Western North Atlantic Ocean
At a glance | Vital stats | Curiosities | Closeup | The role of Fisheries and Oceans Canada
At a glance
Yellowtail flounder are flat, odd-looking fish whose eyes are both on the same side of the head. Their strange appearance doesn't make them any less desirable to fishermen: one of the most valuable commercial flatfish species for human consumption in North America, the yellowtail flounder is a sought-after catch.
Yellowtail flounder go through an unusual transformation as they develop. When these fish hatch, their eyes are on opposite sides of their heads; but as they grow, one eye migrate to the other side of their body—so that the ‘side' becomes the ‘top' of this undersea contortionist.
About the yellowtail flounder
The yellowtail flounder is a small-mouthed Atlantic flatfish that lives on sandy bottom in water 37 to 91 metres deep. Known as the yellowtail, rusty dab and sole, this medium-sized species can grow up to 60 cm long, but more commonly measures 30 to 40 cm.
Its oval-shaped body is compressed—i.e., flattened—and often is reddish brown to olive green in colour on top (with irregular rusty red spots). The underside is white with some lemon-yellow colouring. Its small mouth and thick fleshy lips distinguish the yellowtail from the large-mouthed flounders (halibut and plaice).
With its small mouth, the yellowtail flounder selects smaller types of food. Adults feed primarily on amphipod, a common group of shrimp-like species, shrimp, polychaete worms, small quantities of other invertebrates such as small crabs, mollusks, and occasionally small fish (e.g., small sculpins and sand lance).
Studies have found that this fish is diurnal, meaning it eats during the daytime—starting near sunrise and ending near sunset.
Lifecycle and reproduction
Male and female yellowtail flounder become physically different (sexually dimorphic) after age two, around the time of sexual maturity. Females grow faster, live longer and reach a larger maximum size than males. There may be an evolutionary advantage for larger females: their bodies can hold a greater number of eggs.
Spawning occurs on or near the sea floor during spring and summer, depending on latitude (April-June in New England waters; May-July in Canadian waters). Females produce large numbers of eggs (350,000-4,570,000 depending on body length). These are released in batches and fertilized externally by the males. The fertilized eggs float to the surface layers where they drift during development. Hatching occurs five days later at temperatures of 10-11 degrees Celsius and the larvae remain in the top layers of the water for a short time before drifting downward.
Both males and females grow at the same rate until age 2, after which females grow faster and live longer than males. Growth rates also differ by geographic area, with fish from the southern part of the range (i.e. Georges Bank) growing more rapidly than those from more northern areas (i.e. Gulf of St. Lawrence, Grand Bank). Both males and females become sexually mature by age 2-3 in the southern range and by age 4-6 in the northern range.
The underwater world of the yellowtail flounder
Until recently, the yellowtail flounder was thought to be an inactive fish that lived in shallow, sandy habitats, but data storage tags attached to yellowtail flounder on Georges Bank have revealed that the fish are capable of off-bottom movement patterns and take advantage of midwater tidal currents to move from one area to another. Tagging experiments have suggested yellowtail may migrate considerable distances, although no clear migration patterns have been identified.
Yellowtail flounder are preyed on by skates, monkfish, bluefish, Atlantic halibut and fourspot flounder. Cod and spiny dogfish are the most prominent predators of this species—and on the Scotian Shelf they are also a target food of grey seals.
Yellowtail flounder and American plaice compete for some food items, especially polychaete worms and amphipods, but in general plaice eat larger foods and live at greater depths than yellowtail.
Climate change and the species
While it has not been confirmed that climate change has influenced seasonal and geographic distribution, in recent years yellowtail flounder have not been available to Canadian fishers on Georges Bank during the summer months, when this region is open for commercial harvesting.
Fishing or harvesting the species
Yellowtail flounder is fished primarily for human consumption. Otter trawls are most commonly used to harvest this resource in Canadian waters; however, the fish are also taken as bycatch (caught in fisheries targeted at other species) in the Georges Bank scallop dredge fishery. The main Canadian commercial fisheries for yellowtail are on north-eastern Georges Bank and on the Grand Bank. There is a small industrial fishery for bait in the southern Gulf of St. Lawrence.
While yellowtail flounder has been a candidate species for experimental aquaculture studies in Newfoundland and New Brunswick, it is currently not raised on a commercial basis.
The role of Fisheries and Oceans Canada
The Canadian government uses quota management (setting limits on total allowable catches, or TACs) to regulate this fishery. Other management measures include minimum cod end mesh sizes, seasonal area closures, limited entry of participants, at-sea observer coverage and dockside monitoring of landed catches. Scientists working with Fisheries and Oceans Canada and the U.S. National Marine Fisheries Service continue to assess yellowtail stock status from the Grand Banks, southern Gulf of St. Lawrence and Georges Bank fisheries. For several years, both agencies have conducted annual ecosystem surveys of the Grand Banks, Gulf of St. Lawrence, Georges Bank and Gulf of Maine using special research trawlers.
On the Grand Banks, yellowtail flounder is managed by the North Atlantic Fisheries organization (NAFO), since its distribution in that area extends beyond Canada's Exclusive Economic Zone (EEZ). Canadian scientists work with colleagues from other NAFO member countries to track the status of this species and provide advice to the NAFO Commission on sustainable management.
Revised: October 2009
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