Modelling the krill-predator dynamics of the Antarctic ecosystem

The history of human harvests of seals, whales, fish and krill in the Antarctic is summarised briefly, and the central role played by krill emphasised. The background to the hypothesis of a krill surplus in the mid-20th century is described, and the information on population and trend levels that has become available since the postulate was first advanced is discussed. The objective of the study is to determine whether predator–prey interactions alone can broadly explain observed population trends without the need for recourse to environmental change hypotheses. A model is developed including krill, four baleen whale (blue, fin, humpback and minke) and two seal (Antarctic fur and crabeater) species. The model commences in 1780 (the onset of fur seal harvests) and distinguishes the Atlantic/ Indian and Pacific Ocean sectors of the Southern Ocean in view of the much larger past harvests in the former. A reference case and six sensitivities are fitted to available data on predator abundances and trends, and the plausibility of the results and the assumptions on which they are based is discussed, together with suggested further areas for investigation. Amongst the key inferences of the study are that: (i) species interaction effects alone can explain observed predator abundance trends, though not without some difficulty; (ii) it is necessary to consider other species, in addition to baleen whales and krill, to explain observed trends – crabeater seals seemingly play an important role and constitute a particular priority for improved abundance and trend information; (iii) the Atlantic/ Indian Ocean sector shows major changes in species abundances, in contrast to the Pacific Ocean sector, which is much more stable; (iv) baleen whales have to be able to achieve relatively high growth rates to explain observed trends; and (v) Laws’ (1977) estimate of some 150 million tonnes for the krill surplus may be appreciably too high as a result of his calculations omitting consideration of density-dependent effects in feeding rates.

[1]  T. Branch,et al.  Estimates of abundance south of 60°S for cetacean species sighted frequently on the 1978/79 to 1997/98 IWC/IDCR-SOWER sighting surveys , 2023, J. Cetacean Res. Manage..

[2]  M. Bester,et al.  Diet and estimated food consumption of Antarctic fur seals at Bouvetøya during summer , 2000, Polar Biology.

[3]  M. Huntley,et al.  FEEDING REQUIREMENTS OF KRILL IN RELATION TO FOOD SOURCES , 1984 .

[4]  S. Pickett,et al.  Ecology: Individuals, populations and communities , 1987 .

[5]  24 May 2014 Annex H : Report of the Sub-Committee on Other Southern Hemisphere Whale Stocks , 2022 .

[6]  M. Payne.  Growth of a fur seal population , 1977 .

[7]  J. Hureau.  The significance of fish in the marine Antarctic ecosystems , 1994, Polar Biology.

[8]  J. Arnould,et al.  The diet of Antarctic fur sealsArctocephalus gazella during the breeding season at South Georgia , 1996, Polar Biology.

[9]  W. Bonner.  The fur seal of South Georgia , 1968 .

[10]  R. Hucke‐Gaete,et al.  Examining natural population growth from near extinction: the case of the Antarctic fur seal at the South Shetlands, Antarctica , 2004, Polar Biology.

[11]  Andrew Constable,et al.  Convention on the Conservation of Antarctic Marine Living Resources (CCAMLR) , 2018, Yearbook of International Cooperation on Environment and Development 1998–99.

[12]  A. Brierley,et al.  SIGNIFICANT INTRA-ANNUAL VARIABILITY IN KRILL DISTRIBUTION AND ABUNDANCE AT SOUTH GEORGIA REVEALED BY MULTIPLE ACOUSTIC SURVEYS DURING 2000/01 , 2002 .

[13]  G. Daneri,et al.  The diet of Antarctic fur seals, Arctocephalus gazella, during the summer-autumn period at Mossman Peninsula, Laurie Island (South Orkneys) , 1992, Polar Biology.

[14]  J. Croxall,et al.  Environmental response of upper trophic-level predators reveals a system change in an Antarctic marine ecosystem , 2001, Proceedings of the Royal Society of London. Series B: Biological Sciences.

[15]  S. Bushuev.  Feeding of minke whales, Balaenoptera acutorostrata, in the Antarctic , 1986 .

[16]  S. Nicol,et al.  Krill fisheries: Development, management and ecosystem implications , 1999 .

[17]  B. Jonsson,et al.  Antarctic Fish and Fisheries , 1993 .

[18]  T. Härkönen,et al.  Estimating mean age at sexual maturity in the crabeater seal (Lobodon carcinophagus) , 1995 .

[19]  Peter Rothery,et al.  Long-term decline in krill stock and increase in salps within the Southern Ocean , 2004, Nature.

[20]  J. Croxall.  Southern Ocean environmental changes: effects on seabird, seal and whale populations , 1992 .

[21]  R. Williams,et al.  The diet of Antarctic fur seals Arctocephalus gazella (Peters) during the breeding season at Heard Island , 1989, Antarctic Science.

[22]  M. Saunders,et al.  Plant-Provided Food for Carnivorous Insects: a Protective Mutualism and Its Applications , 2009 .

[23]  R. Williams,et al.  The diet of Antarctic fur seals during the late autumn and early winter around Heard Island , 1991, Antarctic Science.

[24]  S. Levitus,et al.  Warming of the World Ocean , 2000 .

[25]  U. Piatkowski,et al.  Predation on cephalopods by Antarctic fur seals, Arctocephalus gazella, at two localities of the Scotia Arc, Antarctica , 1999, Polar Biology.

[26]  P. Best.  The status of Right whales (Eubalaena glacialis) off South Africa, 1969-1979 , 1981 .

[27]  根本 敬久.  Food of baleen whales with reference to whale movements , 1963 .

[28]  S. Nicol,et al.  Recent trends in the fishery for Antarctic krill , 2003 .

[29]  W. Mare,et al.  Ecosystem Management and the Antarctic Krill , 1993 .

[30]  I. Everson.  The living resources of the Southern Ocean , 1977 .

[31]  Koji Matsuoka,et al.  EVIDENCE FOR INCREASES IN ANTARCTIC BLUE WHALES BASED ON BAYESIAN MODELLING , 2004 .

[32]  T. Tamura,et al.  Feeding habits and prey consumption of Antarctic minke whales , Balaenoptera bonaerensis in JARPA research area , 2005 .

[33]  E. Murphy,et al.  Environmental Change and Antarctic Seabird Populations , 2002, Science.

[34]  A. Brierley,et al.  Setting a precautionary catch limit for Antarctic krill , 2002 .

[35]  R. Laws.  Seals and Whales of the Southern Ocean , 1977 .

[36]  R. Kellogg,et al.  Southern Blue and Fin Whales , 1930 .

[37]  I. Boyd.  Pup production and distribution of breeding Antarctic fur seals (Arctocephalus gazella) at South Georgia , 1993, Antarctic Science.

[38]  Stéphane G. Conti,et al.  New target-strength model indicates more krill in the Southern Ocean , 2005 .

[39]  M. Hanson,et al.  Continental Estimates and Population Trends of Antarctic Ice Seals , 1990 .

[40]  I. Everson,et al.  ACOUSTIC ESTIMATES OF KRILL DENSITY AT SOUTH GEORGIA, 1981 TO 1998 , 1999 .

[41]  Ian L. Boyd,et al.  Population Demography of Antarctic Fur Seals: The Costs of Reproduction and Implications for Life-Histories , 1995 .

[42]  R. Laws.  Scar Group of Specialists on Seals , 1976 .

[43]  V. A. Zemsky,et al.  DATA ON SOVIET WHALING IN THE ANTARCTIC IN 1947-1972 (POPULATION ASPECTS) , 1998 .

[44]  M. Bester,et al.  Changes in population sizes and distribution of fur seals at Marion Island , 1997, Polar Biology.

[45]  R. Hewitt,et al.  The use of acoustic sampling to estimate the dispersion and abundance of euphausiids, with an emphasis on Antarctic krill, Euphausia superba , 2000 .

[46]  N. Voronina.  Comparative abundance and distribution of major filter-feeders in the Antarctic pelagic zone , 1998 .

[47]  D. Butterworth,et al.  Consideration of multispecies interactions in the Antarctic: a preliminary model of the minke whale – blue whale – krill interaction , 2004 .

[48]  D. Costa,et al.  Foraging Energetics of Antartic Fur Seals in Relation to Changes in Prey Availability , 1989 .

[49]  T. Tamura,et al.  Regional assessments of prey consumption and competition by marine cetaceans in the world. , 2003 .

[50]  S. Gille.  Warming of the Southern Ocean Since the 1950s , 2002, Science.

[51]  K. Reid.  The diet of Antarctic fur seals (Arctocephalus gazella Peters 1875) during winter at South Georgia , 1995, Antarctic Science.

[52]  G. Daneri.  Fish diet of the Antarctic fur seal,Arctocephalus gazella, in summer, at Stranger Point, King George Island, South Shetland Islands , 1996, Polar Biology.

[53]  A. Flaherty,et al.  Difficulties in assessing population status of ice seals , 1995 .

[54]  宮下 富夫,et al.  Worldwide map of cetacean distribution based on Japanese sighting data , 1995 .

[55]  H. Kato,et al.  HAS THE AGE AT TRANSITION OF SOUTHERN HEMISPHERE MINKE WHALES DECLINED OVER RECENT DECADES , 1999 .

[56]  G. Duhamel,et al.  Interactions between Cetacean and Fisheries in the Southern Ocean , 2006, Polar Biology.

[57]  F. Fraser.  The Southern Stocks of Whalebone Whales , 1944, Nature.

[58]  V. Loeb,et al.  Krill (Euphausia superba) density, proportional and absolute recruitment and biomass in the Elephant Island region (Antarctic Peninsula) during the period 1977 to 1997 , 1998, Polar Biology.

[59]  I. Hampton,et al.  The Relationship Between Krill Food Requirements and Phytoplankton Production in a Sector of the Southern Indian Ocean , 1985 .

[60]  J. Bengtson,et al.  Trends in Crabeater Seal Age at Maturity: An Insight into Antarctic Marine Interactions , 1985 .

[61]  A. Carlini,et al.  The diet of the Antarctic fur seal Arctocephalus gazella at Harmony Point, Nelson Island, South Shetland Islands , 1998, Polar Biology.

[62]  M. Bester,et al.  Fish prey of fur seals Arctocephalus spp. at subantarctic Marion Island , 1998 .

[63]  H. Kato,et al.  Food and daily food consumption of southern minke whales in the Antarctic , 1991, Polar Biology.

[64]  C. Guinet,et al.  Fish prey of Antarctic fur seals Arctocephalus gazella at Ile de Croy, Kerguelen , 1997, Polar Biology.

[65]  P. Shaughnessy,et al.  Population size and breeding season of the Antarctic fur seal Arctocephalus gazella at Heard Island―1987/88 , 1990 .

[66]  S. Jacobs,et al.  A top–down, multidisciplinary study of the structure and function of the pack-ice ecosystem in the eastern Ross Sea, Antarctica , 2003, Polar Record.