Size in Square Kilometres
Qualifying Species and Criteria
Subantarctic fur seal – Arctocephalus tropicalis
Criterion B (2); C (1; 2)
Southern elephant seal – Mirounga leonina
Criterion C (1; 2)
Marine Mammal Diversity
Tasmacetus shepherdi, Eubalaena australis, Megaptera novaeangliae, Globicephala melas, Orcinus orca, Balaenoptera physalus, Balaenoptera borealis, Balaenoptera bonaerensis, Physeter macrocephalus, Mesoplodon mirus, Mesoplodon bowdoini, Lissodelphis peronii, Caperea marginata, Lagenorhynchus obscurus, Arctocephalus gazella, Hydrurga leptonyx
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This IMMA encompasses the four remote volcanic South Atlantic Ocean islands of the Tristan da Cunha Archipelago including, Inaccessible and Gough, both of which are UNESCO World heritage sites. Gough Island hosts the world’s largest population of subantarctic fur seals (Arctocephalus tropicalis), (comprising around 63% of the global pup production) as well as the smallest and northernmost breeding population of southern elephant seals (Mirounga leonina), which has an estimated pup production of only 18 pups annually. Recent tracking data elucidated the importance of the subtropical front south of Gough Island, as primary foraging region for the fur seals, while the area between and around the archipelago appears to be important for male elephant seal foraging during summer.
The waters of the Tristan da Cunha archipelago are also known to host a diverse range of cetacean species, including southern right whales (Eubalaena australis), humpback whales (Megaptera novaeangliae), southern long-finned pilot whales (Globicephala melas edwardii) and killer whales (Orcinus orca). Records include several sightings and strandings of Shepherd’s beaked whales (Tasmacetus shepherdi) one of the world’s least known cetacean species.
Description of Qualifying Criteria
Criterion B: Distribution and Abundance
Sub-criterion B2: Aggregations
Gough Island hosts the world’s largest population of Subantarctic fur seals, Arctocephalus tropicalis (Bester 1987). Globally, the total population was estimated to be greater than 400,000 animals in the early 2000s (SCAR-EGS 2008). Subantarctic fur seals breed at numerous sites at eight island groups, although numerically almost all (99%) breed at three of these sites (Gough Island, Prince Edward Islands and Amsterdam Island). About 63% of global pup production takes place at Gough Island (Bester et al. 2006), 25% at the Prince Edward Islands (SCAR-EGS 2008; Bester et al. 2009; Wege et al. 2016) and a further 11% at Amsterdam Island (Guinet et al. 1994). Pup weaning masses here are significantly lower than those at the second largest population globally, at the Prince Edward Islands, suggesting some density dependence in their demography (Oosthuizen et al. 2016). The pup production for the species at the Prince Edward Islands seems to be declining (Wege et al. 2016) despite the heavier weaning masses there.
Criterion C: Key Life Cycle Activities
Sub-criterion C1: Reproductive Areas
Gough Island is an important breeding (pupping and lactation) site for Subantarctic fur seals, with more than 63% of global pup production at this island (Bester 1987, Bester et al. 2006). Although Gough Island supports the largest population of Subantarctic fur seals globally (Bester 1990), a complete assessment of this population has never been accomplished (Bester 1987) due to the rough and inaccessible nature of the island coastline. Estimating changes in the population at this site must therefore be inferred by comparisons of a time-series of counts at specific accessible beaches (Bester et al. 2006). Globally, the total population was estimated to be greater than 400,000 animals in the early 2000s and indications are that it has been steadily growing since that time (SCAR-EGS 2008) although recent evidence suggests stabilisation or decline in at least some large populations, such as at the Prince Edward Islands (Wege et al. 2016). Comparison of pup weights with those at the Prince Edward Islands show significantly lower weaning masses for Gough Island pups (Oosthuizen et al. 2016).
Southern elephant seals are distributed in the Southern Ocean between around 35oS and 70oS (Laws 1994). They haul-out onto Subantarctic islands and some mainland sites on the coasts of Argentina and Antarctica to breed, moult and over-winter (Laws 1994; McMahon et al. 2005). Ninety-eight percent of the global stock of southern elephant seals, breed at South Georgia, the Heard and Kerguelen islands populations, Macquarie Island and Peninsula Valdés (McMahon et al. 2005). The remaining 2% occur on islands throughout the Subantarctic and adjoining regions (Laws 1994), including the smallest breeding population at the most northerly limit of the species distribution at Gough Island (Bester 1990). Safeguarding and understanding the demography and ability for persistence of small, peripheral populations is becoming increasingly important in the face of environmental change that may exert greatest adaptive strain on such groups, or conversely allow for range extension depending on the direction of change.
Sub-criterion C2: Feeding Areas
Recent preliminary data from lactating Subantarctic fur seal females tracked from Gough and Tristan da Cunha Islands, demonstrate the importance of the Subtropical front for summer foraging (~October to February) (Mammal Research Institute/Tristan da Cunha Government unpublished data). The region between Gough and Tristan da Cunha Islands (~350 km separation) seems to be an important foraging and migratory zone for these fur seals, and also for adult male southern elephant seals (tracked during the post-breeding foraging phase – Mammal Research Institute, unpublished data).
Best, P.B., Glass, J.P., Ryan, P.G., Dalebout, M.L. 2009. Cetacean records from Tristan da Cunha, South Atlantic. Journal of the Marine Biological Association of the United Kingdom. 89: 1023-1032.
Bester MN. 1980. Population increase in the Amsterdam Island fur seal Arctocephalus tropicalis at Gough Island. South African Journal of Zoology 15: 229–234.
Bester MN. 1990. Population trends of Subantarctic fur seals and southern elephant seals at Gough Island. South African Journal of Antarctic Research 20: 9–12.
Bester MN. 1987. The Subantarctic fur seal Arctocephalus tropicalis at Gough Island (Tristan da Cunha Group). In: Proceedings of the Fur Seal Workshop, Cambridge, April 1984. NOAA Tech. Rep. NMFS 51: 57–60.
Bester MN, Möller H, Wium J, Enslin B. 2001. An Update on the Status of Southern Elephant Seals at Gough Island. South African Journal of Wildlife Research 31: 68–71.
Bester MN, Wilson JW, Burle M-H, Hofmeyr GJG. 2006. Population trends of Subantarctic fur seals at Gough Island. South African Journal of Wildlife Research 36: 191-194.
Guinet C, Jouventin P, Georges JY 1994. Long term population changes of fur seals Arctocephalus gazella and A. tropicalis on subantarctic (Crozet) and subtropical (Saint Paul and Amsterdam) islands and their possible relationship to El Niño Southern Oscillation. Antarctic Science 6, 473-478.
Laws RM. 1994. History and present status of southern elephant seal populations. In: Elephant seals: population ecology, behavior, and physiology, Le Boeuf BJ, Laws RM (eds), pp. 49-65, University of California Press, Berkeley.
McMahon CR, Bester MN, Burton HR, Hindell MA, Bradshaw CJA. 2005. Population status, trends and a re-examination of the hypotheses explaining the recent declines of the southern elephant seal Mirounga leonina. Mammal Rev 35:82-100
Oosthuizen WC, de Bruyn PJN, Wege M, Bester MN. 2016. Geographic variation in Subantarctic fur seal pup growth: linkages with environmental variability and population density. Journal of Mammalogy 97(2): 347-360
SCAR – EGS. 2008. Scientific Committee for Antarctic Research – Expert Group on Seals Report. Available from http://www.seals.scar.org/pdf/statusofstocs.pdf
Thompson CDH, Bouchet PJ, Meeuwig JJ. 2019. First underwater sighting of Shepherd’s beaked whale (Tasmacetus shepherdi). Marine Biodiversity Records 12: 6
Wege M, Etienne MP, Oosthuizen WC, Reisinger RR, Bester MN, de Bruyn PJN. 2016. Trend changes in sympatric Subantarctic and Antarctic fur seal pup productions at Marion Island, Southern Ocean. Marine Mammal Science 32: 960-982.