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Hope and Minion, a Subantarctic and Cape fur seal, released back into the ocean

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Hope (above) and Minion (below), fitted with satellite and flipper tags prior to their release

By Greg Hofmeyr, Curator: Marine Mammals, Port Elizabeth Museum, Bayworld

May 2014 saw two very unusual passengers onboard one of SAEON’s research vessels.

The R/V Honckenii was carrying two young seals that were being taken out to sea for release. Each seal was equipped with a GPS tracking device that would allow its movements to be monitored.

The southern African coastline is home to the Cape fur seal that are found from southern Angola to Algoa Bay and are familiar to most South Africans. However, few people know that another species of seal regularly visits South Africa’s coast.

Subantarctic fur seals are found in the waters of the Southern Ocean and haul out to breed on islands such as Marion Island, which is some 2000 km south of South Africa. But this is a wide-ranging species and every winter a number of them haul out on South African beaches. While many of these seals are in good condition, others are obviously the worse for their long journey and are either starving or suffering injuries.

One of the SAEON Elwandle Node’s partners, the Port Elizabeth Museum at Bayworld, is regularly called out in such cases in the Eastern Cape. The experienced team know how to capture these animals and will then attempt to rehabilitate them.

The team have had great success at getting the animals ready for release in the past, but they never knew what happened to the seals once they were set free. They are normally fitted with plastic flipper tags, but these only allow for visual resighting.

Programme to monitor survival

It was thus an important step forward that a number of individuals and organisations started a programme to monitor the movements and survival of these animals after release. These organisations include the Department of Environmental Affairs (DEA) Oceans and Coasts, Seaworld in Durban, the East London Aquarium, the Mammal Research Institute (University of Pretoria) and Bayworld.

This programme saw Minion, a young male Subantarctic fur seal arrive at Bayworld from Seaworld at the end of April. A few hours later he was joined by Hope, a young female Cape fur seal from the East London Aquarium.

The next day the seals were fitted with satellite tags under anaesthetic by veterinarians Alejandra Vargas and Andrew Mackay, and biologists Mike Meyer of the DEA and Greg Hofmeyr from Bayworld. These tags would allow scientists to follow the seals’ movements at sea and hopefully determine whether they survived and returned home, and therefore whether the efforts to rehabilitate them were valuable.

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The track of Minion, the rehabilitated and released Subantarctic fur seal

The edge of the continental shelf offshore of Port Elizabeth was chosen as the site for release because it was anticipated that the southward moving Agulhas Current would act as a conveyer belt to direct Minion back to his home island in the distant waters of the Roaring Forties.

All was set for the release except for the boat. The boat normally used by Bayworld had been damaged in an accident and the incipient Tuna Classic had ensured that most others were unavailable.

SAEON’s trusty research vessel to the rescue

Fortunately Tommy Bornman of SAEON came to the rescue with the offer of the use of the R/V Honckenii. The next morning both seals were loaded onto this trusty vessel and, under the able skippering of Anthony Opperman, were taken out to sea. Port Elizabeth’s unpredictable weather ensured that it was not possible to take the seals out quite as far as the Agulhas Current, but nevertheless they were released quite a distance from the shore.

Hope’s turn was first. The team did not want to release her too far out since she was a Cape fur seal. She initially splashed around in the water, cleaning herself and then swam circles around the boat before the vessel could head off. Minion was set free further offshore and was in such a hurry that he swam off without a backward glance.

Tracking the seals’ movements

The intervening months brought very different tales for the two seals, via satellite. Hope chose to visit the shore several times over the next few days, but unfortunately her signal was soon lost. It is very likely that the antenna of her device was damaged by one of these shore visits.

Minion, on the other hand, chose to reveal the tale of his long swim over the next two months. With little deviation, he headed south west and was soon in the Roaring Forties. Thereafter he took a more westerly track and at the end of seven weeks was south of Gough Island. This site is home to half the world’s population of Subantarctic fur seals and is likely Minion’s home as well. Unfortunately this could not be ascertained since his device stopped transmitting, likely because of battery failure.

However, the data has shown, for Minion at least, that rehabilitation and release was a success. Analysis of the data received via satellite from Minion, and doing similar studies on subsequent seals, will provide valuable insights into their biology.

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