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INT2023-10 Understnading coral bycatch: assessing large catches  (PDF, 1,186K)

Summary

All coral species in Orders Antipatharia and Scleractinia as well as gorgonian corals in Order Alcyonacea and hydrocorals in Family Stylasteridae are protected under the Wildlife Act 1953. This protection prohibits intentional damage and removal. To better enable delivery of this protection, we need to continually seek to improve our knowledge of these corals – in particular their diversity, distribution, abundance, and vulnerability to human activities.

Coral species are frequently taken as bycatch in commercial fisheries and when this occurs on vessels with scientific observers on board care is taken to identify them as accurately as possible and record the weight of the catch. Frequently observers also retain a sample of the corals caught, especially when identification is uncertain, for examination by expert taxonomists ashore. The coral catch data collected by observers has been used to address many of the gaps in our knowledge, and thus it is vital that the data obtained are as accurate as possible. Records of large catches of coral are particularly valuable as these provide a strong indication of locations of high coral abundance. However, occasional errors in the recording of catch weights are likely to have occurred in the past, and continue to occur, due to recording or transcribing mistakes including the use of an incorrect taxonomic code and mis-weighing or mis-entering measured weights.

In this study a close examination of reported coral catches was made to improve understanding of the extent of genuine large catches and to build a more confident picture of coral bycatch across the New Zealand region, including the location of “hot-spots” of coral abundance. Further benefits include improved catch information for cross-validation of coral abundance models, and provision of guidance for verification of future reported large coral catches when loading observer records into database tables.

A complete extract of historic observed protected coral catches was obtained from the observer (COD) database, and a further set of coral catch data was obtained from research trawl records. These data were used together to establish weight thresholds signifying a “large” catch of coral for the purposes of mapping such occurrences and setting or updating values for flagging suspiciously large catches when loading future data into database tables.

A range of datasets and methods for verification of these large catches was developed. These included examination of:

1. Observer trip reports, diaries, and logbooks
2. Observer photographs
3. Vessel-reported coral catches from matched fishing events
4. Spatial comparison with locations of high abundance predicted in species distribution models
5. Spatial comparison with underwater topographical features (seamounts, etc.)

These verification methods were applied to observed catch records and maps produced for all protected coral taxa to provide a more reliable picture of coral captures in the New Zealand region, especially large catches. Revised large catch threshold values were set so that all 98 recording codes for protected coral taxa are included, updating existing values (many of which were set too high) and providing values for many more recent codes for which no value had been set.

Publication information

Anderson, O., Carswell, S., Connell, A. 2024. Understanding coral bycatch: Assessing large catches. Final report prepared for Project INT2023-10, Conservation Services Programme, Department of Conservation. NIWA Client Report 2025053WN. 53 p.