Analyses/Maps

Fish

English sole HSI map: Potential Distribution

About these maps:
These maps display HSI model results for adult (left) and subadult (right) English sole during June-November. The maps exhibit the potential distribution of the species based on affinities to bathymetry and substrate (see graphics below maps). 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: Ketchen, 1956; Demory et al., 1976; Barss et al., 1977; Day and Pearcy, 1978; Pearcy, 1978; Demory, 1984; and CDFG, 2002;
Validation: Wilkins et al., 1998 and Turk et al., 2001.
Life stage information: Harry, 1959.

Methods:
Bathymetry SI values for adults and subadults were developed from the regression fitting technique. Substrate SI values were developed through literature review. For more detailed descriptions of these techniques, see the discussion of Habitat Suitability Modeling, Section 2.1.2, p. 34.

Results and Discussion:
Males were considered mature at considerably smaller sizes (220 mm) than females (310 mm total length) (Harry, 1959). Minimum size for subadults captured in trawls was 90 mm total length. Adults displayed slightly deeper depth affinity (50-170 m) than subadults (50-150 m). Depth was calculated to be unsuitable beyond 450 m for adults and 410 m for subadults. Substrate affinities were similar for both life stages, with fish exhibiting a preference for mud and sand and an avoidance of hard substrates. Habitats classified as mud/rock were ranked as highly suitable. As such, model results indicate highly suitable habitat on the shelf up to the shelf edge for both life stages. Overall, approximately 16% of the available habitat was considered potentially high suitability for adults and subadults within the study area. These areas are more extensive in the northern portion of the study area than in the area south of Monterey Bay. The proportion of highly suitable habitat within sanctuary boundaries is similar for both life stages: Cordell Bank-60%, Gulf of the Farallones-57%, and Monterey-22%. Potentially high suitable habitats occur to the north and south of sanctuary boundaries, with the northernmost portion consisting of a much broader band than that observed in the southern portion.

Model performance analyses using NMFS trawl data resulted in strong positive correlations with mean abundance and HSI value. Low proportions of moderately suitable habitat may indicate that more data are needed to strengthen SI analyses and to improve the validation dataset.