In our last newsletter, we presented an overview of  red abalone (Haliotis rufescens) throughout California, examining the concepts of refuge by depth, area closure and competition from sea urchins. Since then Peter Haaker, Douglas Albin, Ian Taniguchi, David Kushner and I have joined forces to examine in detail the effectiveness of refuge by depth in protecting red abalone populations. We compared abundance data from three of the Channel Islands, which lack refuge by depth, to Van Damme State Park, which enjoys a de facto deep water refuge. 

  In southern California, management was based on size limit and seasonal closure alone. Abalone were taken at all depths by sportsmen using SCUBA and commercial divers on hookah. North of  San Francisco, abalone take is also limited by size and seasonal closure, but it is a sport fishery only and no SCUBA may be used. In our survey of southern California, we looked at density of abalone per hectare (1 hectare = ~12,000 square yd.) and commercial landings in metric tons (1 mt = 2,205 lbs.) off San Miguel, Santa Rosa and Santa Cruz islands from 1981 to 1997. In northern California, we focused on dive surveys of abalone and sea urchin size and abundance from 1986 to 1992. 

  In southern California, we found significant declines of abalone abundance off  Santa Rosa and Santa Cruz islands, but not off San Miguel Island, during both sport and commercial survey (Figure 1 currently not available). Abalone densities observed in 1997 off Santa Cruz (60 animals per hectare) and Santa Rosa (0 animals per hectare) islands ominously portend localized spawning collapse. In Australia, a study on another species of abalone found that once density fell below 1,000 animals per hectare recruitment failure occurred. (Shepherd and Brown, 1993) 
  In marked contrast, results from Van Damme State Park showed a threefold increase in red abalone abundance from 1986 to 1992.  Densities increased most dramatically in deeper areas (27-60 ft.), from 1,417 to 8,500 abalone per hectare (Figure 2). At shallow, sport-fished depths, densities also increased to about 8,000 abalone per hectare, but leveled off as sport legal adults (7 inches or larger) were picked off by intense sport effort. 

  The importance of deep water for refuge became more apparent when sizes of southern and northern abalone were compared. Only 15% of the red abalone found were sport legal or larger in shallow depths off both Van Damme State Park and Santa Rosa Island. In contrast, 45% were sport legal or larger at deeper Van Damme stations.

  Clearly, our results showed that for one high-use location in northern California, deep water refuge protects a significant portion of the spawning population. Other studies, based on tag and recapture, suggest that deep water adults may move in to shallow depths, replacing picked-out individuals. The  southern California refuge created by the recent closure (see Senator Thompson’s Bill Closes Abalone Fishery to the South) may have come in time for Santa Rosa and Santa Cruz  islands.   Although it  is likely that too few adult  spawners remain  for  localized stock to recover, San Miguel Island, which was not entirely denuded of abalone, could provide  a  source  of  recruits  to  replenish  the  adjacent islands.