Graduate Thesis Or Dissertation


Integration of oceanographic information off the Washington and Oregon coasts into west coast groundfish ecology and fisheries management Public Deposited

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  • 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.
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