Analyses/Maps

Fish

Yellowtail rockfish HSI map: Potential Distribution

About this map:
This map displays HSI model results for adult yellowtail 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; Dark et al., 1983; Allen and Smith, 1988; Love et al., 1990; Weinberg, 1994; Wilkins et al., 1998; Yoklavich et al., 2000; and Love et al., 2002.
Substrate SI: Stein et al., 1990; Stein et al., 1992; Eldridge, 1994; Murie et al., 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 yellowtail 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:
Adult yellowtail rockfish were reported to be greater than 360 mm for females and 320 mm total length for males (Love et al., 2002). Adults typically inhabit rocky substrates which are poorly sampled with trawl gear; therefore SI values were developed exclusively from literature sources. Additionally, only information for adults was adequate for model development. Adults favored depths ranging from 50-249 m with SI’s declining as depth increased. Depths greater than 550 m were considered unsuitable. As previously mentioned, rocky substrates were the preferred substrate for adults, while occasional utilization of sand and mud substrates were reported. Mapped results portray limited areas of highly suitable habitat within the study area (less than 1% of the entire study area), although most of the shelf region was predicted as moderately suitable. All highly suitable areas were located within sanctuary boundaries and comprised small proportions of available habitat within each sanctuary: Cordell-4.5%, Gulf of the Farallones-2.9%, and Monterey-1.7%. Over half of the available habitat within Cordell and Gulf of the Farallones sanctuaries was predicted moderately suitable, but only 24% within Monterey’s sanctuary. Moderate suitability occurred in habitats adjacent to sanctuary boundaries and comprised approximately 450 km2 of available habitat.

CDFG recreational catch data was used to assess model performance. Although limited catches of yellowtail rockfish were available, especially in areas which were predicted highly suitable, strong positive correlation was found between mean abundance and predicted HSI value. Additional information should be collected to further test the model, as well as to strengthen suitability indices.