Analyses/Maps

Fish

Shortspine thornyhead HSI map: Potential Distribution

About these maps:
These maps display HSI model results for subadult (left) and adult (right) shortspine 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: Cross, 1987; Wakefield and Smith, 1990; Jacobsen and Vetter, 1996; 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:
Length at maturity information (PFMC, 1999) was used to distinguish life stages for shortspine thornyheads. Adults were considered > 229 mm total length, while subadults ranged in size from 254 to 40 mm total length. Optimal depths for subadults were predicted to occur at shallower depths (310-649 m) than for adults (450-1149 m). Depths ranging from 50-129 m were unsuitable for adults, and 50-149 m for subadults. Also, depths greater than 809 m were predicted unsuitable for subadults. Suitability was moderate for adults up to 1300 m and may extend to depths of 1400 m (Jacobsen and Vetter, 1996). Substrate preference was identical for both life stages, and occurred over mud substrates, with slightly less preference for sand. Rocky substrates were infrequently utilized by both life stages. Model results for adults displayed high suitability areas in the deeper portions of the sanctuaries, with moderate suitability extending shoreward to the shelf break. The shelf area was predicted to be unsuitable for adults. Highly suitable habitat comprised 25% of the study area, while smaller proportions were predicted highly suitable within Cordell Bank (16%) and Gulf of the Farallones (11%) sanctuaries. A large proprotion of adult and subadult potentially suitable habitats were located in the southernmost portion of the study area, below the southern boundary of Monterey Bay’s sanctuary.

NMFS trawl data were used to assess model performance. Results display a strong positive correlation between mean abundance and predicted HSI value.