The distribution of protected corals in New Zealand

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Summary

A wide variety of deepwater corals exist in New Zealand’s Exclusive Economic Zone (EEZ). These corals are at risk from anthropogenic activities such as bottom trawling. This threat was recognised by the listing of all deepwater black corals, gorgonians, stony corals, and some hydrocorals, as protected species.

This report describes research to (1) expand recent work on identifying areas where deep sea corals are at highest risk of interactions with commercial fishing gear by using additional sources of information relevant to the distribution of corals, including mapping of likely coral distributions using predictive models, and (2) provide recommendations on any future research required to further improve the estimation of risk to protected corals from commercial fishing.

The sources of information considered were from research sampling (58%) and from commercial fishing effort where observers had been present (42%). The resulting dataset contained 7731 records, of which 46% were stony corals (56 genera from 15 families in Order Scleractinia), 33% were gorgonians (57 general from 8 families in Order Alcyonacea), 11% were hydrocorals (16 genera from one family in Order Anthoathecata), and 10% were black corals (26 families from 7 genera in Order Antipatharia). Coral records from the four orders were distributed throughout the Fishery Management Areas, though differences by area and depth were evident at the family and genus level, where lower taxonomic detail was available.

Corals were described and analysed in four functional groups. These groups recognised the structural differences that corals exhibit, and the potential biogenic habitat that different coral structures provide. The four groups were described as “tree-like”, “reef-like”, “solitary small”, and “whip-like”.

Boosted regression tree (BRT) analysis was used to predict the likely distribution of coral groups throughout the New Zealand EEZ, according to a set of 10 environmental variables. The areas where the environmental conditions were most suited to the coral groups were generally in deeper waters where the seafloor had steep slopes. Most of the known coral distributions were within the areas predicted by the models to have suitable environment; however, some deepwater and steep relief areas where corals were known to exist were not identified by the predicted distribution. By grouping the corals by their taxonomic orders and by “functional” groups, some details and differences between species were effectively lost.

Generally the areas predicted to have the greatest probability of conditions suitable for corals were outside the main fisheries areas, except for some deepwater fisheries that occurred on areas of steeper relief. The fisheries that pose the most risk to protected corals are the deepwater trawl fisheries for species such as orange roughy, oreo species, black cardinalfish, and alfonsino. In more shallow waters, scampi trawl fisheries appear to pose the greatest risk to corals in all protected orders. Bottom longline fisheries pose a risk to those corals that have a branching or bushy structure. Setnet fisheries may pose a risk in areas of hard substrate.

Recommendations for future research to inform the level of risk posed by fisheries to protected corals include: update and maintain the existing protected coral dataset; increase observer coverage to attempt to cover all fishery methods with seafloor contact, improve the quality of data collection and, in particular, coral identification; collect more biological information about local coral species to better understand their risk to anthropogenic disturbance; where biological information is lacking, review the international literature to identify relevant information; and investigate species associations and better quantify the value of corals as habitat. 

Publication information

Report prepared by S.J. Baird, D. Tracey, S. Mormede & M. Clark (National Institute of Water & Atmospheric Research Ltd) for the Department of Conservation