Man-made structures could be vital to fur seal survival

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Man-made structure in and around huge water bodies including oceans, seas and rivers have always been pegged as environment-unfriendly and oil rigs and artificial reefs have always been at the cross-hairs on environmentalists for their impact; however, a new research shows that how these man-made structures could actually be proving beneficial for fur seals specifically for their feeding needs.

A research led by Deakin University scientists has found that fur seals are congregating around human-made structures including pipelines, rigs, ship-wrecks as they act as artificial reefs attracting fish, which the seal prey upon.

The study is a result of the investigation of feeding behaviour of the Australian fur seals in Bass Strait carried out by researchers Deakin’s Centre for Integrative Ecology, National Geographic, the University of Tasmania and University of California Santa Cruz. For the investigation some seals were fitted with National Geographic “crittercams”. Further, the researchers tracked the foraging patterns of 36 Australian fur seals from Kanowna Island in Bass Strait, using GPS loggers and dive recorders.

Associate Professor John Arnould said that the findings indicate that man-made structures could play a vital role in helping to improve the recovery rates of fur seals.

“While we know fish congregate around these structures, scientists don’t know a lot about their use by marine mammals and we were surprised at first to find the Australian fur seals were going to these area,” Associate Professor Arnould said.

Researchers found that 72 per cent of the 36 seals that were tracked, spent time around the man-made structures, with pipelines and cable routes being the most frequented. More than a third of animals foraged near more than one type of structure.

Though man-made changes to the natural habitats may negatively impact animals living in the area and around it, there are cases wherein some species adapt to the situation and even benefit from it.

“Indeed, man-made structures can provide a range of benefits for some species, from predator avoidance, thermoregulation, and breeding sites, to acting as important foraging areas.”

Associate Professor Arnould said seals and sea lions around the world had experienced variable rates of population recovery since the end of the sealing era.

“We have seen species that feed close to the surface have experienced rapid growth in numbers, populations of species that feed on the ocean floor, such as the Australian fur seal, have increased very slowly, are stable or in decline,” he said.

“It has been suggested that the low population recovery rates of these species could be due to them hunting in environments which for decades have been the focus of commercial fisheries using bottom trawlers that disrupt the habitat and remove the larger size-classes of species that the seals depend on for food.

“The Australian fur seal (Arctocephalus pusillus doriferus) feeds exclusively on the sea floor of the continental shelf on a wide variety of fish, octopus and squid species.”

Associate Professor Arnould said all but one of the Australian fur seal’s breeding colonies occurred on islands within Bass Strait, between the Australian mainland and Tasmania, which has an average depth of 60 metres and is considered to be a region of low food availability for marine predators.

“Therefore, structures like oil and gas rigs and pipelines that occur on the relatively featureless sea floor could provide a valuable prey habitat and promote foraging success for the species,” he said.

The research is published in the latest edition of science journal PLOS One.