Carter and VanBlaricom Effects of experimental harverst on Strongylocentrotus franascanus In northiern Washington 



663 



on sea urchin populations in Washington. We examined 

 changes in density and size distribution of red sea urchin 

 populations resulting from two levels of experimental har- 

 vest. Our study site was San Juan Channel (SJC), one of two 

 areas in Washington where commercial sea urchin harvest 

 has been prohibited since the 1970s (Fig. 2). We compared 

 density and size distribution data for sea urchins from exper- 

 imentally hai-vested sites in SJC with similar data collected 

 from 1) nearby control sites, and 2) 19 sites in the Strait 

 of Juan de Fuca (SJDF), an area commercially harvested 

 since the early 1970s. We also examined recolonization of 

 hai-vested sites through recruitment and immigration. We 

 discuss implications of our results for management of sea 

 urchin harvest effort and the potential use of marine harvest 

 refuges in enhancing Washington's sea urchin fishery. 



Methods 



We established nine study sites in SJC from November 

 1996 to March 1997 (Fig. 2). Sites were 6-10 m in depth 

 and approximately 10 m x 40 m, with the long axis of each 

 site running parallel to the shoreline along the depth 

 contour (Table 1). Eight permanently marked circular 

 sampling areas (each 7.07 m^) were located along the 

 midline of each site along the depth contour Site selec- 

 tion was based on high red sea urchin density (>1.5lm? in 

 preliminary surveys), substrate (primarily large cobble or 

 bedrock) and safety considerations. 



We applied one of three harvest treatments to each site. 

 "Selective harvest" consisted of annual removal of all legal- 

 size sea urchins (102-140 mm test diameter) each winter 

 (March of 1997 and 1998). Selective harvest simulated the 

 annual commercial harvest of a bed of sea urchins in the 

 San Juan Islands (Pfister and Bradbury, 1996). "Complete 

 harvest" consisted of removal of all sea urchins present in 

 March 1997, and at monthly intervals thereafter through 

 September 1998. The complete harvest treatment did not 

 represent any current management strategy for com- 



25,000 



« 20.000 



o 



^ 15,000 



2 10,000^ 



5,000 



• Washington 



X Northeast Pacific 



° Eastern Central Pacific 



D □ R 



O-^D 



S^s, 



"■■tB««««»' 



• •• 



*?****t 







1975 1980 1985 1990 1995 2000 

 Year 



Figure 1 



Annual harvest of red sea urchins (Strongylocentrotus 

 spp.l in Washington state and in the larger Northeast 

 Pacific and eastern Central Pacific areas of the west 

 coast of the United States. Northeast Pacific includes the 

 area north of 40''30'N (approximately Oregon-California 

 border). Eastern Central Pacific includes the area south 

 of 40°30'N. (Sources: Hoines, 1994, 1998; FAO, 1980, 1981, 

 1992, 2001; Bradbury.^) 



mercial harvest. Rather, the complete harvest treatment 

 represented one extreme (the control treatment being the 

 second) against which effects of selective harvest may be 

 compared. Sea urchin densities were not manipulated in 

 the "control" treatment. Because of logistical constraints, 

 control sites were located in smaller preserve areas within 

 SJC where harvest of all invertebrates and fish is prohib- 

 ited. Harvest treatments were randomly assigned to the 

 remaining six sites. All sea urchins harvested were mea- 

 sured at the surface and released at other locations in SJC 

 well away from the study sites. 



In SJC, we sampled at large (sites) and small (circular 

 areas within sites) spatial scales. Small-scale sampling 

 was more frequent, allowing detection of potential short- 



