Analyses/Maps

Fish

Pacific sanddab HSI map: Potential Distribution

About these maps:
These maps display HSI model results for subadult (left) and adult (right) pacific sanddab during June-November. The maps exhibit the potential distribution of the species based on affinities to bathymetry and substrate. 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: Kravitz et al., 1976; Pearcy, 1978; Love et al., 1996; and CDFG, 2002.
Validation: Wilkins et al., 1998 and Turk et al., 2001.
Life stage information: Arora, 1957.

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 maturation information (Arora, 1957) was used to distinguish adults and subadults from NMFS trawl samples. Females > 305 mm and males > 215 mm total length were considered adults for the models. Subadults ranged in size to 60 mm total length. Affinities for depth and substrate type were similar for adults and subadults. Depth preference was determined to occur between 50 – 89 m. Suitability is expected to be high over depths less than 50 m based on literature and the frequency of occurrence observed within NMFS trawl samples. Depths > 190 m were considered unsuitable. Substrate preference occurs over soft bottoms, with infrequent observations over rocky substrate. As a result of these similarities, potential suitability maps were almost identical for both life stages. High suitability was predicted for a large portion of the continental shelf between 50 – 110 m within and adjacent to the sanctuaries. Approximately 11% of the study area was predicted to contain potentially suitable habitat for adults and subadults. Nearly half of the Gulf of the Farallones sanctuary’s habitat was considered highly suitable; whereas 27% of Cordell Bank’s sanctuary was predicted to be suitable habitat. Only 16% of available habitat within Monterey Bay sanctuary was predicted highly suitable, but due to its large size these areas comprise over 2100 km2.

Model performance was assessed by comparing catch data from NMFS trawl samples with predicted HSI values. Strong positive correlations were observed between these data, however additional data are required to test the models effectiveness throughout the species range.