- If fisheries managers are to effectively manage commercially exploited fish populations, a basic understanding of the factors that influence fish distribution and abundance is required. In 2005, efforts to identify Essential Fish Habitat (EFH) for the 82 groundfish species managed by the Pacific Fishery Management Council along the West Coast resulted in the entire continental margin being designated as EFH. Clearly, our knowledge of EFH needs to be refined, which can be accomplished by gaining insight into how environmental variables shape the distribution of managed species.
Habitat is commonly used to describe a set of environmental variables that are thought to influence occupancy. The aim of this thesis research is to detect and analyze the quantitative relationships between canary rockfish (Sebastes pinniger) presence/absence data, their spatial distribution, and various biotic and abiotic factors. The presence of canary rockfish at various locations was correlated against co-located environmental variables including bottom depths, temperatures, locations (latitude and longitude), seafloor substrate types, canary rockfish hotspots, and the presence/absence of other groundfish and invertebrate species. The statistical analysis was conducted using the generalized additive model (GAM), which is a nonparametric regression technique very well suited to model nonlinear speciesenvironment interactions. The GAM analysis was conducted using information collected from four different data sources. Data collected by the Alaska Fisheries Science Center (AFSC) from 1986 to 2001 provided information at distinct locations and times on the presence/absence of canary rockfish and other groundfish and invertebrate species, and associated depths and temperatures. Seafloor lithology maps for Oregon and Washington and 100-meter gridded bathymetric data, obtained from the Active Tectonics and Seafloor Mapping Lab at Oregon State University, provided information on the physical characteristics of the seafloor. These data were used in conjunction with the AFSC bottom trawl survey data to investigate the relationships between substrate type, slope and rugosity, and the presence of canary rockfish. Finally, locations of canary rockfish hotspots, or areas with high canary rockfish catch, were identified from Oregon commercial trawl logbook data (1995-2001) and provided information on distinct areas where the trawl fishing fleet had successfully caught canary rockfish in the past.
Canary rockfish presence in trawl survey tows was associated with specific locations and ranges of bathymetry, temperatures, and substrate types, as well as proximity to canary rockfish hotspots, and particular fish and invertebrate communities. Survey year had a strong effect on the presence of canary rockfish, as did location (latitude and longitude) and depth. The geographic location of a survey tow had a negative effect on the presence of canary rockfish in the nearshore region, and a positive effect the further the location was from the coastline, with canary rockfish presence being highest off the Washington coast between 47.5°N and 48.5°N. While canary rockfish were found at depths between 57 m and 307 m in the survey, the majority of the tows with canary rockfish catch, over 90%, occurred between the depths of 57 m and 199 m. Though temperature did not have a significant effect on canary rockfish presence in the GAM, canary rockfish were associated with specific temperature ranges, only being caught at temperatures between 6.2°C and 9.0°C in the survey. Over 89% of the tows with canary rockfish catch occurred between 6.2°C and 7.9°C. Since temperature and bottom depth of the trawl survey tows were highly correlated, it was difficult to determine which variable was the causative factor in determining the probability of a canary rockfish being present. Canary rockfish presence was higher in survey tows made closer to canary rockfish hotspots, as well as hard bottom types. Finally, the presence of lingcod, yellowtail, silvergray, or redstripe rockfish in a survey tow increased the likelihood of canary rockfish being present, as did the presence of basketstars and corals.
By studying the relationships between species and their environment, we can begin to understand the relative importance of how environmental variables shape the distribution of managed species. For ecosystem-based management strategies to be successful, the functional relationships between organisms and their habitat must be understood. The predictive model developed in this study can be used to identify areas off Oregon and Washington where canary rockfish are likely to be found in relation to various habitat factors, and can potentially be used to delineate areas that should be sampled in future surveys of canary rockfish. Additionally, this research will help to improve our understanding of the factors that influence canary rockfish distribution, which may produce a more realistic definition of canary rockfish habitat, and improve assessment. This study specifically focuses on canary rockfish, because this species currently constrains many West Coast fisheries for groundfish, however, the methods outlined here could be applied more generally to other species of interest.