Analyses/Maps

Fish

Sablefish HSI map: Potential Distribution

About these maps:
These maps display HSI model results for subadult (left) and adult (right) sablefish 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: McFarlane and Beamish, 1983; NOAA, 1990; Love et al., 1996; and Wilkins et al., 1998.
Validation: Wilkins et al., 1998 and Turk et al., 2001.
Life stage information: PFMC, 1999.

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-maturity information (PFMC, 1999) was used to distinguish adult and subadult individuals captured in NMFS trawls. Adults were considered to be > 508 mm total length. Subadults ranged in size between 40-508 mm total length. Subadults exhibited a shallower depth preference (270-869 m) than adults (490-1300 m), although there was overlap within the ranges of preferred depths. Depths > 1170 m were considered unsuitable for subadults; however, depths to 1300 m were considered highly suitable for adults. High suitability probably continues to depths of approximately 2000 m (Beamish and McFarlane, 1988), however more data are needed to confirm this trend. Sablefish were reported to prefer soft substrates, with infrequent utilization of hard bottom habitats. Model results display potentially suitable habitats in the slope region of the study area over soft substrates. Percentages of suitable habitat within each sanctuary were similar for both models: Cordell Bank – 17%, Gulf of the Farallones – 12%, and Monterey Bay – 32%. Overall, 25% of the study area was potentially suitable habitat, where a large portion of these areas occur south of Monterey Bay’s sanctuary. Suitability for the shelf region was predicted to be low or unsuitable for adults; however, moderate suitability was predicted for subadults within this region.

NMFS trawl data were used to assess model performance. Strong positive correlations were observed between mean abundance and predicted HSI values. Although these results are promising, expanding the environmental data coverage to test model performance throughout the species range should be conducted.