Date of Award
Doctor of Philosophy in Oceanography
Jeremy S. Collie
This research was developed in response to recent interest in offshore wind energy development and the ongoing need for ecosystem-based spatial management planning in Rhode Island’s nearshore waters. Despite heavy use and close proximity to a number of marine science institutions, Rhode Island and Block Island Sounds have been neglected in terms of scientific research, resulting in a poor understanding of the fisheries ecosystem in this area. This research aimed to address this knowledge gap by assessing the biogeography, trophic dynamics and habitat associations of the fish and invertebrate communities in this region. Specifically, the goals of this research were to: 1) Evaluate the fine-scale spatial structure of the demersal fish and invertebrate community, 2) Assess the dietary guild structure and the flow of energy through the fisheries food web, and 3) Investigate the relationship between the fish community and benthic habitat.
Otter trawls and beam trawls were used to sample fish and invertebrates throughout Rhode Island and Block Island Sounds from 2009 to 2012. Fieldwork was conducted in collaboration with two commercial fishing vessels, the F/V Darana R and F/V Mister G, and the Northeast Area Monitoring and Assessment Program. During otter trawl surveys, stomach and white tissue samples were taken from 25 species for analysis of diet composition and nitrogen and carbon stable isotope signatures. A combination of site-specific water column profiles, high resolution acoustic surveys, and seafloor video surveys were used for habitat characterization.
Regionally-grouped abundance, biomass, diversity, and size spectra were used to assess spatial patterns in the aggregate fish community, and nonparametric hierarchical cluster analysis was used to determine species assemblages. Analyses revealed coherent gradients in fish community biomass, diversity and species composition extending from inshore to offshore waters, as well as patterns related to the differing bathymetry of Rhode Island and Block Island Sounds. Species assemblages were characterized by a combination of piscivores (silver hake, summer flounder), benthivores (American lobster, black sea bass, little skate, scup) and planktivores (sea scallop), and exhibited geographic patterns that were persistent from year to year, yet variable by season. Such distributions reflect the cross-shelf migration of fish and invertebrate species in the spring and fall, highlighting the importance of considering seasonal fish behavior when planning construction schedules for offshore development projects.
Stomach content analysis was used to define trophic structure according to dietary guilds, while nitrogen and carbon stable isotopes were used to determine the trophic position of fish and invertebrate species and to assess the relative importance of benthic and pelagic production in supporting the fisheries food web. Results suggest that the fisheries food chain in Rhode Island and Block Island Sounds consists of four trophic levels and six distinct dietary guilds (planktivores, benthivores, shrimp and amphipod eaters, crab eaters, small fish and shrimp eaters, piscivores). Inter-species isotopic and dietary overlap within guilds was high, suggesting that resource partitioning plays a major role in structuring the fish community in this region. Furthermore, carbon isotopes indicate that most fish are supported by pelagic phytoplankton, although there is evidence that benthic production also plays a role, particularly for obligate benthivores such as skates.
Multivariate analysis of otter and beam trawl catch data and acoustic, videographic, and oceanographic benthic habitat parameters suggest that the fish communities in Rhode Island and Block Island Sounds are structured by both permanent (i.e. depth, habitat type) and transient (i.e. bottom water temperature) habitat characteristics. As such, otter trawl and beam trawl species assemblages can be explained by a suite of seafloor and oceanographic habitat parameters, including mean depth, surface and bottom water temperature, standard deviation of benthic surface roughness, minor grain size, mean slope, and surface salinity. Furthermore, spatial patterns in diet composition indicate habitat-specific feeding by demersal fish species, such as winter flounder and silver hake. Feeding on benthic prey is, therefore, an important link between demersal fish assemblages and their habitats in this region. The results of this work not only provide valuable insight into fisheries ecosystem dynamics in a temperate nearshore environment, but will also inform spatial management plans for Rhode Island and Block Island Sounds. Furthermore, the methods for this study are consistent with European guidelines for assessing the impacts of offshore wind turbines on the marine environment and could provide a baseline for measuring the cumulative effects of offshore development projects within Rhode Island and Block Island Sounds.
Malek, Anna, "An Investigation of the Fisheries Ecosystem Dynamics in Rhode Island's Nearshore Waters" (2015). Open Access Dissertations. Paper 352.