Analyses/Maps

Fish

Rex sole HSI map: Potential Distribution

About these maps:
These maps display HSI model results for subadult (left) and adult (right) rex 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: Pearcy, 1978; Stein et al., 1990; Hixon et al., 1991; 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 using the regression fitting technique with NMFS trawl data. For more detailed descriptions of these techniques, see the discussion of Habitat Suitability Modeling, Section 2.1.2, p. 34.

Results and Discussion:
Length-at-maturity information (PFMC, 1999) was used to determine life stage for Rex sole. Females > 305 mm and males > 215 mm total length were considered adults. Subadults ranged in size to 50 mm total length. Little overlap was observed between depth preferences for adults (350-689 m) and subadults (50-489 m). Depth suitability was moderate for adults in waters < 350 m and waters > 809 m were considered unsuitable. Moderate suitability was predicted for subadults in waters between 489-600 m and depths > 709 were predicted unsuitable. Mud and mud/rock substrates were reported to be the preferred habitat. Suitability for sand was also high, but slightly less preferable than mud. Mapped results provide a clear depiction of habitat shifting between subadult and adult life stages. Potential high suitability for subadults occurred over the majority of the shelf but began to decline in depths of approximately 400 m. At these depths, adult suitability increased from moderate to high which extended to depths of approximately 700 m. Within the study area, potentially high suitable habitats comprised greater area for subadults (23%) than adults (13%). The same patterns were evident within sanctuary boundaries. Additionally, significant areas of high suitability were located adjacent to sanctuary boundaries; mostly in the southern portion for adults, and north and south for subadults.

Model performance was assessed using NMFS trawl data. Although strong positive correlations were observed between mean abundance and predicted HSI values, additional fisheries-independent data are needed to further refine the models and increase the number of samples available for model testing. Expanding the environmental data layers are necessary to test model performance throughout the species range.