Analyses/Maps

Fish

Pacific whiting (hake) HSI map: Potential Distribution

About these maps:
These maps display HSI model results for subadult (left) and adult (right) hake 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: Clemens and Wilby, 1961; Alverson et al., 1964; Ermakov and Polutov, 1967; Dark et al., 1980; Inada, 1983; Nelson and Dark, 1985; NOAA, 1990; Dorn et al., 1994; Love, 1996; Allen and Smith, 1988; Nero et al., 1998; Wilkins et al., 1998; and Lauth, 2001.
Substrate SI: Yoklavich et al., 2000.
Validation: Wilkins et al., 1998 and Turk et al., 2001.
Life stage information: PFMC, 1999.

Methods:
Bathymetry SI values for adults were developed using the literature review method, whereas 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:
Lifestage information from PFMC, 1999, was used to delineate sizes of adults from subadults. Females > 300 mm and males > 280 mm total length were considered adults. Subadults ranged in size to 40 mm total length. Although adequate trawl data were available for adult hake SI considerable difficulty was experienced in developing SI values. Consequently, adult SI values for depth were based on ranges reported in the literature. Highest suitability occurred within 50 – 650 m and moderate suitability extended to 900 m. Depths greater than 1300 were considered unsuitable. NMFS trawl data were used to develop depth SI’s for subadults and preferred depths were predicted to occur within 50 – 330 m. Moderate suitability occurred to 430 m and low suitability was observed to 489 m. Depths greater than 490 m were unsuitable for subadults. Information regarding substrate affinities for hake were scarce, with most sources stating that hake were predominantly pelagic. Yoklavich et al., 2000, noted that hake occurred over soft substrates and since hake were abundant in NMFS trawls, mud and sand substrates were chosen to be the preferred substrate for adults and subadults. No information was revealed to define affinity for hard substrates so it was assumed that hake exhibited a moderate affinity for rocky substrates. As such, model results display a ubiquitous distribution of potentially high suitability for adults throughout the study area. Approximately 30% of the study area was predicted to be potentially high for suitability. Large areas within each sanctuary were predicted highly suitable: Cordell Bank – 74%; Gulf of the Farallones – 61%; and, Monterey – 38%. Large areas of high suitability (approximately 8,865 km2) were located outside sanctuary boundaries. Moderate suitability was observed over hard substrates and over soft substrates at depths > 650 m. High suitability for subadults was less extensive than that of adults; however, similar proportions of habitat within sanctuary boundaries. Overall, 20% of the study area was predicted to contain habitats of potential high suitability.

NMFS trawl data were used to assess model performance. Both adult and subadult models exhibited positive correlations between mean abundance and predicted HSI value. Additional attempts to refine the model are recommended. Additional analysis of NMFS trawl data should be conducted to better define depth preferences. In addition, a better understanding of habitat preference is needed to improve model accuracy.