Analyses/Maps

Fish

Chilipepper rockfish HSI map: Potential Distribution

About these maps:
These maps display HSI model results for adult (left) and subadult (right) chilipepper 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: Miller and Hardwick, 1973; Eschmeyer et al., 1983; Eldridge, 1994; PFMC, 1999; CDFG, 2002; and Love et al., 2002.
Validation: Wilson-Vandenburg et al., 1996; Wilkins et al., 1998; and Turk et al., 2001.

Methods:
Bathymetry SI values for adults were developed using the literature review method, while subadult SI values were assigned based on the regression fitting technique using 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 estimates for distinguishing adults from subadults were reported in Love et al., 2002, where adults were defined as: females > 300 mm and males >280 mm total length. Subadult sizes ranged to 90 mm standard length. Adults and subadults exhibited similar bathymetric preference, with subadults displaying a more narrow range (150-210 m) than adults (150-250 m) (see SI graphics below maps). Literature sources revealed a shift in substrate affinity at maturation from soft sediments to hard substrate. This pattern yields significantly different results in the amount of available habitat for each respective life stage. Suitable habitat for adults comprises less than one percent of the study area and, thusly, small percentages within each sanctuary’s boundaries: Cordell Bank – 4.6%, Gulf of the Farallones – 2.9%, and Monterey Bay – 1.7%. In contrast, highly suitable habitat for subadults was considerably more abundant, comprising almost 15% of the study area. Approximately 65% of the available habitat with Cordell Bank sanctuary was predicted highly suitable for subadults, 36% in Gulf of the Farallones, and 19.5% within Monterey.

NMFS trawl data (adults/subadults) and CDFG catch data (adults only) were used to validate models. Validation data were limited for adult high suitability areas, but the pattern of increasing mean abundance with increasing HSI value still emerged. The subadult model performed similarly by exhibiting a positive correlation between predicted and observed values.

Additional data are needed throughout the chilipepper’s range to strengthen SI values and provide adequate data for testing model performance.