Research Document - 2008/065

An Evaluation of Fishery and Research Data Collected during the Phase 1 Sea Cucumber Fishery in British Columbia, 1998 to 2007

By C. Hand, W. Hajas, N. Duprey, J. Lochead, J. Deault, and J. Caldwell

Abstract

Investigations have been underway since 1998 to fill some of the knowledge gaps in the giant red sea cucumber fishery that were originally identified in 1996. The current regime of annual harvest conducted in only 25% of the British Columbia coast, along with experimental fishing, have allowed a thorough study of the effects of harvesting on the density and size of sea cucumbers.

Surveys were conducted in six commercially-open harvesting areas; all had a decline in density ranging from 10% to 23% between 1998 and 2007. There was a decline in the mean weight of sea cucumbers in four of the six open areas ranging from 12% to 17%.

Four experimental fishery areas (EFAs) were developed to study the effects of various harvest levels on density and sea cucumber size. Five sites (no harvest, 2%, 4%, 8%, and 16% harvest rate) were established in each EFA and were harvested annually, based on virgin population estimated at the beginning of the study. The sites with higher harvest rates, 8% and 16%, showed large decreases in density between the first and last year of study. Lower harvest rates (control, 2% and 4%) did not show the same levels of decline. The mean weight of sea cucumbers also declined during this time period, significantly in approximately half of the 20 EFA sites and by up to 37%. The declines in mean split weight were not entirely the result of harvesting levels, as size also declined in control sites.

A latent productivity model was used to estimate the maximum sustainable harvest rate, using the 10 years of data from the experimental fishery areas. Maximum sustainable harvest rates, at the 1 percentile level (i.e. 99% confident that the true harvest rate is higher), ranged between 3.5% and 10.3% of estimated virgin biomass over the four EFAs. In no EFA was the 16% harvest rate found to be sustainable.

A total of 7.7% of the shoreline available for fishing was targeted by harvesters in 2005. The fleet does not target the same pieces of shoreline repeatedly and they appear to harvest different areas from year to year. As was expected, the amount of shoreline targeted by harvesters increased with quota levels, but natural reserves with high densities of sea cucumbers persisted.

Results from these Phase-1 fishery investigations form the basis of recommendations to resource managers to expand the sea cucumber fishery to other areas of the BC coast using a conservative annual harvest rate ranging from 3.5% to 10.3% of virgin biomass. A limit reference point (LRP) of 50% virgin biomass is recommended, and an upper stock reference point (USR) of 60% to 80% virgin biomass is suggested. It is further recommended that the experimental fisheries be continued as they are a valuable tool for monitoring population response to fishing, and that no-harvest reserves be established in fishing areas for comparative monitoring.

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