Study reinforces need for protection of critical habitat at Lord Howe Island Marine Park

A comprehensive study of threatened marine fishes in Lord Howe Island Marine Park has reinforced the need to protect critical habitat, with populations of some endemic species found to be low.

The report, ‘Ecology and critical habitats of threatened and vulnerable marine fishes at Lord Howe Island’, was prepared for the Northern Rivers Catchment Management Authority (NRCMA) by Dr Steve Purcell, Kelvin Rushworth and Sallyann Gudge from Southern Cross University’s National Marine Science Centre and NSW Marine Parks Authority, as part of an ongoing NRCMA project to fill priority gaps in marine knowledge for the region.

The study assessed the critical habitats of seven threatened and potentially threatened marine fishes at Lord Howe - the Elegant wrasse; Double-header wrasse; Half-banded angelfish; Lord Howe butterflyfish; Ballina angelfish; Pygmy seahorse; and a species of pipefish.

The team undertook field work in January 2011, involving 143 dive hours for searches and data collection.

“We studied the habitats of seven fish species that are threatened or vulnerable to extinction in northern NSW, covering rocky subtidal reefs and carbonate (coral) reefs of Lord Howe Island and surrounding islands,” Dr Purcell said.

“Lord Howe Island Marine Park adds quite a lot to the overall biodiversity of New South Wales and northern NSW in particular. There are also some links between fish populations from Lord Howe Marine Park and the mainland coast. Some of the species we were looking at appear to be a lot rarer on the mainland coast, so it seems Lord Howe is a last bastion for those species.”

Dr Purcell said the Ballina angelfish had been recorded in past times off the Coffs Harbour coast, but there had been no reports there in the last couple of decades. The angelfish is very rarely seen by divers off the Tweed coast, but anecdotally has been caught occasionally in fish traps in deep water.

“We also know the Double-header wrasse can be found on rare occasions on northern NSW rocky reefs; one of the original taxonomic specimens was from Byron Bay,” he said.

“Our study shows that Double-header wrasses have a closer association with seagrass than previously understood.”

The researchers found that while populations of some of the vulnerable species were significant, the populations of other vulnerable, endemic species at Lord Howe Island appeared to be quite small.

”The Half-banded angelfish, for instance, was found in relatively low numbers in our searches, in line with findings from other published studies,” Dr Purcell said.

“We searched for 13 hours in seagrass beds for endemic seahorses and pipefishes and found only one.

“Both the Elegant wrasse and Lord Howe butterflyfish were found in areas with relatively high cover of macroalgae and turfing algae that occur on reef surfaces that can be devoured by urchins at some sites. Our study reinforces that one threatening process to the critical habitats of these lagoonal species would be the loss of seagrass and macroalgae.

“Maintaining healthy reef and lagoon habitat should continue to be a management priority. That means regular monitoring and making sure there are no impacting stressors on the seagrasses or macroalgae from things like nutrient discharge from the island or sea urchin outbreaks.

“The report adds significantly to the knowledge base for sustainable management decisions regarding marine threatened species, critical habitat, and use and protection measures for Lord Howe Island, as well as contributing to knowledge about some of these important species and their key habitats off the NSW mainland coast.”

Manager of the World Heritage-listed Lord Howe Island Marine Park, Mr Ian Kerr, applauded the hard work of the research team in conducting the study.

Photo: Southern Cross University researchers surveying threatened marine fishes in the Lord Howe Island Marine Park.