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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 ...
Citation Citation
- Title:
- Identifying habitat factors for canary rockfish (Sebastes pinniger) off Washington and Oregon using environmental data and trawl logbooks
- Author:
- Vestfals, Cathleen D.
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.
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2. [Article] The Responses of Slope-spawning Flatfish to Environmental Variability in the Eastern Bering Sea
When adult spawning and juvenile settling locations of marine fishes are geographically separated, their early life history stages must rely on transport and their own behavior to move them toward suitable ...Citation Citation
- Title:
- The Responses of Slope-spawning Flatfish to Environmental Variability in the Eastern Bering Sea
- Author:
- Vestfals, Cathleen D.
When adult spawning and juvenile settling locations of marine fishes are geographically separated, their early life history stages must rely on transport and their own behavior to move them toward suitable habitats for successful recruitment to the juvenile phase. Variations in climate may reduce the availability of spawning and juvenile nursery habitats and alter ocean circulation patterns, which can disrupt dispersal pathways and affect life cycle closure. This research focused on two commercially- and ecologically-important flatfish species in the eastern Bering Sea (EBS), Greenland halibut (Reinhardtius hippoglossoides) and Pacific halibut (Hippoglossus stenolepis), which may be especially sensitive to climate variability due to strong seasonally and ontogenetically variable distributions and extended pelagic larval phases. Data from fishery-dependent and fishery-independent sources were analyzed to determine the influence of environmental variability on adult habitat use, thus gaining a uniquely comprehensive range of seasonal and geographic coverage of each species' distribution. Transport along and across the Bering Slope was characterized from 23 years (1982 - 2004) of simulations from a Regional Ocean Modeling System (ROMS) ocean circulation model, with the expectation that changes in the strength and position of the Bering Slope Current (BSC) would affect recruitment, and that circulation features along and across the shelf edge would be strongly influenced by atmospheric forcing. To understand the physical mechanisms of larval delivery to shelf nursery areas, Greenland and Pacific halibut dispersal pathways were simulated from their source (e.g., spawning areas over the continental slope) to settlement locations (e.g., juvenile nursery areas on the continental shelf) using DisMELS (Dispersal Model for Early Life Stages), an individual-based particle-tracking model. Spatial patterns of dispersal were characterized for each species and for years with contrasting settlement success to understand the influence of local oceanographic and atmospheric conditions on dispersal corridor use. Adult Greenland and Pacific halibut exhibited strong and contrasting responses to changes in temperature on the shelf, with catches decreasing and increasing, respectively, at approximately 1°C. The effect of temperature was not as prominent along the slope, suggesting that slope habitats may provide some insulation from shelf-associated environmental variability, particularly for Greenland halibut. With warming, Greenland halibut exhibited more of a bathymetric shift in distribution, while the shift was more latitudinal for Pacific halibut. Habitat partitioning may, in part, explain differences in Greenland and Pacific halibut adult distributions. Analysis of modeled circulation revealed strong variations in the strength and position of the BSC, with changes in along-shelf and cross-shelf flow associated with changes in recruitment. Greenland halibut benefitted from decreased along-shelf and on-shelf flow, while Pacific halibut benefitted from on-shelf flows through Bering and Pribilof canyons. Variability in transport and the BSC position was strongly influenced by winds, ice cover, and large-scale climatic drivers. Greenland and Pacific halibut dispersal pathways varied between years, with distinct differences in dispersal characteristics found between the two species. In general, Greenland halibut connected to shelf nursery areas via more northern corridors, while Pacific halibut connected through more southern ones. In years with poor settlement success, the reverse pattern was observed. Greenland halibut dispersal metrics were strongly correlated with along- and cross-shelf transport, as well as NW along-shelf winds and ice, while Pacific halibut had strong associations with SW onshelf winds. Spawning time and location, along with climate-induced changes in circulation, appear to differentially affect Greenland and Pacific halibut dispersal pathways, which can lead to variations in their recruitment. Overall, Greenland and Pacific halibut had contrasting responses to similar environmental forcing, and predicted climate change is expected to impact these species in different ways. With increasing warming on the EBS shelf, they will likely further partition their habitats, with Greenland halibut finding colder refuges along the slope and Pacific halibut inhabiting larger portions of the shelf. Climate-induced changes in circulation were found to affect the transport of halibut eggs and larvae and their recruitment to the juvenile phase, which suggests an important role in their slope-shelf connectivity. Results of this study suggest that Greenland and Pacific halibut use different mechanisms to move from their spawning locations along the slope to their settlement areas on the shelf, and that environmental conditions that increase slope-shelf connectivity for one species will likely result in reduced connectivity for the other. This research improves our understanding of how slopespawning flatfish respond to a changing ocean environment, which is important for effective management of their populations, as predicted climate change will likely alter their habitat use and population dynamics.