This is the final report for project BCBC2020-26: Octocoral bycatch diversity on the Chatham Rise, which focuses on the diversity of octocorals in the family Primnoidae that have been collected through research trawl or bycatch on the Chatham Rise. This project builds upon INT2019-05: Coral biodiversity in deep water fisheries bycatch.


The deep seas of Aotearoa/New Zealand harbour diverse and abundant communities of branched gorgonian corals that overlap with bottom trawling and long-lining commercial fisheries. The incidental contact of fishing gear with gorgonian colonies, particularly those with branched or bushy growth forms, causes damage and entanglement. Although impacts on coral ecosystems and coral biomass have been documented, the extent of species-level diversity affected by bottom trawling is less well understood, especially for gorgonian corals. This is in part due to their highly diverse and variable growth forms, which makes visual identification difficult and prone to error.

This study expanded upon a previous examination of gorgonian coral bycatch (INT2019-05) across the New Zealand EEZ by focusing on a single family (the Primnoidae: ‘sea-fan’ and ‘bottlebrush’ corals) across the Chatham Rise – a region where multiple commercial trawl fisheries occur. Samples of primnoid corals were obtained from the NIWA Invertebrate Collection, with their origins from a mixture of fisheries bycatch sampled by fisheries observers, NIWA research trawl bycatch (incidental catch during fisheries assessment cruises for Quota Management System target species), and samples collected during NIWA biodiversity research cruises using tows of benthic sleds. Genetic barcoding was used to identify the number of unique taxa present and a subset of samples were subjected to high-resolution genomic sequencing, to test the utility of recent technological advancements for biodiversity discovery and to determine whether cryptic species might be overlooked by more traditional barcoding approaches.

One hundred and twenty-two samples produced viable results for at least one of three genetic markers. A phylogenetic analysis based upon two genetic markers indicated that 13 distinct primnoid taxa were present, along with representatives of two other cryptic gorgonian families that were originally misidentified as Primnoidae. One of these two was tentatively identified as the Pleurogorgiidae and, if correct, would represent a first record for this family in New Zealand. The 13 primnoid taxa were comparable in diversity and identity to 15 previous published records for the Chatham Rise and in combination suggests that the full extent of primnoid diversity on the Chatham Rise is at least 17 species in total. Genomic sequencing of a subset of samples resolved fine-scale relationships that distinguished closely related species and could potentially delineate population-level differences for future genetic connectivity studies of protected corals. These results provide a baseline for bottom-trawling impacts on the diversity of a widespread and ecologically important family of protected gorgonian corals in New Zealand.

Publication information

Bilewitch, J.P. (2022) Octocoral bycatch diversity on the Chatham Rise. BCBC2020-26 final report prepared by NIWA for Department of Conservation. 31 pp.


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