Analyses/Maps

Fish

Darkblotched rockfish HSI map: Potential Distribution

About these maps:
These maps display HSI model results for adult (left) and subadult (right) darkblotched rockfish 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: Eschmeyer et al., 1983; PFMC, 1999; Yoklavich et al., 2000; CDFG, 2002; and Love et al., 2002.
Validation: Wilkins et al., 1998 and Turk et al., 2001.
Life stage information: Love et al., 2002.

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:
Love et al., 2002 reported that adults were > 270 mm total length. Smallest subadults captured in trawls measured 60 mm total length. Darkblotched rockfish are considered a slope species (Love et al., 2002) and preferences for depth were considerably deeper than other rockfish modeled for the study area. Adults were predicted to prefer depths within 210-390 m and 170-350 m for subadults. Depths > 490 m and < 110 m were considered unsuitable for adults; whereas, unsuitable depths for subadults occurred in waters > 430 m and < 70 m. Adults and subadults preferred hard substrates, however, darkblotched rockfish were commonly associated with mud and sand substrate. Highly suitable areas for both life stages begin near the shelf edge and continue offshore to depths of 350-390 m over mud and rock substrates. Overall, the distribution of high suitability areas within the study area were similar for adults and subadults, 4.6 and 4.9% of total area, respectively. The distribution of adult and subadult suitable habitat were also similar within each sanctuary: Cordell Bank (9.4, 14.1%), Gulf of the Farallones (2.1, 2.5%), and Monterey Bay (6.1, 6.0%). Different spatial patterns were obvious for areas of moderate suitability within each sanctuary, most notably Cordell Bank, with 10% of the total area for adults and 40.3% for subadults. Areas containing no data (nearshore and waters deeper than 1300 m) are bounded by unsuitable habitat which, it is assumed, could be extended to fill in these areas. The bands of potential high suitability extend north and south outside the boundaries of the sanctuaries and presumably continue beyond the study area.

Limited trawl data were available for testing model performance, but yielded a positive correlation between mean abundance and predicted HSI value. Additional data are required to strengthen the model and provide adequate data for assessing model performance.