Analyses/Maps

Fish

Dungeness crab HSI map: Potential Distribution

About this map:
This map displays HSI model results for adult Dungeness crab during June-November. The map displays the potential distribution based on affinities to bathymetry and substrate. Predicted HSI values range from 10 (highest) to 0 (unsuitable) and were grouped into five classes: highest suitability (10-8), moderate (7-5), low (4-2), lowest (1), and unsuitable (0). SI values for bathymetry and substrate type are shown in the graphics below the mapped HSI results. Model performance graphics and statistical details are displayed in the map insets.

Data Sources:
Bathymetry SI: Wilkins et al., 1998 and Lauth, 2001.
Substrate SI: Pauley et al., 1989; Emmett et al., 1991; Leet et al., 2001; and CDFG, 2002.
Validation: Wilkins et al., 1998 and Turk et al., 2001.

Methods:
Bathymetry SI values for adult Dungeness crab were developed using the regression fitting technique. Substrate SI values were developed through literature review.

Results and Discussion:
Only adults were modeled within the study area because size information was lacking for crabs in the NMFS trawl data and scientific literature was not detailed enough to develop SI values for subadults. Dungeness crabs are an estuarine dependent species (Pauley et al., 1989), with adults exhibiting a shallow distribution (to 90 m) in coastal marine waters. Depth SI values derived from NMFS trawls confirmed this trend by exhibiting high SI values within 50-90 m. Suitability is probably high in the shallower nearshore environment (Emmett et al., 1991); however, trawl information was not available for this area. Literature sources described crab substrate preference to be soft sediments, with occasional utilization of rocky substrate. Habitat suitability based on these data resulted in a broad area of high suitability throughout the shallower waters of the Gulf of Farallones sanctuary (38% of available habitat), and much smaller proportions within Cordell (8.7%) and Monterey (10.4%) sanctuaries. Overall, this amounts to 2,809 km2 of highly suitable habitat within the three sanctuaries. Moderate suitability, encompassing approximately 2,477.8 km2, extends further offshore to approximately 130 m. The potential suitability of habitats rapidly declines to unsuitable beyond 130 m in depth. The model performed well with NMFS validation data and exhibited a strong positive correlation with predicted suitability values.