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

Abstract

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.

The Beat Goes On: Humpback Whale Song Seasonality in Antarctic and South African Waters

“…Due to phytoplankton blooms, large swarms of Antarctic krill Euphausia superba are usually present around the Maud Rise (Everson, 2000). As a result, krill-eating predators, such as seals, blue whales, and humpback whales, return to the Maud Rise annually (e.g., Matthews, 1938;Shabangu et al, 2017;Shabangu and Rogers, 2021).…”

Metabolomics approach for predicting stomach and colon contents in dead Arctocephalus pusillus pusillus, Arctocephalus tropicalis, Lobodon carcinophaga and Ommatophoca rossii from sub-Antarctic region

“…Ross seals ( Ommatophoca rossii ) and crabeater seals ( Lobodon carcinophaga ) are phocid seals (earless seals) with a circumpolar distribution in the Southern Ocean (Antarctica) [ 4 , 5 ]. While crabeater seals are the most abundant pinniped species globally, Ross seals are the rarest, most elusive, pelagic and Antarctic ice-inhabiting species [ 4 – 6 ].…”

“…Ross seals (Ommatophoca rossii) and crabeater seals (Lobodon carcinophaga) are phocid seals (earless seals) with a circumpolar distribution in the Southern Ocean (Antarctica) [4,5]. While crabeater seals are the most abundant pinniped species globally, Ross seals are the rarest, most elusive, pelagic and Antarctic ice-inhabiting species [4][5][6]. Ross seals feed on a more varied diet of squid, crustaceans and fish, while the crabeater seals feed only on specialized diet of the small crustacean, the Antarctic krill (Euphausia superba) [7].…”

Sea‐ice anomalies affect the acoustic presence of Antarctic pinnipeds in breeding areas

“…We extracted daily point values for SIC and drift from an area within a 30‐km radius around PALAOA using the extract function of the R package raster (Hijmans 2020). The radius length represented the probable distance over which pinniped calls were detected at PALAOA and therefore the estimated range of representative ice conditions to which the pinnipeds recorded off PALAOA were exposed to (Shabangu and Rogers 2021). For SIC and sea‐ice drift velocity, we calculated the spatial average and standard deviation across the daily point values within the 30‐km‐radius area, along with the daily drift direction as north‐based azimuth values (0–360°) using the v and u sea‐ice drift components.…”