Research Document - 2013/094
Framework for Estimating Quota Options for the Red Sea Urchin (Strongylocentrotus franciscanus) Fishery in British Columbia Using Shoreline Length and Linear Density Estimates
By D. Leus, A. Campbell, E. Merner, W.C. Hajas, and L.L. Barton
Abstract
Recent analyses of digitized spatial data provided by red sea urchin (RSU) harvesters indicated that the annually fished bed areas had steadily declined in most areas for the last 3-5 years. Harvesters were recording fishing events more accurately than previously, as well as being increasingly selective for areas with high RSU gonad quality within the population at large. Fishery-dependent data indicate fished areas were not representative of the areas occupied by the whole fishable RSU population. These bed area declines presented several problems for the assessment process of RSU stocks in British Columbia (BC), and work was undertaken to develop a modified framework to assess RSU populations in BC. The paper describes a linear density model for estimating current biomass (Bc) combining shoreline length with linear density estimates as an alternative to bed area and spatial density estimates. We suggest that, generally, the shoreline length method is more appropriate than the bed area method, especially with a moderately mobile species in a complex coastal environment and where a RSU “bed” with fixed borders and known depths is hard to define. Preliminary large-scale biomass estimates and quota options from the proposed shoreline length method compare closely to values from the bed area method, yielding a 0.7% and 3.0% increase to coast wide mean quota options, to 4705t and 5371t, for RSU size classes of 90-140mm test diameter (TD) and ≥90mm TD, respectively. Further refinement of the estimation of potential RSU habitat and fishable RSU habitat is required through additional surveys and consultation with managers, First Nations and other stakeholders.
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