ; Sato et al., 2002 ; Wheatley et al., 2008 ). The diving behavior of Weddell seals and the link to their foraging ecology has been widely studied after their molt during fall, winter, and spring (Fuiman et al., 2007 ; Goetz, 2015 ; Heerah et al., 2013 ; Schreer & Testa, 1996 ; Testa, 1994 ).…”

“…Such fine‐scale measurement of prey and predator–prey interactions taking place at scales of meters per second cannot be obtained at the relevant spatial and temporal scales with conventional means (e.g., trawling or active acoustic measurements from a research vessel, which operates at scales of 10–1000s of meters and over hours‐days). To the best of our knowledge, available fine‐scale studies dedicated to the quantitative description of the feeding behavior of lactating females did not take into account information on the prey available to seals (Mitani et al., 2003 ; Sato et al., 2002 ), although some studies used cameras to identify targeted prey (Foster‐Dyer et al., 2023 ). Weddell seals are believed to feed on bentho‐pelagic prey, mostly Antarctic silverfish or other notothenioid fish (Burns et al., 1998 ; Fuiman et al., 2007 ; Goetz et al., 2017 ; La Mesa et al., 2022 ).…”

“…The oscillations in median value (red lines) in panel (c) illustrate alteration in heading angle throughout the approach phase, as opposed to almost static pitch and roll angles. Figures of seals (Chevallay, 2020) are on the right side of each panel to illustrate seal's orientation.the seals' demographic descriptors (breeding history and pup age) to examine foraging behavior(Foster-Dyer et al, 2023).…”