Graduation date: 2006
To date, the use of oceanographic data in fisheries management has been limited by
the scarcity and the difficulty of accessing complete oceanographic datasets.
Consequently, fish stocks are managed with limited knowledge about the habitat where
fish live and incomplete understanding of what oceanographic conditions affect their
populations. With the long-term goal to improve science for ecosystem-based
management of the West Coast groundfish fishery, this study had three objectives.
First, the assembling and merging of disperse oceanographic datasets for temperature,
salinity, chlorophyll-a and current velocity from the 1930s to the year 2004 off the
Washington and Oregon coasts. Second, the generation of oceanographic data products
relevant for fisheries research, consisting of the computation and the plotting of
climatological monthly means, standard deviations and coefficients of variation for a
variety of ocean variables at several depths. Third, the development of an exploratory
example of how oceanographic information collected in this study can be of use to
improve the science and management of groundfish. Thus, a study was developed to
investigate if groundfish distribution and abundances are associated with any ocean
habitat or individual oceanographic variables, using a combination of univariate,
classification and ordination techniques. The fish data were derived from a routine
bottom trawl survey conducted by the National Oceanic and Atmospheric
Administration Northwest Fisheries Science Center (NOAA-NWFSC).
Five ocean habitats with distinct physical and biological characteristics were
identified off the Washington and Oregon coast: Offshore Habitat, Upwelling Habitat,
Highly Variable Upwelling Habitat, River Plume Habitat, and Highly Variable Habitat.
These ocean habitats were characteristic of cold-regime summer upwelling conditions.
Overall, the analyses suggested that the species composition differ among the five
ocean habitats. Some species were highly indicative of some habitats; however, overall
the associations were weak due to the high degree of overlap of ocean habitats in terms
of species composition. All the analyses were consistent in associating shallower
species with the shallowest habitats (the Highly Variable, River Plume and Upwelling
habitats) and the deeper species with the deeper habitats (the Offshore and the Highly
Variable Upwelling habitats), suggesting that groundfish are adapted to wide
environmental ranges. In addition, the overall abundance and diversity of groundfish
was higher in the shallower habitats. In contrast, groundfish species showed strong
associations with individual environmental factors, primarily depth, surface
chlorophyll-a, and salinity and temperature at the bottom of the seafloor, indicating that
groundfish distributions are mainly organized along depth gradients. Latitudinal
variations in upwelling intensity, river discharge and productivity along the coast were
also important factors influencing shallow species distributions and abundances. For
example, three regions with high chlorophyll-a concentrations were associated with
large abundances of specific groundfish species. These regions were found over Heceta
Bank, over the Juan de Fuca canyon and in the Columbia River Plume.
This study began with the assembly of several ocean variables and the development
of some preliminary ocean data products relevant to fisheries studies. However, the
addition of other ocean variables, such as dissolved oxygen, and the computation of
new ocean products, such as mixed-layer depth, and thermocline depth and strength,
would be valuable. Future work should involve more interdisplinary studies between
fisheries and oceanography, the integration of oceanographic information off the west
coast of the U.S., and the collection of concurrent ocean data at each fish trawl location.