Antarctic marine mammals and sea ice

Bester, Marthán N; Bornemann, Horst; McIntyre, Trevor

doi:10.1002/9781118778371.ch22

Cited by 15 publications

(16 citation statements)

References 131 publications

(151 reference statements)

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“…The leopard seal ( Hydrurga leptonyx ) is the only pack‐ice breeding species that we could have mistaken crabeater seals for, given that leopard seals grow up to ~4.5 m long (Laws, 1981). However, leopard seals have a much lower abundance and overall density than crabeater seals (leopard seal global population estimate: 220,000–440,000; Bester et al., 2017), which means that for every leopard seal there are ~32–68 crabeater seals. Furthermore, leopard seals are typically found in higher densities around the pack‐ice edge compared with the inner pack ice (Bester et al., 2002; Siniff, 1991) and some spend winter travelling outside of the pack ice and around neighbouring islands (Walker et al., 1998).…”

Section: Methodsmentioning

confidence: 99%

“…The only Antarctic pack ice seal whose diet is ~90% Antarctic krill is the crabeater seal (Hückstädt et al., 2012; Laws, 1977; Øritsland, 1977; Zhao, Castellini, Mau, & Trumble, 2004). Native to the Southern Ocean, their circumpolar population estimate ranges between 7 and 30 million individuals (Bengtson, 2009; Bester, Bornemann, & McIntyre, 2017; Erickson & Hofman, 1974; Southwell et al., 2012). Although the population estimates are wide and population trends of this species are unknown (but previously suspected to have increased (Erickson & Hofman, 1974)), all evidence suggests that this numerous krill predator likely has a substantial impact on the abundance and distribution of Antarctic krill — and vice versa (Daly & Macaulay, 1991; Forcada et al., 2012).…”

Section: Introductionmentioning

confidence: 99%

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Citizen science and habitat modelling facilitates conservation planning for crabeater seals in the Weddell Sea

Wege

Salas

LaRue

2020

Diversity and Distributions

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Aim Creating a network of marine protected areas in the Southern Ocean requires extensive knowledge on species’ abundances, distributions and population trends especially in the Weddell Sea where year‐round pack ice makes most of the Weddell Sea inaccessible. We combine satellite images and citizen science to model habitat suitability for crabeater seals (Lobodon carcinophaga) throughout the Weddell Sea. Location Weddell Sea, Antarctica. Methods High‐resolution satellite images covering 18,219 km2 of the Weddell Sea during crabeater seal breeding season (October—November) were hosted on the crowd‐sourcing platform Tomnod (DigitalGlobe). Citizen scientists marked “maps” where seals were present/absent and these votes were compared with the votes of an experienced observer. Correction factors were used to correct votes to either a continuous probability of seal presence, or a binary seal presence/absence value. We modelled probability of seal presence using ensemble models of Random Forests (RF), Boosted Regression Trees (BRT) and Support Vector Machines (SVM), and used fitted Maxent models to model seal presence/absence data. Results Model predictive power was low (RF: R2 = 0.076 ± 0.002: BRT: R2 = 0.086 ± 0.0008; SVM: R2 = 0.082 ± 0.003) to average (Maxent: AUC = 0.71 ± 0.004). Distance to the ice edge and bathymetry were the most important variables that influenced crabeater seal distribution. Main conclusions Crabeater seals were more likely to be present over abyssal water, which coincides with typical adult Antarctic krill habitat — crabeater seal preferred prey. Where ice concentrations were more variable, that is more accessible, crabeater seals were also more likely to occur. Results agreed with the known ecology of crabeaters seals and the abundance, distribution and ecology of Antarctic krill. We were able to survey the largest area ever surveyed in the Weddell Sea and provide a model to assist furthering policy around the proposed protected area.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Citizen science and habitat modelling facilitates conservation planning for crabeater seals in the Weddell Sea

Wege

Salas

LaRue

2020

Diversity and Distributions

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“…Our results indicate little spatio-temporal overlap in the acoustic occurrence of Ross and leopard seals in the circumpolar Antarctic pack ice using 9 years of bioacoustic data collected in austral summers. Ross seal calls were concentrated within restricted regions in the pack ice with high call numbers detected close to the sea ice edge in areas between 0° and 20° E, and between 60° and 130° E. There are more Ross seals seen, particularly off the eastern Weddell Sea, compared to any other region of the Antarctic pack ice, except for the Ross Sea (Bester et al 2017). From previous visual surveys, Ross seals were abundant in the eastern Weddell Sea, particularly off Dronning Maud Land, during the austral summer/autumn; the seals are generally seen east of 30° W, and rarely venture further south than ~ 73° S (Bester et al 2019(Bester et al , 2020.…”

Section: Acoustic Occurrencementioning

confidence: 97%

Summer circumpolar acoustic occurrence and call rates of Ross, Ommatophoca rossii, and leopard, Hydrurga leptonyx, seals in the Southern Ocean

Shabangu

Rogers

2021

Polar Biol

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Two of the Antarctic pack ice seals, Ross, Ommatophoca rossii, and leopard, Hydrurga leptonyx, seals, are extremely difficult to study via traditional visual survey techniques, yet are ideal for an acoustic survey as they are highly vociferous and produce an array of underwater sounds during the austral summer. To determine their acoustic occurrence in the Antarctic pack ice, we use their calls, detected within 680 acoustic recordings made between 1999 and 2009 as part of two multinational programmes. Siren calls of Ross seals were detected mainly in January, and 9.88 calls per minute from low siren calls was the highest call rate for this species. High numbers of Ross seal calls were detected close to the ice edge in areas between 0° and 20° E and 60° and 130° E, suggesting these are important summer habitats. Leopard seal calls were detected mainly in December and January, and December had the highest percentage of calls. Call rate of 11.93 calls per minute from low double trills was the highest call rate for leopard seals. Leopard seal calls were detected throughout the Southern Ocean with more calls detected throughout the pack ice. There was little spatio-temporal overlap in call occurrence of Ross and leopard seals, but both species were more vocally active during the day. Longitude and latitude were the most important predictors of Ross seal occurrence, and month of the year highly predicted leopard seal occurrence. This is the first study to examine the circumpolar acoustic occurrence of Ross and leopard seals in the Southern Ocean pack ice.

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“…These pack-ice seals (crabeater seal Lobodon carcinophaga, Weddell seal Leptonychotes weddelli, leopard seal Hydrurga leptonyx and Ross seal Ommatophoca rossii) breed on ice and are therefore especially sensitive to biological and physical variations in the sea ice environment (Siniff et al 2008). Two other seal species, the southern elephant seal Mirounga leonina and Antarctic fur seal Arctocephalus gazella, also forage within pack ice habitats (Bornemann et al 2000, Tosh et al 2009), but these seals almost exclusively breed on ice-free islands (Bester et al 2017). Crabeater seals are by far the most abundant of the pack-ice seals, but even regional population abundance estimates are highly uncertain (Southwell et al 2012).…”

Section: Introductionmentioning

confidence: 99%

Habitat-based density models of pack-ice seal distribution in the southern Weddell Sea, Antarctica

Oosthuizen

Reisinger

Bester

et al. 2021

Mar. Ecol. Prog. Ser.

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Climate variability and changes in sea ice dynamics have caused several ice-obligate or krill-dependent populations of marine predators to decline, eliciting concern about their demographic persistence and the indirect ecological consequences that predator depletions may have on marine ecosystems. Pack-ice seals are dominant ice-obligate predators in the Antarctic marine ecosystem, but there is considerable uncertainty about their abundance and population trends. We modelled the density and distribution of pack-ice seals as a function of environmental covariates in the southern Weddell Sea, Antarctica. Our density surface modelling approach used data from aerial surveys of pack-ice seals collected in the 2013/14 austral summer. Crabeater seals Lobodon carcinophaga, the most numerous pack-ice seal we observed, occurred at the highest densities in areas with extensive sea ice near the continental shelf break, but were almost absent in areas of similar sea ice concentration in the southern extent of the Weddell Sea. The highest densities of Weddell seals Leptonychotes weddelli, which were less abundant than crabeater seals within the pack-ice habitat, were predicted to occur over the continental shelf, near the shelf break. The distribution of both seal species broadly corresponded with the distribution and relative abundance of their main prey (Antarctic krill Euphausia superba and Antarctic silverfish Pleuragramma antarctica) obtained from concurrent ecosystem surveys. Ross seals Ommatophoca rossii and leopard seals Hydrurga leptonyx were not detected at all and are apparently rare within the southern Weddell Sea. These results can contribute to biodiversity assessments in the context of marine protected area planning in this region of the Southern Ocean.

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Antarctic marine mammals and sea ice

Cited by 15 publications

References 131 publications

Citizen science and habitat modelling facilitates conservation planning for crabeater seals in the Weddell Sea

Citizen science and habitat modelling facilitates conservation planning for crabeater seals in the Weddell Sea

Summer circumpolar acoustic occurrence and call rates of Ross, Ommatophoca rossii, and leopard, Hydrurga leptonyx, seals in the Southern Ocean

Habitat-based density models of pack-ice seal distribution in the southern Weddell Sea, Antarctica

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