Today’s blog has been written by Christopher Jones, on the Gough team’s latest paper.
That is an awfully large boulder on the beach over there, oh wait, oh no that is not a boulder, it’s moving, must be an elephant seal!
Southern elephant seals are the largest of all the seals and in fact the largest carnivore on earth. The males can reach four meters in length and weigh up to four tonnes. Truly impressive beasts and rather intimidating to encounter as they rear up taller that two meters and can move surprisingly fast over a boulder beach.
Chris admiring a lone bull elephant seal after inspecting it for tags © Michelle Risi
These aquatic giants have a circumpolar distribution in the Southern Ocean with major breeding populations close to the Antarctic Polar Front. The worldwide population of southern elephant seals is estimated at 650 thousand individuals. The northernmost breeding locality for the species is Gough Island (40°19S, 9°57 W) in the south Atlantic, which supported a small population at last count in 1998. Since the last survey was more than 20 years ago at Gough, we took it upon ourselves to determine the present status of the southern elephant seal population at Gough Island.
Following methods of previous elephant seal surveys at Gough Island from 1973 to 1998, Michelle and I set out to survey Gough’s elephant seals during their breeding season in October along the north-east coast between Sophora Glen and North-East Point on Gough Island (the only stretch of coastline where elephant seals are known to breed on Gough).
It was quite a harrowing but exciting journey as we had to depart from the research station down a cliff via the crane in order to hitch a ride with a motor boat from the lobster fishing vessel, the MV GeoSearcher. From the motor boat we had to swim the last little stretch ashore in the 10°C water as landing the boat on the boulder beaches on Gough was not possible. Once ashore we dried off, gathered our wits and set off to find the mighty beasts.
Long Beach on the east coast of Gough Island (c) Christopher Jones
Map of Gough showing the survey sites on the east coast
Soon after walking along Long Beach we encountered a large beach-master, at the Wild Glen waterfall, with his harem of two females each tending to their young pups. We were excited that we had found our first seals of the day, and gosh were those little plump pups cute! After taking photos and checking them for tags we continued along the beach eager to find more seals. Alas, little did we know at the time that would be the only harem we found that day. Further along the beach we were treated to sights of some of Gough’s other charismatic wildlife, however no more breeding elephant seals and only two other lone male elephant seals.
Michelle saying hello to a female elephant seal and her pup (c) Christopher Jones
Comparing with past surveys tells a troubling story about the number of elephant seal births on Gough Island in the last 45 years. The highest numbers were recorded in the 1970s (38 to 27 births), followed by lower numbers in the 1990s (23 to 11 births), making our count of two pups in 2019 the lowest on record.
Tristan da Cunha (37°S, 12°W), 380 km north-east of Gough Island and north of the sub-Tropical Front (STF), supported a large breeding population before the seal exploitation period of the 19th century, with approximately 1000 pups born in the early 1800s; however, only sporadic births were recorded there since 1973. Similarly, in recent decades only single births have been recorded at Amsterdam Island (37°S, 77°E), north of the STF in the South Indian Ocean. Likewise, before the 1800s elephant seals bred north of the STF near Australia and New Zealand, now only infrequent pupping occurs on the New Zealand mainland.
The current population of southern elephant seals at Gough Island, located just to the south of the STF in colder waters, is also likely to become extinct as at the former breeding colony islands north of the STF. Our data suggest that this will occur at some point in the next 20 years.
Michelle keeping her distance from the beach-master © Christopher Jones
Reasons for the decline in elephant seal numbers at Gough Island and elsewhere in the Southern Ocean remain obscure, although it is thought to be most likely a result of foraging habitat and ecosystem changes mediated by shifts in oceanic temperatures and circulation patterns affect by climate change. We've published our findings in the journal Polar Biology.
Although these aquatic giants are not under threat from global extinction, it is sad that it will not be too long before they're gone from Gough Island. Thankfully the RSPB’s Gough Island Restoration Programme is working hard to prevent the same fate of the iconic seabirds of Gough Island.
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The Gough Island Restoration Programme is being carried out by the RSPB in partnership with Tristan da Cunha, BirdLife South Africa and the Department of Environmental Affairs in South Africa, and Island Conservation. The programme is part-funded by the RSPB, the UK Government, the National Fish and Wildlife Foundation and other generous individuals and organisations.
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