Download FAR 2024/81 Estimation of shellfish release survival from New Zealand commercial fisheries

Johnson, K.S.; Jordan, L.K.; McKenzie, J.R.; Bian, R.; Williams, J.R.; Underwood, M.J.; Morrison, M.A. (2024). Estimation of shellfish release survival from New Zealand commercial fisheries. New Zealand Fisheries Assessment Report 2024/81. 87 p.

This study estimated the survival of four shellfish species (scallops, queen scallops, paddle crabs, and sea cucumbers), when returned to the sea after being caught in New Zealand commercial fisheries. For species such as scallops with a minimum legal size (MLS), those below the MLS must be returned dead or alive, while for others such as sea cucumbers, their release is dependent not on size but on being alive and considered likely to survive (destination type code X). Estimates are based on previous local research, or studies with similar species overseas, along with responses to a questionnaire from fishers and fisheries managers with direct observations of immediate or at-release survival, and researchers with knowledge on post-release or longer-term survival. This information was analysed along with reported fishery data on how the shellfish returned to the sea were caught (such as dredge tow duration, speed, and catch size), to provide a range of likely survival estimates for each species and gear combination (differences between target and non-target fisheries are mainly due to differences in durations, speeds, catch sizes and/or seasons):

For New Zealand scallops, the survival estimates were “medium-high” (between 25% and 100% expected survival) for both box dredge and ring bag dredge.

For queen scallops, the survival estimate was “uncertain” (from 0–100% expected survival) for both target and non-target fisheries mainly due to the depth of this species and fishery compared to other scallop species that have been studied.

Paddle crabs below the minimum legal size had survival estimates that were “high” (over 50% expected survival) for potting and “low-medium” (0–75% expected survival) for trawl. For crabs released and considered likely to survive (destination type code X), the survival estimate from potting was also “high” and from trawling was “medium” (between 25% and 75% survival).

Sea cucumbers had a “medium-high” expected survival for the target trawl fishery, but “low-medium” for the non-target trawl fisheries and for dredge fisheries. For sea cucumbers released and considered likely to survive (destination type code X), survival estimates were “high” for the target trawl fishery, “medium-high” for the non-target trawl fisheries, and “medium” when caught by dredge.