Ross Sea Ecosystem IMMA

Size in Square Kilometres

1,860,969 km2

Qualifying Species and Criteria

Weddell Seal – Leptonychotes weddellii

Criterion B (1; 2); C (1; 2); D (1)

Crabeater seal – Lobodon carcinophaga

Criterion B (2); C (2)

Leopard seal – Hydrurga leptonyx

Criterion B (2); C (2)

Ross seal – Ommatophoca rossii

Criterion B (2); C (2)

Killer whale – Orcinus orca

Criterion B (2); C (2; 3)

Antarctic Minke whale – Balaenoptera bonaerensis

Criterion B (2); C (2)

Arnoux’s beaked whale – Berardius arnuxii

Criterion B (2); C (2)

Marine Mammal Diversity 

Balaenoptera acutorostrata, Balaenoptera musculus intermedia, Balaenoptera physalus, Megaptera novaeangliae

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The Ross Sea is covered by pack ice for 9 months of the year, yet it is viewed as one of the most pristine natural regions in the world, as well as one of the most productive regions of the Southern Ocean. Occupying a large, high-latitude embayment in the Antarctic continental shelf, it has an average depth of 500m and a shelf break at 700m. This area represents the southernmost range for any mammal. It hosts what is likely the largest concentration of Weddell seals (Leptonychotes weddellii) anywhere in the Antarctic, providing year-round habitat and breeding grounds for the species, including a small isolated population on White Island and two much larger colonies in Terra Nova Bay. Leopard seals (Hydrurga leptonyx), crabeater seals (Lobodon carcinophaga) and Ross seals (Ommatophoca rossii) also feed in the Ross Sea’s highly productive waters, and are often associated with pack ice and (in the case of Leopard seals) penguin colonies.

The Ross Sea’s continental slope is a hotspot for Arnoux’s beaked whales (Berardius arnuxii). Killer whales (Orcinus orca) are also abundant, with both the dwarf or C-type and B1 morphotypes observed regularly in the McMurdo Sound. Antarctic minke whales (Balaenoptera bonaerensis) appear seasonally, and are commonly seen foraging in the leads that develop in the fast/pack ice as it breaks up.

Description of Qualifying Criteria

Criterion B: Distribution and Abundance

Sub-criterion B1: Small and Resident Populations 

A small distinct population of Weddell Seals exists at White Island. The presence of this small isolated population led to the designation of White Island as an ASPA (Testa and Scotton, 1999). The Weddell seal colony appears unable to relocate to another area because of its distance from the open ocean of McMurdo Sound, and as such it is highly vulnerable to any human impacts that might occur in the vicinity. The colony is not thought to have been present in the early 1900s, as there is no mention of seals by naturalists who visited White Island many times during Scott’s 1902, 1903 and 1910 expeditions. An ice breakout occurred in the region between 1947 and 1956, and the first two seals were observed near the north-eastern end of the island in 1958 (R. Garrott, pers. comm). Year-round studies have detected no evidence of immigration or emigration of seals from the population, which appears to have grown to around 25 to 30 animals from a population of around 11 in the 1960s. The seals do not have the breathing capacity needed to dive the 20km
required to reach the open ocean, and there is only one record of a seal from the colony making the journey over the ice shelf surface.

Sub-criterion B2: Aggregations

Arnoux’s beaked whales, killer whales and Antarctic minke whales are seasonally abundant in the Ross Sea, taking advantage of the highly productive waters and associated prey that becomes available as the ice breaks up (Kasamatsu, et al. 1993, Ponganis, et al. 1995, Hobson and Martin 1996, Murase, et al. 2013). The Ross Sea continental slope is a hotspot for Arnoux’s beaked whales that are regularly seen in the area between McMurdo Sound and Terra Nova Bay where they may be summer residents (Smith et al. 2007). Antarctic minke whales occur in large numbers feeding throughout the Ross Sea (Ballard, et al. 2012) and have been estimated to consist of some 14,000 individuals in this region (Ainley, 1985). Among cetaceans, killer whales are seasonally prevalent in the Ross Sea (Lauriano et al., 2011). The dwarf killer whale form (C type) is found in McMurdo Sound (Pitman et al., 2007, 2018). Here, two population clusters have been identified: ‘regulars’ with strong inter- and intra-annual site fidelity and an average annual abundance of 73 individuals and a larger population estimated at 397 individuals, which were less frequently encountered. In McMurdo Sound type C killer whales have been recently assessed after 14 years of study (Pitman et al., 2018). A high degree of individual turnover in the area has been described. Nevertheless, in the sound two main population clusters have been discovered: regulars with strong inter and intra annual site fidelity and irregulars with nomadic lifestyle, which can travel along the coastal area spotting feeding areas (Pitman et al., 2018). Inter-annual site fidelity has been observed with 73 individuals that are regularly seen while 397 were irregularly observed in the area (Pitman et al., 2018). Less regular data are available from the TNB area, where type C and B1 killer whales were studied in the austral summers 2003-4 and 2014-15; C type individuals were re-sighted between the two periods in the same location along the ice shelf (Lauriano and Panigada, 2015).

High site fidelity of Weddell seals population is based on two colonies occurring in Terra Nova Bay that have persisted for long periods of time in the same area. Weddell are concentrated during the summer on coastal fast ice. The unique and outstanding ecological and scientific value of the region has consistently attracted international scientific interest and led to the establishment of the Ross Sea Region Marine Protected Area (MPA) by the Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR) in October 2016. The extensive continental shelf, combined with considerable shore-fast and pack ice habitat, creates ideal habitat for Weddell seals. Weddell seals inhabit cracks in the fast ice formed along the shoreline, ice tongues and islands resulting from tidal fluctuations (Hückstädt 2018b). They favour cracks that are far away from open water, close to the shoreline. The abundance of this habitat has enabled what appears to be the highest density and thus population of Weddell seals anywhere in Antarctica (M. Le Rue pers comm). Recent tracking revealed that Weddell seals (Goetz 2015) move throughout the western reaches of the Ross Sea throughout the year; the movement patterns of the other seal species are not as well documented but they are considered to be resident (Meade, Ciaglia et al. 2015, Krause, et al. 2016).

Leopard seals remain near the coastal zone when the ice is offshore, but move with the ice when it is closer to land (Meade et al. 2015). They are most commonly observed near penguin colonies during the spring and summer months (Krause,et al., 2016; Pinkerton et al., 2010). Crabeater and Ross seals are associated with the pack ice (Southwell, et al. 2012, Bengtson and Stewart 2018). While Ross seals are known to occur in the Ross Sea, their abundance, distribution and general biology are poorly known (Arcalis-Planas, et al. 2015, Hückstädt 2018a). Given their abundance and their broad diet (krill, fish to seals and penguins) the four species of seals represent a significant energy transfer within the Ross Sea food web (Pinkerton et al. 2010).

Criterion C: Key Life Cycle Activities

Sub-criterion C1: Reproductive Areas

There are numerous breeding aggregations of Weddell seals along the Victoria Land Coast that are associated with the coastal tidal cracks in the shore-fast ice. Another significant breeding aggregation is associated with Cape Colbeck in the eastern Ross Sea (Davis et al., 2008). The breeding colony at White Island is composed of some 84 Weddell seals that were known to have existed between 1990 and 2000 (Testa and Scotton 1999, Gelatt, et al. 2009). Between 2003 and 2007, 11 females have been sighted at White Island, but only six of these individuals have produced pups. Between two and four live pups were recorded in 1963-1968, 1981, and 1991. Annual censuses since 1991 recorded between four and ten pups from 1991 to 2000, but lower numbers (between two and four pups each year) from 2000 to 2007. Pup mortality is high, possibly due to inbreeding and pup production is low in comparison to the population in Erebus Bay.

Sub-criterion C2: Feeding Areas

The area is an important summer feeding habitat for the three whale species and is a year-round feeding habitat for the four seal species. Minke whales feed on krill, while killer whales feed on penguins, crabeater and Weddell seals, as well as Antarctic toothfish (Dissostichus mawsonii). The B1 type killer whales prey primarily on ice seals and occur commonly along to the ice shelf in austral summer to take advantage of both the seals and the Adelie and emperor penguin colonies (Cape Washington, Edmonson point, Adelie Cove, Inexpressive Island) in the Ross Sea coastal area. Extensive movements from McMurdo Sound and Terra Nova Bay by B1 type killer whales have been described for this killer whale ecotype (Andrews et al., 2008; Lauriano et al., 2007). Satellite studies conducted in both McMurdo Sound and TNB show areas along the western Ross Sea coastline where C killer whales have been engaged in feeding activities and long-distance travel beyond the coast, outside the polar front (Pitman et al, in prep.; Lauriano & Panigada, 2015; Eisert et al., 2015). This killer whale type feeds only on fish. B1 ecotype is a mammal eating form, which preys primarily on ice seals and occur commonly along to the ice shelf in austral summer to take advantage of both the seal and Adelie penguin colonies in the area (Andrews et al., 2008; Lauriano et al., 2007a,b). The most important component in their diet is the Antarctic toothfish, which is by far the largest species of fish in Antarctic waters. Moreover, other species have been considered in type C killer whales’ diet and these all belong to the Nototheniodae, a suborder that includes pelagic and semi pelagic species which dominate the fish fauna at > 90% levels of abundance and biomass in the Ross Sea and in the cIMMA. The Antarctic silverfish (Pleurogramma antarcticum) is one of the most abundant fish in the suborder and a prey of the toothfish; a nursery area has been described in the Terra Nova Bay where type C killer whales feed regularly along the ice shelf (Lauriano & Panigada, 2015). Satellite tracking studies conducted in both Mcmurdo Sound and Terra Nova Bay show that type C killer whales engage in feeding activities (Area Restricted Search – ARS and diving activities) in both Terra Nova Bay and Lady Newnes Bay, and they travel long distances away from the coast, outside the polar front (Lauriano & Panigada, 2015; Eisert et al., 2015).

Antarctic minke whales feed in large numbers in the whole Ross Sea area (Ainley et al., 1985; Ballard et al., 2012; Ainley et al (1985). They are commonly seen foraging in the leads that develop in the fast/pack ice (Friedlaender et al. 2014) as far south as Cape Armitage. The Arnoux’s beaked whales are regularly seen, and presumably feed, in the area between McMurdo Sound and Terra Nova Bay (Lauriano et al., 2011) where the species has been considered as resident in summer (Smith et al., 2007). Leopard seals prey on Adélie penguins (Pygoscelis adeliae), crabeater seals, and Emperor penguins (Aptenodytes forsteri). Leopard seals remain near the coastal zone when the ice is offshore, but move with the ice when it is closer to land (Meade, et al. 2015 ). They are most commonly observed near penguin colonies during the spring and summer months (Krause et al., 2016; Pinkerton et al., 2010). Recent tracking revealed that Weddell seals (Goetz 2015) move throughout the western reaches of the Ross Sea throughout the year; the movement patterns of the other seal species are not as well documented but they are considered to be resident (Meade,et al., 2015, Krause et al., 2016).

Sub-criterion C3: Migration Routes

Migration routes for C Type killer whale along the Ross Sea coast were described in 2015 (Lauriano and Panigada, 2015; Eisert et al., 2015). Movements with high persistence and low turning angle along with shallow diving activities, occurred alongside the coastal area between the tagging location (TNB) and outside the polar front; this transiting behaviour show a migratory pattern beyond the polar front towards New Zealand sub-tropical waters (Lauriano and Panigada, 2015; Eisert et al., 2015).

Criterion D: Special Attributes

Sub-criterion D1: Distinctiveness

This is the southernmost range extension for the whale and seals species and as such represents the southernmost natural habitat for any mammal (besides humans). The breeding colony at White Island is composed of some 84 Weddell seals that were known to have existed between 1990 and 2000. This is an isolated breeding aggregation that was likely founded by a small group of individuals (three females and two males) that accessed the island during a brief break in the surrounding sea ice in the mid-1950s) and is genetically isolated (Testa and Scotton 1999, Gelatt, et al. 2009).

Supporting Information

Ainley, D.G. 1985. ‘Biomass of Birds and Mammals in the Ross Sea Antarctica’.In:  W.R. Siegfried, P.R. Condy and R.M. Laws (eds,)  Antarctic Nutrient Cycles and Food Webs; 4th SCAR (Scientific Committee on Antarctic Research) Symposium on Antarctic Biology, pp 498-515. New York, Berlin: Springer-Verlag

Ainley, D.G., Ballard, G.and Weller, J. 2010. ‘Ross Sea Biodiversity Part I: Validation of the 2007 CCAMLR Bioregionalization Workshop Result Towards Including the Ross Sea in a Representative Network of Marine protected Areas in the Southern Ocean’ CCAMLR Report, WG-EMM-10/11. Hobart, Tasmania.

Ainley, D.G. and Ballard, G. 2012. ‘Trophic Interactions and Population Trends of Killer Whales (Orcinus orca) in the Southern Ross Sea’. Aquatic Mammals 38:153-160.

Ainley, D.G., Larue, M.A., Stirling, I., Stammerjohn, S. and Siniff, D. B. 2015. ‘An apparent population decrease, or change in distribution, of Weddell seals along the Victoria Land coast.’ Marine Mammal Science 31:1338-1361.

Andrews, R.D., Pitman, R.L. and Ballance L.T 2008. ‘Satellite tracking reveals distinct movement patterns for Type B and Type C killer whales in the southern Ross Sea, Antarctica.’ Polar Biology 31(12):1461-1468.

Arcalis-Planas, A., Sveegaard, S., Karlsson, O., Harding, K.C., Wahlin, A., Harkonen, T. and Teilmann, J.  2015. ‘Limited use of sea ice by the Ross seal (Ommatophoca rossii), in Amundsen Sea, Antarctica, using telemetry and remote sensing data.’ Polar Biology 38(4): 445-461.

Ballard, G., Jongsomjit, D,. Veloz S.D., and Ainley D.G., 2012. ‘Coexistence of mesopredators in an intact polar ocean ecosystem: The basis for defining a Ross Sea marine protected area.’ Biological Conservation 156:72-82.

Bengtson, J.L. and Stewart, B.S. 2018. ‘Crabeater seals’ In: B. Wursig, J.G.M. Thewissen and K.M. Kovacs (eds). Encyclopedia of Marine Mammals. pp.230-232. San Diego, Academic Press:

Cameron, M.F. and Siniff, D.B. 2004. ‘Age-specific survival, abundance, and immigration rates of a Weddell seal (Leptonychotes weddellii) population in McMurdo Sound, Antarctica.’ Canadian Journal of Zoology 82:601-615.

Davis C.S,  Stirling I., Strobeck C And Coltman D.W. Population structure of ice-breeding seals. 2008.

Molecular Ecology (2008) 17, 3078–3094

Eisert R, Lauriano G, Panigada, S, et al. 2015. Activity, seasonal site fidelity, and movements of type-c killer whales between the Ross Sea, Antarctica and New Zealand. CCAMLR Working Group EMM 2015

Friedlaender, A.S., Goldbogen, J.A., Nowacek, D.P.,  Read, A.J., Johnston D. and Gales N. 2014. ‘Feeding rates and under-ice foraging strategies of the smallest lunge filter feeder, the Antarctic minke whale (Balaenoptera bonaerensis).’ Journal of Experimental Biology 217(16): 2851-2854.

Gelatt, T.S., Davis, C.S.  Stirling, I. Siniff, D.B., Strobeck C. and Delisle I. 2009. ‘History and fate of a small isolated population of Weddell seals at White Island, Antarctica.’ Conservation Genetics 11(3):721-735.

Goetz, K. T. 2015. ‘Movement, Habitat, and Foraging Behavior Of Weddell Seals (Leptonychotes Weddellii) In The Western Ross Sea, Antarctica’ Ph.D. Dissertation, Uniersity of California Santa Cruz.

Hobson, R.P. and Martin, A.R. 1996. ‘Behaviour and dive times of Arnoux’s beaked whales, Berardius arnuxii, at narrow leads in fast ice.’ Canadian Journal of Zoology 74(2):388-393.

Hückstädt, L.A. 2018a. ‘Ross Seal’ In: B. Wursig, J.G.M. Thewissen and K.M. Kovacs (eds). Encyclopedia of Marine Mammals. pp. 835-837. San Diego, Academic Press.

Hückstädt, L.A. 2018b. ‘Weddell Seal.’ In: B. Wursig, J.G.M. Thewissen and K.M. Kovacs (eds). Encyclopedia of Marine Mammals. pp. 1048-1051. San Diego, Academic Press.

Kasamatsu, F., Yamamoto, Y., Zenitani, R., Ishikawa, H., Ishibashi, T., Sato, H., Takashima K. and Tanifuji, S.1993. ‘Report of the 1990/91 southern minke whale research cruise under scientific permit in Area V.’ Report of the International Whaling Commission 0(43):505-522.

Krause, D.J., Goebel, M.E., Marshall G.J., and Abernathy, K. 2016. ‘Summer diving and haul-out behavior of leopard seals (Hydrurga leptonyx) near mesopredator breeding colonies at Livingston Island, Antarctic Peninsula.’ Marine Mammal Science 32(3):839-867.

LaRue, M.A., Rotella, J.J. Garrott, R.A., Siniff, D.B., Ainley, D.G., Stauffer, G.E., Porter, C.C. and Morin, P.J. 2011. ‘Satellite imagery can be used to detect variation in abundance of Weddell seals (Leptonychotes weddellii) in Erebus Bay, Antarctica.’ Polar Biology 34:1727-1737.

Lauriano, G., Vacchi, M., Ainley D. and Ballard, G. 2007. ‘Observations of top predators foraging on fish in the pack ice of the southern Ross Sea.’ Antarctic Science 19(4):439-440.

Lauriano, G., Fortuna. C.M., and Vacchi, M. 2011. ‘Occurrence of killer whales (Orcinus orca) and other cetaceans in Terra Nova Bay, Ross Sea, Antarctica.’ Antarctic Science 23(2): 139-143.

Lauriano, G, Panigada. S. 2015. ‘Ross Sea killer whales activities from Terra Nova Bay (Ross Sea Antarctica) to New Zealand,’ SC66a/Sm/11 San Diego

LeDuc, R.G., Robertson, K.M., Pitman R.L,. 2008. ‘Mitochondrial sequence divergence among Antarctic killer whale ecotypes is consistent with multiple species.’ Biology Letters 4:426–429

Meade, J., Ciaglia, M.B., Slip, D.J., Negrete, J., Marquez, M.E., Mennucci, J. and Rogers, T.L. 2015. ‘Spatial patterns in activity of leopard seals Hydrurga leptonyx in relation to sea ice.’ Marine Ecology Progress Series 521:265-275.

Murase, H., Kitakado,T., Hakamada, T., Matsuoka, K., Nishiwaki, S. and Naganobu, M. 2013. Spatial distribution of Antarctic minke whales (Balaenoptera bonaerensis) in relation to spatial distributions of krill in the Ross Sea, Antarctica. ‘Fisheries Oceanography’ 22(3): 154-173.

Pinkerton, M.H., Bradford-Grieve, J.M., Hanchet, S.M. 2010. ‘A Balanced Model of the Food Web of the Ross Sea, Antarctica.’ CCAMLR Science 17:1-31.

Pitman, R.L., Perryman, W.L., LeRoi, D, Eilers, E. 2007. ‘A dwarf form of killer whale in Antarctica.’ Journal of Mammalogy 88:43–48.

Pitman, R.L., Fearnbach, H., Durban, J.W. 2018. ‘Abundance and population status of Ross Sea killer whales (Orcinus orca, type C) in McMurdo Sound, Antarctica: evidence for impact by commercial fishing?’ Polar Biology 41(4):781-792.

Ponganis, P.J., Kooyman, G.L. and Castellini, M.A. 1995. ‘Multiple Sightings of Arnoux Beaked Whales Along the Victoria Land Coast.’ Marine Mammal Science 11(2):247-250.

Rotella, J.J., Link, W.A., Nichols, J.D., Hadley, G.L., Garrott, R.A. and Proffitt, K.M. 2009. ‘An evaluation of density-dependent and density-independent influences on population growth rates in Weddell seals.’ Ecology 90:975-984.

Southwell, C., Bengtson, J., Bester, M.,  Blix, A. S., Bornemann, H., Boveng, P., Cameron, M., Forcada, J., Laake, J., Nordoy, E., Plotz, J., Rogers, T., Southwell, D., Steinhage, D., Stewart, B.S., and Trathan. P. 2012. ‘A Review of Data on Abundance, Trends in Abundance, Habitat Use and Diet of Ice- Breeding Seals in the Southern Ocean.’ CCAMLR Science 19:49-74.

Smith, W.O., Ainley D.G and Cattaneo-Vietti, R. 2007. ‘Marine Ecosystems: the Ross Sea.’ Philosophical Transactions of the Royal Society B 362:95–111.

Testa, J.W. and Siniff, D.B. 1987. ‘Population Dynamics of Weddell Seals (Leptonychotes weddelli) in McMurdo Sound, Antarctica.’ Ecological Monographs 57:149-165.

Testa, J.W. and Scotton, B.D. 1999. ‘Dynamics of an isolated population of Weddell seals (Leptonychotes weddellii) at White Island, Antarctica.’ Journal of Mammalogy 80:82-90.

Younger, J.L., van den Hoff, J., Wienecke, B., Hindell, M, and Miller, K.J. 2016. ‘Contrasting responses to a climate regime change by sympatric, ice-dependent predators.’ BMC Evolutionary Biology 16.


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