Telemetry methods and remote sensing now make it possible to record the spatial usage of wide-ranging marine animals and the biophysical characteristics of their pelagic habitats. Furthermore, recent statistical advances mean that such data can be used to test ecological hypotheses and estimate species' distributions. Black-browed Albatrosses Thalassarche melanophrys are highly mobile marine predators with a circumpolar breeding and foraging distribution in the Southern Hemisphere. Although they remain relatively abundant, increased fisheries bycatch has led to their listing as endangered by conservation bodies. We satellite-tracked 163 breeding Black-browed Albatrosses and eight closely related Campbell Albatrosses T. impavida from nine colonies. We then quantified habitat usage, and modeled population-level spatial distribution at spatiotemporal scales .50 km and 1 month, as a function of habitat accessibility, habitat preference, and intraspecific competition, using mixed-effects generalized additive models (GAMM). During incubation, birds foraged over a wider area than in the post-brood chick-rearing period, when they are more time constrained. Throughout breeding, the order of habitat preference of Black-browed Albatrosses was for neritic (0-500 m), shelf-break and upper shelf-slope (500-1000 m), and then oceanic (.1000 m) waters. Black-browed Albatrosses also preferred areas with steeper (.38) bathymetric relief and, in addition, during incubation, warmer sea surface temperatures (peak preference ;168C). Although this suggests specialization in neritic habitats, incubation-stage Blackbrowed Albatrosses from South Georgia also foraged extensively in oceanic waters, preferring areas with high eddy kinetic energy (.250 cm 2 /s 2 ), especially the Brazil-Malvinas Confluence, a region of intense mesoscale turbulence. During chick-rearing, this species had a more southerly distribution, and following the seasonal retreat of sea ice, birds from some populations utilized neritic polar waters. Campbell Albatrosses showed similar bathymetric preferences but also preferred positive sea level anomalies. Black-browed Albatross foraging areas were partially spatially segregated with respect to colony and region, with birds preferring locations distant from neighboring colonies, presumably in order to reduce competition between parapatric conspecifics. At the global scale, the greatest concentrations of breeding Black-browed Albatrosses are in southern South American neritic, shelf-break, and shelf-slope waters. These regions also hold large fisheries and should therefore be a priority for introduction of bycatch mitigation measures.
The foraging location, diving behavior, dietary composition, and feeding rates of female Emperor Penguins (Aptenodytes forsteri) from the Auster and Taylor Glacier colonies in Antarctica were investigated during the 1993 austral winter. The study was conducted between late May and early August, when male emperors remain at the colonies to incubate eggs and females forage at sea for self-maintenance.During winter, two satellite-tracked penguins from Auster foraged ഠ100 km northeast of the colony in open water 200-500 m deep, over the outer continental shelf and shelf slope. Ten Auster and four Taylor Glacier penguins that carried time-depth recorders took ഠ8 d to reach the ice edge, spent 50-60 d at sea foraging, and took 4 d to return across the fast ice to the colony. The females occasionally huddled together to minimize heat loss while in transit to the ice edge and between foraging days. The penguins foraged on 93.2% of their days at sea and rested for the remainder. On each foraging day, penguins usually entered the water just after dawn and averaged 4.71 h in the water before exiting at dusk. The hourly dive rate was constant throughout winter, but the daily dive rate increased as day length increased, suggesting that day length is a primary determinant of hunting effort. Penguins exhibited behavior indicative of foraging on 47% of their dives, the remainder being travel or search dives. Penguins made, on average, 26 foraging dives/d. Females from Auster targeted prey at water depths of 20-70 m and 100-150 m, whereas Taylor Glacier birds targeted prey at 10-70 m, 250-300 m, and 330-400 m, suggesting between-colony differences in prey distribution.The stomach contents of 17 females returning to Auster to brood their chicks were dominated by pelagic prey species: Antarctic krill (Euphausia superba, 70% by mass) and Antarctic silverfish (Pleuragramma antarcticum, 13% by mass). Food consumption rates during winter for five penguins from both colonies were similar and averaged 62.6 Ϯ 5.8 g·kg Ϫ1 ·d Ϫ1 (1.8 Ϯ 0.1 kg/d for a 28.8 kg female), which equated to a metabolizable energy intake of 236.6 Ϯ 22.0 kJ/kg for each day they foraged (all values are mean Ϯ 1 SD). This enabled the birds to gain ഠ6.1 kg for a trip spanning ഠ70 d. Based on mean prey masses and the penguins' dive rates, the penguins consumed ഠ115 ϫ 0.6 g krill or 16 ϫ 4.3 g Antarctic silverfish per foraging dive, or some combination of both. In their winter trip, each breeding female consumed ഠ100 kg of prey. The female populations at Auster and Taylor Glacier consumed an estimated 1350 Mg and 250 Mg of prey, respectively, in winter.
Wandering Albatrosses Diomedea exulans are frequently killed when they attempt to scavenge baited hooks deployed by long‐line fishing vessels. We studied the foraging ecology of Wandering Albatrosses breeding on Marion Island in order to assess the scale of interactions with known long‐line fishing fleets. During incubation and late chick‐rearing, birds foraged further away from the island, in warmer waters, and showed high spatial overlap with areas of intense tuna Thunnus spp. long‐line fishing. During early chick‐rearing, birds made shorter foraging trips and showed higher spatial overlap with the local Patagonian Toothfish Dissostichus eleginoides long‐line fishery. Tracks of birds returning with offal from the Toothfish fishery showed a strong association with positions at which Toothfish long‐lines were set and most diet samples taken during this stage contained fishery‐related items. Independent of these seasonal differences, females foraged further from the islands and in warmer waters than males. Consequently, female distribution overlapped more with tuna long‐line fisheries, whereas males interacted more with the Toothfish long‐line fishery. These factors could lead to differences in the survival probabilities of males and females. Non‐breeding birds foraged in warmer waters and showed the highest spatial overlap with tuna long‐line fishing areas. The foraging distribution of Marion Island birds showed most spatial overlap with birds from the neighbouring Crozet Islands during the late chick‐rearing and non‐breeding periods. These areas of foraging overlap also coincided with areas of intense tuna long‐line fishing south of Africa. As the population trends of Wandering Albatrosses at these two localities are very similar, it is possible that incidental mortality during the periods when these two populations show the highest spatial overlap could be driving these trends.
Although huddling was shown to be the key by which emperor penguins (Aptenodytes forsteri) save energy and sustain their breeding fast during the Antarctic winter, the intricacies of this social behavior have been poorly studied. We recorded abiotic variables with data loggers glued to the feathers of eight individually marked emperor penguins to investigate their thermoregulatory behavior and to estimate their "huddling time-budget" throughout the breeding season (pairing and incubation period). Contrary to the classic view, huddling episodes were discontinuous and of short and variable duration, lasting 1.6 ± 1.7 (SD) hours on average. Despite heterogeneous huddling groups, birds had equal access to the warmth of the huddles. Throughout the breeding season, males huddled for 38 ± 18% (SD) of their time, which raised the ambient temperature that birds were exposed to above 0°C (at average external temperatures of -17°C). As a consequence of tight huddles, ambient temperatures were above 20°C during 13 ± 12% (SD) of their huddling time. Ambient temperatures increased up to 37.5°C, close to birds' body temperature. This complex social behavior therefore enables all breeders to get a regular and equal access to an environment which allows them to save energy and successfully incubate their eggs during the Antarctic winter.
To determine the foraging space of emperor penguins Aptenodytes forsteri in winter, 12 females from Auster colony (13400 pairs) were equipped with satellite transmitters and time-depth recorders before departing on their 76 * 9 d winter (June to August) foraging trip. The females were also injected with tritiated water (HTO) to estimate food consumption, and non-instrumented females were stomach sampled upon return to the colony to determine their diet. The same data were collected in August/September from 3 males foraging after their 4 mo prenuptial and incubation fast. Both females and males foraged in pack-ice within 120 km of the colony along a relatively narrow band of the continental shelf in water depths ranging from 200 to 500 m. Only rarely did penguins leave shelf waters to forage in deeper waters over the shelf break. The size of the general foraging area for females was about 11 410 km2, but 50% of all foraging days were spent in only about 15% (1700 km2) of the total foraging area. A female of average mass (25 kg) hunted for about 6 h d-l, and consumed 1.8 * 0.3 kg of food per foraging day. This indicates that females from Auster consumed in winter about 1520 t, about half of which is likely to have been taken from an area measuring only 60 X 28 km. Males were active for about 10 h d ' and consumed about twice as much (3.7 * 7.2 kg d-I for a 24 kg male) as the females during the early phase of brooding. The diet of females comprised 7 2 % fish (by mass). 16% squid and 12% Antarctic krill Euphausia superba whereas that of the males comprised 53% fish. 2U/o squid and 43% krill. Most foraging dives of females (81 %) and males (64 %) were to
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.