The Rhode Island South Shore Coastal and Adult Winter Flounder Survey.
Since 1999 Rhode Island Division of Fish and Wildlife staff have been monitoring the population of spawning adult winter flounder in the coastal ponds of RI using a type of fixed gear called a fyke net. Fyke netting is a passive fishing method commonly used in commercial fishing but in this case an excellent tool for biological fishery sampling to assess fish populations utilizing shallow water habitats. Fyke nets have been used to catch fish for hundreds of years; originally used in Finland to harvest herring, whitefish and salmon. The net is set with a stake that is driven close to shore at low tide which is attached to a long leader, similar to the coastal fish traps encountered throughout the Rhode Island shoreline but on a smaller scale. The leader runs perpendicular to shore and is connected to the main body of the net which is comprised of a series of parlors terminating in a codend. A buoy tied to a weight is fastened to the codend for retrieval of the net, catch and to keep the net straight and on the bottom. Typically where the leader meets the opening of the net there are two smaller wings splayed out in a “V” and spread apart with either a bar or stakes. A fish swimming along the shore line will encounter the leader and be directed into the net with a small likelihood of escape. One benefit of using a fyke net to sample fish is that the gear does not result in high mortality, typically the fish are returned to the water unharmed after information is collected on size, sex and stage of maturity.
The focus of this study has been in Point Judith Pond, in Washington County, RI. Nets are tended from three to seven days depending on the size of the catch and weather conditions. Fish caught in the survey are counted, measured, sexed and their spawning stage determined. Spawning stage is defined as ripe (pre-spawn), ripe/running (active spawn), spent (post-spawn), resting (non-active spawn) and immature. When possible, healthy flounder are tagged with Peterson disc tags and returned to the water. There is a reward of a hat for fishermen who give information on location of catch and the size of the tagged fish. Water quality parameters such as temperature, salinity, and dissolved oxygen are also recorded. Abundance is measured using a relative index based on catch per unit effort, in this case net hauls.
The RIDFW fyke net survey monitors adult winter flounder returning to the coastal ponds to spawn in the winter months (December – April). Winter Flounder enter Narragansett Bay and the south shore coastal pond systems in Rhode Island to spawn in the early part of winter (November) and engage in spawning activity from January through May annually. Spawning and egg deposition takes place on sandy bottoms and algal accumulations. Winter Flounder eggs are non-buoyant and clump together on these substrates. Survey data indicate that peak-spawning activity takes place during the month of February, however this appears to vary annually in relation to average water temperatures.
Historically, winter flounder are a recreationally and commercially important species sought after in Rhode Island waters. Once abundant, locally their population has declined in recent years to all time lows. A 2011 assessment of the Southern New England stock revealed that the stock is overfished but overfishing is not occurring. What this means is that the number of adults is lower than needed to maintain a sustainable population. Fishing mortality is below a target threshold allowing the stock to rebuild. The life history of the winter flounder makes it more vulnerable to localized depletion, particularly as a result of spawning site fidelity. Tagging study recapture data has shown that winter flounders display a strong tendency to return to natal areas to spawn. On multiple occasions, tagged fish have been caught in the same net the following year from where they were first captured, thus even if the stock as a whole is rebounding some areas may not due to the lack of returning reproductive adults. Winter flounder tagged in the coastal ponds and recaptured at sea display a migration pattern moving south and to the east as they return to the ocean which has been documented by other regional studies.
The results of the survey have shown that in Point Judith Pond the adult spawning winter flounder population has been in decline since 2001 from an average 24 to 2 fish per net haul in 2012. By way of comparison data collected by our partners at the US Environmental Protection Agency from Charlestown pond have remained steady in recent years with an average of 11 fish per net haul in 2012. These results are indicative of a localized depletion of winter flounder in Point Judith pond. A companion survey which examines juvenile fish population abundance mirrors these results, Point Judith Pond young of the year winter flounder are at an all time low while young of the year in Charlestown pond are at an average level for the time series. The low population levels found in Point Judith pond have prompted management action to close the pond to all winter flounder fishing to aid in the recovery. Other factors may be contributing to the low abundance in Point Judith besides fishing pressure. Predation of adult and juveniles by cormorants, egrets and seals contribute to a natural mortality that could be keeping the population at low levels. Observations of seals in Point Judith and Charlestown ponds indicate a resident population of seals in Point Judith pond during the winter which is not found in Charlestown pond. In fact, seals are often observed swimming around the survey nets set in Point Judith pond. On occasion, the flounder trapped inside these nets will have visible injuries or damaged fins, an almost sure sign that seals are present. Aside from predation, warming water temperatures resultant of climate change may also be holding the population in check. It has been documented that young of the year winter flounder experience higher mortality during warmer winters. It is possible that the population in Point Judith pond is no longer large enough to overcome these factors and will see little or no recovery.
The abundance and spawning index in concert with tag / recapture data collected in this survey is a tool to aid in estimation of population size and year class structure. Studies such as this one are especially useful when collected for a long period of time. A long-term approach to adult winter flounder assessments in Rhode Island south shore coastal ponds is paramount and will enable fisheries biologists to fine tune the management strategy for this species. This research project will continue to provide valuable information about flounder movement, population size, exploitation rates, growth rates, natural mortality and fishing mortality. RIDFW in partnership with US EPA will continue conduct this survey in the coastal ponds to better understand the connection between local populations and the Southern New England stock of winter flounder as a whole.
Regulations in red are new this year.
Purple text indicates an important note.