Download FAR 2024/85 Longline observer data coverage in ling fisheries and their use in stock assessments

Mormede, S. Dunn, A.; Webber, D. (2024). Longline observer data coverage in ling fisheries and their use in stock assessments. New Zealand Fisheries Assessment Report 2024/85. 30 p.

Ling (Genypterus blacodes) is an important commercial fish species in New Zealand middle depths waters and is caught mainly by bottom trawls, bottom longlines, and increasingly by potting.

On board cameras will be rolled out on all bottom longline vessels in December 2024, which is expected to lead to a reduction in the collection of biological samples that are used in ling stock assessments. This report investigates the observer coverage of the ling fisheries to date and the potential effect of the loss of longline observer data on the stock assessments.

Observer coverage has typically been lower for bottom longline vessels than trawl vessels, and less representative of the fishery. The bottom longline observer data was the most influential for the stock assessment of LIN 3&4 Removing bottom longline data in the assessment model of this stock resulted in a different estimate of biomass and status of the stock, highlighting the importance of these data to inform the stock assessment.

For the other ling stocks, the removal of the bottom longline data from the model did not result in a marked changed, possibly due to a lack of adequate observer coverage of these stocks. An increase in observer coverage may lead to a better-informed stock assessment and potentially different understanding of the status of these stocks.

The Deepwater Working Group recommended that observer coverage should be increased in bottom longline fisheries to inform the stock assessments better and that scientific research programmes using both observers and on-board cameras should be developed to leverage the most benefit from both systems.