Antarctic Shag Research Articles

Fish in the diet of the Antarctic Shag Leucocarbo bransfieldensis breeding at Paradise Bay, Antarctic Peninsula

Fish in the diet of the Antarctic Shag Leucocarbo bransfieldensis breeding at Paradise Bay, Antarctic Peninsula

Using machine learning to count Antarctic shag (Leucocarbo bransfieldensis) nests on images captured by remotely piloted aircraft systems

Using 51 orthomosaics of 11 breeding locations of the Antarctic shag (Leucocarbo bransfieldensis), we propose a method for automating counting of shag nests. This is achieved by training an object detection model based on the “You Only Look Once” (YOLO) architecture and identifying nests on sections of the orthomosaic, which are later combined with predictions for the entire orthomosaic. Our results show that the current use of Remotely Piloted Aircraft Systems (RPAS) to collect images of areas with shag colonies, combined with machine learning algorithms, can provide reliable and fast estimates of shag nest counts (F1 score > 0.95). By using data from only two shag colonies for training, we show that models can be obtained that generalise well to images of both spatially and temporally distinct colonies. The proposed practical application opens the possibility of using aerial imagery to perform large-scale surveys of Antarctic islands in search of undiscovered shag colonies. We discuss the conditions for optimal performance of the model as well as its limitations. The code, data and trained model allowing for full reproducibility of the results are available at https://github.com/Appsilon/Antarctic-nests.

Identifying Important Bird and Biodiversity Areas in Antarctica Using RPAS Surveys—A Case Study of Cape Melville, King George Island, Antarctica

A remotely piloted aircraft system (RPAS) survey of an area containing the eastern extremity of King George Island, including Cape Melville and an extensive part of Destruction Bay, as well as small offshore islands, was undertaken in December 2022. Using RPAS, an inventory of the Destruction Bay area was performed. Chinstrap penguin and Antarctic shag nests were found on Cape Melville and on Trowbridge Island, Middle Island, and an unnamed area located between the Ørnen Rocks formation and Trowbridge Island. During the survey, 507 Antarctic shag nests and over 9000 chinstrap penguin nests were mapped in the investigated area; 458 Antarctic shag nests and 4960 ± 19 chinstrap penguin nests aggregated together on an 8.61 ha land section of Cape Melville were identified. The quantity of Antarctic shag nests found allows for the classification of the area of Cape Melville as an IBA. Among the 175 currently known colonies of Antarctic shags in Antarctica, this is the fifth largest. In this paper, we present the results of the survey, including orthophotos with mapped nest locations. We propose the following recommendations to policy makers and the scientific community: (1) the area of Cape Melville should be classified as an Antarctic Important Bird and Biodiversity Area; (2) based on the RPAS flight, a new boundary of the Cape Melville IBA is proposed; (3) the threshold value (based on >1% of species) to establish an IBA for Antarctic shags should be changed to 122 to reflect the increased estimate of the global population of Antarctic shags; and (4) an inventory of all areas, including previous IBAs that can be qualified as “major colonies of breeding native birds”, should be recommended at the Antarctic Treaty Consultative Meeting (ATCM). In logistically inaccessible bird breeding sites, such as the one presented here, RPASs should be used to carry out regular monitoring of Antarctic Important Bird and Biodiversity Areas.

The role of wind fetch in structuring Antarctic seabird breeding occupancy

Avian breeding sites located along shorelines may allow easy access to aquatic food sources, but risk exposing birds and nests to high wind and wave action. One measure of exposure is wind fetch, the distance of open water over which wind can blow uninterrupted. By calculating fetch weighted by prevailing wind direction for breeding colonies of pursuit‐diving seabirds in the Antarctic Peninsula, we show that different members of this guild have opposing relationships to coastline exposure. Gentoo Penguins Pygoscelis papua preferentially occupied more enclosed sites with lower fetch. Surprisingly, however, Chinstrap Penguins Pygoscelis antarcticus and Antarctic Shags Leucocarbo bransfieldensis appear to prefer more exposed sites. Although considerable research has been devoted to understanding Antarctic seabird habitat suitability, the role of wind and wave exposure has not been considered in depth, in part because comprehensive data on colony presence and absence have only recently been made available. We propose several mechanisms for why fetch may act to differentiate niches among this guild. These findings may increase our ability to identify suitable breeding areas for these and other near‐shore breeding species as they respond to climate change.

Assessing colonies of Antarctic shags by unmanned aerial vehicle (UAV) at South Shetland Islands, Antarctica

AbstractDue to the remote location of colonies of Antarctic shags (Phalacrocorax(atriceps)bransfieldensis) in Antarctica, there is only sparse data on the abundance of this species. An unmanned aerial vehicle (UAV) survey for known and unknown Antarctic shag colonies along the coasts of Nelson Island and western King George Island, Antarctica, was conducted in December 2016. Four colonies, one of them previously unknown, were detected. For the first time since the 1980s, the total population size of the colonies in that area was determined. A comparison with previous estimates revealed evidence of a population increase by a factor of 2.86. To support future survey campaigns, several characteristic features of Antarctic shag colonies, nests and individuals in aerial imagery were identified. This makes possible more reliable detection and determination of population size in Antarctic shag colonies. These characteristic features were compared with those of chinstrap penguin colonies (Pygoscelis antarcticus) because these species often overlap spatially and are difficult to distinguish. In addition, the optimal weather conditions and flight parameters for an aerial survey were specified.

Unmanned aerial vehicle (UAV) survey of the Antarctic shag (Leucocarbo bransfieldensis) breeding colony at Harmony Point, Nelson Island, South Shetland Islands

Monitored seabird populations—useful sentinels of marine ecosystem health—have been declining worldwide at a rapid pace. Yet, lack of reliable long-term monitoring data constrains assessment of the conservation status of many seabird populations. Unmanned aerial vehicles (UAVs) have the potential to increase survey efficiency and count precision of seabird populations, especially where time constraints or inaccessible terrain, such as sea stacks, limit meaningful ground-based surveys. Furthermore, tremendous potential exists to combine fine-scale spatially integrated habitat mapping obtained from UAV images with occupancy to unravel how abiotic factors such as topography affect animal populations. In late December 2018, we used an UAV to create a georeferenced orthomosaic image and digital elevation model (DEM) from which we determined the size of the Antarctic shag (Leucocarbo bransfieldensis) breeding colony at Harmony Point, Nelson Island, South Shetland Islands. Our population estimate of 69 breeding pairs is approximately double that reported for the early 2000s and the highest count since the late 1980s. Most nests were located 10 to 20 m above sea level, on relatively shallow gradients that predominantly faced southeast. While it is difficult to compare historical ground-based counts with the UAV-derived estimates presented here, our new data provide robust baseline information for future monitoring of the colony population size using comparable survey methods. Our basic mapping of the topography of the breeding colony also highlights how UAV-derived habitat information can facilitate our understanding of the influence of landscape structure on animal population dynamics.

Cephalopods in the diet of keystone-species animals in the region of the Argentine Islands Archipelago (West Antarctica)

Оbjective. The study of diet of keystone-species vertebrates (Nothotenia coriiceps, Phalacrocorax bransfieldensis, Leptonychotes weddellii) in the ecosystem of the Argentine Islands Archipelago. Methods. Biological researches were conducted on Akademik Vernadsky station during wintering in 2006—2007, 2009—2010, 2011—2012, 2019 accordance with tasks of the State Special-Purpose Research Program in Antarctica for 2011–2020. In total, the content of 30 faeces of the L. weddellii, 64 pellets and three stomachs of the Ph. bransfieldensis and 40 stomachs of the N. coriiceps were analyzed. Material was collected at all seasons. Results. The L. weddellii diet is dominated by three squid species Galiteuthis glacialis (39,5%), Brachiotheutis picta (21%) and the fishery species Psychroteuthis glacialis (15.8%). In the diet of Ph. bransfieldensis were found the main four Octopus species such as Adelieledone polimorpha – 20%, Pareledone turqueti – 20%, and Graneledone sp. – 24% and Benthoctopus sp. – 16%, who owns the highest proportion of hits. In the nutrition of N. coriiceps, cephalopods are rarely recorded. Only one species of Octopus has been registered and has been identified only to the Cirroteuthidae family. Conclusions. Found that in the diet of keystone-species vertebrates (N. coriiceps, Ph. bransfieldensis, L. weddellii) in the ecosystem of the Argentine Islands Archipelago there are 13 species of Cephalopods, of which 4 species belong to squid Decapoda and 9 species to octopuses Octopoda (3 species are identified to the genus and one to the family). The findings are important not only to establish the actual status of the Antarctic ecosystem and to conserve biodiversity in the Antarctic region.

Dynamics of Numbers and Occurrence of Colonial Species of Birds in the Area of Ukrainian Antarctic Station Akademik Vernadsky

Abstract The research covers water area, island archipelagos and coastal line of the Antarctic Peninsula from 65°31ʹ S, 64°25ʹ W in the South to 65°03ʹ S, 63°53ʹ W in the North. There was time gap of 7 years between the researches (2011 and 2018), which allows to define tendencies in development of individual colonies and to make conclusion about success of existence of a given species. The work itself was carried out during the first half of January, that is in the time when the stage of brooding ends and the period of hatching starts. As of 2011, 12 nesting points of gentoo penguin (Pygoscelis papua) with total number of 8,342 pairs were found in the region under investigation. Till 2018, quantity of the colony grew to 14, with total number of 14,105 pairs. For seven years, quantity of nesting points of aelie penguin (Pygoscelis adeliae) almost did not change (4 colonies). Instead, total number of the species decreased somewhat: from 3559 pairsin 2011 to 3295 onesin 2018. Number of chinstrap penguin (Pygoscelis antarctica) in united stable locality for nesting also decreased from 26 pairsin 2011 to19 onesin 2018. Booth Island (65°04ʹ S, 64°02ʹ W) for chinstrap penguins and Green Island (65°19ʹ S, 64°09ʹ W) for gentoo penguins are the southern most points of nesting range of the species. Also, 7 colonies of antarctic shag (Phalacrocorax bransfieldensis) were revealed in the region under investigation. For seven years from 2011 to 2018 total number of the species in the region under investigation grew from 190 pairs to 299, and in most cases the antarctics shag forms settlements jointly with penguins.

Surveys reveal increasing and globally important populations of south polar skuas and Antarctic shags in Ryder Bay (Antarctic Peninsula)

Despite their importance in ecosystems, population sizes and trends are unknown for many seabirds, including in the Antarctic. Here we report on the first comprehensive survey of south polar skuas Stercorarius maccormicki and Antarctic shags Leucocarbo bransfieldensis in Ryder Bay, and collate previous count data. In austral summer 2017/18, totals of 259 skuas at club sites and 978 occupied skua territories were counted in 2.3 km2 of suitable habitat at Rothera Point and adjacent islands. Based on the mean nearest neighbour distance (23.2 m), skua nest densities were comparable with colonies elsewhere. Long-term monitoring of skuas at Rothera Point indicated considerable annual variation and overall increases of 1.9 and 1.3% per annum, respectively, in breeding pairs from 1975/76 to 2017/18, and occupied territories from 1988/89 to 2017/18. In total, 405 pairs of Antarctic shags bred at two known and one newly discovered colony in 2017/18. Previous counts at the two known colonies indicated substantial annual variation and increases of 5.5 and 3.3% per annum, respectively, from 1985/86 to 2017/18 and 1989/90 to 2017/18. Factors leading to overall increases in both species, and the intermittent seasons of near-complete failure to breed, are unclear, but likely to reflect impacts of environmental change on their marine prey or sea ice. The breeding populations of south polar skuas and Antarctic shags in Ryder Bay represent 10.3 and 3.5%, respectively, of revised global estimates of 9500 and 11,684 breeding pairs. We recommend that the breeding colonies be included as important bird areas (IBAs) and within the Antarctic Specially Protected Area (ASPA) system, and provision made to conserve foraging areas at sea.

Population status of the Antarctic shag Phalacrocorax (atriceps) bransfieldensis

AbstractAntarctic shags Phalacrocorax (atriceps) bransfieldensis are the southernmost cormorants in the world and assessment of their conservation status has been complicated by the logistical challenges of obtaining regular estimates of population size, as well as by taxonomic ambiguity of the blue-eyed shag complex. The available information on the taxonomy, distribution and population size of Antarctic shags are reviewed and a refined estimate of the global population is presented: 11 366 breeding pairs, plus an additional 1984 pairs of uncertain taxonomic status in the South Orkney Islands. This analysis suggests a possible spatial shift in the distribution of Antarctic shags similar to that reported for other Antarctic seabirds, which probably reflects a gradient in environmental changes along the western Antarctic Peninsula. This review should aid future conservation and management assessments.

Linking population trends of Antarctic shag (Phalacrocorax bransfieldensis) and fish at Nelson Island, South Shetland Islands (Antarctica)

This study aims to provide consistent information to explain the steady declining trend in the number of breeding pairs of Antarctic shag Phalacrocorax bransfieldensis in two colonies on Nelson Island, South Shetland Islands, southern Atlantic sector of Antarctica, which was observed during the 1990s up to the mid 2000s over an overall monitoring period of over two decades. It addresses correspondence between long-term population trends of inshore demersal fish and inshore-feeding Antarctic shags of this area, where an intensive commercial fishery for shag prey once operated. The analysis also includes comparable information on diet (by examination of regurgitated pellets), foraging patterns, and breeding output of shags from the Danco Coast, western Antarctic Peninsula, an area where no commercial finfish fishery has ever existed. Integral study of these parameters there showed that, in Antarctic shags, low breeding success and high foraging effort might imply low recruitment and high adult mortality, respectively, with both factors adversely affecting the population trends of this bird. In line with these premises, the declining trend observed in shag colonies on the South Shetland Islands appears to have been influenced by the concomitant decrease in abundance of two of their main prey, the nototheniids Notothenia rossii and Gobionotothen gibberifrons, due to intensive industrial fishing in the area in the late 1970s. In comparison, no such pattern occurred for the Danco Coast colonies.

Does prey availability affect the foraging effort and breeding success in the Antarctic Shag (Phalacrocorax bransfieldensis)?

Does prey availability affect the foraging effort and breeding success in the Antarctic Shag (Phalacrocorax bransfieldensis)?

Abundance and breeding distribution of seabirds in the northern part of the Danco Coast, Antarctic Peninsula

Seabird abundances and breeding distribution have the potential to serve as ecological indicators. The western Antarctic Peninsula is one of the three sites in the world with the greatest increases in local temperature during the last 50 years. The aim of this study was to monitor the distribution and abundance of breeding populations of seabirds in the northern sector of the Danco Coast, north-west of the Antarctic Peninsula, during the breeding season 2010/11. The birds were the Wilson's storm petrel ( Oceanites oceanicus ), South Polar skua ( Stercorarius maccormicki ), kelp gull ( Larus dominicanus ), Antarctic tern ( Sterna vittata ), snowy sheathbill ( Chionis alba ), chinstrap penguin ( Pygoscelis antarctica ), southern giant petrel ( Macronectes giganteus ), gentoo penguin ( Pygoscelis papua ), Cape petrel ( Daption capense ) and Antarctic shag ( Phalacrocorax bransfieldensis ). Annual breeding population growth increased in pygoscelids, southern giant petrel and sheathbill, and for the remaining species, breeding population trends were stable. Given that seabird populations can provide valuable information on the conditions of their feeding and nesting environments, this study highlights the need to maintain basics monitoring studies. Keywords: Seabird abundances; breeding distribution; Danco Coast; Antarctic Peninsula (Published: 28 February 2013) Citation: Polar Research 2013, 32 , 11133, http://dx.doi.org/10.3402/polar.v32i0.11133

The diet of post-breeding Antarctic shagsPhalacrocorax bransfieldensisat the Danco Coast, Antarctic Peninsula

AbstractThe diet of post-breeding Antarctic shagsPhalacrocorax bransfieldensiswas investigated at four colonies at the Danco Coast, Antarctic Peninsula, by the analysis of 399 pellets (regurgitated casts) collected during February and March 1998 and 2000. Overall, demersal-benthic fish were the most frequent and important prey at all the colonies sampled, followed by octopods and gastropods. Amongst the fish,Notothenia coriicepsandGobionotothen gibberifronswere the main prey in all of the sampling sites in both seasons. The composition of the diet of post-breeding shags differed from that observed in the previous breeding season. Post-breeders preyed on the same fish species consumed by breeders, although in different proportions and on larger specimens. The information provided here differs from that reported for post-breeding individuals belonging to other shag species and also for post-breeding Antarctic shags. Our results, as well as the differences with previous studies, are discussed in relation to differences in prey availability among localities and to the use of alternative foraging grounds at the end of the breeding period.

Short Note: A method for sexing the chicks of Antarctic shags

Several studies have been carried out during the last fifteen years on reproduction, population dynamics and diet of the Antarctic shag, Phalacrocorax bransfieldensis Murphy, at different localities in the South Shetland Islands (reviewed in Casaux & Barrera-Oro 2006). In both the colonies studied and in other colonies counted we observed that the number of breeding pairs was steadily decreasing (Casaux & Barrera-Oro 2006). Casaux & Baroni (2002) had earlier suggested that such a decreasing trend might be related, at least partially, to a marked decrease in the inshore populations of two fish prey species, the marbled notothen Notothenia rossii Richardson and the humphead notothen Gobionotothen gibberifrons Lönnberg (Barrera-Oro et al. 2000), which had been studied over a period of 19 years in coastal waters of the South Shetland Islands. Exactly how a reduction in prey availability affects the shag populations (e.g. migration of breeders to other colonies in the area or to new breeding areas, a decrease in the rate of recruitment, an increase in adult mortality, variation in the age at first breeding, etc) is not clear. To investigate this, we started a banding programme at Nelson Island, South Shetland Islands. We postulated that the processes might operate with different intensities on individuals of different sexes, so all individuals in each population studied needed to be sexed. This posed problems for chicks which have monomorphic plumage and no differences in vocalisations (Casaux & Baroni 2000), so that the normal methods for sexing in the field would not work. As most of the external morphological characters in the chicks of Antarctic shags have stabilized by 45–50 days old (Casaux 1998), Casaux & Baroni (2000) had suggested that the use of discriminant functions originally developed for adults could be an appropriate method to sex chicks more than 50 days old.

Shags in Antarctica: their feeding behaviour and ecological role in the marine food web

Feeding behaviour, ecological role in the marine food web and population trends of the Antarctic shag Phalacrocorax bransfieldensis and the South Georgia shag P. georgianus in Antarctica are analysed. The diving depths and duration recorded for these shags are the deepest and longest among all flying birds in Antarctica and match deep dives performed by small Antarctic penguins. Individual shags of both sexes partition foraging depths and food resources, which might diminish intra-specific competition. Like other sub-Antarctic shags, P. bransfieldensis and P. georgianus are bottom feeders that prey predominantly on demersal fish. In the southern Scotia Arc and west Antarctic Peninsula, nototheniids, mainly Notothenia coriiceps, constitute their main prey. Shag partners alternate the time at sea and, as the energy requirements at the nest increase, they increase the number but reduce the duration of the feeding trips. A steady declining trend in the number of breeding pairs of both species has been observed in the last decade at several Antarctic localities; this phenomenon at the South Shetland Islands might be at least partially explained by the effect of the commercial fishery on their prey. In inshore shallow waters shags occupy the trophic niche of main predators of demersal fish and play an important ecological role as regulators of populations of particular fish prey that have marked site fidelity. The potential use of shags as biomonitors in Antarctica is discussed.

Diving Patterns in the Antarctic Shag

The diving patterns of the Antarctic Shag (Phalacrocorax bransfieldensis) were studied by direct observation on individuals foraging at Harmony Cove, Nelson Island, South Shetland Islands, during the 1995/96 and 1996/97 breeding seasons. The individuals observed foraged in shallow waters, mainly solitarily and presumably dived aerobically. The shags displayed relatively short diving bouts composed of few dives. During the 1995/96 breeding season, the duration of the dives decreased with the increase in the number of dives per bout and increased with the diving depth. These relationships were not statistically significant in 1996/97. In both seasons, the duration of the dives was positively related with both the surface resting time preceding and succeeding the dive, which may indicate that these birds display anticipatory or reactive dives probably according to the foraging conditions. Shags at the surface were seen swallowing fish longer than 15 cm; smaller fish as well as invertebrates may have been ingested underwater. The mean diving efficiencies of the bouts fall within the range reported for phalacrocoracids, but values of diving efficiency below unity were observed.

Fish in the diet of the Antarctic shag at four colonies on the Danco Coast, Antarctic Peninsula

The diet of breeding Antarctic shags (Phalacrocorax bransfieldensis) was investigated at four colonies on the Danco Coast, Antarctic Peninsula, by the analysis of 616 pellets (regurgitated casts) collected from December 1997 to February 1998. Overall, demersal-benthic fish were the most frequent and important prey at all the colonies, followed by octopods and gastropods. Amongst fish, Notothenia coriiceps was the main prey in all of the sampling sites, followed in similar importance by Gobionotothen gibberifrons at Cape Herschel, Primavera Island and Midas Island and in less importance by Harpagifer antarcticus at Py Point. There were marked differences among colonies in the size of the fish consumed. The largest and the smallest specimens were eaten by shags from Midas Island and Py Point respectively. This was mainly influenced by the number of specimens of the smallest fish species, H. antarcticus, consumed at Py Point. The differences in the diet composition may be related to the different foraging areas used by the shags. Results from this study differ from previous studies around the Antarctic Peninsula. The shags at the Danco Coast preyed markedly more intensively than those at the South Shetland Islands on G. gibberifrons. This finding reflects the low abundance of this fish species in inshore waters (< 100 m depth) at the South Shetland Islands and supports the use of the Antarctic shags to monitor trends in local populations of coastal fish species.

SEX DIFFERENCES IN DIVING DEPTHS AND DIET OF ANTARCTIC SHAGS AT THE SOUTH SHETLAND ISLANDS

Abstract Sexual differences in maximum diving depths and in the composition of the diet of the Antarctic Shag (Phalacrocorax bransfieldensis) were investigated at Harmony Point, Nelson Island, South Shetland Islands, Antarctica, during the 1995–1996 and 1996–1997 breeding seasons. The mean maximum diving depth estimated by the capillary-tube depth gauge technique was 37.8 m which, when compared with other studies, reflects good food availability in shallow waters around Harmony Point. Females dived significantly deeper than males and also reached the maximum dive depth registered (112.6 m). The analysis of the stomach contents recovered when the individuals with capillary-tubes returned to the nest from foraging trips indicated that males ingested almost exclusively large Notothenia coriiceps specimens, whereas females preyed more intensively on smaller fish. The differences observed suggest that individuals of both sexes partitioned foraging depths and food resources.

Sexual Size Dimorphism in the Antarctic Shag

-Analysis of the morphology of 141 Antarctic Shags (Phalacrocorax bransfieldensis) breeding at Harmony Point (62017'S, 59014'W), South Shetland Islands, and 85 at Danco Coast (64009'S, 60057'W), Antarctic Peninsula, indicated that males are significantly heavier and larger than females. However, there are overlaps in the morphometric variables (mass, culmen, bill, tarsus and wing length, and bill depth and width) between sexes. Two discriminant functions correctly classified 97.8% and 97.6% of the males and females considered to generate them. When the validity of the discriminant functions was checked on other Antarctic Shags breeding at Harmony Point and at Danco Coast, the rate of correct classification remained high. These discriminant functions could be used to sex chicks older than 45-50 days and juveniles. Received 17 November 1999, resubmitted 4 May 2000, accepted 8 May 2000.