December 2014
This report describes the results of a preliminary assessment of the relative risk to protected coral species from deepwater bottom trawling.

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Deep sea stony corals.
Deep sea stony corals

POP2013-05 Pilot benthic risk assessment final report (PDF, 1, 297K)


Protected corals are diverse and widespread in the New Zealand region. They are vulnerable to impact from bottom trawling, and other human activities in the deep sea such as mineral exploration. In this study we undertake a preliminary assessment of the relative risk to protected coral species from deepwater bottom trawling. We apply the methodology to the orange roughy fishery on the Chatham Rise as a case study.

A Productivity-Susceptibility-Analysis (PSA) was carried out for 15 species or groups of coral. These were chosen to encompass a range of characteristics to illustrate the type of results from such a risk assessment, and how this could inform management. The analysis considers the extent of impact on the relevant species due to fishing activity (“susceptibility”), and the potential of the species to recover from the impact (“productivity”). The corals selected included reef-forming scleractinian stony corals, “tree-like” gorgonian corals and black corals, and smaller scleractinian cup corals and hydrocorals.

The assessment considered various sources of information on the distribution of corals and fishing that provided information on the “availability” and “encounterability” attributes. Knowledge of the shape and size of corals, and studies on trawling impacts helped assess the “selectivity” of a trawling encounter, and then biological data such as age, growth, reproduction, colonisation, and dispersal were used to rank the “productivity” of a coral species or group, which reflects its ability to recover from trawling.

The PSA produces a plot of susceptibility and productivity scores, and also derives an overall relative risk index. Black corals (at the order level, and the genus Bathypathes) and the gorgonian coral genus Paragorgia, were classified as high risk. Most reef-building scleractinian corals, as well as other gorgonian coral taxa, were medium risk, and cup corals and hydrocorals were relatively low risk. These results were consistent with expectations based on the form and biology of the corals, and knowledge of trawling impacts.

The method allows sufficient transparency to track and understand where and how certain attribute scores affect results. It also enables the sources of susceptibility or productivity to be evaluated when considering the efficacy of management options to reduce or mitigate risk. Although only a pilot assessment, the study should provide scientists and managers with a better understanding of this type of ERA methodology, as well as the various aspects and characteristics of coral species and the fishery that contribute to risk determination, and inform potential management approaches.

Publication information

CLark, M., Tracey, D., Anderson, O., and Parker, S. 2014. Pilot ecological risk assessment for protected corals. Report prepared by the National Institute of Water and Atmospheric Research for the New Zealand Department of Conservation, Wellington. 32p.


Conservation Services Programme
Department of Conservation
PO Box 10-420
Wellington 6143


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