The winter flounder, blackback, or lemon sole,
Psuedopleuronectes americanus, is a demersal flatfish
distributed in the Northwest Atlantic from Labrador to Georgia.
Important U.S. commercial and recreational fisheries exist from
the Gulf of Maine to the the Mid-Atlantic Bight. In USA waters,
the resource is assessed and managed as three stocks: Gulf of
Maine, Southern New England/Mid-Atlantic Bight (SNE/MAB), and
Georges Bank (Figure
11.1). Winter flounder generally occur in inshore bays and
estuaries during the winter, and move to deeper water in the summer.
Spawning occurs during the winter and spring months (Pereira et
al. 1999). Growth and maturity vary by stock; Georges Bank fish
have the fastest growth and reach the largest size, and reach
maturity at the earliest age and smallest size. Gulf of Maine
fish grow the slowest and reach the smallest size, and reach maturity
at the oldest age and largest size (O’Brien et al. 1993).
Winter flounder may grow up to 58 cm in total length and attain
15-20 years of age (Pentilla et al. 1989, Pereira et al. 1999).
U.S. commercial
and recreational fisheries for winter flounder are managed in
federal waters under the New England Fishery Management Council’s
Northeast Multispecies Fishery Management Plan (FMP), and in state
waters under Atlantic States Marine Fisheries Commission’s
Fishery Management Plan for Inshore Stocks of Winter Flounder.
FMP provisions include restrictions on commercial permits, limits
on commercial fishery days-at-sea, commercial and recreational
fishery time-area closures, commercial fishery mesh sizes, commercial
and recreational fishery fish size limits, and commercial and
recreational fishery possession limits. The information provided
herein reflects the results of the most recent peer-reviewed assessments
for the Gulf of Maine, Georges Bank, and Southern New England
winter flounder stocks (Mayo and Terceiro 2005).
GULF OF MAINE WINTER FLOUNDER
The
Fishery
Commercial landings from the
Gulf of Maine (GOM) winter flounder stock increased from an annual
average of about 1,000 mt during 1964 to 1975 to nearly 3,000
mt in 1982 (Figure
11.2
[Fig 11.2 Data]). Commercial landings have since declined
to 300 mt in 2005. Otter trawls accounted for about 95% of the
GOM commercial winter flounder landings during 1964-1985, but
their percentage declined to 75% between 1986 and 2001 because
of increased landings from gillnets (average of 20% from 1986-2001).
Since 2001, gillnets have accounted for 15% of the landings. The
recreational rod-and-reel fishery historically harvested a significant
proportion of the total landings, but recreational catches have
sharply declined over the last decade from over 2,500 mt in the
early 1980s to less than 100 mt during 1997-2005 (Table
11.1).
GOM winter flounder landings
in numbers have generally been dominated by age 3-5 fish (Figure
11.3
[Fig 11.3 Data]). The proportion of ages 2 and 3 winter
flounder in the commercial and recreational landings has been
greatly reduced by the effects of increasing minimum landing sizes
and increasing minimum trawl mesh size in the commercial fishery
since the late-1990s.
Research Vessel Survey
Indices
Bottom trawl survey biomass
indices from the Massachusetts Division of Marine Fisheries (MADMF)
spring and fall surveys declined after 1983. The fall survey attained
a record low in 1986 while the spring reached a record-low in
1994. Between 1996 and 2000, both survey indices increased. The
2000 spring index was the highest on record and the 2000 fall
index was the 2rd highest in the 28-year time series (Figure
11.4
[Fig 11.4 Data]). However, subsequently the indices
have declined. As stock biomass declined in the late 1980s, the
age structure of the winter flounder population became truncated,
with a low proportion of fish at ages 5 and older (Figure
11.5
[Fig 11.5 Data]). The age structure has expanded slightly
since the mid 1990s.
Figure
11.2
Figure
11.3
Figure
11.4
Figure
11.5
Figure
11.6
Figure
11.7
Figure 11.8
Figure
11.9
Figure
11.10
Assessment Results
The assessment for GOM winter
flounder was last updated at the Groundfish Assessment Review
Meeting (GARM) in 2005 (NEFSC 2005). Average fishing mortality
(ages 5-6, unweighted) varied between 0.5 and 2.1 during the
1980s and mid 1990s, but declined to a record low of 0.13 in
2004 (Figure
11.6
[Fig 11.6 Data]). Spawning stock biomass declined
from 4,800 mt in 1982 to 500 mt in 1996 and then increased to
3,400 mt by 2004 (Figure
11.7
[Fig 11.7 Data]). Recruitment at age 1 declined from
12 million fish in 1982 to 3 million fish in 1993, (Figure
11.7
[Fig 11.7 Data]) but has since increased to 18 million
in 2005. Over the 1982-2004 time period, geometric mean recruitment
was 5 million fish.
Biological
Reference Points
Biological reference points (Figure
11.8
[Fig 11.8 Data]) were last reviewed by SARC 36 (NEFSC
2002) and the values are presented in Table
11.2. The relationship between spawning stock biomass and
recruitment for winter flounder over the period covering the
1982-2004 year classes is illustrated in (Figure
11.9
[Fig 11.9 Data]). The stock-recruitment trajectory
suggests that increases in recent SSB have been accompanied
by improvement in recruitment. The solid horizontal line indicates
the geometric mean recruitment over the same period. Survival
ratios, recruits per unit of spawning biomass (Figure
11.10
[Fig 11.10 Data]), illustrate a general increasing
trend in the survival rate over time.
Summary
Spawning stock biomass in 2004 was 3,400 mt
or about 84% of BMSY = 4,100 mt. Fishing mortality
in 2004 was 0.13 or about 30% of FMSY = 0.43. Thus,
the stock is not in a overfished condition and overfishing is
not occurring.
Commercial landings of Georges Bank winter flounder are predominately
from U.S. fisheries, but a small percentage (< 12% during
most years) is from Canadian fisheries (Table
11.3, Figure
11.11
[Fig 11.11 Data]). Canadian landings
gradually increased after 1993, reached a peak of 500 mt in
2001, and subsequently declined to 200 mt in 2004. During 1965-1977,
the USSR also landed winter flounder from Georges Bank, with
Soviet landings accounting for 23% to 38% of the total harvest
during 1971-1973. Recreational landings of winter flounder from
Georges Bank are insignificant.
After reaching a peak of 4,500 mt in 1972, total landings of
Georges Bank winter flounder declined to 1,900 mt in 1976. During
1977-1984, total landings ranged between 3,000 and 4,000 mt,
but thereafter declined to a record low (800 mt) in 1995. Total
landings increased between 1995 and 2003 then declined to 2,200
mt in 2005.
Discarding of Georges Bank winter flounder occurs in the Northeast
multispecies bottom trawl fishery and the sea scallop dredge
fishery. However, data from the Fisheries Observer Program and
Vessel Trip Report databases have been insufficient to produce
reliable estimates of the magnitude or size and age composition
of these discards (NEFSC 2002a).
Research Vessel Survey Indices
Autumn relative abundance and
biomass indices declined between 1976 and 1991 to reach a record
low (Figure
11.12
[Fig 11.12 Data]). Thereafter, biomass increased through
2002, then declined to a level near the time series average in
2005.
Assessment Results
The assessment of Georges Bank
winter flounder was last updated in 2005 using a surplus production
model (Mayo and Terceiro 2005). Model estimates of relative total
biomass (Bt/BMSY) and fishing mortality
rates (Ft/FMSY) are utilized because they
more precisely estimated than absolute values (Prager 1994).
Relative fishing mortality rates
(Ft/FMSY) were highest during 1983-1993,
declined sharply during 1996-1999, but have since increased to
above FMSY during 2000-2004 (Figure
11.13
[Fig 11.13 Data]). During 1977-1994, relative biomass
indices consistently declined reaching a record low in 1994. Subsequently,
relative biomass increased through 2003, but has since declined
to a level just below the threshold in 2005 (Figure
11.13
[Fig 11.13 Data]).
Figure 11.11
Figure 11.12
Figure
11.13
Biological Reference Points
MSY-based reference points for
Georges Bank winter flounder (Table 11.4)
were estimated in the 2001 assessment using a surplus production
model (NEFSC 2002a) and the reference points implemented in May
of 2004 (NEFMC 2003). The MSY estimate (3,000 mt) does not include
discards. FMSY = 0.32 and BMSY = 9,400 mt.
Stock status is determined by comparing relative estimates of
biomass and fishing mortality with a relative biomass threshold
(50% of BMSY) of 0.5 and a relative fishing mortality
rate threshold (FMSY) of 1.0 because these relative
metrics are more precise than the absolute estimates of fishing
mortality rate and biomass (Mayo and Terceiro 2005).
Summary
Relative fishing mortality has
exceeded FMSY since 2000 and was 1.86 in 2004. Relative
biomass exceeded the threshold level in 2004 but declined below
the threshold, to 0.46, in 2005. Therefore, in 2004, the stock
was not overfished but overfishing was occurring (Mayo and Terceiro
2005).
U.S. commercial landings of
SNE/MAB winter flounder peaked at 12,000 mt in 1966, declined
through the 1970s, and then peaked again at over 11,000 mt in
1981 (Figure
11.14
[Fig 11.14 Data]). Commercial landings subsequently
declined during the 1980s and early 1990s, falling to 2,200 mt
in 1994. Commercial landings then increased to 4,700 mt in 2001
but have since declined to 1,200 mt in 2005, a record low (Table
11.5, Figure
11.14
[Fig 11.14 Data]). The principal gear used in the SNE/MAB
winter flounder fishery is the otter trawl. The recreational rod-and-reel
fishery for winter flounder historically harvested a significant
proportion of the total catch, but recreational landings have
markedly declined during the last decade. After peaking at 5,800
mt in 1984, recreational landings of winter flounder averaged
1,600 mt annually during 1986- 1995, but have since declined to
120 mt in 2005 (Table 11.5).
SNE/MAB winter flounder landings
in numbers have generally been dominated by age 2-4 fish (Figure
11.15
[Fig 11.15 Data]). Since the mid-1990s, the proportion
of ages 1 and 2 fish in the commercial and recreational landings
has been greatly reduced by the effects of increasing minimum
landed sizes and increases in the minimum trawl mesh size in the
commercial fishery.
Research Vessel Survey
Indices
NEFSC spring and autumn biomass
indices for SNE/MAB winter flounder indicate peaks in abundance
during the mid-1960s, early 1980s, and late 1990s, and have exhibited
a declining trend since 1999 (Figure
11.16
[Fig 11.16 Data]). As stock biomass declined, the age
structure of the winter flounder population became truncated,
with a low proportion of fish at ages 5 and older (Figure
11.17
[Fig 11.17 Data]).
Assessment Results
The assessment for SNE/MAB winter
flounder was last updated at the Groundfish Assessment Review
Meeting (GARM) in 2005 (NEFSC 2005). Average fishing mortality
(F, ages 4-5, unweighted) ranged between 0.5 and 1.5 during the
1980s and mid 1990s, but has steadily declined since 1997 and
in 2004 was F = 0.4, a record low (Figure
11.18
[Fig 11.18 Data]). Spawning stock biomass declined
from 14,800 mt in 1983 to 2,700 mt in 1994, slowly increased to
5,000 mt in 2001, and has since stabilized at about 4,000 mt (Figure
11.19 [Fig
11.19 Data]). Since 1982, recruitment at age 1 has
ranged from 57 million fish (1982 year class in 1983) to 4 million
fish (2001 year class in 2002) (Figure
11.19 [Fig
11.19 Data]). Over the 1982-2004 period, the geometric
mean recruitment was 16 million fish.
Figure 11.14
Figure 11.15
Figure
11.16
Figure 11.17
Figure 11.18
Figure
11.19
Figure 11.20
Figure
11.21
Figure
11.22
Biological Reference Points
Biological reference points (Figure
11.20 [Fig
11.20 Data]) were last calculated by the 2002 Working
Group on Re-Evaluation of Biological Reference Points for New
England Groundfish (NEFSC 2002) and are presented in Table
11.6. The relationship between spawning stock biomass and
recruitment for winter flounder over the period covering the
1981-2004 year classes is illustrated in (Figure
11.21 [Fig
11.21 Data]). The stock-recruitment trajectory shows
that recent levels of SSB and recruitment occur on the lower-left
side of the plot. The solid horizontal line indicates the geometric
mean recruitment (16 million fish at age 1) over the same period.
Survival ratios (Figure
11.22 [Fig
11.22 Data]), illustrate fluctuating survival over
time.
Summary
Spawning stock biomass of SNE/MAB winter flounder
in 2004 was 3,900 mt, about 13% of BMSY (30,100 mt). Fishing
mortality was 0.40 in 2004, 25% above FMSY = 0.32. Thus, the
stock in 2004 was in an overfished condition and overfishing
continues to occur.
Mayo, R. K. and M. Terceiro.
2005. Assessment of 19 Northeast groundfish stocks through 2004.
2005 Groundfish Assessment Review Meeting (2005 GARM), Northeast
Fisheries Science Center, Woods Hole, Massachusetts, 15-19 August
2005. U.S. Dep. Commer., Northeast Fish. Sci. Cent. Ref. Doc.
05-13, 499 p.
NEFMC [New England Fishery Management Council].
2003. Final Amendment 13 to the Northeast Multispecies Fishery
Management Plan Including a Final Supplemental Environmental Impact
Statement and an Initial Regulatory Flexibility Analysis. 1,660
p. plus Appendices.
NEFSC [Northeast Fisheries Science Center]. 2002a.
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. Northeast Fish. Sci. Cent. Ref. Doc. 02-16. 511 p.
NEFSC [Northeast Fisheries Science Center]. 2002b.
Final Report of the Working Group on Re- Evaluation of Biological
Reference Points for New England Groundfish. Northeast Fish. Sci.
Cent. Ref. Doc. 02-04, 249 p.
NEFSC [Northeast Fisheries Science Center]. 2003.
Report of the 36th Northeast Regional Stock Assessment Workshop
(36th SAW), Stock Assessment Review Committee (SARC) consensus
summary of assessments. Northeast Fish. Sci. Cent. Ref. Doc. 03-06,
453 p.
NEFSC [Northeast Fisheries Science Center]. 2006.
Report of the 34th Northeast Regional Stock Assessment Workshop
(34th SAW): Stock Assessment Review Committee (SARC) consensus
summary of assessments. Northeast Fish. Sci. Cent. Ref. Doc. 02-06,
346 p.
O’Brien, L., J. Burnett, and R.K. Mayo.
1993. Maturation of nineteen species of finfish off the northeast
coast of the United States, 1985-1990. NOAA Tech. Report. NMFS
113, 66 p.
Pereira, J.J, R. Goldberg, J.J. Ziskowski, P.L.
Berrien, W.W. Morse, and D.L. Johnson. 1999. Essential fish habitat
source document: winter flounder, Pseudopleuronectes americanus,
life history and habitat characteristics. NOAA Tech. Mem. NMFS-NE-138,
39 p.
Pentilla, J.A., G.A. Nelson, and J.M. Burnett,
III. 1989. Guidelines for estimating lengths at age for 18 Northwest
Atlantic finfish and shellfish species. NOAA Tech. Mem. NMFS-F/NEC-66,
39 p.
Prager, M. H. 1994. A suite of extensions to
a nonequilibrium surplus-production model. Fish. Bull. 92: 374–389.