Marine Sanctuaries Help The Predators More Than The Threatened Sydney Seahorse

A Sydney Seahorse hiding in a soft coral. Image: UTS

Marine sanctuaries along the coast near Sydney may not be benefiting the seahorse population because they tend to encourage the predators of the iconic species.

The results of a four-year study assessing the benefits of no-take Marine Protected Areas (MPAs) on White’s seahorse (Hippocampus whitei), also known as the Sydney Seahorse, has revealed that establishing marine reserves may not be the best strategy for protecting the seahorses.

Fishing is prohibited in no-take marine reserves, also known as sanctuary zones in NSW.

Although the benefits of areas are well known for increasing fish diversity, abundance and size, this research indicates that establishing no-take marine reserves could instead put threatened seahorse populations at risk and should be used cautiously as a management strategy.

“The results from this project were not completely expected as the published literature suggests that seahorses should benefit from the creation of small scale marine reserves,” says marine scientist Mr David Harasti who recently completed a Phd of the University of Technology, Sydney (UTS).

“Our results are contrary to what has previously been suggested.”

The findings are published in the journal PLOS ONE.

Harasti monitored populations of White’s seahorse, and their major predators such as octopus, flathead and scorpionfish, at four sites near Nelson Bay in the Port Stephens-Great Lakes Marine Park on the NSW mid-north coast.

“We found that seahorse and predator numbers were negatively correlated, in other words, White’s seahorse numbers were higher outside the no-take sites and predator numbers were higher inside the no-take marine reserve sites,” he says.

“When the numbers of predators went up, the numbers of seahorses went down.”

Within marine reserves there will be winners and losers and it appears seahorses may end up being one of the losing species as a result of increased numbers of predators following the stopping of fishing.

Harasti’s supervisor, Professor Bill Gladstone, UTS Head of School of the Environment says the results of the research will cause a re-think of the conservation measures needed to safeguard populations of White’s seahorse.

The team’s other study, into the habitat preferences of the Sydney Seahorse, recently published in Journal of Fish Biology, supports using a much broader approach to seahorse conservation than just relying on the establishment of marine reserves.

Seahorses use a variety of habitat types, from sponge gardens to soft corals, and juveniles prefer different habitats to adults.

They also tend not to move very far. One individual male was observed living in the same sponge for 17 months.

White’s seahorse only occurs in estuaries from Forster to Wollongong, covering Australia’s most densely populated region.

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