The American
plaice or dab, Hippoglossoides platessoides, is a large
mouthed, "right handed" flounder, distributed along the
Northwest Atlantic continental shelf from southern Labrador to Rhode
Island in relatively deep waters (Collette and Klein-MacPhee 2002).
Off the U.S. coast, American plaice are managed as a single stock
in the Gulf of Maine-Georges Bank region (Figure
9.1). The greatest commercial concentrations exist between 90
and 182 m (50 and 100 fathoms). Maturation begins between ages 2
and 3, but most individuals do not reach sexual maturity until age
4 (O’Brien et al. 1993). Spawning occurs in spring, generally
during March through May. Growth is rather slow; 3 year old fish
are normally between 22 and 28 cm (9 to 11 in.) in length, and weigh
between 90 and 190 g (0.2 to 0.4 lb). After age 4, females grow
faster than males (Sullivan 1982). American plaice from Georges
Bank have faster growth at age than fish from the Gulf of Maine
(Esteves and Burnett 1993).
The principal commercial
fishing gear used to catch American plaice is the otter trawl. Recreational
and foreign catches are insignificant. The U.S. fishery is managed
under the New England Fishery Management Council's Northeast Multispecies
Fishery Management Plan (FMP). Under this FMP, American plaice are
included in a complex of 15 groundfish species managed by time/area
closures, gear restrictions, minimum size limits, and, since 1994,
by direct effort controls including a moratorium on permits and
days-at-sea restrictions. Amendment 9 established biomass rebuilding
targets, (NEFMC 1998) and defined control rules which specified
target fishing mortality rates and corresponding rebuilding time
horizons. Amendment 13 implemented formal rebuilding plans within
specified time frames based on revised biomass and fishing mortality
targets derived by the Working Group on Re-Evaluation of Biological
Reference Points for New England Groundfish (NEFSC 2002a). The goal
of the management program is to reduce fishing mortality to allow
stocks to rebuild above minimum biomass thresholds, and attain and
remain at or near target biomass levels.
The Fishery
During 1972-1976, total commercial
landings averaged 2,300 mt, and increased during 1979-1984 to an
average of 12,700 mt (Figure
9.2[Fig
9.2 Data]). Landings have since generally declined, with the
exception of 1991, when the large 1987 year class recruited to the
fishery. Total landings of Gulf of Maine-Georges Bank American plaice
were 1,711 mt in 2004, the lowest since 1962 (Table
9.1, Figure
9.2[Fig
9.2 Data]). USA landings account for about 98% of the total
landings in recent years (2002-2004) with Canada accounting for
the remainder. The otter trawl fleet accounts for more than 95%
of the landings with the majority of the catch harvested during
the 2nd and 3rd calendar quarter of the year. The total catch at
age by numbers (Figure
9.3[Fig
9.3 Data]), which includes estimates of discarded fish, is dominated
by ages 4 and 5. Discarding of American plaice occurs in the northern
shrimp fishery during the 1st and 4th calendar
quarter, and year-round in the large mesh fishery. During 2002-2004
discards accounted for about 40% of the total catch by number and
for about 25% of the total catch by weight.
Research Vessel
Survey Indices
NEFSC spring and autumn biomass
indices for Gulf of Maine-Georges Bank American plaice have generally
exhibited similar trends throughout the survey time series (Figure
9.4[Fig
9.4 Data]). ). Biomass indices declined during the early and
mid-1980s, but generally increased during the 1990s. Since 2000,
the indices have declined and are presently at record low levels.
Recruitment indices (number of age 1 fish per tow in NEFSC autumn
surveys) indicate that the 1979, 1987,1989, 1993, 1997 and 1998
year classes were all above average and the 2001 year class is just
about average (Figure
9.5[Fig
9.5 Data]).
Figure
9.2 Figure
9.3 Figure
9.4
Figure 9.5
Figure
9.6
Figure
9.7
Assessment Results
Fishing mortality (ages
5-8, unweighted) doubled from 1990 to 1992, continued at a record
high through 1995, and then subsequently declined to 0.15 in 2004
(Figure
9.6[Fig
9.6 Data]),the lowest value in the time series. Spawning stock
biomass steadily declined from 46,700 mt in 1980 to 7,500 mt in
1989 but increased during 1990-1992 to an average 12,500 mt as the
strong 1987 year class recruited to the spawning stock. During 1997-1998,
spawning stock biomass again increased due to the strong 1992 and
1993 year classes. Spawning stock biomass in 2004 was estimated
to be 14,000 mt (Figure
9.7[Fig
9.7 Data]). Since 1980, recruitment has ranged from 12 million
(2000 year class) to 69 million (2004 year class) age 1 fish, with
an average geometric mean recruitment of 30 million fish (Figure
9.7[Fig
9.7 Data]). The 1987 year class (53 million fish) had been the
largest year class in the time series until the 2003 (55 million
fish) and 2004 (69 million fish) year classes.
Figure
9.8 Figure
9.9 Figure
9.10
Biological Reference Points
Yield and spawning stock biomass biological
reference points (Figure
9.8[Fig
9.8 Data])
were last calculated by the Working Group on Re-Evaluation of
Biological Reference Points for New England Groundfish (NEFSC
2002a) using assessment results from the 2000 assessment (O’Brien
and Esteves 2001). These estimates are reported in the 2002 and
2005 GARM assessments (NEFSC 2002b, Mayo and Terceiro 2005; O’Brien
et al. 2002, 2005) and presented in Table 9.2.
The relationship between spawning stock biomass
and recruitment for Gulf of Maine - Georges Bank American plaice
over the period covering the 1976-2004 year classes is illustrated
in Figure
9.9[Fig
9.9 Data]. The solid horizontal line indicates the
geometric mean recruitment (30 million age 1 fish) over the same
period. For this stock, high recruitment is atypically associated
with low spawning stock biomass. This is illustrated by the most
recent 2003 and 2004 year classes, and the 1987 year class, which
were all produced from spawning stock biomasses of less than 20,000
tons. Survival ratios, recruits per unit of spawning biomass (Figure
9.10[Fig
9.10 Data]), illustrate the relatively high survival
of the 1987 and 2004 year classes.
MSY-based reference points
were last calculated by the Working Group on Re-Evaluation of
Biological Reference Points for New England Groundfish (NEFSC
2002a). A yield-per-recruit analyses was conducted using data
and results from the 2000 assessment (O’Brien and Esteves
2001), and F40% was used as a proxy for FMSY.
A complete description of the approach is given in NEFSC (2002a).
The MSY-based reference points calculated using this method are
shown in Table 9.2. The MSY estimate includes
both commercial landings and discards.
Summary
In 2004, spawning stock biomass was estimated
at 14,149 mt, about 49% of the target SSBMSY. The stock
is considered to be overfished, although the upper 80% confidence
interval includes biomass >50% SSBMSY. Overfishing
is not occurring on this stock since F2004= 0.15 <
FMSY, although the upper 80% confidence interval about
F2004 is above FMSY.
Collette, B.B. and G. Klein-MacPhee
(editors). 2002. Bigelow and Schroeder's Fishes of the Gulf of Maine.
Smithsonian Institution Press, Washington, D.C.
Esteves, C. and J. Burnett 1993. A comparison of growth rates for
American plaice, Hippoglossoides platessoides, in the Gulf
of Maine-Georges Bank region derived from two different data sources.
NEFSC Ref. Doc. 93-09, 8 p.
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groundfish stocks through 2004. 2005 Groundfish Assessment Review
Meeting (2005 GARM), Northeast Fisheries Science Center, Woods Hole,
Massachusetts, August 15-19, 2005. NEFSC Ref. Doc. 05-13, 499 p.
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for New Overfishing Definitions To Comply with the Sustainable Fisheries
Act. Report of the Overfishing Definition Review Panel.
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groundfish stocks through 2001. A report of the groundfish assessment
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Hole, Massachusetts, October 8-11, 2002. NEFSC Ref. Doc. 02-16,
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species of finfish off the northeast coast of the United States,
1985-1990. NOAA Tech. Report NMFS 113, 66 p.
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in the Gulf of Maine - Georges Bank Region for 2000. NEFSC Ref.
Doc. 01-02, 114 p.
O’Brien, L., C. Esteves, and L. Col 2002. H. Gulf of Maine-Georges
Bank American plaice in: Assessment of 20 Northeast groundfish stocks
through 2001. A report of the groundfish assessment review meeting
(GARM), Northeast Fisheries Science Center, Woods Hole, Massachusetts,
October 8-11, 2002. NEFSC Ref. Doc. 02-16, 522 p.
O’Brien, L., J. Burnett, and L. Col. 2005. H. Gulf of Maine
- Georges Bank American Plaice in: Assessment of 19 Northeast
groundfish stocks through 2004. 2005 Groundfish Assessment Review
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Sullivan, L.F. 1982. The American plaice, Hippoglossoides platessoides,
in the Gulf of Maine. Kingston, R.I. University of Rhode Island,
Master's Thesis.