Red Sea Urchin Fishery

Collaborators:

• Steve Wing - University of Otago
• Lance Morgan - Marine Convervation Biology Institute
• David Kaplan - University of California, Davis
• Carolyn Lundquist - NIWA, New Zealand

Current Funding:

California Sea Grant

Focus:

Assessment of the current state of the fishery/population, and analysis of the dynamic response of this fishery to different types of management, in particular, spatial management.

We began work on this fishery because of concern that the decline in catch since the inception of the northern California fishery (Fig.1) was due to overfishing. We began with modeling analyses of the potential effectiveness of two types of spatial management: (1) rotating spatial harvest (Botsford, et al. 1993) and (2) marine reserves (Quinn, et al. 1994).

We then began collecting data to better understand the spatial dynamics of this metapopulation. We developed a new method for estimating growth and mortality from size distributions and growth increment data(Botsford, et al. 1994, Smith and Botsford 1998, Smith, et al. 1999). That method required size distributions from reserves to estimate growth parameters and natural mortality rate, then could use those estimates to determine fishing mortality rates (Fig.2) . We then applied it to the red sea urchin at several points along the coast. We used several reserve populations to estimate growth and natural mortality parameters, then estimated fishing mortality rate at several points along the coast (Table1,   Fig.3) (Morgan, et al. 2001).

We are also in the process of identifying the dynamic effects of one of the Allee effects in this species, the declining efficiency of broadcast spawning.

In another study we showed that much of the decline in catch observed in this fishery was due to the "fishing down" of the older, larger individuals that have not been replaced (Botsford, et al. 1994). This population may still be overfished, but whether it is remains uncertain.

We recently assessed whether marine reserves would be useful in increasing the yield in this fishery. Because the usefulness of marine reserves depends on how much recruitment has been depressed by the fishery, and the degree to which that has occurred is uncertain, we took a decision analysis approach, with the slope of the stock-recruitment relationship as the uncertain variable. The result was that long term yield from the fishery could be improved by placing about fifteen percent of the area in reserves (Table 2) .

Our collaboration with Jim Wilen and his students on the effects of fisher behavior has shown its importance in this problem. They have analyzed data on fisher behavior from the fishery and used the resulting model in our model of the red sea urchin. This changes the dynamic response to marine reserves such that they are less likely to increase yield (Wilen, et al., in press).

We have recently participated in a major review of all of the world's sea urchin fisheries (Neil, et al., in press).