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Rhode Island

Saltwater Fishing

Who is Coming and Going?

New State Efforts to Study Fish Movement Ecology in Rhode Island

By Conor McManus, Chris Parkins, Eric Schneider (RIDEM DMF) Jon Dodd (Atlantic Shark Institute)
Many of Rhode Island’s top recreational fish make seasonal migrations each year. Some species travel short distances, like tautog, whereas others undergo coastwide migrations each year, like striped bass. These migrations are often tied directly to a species’ spawning and feeding needs, and allow them to complete their life cycle. However, these seasonal timing and patterns of movements are often controlled by environmental drivers. Thus, long-term monitoring is paramount to understanding how the timing of seasonal arrival or departure of species to and from Rhode Island will change in response to or vary with the environment. Understanding long-term or interannual changes in the residence time for these species is important to both resource managers and anglers. Managers can use this information to make more informed decisions regarding how species are responding to environmental changes and select optimal recreational management strategies and seasons. Anglers benefit from understanding where and when a species is most available to harvest in Rhode Island waters, and like resource managers, what is influencing movement patterns. Historically, scientific studies have used trawl or other traditional fishery-independent surveys to describe species’ migrations. However, these gears do not necessarily document patterns well for demersal-structured or pelagic fish, of which many recreational species are. Acoustic telemetry has emerged as a powerful tool to monitor species’ movements. By deploying receivers that “listen” for fish tagged with an acoustic transmitter, scientists and managers can follow the movement patterns of individual fish to provide guidance on when and where fish either hang out or pass through. Researchers and management agencies along the entire East Coast are currently using the same acoustic telemetry and data sharing systems, allowing researchers to track fish over large distances and multiple years. In 2019, the Rhode Island Department of Environmental Management’s Division of Marine Fisheries (DMF) in partnership with the University of Rhode Island Department of Ocean Engineering (URI) and the Atlantic Shark Institute (ASI) established acoustic receiver arrays. Arrays consist of buoy locations throughout Rhode Island waters that are equipped with the receivers to detect fish that have been acoustically tagged by researchers up and down the U.S. east coast. As of 2020, the teams deployed 19 receivers in Rhode Island state waters, listening for tagged fish anywhere from Watch Hill to Block Island, and the Sakonnet River (Figure 1).

Figure 1. 2020 acoustic receiver locations within Rhode Island state waters.

The RI DEM acoustic receivers are deployed with a setup modeled after the design used by MA Division of Marine Fisheries (Figure 2). The setup consists of a surface buoy attached to an up and down line that is anchored to the bottom using a 100 lb. I-beam. There is a length of ground line that runs away from the I-beam and has an anchor on the end that prevents the drifting of the receiver in heavy current or rough seas. The receiver is located ~10feet off the bottom on the up and down line. The receiver is attached using a short length of line with a trawl float to keep the receiver vertically oriented in the water column. This design allows for easy deployment and retrieval using a variety of vessels as well as allowing for regular maintenance by divers.

Figure 2. Diagram of a typical receiver setup used by RI DEM and URI.

The arrays were established to understand the movement ecology of Atlantic sturgeon and shark species utilizing Rhode Island waters, but the technology allows for the monitoring of any species tagged with acoustic transmitters. To date, the receivers have detected a variety of species, including sand tiger sharks, river herring, Atlantic sturgeon, and skates. By far the most common species detected from these receivers is striped bass, which several researchers from universities and government agencies have tagged over the last ten years. By looking at receiver detections of species like striped bass that were tagged by our partners and other researchers, we can begin to obtain quantifiable information on when these species typically show up in Rhode Island. An example of this can be seen from striped bass tagged in Massachusetts (MA), as part of the MA Division of Marine Fisheries tagging program, and detected by arrays in Rhode Island. These tagged fish can reveal a true description of striped bass seasonality, including arrival and departure in Rhode Island waters (Figure 3).

Figure 3. Individual striped bass, as indicated by their unique ID code on the y-axis, that were originally tagged in Massachusetts state waters by MA DMF and later moved through Rhode Island state waters. Detections are presented for both 2019 and 2020. Individual dots represent a detection from one of the Rhode Island receivers. The plots show the seasonal movement patterns of striped bass, and whether we see the same fish over multiple years.

DMF hopes to use such data, as well as develop new tagging projects to better answer ecological questions for Rhode Island species in the future, from striped bass to tautog and winter flounder, and some coastal shark species. In 2021, the partners will be expanding the array with at least 8 new locations throughout Rhode Island state waters. For more questions on the array or to learn how to get involved in this work, please contact Conor McManus. The DMF receiver array was supported by the U.S. Fish and Wildlife State Wildlife Grant Program. You can learn more about the Atlantic Shark Institute at atlanticsharkinstitute.org.