Analyses/Maps

Fish

Widow rockfish HSI map: Potential Distribution

About this map:
This map displays HSI model results for adult widow rockfish during June-November. The map exhibits the potential distribution of the species based on affinities to bathymetry and substrate (see graphics below map). 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: Alverson et al., 1964; Gunderson and Sample, 1980; Tagart and Kimura, 1982; Allen and Smith, 1988; Wolotira et al., 1993; Wilkins et al., 1998; Yoklavich et al., 2000; and Love et al., 2002.
Substrate SI: NOAA, 1990; Eldridge, 1994; Love et al., 1996; and CDFG, 2002.
Validation: Wilson-Vandenburg et al., 1996.
Life stage information: Love et al., 2002.

Methods:
Bathymetry SI values for adult widow rockfish were developed using the literature review method. For more detailed descriptions of these techniques, see the discussion of Habitat Suitability Modeling, Section 2.1.2, p. 34.

Results and Discussion:
Females > 370 mm and males > 320 mm total length were considered adults (Love et al., 2002). Trawl data were inadequate to develop depth SI’s, thus SI values for depth and substrate were generated through literature sources. Depth preference was reported to occur between 50-299 m, with moderate preference occurring to depths of 399 m. Suitability was low to 549 m and unsuitable at depths > 549 m. According to literature sources, rocky substrates were preferable with occasional occurrences over mud and sand substrates. Mapped results exhibit limited areas of predicted high suitability. Approximately 4.6% of the total area within Cordell Bank sanctuary was considered highly suitable; however, moderate suitability accounted for nearly 67% of the sanctuary. This proportion was similar within Gulf of the Farallones sanctuary: high suitability – 3% and moderate suitability – 58%. Within Monterey Bay sanctuary, high suitability comprised 1.7% of the total available habitat, while moderate suitability accounted for 25%. Overall, less than 1% of the study area was predicted highly suitable, and 19% moderately suitable, for adult widow rockfish.

CDFG recreational data were used to assess model performance. While positive trends were evident between mean abundance and predicted HSI values, additional data are needed to further support the model. In addition, more data are required to quantify depth SI’s to further refine model efforts.