Analyses/Maps

Fish

Longspine thornyhead HSI map: Potential Distribution

About these maps:
These maps display HSI model results for subadult (left) and adult (right) longspine thornyhead 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: Wildebuer, 1986; Cross, 1987; Wakefield and Smith, 1990; Jacobsen and Vetter, 1996; Bloeser, 1999; PFMC, 1999; CDFG, 2002; and Love et al., 2002.
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:
Individuals > 254 mm total length were considered adults (PFMC, 1999). Subadults ranged in size from 254 – 40 mm total length. Longspine thornyheads are deep water fishes, with adults preferring deeper waters (690-1300+ m) than subadults (650-1230 m). Preferred depth for adults may extend beyond 1300 m (Jacobsen and Vetter, 1996; Wakefield and Smith, 1990); however, SI’s for depths > 1300 m could not be calculated. Mud and sand were clearly the preferred substrate for adults and subadults. Mapped HSI results were similar for adults and subadults with highest suitability occurring over mud and sand substrates within deep slope waters. These areas correspond to the outer edges of Cordell Bank and Gulf of the Farallones sanctuaries and large areas of Monterey Bay sanctuary. Due to depths beyond 1300 m, no data were available for a large area within Monterey’s sanctuary and smaller portions of Cordell and Gulf of the Farallones sanctuaries; however, areas to 1800 m could be suitable habitat (Barss, 1989). Within the study area, approximately 17-19% of the available habitat was predicted highly suitable for adults and subadults. Smaller proportions of habitat (6%) were predicted to be moderately suitable for both life stages. The extent of highly suitable habitat was similar for adults and subadults within each sanctuary: Cordell – 12%, Gulf of the Farallones – 10%, and Monterey – 24%. Most of the area within Cordell and Gulf of the Farallones sanctuaries was predicted to be unsuitable, while a smaller proportion of Monterey’s sanctuary was predicted unsuitable. Large areas of potentially high habitat suitability for adults and subadults were located in the southern portion of the study area (south of Monterey Bay sanctuary) and a more limited distribution north of Cordell Bank sanctuary. These areas comprise a significant amount of area (approximately 900 km2).

NMFS trawl data was used to assess model performance. Results indicate a strong positive relationship with mean abundance and predicted HSI values.