Structure, Drivers, and Trophic Interactions of the Demersal Fish Community in Chesapeake Bay

Management of fisheries resources is increasingly broadening its scope from single-species approaches to more holistic, ecosystem-based approaches that account for interactions of fish with a variety of ecological factors, such as predators, prey, and habitat. This ecosystem based fisheries management (EBFM) approach requires thorough biological and ecological understanding of systems pertaining to community structure, habitat suitability, and food web interactions. to strengthen the ecological underpinnings of EBFM efforts in Chesapeake Bay, the largest estuary in the USA, I conducted synoptic analyses examining the structure, function, and patterns of the bay\u27s demersal fish community. This research relied on I0 years of data from a multi-species, bimonthly bottom trawl survey of the Chesapeake Bay mainstem. The unifying objectives of this work were to 1) synthesize basic biological and ecological information of many Chesapeake Bay fishes, and 2) examine the environmental drivers of community structure and trophic interactions in the Bay. One major hypothesis underlying the more detailed research objectives for each component was that bay-wide patterns in biomass and feeding habits of Chesapeake Bay fishes were mostly driven through bottom-up processes governed by a blend of small- and large-scale environmental factors. as food web structure and trophic interactions are governed by the presence, distribution, abundance, and behavior of species, Chapter 1 focused on evaluating patterns for these basic biological characteristics for a large suite of 50 species and investigating environmental factors that influence the community trends. Univariate and multivariate statistical modeling revealed that the demersal fish community (dominated by five species) was strongly structured along a salinity gradient, and other factors (e.g. dissolved oxygen, temperature, month, and year) helped regulate biomass and diversity trends. Chapter 2 synthesized diet information for 47 fish species, demonstrated the role of five prey groups (mysids, fishes, bivalves, polychaete worms, and crustaceans) in differentiating feeding guilds, and highlighted the importance of non-pelagic prey groups (especially the hyper-benthic mysids) in supporting the nutritional needs of fishes. Diets of 12 predator species were investigated in more detail in Chapter 3 to infer the dynamics of four important prey groups (mysids, bay anchovy, polychaetes, and bivalves) using advanced statistical modeling techniques. Results revealed generally coherent consumption trends across predators for a given prey, suggestive of prey availability driving consumptive patterns. Synchronous annual peaks in prey consumption were indicative of pulses in prey production (particularly mysids and bivalves) that were exploited by predator populations. to evaluate the population-scale effects of these bottom-up alterations in prey productivity, Chapter 4 relied on a simulation model to examine the potential effects that these annual changes in prey availability could have on consumption and production of one representative predator species. The model indicated that enhanced individual growth resulting from pulses in prey production could generate substantial gains in predator spawning stock biomass, recruitment, and fishery yield. However, the bottom-up effects on predator production had only modest effects on rebuilding times of a depleted population relative to controls on fishing mortality. This research represents one of the largest studies on community structure and trophic interactions for demersal fishes in an estuarine environment, contributing to a broader understanding of fish ecology within a complex and dynamic system. By filling research gaps identified for EBFM in Chesapeake Bay, this body of work also supports a more holistic management approach for the sustainable use of resources from the Chesapeake Bay and coastal waters of the Northwest Atlantic Ocean

Regional variation in the annual feeding cycle of juvenile walleye pollock (Theragra chalcogramma) in the western Gulf of Alaska

Juvenile fish in temperate coastal oceans exhibit an annual cycle of feeding, and within this cycle, poor wintertime feeding can reduce body growth, condition, and perhaps survival, especially in food-poor areas. We examined the stomach contents of juvenile walleye pollock (Theragra chalcogramma) to explain previously observed seasonal and regional variation in juvenile body condition. Juvenile walleye pollock (1732 fish, 37–250 mm standard length) of the 2000 year class were collected from three regions in the Gulf of Alaska (Kodiak, Semidi, and Shumagin) representing an area of the continental shelf of ca. 100,000 km2 during four seasons (August 2000 to September 2001). Mean stomach content weight (SCW, 0.72% somatic body weight) decreased with fish body length except from winter to summer 2001. Euphausiids composed 61% of SCW and were the main determinant of seasonal change in the diets of fish in the Kodiak and Semidi regions. Before and during winter, SCW and the euphausiid dietary component were highest in the Kodiak region. Bioenergetics modeling indicated a relatively high growth rate for Kodiak juveniles during winter (0.33 mm standard length/d). After winter, Shumagin juveniles had relatively high SCW and, unlike the Kodiak and Semidi juveniles, exhibited no reduction in the euphausiid dietary component. These patterns explain previous seasonal and regional differences in body condition. We hypothesize that high-quality feeding locations (and perhaps nursery areas) shift seasonally in response to the availability of euphausii

Combining Ecosystem and Single-Species Modeling to Provide Ecosystem-Based Fisheries Management Advice Within Current Management Systems.

Although many countries have formally committed to Ecosystem-Based Fisheries Management (EBFM), actual progress toward these goals has been slow. This paper presents two independent case studies that have combined strategic advice from ecosystem modeling with the tactical advice of single-species assessment models to provide practical ecosystem-based management advice. With this approach, stock status, reference points, and initial target F are computed from a single-species model, then an ecosystem model rescales the target F according to ecosystem indicators without crossing pre-calculated single-species precautionary limits. Finally, the single-species model computes the quota advice from the rescaled target F, termed here Feco. Such a methodology incorporates both the detailed population reconstructions of the single-species model and the broader ecosystem perspective from ecosystem-based modeling, and fits into existing management schemes. The advocated method has arisen from independent work on EBFM in two international fisheries management systems: (1) Atlantic menhaden in the United States and (2) the multi species fisheries of the Irish Sea, in the Celtic Seas ecoregion. In the Atlantic menhaden example, the objective was to develop ecological reference points (ERPs) that account for the effect of menhaden harvest on predator populations and the tradeoffs associated with forage fish management. In the Irish Sea, the objective was to account for ecosystem variability when setting quotas for the individual target species. These two exercises were aimed at different management needs, but both arrived at a process of adjusting the target F used within the current single-species management. Although the approach has limitations, it represents a practical step toward EBFM, which can be adapted to a range of ecosystem objectives and applied within current management systems.publishedVersio

Dimensions of biodiversity in Chesapeake Bay demersal fishes: patterns and drivers through space and time

Biodiversity has typically been described in terms of species richness and composition, but theory and growing empirical evidence indicate that the diversity of functional traits, the breadth of evolutionary relationships, and the equitability with which individuals or biomass are distributed among species better characterize patterns and processes within ecosystems. Yet, the advantages of including such data come at the expense of measuring traits, sequencing genes, and counting or weighing individuals, and it remains unclear whether this greater resolution yields substantial benefits in describing diversity. We summarized a decade of high-resolution trawl data from a bimonthly trawl survey to investigate spatial and seasonal patterns of demersal fish diversity in the Chesapeake Bay, USA, with the goal of identifying areas and times of mismatch between different dimensions of diversity, and their response to environmental forcing. We found moderate to strong positive relationships among all metrics of diversity, and that functional and phylogenetic differences were well-reflected in an index derived from taxonomic (Linnaean) hierarchy. Compared with species richness and species diversity, functional, phylogenetic, and taxonomic indices peaked later in the year, which was a consequence of the distribution of biomass among functionally and evolutionarily divergent species. Generalized additive models revealed that spatial, temporal, and environmental variables explained roughly similar proportions of deviance across all aspects of diversity, suggesting that these three factors do not differentially affect the functional and phylogenetic aspects of community structure. We conclude that an index of diversity derived from taxonomic hierarchy served well as a practical surrogate for functional and phylogenetic diversity of the demersal fish community in this system. We also emphasize the importance of evenness in understanding diversity patterns, especially since most ecological communities in nature are dominated by one or few species

Combining Ecosystem and Single-Species Modeling to Provide Ecosystem-Based Fisheries Management Advice Within Current Management Systems

Pubication history: Accepted - 7 December 2020; Published online - 8 January 2021Although many countries have formally committed to Ecosystem-Based Fisheries Management (EBFM), actual progress toward these goals has been slow. This paper presents two independent case studies that have combined strategic advice from ecosystem modeling with the tactical advice of single-species assessment models to provide practical ecosystem-based management advice. With this approach, stock status, reference points, and initial target F are computed from a single-species model, then an ecosystem model rescales the target F according to ecosystem indicators without crossing pre-calculated single-species precautionary limits. Finally, the single-species model computes the quota advice from the rescaled target F, termed here Feco. Such a methodology incorporates both the detailed population reconstructions of the single-species model and the broader ecosystem perspective from ecosystem-based modeling, and fits into existing management schemes. The advocated method has arisen from independent work on EBFM in two international fisheries management systems: (1) Atlantic menhaden in the United States and (2) the multi species fisheries of the Irish Sea, in the Celtic Seas ecoregion. In the Atlantic menhaden example, the objective was to develop ecological reference points (ERPs) that account for the effect of menhaden harvest on predator populations and the tradeoffs associated with forage fish management. In the Irish Sea, the objective was to account for ecosystem variability when setting quotas for the individual target species. These two exercises were aimed at different management needs, but both arrived at a process of adjusting the target F used within the current single-species management. Although the approach has limitations, it represents a practical step toward EBFM, which can be adapted to a range of ecosystem objectives and applied within current management systems.The Atlantic menhaden work was supported by National Oceanic and Atmospheric Administration Award No. NA15NMF4740069 and Lenfest Ocean Program grants nos. 00025536 and 00032187, and thanks all of the members of the ASMFC Menhaden Technical Committee and the ERP WG for their critical contributions to model development and helpful discussions. We acknowledge the members of the ICES Benchmark Workshop WKIrish for their participation and collaboration, and the NWWAC and BIM for facilitating the meetings. The EwE modeling work was carried out with the support of the Marine Institute and funded under the Marine Research Sub-programme by the Irish Government (Grant-Aid Agreement No. CF/16/08). DP was supported by the Science Foundation Ireland (www.sfi.ie) Investigator Programme (grant no. 14/IA/2549), and DR by Project FishKOSM funded by the Department of Agriculture, Food and the Marine’s Competitive Research Funding programmes. DH acknowledges support from the Institute of Marine Research strategic project Reduced Uncertainty in Stock Assessment (REDUS). Open access funding was provided by the Institute of Marine Research, Norway

Place-Based Learning Communities on a Rural Campus: Turning Challenges into Assets

At Humboldt State University (HSU), location is everything. Students are as drawn to our spectacular natural setting as they are to the unique majors in the natural resource sciences that the university has to offer. However, the isolation that nurtures the pristine natural beauty of the area presents a difficult reality for students who are accustomed to more densely populated environments. With the large majority of our incoming students coming from distant cities, we set out to cultivate a “home away from home” by connecting first-year students majoring in science, technology, engineering and math (STEM) to the communities and local environment of Humboldt County. To achieve this, we designed first-year place-based learning communities (PBLCs) that integrate unique aspects and interdisciplinary themes of our location throughout multiple high impact practices, including a summer experience, blocked-enrolled courses, and a first-year experience course entitled Science 100: Becoming a STEM Professional in the 21st Century. Native American culture, traditional ways of knowing, and contemporary issues faced by tribal communities are central features of our place-based curriculum because HSU is located on the ancestral land of the Wiyot people and the university services nine federally recognized American Indian tribes. Our intention is that by providing a cross-cultural, validating environment, students will: feel and be better supported in their academic pursuits; cultivate values of personal, professional and social responsibility; and increase the likelihood that they will complete their HSU degree. As we complete the fourth year of implementation, we aim to harness our experience and reflection to improve our programming and enable promising early results to be sustained

Stable Isotope Dynamics in Summer Flounder Tissues, with Application to Dietary Assessments in Chesapeake Bay

The print version is considered the official and archival copy of this dissertation or thesis. Researchers are encouraged to consult the archival copy of this dissertation or thesis when citing this work

Dynamic trophic linkages in a large estuarine system – support for supply-driven dietary changes using delta generalized additive mixed models

Trophic dynamics within aquatic systems are a predominant regulator of fish production and an important consideration for implementing ecosystem approaches to fisheries management. We analyzed ten years of fish diet data from Chesapeake Bay, USA to 1) evaluate the effects of environmental variables on trophic interactions of 12 common predatory fishes, 2) infer dynamics of four key prey groups (mysids, bay anchovy, bivalves, and polychaetes), and 3) evaluate whether interannual dietary trends were coherent among predators and regulated by prey availability. Based on delta generalized additive mixed models (delta-GAMM), predator length was the most important covariate in modeling prey consumption. When significant, latitude, temperature, and depth effects were largely similar across predators for a given prey. Annual patterns of mysid and bivalve consumption each showed a single, dramatic peak shared by multiple predators with varied feeding preferences and distributional characteristics, but annual trends were not correlated with available survey-based measures of prey availability likely due to methodological differences. Overall, the coherence in consumption patterns across predators was consistent with supply-driven dynamics controlled by regional and annual changes in prey availability. Also, the novel application of delta-GAMM to fish diet data was useful in characterizing the dynamics of poorly sampled prey groups and the trophic interactions for ubiquitous species from the Northwest Atlantic Ocean.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Ecology of small neritic fishes in the western Gulf of Alaska. II. Consumption of krill in relation to krill standing stock and the physical environment

Krill (Euphausiacea) is a patchily distributed taxon whose availability may limit neritic fishes in temperate oceans. In the western Gulf of Alaska, krill-fish aggregations were associated with high-flow areas over the shelf. We examined fish impacts on krill standing stocks in areas of different temperature, salinity, and net current velocity. Samples were collected during September 2000, 2001, and 2003 over a 48-site grid within a known walleye pollock nursery. Krill were a dietary staple of the dominant fishes: walleye pollock Theragra chalcogramma, capelin Mallotus villosus, and eulachon Thaleichthys pacificus, but their proportion in diets varied by predator species and predator length. Predators daily consumed 120 mm) walleye pollock were, on average, large compared to krill in plankton samples; therefore, standing stock sizes might have been overestimated by including small krill. A compensatory response in consumption occurred during 2001 in proximity to the Shelikof sea valley due to increased per capita predation rates and local concentration of Age-1+ walleye pollock and eulachon. High abundance of krill in 2001 was associated with high ocean current flow. No compensatory response was observed where local standing stocks were dominated by small krill. Thus, apparent bottom-up influences of ocean currents on krill abundance in neritic areas can be partly compensated by localized top-down predation from nektonic fishes having prey size preferences that match available prey sizes