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Arrowtooth flounder fish identification, Habitats, Fishing methods, fish characteristics
Arrowtooth flounder are members of the family Pleuronectidae, the right-eyed flounders. It distributed over the continental shelf from the Bering Sea to Santa Rosa Island, California. In Alaska waters, they are distributed over the continental shelf through age 4 and then at older ages disperse to occupy both the continental shelf and the slope. Spawning occurs from December through February. This species of flounder can live up to 27 years.
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Arrowtooth flounder (Atheresthes stomias), also known as Arrow Tooth flounder, Turbot, Long Jaw Flounder, Long-Jawed Flounder, Needle-Toothed Halibut, French sole, Arrow-Toothed Halibut, Палтус Стрелозубый Американский (in Russian), are a relatively large flatfish range from Northern California to the eastern Bering Sea and is most abundant at the northern part of its range. It is the dominant flounder species on the outer continental shelf from the western Gulf of Alaska to Oregon. They distinguished off the west coast of Vancouver Island, in Hecate Strait and in Queen Charlotte Sound.
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Description:
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Arrowtooth flounder has elongate diamond body shape; depth is 1/3rd of a length. Head long, about 1/4th in length, the snout protruding, somewhat truncate at tip. Eyes are large, 1/5th in head. Upper eye with its range entirely vertical. Interorbital space scaly, ridged, not a third width of eye. Mouth extremely large, terminal, near symmetrical with wide gape. Maxillary is larger than a head; extends beyond posterior margin of lower eye; premaxillary in front above the level of the lower eye. Left eye on dorsal ridge (visible from blind side). Caudal fin slightly lunate, crescent-shaped. Lateral line nearly straight with slight curve over pectoral fin; accessory dorsal branch absent. Dorsal fin beginning just behind the middle of the upper eye; dorsal branch absent on lateral line; caudal peduncle nearly as long as the pectoral fin, about half length of head.
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Two rows of large, and sharp well developed arrow-shaped teeth. No fang-like tooth on vomer (bone inroof of mouth). Teeth in upper jaw anteriorly in a single series, long, slender, and wide set, much smaller and closer set behind; on sides of jaw the teeth are very small and in 2 separate series, the inner of which corresponds to the single series in front, the teeth thus gradually increasing in size forward; teeth in inner series of lower jaw very sharp and slender, longer than the upper teeth, wide set, alternating with shorter, depressed teeth; outside of these larger teeth is a series of fixed small teeth; all of the long teeth in both jaws depressible and conspicuously arrow-shaped toward their tips; inner series of small teeth in upper jaw also arrow-shaped, depressible.
Gill rakers long and strong, about 4 + 13 in number, the longest more than a diameter of eye. 2 gill rakers on the second upper arch. Anal spine absent. Preopercle C-shaped (not angular). Anterior nostril on blind side has small flap. Pectorals small. Scales extremely thin, irregular in size, moderate. Position of Scales on Body: on lateral line canal; approximately 135 scales; unevenly imbricated pattern; deciduous; ctenoid on eyed side, cycloid on blind side.
Key characters
A relatively large, brownish colored flatfish with a large mouth and two rows of large, arrow-shaped teeth. Maxillary extends beyond posterior margin of lower eye. Dorsal origin over middle of upper eye. Left eye on upper margin of head. Caudal slightly lunate. Pectorals small.
92-109 Dorsal soft rays
72–90 Anal soft rays
47–49 Vertebrae (12 + 35–37)
135 Scales
4+13 Gill rakers
Max length: 84 cm; common: 50 cm
Max weight: 8.6 kg
Max age: 27 years
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Eyed side uniform dark grayish brown to olive brown, the margins of the scales darker. Blind side dirty white, dusted to light gray with black points.
Habitats:
Arrowtooth flounder inhabit depths between 50 and 900 m and show preference for a narrow range of bottom temperature between 7 and 8 °C. Eggs and larvae are found in the water column; juveniles and adults are found on the ocean bottom on sand or sandy gravel or occasionally over low-relief rock-sponge bottoms. As adults they show little preference for bottom type but juveniles apparently prefer soft sand and mud bottoms. Arrowtooth flounder occupy separate winter spawning and summer feeding areas, undertaking a seasonal bathymetric movement from shallower water in summer to deeper water in winter. In the summer adults are found on the continental shelf in the median depth between 75 and 175 m. In the winter, they move to the continental slope with the median depth between 275 and 525 m (1,640 feet). Arrowtooth flounder migrate from shallow water on the continental shelf where they feed in the summer to deep water over the continental slope where they spawn.
Larvae eat copepods (a type of small crustacean) and their eggs and larvae. Juvenile Arrowtooth flounder feed on mobile prey such as cumaceans, carideans and gammarid amphipods, crustaceans (mainly ocean pink shrimp and krill). Adults are more piscivorous and cannibalistic, feeding on crustaceans (ocean pink shrimp and krill) and fish (mainly herring, juvenile pollock, anchovy, sand lance, and Pacific sandlance.
Spawning:
Arrowtooth flounder are batch spawners and peak spawning occurs in fall and winter at depths deeper than 1,180 feet (350 m) in the Bering Sea and Gulf of Alaska, and deeper that 1,640 feet off the coast of Washington. They spawn multiple times during a spawning season. Arrowtooth flounder males mature at 3 to 7 years and between 12 and 16.5 inches. Females mature at 4 to 8 years and between 15 and 16.5 inches. The rate of maturity-at-length is different among the sexes with males maturing at smaller lengths than females. The length, at which 100% of the species are mature, is 43 cm for males and 55 cm for females. They lay pelagic eggs which are drift with the ocean currents and fertilized externally. The larvae are large, thin, and long. A notable feature of the larvae is the presence of spines over the eyes and on the operculum, which are absent in the larvae of other halibut. Their larvae spend around 4 weeks in the upper 100 m of the water column then settle to the bottom in the late winter and early spring. Young juveniles 1-2-year-olds are found in shallow waters, whereas 3-4-year-olds are generally found in deeper water with the adults.
Arrowtooth flounder exhibit sexual dimorphism. As juveniles (< 38 cm), males and females grow at the same rate. However, after sexual maturity at about five years of age, females grow faster than males and attain larger maximum size. The maximum length observed for males in biological samples over the last 20 years is 2 feet (75 cm). The maximum length for females over the same period is 2.8 feet (84 cm). The maximum weights of males and females determined from biological samples are 1.7 kg and 3.1 kg, respectively. Arrowtooth flounder can live up to 27 years.
Fishing Methods:
Arrowtooth flounder is mainly caught by bottom trawl gear, including a specialized bottom trawl gear called selective flatfish trawl gear. Trawling involves the towing of a funnel shaped net or nets behind a fishing vessel on or near the bottom. The doors and/or the footrope of the net of a bottom trawl come in contact with the seabed.
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