High mortality among Hooker’s sea lion pups

Press, 6 July 1983, Page 22

High mortality among Hooker’s sea lion pups

Large-scale mortality among the Hooker’s sea lion pups on the Auckland Islands means the species remains highly endangered. A scientific expedition which has just returned from the islands found that only half of the pups born during the 1982-83 season at one rookery had survived. The leader of the expedition was Mr Martin Cawthorn of the Fisheries Research Division of the Ministry of Agriculture and Fisheries. He said that only about 200 of the 400 pups born in the Enderby Island rookery had survived. Mr Cawthorn said that the main causes of death appeared to be starvation and entrapment in the marshy peat soil which covered most of the island.

“Heavy rainfall this year saturated the peat,” he said. “At the end of February, the pups are congregated on the edge of the forest and if one pup falls through the surface and gets trapped in the boggy jieat, many others will follow it, interpreting

its struggles as a game.” This year 82 dead pups were found trapped in the peat in the Enderby Island rookery. Many immature animals were also found with shark bites. Besides sharks, young sea lions can also fall victim to killer whales and leopard seals in seas around the Auckland Islands. Mr Cawthorn said that the large squid fishery in Area E of the exclusive economic zone also affected Hooker’s sea lion mortality. Vessels trawling for squid near the islands can net up to 100 sea lions a year.

“Hooker’s sea lions give birth in December and mate again about a week after pupping,” Mr Cawthorn said.

“This means that a female that is drowned by capture at this time of year is almost certainly pregnant and suckling a pup ashore.

“As a result,.each time a mature female is killed, jot one but three sea lions die.”