Research Document - 2001/152

Results of surveys of intertidal razor clams (Siliqua patula) on beaches near Massett, Haida Gwaii and recommendations on fishery management

By R. Jones, C. Schwarz, B. DeFreitas and L. Lee

Abstract

Intertidal razor clam populations and biomass on beaches near Massett, Haida Gwaii were estimated using a three stage sampling design stratified by beach section for the period 1994 to 2000. The 2000 razor clam population on 18.8 km of beach accessible to the commercial fishery was estimated by the ratio method to be 36.3 x 106 (CV 17%) clams > 4 mm, 22.3 x 106 (CV 8.5%) clams > 20 mm, and 10.5 x 106 (CV 8%) clams > 90 mm). Estimates using the inflation method in 2000 were similar, at 36.4 x 106 (CV 14%) clams > 4 mm, 22.9 x 106 (CV 7%) clams > 20 mm and 12.5 x 106 (CV 6%) clams > 90 mm. The two methods varied considerably in some years mainly due to assumptions about average transect length (and the area of the beach). The inflation method estimate provides a lower bound since it is based on the number of clams found on a transect. Also it was independent of transect length, which varied between years. The 2000 biomass of clams > 90 mm at the time of the survey was estimated to be 1699 t (SE 157 t). Age-at-maturity studies showed that razor clams do not start to mature until they reach 80 mm, 50% are mature at 87 mm and all are mature at 97 mm. The surveys show that the biomass was at a historic high in 2000 and that a large number of two year old clams were in the population, most of which will recruit to the fishery in 2001.

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