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INT2022-04 Risk Assessment for Protected Corals (PDF, 3,862K) 

Summary

This research, undertaken for the Department of Conservation, used three different methods to determine the relative risk of commercial fisheries to several types of protected corals. Bottom trawling physically damages fragile corals, and they recover from damage extremely slowly, if at all. Understanding relative risk from fisheries can inform measures of coral vulnerability and resilience, and guide coral conservation measures.

Three methods were applied to evaluate risk: 1) a Productivity-Susceptibility Analysis (PSA) approach, which examines the extent of fishing impact using coral ‘productivity’ values (determined from biological traits and susceptibility) that infer recovery potential; 2) the dynamic Relative Benthic Status (dRBS) method, which combines modelled coral distributions, impact and recovery rate metrics, and fishing effort data to produce annual estimates of the spatial distribution of coral abundance, and 3) Bayesian Networks (BNs), a graphical framework building on PSA methodology that indicates the likelihood of a scenario with allowances for uncertainties and limited data.

The first part of the project included compilation of the most recent information on coral biology (e.g., how fast they grow, how often they reproduce etc.) and knowledge on how susceptible they could be to fishing (based on, for example, their physical characteristics and location). There have been several knowledge advances in this field in recent years, but as there are hundreds of coral species in New Zealand, information is lacking for most of them, and not all data were available for all species included. It is noteworthy that there is therefore an element of uncertainty in model input values, and consequently, model outputs must be interpreted with caution.

In total, eleven different coral groups were assessed, including representatives of the four main protected coral groups in the Wildlife Act; stony corals, black corals, gorgonians and a family of lace corals. Some corals were assessed at individual species level (e.g. the stony coral Solenosmilia variabilis), other groups represented several species (e.g., bamboo corals). Each method differed in their assessment of risk among these groups, but generally, stony corals, black corals and tree-like gorgonians were deemed to be at higher risk from fishing than cup corals, hydrocorals and sea pens.

Spatial scale considerations are highly relevant when interpreting the outputs of this project. Risk was assessed across the entirety of the Exclusive Economic Zone (EEZ), within multiple NZ bioregions, and finally at the scale of the orange roughy trawl fishery (from which most coral bycatch originates) divided into Quota Management Areas. The results demonstrate that the spatial scale used to assess status is critical, and much lower status may be expected if the assessed area was limited to fishable depths or to specific fished features or groups of features such as seamount complexes.

Results presented here are informative but need careful interpretation, as large variation in fishing pressure and coral abundance across the scales assessed can provide misleadingly favourable relative risk scores and benthic statuses that do not reflect localised or smaller scale fishing impacts.

Consequently, coupled with uncertainty in model input values, results should not be used to manage fishery impacts locally and should not be used when assessing and managing localised fishing impacts, such as at fishing stock level.

Further research could include the application of the methods demonstrated here to specific spatial scales and specific fisheries management approaches.

Publication information

Clark, M., Anderson, O., Kaikkonen L., Stephenson, F. Tracey, D., Finucci, B. Risk Assessment for Protected Corals. Final report for CSP project INT2022-04, prepared by NIWA for the Department of Conservation. 100 p.