Common names
Turbot
French Sole
Long Jaw Flounder
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Range
Arrowtooth flounder range from Baja California to the eastern Bering Sea and is most abundant at the northern part of its range. Little is known about the stock structure on the Pacific Coast. The population of arrowtooth flounder off the west coast of Vancouver Island is thought to be separate from the population in Hecate Strait. Another population is distinguished in Queen Charlotte Sound but again, it is unknown if this stock is separate or contiguous with the stock in Hecate Strait or west coast Vancouver Island.
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Habitat and Distribution
Arrowtooth flounder off the BC coast inhabit depths between 50 and 900 m and show preference for a narrow range of bottom temperature between 7 and 8 °C. As adults they show little preference for bottom type but juveniles apparently prefer 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 BC bottom trawl fishery, adults are found on the continental shelf in summer; the median depth of catch is 140 m with 90% of catch between 75 and 175 m. In the winter, they move to the continental slope with the median depth of catch at 360 m and 90% of the catch between 275 and 525 m.
Arrowtooth flounder commercial fishery catch distribution maps are at the following links:
- BC Bottom Trawl Fishery 1996-2003
The seasonal depth distribution of arrowtooth flounder catch in the BC bottom trawl fishery from 1996 to 2003 is shown below.
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Reproduction
Limited research has been carried out on the species' life history. Arrowtooth flounder are batch spawners and peak spawning occurs in fall and winter at depths deeper than 350 m. The mature population off Washington migrates seasonally from depths of about 183 m in summer to depths exceeding 475 m in winter. There is some evidence to suggest that the time of first spawning and the time of peak spawning vary between years. The species produces pelagic eggs that drift with the ocean currents. Fecundity of arrowtooth flounder is not known. Larvae remain in the upper 100m of the water for about 4 weeks, however there is some evidence of an extended larval period of several months. Young of the year as well as one and two-year-olds are found in shallow waters, whereas three and four-year-olds are generally found in deeper water with the adults.
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Growth
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 75 cm. The maximum length for females over the same period is 84 cm. The maximum weights of males and females determined from biological samples are 1.7 kg and 3.1 kg, respectively.
The length-weight relationship for arrowtooth flounder was calculated using data collected during research surveys of Hecate Strait from 1998 to 2002. The weight-at-length was similar for males and females. The calculated functional regression relationship for males was:
W = 1.52*10-5 * L2.91
Length-at-age has been examined by applying the von Bertalanffy growth curve to data for both males and females using the equation:
La = L∞(1-e-k*(a-ta))
where La is length at age a in mm, L∞ is the maximum average length, k is the growth rate coefficient, and to is the estimates age where L = 0. Female arrowtooth flounder are larger at age than males. The parameters for the different relationships are given in the table below.
|
Male |
Female |
| L∞ |
476 |
618 |
| k |
0.265 |
0.193 |
| to |
-0.266 |
-0.266 |
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Maturity
Age at 50% maturity of arrowtooth flounder males is 4 years and for females is 5 years. Males mature at a size of about 31 cm compared to females at about 38 cm. The rate of maturity-at-length is different among the sexes with males maturing at smaller lengths than females. L 100 , the length at which 100% of the fish are mature, is 43 cm for males and 55 cm for females.
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Longevity and Mortality
The maximum age recorded for arrowtooth flounder in BC is 25 years, although most of the fished population is less than 15 years of age. It has been estimated that approximately 18% of adult fish die of natural causes each year. Put another way, it would take 15 years for 95% of the fish of the same age to die of natural causes. Fishing increases the total mortality rate. Under average fishing conditions, it has been estimated that about 30% of the adult fish die each year. Under these conditions, it would take 9 years for 95% of the fish of the same age to die.
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Diet
Juvenile arrowtooth flounder feed on mobile prey such as cumaceans, carideans and gammarid amphipods. Adults are more piscivorous and cannibalistic, feeding on herring, juvenile pollock, and Pacific sandlance. In Hecate Strait, a study of groundfish diet over 1984 -1987 showed that adult arrowtooth flounder fed mainly on unidentified fish (53%), herring (14%), forage fish (11%) and macrobenthos (9%). Juvneiles also fed primarily on unidentified fish (38%) but ate greater amounts of macrobenthos (26%) as well as euphausiids (11%) and shrimp (8%), but less forage fish (5%) than adults.
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Predators
A study of groundfish stomach contents in Hecate Strait from 1984 - 1987 found arrowtooth flounder eaten by Pacific halibut, Pacific cod, bocaccio rockfish, Pacific sanddab, and rock sole. Other studies have shown that juvenile arrowtooth flounder are prey for large walleye pollock.
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Fishery
Arrowtooth flounder is an important component of the bottom trawl fishery, although over the past 45 years, most of the arrowtooth flounder catch has been discarded. This is because the species is soft-fleshed, and after death there is rapid proteolysis (deterioration) of the muscle tissue, resulting in a mushy flesh. Thus, there was little market demand for the filets and arrowtooth flounder were mainly caught as bycatch in other directed fisheries. In 2003, the landed value of the fishery was $ 1.3 million.
The reported catch of arrowtooth flounder in the BC bottom trawl fishery by trawl management area is shown below.
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Population Trends
Biomass estimates for arrowtooth flounder are available for the west coast of Vancouver Island from US triennial surveys and for Hecate Strait from the Fisheries and Oceans Canada long-term multispecies survey. However, there are no biomass estimates for Queen Charlotte Sound despite the presence of a substantial population in that region. Size composition of the surveyed arrowtooth flounder areas has remained relatively constant since 1984.
Biomass appeared to increase in Hecate Strait between 1980 and 1991, then declined from 1991 to 1998, increasing again in 2000 to 1991 levels.
Catch per unit effort (CPUE) of arrowtooth flounder in BC has shown no overall trend, but there have been fluctuations from relative lows in 1984 to high levels in 1989, followed by a decline in 1993 and another increase in 2000. Results from an analysis of observer data indicate that the variability in the CPUE index from the commercial fishery is mainly due to area and seasonal effects (and in some cases depth) and that these variables can change among years.
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References
DiCosimo, J.D. 1998. Groundfish of the Gulf of Alaska Area: A Species Profile. 1998 North Pacific Fishery Management Council. 605 West 4th Avenue, Suite 306 Anchorage, Alaska 99501.
Fargo, J. 1999. Flatfish Stock Assessments for the west coast of Canada for 1999 and recommended yield options for 2000. Canadian Stock Assessment Secretariat Research Document 99/1999. 30p.
Fargo, J. and P. Starr 2001. Turbot stock assessment for 2001 and recommendations to management for 2002. Canadian Stock Assessment Secretariat Research Document 2001/150
Hoenig, J.M. 1983. Empirical use of longevity data to estimate mortality rates. Fish. Bull. 82: 898-903.
Perry, R.I. M. Stocker, and J. Fargo. 1994. Environmental effects on the distributions of groundfish in Hecate Strait , British Columbia . Can. J. Fish. Aquat. Sci. 51: 1401-1409.
Rickey, M.H. 1995. Maturity, spawning and seasonal movement of Arrowtooth flounder, Atheresthes stomias, off Washington. Fish. Bull. U.S. 93(1):127-138.
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