Graduate Thesis Or Dissertation

Change in Oregon’s Nearshore Groundfish Trawl Fishery: Perspectives from Science and Industry Data

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  • The commercial groundfish fishing industry and groundfish research have a long concurrent history of activity on the Oregon continental margin. Within the non-whiting groundfish fishery, the target species are primarily flatfishes, sablefish, lingcod, and rockfishes, though landings of each have fluctuated over time. Recent work shows that over the past two decades, fishing effort has shifted offshore likely due to implementation of gear regulations, area closures, and lower catch limits. Although federal fishery-independent surveys have been conducted across most of the groundfish fishery’s depth range, data is limited by years and seasons surveyed as well as absence of data in the shallowest waters (< 55 m). Fishery-dependent data covers those shallow waters and a broader temporal range, but at a coarse scale. Limitations in data coverage combined with a historical focus on deep-water groundfishes has led to a gap in understanding of dynamics within the nearshore fishery, particularly regarding the influence of environmental factors on abundance and distribution. Through this thesis, I analyzed changes in spatiotemporal dynamics of the Oregon nearshore non-whiting groundfish trawl fishery and assessed gaps in each data source over the past four decades. Statistical modeling was used to elucidate distribution shifts in species as well as temporal changes in community composition. These analyses revealed how individual species’ distributions have geographically shifted over time, what environmental variables affect their spatial distribution, and how depth and habitat type strongly influence nearshore community composition. I found that physical shelf structure drives the distribution of certain groundfish assemblages in that there are separate groups associated with different habitat types and depth zones. Individual species had strong depth preferences grouped in either shallow (< 80 m, e.g., starry flounder and sand sole), midshelf (e.g., petrale sole and lingcod), or deep (> 120 m, e.g., Sebastes spp.) clusters, which explains the importance of bathymetry in groundfish assemblage composition. The large-scale climate indices tested did not explain the variability in either individual species abundance or assemblages, while temperature and depth drove abundance for most groundfish populations. It is clear from the results of this study that there have been spatiotemporal changes in the nearshore groundfish populations and assemblages during the past four decades, and that temperature is influential for some species distributions. Portions of the shelf that have experienced anomalous hypoxic events over the last two decades exhibit reductions in presence of hypoxia-intolerant species (e.g., petrale sole and lingcod), while shallow-water species that tolerate warmer water as well as low dissolved oxygen concentrations (e.g., English sole and Pacific sanddab) exhibit shoreward compressed distributions. Visualization of both fishery-independent and -dependent data allowed for a qualitative comparison of data coverage as well as an assessment of differences in species distribution when mapping each dataset. I found that the earliest years of the NOAA surveys (1980 – 1998) have the most information gaps and had the highest potential to benefit from complementary use of fishery-dependent data for spatial and temporal analyses. This was largely due to (1) triennial rather than annual sampling and a transect-based design in the NOAA surveys, and (2) the larger spatial and temporal coverage of logbook data (inshore and latitudinal) during that period. Commonly caught species (e.g., Dover sole and petrale sole) had better spatial sampling coverage of their populations compared to species that live in shallow water and are less frequently targeted (e.g., starry flounder and sand sole). These analyses illuminate where knowledge gaps lie in both data types and how they complement one another, providing more context for future management of nearshore groundfishes.
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