Analyses/Maps

Fish

Potential Areas of Habitat Importance

About these maps:
These maps display the results of two approaches that provide a synoptic view of overall habitat importance based on all the HSI models developed for the study area. Areas of potential habitat importance was first defined as an average view of habitat suitability across species and life stages. Secondly, individual maps of highly suitable habitats were overlain and areas or regions with the most overlap were considered important habitat or hot spots.

Data Sources:
See Individual HSI model results - CD ROM

Methods:
Mean HSI: HSI maps for all fish species and life stages were overlain and averaged by grid cell to evaluate overall suitability. Results were scaled in the same manner as individual HSI model results: Highest suitability (10-8), moderate (7-5), low (4-2), lowest (1) and unsuitable (0).

Cumulative Suitability: Frequency of occurrence of predicted HSI values for each fish species life stage were calculated and values greater than one standard deviation above the mean were chosen to represent highest suitability. New individual maps were created and grid cells were reclassified as highest suitability (1) or other (0). All maps were overlain and summed to create a map of suitability overlap within the study area. These areas represent potential groundfish hot spots.

Results and Discussion:
The techniques described above are two possible approaches to estimate potential hot spots or areas of habitat importance. Composite maps displaying these areas were developed using all fish HSI model results to simulate the groundfish management strategy employed by NMFS, where all groundfish (83 species) are managed under one Fishery Management Plan. Mean HSI values across all 32 fish species and life stages yield no areas ranked as highly suitable (HSI values 10-8). Moderate suitability (7-5) occurs over the majority of the shelf region (to approximately 200 m) throughout the study area, most notably in the northern portion, where the shelf extends significantly farther offshore than in the southern portion. The majority of the area north of Monterey canyon consists of moderate suitability (to approximately 200 m), with low suitability extending through the deeper slope habitat. Smaller localized areas of low suitability exist within the shelf and represent areas of hard substrate. South of the Monterey canyon, low suitability comprises most of the study area, with a narrow zone of moderate suitability along the shallower shelf waters. Suitability drops from moderate to low just beyond the shelf edge throughout the study area.

Throughout the study area, maximum overlap of cumulative high suitability occurs on the shelf edge over soft sediments which closely contour the 100 m isobath. Approximately half of the models overlap in this zone. The top two quantiles encompass most of the shelf region and the zones of overlap are much broader in the northern portion of the study area compared to the southern.

These analyses reveal patterns of suitability related to depth and substrate. Highest suitability occurs on the continental shelf, over soft sediments, based on the two analytical approaches using the 33 HSI maps. These areas could be considered as habitats of importance that support fish abundance and diversity. Both methods portray highest suitability over the shelf that decline beyond the shelf edge. This pattern conforms to literature sources which state that the shelf, and more importantly the shelf break, are important areas for fish abundance and diversity (Yoklavich et al., 2000; Williams and Ralston, 2002). In addition, soft sediments are potentially more suitable than hard bottom throughout the study area. It is important to note that the results of these analyses are based on 19 species and are only a subset of the many groundfish species that occur within the study area. These results are clearly biased based on the species modeled and may not provide adequate representation of groundfish as a whole within the study area. Most of the species modeled have substrate affinities for soft sediments, and most exhibit depth preferences that fall within the shelf region. Ideally, many more models should be developed for additional species and analyzed to provide a more representative depiction of groundfish distribution within the study area.