G. A. Daneri

Responses of Pygoscelis adeliae and P. papua populations to environmental changes at Isla 25 de Mayo (King George Island)

As part of a monitoring study of Adélie and Gentoo penguin colonies, birds occupying nests with eggs and chicks in crèches were counted annually from the 1995/1996 to the 2006/2007 seasons at Stranger Point, Isla 25 de Mayo (King George Island), Antarctica. During the study period the Adélie penguin population showed a decrease of 62%. The number of chicks in crèches followed a similar trend, the smallest number occurring in 2002, when it was 63% lower than in 1995/1996. In contrast, the Gentoo breeding population size increased by 68%, while chicks produced increased by 63%. Despite the opposing trends in population size between species, there was a positive relation in their interannual variation, although the extent, and for some years the direction, of the change observed always favoured Gentoo penguins. Breeding success (chicks in crèches/nests with eggs) fluctuated between 0.65 and 1.26 for Adélies and between 0.76 and 1.27 for Gentoo penguins, and did not differ significantly between species. The similar breeding success of these species suggests that the contrasting population trends observed were driven by factors operating over winter. We suggest that current changes in environmental conditions may affect adult birds of both species during the previous winter with different intensity but in a roughly similar way, but that juvenile survival of both species and thus the recruitment of new breeders might be affected differentially, with a much lower survival rate of juvenile Adélie penguins.

Mass transfer from mothers to pups and mass recovery by mothers during the post-breeding foraging period in southern elephant seals (Mirounga leonina) at King George Island

Abstract Mass transfer from mother to pup during the lactation period, and mass recovery for the same females during the foraging period were measured in the southern elephant seal at King George Island, Antarctica. During the 19.2 ± 0.9-day lactation period measured (which represented 87% of the entire nursing), females lost a mean mass of 10.56 ± 1.76 kg/day (n = 27), while their pups gained a mean mass of 5.27 ± 1.1 kg/day. There was a correlation between daily body weight gain in pups and daily weight loss by their mothers. Pup weaning mass was positively related to maternal post-partum mass. Serial samples showed that weight losses by females and gains by their pups were not linear over lactation, but showed lower values at the beginning and at the end of lactation. During the 60.5 ± 6.2-day foraging phase between the end of lactation and molt, females gained 2.21 ± 0.65 kg/day (n = 12), or 54% of the mass lost during nursing. Growth rates reported here are higher than those reported in other breeding sites. However, the ratio of body mass loss by females to gain by their pups was similar, suggesting that higher growth rates and greater weaning mass at South Shetland are due to a higher mean weight of females on arrival at this breeding site. The foraging period was shorter and the mass gained greater than those measured at South Georgia; this could be related to relatively shorter distances to foraging areas.

Predation on cephalopods by Antarctic fur seals, Arctocephalus gazella, at two localities of the Scotia Arc, Antarctica

Abstract The cephalopod remains from 206 Antarctic fur seal (Arctocephalus gazella) scats collected at Mossman Peninsula, South Orkney Islands (n = 105) and at Stranger Point, South Shetland Islands (n = 101) contained 148 beaks (57 lower and 91 upper). The lower beaks were sorted and measured. Identification of 33 of the lower beaks that were collected at Mossman Peninsula revealed two squid species, Brachioteuthis ?picta (n = 26) and Psychroteuthisglacialis (n = 7), with lower rostral lengths (LRL) of 2.0–3.5 mm, and 1.0–2.5 mm, respectively. Identification of 15 of the lower beaks collected at Stranger Point revealed the same squid species, with the LRL of B. ?picta ranging from 3.0–3.4 mm (n = 9), and that of P. glacialis from 2.0 to 3.5 mm (n = 6). Estimated squid sizes and wet masses indicate that Antarctic fur seals feed on the small sub-adult squid which inhabit the surface layers. We have compared the squid diet estimated for the seals with that reported for its congeners in lower latitudes and other Antarctic seals, and conclude that cephalopods do not form an important food resource for Antarctic fur seals.

Mass changes during their annual cycle in females of southern elephant seals at King George Island

Abstract Mass changes in female southern elephant seals, sampled sequentially at different points through their annual cycle, were measured at King George Island, South Shetland Islands, during the 1995/1996 and 1996/1997 field seasons. Females weighed after they had given birth showed an increase of 37 ± 36 kg (mean ± SD), which represented 6.2 ± 6.4% in relation to their mass in the first breeding season. During the first aquatic phase, between the end of lactation and the beginning of moult, females gained a mean of 128 ± 35 kg, (n = 18) (2.19 ± 0.65 kg day−1), which represented between 27 and 83% of the mass they had lost during lactation. Nine females followed during moulting showed a mass loss rate of 5.0 ± 0.4 kg day−1, which was half the rate during lactation. Total mass loss during moulting (129 ± 22 kg) was not significantly different from mass gain for the same females between lactation and moult (135 ± 37 kg). Furthermore, at the end of moulting, female mass was not significantly different from the mass at the end of lactation. These masses represented 65 ± 5% and 64 ± 5%, respectively, of their initial mass after parturition. During the second period at sea, from the end of the moult until females hauled out to give birth in the following breeding season, the estimated mass gain was 1.45 ± 0.24 kg day−1 (n = 5), which was not significantly different to the rate of mass gain shown by the same females during the first period at sea (2.26 ± 0.70 kg day−1). Total mass gain during the second aquatic phase (364 ± 63 kg) was not correlated with the mass at the end of moulting, but it was positively related to the mass loss experienced by females from parturition until the end of the moulting period in the first breeding season.

Energy gain and loss during lactation and postweaning in southern elephant seal pups (Mirounga leonina) at King George Island

Abstract Deuterium-labeled water was used to measure changes in the proximate body composition during the lactation period and after weaning in southern elephant seal pups at King George Island, South Shetland Islands, Antarctica. During the lactation period (23.0 ± 1.4 days) pups gained a mean of 4.9 ± 0.5 kg/day (n=7). Of the total mass gain (112 ± 8 kg), 38% was water, 48% was fat, and 11% was protein. This represented an increase in total body gross energy of 2437 ± 145 MJ. The proportion of body mass represented by fat was less than 2% at birth, increasing to 35 ± 2% at weaning. We followed the pups during a mean period of 36 ± 3 days after weaning. During this period, pups had a mean loss of 1.21 ± 0.10 kg/day (n=7) comprising 39% water, 48% fat, and 12% protein. The energy cost over this period was 952 ± 168 MJ, which represented, on average, 39% of the total energy gained during the suckling period.

Haul-out pattern of itinerant male Antarctic fur seals (Arctocephalus gazella) at Laurie Island, South Orkney Islands

The seasonal haul-out pattern of itinerant male Antarctic fur seals (Arctocephalus gazella) was determined by regular counts at Mossman Peninsula, Laurie Island, South Orkney Islands, from 1996 to 2005. Small numbers of animals began to arrive at the beach in late December / early January (mean date 28 December ± 15 days, n = 10). Peak numbers of animals ashore changed considerably between seasons. In 1996, 1998 and 2001, peak numbers were registered in March (6/3, 18/3 and 6/3, respectively). Numbers peaked in 1997, 1999 and 2005 at the end of January / beginning of February (26/1, 2/2 and 28/1, respectively). In 2000, 2002, 2003 and 2004 peaks were registered in the third week of February (15/2, 22/2, 14/2 and 20/2, respectively). Peaks in numbers of seals ashore also varied between years, being minimum during 2001 (2531 individuals) and maximum during 2006 (16 610 individuals). In March 1998 the coasts of Laurie Island were surveyed by navigating inflatable boats near the shoreline; 18 haul-out places were identified. The big differences in peak numbers, as well as in the dates of peak events among years, suggest that local conditions could have an effect on the numbers of animals hauled out in a given year. It may therefore be difficult to predict trends from summer censuses in non-breeding places.

Fish prey of Weddell seals, Leptonychotes weddellii , at Hope Bay, Antarctic Peninsula, during the late summer

The study of the feeding habits of Weddell seals, Leptonychotes weddellii, in the area of west Antarctic Peninsula is essential to understand the role they play in the marine food webs, especially considering that this is one of the regions most affected by climate change. With the aim of detecting temporal changes in the fish predation pattern of seals, a total of 217 scats were collected at Hope Bay, during three consecutive summers (2003, 2004 and 2005). The family Nototheniidae comprised over 80% in numbers of fish preyed by seals. The Antarctic silverfish, Pleuragramma antarctica, was, by far, the most frequent and abundant prey species with a mean percentage frequency of occurrence of 48.7% and representing in average 52.1% in numbers of the fish consumed by seals. Other fish species of lesser importance were the nototheniids Trematomus newnesi, Lepidonotothen larseni, Gobionotothen gibberifrons and the channichthyid Chionodraco rastrospinosus. Temporal variation was observed not only in the relative proportions of the different fish prey taxa but also in the sizes of the dominant prey, P. antarctica. Given the high trophic vulnerability of this species to changes in abiotic factors and food web structure and dynamics, a possible influence of El Niño Southern Oscillation events of 2002–2003 and 2004–2005 should not be discarded. Moreover, special attention should be addressed to its population status, distribution and spatial/temporal availability as prey resource of upper trophic level consumers such as L. weddellii which largely depend on P. antarctica.