Continued range expansion of introduced reindeer on South Georgia

Reindeer were introduced 70 years ago to the Stromness Bay area on the subantarctic island of South Georgia, and the herd is still surviving. Two glaciers confine the herd, and movements are restricted even within the area due to a rugged topography. The Husvik herd has recently expanded its range within this area, and today approximately 88% of the vegetated area is affected by grazing. The grazing effects are described, and the value of the introduction as a natural experiment is discussed.     

Introduced reindeer and their effects on the vegetation and the epigeic invertebrate fauna of South Georgia (subantarctic)

Summary The introduced reindeer of South Georgia have had a serious impact on the vegetation throughout the range of three populations on the island. Exclosure experiments in areas where the reindeer were introduced have resulted in a dramatic change in the composition of the protected vegetation. Poa flabellata (the major winter food) and Acaena magellanica (a major summer food) have recovered to their former status inside the exclosures, while Deschampsia antarctia and the introduced grass Poa annua tolerate grazing and trampling and have spread over the grazed areas. Festuca contracta and Rostkovia magellanica are not eaten by the reindeer. Trampling has resulted in a high proportion of bare soil and peat in sites freely accessible to reindeer. However, the changes in the vegetation have not had such a significant effect on the associated invertebrate fauna. Thus in grazed and protected areas the faunistic composition is qualitatively similar, although there are quantitative differences, and some of the trends can probably be attributed to the presence of the reindeer. Compared with reindeer-free areas, the abundance of the perimylopid beetle Hydromedion sparsutum (a major primary decomposer) is reduced. The frequency of their egg parasite Notomymar aptenosoma (Hymenoptera, Mymaridae) increases. Consequently the ratio of perimylopoids to mymarids found in pitfall traps shifts from 1:0.01 (ungrazed areas) to 1:0.54 (grazed areas). Also the frequency of sciarids was found to be higher in reindeer areas. The larvae of these probably introduced gnats do not play a role in the natural terrestrial ecosystem of South Georgia, but in reindeer areas they appear to establish larger populations because they are able to live deeper in the soil and in hardened substrates. There is also a shift in the ratio between Collembola (major prey) to spiders from 1:1.3 (ungrazed areas) to 1:0.82 (grazed areas), for animals collected in pitfall traps. This may be a result of the trampling effect of the reindeer.     

Age determination of Reindeer introduced into South Georgia

The ages of South Georgia Reindeer collected from the introduced herds, and of carcasses from natural deaths were determined using patterns of tooth replacement and eruption, and annulations in the cementum of incisor teeth. Replacement and eruption patterns are typical of the species. The difficulties encountered with the patterns of cementum deposition on the incisors, and consequently with the assignment of age to animals with established permanent dentition, are described in detail. The overall result is the underageing of a proportion of the specimens, and the problems demonstrated are ascribed to the influence of the alien environment and oceanic climate in which the animals live.     

Seasonal trends in chemical composition of reindeer forage plants on South Georgia

Summary Systematic observations were made on reindeer feeding behaviour during 1973–74, and seven phanerogams and three bryophytes were selected for sampling during the following year. Material of the principal plant species in the main communities at a study site was harvested and analysed for crude fibre, holocellulose, nitrogen, phosphorus, potassium, calcium, magnesium and ash. Contrary to expectation, crude fibre data show an early season peak in most species, whereas holocellulose data are more variable. Seasonal trends in mineral elements were similar to those found in nearby ungrazed vegetation, and to those in northern temperate species, although absolute values were often higher than in the latter. Data from material collected within and outside a deer-proof exclosure suggest some degree of nutrient input by the animals in the grazed situation, and nutrient enrichment was also apparent at a site colonized by white-chinned petrels. Differences in nutrient content occurred in species collected from both a freely-drained, exposed site and a wetter, more sheltered area, but these were not consistent. Data are considered in relation to the diet of South Georgia reindeer as determined by rumen content analysis, and are compared with those of forage species of northern reindeer and caribou.     

Diving behaviour and diet of the blue-eyed shag at South Georgia

Summary This paper describes a concurrent investigation of individual variation in diet, diving patterns and performance of blue-eyed shags Phalacrocorax atriceps breeding at South Georgia. Within one day individual shags exhibited one of three foraging strategies: short diving (4 birds, all dives 120 s) and mixed diving (15 birds, predominantly long but with a few short dives). The mean number of dives per day was significantly higher in shags that only made short dives (mean=172.0, SE=43.2) than birds with a mixed diving strategy (mean=40.5, SE=4.7) and birds that made only long dives (mean=30.8, SE=1.8). Diet was assessed using hard remains recovered from pellets regurgitated by the shags. Small nototheniid fish (c. 10 kJ per item) were by far the commonest prey but most pellets contained additional items. The frequency of pellets with additional items of higher energy value than nototheniid fish (10.c. 900 kJ per item), lower energy value (>1–10 kJ per item) and both higher and lower energy items was strikingly similar to the frequency of shags making long, short and both long and short dives respectively. Predicted aerobic dive limits suggested that during long dives, blue-eyed shags were probably sustained by anaerobic metabolism. Models of prey capture rates demonstrated that for both long and short diving, many items must be caught per dive when birds are feeding on prey at the lower end of the energy range. Predicted capture rates for the commonest recorded prey (small fish) differ markedly between the two diving strategies.     

Spatial dynamics of two introduced species of carabid beetles on the sub-Antarctic island of South Georgia

On the sub-Antarctic island of South Georgia two species of predatory beetle, Trechisibus antarcticus and Oopterus soledadinus (Coleoptera, Carabidae), were accidentally introduced. The colonisation process offers unique opportunities for testing ecological hypotheses in the field. As a basis for such studies, the spatial dynamics of the two species in the coastal lowland around Stromness Bay and Cumberland Bay were monitored during the period 1988–1996. Data are presented on the expansion of the two species and on the thermal characteristics of the tussock-forming grass Parodiochloa flabellata, which dominates the coastal lowlands. The largest expansion was shown by T. antarcticus, occurring as two populations in the Stromness Bay area. The origin of one of the populations, discovered in 1982, is Husvik Harbour, from where the species has colonised the central part of Stromness Bay. The second population, discovered in 1988 at Harbour Point, is invading the northern part of the area around Stromness Bay. Up to the present, three populations of O. soledadinus have been discovered. One population was found in 1988 at Husvik Harbour, co-existing with T. antarcticus, from where it is slowly expanding its distribution into the coastal zone. A second, very small, population of O. soledadinus was found in 1996 at Jason Harbour (Cumberland West Bay). The largest population of O. soledadinus, first reported in 1963, inhabits the area around Grytviken and King Edward Point (Cumberland East Bay), where it is the sole carabid species. The tussock grass vegetation offers a highly stable thermal environment compared with the more variable surroundings. Together with an ample food supply in the form of small arthropods and beetle larvae, and a vacant niche for arthropod predators, the benign microclimate of the tussock vegetation may explain the success of these predator introductions. Results of field observations on population parameters of the carabids, and laboratory measurement of egg production indicate the potential for large-scale co-existence. Accepted: 10 November 1998     

Demographics in an alpine reindeer herd: effects of density and winter weather

We examined how population density, winter weather, snow conditions, and 2 large-scale climatic indices (North Atlantic Oscillation, NAO, and Arctic Oscillation, AO) influenced demography (reproduction and mortality) in an alpine herd of semi-domesticated reindeer Rangifer tarandus between 1959 and 2000 in Finnish Lapland. The herd lived on heavily grazed lichen pastures, with winter densities between 0.8 and 3.9 individuals km⁻². Icing conditions occurred every 7th yr, on an average, and decreased reproductive rate (calves/females) by 49%. In general linear models icing remarkably increased the fit of snow models to reproductive rate. Incorporation of an interaction term between icing and the snow depth index provided better fit than a model without interaction. Delayed snowmelt decreased reproductive rate. For the day of snowmelt, however, the model without interaction was better than the interaction model. These 3 models provided the best fit to the data and accounted for 51–54% of the variation in reproductive rate. Winter mortality was related to density and large-scale climatic indices, but not to local winter weather except a slight increase in mortality during an icing winter. The best model for winter mortality, including reindeer density and NAO, accounted for 26% of variation in mortality. Three factors may be involved explaining weak density dependence or the lack of such dependence; climate change scenarios that predict higher winter temperature, more frequent thawing-freezing periods, and deeper snow would be expected to decrease reproductive rate and increase winter mortality of reindeer and thus to reduce profitability of reindeer husbandry. In contrast, early springs would be advantageous for reindeer in the short term.     

Growth, diet and condition of goldsinny on the west coast of Scotland

A study of seasonal, locational and sexual variations of growth, diet, somatic condition ( K _s), gonadosomatic condition (GSI) and hepatosomatic condition (HSI), of the goldsinny wrasse, Ctenolabrus rupestris , was made on specimens taken from three areas (Millport, Oban and Luing) of the west coast of Scotland from May 1992 to June 1993. Capture throughout the year was by either baited creel or by anaesthetics applied underwater. Male goldsinny of age 1 year and older ranged in total length from 67-155 mm, total weight 3.8-58.8 g, and had a maximum age of 14+ years. Females of 1 year and older ranged in total length from 59-159 mm, total weight 2.4-65.4 g and had a maximum age of 20+ years. Juvenile (0 +) goldsinny were mostly of indeterminate sex, ranged in total length from 16-57 mm, and total weight 0.08-1.97 g. Female growth was slower than that of males for all three locations; growth of male and female goldsinny from Millport was slower than the respective sexes at the other two locations. Length-weight relationships varied with age and location. There were differences in K _s, GSI, HSI and dietary trends associated with variation in season, sex and location. The implications of this variation are discussed in relation to the management of a sustainable goldsinny fishery.     

The diet of the South Georgia shag Phalacrocorax georgianus at South Orkney Islands in five consecutive years

The diet of the South Georgia shag Phalacrocorax georgianus at Laurie Island, South Orkney Islands, was studied by the analysis of 420 pellets (regurgitated casts) collected from the 1995 to 1999 breeding seasons. Demersal-benthic fish were by far the main prey, followed by molluscs (mainly octopods and bivalves) and polychaetes. Harpagifer antarcticus (in 1995, 1998, 1999) and Lepidonotothen nudifrons (1996, 1997) were the most frequent prey, followed by Gobionotothen gibberifrons or Trematomus newnesi. Harpagifer antarcticus, followed by L. nudifrons or T. newnesi, was the most numerous prey in all of the seasons and predominated in mass in 1995 and 1996, followed by Notothenia coriiceps and L. nudifrons. In 1997 and 1999, G. gibberifrons and N. coriiceps were the species that most contributed to the diet whereas N. coriiceps and H. antarcticus contributed most in 1998. Our results differ from those reported for the South Orkney Islands in previous studies. These differences could be due to the use of different diet-analysis methods and to shags-related and/or fisheries-related changes in the food availability around the colonies. These alternative explanations are analysed and discussed.     

Comparative nutritional ecology of grass-feeding in a sub-Antarctic beetle: the impact of introduced species on Hydromedion sparsutum from South Georgia

South Georgia has many introduced plant and animal species, a consequence of its long history of human habitation. Introduced reindeer have a strong effect on the vegetation of the Stromness Bay area by causing the replacement of indigenous species by grazing-tolerant grasses such as the exotic Poa annua, and in certain circumstances, the indigenous Festuca contracta. Recently it has been argued that an introduced predatory carabid has contributed to declines in the abundance and an increase in the body size of adults of the indigenous perimylopid beetle Hydromedion sparsutum. However, it also appears that body size of these beetles is smaller in areas where exotic grasses predominate compared to undisturbed areas. Here we test the hypothesis that by causing the spread of poorer quality grasses, especially the exotic Poa annua, reindeer may be having an indirect effect on H. sparsutum. To do this we examined the nutritional ecology of H. sparsutum larvae on four grass species which form a major part of its diet, viz. the indigenous Parodiochloa flabellata, Phleum alpinum and Festuca contracta, and the exotic Poa annua. Larvae showed the highest growth rate on Parodiochloa flabellata, followed by Phleum alpinum, F. contracta and Poa annua. These differences are due to poorer absorption of the exotic grass, and poorer utilization of the absorbed material in the case of F. contracta. Poor growth of larvae on F. contracta appears to be due to its low water and nitrogen contents, whereas in the case of P. annua a combination of low water content and high nitrogen content may be responsible for low growth rates. Low growth rates associated with poor-quality food may lead either to a prolongation of the life cycle or of the length of feeding bouts of an insect. Neither option appears to be feasible for H. sparsutum, and this means that the outcome of feeding on poorer-quality foods would be a reduction in final adult size. This has fitness consequences for the beetle. Hence it appears that by causing the spread of grasses that are unsuitable for growth of H. sparsutum, reindeer may be having an indirect effect on this beetle species. Received: 18 August 1996 / Accepted: 7 February 1997     

The diet of Antarctic fur sealsArctocephalus gazella during the breeding season at South Georgia

 The diet of lactating female Antarctic fur seals Arctocephalus gazella at South Georgia was investigated during the pup-rearing period (January/March) of 1991–1994. Antarctic krill Euphausia superba was the main prey item, occurring in 88% of all scats (n=497), whereas fish occurred in 47% and squid in 5% of all scats. There was considerable intra- and inter-annual variation in the characteristics of krill taken by fur seals. The distribution of krill sizes taken suggests that fur seals are not actively selecting particular sizes of krill and, therefore, that the krill in the diet reflects the krill available around South Georgia. The absence of group 3 krill (44–48 mm in length) in the South Georgia area, as indicated by their absence in the diet of seals, is suggested as a possible reason for low availability of krill and the subsequent reproductive failure among krill predators. The frequency of occurrence of fish was much higher than in previous studies; the pattern of fish consumption showed a consistent seasonal pattern in 3 of the 4 years studied. Of the total number of the myctophid Protomyctophum choriodon, the most numerous fish taxon, 98% were taken between early February and the middle of March. Champsocephalus gunnari and Lepidonotothen larseni agg., which both feed on krill, dominated the fish component of the diet outside this period and together constituted 94% of the total estimated biomass of fish consumed. The intra- and inter-annual variability in the diet of Antarctic fur seals emphasise the need for diet studies to be conducted during the entire pup-rearing periods of several years. Received: 15 March 1995/Accepted: 13 May 1995     

Absorption,retention and tissue distribution of radiocaesium in reindeer: effects of diet and radiocaesium source

Radiocaesium absorption and retention in reindeer (Rangifer tarandus) calves was compared in groups fed diets containing different proportions of lichen and concentrates, and different chemical forms of radiocaesium ((134)CsCl in solution or fallout from the Chernobyl accident). Daily intakes of fallout radiocaesium were 15-23 kBq, while daily intakes of (134)CsCl ranged from 70 kBq to 1,160 kBq. The half-life for radiocaesium in red blood cells (RBC) in animals fed with a pure lichen diet exceeded that in animals fed with a combined diet of lichen and concentrates by 40% (17.8+/-0.7 days vs. 12.7+/-0.4 days). Corresponding differences in the half-lives for urinary and faecal excretion were about 60% and 40%, respectively. Transfer coefficients (F(f)) to reindeer meat were estimated to be 0.25+/-0.01 days kg(-1) for fallout radiocaesium and 1.04+/-0.03 days kg(-1) for (134)CsCl, reflecting differences in both radiocaesium bioavailability and retention. The bioavailability of the Chernobyl radiocaesium in lichen in 1988 was estimated at ca. 35% compared to (134)CsCl.     

Diet of the King Penguin Aptenodytes patagonicus during three summers at South Georgia

King Penguins Aptenodytes patagonicus which were rearing chicks were studied during three summers from November 1991 to March 1994 at South Georgia. Stomach samples ( n =115) collected by flushing had a mean mass of 1308 g. Fish mass was allocated to each species based on the relationship between fish mass and otolith length. Three mesopelagic lanternfishes (Myctophidae), Krefftichthys anderssoni, Electrona carlsbergi and Protomyctophum choriodon , dominated the diet both by numbers and mass. They were small fish with mean mass of 3–7 g. Overall, K. anderssoni dominated the diet in terms of numbers and mass. Although Barracudina Notolepis coatsi occurred in <3% of the diet by numbers, it was large (106 g) and was second most important in terms of mass. Squid represented <3% of the diet by mass. Although the chick-rearing success was poor in the 1993–1994 summer, meal size was not reduced but foraging trips were longer. In the 1993–1994 summer, a larger proportion of the otoliths were not identifiable because they were more completely digested. Fewer otoliths were identified as being those of K. anderssoni , but we argue that about 90% of the unidentified otoliths were K. anderssoni. There was also more squid and N. coatsi in the diet during the poor summer. A consistent trend was that P. choriodon was rare or absent in early summer but more important later in the year, and at the end of 1992–1993, it was the dominant prey. We conclude that myctophid fish, especially K. anderssoni , are the main summer prey of King Penguins rearing chicks at South Georgia, as found in other recent studies in the Southern Ocean.     

Observations on life cycle and feeding ecology of two recently introduced predatory beetle species at South Georgia,sub-Antarctic

On South Georgia, two recently introduced species of predatory beetle,Oopterus soledadinus andTrechisibus antarcticus (Coleoptera, Carabidae), were studied in the period November 1991–April 1992. The study area comprised the coastal area around Stromness Bay, in particular the surroundings of the abandoned whaling station at Husvik. The study investigated the life cycle of both species and, forT. antarcticus, aspects of feeding. The occurrence of both teneral and gravid beetles was observed for the whole of the summer period.Trechisibus antarcticus appeared to be the more voracious predator of the two; its impact on other populations of soil animals may be large as shown by its effect on the endemic detritivorous beetleHydromedion sparsutum (Perimylopidae).     

Variation of plasma protein parameters in four free-ranging reindeer herds and in captive reindeer under defined feeding conditions

Plasma total protein (TP), albumin (ALB) and globulin (GLOB) concentrations and albumin/globulin ratio (A/G) were analysed from blood samples collected from free-ranging reindeer (Rangifer tarandus tarandus) herds at varying times of year. The same parameters were followed in nine captive reindeer with varying protein and energy intake. Variation in the blood constituents of free-ranging reindeer was analysed in relation to different extrinsic and intrinsic factors and compared to findings from captive animals, allowing the analysis of effects of protein and energy intake. There was large overall variation in TP, ALB, GLOB and A/G ratio in the free-ranging animals, ranging between 36-110 g/L, 18-59 g/L, 17-59 g/L and 0.5-2.1. The variation between months and years was significant for all variables except the A/G ratio, where no year effect was noted. Increase in live body mass was associated with a small significant increase and pregnancy with a small significant decrease in all dependent variables, except for the A/G ratio. Age did not have a significant effect on any of the blood constituents when body mass was included in the same model. In captive animals, feeding lichens with low protein content was related to a significant decline in TP, ALB and GLOB, but not in the A/G ratio, whereas feeding commercial ration increased plasma TP, ALB and GLOB significantly. Extrinsic factors such as season and year explained majority of variation in the blood constituents of free-ranging reindeer, whereas body mass, pregnancy and age had only a minor influence. It is concluded that plasma TP and ALB, and to a lesser extent GLOB and A/G ratio may serve as nutritional biomarkers of reindeer.     

The fish diet of black-browed albatrossDiomedea melanophris and grey-headed albatrossD. Chrysostoma at South Georgia

 The fish component of the diet of black-browed and grey-headed albatrosses at South Georgia was investigated by intercepting 155 meals from adults arriving to feed chicks during February 1986 and 1994. Fish represented 30% and 72% by mass of the diet of black-browed albatrosses and 14% and 60% by mass of the diet of grey-headed albatrosses in 1986 and 1994 respectively. We determined the identity and quantified the contribution (by numbers, size and mass) of fish species mainly by using otoliths (54 representing 9 taxa and 57 representing 17 taxa in black-browed and grey-headed albatross samples respectively). For black-browed albatrosses in 1986 the main fish prey was Patagonotothen guntheri (77% of otoliths, 51% of estimated fish biomass) and a single large specimen of Icichthys australis (40% estimated biomass), whereas in 1994 Pseudochaenichthys georgianus was the main fish prey (57% of estimated biomass) with Magnisudis prionosa (30%) and Champsocephalus gunnari (12%) also making substantial contributions. Grey-headed albatross samples from 1986 were dominated by southern lampreys (40% by number, 79% of estimated biomass), lanternfish (32% of numbers, 9% by mass) and Patagonotothen guntheri (11% by mass); in 1994 Champsocephalus gunnari (42% by numbers, 24% by mass), Magnisudis prionosa (13% by number, 36% by mass), Muraenolepis microps (90% by number), Pseudochaenichthys georgianus (15% by mass) and lanternfish (18% by number but only 1% by mass) were the main prey. The importance of Patagonotothen guntheri to both species in 1986 and its absence in 1994 probably reflect albatrosses obtaining it from the commercial fishery, which was active in 1986 but closed in 1994. Otherwise the fish diet of black-browed albatrosses is dominated by krill-feeding fish, characteristic of the waters of the South Georgia shelf. In contrast, the grey-headed albatross diet comprises deeper water mesopelagic species, especially lanternfish, which reflect its affinity for the Antarctic Polar Frontal Zone and associated oceanic upwellings. Received: 28 June 1995 / Accepted: 8 October 1995     

Growth rates of Antarctic fur seal Arctocephalus gazella pups at South Georgia

Large numbers of pups of the Antarctic fur seal were weighed at regular intervals through their rearing period in six seasons between 1972 and 1981 at South Georgia. Growth rates and birth and weaning weights were estimated from linear regressions of mean weight on mean age. Female pups had significantly lower growth rates and weaning weights than males, but higher variances for all growth parameters. This may reflect the importance to males of polygynous species of attaining high body weight. Except for an inverse relation between growth rate and birth weight there were no systematic relationships between growth parameters. Seasonal differences in growth rates were substantial and there was no indication that the continuing rapid population increase was affecting pup growth rates. The use of these data in detecting seasonal variations in local food availability is discussed. Preliminary estimates of the energy costs of pup rearing indicate that pup existence metabolism consumes c. 80% and mass gain to weaning only c. 15% of the energy provided by the female.     

Distribution of cephalopods recorded in the diet of the Patagonian toothfish (Dissostichus eleginoides) around South Georgia

The cephalopod component of the diet of Patagonian toothfish, Dissostichus eleginoides, around South Georgia was analysed from stomach contents collected between March and May 2000. Cephalopods occurred in 7% of D. eleginoides stomachs. A total of 363 cephalopod beaks were found, comprising 16 cephalopod species, of which 15 had not been previously recorded in the diet. Octopodid A (probably Pareledone turqueti) was the most important cephalopod species by number of lower beaks (36 beaks; 20.2% of the lower beaks) and Kondakovia longimana was the most important in terms of estimated mass (76% of the cephalopod component). When the cephalopod component of D. eleginoides was compared with other predators between March and May 2000, D. eleginoides fed more on octopods (25% of the lower beaks) than black-browed and grey-headed albatrosses (<1% of the lower beaks). The low frequency of the squid Martialia hyadesi in the diet of D. eleginoides around South Georgia was also noticed in the diet of albatrosses, and suggests that M. hyadesi was not present in these waters in 2000 (probably due to migratory movements or reproduction failure), despite being a candidate for commercial exploitation. The presence of the squid Mesonychoteuthis hamiltoni in the diet of D. eleginoides and being caught by a longline hook whilst presumably feeding on D. eleginoides, may indicate that juveniles of Mesonychoteuthis hamiltoni are prey of D. eleginoides adults, and when Mesonychoteuthis hamiltoni reach a large size as adults, they become the predator.