Population changes,movements of southern elephant seals on Crozet and Kerguelen Archipelagos in the last decades

Summary The elephant seal populations breeding on the Crozet and Kerguelen Archipelago were surveyed during the eighties. Elephant seals were observed moving between Kerguelen, Amsterdam, Heard Islands and Vestfold Hills and between Crozet and Prince-Edward Archipelagos. No exchanges were observed between Crozet and Kerguelen Archipelagos suggesting that the two populations are more isolated than previously stated. On the Crozet Archipelago, since 1966, the Possession Island population showed at 70% reduction in numbers of cows ashore and the population is still decreasing. On Kerguelen Island there has been a decline of 44% from 1956 to 1989 but the population appears to have stabilized since 1984. It is suggested that elephant seal populations in the Southern Indian Ocean may have been affected by a change at the trophic level over the last four decades. But the highest rate of decrease observed on the Crozet Archipelago and the fact that the population is still decreasing may be explained by additional factors, in particular by killer whale predation.     

Role of bay, fjord and seamount on the early life history of Lepidonotothen squamifrons from the Kerguelen Islands

Among the Kerguelen Islands' demersal fish, larvae of Lepidonotothen squamifrons are dominant during the summer over the island shelf and surrounding seamounts. Distribution of larval stages from different scientific surveys confirmed the position of the two known spawning grounds (south of the Kerguelen shelf and at the Kerguelen-Heard bank) and may indicate other spawnings on the Skiff bank and in bays and fjords. Different larval cohorts were observed for the shelf and the coastal zone whereas a unique one was observed for Skiff and Kerguelen-Heard seamounts. Larvae from the spawning ground south of the Kerguelen shelf appear in early summer and show a northwards dispersal to the northeastern nearshore zone, the Baleiniers Gulf, following the scheme of fish migration shown by Harden-Jones. Later on, larvae from the northern inshore spawning zone occur in the same area, which presumably then avoid intraspecific competition with the previous larvae. Larval distribution and migration strategy seemed to be in accordance with the island mass or seamount effect under a regular current. Accepted: 2 December 1999     

Effects of warm sea-surface temperature anomalies on the blue petrel at the Kerguelen Islands

Several long-term studies on Southern Ocean seabirds and seals have suggested a possible link between major declines in breeding performance and El Niño Southern Oscillation events. We report that the breeding performances and body condition of the blue petrel (Halobaena carulea) on the Kerguelen Islands is depressed by episodic, warm sea-surface temperatures (SSTs) in the winter before breeding. Lagged cross correlations between SSTs in the Kerguelen sector and the Southern Oscillation Index indicate that warm SSTs were found south of Kerguelen Islands within a year of, and between 4.2 and 5.4 years after, an El Niño event took place. These results can be discussed with respect to the recently described Antarctic Circumpolar Wave that drives climatic anomalies eastward around the Southern Ocean.     

Cadmium and copper contents in a freshwater fish species (brook trout, Salvelinus fontinalis) from the subantarctic Kerguelen Islands

The subantarctic Kerguelen Islands (49°S, 70°E) contain freshwaters among the most isolated in the world from direct human activities. Cadmium and copper concentrations were analyzed in muscle and liver tissues of 57 non-migratory brook trout (Salvelinus fontinalis) inhabiting the Sud River of Kerguelen Islands. The mean cadmium concentration in liver was 1.13 μg/g dry wt, within the range of levels measured in liver of marine fish from the Southern Ocean. Muscular Cd levels (0.12 μg/g dry wt) were roughly ten times higher than those measured in Kerguelen’s marine fish species. Copper levels were very high in the two organs (62.27 μg/g dry wt in liver and 3.02 μg/g dry wt in muscle) compared to those detected in fish from the Southern Ocean. Regarding the seasonal trend, the highest Cu and Cd muscular levels were measured in fish at the end of the austral winter, whereas the highest hepatic levels were observed at the end of the austral summer. Moreover, hepatic cadmium levels were higher in females than in males. These results could be related to brook trout spawning physiological preparations and foraging behavior during the summer period. We provide here the first results about Cu and Cd levels in liver and muscle of a freshwater fish species in an insular subantarctic context. They are in agreement with the high cadmium contamination found in fish of the Southern Ocean.     

The surface structure of Antarctic fish eggs and its use in identifying fish eggs from the Southern Ocean

Summary The surface structure of eggs of Notothenia neglecta, Nototheniops larseni, Nototheniops nudifrons (Nototheniidae), Champsocephalus gunnari and Chaenocephalus aceratus (Channichthyidae), collected near Elephant Island (Atlantic sector of the Southern Ocean) and of Notothenia rossii rossii (Nototheniidae) from Kerguelen waters (Indian sector of the Southern Ocean) was studied by scanning electron microscopy (SEM). Eggs of N. larseni differed from the other species by containing a micropyle with two micropyle pits. External morphological characteristics of the egg envelope such as the ultrastructure of the zona radiata, its interpore distances and the diameter of the micropyle were species-specific and could aid in the identification of fish eggs collected from the Southern Ocean.     

First demographic insights on historically harvested and poorly known male sperm whale populations off the Crozet and Kerguelen Islands (Southern Ocean)

Age and sex dependent spatial segregation has resulted in limited knowledge of the ecology and demography of sperm whale adult males feeding seasonally in high latitudes. This study focused on adult males interacting with the Patagonian toothfish (Dissostichus eleginoides) fishery operating off the Kerguelen and Crozet Archipelagos. Demographic parameters were estimated using a 10‐yr‐long photo‐identification data set paired with multistate closed robust design capture‐mark‐recapture models. The examination of a set of 29,078 photographs taken from fishing vessels during sperm whale depredation events resulted in identification of 295 individuals with nine visiting both study areas. Dispersal between both study regions was estimated to be 1% per year. The mean annual number of interacting sperm whales was estimated to n = 82 (95% CI 58–141) in Crozet and n = 106 (95% CI 76–174) in Kerguelen. Transient proportions were 13% in Crozet and 26% in Kerguelen. Corrected for transience, apparent survival estimates were 0.953 (95% CI 0.890–0.993) in Crozet, and 0.911 (95% CI 0.804–0.986) in Kerguelen. These survival and population size estimates are the first for depredating adult males in high latitudes, and can be used in evaluating the current conservation status of this historically harvested stock and to investigate depredation trends in 35 both Crozet and Kerguelen Islands.     

A northern rockhopper penguin unveils dispersion pathways in the Southern Ocean

We report the first record of a northern rockhopper penguin Eudyptes moseleyi on the Kerguelen Islands, Southern Indian Ocean. The penguin must have crossed the subtropical convergence to reach the island. This species was recently proved to be genetically different from the subantarctic eastern rockhopper penguin E. filholi that normally breeds on the Kerguelen Islands. The sequencing of a part of the mitochondrial control region shows that this bird may come from the population of Gough Island, 6,000 km away, in the south Atlantic Ocean. This finding confirms that the genetic isolation between these two penguin species is complete, although some individuals may sporadically disperse between the breeding sites. This first direct observation of a disperser from the Atlantic to the Indian Ocean also adds further support to a biogeographic dispersion pattern already suggested by phylogeographic patterns in other species from the Southern Ocean.     

Adjustment of pre‐moult foraging strategies in Macaroni Penguins Eudyptes chrysolophus according to locality,sex and breeding status

The annual moult creates the highest physiological stress during a penguin's breeding‐cycle and is preceded by a period of hyperphagia at sea. Although crucial to individual survival, foraging strategies before moult have been little investigated in keystone marine consumers in the Southern Ocean. The Macaroni Penguin Eudyptes chrysolophus demonstrates how individuals may adjust their foraging strategies during this period in line with constraints such as potential intraspecific competition between localities, foraging ability between dimorphic sexes and timing at sea between breeding and non‐breeding population components. We recorded pre‐moult behaviour at sea for 22 Macaroni Penguins from Crozet and Kerguelen Islands (southern Indian Ocean) during 2009 and 2011, using light‐based geolocation and stable isotope analysis. Penguins were distributed in population‐specific oceanic areas with similar surface temperatures (3.5 °C) south of the archipelagos, where they foraged at comparable trophic levels based on stable isotopes of their blood. Bayesian ‘broken stick’ modelling with concurrent analysis of seawater temperature records from the animal‐borne devices showed that within each population, females remained 6 days longer than males in the colder waters before heading back towards their colonies. Finally, 17 other non‐breeding individuals that moulted earlier had a higher mean blood δ¹⁵N value than did post‐breeding birds, meaning that early moulters probably fed more on fish than did late moulters. Our findings of such adjustments in foraging strategies developed across locality, sex and breeding status help understanding of the species' contrasted pre‐moult biology across its range and its ecology in the non‐breeding period.     

Gentoo penguin Pygoscelis papua diet as an indicator of planktonic availability in the Kerguelen Islands

Since penguins rely on the main planktonic resources of the Southern Ocean, knowledge of their diet may be used for monitoring these resources During winter and spring of 1987 and 1989, we investigated the composition of the diet of gentoo penguins. Pygoscelis papua, in relation to changes in the availability of two prey species, Euphausia vallentini and Themisto gaudichaudii, sampled during plankton surveys in the Kerguelen Islands. The comparison between plankton surveys and diet analysis was performed on samples taken 2–4 km from the studied colonies. Data on the abundance of Zooplankton derived from penguins' diet matched closely those from net hauls during a year of high plankton availability (1987). On the other hand, a weaker correspondence was found during a year of restricted availability (1989). The mean sizes of amphipods caught by penguins and net hauls were very similar but the size distribution showed comparatively fewer small and large individuals in net-hauls than in penguin stomachs. Detailed studies on the feeding range and foraging effort of penguins are therefore needed in the near future to validate the potential of penguin diet as a measure of plankton abundance.     

Biology and population dynamics of Notothenia rossii rossii from the Kerguelen Islands (Indian sector of Southern Ocean)

Summary Recent cruises on board research vessels and trawlers have followed the adult fishes of the Notothenia rossii rossii Richardson, 1844 population from the Kerguelen Islands. The food of this Nototheniidae being mainly planktonic, the movements of shoals are connected with the high productivity areas. In the Southern Ocean these areas are localized around the Antarctic Convergence. At the Kerguelen Islands the irregular configuration of the shelf and seasonal variations in water masses change the positions of the productive areas. For this reason the adult population can be to the north or south off the archipelago. Spawning only gathers the mature fishes in the southeast of Kerguelen during winter. At that time this species is very vulnerable to fishing efforts. The population dynamics of this Antarctic fish is studied with fishery statistics and biological data. A decline of the average length and catches per unit effort are observed from one year to the next.

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Resumé De récentes missions à bord de navires de recherche et de chalutiers ont permis de suivre la population adulte de Notothenia rossii rossii Richardson, 1844 des îles Kerguelen. Le régime alimentaire de ce Nototheniidae étant principalement de nature planctonique, les mouvements des bancs de poissons sont liés aux zones de haute productivité. Dans l'océan austral ces zones sont localisées au niveau de la convergence antarctique. Aux îles Kerguelen la topographie du plateau continental et les variations saisonnières de l'hydrologie modifient continuellement la position des zones de productivité. Pour cette raison la population adulte peut se trouver soit au nord soit au sud de l'archipel. Seule la ponte réunit les poissons matures dans le sud-est des îles Kerguelen pendant l'hiver. A cette période l'espèce est très vulnérable à un effort de pêche. La dynamique de la population de ce poisson antarctique est étudiée à partir des statistiques de pêche et des données biologiques. Une baisse de la longueur moyenne de la population ainsi qu'une diminution des valeurs de la prise par unité d'effort sont observées pendant la période considérée.

     

Subantarctic flowering plants: pre‐glacial survivors or post‐glacial immigrants?

Aim The aim here was to assess whether the present‐day assemblage of subantarctic flowering plants is the result of a rapid post‐Last Glacial Maximum (LGM) colonization or whether subantarctic flowering plants survived on the islands in glacial refugia throughout the LGM. Location The circumpolar subantarctic region, comprising six remote islands and island groups between latitudes 46° and 55° S, including South Georgia in the South Atlantic Ocean, the Prince Edward Islands, Îles Crozet, Îles Kerguelen, the Heard Island group in the South Indian Ocean and Macquarie Island in the South Pacific Ocean. Methods Floristic affinities between the subantarctic islands were assessed by cluster analysis applied to an up‐to‐date dataset of the phanerogamic flora in order to test for the existence of provincialism within the subantarctic. A review of the primary literature on the palaeobotany, geology and glacial history of the subantarctic islands was carried out and supplemented with additional palaeobotanical data and new field observations from South Georgia, Île de la Possession (Îles Crozet) and Îles Kerguelen. Results First, a strong regionalism was observed, with different floras characterizing the islands in each of the ocean basins, and endemic species being present in the South Indian Ocean and South Pacific Ocean provinces. Second, the majority of the plant species were present at the onset of accumulation of post‐glacial organic sediment and there is no evidence for the natural arrival of new immigrants during the subsequent period. Third, a review of geomorphological data suggested that the ice cover was incomplete during the LGM on the majority of the islands, and ice‐free biological refugia were probably present even on the most glaciated islands. Main conclusions Several independent lines of evidence favour the survival of a native subantarctic phanerogamic flora in local refugia during the LGM rather than a post‐LGM colonization from more distant temperate landmasses in the Southern Hemisphere.     

A new species and new records of lithodid crabs (Crustacea: Decapoda: Lithodidae) from the Crozet and Kerguelen Islands area (Subantarctica)

Four species of lithodid crabs from waters (240–2,005 m) in the Crozet and Kerguelen Islands area were studied. One new species, Neolithodes duhameli, is described. Three other species, N. capensis Stebbing, Paralomis anamerae Macpherson and P. birsteini Macpherson are reported for the first time from these localities. The new species, N. duhameli (620–1,500 m), is the fourth representative of the genus in Subantarctic waters and belongs to the group of species possessing a carapace, chelipeds and walking legs covered with numerous spinules or spiniform granules in addition to spines. However, the new species is distinguishable from others in the genus by the long, strong spines on the carapace and pereiopods. The finding of two species of Paralomis clearly extends their geographic ranges in the Southern Ocean: P. anamerae was previously known only in waters of the Falkland Islands and the circumpolar distribution of P. birsteini is supported. The observation of N. capensis also extends its previously described range from South Africa, in the Cape region, to Subantarctic waters. As a result of this study, 14 species of the family Lithodidae are now known from Antarctic and Subantarctic waters; and most can be considered endemic to these waters.     

The effect of habitat temperature on serum antifreeze glycoprotein (AFGP) activity in Notothenia rossii (Pisces: Nototheniidae) in the Southern Ocean

The marble notothen, Notothenia rossii, is widely distributed around the waters of sub-Antarctic islands in the Southern Ocean and is exposed to different temperatures that range from ?1.5 to 8 °C. This study investigates whether the different environmental conditions experienced by N. rossii at different latitudes in the Southern Ocean affect the levels of its blood serum antifreeze glycoprotein (AFGP). N. rossii specimens were collected from four localities, including the Ob’ Seamount in the Indian Ocean sector, and South Georgia Island, South Shetland Islands and Dallman Bay in the Atlantic Ocean sector. Serum AFGP activity was determined in terms of thermal hysteresis, i.e. the difference between the equilibrium melting and non-equilibrium freezing points (f.p.s.). Among the four populations, the Ob’ Seamount specimen had the lowest serum AFGP activity (0.44 °C) and concentration (4.88 mg/mL), and the highest non-equilibrium f.p. (?1.39 °C). These results are consistent with the warmer, ice-free waters around the Ob’ Seamount. The other three higher latitude populations have 2–3 times greater serum AFGP activity and concentration, and much lower non-equilibrium f.p.s. In contrast, the physiological profiles of serum AFGP size isoforms revealed that all N. rossii populations, including the Ob’ Seamount specimen, possess an extensive complements of AFGP proteins. Isoform variation was observed, especially in the large size isoforms (AFGPs 1–5), when compared to AFGP of the high Antarctic Dissostichus mawsoni. The lower levels of AFGP and the absence of some of the large isoforms are likely responsible for higher non-equilibrium f.p.s. of the Ob’ seamount specimen.     

Diversity, relative abundance, new locality records and population structure of Antarctic demersal fishes from the northern Scotia Arc islands and Bouvetøya

A primary objective of the ICEFISH 2004 cruise was to collect and study notothenioid fishes from remote localities in the Atlantic sector of the Southern Ocean. Nearly 1 month was devoted to bottom trawling for fishes on the shelf and upper slope (to 1,000 m) areas around Shag Rocks, South Georgia, South Sandwich Islands and Bouvetøya. The focus was on the latter two locations, because their faunas are more poorly known. Eight species were collected at Shag Rocks with Patagonotothen guntheri most abundant; 17 at South Georgia with Lepidonotothen nudifrons, L. larseni and Gobionotothen gibberifrons most abundant; 13 at the South Sandwich Islands with L. larseni, L. nudifrons and G. gibberifrons most abundant; and 11 at Bouvetøya with L. larseni, Macrourus holotrachys and L. squamifrons most abundant. Ten new locality records were established: Shag Rocks (1), South Georgia (1), South Sandwich Islands (5), South Sandwich Trench at 5,350 m (1) and Bouvetøya (2). Total known demersal fish diversity on the shelf and upper slope at Shag Rocks/South Georgia, South Sandwich Islands and Bouvetøya is 42, 31 and 17 species, respectively. To examine population structure in the four most abundant notothenioids at Bouvetøya (L. larseni, L. squamifrons, Notothenia coriiceps and Chaenocephalus aceratus), we examined the ND2 portion of mitochondrial DNA. Chaenocephalus aceratus, N. coriiceps and L. larseni exhibited no significant genetic differentiation in comparison with samples from localities in the Scotia Sea and the Antarctic Peninsula. However, L. squamifrons showed significant genetic differentiation between the South Shetlands and Bouvetøya populations (F _ST = 0.189, P = 0.015). Thus, these data combined with previous studies of two other notothenioids suggest that five of the six notothenioid species at Bouvetøya are not genetically differentiated from other localities in the Atlantic sector of the Southern Ocean. The location of Bouvetøya within the Antarctic Circumpolar Current and the long (1–2 years) pelagic stages of the notothenioids at Bouvetøya may be at least partly responsible for this genetic homogeneity.     

Half a World Apart? Overlap in Nonbreeding Distributions of Atlantic and Indian Ocean Thin-Billed Prions

Distant populations of animals may share their non-breeding grounds or migrate to distinct areas, and this may have important consequences for population differentiation and dynamics. Small burrow-nesting seabirds provide a suitable case study, as they are often restricted to safe breeding sites on islands, resulting in a patchy breeding distribution. For example, Thin-billed prions Pachyptila belcheri have two major breeding colonies more than 8,000 km apart, on the Falkland Islands in the south-western Atlantic and in the Kerguelen Archipelago in the Indian Ocean. We used geolocators and stable isotopes to compare at-sea movements and trophic levels of these two populations during their non-breeding season, and applied ecological niche models to compare environmental conditions in the habitat. Over three winters, birds breeding in the Atlantic showed a high consistency in their migration routes. Most individuals migrated more than 3000 km eastwards, while very few remained over the Patagonian Shelf. In contrast, all Indian Ocean birds migrated westwards, resulting in an overlapping nonbreeding area in the eastern Atlantic sector of the Southern Ocean. Geolocators and isotopic signature of feathers indicated that prions from the Falklands moulted at slightly higher latitudes than those from Kerguelen Islands. All birds fed on low trophic level prey, most probably crustaceans. The phenology differed notably between the two populations. Falkland birds returned to the Patagonian Shelf after 2-3 months, while Kerguelen birds remained in the nonbreeding area for seven months, before returning to nesting grounds highly synchronously and at high speed. Habitat models identified sea surface temperature and chlorophyll a concentration as important environmental parameters. In summary, we show that even though the two very distant populations migrate to roughly the same area to moult, they have distinct wintering strategies: They had significantly different realized niches and timing which may contribute to spatial niche partitioning.     

Length–weight relationships of five fish species associated with krill fishery in the Atlantic sector of the Southern Ocean

Length–weight relationships (LWRs) of five fish species commonly associated with Antarctic krill fishery, were determined. Samples were collected with Chinese krill trawler (codend mesh size 2 cm) in the Atlantic sector of the Southern Ocean from January to August 2016. Data on LWRs and the relationships between weight and standard length as well as weight and total length of those species were updated for the database of FishBase. Those data on fish species derived from Antarctic krill fishery will be very helpful in understanding the interaction between krill fishery and the associated fish community.     

A new species of the genus Paralomis (Crustacea: Decapoda: Lithodidae) from the Spiess seamount near Bouvet Island (Southern Ocean), with notes on habitat and ecology

A new species of the genus Paralomis, Paralomis elongata, has been collected from the Spiess seamount near Bouvet Island in the Southern Ocean. The species shows close affinity with P. anamerae Macpherson, 1988, from the Patagonian Shelf, P. africana Macpherson, 1987, from the south-western African shelf, and P. aculeata Henderson, 1888, from Crozet Islands. Morphological differences among the species and ecological characteristics are discussed.     

Day and night mesopelagic fish assemblages off the Kerguelen Islands (Southern Ocean)

Mesopelagic fish assemblages were investigated in the Polar Frontal Zone off the Kerguelen Islands during summer 1995, in parallel with a king penguin tracking study. During the day, the upper offshore water layers (0–200 m) have low potential prey diversity and abundance with only three fish species: a lanternfish, Krefftichthys anderssoni, a member of the Muraenolepididae, Muraenolepis marmoratus, and the early stages of the nototheniid, Lepidonotothen squamifrons. The mesopelagic fish community, including the typical myctophids, first appears in the deeper layer (300 m). At night, the surface layer (50 m) is invaded by the mesopelagic Myctophidae Electrona antarctica, Gymnoscopelus braueri, G. piabilis, G. fraseri, G. nicholsi, Protomyctophum bolini and P. tenisoni. Deeper (>100 m), a cline of species assemblages from the coast to offshore is observed. Accepted: 4 August 1999     

Assessing the impact of toothed whale depredation on socio-ecosystems and fishery management in wide-ranging subantarctic fisheries

Marine predators feeding on fisheries catches directly on the fishing gear, a behaviour termed “depredation”, has emerged as a major human-wildlife conflict globally, often resulting in substantial socio-economic and ecological impacts. This study investigated the extent of this conflict in commercial Patagonian toothfish (Dissostichus eleginoides) fisheries across subantarctic waters where both killer whales (Orcinus orca) and sperm whales (Physeter macrocephalus) feed on toothfish caught on longline hooks. Using long-term datasets from six major fishing areas, from southern Chile to the Indian Ocean sector of the Southern Ocean, statistical models were developed to quantify the catch removals due to whale depredation interactions. The results indicated that these removals were large, totalling more than 6600 t of toothfish between 2009 and 2016 with an annual mean of 837 t [95% CI 480–1195 t], comprised of 317 t [232–403 t] and 518 t [247–790 t] removed by killer whales and sperm whales, respectively. Catch removals greatly varied between areas, with the largest estimates found at Crozet, where on average 279 t [179–379 t] of toothfish per year, equivalent to 30% [21–37%] of the total catches. Together, these findings provide metrics to assess the impacts of depredation interactions on the fishing industry, whale populations, fish stocks and associated ecosystems. With an estimated $15 M USD worth of fish depredated every year, this study highlights the large geographic scale and economic significance of the depredation issue and its potential to compromise the viability of some toothfish fisheries which are the primary socio-economic activity in subantarctic regions.