Horst Bornemann

Understanding the trophic ecology of pinnipeds is essential to define their role in ecosystems and anticipate their responses as top predators to environmental changes. Incremental analyses of carbon ( δ ¹³ C) and nitrogen ( δ ¹⁵ N) stable isotopes along their whiskers provide valuable records of their foraging habitat and trophic level over time. The effectiveness of this approach relies on knowledge of species-specific whisker shedding dynamics and growth rates. We investigated the shedding dynamics of Ross seal ( Ommatophoca rossii ) whiskers and attempted to evaluate the time captured in these tissues by combining whiskers’ bulk δ ¹³ C and δ ¹⁵ N incremental measurements with satellite tracking data, collected after whisker growth. Our tracking data are consistent with previous studies, in that Ross seals migrate post-moult between the marginal ice zone and the Antarctic Polar Front. Stable isotope profiles of whiskers did not show the typical decrease in δ ¹³C and increase in δ ¹⁵N values at the whiskers’ tip that would be expected if shedding coincided with the annual fur moult, when fasting typically occurs. The occurrence of similar isotope variations, which were offset between the left and right whiskers of the same individual in relation to distance from the muzzle, further suggest asynchronous, non-seasonal whisker shedding. Our inability to identify known cyclic phenological events (i.e., fasting periods or seasonal migrations) prevented the determination of the average growth rate of whiskers. The additional data on whisker shedding dynamics of Ross seals is a valuable first step in support of future ecological studies based on the whiskers of this species.

Arnoux's beaked whales (Berardius arnuxii) are generally considered to be uncommon to rare, and likely to prefer deep oceanic waters of the Southern Hemisphere. During many top‐predator surveys in the Southern Ocean since 1988 we did not sight the species. However, in April 2022 we encountered three groups in the marginal sea‐ice zone of the Weddell Sea. This study provides detailed descriptions of the sighted animals and their environment and report on unpublished sightings of this species from 1986 to 1998. A search of published information on the distribution of the species revealed 108 documented sightings with a total of 1,125 individuals. In combination these sources of information for the Southern Ocean, suggest a frequent occurrence in ice‐covered waters, often close to the continental coast and edges of fast ice and ice‐shelves. North of 60°S, in the temperate regions of the Southern Hemisphere, the species was also regularly sighted near continents, even far inshore, in fjords surrounded by land.

Ross seals (Ommatophoca rossii) travel away from the pack ice and spend most of their year foraging pelagically. Here, we augment the few existing records of Ross seal diving and haul-out behaviour, providing novel insights into how these are influenced diurnally and seasonally. We used biologging devices that recorded the dive behaviour (n = 5) and/or haul-out behaviour (n = 9) of Ross seals in the eastern Weddell Sea (2016–2019). Ross seals mostly dived between 100 and 200 m deep, often > 300 m, and for 5–12 min in duration, often > 20 min. During March–July, when Ross seals forage pelagically, diving metrics varied diurnally. The seals dived deeper during twilight and shallowest at night, while the number of dives and diving duration did not follow a clear diurnal pattern. Consequently, diving effort was highest during the night. Ross seals preferentially hauled out in the middle of the day during September, October, February and December, but not during the rest of the year. Three females that entered the pack ice during breeding season were hauled out continuously for 5–7 days, punctuated by water entries for 1–3 h during and/or after such continuous haul-outs over the breeding season. This behaviour might suggest that Ross seals alternate between capital and facultative income breeding.