New Winter Flounder Research Reveals Multiple Lifestyles

The discovery of multiple winter flounder life-history strategies could help inform new management approaches.

Winter Flounder

Few species better embody the wistful notion of the “good old days” than winter flounder. Through the 1980s, inshore anglers from Maine through New Jersey enjoyed these tasty fish by the bucketful each spring. These days, however, flatties are hard to come by even in their most historically fabled haunts, although the dedicated angler armed with ample patience and chum can still, at times, put a respectable catch together.

Winter Flounder
Although their abundance is just a shadow of the past, winter flounder can still be taken by dedicated anglers.

Winter flounder are managed as three stocks—the Gulf of Maine, Georges Bank, and Southern New England-Mid-Atlantic (SNEMA)—and the latter two are overfished, while stock status for the Gulf of Maine is highly uncertain but biomass is known to be low. A puzzle has been the failure of winter flounder numbers to rebound even as managers have ratcheted down both commercial and recreational catch limits.

The absence of flounder recovery has led scientists to revisit what we know about the species’ biology and movements. Fisheries biologists have long assumed that all winter flounder spawn in coastal bays and estuaries during the winter and early spring months. They then migrate offshore later in the spring, which is the transitional period when anglers traditionally target them. However, a combination of angler reports and tagging data have consistently shown fish in the “wrong” location—for example, spawning-condition blackbacks in offshore waters during the winter. This could mean the winter flounder population structure is more complicated than we thought, impeding managers’ rebuilding efforts.

Examining Winter Flounder Ear Bones (Otoliths)

Otolith Definition: each of three small oval calcareous bodies in the inner ear of vertebrates, involved in sensing gravity and movement.

To investigate a winter flounder’s long-term behavior requires actually getting inside its head: examining chemical tracer ratios deposited on otoliths, or ear bones. “Because different environments—marine, brackish, fresh—have different chemical compositions, an otolith can provide a full record of the habitats a fish has inhabited throughout its lifetime,” explains Dr. Matt Siskey, a postdoctoral fellow at the University of Washington and NOAA Fisher[1]ies, who studied winter flounder as part of his Ph.D. research at Stony Brook University.

Winter Flounder Ear Bones Otolith
Otolith photo courtesy of Matt Siskey.

In this case, Siskey and his colleagues were curious to learn whether all flounder spawn inshore and undertake seasonal migrations, as is currently assumed. They collected otoliths from winter flounder of different sizes caught in both inshore (bay) and offshore (ocean) environments in the SNE-MA stock area, using young-of-year fish from each environment to establish baseline chemical ratios for otolith analysis. They also collected individuals from the ocean habitats of the Gulf of Maine and Georges Bank. “We were able to identify chemical proxies for both dissolved oxygen and salinity, which we could use to distinguish whether winter flounder were predominantly spending their time in inshore or offshore habitats, or both,” says Siskey.

The team found that, as opposed to all fish being spawned inshore and inhabiting coastal nurseries as juveniles, a substantial proportion of baby flounder spent the first part of their lives offshore: 23%, 40%, and 84% for the SNE, Georges Bank, and Gulf of Maine stocks, respectively. In addition, despite the current assumption that all winter flounder undertake seasonal migrations, otoliths revealed that across all stocks, only about half of the fish sampled made such movements, with the other half staying put in either coastal or offshore environments year-round. This phenomenon, known as “partial migration,’ occurs in many fish species and is thought to be a form of “bet[1]hedging” to maximize a population’s overall resilience.

“Overall, we found winter flounder across our sample to be more or less evenly split across four life-history strategies: bay residents, bay migrants, ocean residents, and ocean migrants,” Siskey explains. “In addition, we found that growth rates differed between fish that inhabited bay versus ocean nurseries, as well as between those with resident versus migratory life-history strategies.”

A New Model for Winter Flounder Management

While the sample size for this study was relatively small, the work of Siskey and his colleagues leaves little doubt that the current thinking about winter flounder biology needs to be revisited. “Only about 25% of the fish sampled demonstrated the assumed bay nursery/migrant life-history strategy,” Siskey says. “We need to make sure that our management approach distributes fishing effort across the four different life histories so that we don’t risk losing any of these groups permanently,” he adds, pointing out, for example, that because migrants grow faster than residents in early life, they may be disproportionately harvested at a given minimum size limit.

Winter Flounder Close-up
A close-up of a winter flounder head. Photo Credit: Willy Goldsmith

A logical next step may be to apply these new findings to a stock assessment simulation to see how the species’ outlook changes when multiple life-history strategies are incorporated. In addition, more sampling from each of the three stocks will help refine estimates of each strategy’s relative representation and whether environmental stressors like climate change may affect the proportions through time.

Overall, this research shows that, despite our best efforts to neatly package fisheries in a way that’s convenient for us to study and manage, reality is often far messier. “We have to listen to what the animals are telling us and manage accordingly because fish don’t necessarily stay in the boxes we try to place them in,” says Siskey.

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9 on “New Winter Flounder Research Reveals Multiple Lifestyles

  1. Logic1.0

    Interesting article. what was true yesterday may not be true tomorrow.

  2. peter okeefe

    So stopping “over fishing” has done??nothing?? gee who would have thought..LOL

  3. Jim

    Challenge will be to hold onto bay residents and bay migrants with climate warming waters and increased interspecies competition and coastal habitat changes. Better manage Black Sea bass now moving northward is one way, but it may be too late for black backs in SNE.

  4. John hawryluk

    One non consideration of all these studies is the runoff into our bays and our coastal waters. Something has changed and fish are staying further offshore along with our bays not having anywhere near the abundance of life in them that was there 50 years ago. All the models size limits bag limits etc will nit change the environment along coast and in the bays. Possibly a study on that may provide more of an answer. But…….. no way to replicate what the bays and coastal waters were like as a starting point.

  5. Frankb

    Cormorants….. eating all the juvenile flounder. Disappearance of eel grass from the bays….lots of reasons for the fish not making a comeback.

  6. RK

    Could be like geese – resident birds, plus migratory birds, with some movement between populations.

    Various trout species are the same – salter brookies/stream brookies, rainbows/steelhead, bulltrout/Dolly Vardens.

    Orcas in different parts of the world have different diets and different migration patterns and social interactions.

    It probably makes sense for a species to have more than one mode of operation, because if one gets shut down temporarily the other might work long enough for the one shut down to come back.

  7. dennis z skiper

    the habitat has my life(70+)old, I have seen winter flounder go from a 3 man catch of over 100flounder in 6hrs. to none@all. in N.J. we can keep 2 winter flouder p/day. I was in a enviremental field of can’t believe how our ocean water has cleaned see rays&other fish @your feet was just not possible imagine a predator fish that loves flounder more than we do! they used to “bump” bottom for food. now they see their pray scoot to save themselves. you can say codfish,pollack,striped bass, bluefish etc. have the final word!! my views are mine. so many eaters of the fish young. hope mother nature helps us out.want my family to enjoy this w.flounder again.

  8. Dennis Vance

    I agree that run off from over development around our bays has killed the water quality Barnegat bay is dead .Since I came of age to salt water fish the Mackerel Whiting Weakfish and Winter Flounder have disappeared also the Ling are a fraction of what they once were and for that I blame the commercial fisherman.

  9. Kenny Ben David

    I love that flatfish are more accepting of alternative lifestyles than people…

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