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The nascent recovery of the Georges Bank haddock stock


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World-wide many fish stocks have been depleted by overfishing. In this study, we describe the nascent recovery of the Georges Bank haddock stock. This mainstay of the New England groundfish fishery was overfished for decades prior to mid-1990s and experienced long-term declines in spawning biomass and recruitment. The stock was considered to have collapsed in the early-1990s when a lawsuit by the Conservation Law Foundation led the New England Fishery Management Council (NEFMC) and the National Marine Fisheries Service (NMFS) to take actions to cease overfishing and to recover Georges Bank haddock and other groundfish stocks. Under restrictive management measures, stock size increased 10-fold from 1995 to 2005. In 2003, an exceptionally abundant year class (YC) was produced. Although this YC may rebuild the haddock stock to pre-1930s abundance if properly fished, monitoring changes in life history parameters and recruitment will be important for sustaining stock recovery. Mean weights and sizes at age of adult haddock have decreased in recent years, and compensatory responses of haddock growth and recruitment to changes in stock density are assessed. We discuss some remaining challenges to managing this recovering transboundary resource in a dynamic multispecies fishery.
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Fisheries Research 94 (2008) 123–132
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The nascent recovery of the Georges Bank haddock stock
Jon Brodziak, Michele L. Traver, Laurel A. Col
Northeast Fisheries Science Center, 166 Water Street, Woods Hole, MA 02543, United States
article info
Article history:
Received 30 October 2007
Received in revised form 19 March 2008
Accepted 27 March 2008
Georges Bank
Stock assessment
Fishery management
World-wide many fish stocks have been depleted by overfishing. In this study, we describe the nascent
recovery of the Georges Bank haddock stock. This mainstay of the New England groundfish fishery was
overfished for decades prior to mid-1990s and experienced long-term declines in spawning biomass and
recruitment. The stock was considered to have collapsed in the early-1990s when a lawsuit by the Con-
servation Law Foundation led the New England Fishery Management Council (NEFMC) and the National
Marine Fisheries Service (NMFS) to take actions to cease overfishing and to recover Georges Bank haddock
and other groundfish stocks. Under restrictive management measures, stock size increased 10-fold from
1995 to 2005. In 2003, an exceptionally abundant year class (YC) was produced. Although this YC may
rebuild the haddock stock to pre-1930s abundance if properly fished, monitoring changes in life history
parameters and recruitment will be important for sustaining stock recovery. Mean weights and sizes at
age of adult haddock have decreased in recent years, and compensatory responses of haddock growth and
recruitment to changes in stock density are assessed. We discuss some remaining challenges to managing
this recovering transboundary resource in a dynamic multispecies fishery.
Published by Elsevier B.V.
1. Introduction
Rebuilding depleted marine fishery resources in the U.S. is
mandated by the Sustainable Fisheries Act. This law requires
that management measures prevent overfishing and achieve BMSY,
the stock size that produces maximum yield, for the purpose of
achieving optimum yields. However, reducing fishing mortality
and implementing successful rebuilding plans for depleted fish-
ery resources has proven to be challenging in practice (Rosenberg
et al., 2006). Nowhere in the U.S. has this been more apparent
than in the New England region, where there have been ongoing
controversies over stopping overfishing and rebuilding fisheries
The Georges Bank haddock (Melanogrammus aeglefinus)stock
(Fig. 1) was the mainstay of the New England groundfish fishery
in the mid-20th century. Annual haddock landings from Georges
Bank averaged 46kt during 1931–1960 (Fig. 2), roughly 100 million
pounds a year. Foreign distant water and domestic fleets severely
overharvested the stock in the 1960s, and by the early-1970s,
Georges Bank haddock stock size and annual yield had dropped to
record lows (Figs. 2 and 3). The stock experienced a brief recovery
Corresponding author. Currentaddress: Pacific Islands Fisheries Science Center,
2570 Dole Street, Honolulu, HI 96822-2326, United States. Tel.: +1 808 983 2964;
fax: +1 808 983 2902.
E-mail address: Jon.Brodziak@NOAA.GOV (J. Brodziak).
in the late-1970s when two strong year classes (YCs) (1975 and
1978) were produced. By the mid-1980s, however, the stock had
again declined due to chronic overfishing. U.S. landings of Georges
Bank haddock declined more than 100-fold in 30 years, falling
from 52.918 kt in 1965 to a record low of 0.218kt in 1994–1995
(Fig. 2). By the early-1990s, the stock was again at record-low
abundance and was considered to be collapsed (NEFSC, 1994). In
effect, this productive stock was overfished for several decades
prior to mid-1990s (Brodziak and Link, 2002) and as a result, expe-
rienced long-term declines in spawning biomass and recruitment
(Brodziak et al., 2001).
Management of New England groundfish stocks has been the
subject of legal disputes for over 20 years. The U.S. and Cana-
dian maritime border dispute over territorial waters in the Gulf
of Maine-Georges Bank region was decided by the International
Court in 1984. The settlement established the Hague Line demar-
cating the maritime border between U.S. and Canadian fishing areas
on Georges Bank. In this case, the U.S. lost access to the produc-
tive Northeast Peak of Georges Bank, an important haddock fishing
area. As a result, the Georges Bank haddock stock is a transboundary
resource shared by the U.S. and Canada (Christie, 1987). The east-
ern Georges Bank haddock management unit is jointly managed
by the two countries (Fig. 1) while the U.S. manages the western
Georges Bank management unit. In May 2004, a formal quota shar-
ing agreement between Canada and the U.S. was implemented to
share the harvest of the transboundary eastern Georges Bank had-
dock management unit. This agreement includes total allowable
0165-7836/$ – see front matter. Published by Elsevier B.V.
124 J. Brodziak et al. / Fisheries Research 94 (2008) 123–132
Fig. 1. The geographic range of the Georges Bank haddock stock off New England (enclosed by solid red lines) showing the western and eastern management units along
with the Hague Line demarcating the boundary between U.S. and Canadian waters and four year-round groundfish closed areas (CA): CA I, CA II, the Nantucket Lightship CA,
and the Western Gulf of Maine (WGOM) CA. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)
catch quotas for each country as well as in-season monitoring of
the catch of haddock on eastern Georges Bank.
Another dispute arose in 1991 when the National Marine Fish-
eries Service (NMFS) was sued by the Conservation Law Foundation
(CLF) to cease overfishing of New England groundfish stocks,
including Georges Bank haddock. As a direct result of this lawsuit,
the New England Fishery Management Council (NEFMC), which has
advisory authority to put forward fishery management measures
for approval by NMFS, agreed to three large-scale area closures on
Georges Bank and in Southern New England. The three areas closed
were Closed Area I, Closed Area II, and the Nantucket Lightship
Closed Area (Fig. 1). These areas were closed to all fishing gears that
were capable of catching groundfishes, including otter trawls, gill-
nets, longlines, and scallop dredges. Year-round closed areas were
established in the Western Gulf of Maine in 1998 and on Cashes
Ledge in 2002 to reduce fishing mortality on Gulf of Maine cod. Indi-
vidual vessels were allocated a baseline number of days at sea based
on their recorded fishing history. Thus, restrictive management
measures were imposed on the U.S. groundfish fishery in the mid-
1990s toreduce fishing mortality on groundfish stocks, in particular
Atlantic cod, haddock, and yellowtail flounder on Georges Bank.
These management measures were effective for some ground-
fish stocks like Georges Bank haddock, but not for others. In
particular, the Gulf of Maine and Georges Bank Atlantic cod stocks
Fig. 2. Trends in commercial catch biomass (shaded area, kt) and fishing mortality
(solid line, average for ages 4–7) for Georges Bank haddock from 1931 to 2004.
J. Brodziak et al. / Fisheries Research 94 (2008) 123–132 125
Fig. 3. Trends in Georges Bank haddock spawning biomass (SB, solid line) during
1931–2004 and recruitment (R, solid bar) during 1931–2005 along with projected
spawning biomass (median and interquartile range) during 2005–2009 and pro-
jected recruitment (average plus one standard error) during 2006–2009 under the
Amendment 13 stock rebuilding plan.
continued to experience overfishing through the late-1990s. The
lack of progress in reducing fishing mortality on cod led the CLF
and four other environmental organizations to sue NMFS again in
1999. In this lawsuit, the Plaintiffs asserted that NMFS was not in
compliance with its legal mandate to cease overfishing (reduce F
to or below FMSY) on Atlantic cod and other groundfish stocks. The
environmental organizations prevailed in this lawsuit. As a result,
the U.S. District Court for the District of Columbia required that
NMFS and the NEFMC complete Amendment 13 (NEFMC, 2003,
see below), a comprehensive plan to end overfishing on all New
England groundfish stocks.
In this study we describe the nascent recovery of the Georges
Bank haddock stock. Research survey and stock assessment data
are used to assess changes in stock status and population dynamics
from the 1930s to the present. We focus special attention on the
exceptional 2003 year class and consider the confluence of factors
that led to increased stock productivity. Mean weights and sizes at
age of adult haddock have decreased in recent years and compen-
satory responses of haddock growth and recruitment to changes in
stock density are also assessed. We discuss some remaining chal-
lenges to managing this recovering transboundary resource in a
changing multispecies fishery.
2. Methods
Research survey data from the Northeast Fisheries Science Cen-
ter (NEFSC) autumn and spring bottom trawl surveys were used
to index the relative abundance at age, growth, weight at length,
and spatial distribution of haddock. The NEFSC has conducted bot-
tom trawl surveys of the NE continental shelf ecosystem since
the 1960s (Grosslein, 1969; Azarovitz, 1981); the autumn bottom
trawl survey began in 1963 and the spring bottom trawl survey
began in 1968. These standardized survey data include indices
of cohort abundance for GB haddock in autumn for 1963–2005
and in spring for 1968–2005 (Brodziak et al., 2006). They also
include size-at-age data for individual cohorts since 1961, individ-
ual weight-at-length data since 1992, and spatial distribution data
since 1963. In addition, the Canadian Department of Fisheries and
Oceans (DFO) initiated a winter bottom trawl survey on Georges
Bank in 1986. This survey also provides age-specific number per
tow indices for Georges Bank haddock during 1986–2004 (Van
Eeckhaute and Brodziak, 2004). Together, these surveys track the
relative abundance of year classes for estimation of stock size and
fishing mortality and are used to compare the abundance, growth,
condition factor, and spatial distribution of the 2003 YC in compar-
ison to other cohorts of Georges Bank haddock.
We collected data from recent stock assessments of the Georges
Bank haddock stock (Brown and Munroe, 2000; Brodziak et al.,
2006) to document changes in stock abundance and fishery impacts
through time. The most recent stockassessment provided estimates
of spawning biomass, recruitment, and fishing mortality through
calendar year 2004 (Brodziak et al., 2006). These estimates were
derived from tuned virtual population analysis (VPA) as in Brown
and Munroe (2000) and Brodziak et al. (2006). These data were
also used to evaluate the association between survival ratios and
spawning through time. Fishery mean weights at age of haddock
were collected from Clark et al. (1982) and Brodziak et al. (2006) to
assess changes in mean weight across cohorts through time.
The research survey and stock assessment data were analyzed
to assess changes in stock status and population dynamics from the
1930s to the present. Research survey data were used to fit cohort-
specific von Bertalanffy growth curves during 1961–1996 using
the likelihood method of Kimura (1980). Allometric length–weight
parameters were fitted to research survey weight-at-age data from
1992 to 2002 using the low-bias estimator of Hayes et al. (1995).
Spearman rank correlations between annual Georges Bank had-
dock commercial fishery weights at age (age-2 through age-9+)and
spawning biomass were calculated to investigate the associations
between fish weight and biomass density. Associations between
haddock recruitment strength on Georges Bank and in the Gulf of
Maine (Fig. 1) were assessed using the Spearman correlation coef-
ficient between VPA estimates of recruitment and age-1 survey
abundance indices from the Gulf of Maine. Similarly, the associ-
ation between the NEFSC autumn survey age-0 haddock survey
index and VPA estimates of recruitment was evaluated using the
Spearman correlation coefficient. The odds of achieving recruit-
ment above its 1931–2005 median value when spawning biomass is
over 75 kt were evaluated using Fisher’s exact test applied to a 2×2
contingency table of stock-recruitment data using the approach of
Brodziak et al. (2001).
3. Results
3.1. Survey abundance indices
The NEFSC spring and autumn abundance indices exhibit sim-
ilar trends through time (Fig. 4). Autumn indices declined from
record highs in the 1960s to low levels in the early-1970s. The
Fig. 4. U.S. and Canadian research survey abundance indices for Georges Bank had-
dock, 1963–2005.
126 J. Brodziak et al. / Fisheries Research 94 (2008) 123–132
spring and autumn indices both increased in the mid-1970s due
to the strong 1975 and 1978 year classes and then declined in the
early 1980s. Both U.S. and Canadian abundance indices were low
from the mid-1980s to the mid-1990s and have since increased.
The NEFSC autumn survey age-0 haddock index exhibited a signifi-
cant positive rank correlation with estimated recruitment (R=0.83,
P< 0.001). Overall, the survey indexseries show a consistent pattern
of a rapid increase in haddock abundance since 2000.
3.2. Spawning biomass
During 1931–1960, Georges Bank haddock biomass was rela-
tively high, averaging 102kt (Fig. 3). Spawning biomass increased
in the late-1950s through early 1960s coincident with the impo-
sition of a minimum trawl mesh size of 4.5in. in 1954 (Graham,
1952), the first regulatory measure applied to the haddock fishery.
The increase in mesh from an average of about 2.5 in. undoubt-
edly reduced the wasteful discard of undersized haddock that had
diminished fishery productivity since the 1930s(Herrington, 1935).
The reduction in juvenile mortality is believed to have been an
important factor in building haddock spawning biomass to roughly
200 kt in 1962, the highest ever observed.
Georges Bank haddock spawning biomass changed substan-
tially during the next four decades. While spawning biomass
remained relatively high during the mid-1960s averaging 132kt
during 1963–1968 (Fig. 3), it subsequently declined to a near-
record low of 15 kt in 1973 due to overfishing. Spawning biomass
almost doubled to an average of 48kt during 1975–1984 with
the production of two large year classes. Spawning biomass then
declined again to average about 23kt during 1985–1994, reach-
ing a record low of 15 kt in 1993. During the mid-1990s, spawning
biomass began to increase and averaged 50 kt during 1995–2000.
Since 2001 spawning biomass has approached levels observed
in the 1960s and averaged 115 kt during 2001–2004. Spawning
biomass increased by 22% from 96 kt in 2001 to 117 kt in 2004.
Despite marked increases in recent years, however, spawning
biomass in 2004 was still less than 50% of the rebuilding target
of BMSY = 250.3 kt.
3.3. Recruitment
Recruitment of Georges Bank haddock also fluctuated substan-
tially during 1931–2005 (Fig. 3). Recruitment was relatively high
and stable during 1931–1960, averaging 75 million age-1 recruits
(Fig. 3). Recruitment during 1961–1968 averaged 93 million fish and
was dominated by the exceptional 1963 year class (462 million age-
1 fish). Recruitment declined to average only 8 million fish during
1969–1974 and subsequently increased to average 26 million fish
during 1975–1984 primarily due to the strong 1975 (106 million)
and 1978 (84 million) year classes. Recruitment declined again to
average only 8 million fish during 1985–1994. In the mid-1990s,
recruitment steadily increased to average 22 million fish during
1995–2000. Since 2001, recruitment has averaged 179 million fish.
In particular, the 2003 YC is the highest recruitment on record,
with an estimated size of 789 million age-1 fish. Bootstrap anal-
ysis indicates that the CV on the size of this cohort at age-2 at the
start of 2005 (645 million fish) was about 41%. Thus, although the
2003 YC is very abundant, its absolute magnitude remains uncer-
3.4. Fishery yield
The Georges Bank haddock stock has been commercially
exploited since the 19th century with stock assessment informa-
tion beginning in 1931 (Fig. 2). Since then, the fishery for Georges
Bank haddock has gone through sevenperiods: (1) the initial expan-
sion from 1904 to 1923 when annual nominal catches averaged
17.4kt; (2) the rapid expansion and decline during 1924–1930 when
catches averaged 73.2 kt; (3) the 30-year period of fishery sta-
bility during 1931–1960 when annual catch averaged 46.3kt; (4)
the rapid expansion and decline during 1961–1968 when catches
averaged 73.0kt; (5) the pre-Hague line fishery during 1969–1984
when catches averaged about 13.5 kt; (6) the fishery nadir during
1985–2000 when catches averaged only 5.6kt; and (7) the nascent
recovery from 2001 to 2004 when annual catches have increased
to average 13.7kt per year. Catches have increased each year since
1995 with the exception of 2003 as the stock has been rebuild-
ing under restrictive management measures in the Georges Bank
region. In 2004, total commercial catch was 17.6 kt, over sevenfold
larger than the lowestrecorded catch taken in 1995 but less than 1/3
of the yield sustained during 1931–1960. Thus, fishery yields have
not increased as rapidly as stock size, in part due to restrictions on
the bycatch of cod.
3.5. Fishing mortality
Fishing mortality on Georges Bank haddock has also changed
substantially through time. The fishing mortality (F) rateon Georges
Bank haddock was relatively high with a long-term decline dur-
ing 1931–1960 (Fig. 2). Since 1963, Fhas ranged from less than
0.1 to over 0.6 (Fig. 2). Fwas high during the 1960s averaging
0.52 during 1963–1968 and subsequently declined to a low of
0.06 in 1974. Fincreased substantially in the mid-1980s and aver-
aged 0.35 during 1985–1994. Fishing mortality declined in the
mid-1990s and has remained below the overfishing threshold of
FMSY = 0.26 since 1995. In particular, the 1995–2004 decade is the
longest continuous period of time that the Georges Bank had-
dock stock has not been experiencing overfishing since the early
3.6. Growth
Cohort-specific growth curves based on research survey size-at-
age data show that the exceptional 1963 YC grew slower than the
average cohort-specific growth pattern during 1961–1996 (Fig. 5).
Predicted curves indicate that mean lengths at ages 2 and 3 were
about 15% lower than average for the 1963 YC. In comparison, the
strong 1975 YC, which was about 1/4 of the size of the 1963 YC,
exhibited close to average growth through its lifetime. This suggests
Fig. 5. Observed mean size at age and 80% confidence interval for the 2003 Georges
Bank haddock year class collected during NEFSC during autumn20 03 through spring
2007 in comparison to von Bertalanffy estimates growth curves for the 1963 and
1975 year classes and the 1961–1996 average growth curve. Age-1 on the x-axis
corresponds to the observation of the 2003 YC at age-1 during spring 2004.
J. Brodziak et al. / Fisheries Research 94 (2008) 123–132 127
Fig. 6. Observed weight at length (solid dot) and 95% confidence interval along with average length (OBS) of the 2003 Georges Bank haddock year class during the NEFSC
(a) autumn 2003, (b) spring 2004, (c) autumn 2004, (d) spring 20 05, (e) autumn 2005, and (f) spring 2006 surveys in comparison to the average length–weight curves (solid
line) during NEFSC autumn and spring surveys during 1992–2002.
that strong year classes of Georges Bank haddockmay have a typical
growth pattern whereas exceptional year classes on the order of
200 million or more age-1 fish may experience density-dependent
growth with a smaller mean size at age.
Mean size at age of the 2003 YC has been well-below average
since it was first observed in autumn 2003 (Fig. 6), and it appears
to be smaller than that exhibited by the 1963 YC, the previous
record YC (486 million age-1 fish). The slower growth of the 2003
YC indicates it will begin to recruit to the fishery at age-4 in 2007,
instead of the typical pattern of recruitment to the fishery at age-3.
In particular, if the 2003 YC has a similar growth pattern as the
1963 YC, then it will reach the U.S. minimum legal commercial
size of 48 cm at least 1 year later than an average cohort. This sug-
gests that density-dependent growth will delay the availability of
the 2003 YC to be landed in the commercial fishery by at least 1
3.7. Weight at length
Allometric length–weight relationships show that the excep-
tional 2003 YC had significantly lower mean weight at length
than the recent average length–weight relationship for 1992–2002
(Fig. 6). The condition factor of the 2003 YC at age-0 was near or
slightly below the recent average during autumn 2003 (Fig. 6a). The
percentage of the age-0 autumn 2003 samples with below average
weight at length was 71%with a 95% confidence interval (CI) of (66%,
75%). At age-1 in spring 2004, the condition factor of the 2003 YC
was also significantly lower than average (Fig. 6b) and the propor-
tion of age-1 spring 2004 samples with below average weight was
97% with a CI of (93%, 99%). Similarly, during autumn 2004 through
autumn 2005, the condition factor of the 2003 YC was significantly
below average. The percentages of the 2003 YC samples with below
average weight at length during autumn 2004, spring 2005, and
128 J. Brodziak et al. / Fisheries Research 94 (2008) 123–132
Fig. 7. Trends in Georges Bank haddock commercial fishery mean weights at age
(kg) for age classes 3–7 (solid lines with numbered circle indicating age class) along
with trends in spawning biomass (dashed line), 1931–2004.
autumn 2005 NEFSC surveys were 93% (CI of (89%, 96%)), 94% (CI of
(91%, 96%)), and 87% (CI of (83%, 90%)). Overall, the condition fac-
tor of the 2003 YC has been consistently below average, suggesting
that intraspecific competition for food may be limiting growth of
this cohort.
To investigate this possibility, the food habits of the 2003 YC
were opportunistically sampled during the NEFSC autumn 2003
and spring 2004 surveys to discern whether the diet composition
was anomalous. Analyses of over 1000 stomachs indicated that the
diet composition of the 2003 YC was not atypical and consisted pri-
marily of gammarids, caprellids, and other small crustaceans (see,
for example, Brodziak, 2005). The observation of a normal diet of
the 2003 YC combined with its low observed condition factor sug-
gested that a reduced per capita ration was likely the cause of its
smaller weight at length, on average.
3.8. Fishery mean weights at age
Commercial fishery mean weights at age fluctuated syn-
chronously across ages throughout the 1930s–1960s (Fig. 7). Mean
weights at age increased substantially in the 1970s when spawn-
ing biomass declined. Weights at age for age classes 5–7 gradually
declined through the from peak values in the early 1970s to long-
term average in the 2000s. In contrast, weights at age for age classes
3 and 4 were more stable during the 1980s–1990s but also show
a sharp decline in recent years. Overall, the trends in spawning
biomass and mean weights appeared to suggest an association of
increasing weight at age with declining adult biomass.
Correlation analyses indicated there was a strong positive asso-
ciation between changes in weight at age between age classes
(Fig. 8). Correlations () among weight-at-age values were positive
and ranged from a low of =0.46 to a high of = 0.92. In contrast,
there was a negative association between means weights at age
and spawning biomass (Fig. 8). Significant negative associations
were detected between spawning biomass and mean weights at
Fig. 8. Scatterplots of Georges Bank haddock commercial fishery mean weights at age for age-2 (Age2)through age-8 (Age8) and age-9 and older (Age9) along with spawning
biomass (SB) during 1931–2004.
J. Brodziak et al. / Fisheries Research 94 (2008) 123–132 129
Fig. 9. Spatial distribution of the 1963 and 2003 year classes of Georges Bank haddock in the Georges Bank–Gulf of Maine regioncaptured at age-0 during the 1963 and 2003
NEFSC autumn bottom trawl surveys.
age-2 through age-9+ (P<0.001), with negative rank correlations
ranging from R=0.66 to 0.75. Overall, changes in commercial
fishery weight at age were inversely related to changes in spawn-
ing biomass, indicating possible density-dependence in haddock
3.9. Spatial distribution
Spatial distribution plots of the 1963 and 2003 year classes at
age-0 (Fig. 9) show that the 2003 YC had a more southwesterly dis-
tribution than the comparably abundant 1963 YC. In particular, the
distance between the centroids of distribution of the 2003 and 1963
YCs was about 177km. In 1963, age-0 haddock were abundant in the
Gulf of Maine, but in 2003, they were largely absent. This difference
in abundance of age-0 haddock in the Gulf of Maine and Georges
Bank is atypical since recruitment of Georges Bank haddock was
significantly positively correlated with NEFSC age-0 survey catch
number per tow in the Gulf of Maine during 1963–2004 (R= 0.53).
This suggested that haddock recruitment strength in the Gulf of
Maine and Georges Bank regions was typically synchronous, but
that this pattern did not occur in 2003.
3.10. Survival ratios
Survival ratios of Georges Bank haddock, as indexed by recruit-
ment per spawning biomass, have fluctuated about an average of
0.70 recruits per kg (R/S) during 1931–2004 (Fig. 10). Survival ratios
averaged 0.76 R/S with a standard error of 0.06 during 1931–1960
when spawning biomass averaged 102 kt. Since then survival ratios
have declined 13% on average to 0.66 R/S with a standard error
of 0.18 during 1961–2004 when spawning biomass averaged 64 kt.
Although the decline in survival ratios since the 1960s is not statisti-
cally significant, it may reflect an important change in productivity
of the Georges Bank haddock stock. Similarly, the coefficient of vari-
ation of survival ratios during 1961–2004 (27%) was over threefold
higher than during 1931–1960 (8%) indicating that variability in
early life history survival has also increased in recent decades.
Since 1961, three strong year classes (>100 million recruits) had
survival ratios of roughly 3 or more; these were the 1963, 1975,
and 2003 year classes (Fig. 10). Each of these year classes experi-
enced high survival during early life history stages, suggesting the
influence of favorable environmental conditions for large recruit-
ment events. Regardless, a positive association between spawner
130 J. Brodziak et al. / Fisheries Research 94 (2008) 123–132
Fig. 10. Annual survival ratios of Georges Bank haddock, indexed by the number
of recruits per kilogram of spawning biomass, along with the average survival ratio
(dashed line) during 1931–2004.
abundance and survival ratios was also suggested since survival
ratios average 0.82 when spawning biomass is over 75kt in com-
parison to only 0.59 (28%) when spawning biomass is less than
75 kt.
3.11. Stock–recruitment relationship
Spawner abundance is clearly an important determinant of
Georges Bank haddock recruitment strength (Fig. 11). Analyses of
stock–recruitment data indicate that spawning stock size affects
recruitment of Georges Bank haddock (Brodziak and Legault, 2005;
Brodziak et al., 2001; NEFSC, 2002). In particular, Brodziak et al.
(2001) found that when spawning stock biomass is above 82 kt, the
odds of recruitment being above average is 20 times greater than
when biomass is below that level and the average YC size is fivefold
higher using data from 1931 to 1998.
In a subsequent analysis, the Working Group on the Re-
evaluation of Reference Points for New England Groundfish
determined that an appropriate productivity threshold for Georges
Bank haddock was 75kt of spawning biomass (NEFSC, 2002).
Using this cutoff and the most recent stock assessment data, aver-
age recruitment at high spawning biomass (>75kt) is 94 million
age-1 fish (Fig. 11) while average recruitment is about 20 mil-
lion fish at low spawning biomass (<75kt). The odds of achieving
recruitment above its 1931–2005 median value when spawning
Fig. 11. Relationship between Georges Bank haddock recruitment strength (age-1
fish) and spawner abundance (kt) during 1931–2004 along with mean recruitment
() above and below the threshold spawner abundance of 75kt.
biomass is over 75 kt are 23 times greater than when spawning
biomass is less than 75 kt. This difference is statistically significant
(P< 0.001) based on Fisher’s exact test applied to the 2 ×2 contin-
gency table of stock–recruitment data. Furthermore, the average
spawning biomass that produced the 12 large year classes of over
100 million age-1 fish since 1931 was 110kt. Of these 12 YCs, the
smallest was the 1975 year class which wasproduced by a spawning
biomass of 22 kt. The remainder of the large haddock YCs (the 1936,
1939, 1940, 1948, 1950, 1952, 1958, 1959, 1962, 1963 and 2003)
were all produced by spawning biomasses of greater than 75 kt.
This underscores the importance of maintaining adequate spawner
abundance on the productivity of the Georges Bank haddock stock.
3.12. Biological reference points
Biological reference points provide benchmarks for determin-
ing whether Georges Bank haddock are being overfished or are
in an overfished condition. Georges Bank haddock are currently
managed according to the U.S. Sustainable Fisheries Act of 2007
(NOAA, 2007) which requires that fishery conservation and man-
agement measures prevent overfishing and rebuild depleted stocks
to biomasses consistent with producing maximum sustainable
yield (MSY). Overfishing occurs wheneverfishing mortality exceeds
a threshold that jeopardizes the reproductive capacity of a stock to
produce maximum sustainable yield. For Georges Bank haddock,
spawning biomass (BMSY) and the fishing mortality to produce MSY
(FMSY)areBMSY = 250.3 kt and FMSY = 0.26 (NEFSC, 2002). Guide-
lines to the Act also specify that an overfished resource is one
that has been reduced below a minimum stock size threshold.
For Georges Bank haddock, the minimum stock size threshold
is one-half the biomass needed to produce MSY (BMSY). That
is, the overfished threshold (BTHRESHOLD) for Georges Bank had-
dock is BTHRESHOLD = (1/2)BMSY =125.2kt. The overfishing threshold
(FTHRESHOLD) for Georges Bank haddock is FTHRESHOLD =FMSY = 0.26. It
is possible for a stock to be classified as overfished (due to previous
overharvesting) even though the annual harvest rate is below the
overfishing threshold. This has been the case for haddock, which
has been rebuilding under low fishing mortality rates in recent
3.13. The recovery plan
The formal rebuilding plan for Georges Bank haddock adopted
in Amendment 13 calls for fishing at the overfishing threshold
FMSY = 0.26 during 2004–2008 (NEFMC, 2003). In 2009, the fishing
mortality would be reduced marginally to FREBUILD = 0.245, a value
projected to produce at least a 50% chance that spawning biomass
will meet or exceed BMSY =250.3 kt in 2014. This rebuilding strategy
is subject to change in 2008 if observed progress towards rebuilding
spawning biomass or reducing fishing mortality is not consistent
with the projected rebuilding trajectory.
To measure progress towards stock recovery, the projected
Amendment 13 rebuildingtrajectory for Georges Bank haddock was
compared to VPA estimates of spawning biomass and fishing mor-
tality in 2004. Haddock has an adaptive rebuilding plan in which
the fishing mortality to rebuild the stock is equal to the overfish-
ing threshold during 2004–2008, i.e., FREBUILD =FMSY = 0.26, and in
2009 the rebuilding Fwill be adjusted to meet the goal of achieving
BMSY by 2014. Median spawning biomass for the haddock rebuilding
trajectory (SBREBUILD) was projected to be 130 kt in 2004. In compar-
ison, the 80% confidence interval for SB2004 was (98, 139)kt. Thus,
the SBREBUILD value falls within the probable range of the VPA esti-
mate of SB2004. Similarly, the 80% confidence for F2004 was (0.21,
0.31) and the FREBUILD =0.26 value falls within the probable range
of the VPA estimate of F2004. Overall, 2004 estimates of spawning
J. Brodziak et al. / Fisheries Research 94 (2008) 123–132 131
biomass and fishing mortality indicate that Georges Bank haddock
is on the path to stock recovery.
In addition, projected increases in Georges Bank haddock
spawning biomass from the most recent assessment (Fig. 3;
Brodziak et al., 2006) suggest that the spawning biomass will likely
reach BMSY in a few years. If this projection is realized, the Georges
Bank haddock stock will have been rebuilt in less than the legally
mandated 10-year time horizon.
4. Discussion
The Georges Bank haddock stock responded positively to
changes in fishing mortality during the 1990s. Under persistent
overfishing in the 1980s, Georges Bank haddock spawning biomass
declined almost 80% from 67 kt in 1980 to less than 15 kt in 1993.
Since 1994, spawning biomass has increased substantially as fish-
ing mortality decreased. By 2003, spawning biomass had increased
to 132kt, the highest abundance of adult spawners since 1966
and over a ninefold increase since 1993. Even though stock size
has increased markedly in recent years, the Georges Bank haddock
stock was still considered to be overfished in 2004 since spawning
biomass was less than one-half of the rebuilding target. Nonethe-
less, estimates of stock size indicate that the stock is on the path
to recovery and projections indicate that the stock is likely to be
rebuilt in a few years.
One of the challenges facing U.S. fishery management is the
question of how to access a recovering haddock stock with year-
round groundfish closures. Several innovative gear designs have
been developed to reduce the catch of cod in otter trawl gear.
These so-called haddock separator trawls are now a requirement
for participation in the haddock Special Access Program in the east-
ern Georges Bank haddock management area. Another innovative
development was the use of fabricated baits by hook and line fish-
ermen. Experimental data show that using the fabricated bait to
target haddock also reduced the bycatch of cod to acceptable lev-
els. This innovation allowed for the developmentof a Special Access
Program for hook and line fishermen to fish for haddock in Closed
Area I. This, in turn, provided an economic opportunity for small-
vessel operators who previously only targeted cod using traditional
baits like squid, mackerel, or herring. Overall, the innovation of the
fishing industry may help it to survive through lean times when
many New England groundfish stocks are still well below their
biomass targets.
Recruitment of Georges Bank haddock also displayed a positive
response to reduced fishing mortality. Recruitment averaged only 8
million age-1 recruits per year during 1980–1993. Since 1994, aver-
age recruitment has increased over 10-fold to about 87 million fish.
Further, prospects remain positive for continued high recruitment
since spawning biomass is currently above the 75kt threshold.
Recent U.S. and Canadian assessments and research survey data
provide empirical support to the assessment model estimates that
the 2003 year class is exceptionally abundant. If this exceptional
cohort can be protected from excessive discarding and high fishing
mortality, it has the potential to rebuild the Georges Bank had-
dock spawning biomass to over its estimated BMSY of 250 kt in
the near future. This would be a remarkable change in resource
abundance given that spawning biomass reached a record low of
15kt in 1993.
Recruits per spawner data shows that survival ratios for Georges
Bank haddock were relatively low from the late-1960s to early-
1990s in comparison to historic ratios during the 1930s–1960s. The
impact of the large-scale area closures, reductions in fishing effort,
and trawl mesh size increases during the 1990s appears to have had
a positive effect on recruits per spawning biomass (R/SB). During
1980–1993, R/SB averaged about 0.33 recruits per kilogram. Since
1994, average R/SB, excluding the exceptional 2003 year class, has
increased to 0.46 recruits per kilogram. Further increases in R/SB
may still occur since, at least historically, the expected value of R/SB
was higher. Overall, the recent increases in R/SB indicate that sur-
vival ratios are approaching the historical average of about 0.76
recruits per kilogram observed during 1931–1960, despite recent
decreases in fish size at age. If the recent increases in recruitment
and survival can be sustained, it is possible that historical yields on
the order of 50 kt per year may be achievable.
The exceptional 2003 haddock year class was influenced by pos-
itive maternal and environmental conditions. Haddock spawning
biomass in 2003 was the highest since 1967. Further, the spawn-
ing biomass of repeat spawners (age-5 and older) was 56.9kt in
2003, the highest observed since 1968. High spawning output
from a broad age structure of mature spawners combined with
favorable environmental conditions to produce very high early life
history survival. One favorable environmental condition appears to
have been the geostrophic currents caused by southwesterly wind
stresses during spring 2003 which led to the southerly distribu-
tion of age-0 haddock in the Mid-Atlantic Bight during the autumn
NEFSC survey, similar to that observed in 1987 (Polachek et al.,
1992). This wind pattern would be expected to enhance retention
of haddock eggs and larvae on Georges Bank and improve survival
of the 2003 YC (Fig. 10). In addition, a strong fall phytoplankton
bloom in 2002 appears to have been a key factor in the formation
of the 2003 YC (Friedland et al., in press). In this case, an increase
in the quantity and quality of haddock reproductive output would
be expected due to enhanced adult feeding conditions.
Our analyses of haddock size at age and condition factor indicate
that the 2003 year class is experiencing compensation in growth
rate. The pattern of density-dependent growthof the 20 03 YC needs
to be considered in near-term management measures. If this YC
was heavily targeted in 2006, many of the fish would have been
below the U.S. legal minimum size of 48 cm. Based on our analyses,
the potential for high discard rates appears to have been substan-
tial. For Canadian fishermen, this issue is less of a concern because
Canada does not impose a minimum haddock size and the Cana-
dian fishermen are mandated to bring in all of their catch to count
against their TAC. Regardless, setting an appropriate minimum size
is important for U.S. fishery management giventhe observed reduc-
tions in mean length at age of recent Georges Bank haddock cohorts
and the apparent density-dependent growth of this stock (Brodziak
and Link, in press).
One of the striking aspects of the haddock stock is the threshold
in productivity that appears around 75–85 kt of spawning biomass.
There are several hypotheses that may explain whysuch a threshold
might exist including expansion of spawning activity in space and
time to hedge risks of egg and larval survival, fecundity increases
more than linearly with weight at age for older haddock, improved
egg quality due to higher proportions of multiple spawning females
in the stock, increased chances of secondary fertilization due to
adequately sized spawning aggregations, and more eggs to escape
opportunistic zooplankton predators. Of these, the two hypotheses
that are most readily testable are the questions of increased fecun-
dity at older ages and improved egg quality from older females
(Berkeley et al., 2004). While there was a small-scale cooperative
research effort to estimate haddock fecundity in 2005, there is no
long-term research effort to assess changes in fecundity through
time. While it is not surprising in this era of reduced scientific bud-
gets that there is a lack of funding for expanding fecundity research
initiatives, we believe investigating the importance of parental con-
dition is an important research topic that needs to be addressed.
The challenges of joint management of the transboundary
Georges Bank haddock stock became evident in 2005. While the
132 J. Brodziak et al. / Fisheries Research 94 (2008) 123–132
Canadian fishery took its allocated share of the total TAC, the U.S.
fishery on eastern Georges Bank was closed in August 2005 because
the Atlantic cod bycatch TAC was projected to be taken. Protection
of the depleted Georges Bank cod stock required that some U.S.
haddock yield had to be forgone. This situation may continue to
occur in the near future until the cod stock begins to show signs
of recovery as well. Overall, fishery closures due to restrictions on
cod bycatch may also contribute to faster rebuilding of the Georges
Bank haddock stock.
One of the salient points of the nascent haddock recovery is that
fishery management can work. Keeping fishing mortality below the
overfishing threshold can produce tangible economic benefits in
the near term. Instead of writing off the haddock stock in the mid-
1990s, the New England fishery management system responded
with restrictive measures that reduced fishery mortality on this
stock. The realization that depleted stocks can recover needs to
be taken to heart by skeptical resource stakeholders (Safina et
al., 2005). Hopefully, Georges Bank haddock stock will not be an
isolated case and other New England groundfish stocks, such as
Georges Bank cod, will recover despite recent declines in stock
productivity (Shelton et al., 2006).
We thank Drs. E. Brooks and C. Needle for their helpful com-
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... This difference in ontogenetic diet shift between M. aeglefinus and G. morhua can be explained by the smaller gape size and body size of M. aeglefinus, which limit the size of prey that it can consume (Løkkeborg et al., 1989). 1975 1980 1985 1990 1995 2000 2005 2010 2015 1975 1980 1985 1990 1995 2000 2005 2010 2015 1975 1980 1985 1990 1995 2000 2005 2010 2015 1975 1980 1985 1990 1995 2000 2005 the Scotian Shelf and, thus, do not appear to be suffering from reduced productivity due to their reliance on low-nutrient food sources (Brodziak et al., 2008;Bogstad et al., 2013;Pecuchet et al., 2015). Eating food of high calcium carbonate and low energy may have developed in M. aeglefinus to reduce competition with other gadoids by obtaining a consistent, albeit low-energy food source. ...
... While traditional conservation strategies, such as fisheries closures, are not always effective at increasing target fish stocks (Fisher & Frank, 2002;Kelly et al., 2006), M. aeglefinus have historically responded well to these management options (Brodziak et al., 2008). In the mid-1990s, M. aeglefinus stocks in the north-west Atlantic Ocean were the lowest on record (Hutchings, 2000). ...
... In the mid-1990s, M. aeglefinus stocks in the north-west Atlantic Ocean were the lowest on record (Hutchings, 2000). After strict closures as a response to the declining stock status, M. aeglefinus stocks increased dramatically (Murawski et al., 2000;Brodziak et al., 2008). Melanogrammus aeglefinus are also known to have a restricted daily ambit compared with other gadoids, indicating a strong association with local habitats (Perry & Smith, 1994;Fogarty et al., 2001). ...
The food habits of Melanogrammus aeglefinus were explored and contrasted across multiple north-eastern and north-western Atlantic Ocean ecosystems, using databases that span multiple decades. The results show that among all ecosystems, echinoderms are a consistent part of M. aeglefinus diet, but patterns emerge regarding where and when M. aeglefinus primarily eat fishes v. echinoderms. Melanogrammus aeglefinus does not regularly exhibit the increase in piscivory with ontogeny that other gadoids often show, and in several ecosystems there is a lower occurrence of piscivory. There is an apparent inverse relationship between the consumption of fishes and echinoderms in M. aeglefinus over time, where certain years show high levels of one prey item and low levels of the other. This apparent binary choice can be viewed as part of a gradient of prey options, contingent upon a suite of factors external to M. aeglefinus dynamics. The energetic consequences of this prey choice are discussed, noting that in some instances it may not be a choice at all.
... (C) Population age-length relationships for Melanogrammus aeglefinus, determined from otolith-based ageing of thousands of specimens and then fitted with von Bertalanffy growth curves. Strong year-classes cause intra-specific competition for food and result in slower population growth (blue: 1963 YC, red symbols: even bigger 2003 YC) compared to the long-term average (redrawn from Brodziak et al. 2008). (D) Insights from otolith microstructure analysis on newly recruited sprat. ...
With about 28,000 known species, fishes make up more than half of all known vertebrates (Helfman et al. 2009). Over the course of their long evolutionary history, they radiated in every conceivable aquatic habitat, from the open ocean and deep-sea trenches to shelf seas, estuaries and lakes, to rivers and the smallest streams and ponds. They are found in subzero Antarctic waters, altitudes of over 4,000 m and even acidic desert springs of > 40°C (Moyle and Cech 2004). The fascinating adaptations to these habitats have produced a mind-bending diversity of form and function, a difference in size that spans more than three magnitudes (0.01–18 m), and a profusion of reproductive strategies. Apart from their diversity and unique evolutionary history, fishes are of intense scientific interest for economic reasons because they comprise the nutritional foundation for a large part of humanity (Costanza et al. 1997) and their exploitation over time has led to thriving—and warring—civilizations. Today, the impetus of sustainable fish management at a time of rapid ecological re-organization due to man-made climate change has made the study of fish ecology and fish stock productivity as urgent and important as ever. The aim of this chapter is to provide a highly abridged introduction to select major topics in fish evolution, distribution, ecology, and fisheries science. To gather a more in-depth understanding, students of ichthyology are encouraged to seek out a number of excellent textbooks on the different subjects, for example The Diversity of Fishes (Helfman et al. 2009) or An Introduction to Ichthyology (Moyle and Cech 2004). To delve further into ecological aspects, Ecology of Teleost Fishes (Wootton 1998) is still the go-to textbook, while students interested in a more detailed introduction to fisheries topics are recommended Fishery Science—The Unique Contributions of Early Life Stages (Fuiman and Werner 2009) and Marine Fisheries Ecology (Jennings et al. 2009).
... Monitoring changes in life history parameters for fish stocks can help understand recruitment dynamics and help avoid stock depletion or provide insights into the probability and timeline for stock recovery for already depleted stocks (e.g., Tomkiewicz et al., 2003;Brodziak et al., 2008;Morgan, 2008). Fecundity is an important reproductive life history parameter, but is particularly lacking in the fisheries literature. ...
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... There arose an acute need to ascertain the spatial distribution of these resources as well as to coordinate harvest strategies in order to avoid overfishing. Hence, a substantial share of the articles in this dimension focuses on understanding relative abundance, fish assemblages, and migration patterns of transboundary resources (e.g., [77][78][79][80]). Secondly, beyond merely studying stock characteristics, a number of papers have relied on bioeconomic principles and modelling techniques to predict the optimal level of total allowable catch (TAC) and allocation of quotas among the involved countries (e.g. ...
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... Certain species that have sustained exploitation with bottom trawls for decades, such as plaice, may have benefited from trawling through increases in their food supply, while having little reliance on complex refuges as they bury in the sediment for protection (Gibson 1994;Brown and Trebilco 2014). The occurrence of density-dependent growth in some benthivorous fish, such as haddock on Georges Bank (Brodziak et al. 2008), suggests that the per capita availability of prey resources increases when the fish stock declines. In this case, the reduction in predation on benthos outweighs the direct mortality of the fishing gear on benthos. ...
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One quarter of marine fish production is caught with bottom trawls and dredges on continental shelves around the world. Towed bottom-fishing gears typically kill 20–50 per cent of the benthic invertebrates in their path, depending on gear type, substrate and vulnerability of particular taxa. Particularly vulnerable are epifaunal species, which stabilize the sediment and provide habitat for benthic invertebrates. To identify the habitats, fisheries or target species most likely to be affected, we review evidence of the indirect effects of bottom fishing on fish production. Recent studies have found differences in the diets of certain species in relation to bottom fishing intensity, thereby linking demersal fish to their benthic habitats at spatial scales of ~10 km. Bottom fishing affects diet composition and prey quality rather than the amount of prey consumed; scavenging of discarded by-catch makes only a small contribution to yearly food intake. Flatfish may benefit from light trawling levels on sandy seabeds, while higher-intensity trawling on more vulnerable habitats has a negative effect. Models suggest that reduction in the carrying capacity of habitats by bottom fishing could lead to lower equilibrium yield and a lower level of fishing mortality to obtain maximum yield. Trawling effort is patchily distributed – small fractions of fishing grounds are heavily fished, while large fractions are lightly fished or unfished. This patchiness, coupled with the foraging behaviour of demersal fish, may mitigate the indirect effects of bottom fishing on fish productivity. Current research attempts to scale up these localized effects to the population level.
Haddock (Melanogrammus aeglefinus) is an important commercial fish species in the Northwest Atlantic, with the Eastern Georges Bank population a transboundary resources utilized by both Canada and the United States. With the dramatic increase recruitment of this population in the last decade, in particular concentrations of fish on the eastern portion of the Bank, there has been a precipitous decrease in somatic growth, raising concerns for managers and stakeholders. In this study, the effect of environmental factors and density-dependence on somatic growth of eastern Georges Bank haddock was studied using a 2-step Generalized Additive Model (GAM) regression approach. The biotic and abiotic factors examined in the regression analysis included haddock density, sampling location, local sea surface and bottom temperature, salinity and short time series of phytoplankton bloom statistics. The relative importance of each covariate in the best selected model was investigated using the nested GAMs. We found that density-dependence explained most of the variation in haddock growth, where the impact of temperature varied by season. Though of less model importance, annual winter salinity and phytoplankton bloom magnitude (lagged by one year) also contributed the growth model fits. These relationships have the immediate application of contextualizing the observed change in haddock growth, but may also inform various aspects of the stock assessment process.
The OECD Review of Fisheries 2020 aims to support policy makers and sector stakeholders in their efforts to deliver sustainable and resilient fisheries that can provide jobs, food, and livelihoods for future generations. The Review updates and analyses the OECD fisheries support estimate (FSE) database, the most comprehensive, detailed, and consistent collection of country level data on governments support to fisheries. It also presents and analyses newly-assembled data on the health of fish stocks; on the management of key stocks of commercial interest; and on the governance of fisheries across OECD countries and emerging economies with large fishing sectors. The report sheds light on how governments are managing fisheries to minimise detrimental impacts on resources and ecosystems, eliminate illegal, unregulated and unreported (IUU) fishing, while increasing the socio-economic benefits from fishing. It suggests priorities for action both at the national level and for the international community.
In the past four decades, summer flounder abundance in the Northwest Atlantic shifted with no definitive explanation for this shift. Here, we extract patterns in population-level size variability from summer flounder mean length-at-age data from 1992 – 2015 using an autoregressive state-space modeling approach and annual fishing and oceanographic covariates. We found that summer flounder length-at-age varies annually, suggesting that productivity can vary annually due to variable sizes. We found that location and depth of the observed fish, exploitation, and the Gulf Stream appeared to influence the magnitude of length-at-age variation, whereby lengths-at-age were above the mean length at greater depth, northern latitudes, and during periods characterized by a northerly Gulf Stream position or higher fishing exploitation. These factors should be considered as indicators to track size and more accurately understand productivity as the summer flounder population changes and the fishery adapts in response. This study brings us closer to annual proxies for summer flounder length-at-age variation, an important tool for fisheries managers and stock-assessment scientists to more accurately predict fish stock abundances and productivity.
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ABSTRACf Likelihood methods for the von Bertalanffy growth curve are examined under the assumption of independent, normallydistributederrors. The following are examined: determiningthe bestmethod of estimation, relationships between methods of estimation, failure of ll88U.IIlptions, constructing con­ fidence regions, and applying likelihood ratio teats. An example is presented illustrating many of the. methods discussed in theory. The paper may be viewed as an application of classic nonlinear least squares methods to the von Bertalanffy curve. Assuch, the concepts diBCUBBed are generallyapplicable and the papermay serve as an introduction to nonlinear least squares.
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Numerous groundfish stocks in both the Atlantic and Pacific are considered overfished, resulting in large-scale fishery closures. Fishing, in addition to simply removing biomass, also truncates the age and size structure of fish populations and often results in localized depletions. We summarize recent research suggesting that an old-growth age structure, combined with a broad spatial distribution of spawning and recruitment, is at least as important as spawning biomass in maintaining long-term sustainable population levels. In particular, there is evidence that older, larger female rockfishes produce larvae that withstand starvation longer and grow faster than the offspring of younger fish, that stocks may actually consist of several reproductively isolated units, and that recruitment may come from only a small and different fraction of the spawning population each year. None of these phenomena is accounted for in current management programs. We examine alternative management measures that address these specific issues and conclude that the best and perhaps only way to ensure old-growth age structure and complex spatial structure in populations of groundfish is through interconnected networks of marine reserves.
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Excessive and unsustainable fishing mortality was the predominant factor in the depletion of Northwest Atlantic cod (Gadus morhua) stocks. However, despite imposition of severe catch restrictions for over a decade, stocks have mostly failed to recover at predicted rates. A number of explanations have been considered. Our analysis of demographic characteristics of 12 of these stocks indicates that recent productivity over the northern portion of the range is much lower than 20 years previous when several stocks recovered from less severe declines. Main contributing factors are, in rank order, increased natural mortality, decreased body growth, and in a few cases, reduced recruitment rates. Continued fishing in directed and bycatch fisheries is also an important factor. Under current conditions, we estimate negative or very low (< 2% per year) average growth rates in eight stocks. If fishing ceases, growth rates of > 5% would be expected in six stocks, with > 10% in four of these. Although productivity is low, we conclude that fishing mortality is further delaying recovery.
We evaluated the effects of spawning-stock size on the recruitment abundance of 11 groundfish stocks in waters off New England. Empirical patterns of association between spawning biomass and recruitment were investigated using nonparametric approaches. For most stocks, higher recruitment occurred at high stock sizes and lower recruitment at low stock sizes. Survival ratios, indexed by recruitment per unit of spawning biomass, were higher at low stock sizes and lower at high stock sizes-as expected under density dependence. To assess assumptions about recruitment dynamics, we analyzed constant-recruitment and compensatory and overcompensatory stock-recruitment models with uncorrelated and autocorrelated error structures, using Bayesian methods of statistical inference. Although no single model was adequate for all stocks, most groundfish had better than even odds of having density-dependent dynamics, and most had better than even odds of having dynamics with uncorrelated environmental variation. While some geographic and taxonomic differences in potential productivity were apparent, all stocks exhibited compensation in survival ratio at low stock sizes, albeit with substantial variation. These results indicate that conservation measures intended to increase the spawning biomass of New England groundfish will, on average, result in higher recruitment and, eventually, in increased and more stable fishery yields.Nous avons examiné les effets de la densité des reproducteurs sur l'importance du recrutement chez 11 stocks de poissons benthiques au large de la Nouvelle-Angleterre. Les patterns empiriques d'association entre la biomasse des reproducteurs et le recrutement ont été étudiés à l'aide de méthodes non-paramétriques. Pour la plupart des stocks, il y a un recrutement plus élevé lorsque la densité des reproducteurs est grande, et un recrutement faible lorsque la densité est faible. Les rapports de survie, exprimés comme le recrutement par unité de biomasse des reproducteurs, sont plus élevés lorsque la densité des reproducteurs est faible et plus bas lorsque la densité est élevée-comme cela arrive dans les cas de densité-dépendance. Pour évaluer diverses suppositions sur la dynamique du recrutement, nous avons analysé, à l'aide de méthodes bayésiennes d'inférence statistique, des modèles reliant la densité des reproducteurs et le recrutement, modèles de type constant, compensatoire et surcompensatoire, avec des structures d'erreur non-corrélées et autocorrélées. Bien qu'aucun modèle particulier ne se soit montré adéquat pour tous les stocks, la plupart des stocks ont une probabilité plus qu'aléatoire d'avoir une dynamique densité-dépendante et cette dynamique tend à n'être pas corrélée à l'environnement. Malgré certaines différences géographiques et taxonomiques dans la productivité potentielle, tous les stocks montrent de la compensation, bien qu'avec beaucoup de variation, dans le rapport de survie lorsque les densités des reproducteurs sont basses. Ces données indiquent que les mesures de conservation destinées à accroître la biomasse des reproducteurs chez les poissons benthiques de la Nouvelle-Angleterre résulteront, en moyenne, en un recrutement plus élevé et, éventuellement, en des rendements de pêche plus grands et plus stables.[Traduit par la Rédaction]
The Georges Bank and Gulf of Maine haddock resource and fishery is reviewed. Nominal catches for Georges Bank averaged 46,000 metric tons annually during 1935-60 and then increased to a peak of 150,000 tons in 1965 as Canadian and distant water (European) fleets entered the fishery. Catches subsequently declined to an average of 5,000 tons during 1974-76 under quota and incidental catch limitations and then increased rapidly to an average of 21,000 tons in 1978-79. Nominal catches for the Gulf of Maine averaged 5,000 tons during 1935-66, declined to less than 1,000 tons during 1972-74 and increased to an average of 5,000 tons in 1978-79. Minor recreational catches have also been reported from the western Gulf of Maine in recent years. Total stock size (age 2 and older haddock) for Georges Bank, determined from virtual population analysis, averaged 140 million fish (153,000 tons) during 1935-60, increased to 530 million fish (427,000 tons) in 1965 and declined precipitously to 8 million fish (22,000 tons) in 1972. Subsequently, there was a substantial increase in stock size due to recruitment of the 1975 year-class. The 1978 year-class appears to be comparable in size to that of 1975. Instantaneous fishing mortality (F) for age 3 and older fish averaged 0.44 during 1935-60, increased to a peak of 0.79 in 1966 and subsequently declined as abundance decreased and fishing effort was diverted to other species. Trends in abundance and mortality evidenced by data from research vessel surveys since 1963 have been generally consistent with those indicated by virtual population analysis. Variability in growth of Georges Bank haddock during 1931-65 and pronounced