Concerns for the north coast recreational abalone fishery include:
- Thirty-five percent decline in overall density at eight fishery index sites
- Sixty percent decline in density in Sonoma County due to a mass mortality event in 2011
- Particularly low density at Fort Ross
The California Department and Wildlife performs scuba surveys at eight index sites in Mendocino and Sonoma Counties in order to quantify the resource available for fishing and to assess the relative health of the populations. These index sites represent nearly 50% of the recreational abalone catch. The results of the surveys indicate that the average density (number per unit area) of emergent abalone (sublegal and legal sized) has continued to trend downward from densities reported in the 2010 fishery status report (PDF). The average density across all index sites is less than the 0.5 per square meter (5,000 per hectare), the level in the Abalone Recovery and Management Plan (ARMP) which requires a 25 percent reduction in catch (Figure 1).
An unprecedented die-off of abalone and other marine invertebrates associated with a harmful algal bloom (red tide) occurred in late August 2011 along the Sonoma County coast. Concern over the impact of the die-off on Sonoma County abalone populations prompted an intensive monitoring effort to complete surveys of all four Sonoma County index sites in 2012. Survey results show the large scale die-off coupled with the prior downward trend in density at the index sites has reduced overall abalone densities by approximately 35 percent. Sonoma County experienced a 60 percent in density whereas Mendocino population density is unchanged from baseline (Figure 2). The current density at the Fort Ross site is of particular concern because it is now below 0.25 per square meter (2,500 per hectare), the level requiring site closure in the ARMP (Figure 3).
Figure 1. Average red abalone densities per square meter for all index sites from 2003-2007 and 2009-2012. Criteria for 25 percent take reduction is indicated by the bold red line at 0.5 abalone per square meter.
Figure 2. Average red abalone density per meter square for the Sonoma and Mendocino index sites from 2003-2007 and 2009-2012.
Figure 3. Average red abalone densities per square meter by index site from 2003-2007 and 2009-2012. The dashed line (0.25 abalone per meter square) indicates the density trigger for site closure. Sonoma County sites are circled.