Hawaiian Monk Seal: numbers not increasing within protected reserve

Back in June, I wrote about the tenuous state of the Hawaiian monk seal, one of the most endangered marine mammals on the planet. The northwestern Hawaiian islands contains one of the largest marine reserves, the Papahānaumokuākea Marine National Monument, and this was hoped to provide the monk seal with a suitable area of refuge to rebuild its numbers.

However, according to researchers, led by conservation biologist Leah Gerber of Arizona State University, the population of monk seals within the reserve is shrinking by 4% each year, while outside of the reserve the seals are increasing by 7% annually.

As reported in NatureNews, "The difference in the seals' survival rates could be a result of an increase in shark predation within the reserve. Locals in the French Frigate Shoals, a group of islands that are part of the protected area, have noticed a steep increase in shark predation, says Gerber. 'They actually started a shark-culling program' to control 'problem sharks', she says. 'It's not something they like to broadcast,' she adds, because of the conservation status of sharks.

Although the authors don't know for sure whether shark numbers have gone up, they speculate that the population could have been boosted by fishing discards before all fishing in the area was banned in 2006. A few of those sharks could now be wreaking havoc on seal pups. 'All you need on each atoll is one really hungry rogue shark,' says conservation biologist Les Kaufman.

Other possible explanations for the decline, which is being caused by a low survival rate of seal pups, include a change to the food supply owing to warming waters; competition for food from large fish called jacks; or the possibility that the reserve is simply too new for its ecosystem to have settled down. It can take 15 years of monitoring, says Kaufman, to properly understand the dynamics of an ecosystem."

Proposals to address the problem have included relocating pups to outside of the reserve until they have grown to an age where they are less vulnerable and could better withstand whatever perils exists within the reserve and then relocate them back. Others have suggested that may not be feasible and it would be better to let nature take its course and find ecological stability at its own pace. Eliminating sharks or jacks may simply put the marine ecology within the reserve further out of whack.

"It depends how you define success," says Gerber. "Is it about saving endangered species, or preserving a functioning ecosystem? It's worth taking a step back. Marine preservation areas may not be the solution in all situations."

Read prior post on Hawaiian monk seal protections.
Read about current Hawaiian monk seal populations in NatureNews.