Analyses/Maps

Fish

Dover sole HSI map: Potential Distribution

About these maps:
This figure displays the HSI model results for subadult (left) and adult (right) Dover sole during June-November. The maps exhibit the potential distribution based on affinities to bathymetry and substrate. Predicted HSI values range in scale 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: Demory, 1975; Demory et al., 1976; Barss et al., 1977; Pearcy, 1978; NOAA, 1990; Stein et al., 1992; and CDFG, 2002.
Validation: Wilkins et al., 1998 and Turk et al., 2001.
Life stage information: PFMC, 1999.

Methods:
Bathymetry SI values for adults and subadults were developed from the regression fitting technique. Substrate SI values were developed through literature review.

Results and Discussion:
Adult Dover sole are reported to be >300 mm total length for male and female individuals (PFMC, 1999). Both adult and subadult Dover sole inhabit deep water slope habitats; subadults exhibited a shallower range of depth preference (130-650 m) than adults (290-1070 m) (Figs). Adults and subadults prefer soft sediments (sand and mud) throughout their range. Highest habitat suitability for subadults was predicted to occur along the shallower portions of the continental slope (200-550 m). A large area of moderate suitability was also predicted for an area that extends throughout the majority of the continental shelf. The most suitable habitats for adults consisted of deeper slope waters, with only moderate suitability extending onto the shelf region. Within Cordell Bank sanctuary, high subadult suitability (values 8-10) was calculated for 22% of the available habitat, 6.4% within Gulf of Farallones, and 19% within Monterey sanctuaries. Cordell Bank and Gulf of the Farallone sanctuaries are comprised of shallower (50-300m) shelf waters, thus the percentage of highly suitable habitat for adults is lower (based on their calculated affinity for deeper waters) than that observed for subadults (21% and 12%, respectively). However, Monterey’s sanctuary is considerably deeper and a larger proportion of available habitats (30%) were predicted to be highly suitable for adults. Approximately 50% of areas that were predicted to be potentially suitable habitats for both adults and subadults occurred outside of sanctuary boundaries. These areas are most prominent south of Monterey’s sanctuary.

Model performance was assessed by regressing predicted HSI values on mean log abundance values from NMFS trawl samples (1998-2001). Significant positive correlations were observed for both adult and subadult models, however, these are based on limited trawl samples (N = 311). Discrepancies in model performance, such as small peaks of mean abundance within low suitability areas, are a result of limited observations within that category. Additional trawl information would strengthen model development and performance.