Scotia Arc IMMA
Size in Square Kilometres
614,480 km2
Qualifying Species and Criteria
Southern right whale – Eubalaena australis
Criterion C (2)
Humpback whale – Megaptera novaeangliae
Criterion C (2)
Fin whale – Balaenoptera physalus
Criterion A
Antarctic blue whale – Balaenoptera musculus intermedia
Criterion A
Sei whale – Balaenoptera borealis
Criterion A
Sperm whale – Physeter macrocephalus
Criterion A
Marine Mammal Diversity
Criterion D2
Arctocephalus gazella, Leptonychotes weddellii, Mirounga leonina, Hydrurga leptonyx,
Balaenoptera bonaerensis, Orcinus orca, Globicephala melas,
Lagenorhynchus cruciger, Hyperoodon planifrons
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Summary
The Scotia Arc comprises South Georgia, South Sandwich, South Orkney and South Shetland Islands, which are all fragmented remnants of what once formed a land bridge between South America and the Antarctic Peninsula. Large colonies of seals and seabirds breed at South Georgia, and the region supports important commercial fisheries for krill and various species of fish. For more information on the seals that breed in this IMMA, please see the summary for the South Georgia IMMA: https://www.marinemammalhabitat.org/portfolio-item/south-georgia/
The region is dominated by the Antarctic circumpolar current, which transports nutrients and organisms, particularly krill, from the Antarctic Peninsula across the Scotia Sea to South Georgia. The area is known to serve as a rich seasonal feeding ground for Critically Endangered Antarctic blue whales (Balaenoptera musculus intermedia), Vulnerable fin whales (B. physalus), Endangered sei whales (B. borealis) and Vulnerable sperm whales (Physeter macrocephalus). The area surrounding South Georgia includes an important feeding ground for the southern right whale (Eubalaena australis) population that breeds off the coast of Argentina. Furthermore, the area northeast of South Georgia and the Sandwich Islands comprises an important foraging ground for humpback whales (Megaptera novaeangliae) from the population that breeds off the coast of Brazil.
Description of Qualifying Criteria
Criterion A – Species or Population Vulnerability
Antarctic blue whales are estimated to be at less than 2% of their pre-whaling abundance, and the population is classified as “Critically Endangered” in the IUCN Red List (Cooke et al. 2018). Both Fin and Sei whales are estimated to be at about 25% of their pre-exploitation levels in the Southern Hemisphere, and the species are considered “Vulnerable” and “Endangered”, respectively (Cooke et al. 2018). Catches of Blue whales in the Antarctic began from land stations on South Georgia in 1904 and peaked at over 30,000 per year in the 1931/32 season (Allison 2017), with the total historical kill being about 350,000 animals. An estimate of their numbers from Japanese surveys covering just half of the Antarctic (35°E to 145°W) south of 60° S is only 1,223 individuals (CV 0.35) in 2008 (Matsuoka and Hakamada 2014). Over 725,000 Fin whales have been recorded caught in the Southern Hemisphere during 1905-76 (Allison 2017). For Fin whale the current circumpolar abundance remains highly uncertain until all existing data are worked up and more data are collected from the zone 50°- 60°S. However, for some areas in the Scotia Arc, Viquerat and Herr (2017) estimated abundances of about 500 and 800 Fin whales around Elephant Island and the South Orkneys, respectively.
Over 200,000 Sei whales were recorded taken by modern whaling in the Southern Hemisphere during 1905–1979 (Allison 2017), and the last stock assessments of Sei Whales conducted by the IWC Scientific Committee were in 1979 for the Southern Hemisphere (IWC 1980). Nowadays in the absence of dedicated surveys and corresponding abundance estimates, it is not possible to verify whether there has been any increase in Southern Hemisphere Sei whales since the cessation of whaling. Nevertheless, while the available data do not permit a scientifically rigorous estimation of the extent of population reduction, a conventional population assessment model was used to provide an illustration of the extent of possible reduction, and fitted population sizes for the aged 1+ were 10,000 whales in 1983 in the Southern Hemisphere (Cooke et al. 2018). Antarctic blue whale, Fin and Sei whales have been protected in the Southern Hemisphere since 1976, thus the direct exploitation threat is part of the past. However, a new threat for these species in Antarctica might be food availability in a near future, which we can take into consideration the Scotia Arc waters which is an important foraging ground for these species. The main food of these baleen whales in the Southern Ocean, Euphausia superba and E. crystallorophias, are predicted to decline during the 21st century due both to reduced ocean productivity associated with warming (Piñones and Fedorov 2016) and to increasing ocean acidity that limits their shell-building (Kawaguchi et al. 2013).
The Sperm whale, classified as “Vulnerable” in the IUCN Red List, was commercially hunted at a large scale in the Antarctic region, with the population of mature and maturing males in the Antarctic heavily whaled between 1950-1980 (Taylor et al. 2008). The expected rate of increase for exploited populations of sperm whales was estimated to be approximately 1.1 percent per year (Whitehead 2002). Systematic surveys of Sperm whales in the Antarctic showed no substantial or statistically significant increase between 1978 and 1992 (Branch and Butterworth 2001). Yet, heavily exploited populations of sperm whales in the Southern Hemisphere have shown little evidence of population increase decades after the end of their commercial hunting (Carroll et al. 2014). Sperm whales have been reported to depredate Patagonian toothfish (Dissostichus eleginoides) from long-lines in Sub-Antarctic and Antarctic regions, and it appears to be an increasing phenomenon occurring in South Georgia and several other Southern Ocean island areas (Purves et al. 2004, Guinet et al. 2015, Janc et al. 2018). This interaction has resulted in some threats to the species as entanglements and deaths (Hucke-Gaete et al. 2004) and has incurred hostility from some fishermen (Donoghue et al. 2003, González and Olavarria 2002, Guinet et al. 2015).
Criterion C: Key Life Cycle Activities
Sub-criterion C2: Feeding Areas
The area includes an important feeding ground for Southern right whales from breeding grounds off along the coast of Argentina, Uruguay and Brazil (Best et al. 1993, Rowntree et al. 2001, Ott et al. 2011, IWC 2012, Nijs and Rowntree 2017). The International Whaling Commission (IWC) divided the Southern Hemisphere into 11 management units for Southern right whales based on the distribution patterns and locations of breeding aggregations (IWC, 2001). One of these units corresponded to breeding grounds off Peninsula Valdés, Argentina, which has the largest aggregations of Southern right whales in the western South Atlantic Ocean (IWC, 2001). Valenzuela et al (2011), assessing genetic differentiation on Southern right whale calving and feeding grounds, confirmed the lack of differentiation between Peninsula Valdés (Argentina) and the feeding ground off South Georgia (IWC 2012), supporting that South Georgia is an important feeding destination for Southern right wintering off Peninsula Valdés. Moreover, recent studies using satellite tags have confirmed feeding areas surrounding South Georgia for Southern right whales tagged in Argentina (Zerbini et al. 2016, 2018). Additionally, the occurrence of Southern right whales around South Georgia has been well documented from early 20th century and the 1960s whaling (Tormosov et al. 1998, IWC 2001) as well as sighting data (Moore et al. 1999, Richardson et al. 2012, IWC SOWER Cruises).
Traditionally the IWC managed Humpback whale stocks on the basis of the six Antarctic areas (I through VI) although the Scientific Committee recognizes seven major breeding stocks, A through G. The wintering ground of stock A is the Southwest Atlantic (coast of Brazil), and the northeast of South Georgia and the waters around the South Sandwich Islands (Antarctic area II) is an important foraging ground for Humpback whales from this stock according to satellite tracking studies (Zerbini et al. 2006, 2011). Photo-identification, genetic, and old Discovery mark data also support the relationship of breeding stock A (Brazil) feeding ground around the South Sandwich Islands, and also suggest areas close to South Georgia might be important (Zerbini et al. 2006, 2011, Engel et al. 2008, Fleming and Jackson 2011, Jackson et al. 2015).
Criterion D: Special Attributes
Sub-criterion D2: Diversity
Many cetacean species have been recorded in the northwest parts of the Scotia Arc. Historical catch records, surveys transect, opportunistic sightings, and tracking data all document the presence of whales around the islands (Mizrov et al. 1985, Moore et al. 1999, Richardson et al. 2012, Ropert-Coudert et al. 2014, 2018, IWC SOWER Cruises, OBIS 2018). Records of catches at South Georgia (1904 to 1965) included: Blue whale, Fin whale, Sei whale, Humpback whale, Minke whale, Southern right whale and Sperm whale in great numbers (evidencing aggregations of many baleen species), although most species were depleted to <10% of their original stock size (Clapham and Baker 2009). Large whale species that were depleted during the whaling era at South Georgia are recovering, but at variable rates (Richardson et al. 2012). No data sources suggest major concentration of baleen whales, but the area still representing the full richness of marine mammal species diversity and the high densities of krill undoubtedly are an attractant for marine mammals. From recent studies analysing opportunistic sightings from 1992 to 2001, the four most commonly reported species around South Georgia were Southern right whales, Humpback whales, Minke whales and Killer whales (Richardson et al. 2012). Other species seen around South Georgia, western and southeast of the islands include Blue whales, Fin whales, Hourglass dolphins, Long-finned pilot whales, Sei whales, Sperm whales, and Southern bottlenose whales (Mizrov et al. 1985, Moore et al. 1999, Richardson et al. 2012, Ropert-Coudert et al. 2014, 2018, IWC SOWER Cruises, OBIS 2018). See Annex 1 (figure 4). South Georgia island is the main breeding area for the Antarctic fur seal (Reijnders et al. 1993, Wynen et al. 2000, SCAR EGS 2008); a small population of Weddell seal lives all year (Southwell et al. 2012), and more than 50% of Southern elephant seal pup production takes place at South Georgia (Boyd et al. 1996, M. Fedak pers. comm. in SCAR EGS 2008). Leopard seal births at South Georgia occur from late August to the middle of September (Southwell et al. 2012) and moving all year-round on South Georgia close proximity (Jessopp et al. 2004).
Supporting Information
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