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Rhode Island

Saltwater Fishing

Striped Searobin Diet

By Rich Balouskus, Principal Marine Biologist, RI DEM Division of Marine Fisheries

About The Species

A flatfish species once abundant throughout southern New England, the winter flounder population has markedly declined since the 1980s to its lowest biomass levels on record. A 2020 assessment of the Southern New England stock revealed that the stock is overfished but overfishing is not occurring, and the spawning stock biomass was at only 32% of the target. This means the number of adults is lower than needed to maintain a sustainable population even though fishing levels are low. While fishing mortality has been attributed to initiating these declines, the southern New England population has not recovered even with significant reductions in commercial and recreational harvest. Though stock-wide reductions in fishing mortality were implemented, deterioration of local subpopulations persisted. Therefore, additional efforts tailored to specific estuarine spawning habitats were needed. Within Narragansett Bay, the RI Division of Marine Fisheries implemented multiple measures intended to reduce fishing mortality and improve flounder survivorship through the first year of life, including prohibiting commercial harvest, gear restrictions during spawning season, and spatially restricting bottom trawling. These efforts were needed because the life history, particularly spawning site fidelity, of winter flounder makes it vulnerable to localized depletion.

Some adult winter flounder remain in shallow coastal waters year-round while others return to estuaries from offshore to spawn in the winter months (December – April). Winter flounder enter Narragansett Bay and the south shore coastal pond systems in RI to spawn in the early part of winter (November) and engage in spawning activity from roughly January through April annually. Spawning and egg deposition takes place predominantly 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.

Fyke Net Survey

Since 1999 the RI Division of Marine Fisheries 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 that was commonly used in commercial fishing. However, in this case fyke nets serve as an excellent tool for biological fishery sampling to assess fish populations that utilize 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 RI shoreline but on a much 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. 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 shoreline 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 spawning stage.

The focus of this study has been in Point Judith Pond, Potter Pond, and Ninigret Pond, in Washington County, RI. Nets are tended every 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 (see Table 2). 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 including 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.

Tagging study recapture data has shown that winter flounder display a strong tendency to return to natal areas to spawn. On multiple occasions, tagged fish have been caught in the same exact location the following year from where they were first captured, thus it may be difficult for local populations to recover 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. Beginning in the winter of 2021/2022 a more advanced acoustic tagging methodology began to be deployed in Ninigret Pond. An array of 12 receivers was positioned throughout the pond to track movements of tagged winter flounder within the system. This information will help elucidate both within estuary habitat use as well as frequency and timing of entries and exits from the ocean to the pond.

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 of about 24 to 2 fish per net haul in 2019. Companion surveys which examine juvenile fish population abundance in the coastal ponds and Narragansett Bay mirror these results closely. While juvenile winter flounder abundance is variable among coastal ponds and Narragansett Bay, an overall downward trend over the last two decades is clear.

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 juvenile winter flounder by sea robins, summer flounder, cormorants, egrets, and seals, among many others contribute to natural mortality resulting in low population levels. Aside from predation, warming winter water temperatures due to 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 Southern New England stock is no longer large enough to overcome these external factors and will see little or no recovery.

Future Management

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 RI 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.

The prospects of rebuilding the Southern New England winter flounder stock have been discussed extensively by scientists and managers, as the stock’s outlook has not looked promising. With warming waters found to negatively influence the stock’s productivity, coupled with a projected warming ocean for foreseeable decades, winter flounder population models incorporating future climate conditions project that even under fishing moratoriums, it may not be possible to rebuild winter flounder to previous stock levels. Despite ominous stock-wide outlooks, fisheries managers should not be deterred from developing informed strategies for stock resiliency. In concert with rebuilding targets that consider temperature-induced productivity, this research suggests future management measures should focus at spatial scales where winter flounder persist and provide the greatest chance for survival success.

Table 1: Definitions of Important Terms

Glossary

Fishing Mortality

The rate at which fish die from all causes other than harvest (ASMFC 2009).

Natural Mortality

The rate at which fish in a stock die because of fishing (ASMFC 2009).

Spawning Stock Biomass

The total weight of the mature females within a stock of fish; frequently used instead of total biomass as a better measure of the ability of a stock to replenish itself (ASMFC 2009).

Table 2: Spawning Stages of Winter Flounder Explained

Winter Flounder Spawning Stages

Immature

A fish that has not yet reached sexual maturity and does not contribute to spawning

Ripe

The pre-spawn stage

Running Ripe

The active spawning stage

Spent

The post-spawn stage

Resting

The non-active spawning stage