Winter Flounder

Fascinating facts about the Winter Flounder

• A single winter flounder can lay up to 3.3 million sticky eggs that stick to the seafloor, turning a spawning ground into a hidden nursery of millions of future fish. This massive reproductive output shows how the species bets on sheer numbers to survive in a changing ocean.
• When the larvae are just 3 mm long, they hatch in two to three weeks and spend the next five to six weeks drifting in the water column before their left eye migrates to the right side, giving them the classic flatfish shape. The eye shift illustrates a dramatic body-plan rewrite that lets them become masters of the seafloor.
• In the cool waters of Georges Bank, winter flounders can grow to 70 cm and weigh as much as 3.6 kg, compared with a typical maximum of 61 cm and 2.25 kg elsewhere. Their larger size there highlights how local conditions can boost growth, a clue for managing their habitats.
• Peak harvests once reached 40.3 million pounds for commercial and 16.4 million pounds for recreational fishers, but by 2013 those numbers fell to just 6 million and 77 000 pounds. The steep decline reveals how overfishing and habitat loss have sharply cut a once-abundant resource.
• Genetic and tagging studies show almost no mixing between winter flounder populations in the Gulf of Maine, south of Cape Cod, and on Georges Bank, meaning each group is a largely separate gene pool. This isolation makes each stock especially vulnerable to local threats and underscores the need for region-specific protection.

At a glance

About the Winter Flounder

The winter flounder (Pseudopleuronectes americanus), nicknamed the black back, is a right-eyed flatfish that lives in shallow, coastal waters of the western North Atlantic, from Labrador, Canada down to Georgia, United States, though it is less common south of Delaware Bay. In the bustling estuaries and protected bays where juveniles settle, the fish can reach 100 mm in its first year, later growing to a maximum of about 70 cm and 3.6 kg on Georges Bank, where richer feeding grounds allow the biggest individuals. Adults are opportunistic sight-feeders, snapping up annelids, crustaceans, bivalves, and small fish, while their larvae, just 3 mm long, drift in the plankton feeding on nauplii, harpacticoids, and phytoplankton before undergoing the dramatic eye-migration that flips them onto their right side.

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