Northeast Fisheries Science Center Reference Document 04-05
Proceedings
of the Seventh Meeting
of the Transboundary Resources Assessment
Committee (TRAC), Woods Hole, Massachusetts,
May 27-29, 2003
by W.J. Overholtz, TRAC Chairman
National Marine Fisheries Serv., Woods Hole Lab., 166 Water St., Woods
Hole, MA 02543
Print
publication date February 2004;
web version posted February 2, 2004
Citation: Overholtz, W.J., TRAC chairman. 2004. Proceedings of the seventh meeting of the Transboundary
Resources Assessment Committee (TRAC), Woods Hole, Massachusetts, May 27-29, 2003. Northeast
Fish. Sci. Cent. Ref. Doc. 04-05; 19 p.
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ABSTRACT
The seventh Transboundary Resources Assessment Committee (TRAC) meeting
was held at the Northeast Fisheries Science Center, Woods Hole Laboratory
in Woods Hole, MA, USA during May 27-29, 2003. Updated assessments for Eastern Georges Bank
cod and haddock and Georges Bank yellowtail flounder were presented
and
reviewed during the meeting. These discussions
produced Transboundary Status Reports (TSRs) for Eastern Georges Bank cod, haddock
and Georges Bank yellowtail flounder to be used by the Transboundary Management
Guidance Committee (TMGC) in developing advice for the
management of these resources. This was
the first attempt to produce a stock status document that combined both the Canadian
Stock Status Report (SSR) and the US Northeast Regional Advisory Report on Stock
Status into a single document. Technical issues related to the assessments were
discussed throughout the meeting and several research
recommendations were advanced.
INTRODUCTION
The seventh meeting of the Transboundary Resources Assessment Committee
(TRAC) was held in Woods Hole, MA during May 27-29, 2003. The meeting
was attended by 19 scientists and industry representatives involved
in fishery management (Appendix I) and was chaired
by Dr. W.J. Overholtz (NMFS, USA). Updated assessments for Eastern Georges
Bank cod and haddock and Georges Bank yellowtail flounder were reviewed
at the meeting. Transboundary Status Reports (TSR) from the meeting
will provide information to inform the process for setting quotas and
shares (US and Canada) for the 2004 fishing year. Terms of reference,
and the agenda for the meeting are presented in Appendices
II and III. Pre-assessment consultations with
Canadian stakeholders were held in Yarmouth, Nova Scotia on 28 April
2003 (Appendix IV).
All participants introduced themselves and identified their goals
for the meeting. The meeting specifics were then outlined by the Chair
including the agenda, terms of reference, and expected products. It
was agreed that the TRAC would produce a Proceedings report from the
meeting and a separate TSR report for each stock. In the past, Canada
has produced Stock Status Reports (SSR) and the USA has produced Northeast
Regional Advisory Reports on Stock Status, each report independently
presenting scientific advice for management of the transboundary groundfish
resources in the Georges Bank/Gulf of Maine region.
The objective of the seventh TRAC was to produce a single document
that would be useful for the management processes in both countries. Under
the direction of the Transboundary Management Guidance Committee (TMGC), the
TRAC produced a Transboundary Status Report (TSR) that contains the
requisite scientific information for the TMGC to develop annual quota
guidance for the Eastern Georges Bank cod and haddock stocks and for
the Georges Bank yellowtail flounder stock.
Five working papers were prepared for the meeting (Appendix
V). Rapporteurs were assigned to each stock.
| Eastern Georges Bank cod |
Loretta O’Brien |
| Eastern Georges Bank haddock |
Jon Brodziak |
| Georges Bank yellowtail flounder |
Steve Cadrin |
One or more of the authors of the working papers presented the assessment
results. This was followed by a thorough discussion of the input data
and details for each assessment. Presentations were also made on estimating
discards in the cod fishery, yellowtail flounder tagging results, sensitivity
analysis of the yellowtail flounder VPA, and the results from an alternate
assessment model formulation (ASAP) for yellowtail flounder. In addition,
Chris Glass (Manomet Center for Conservation Sciences) provided an
overview of a cooperative research study examining temporal/spatial
catch patterns of commercial vessels targeting yellowtail flounder
in an experimental fishery in Closed Area II on Georges Bank.
TSRs for each species were developed and reviewed, and the meeting
was adjourned after all the Terms of Reference had been successfully
addressed.
Stock
Assessments
Eastern
Georges Bank Cod (WPs 2003/11 and 2003/14)
Working Paper:
Hunt, J.J. and B. Hatt. 2003. Population status of eastern Georges Bank
cod (unit areas 5Zjm) for 1978-2004. Working Paper 2003/11.
Summary
Information was presented on the Canadian and USA commercial cod fisheries,
and DFO and NMFS research survey indices of abundance and population
status. A substantial reduction in total landings occurred between
2001 and 2002 due to a 33% decline in Canadian catches (from 2,100
t in 2001 to 1,400 t in 2002). No changes in either the spatial or
temporal distribution of the fishery were evident. The 1998 and 1996
year-classes accounted for the bulk of the catches in 2002. Two approaches
to estimating possible discards in the Canadian fishery were presented: one
approach was associated with estimating the size and age composition
of the discards, while the other approach addressed estimating the
total amount of discards. Both methods were adopted as candidates
for estimating the catch at age associated with annual discards.
Results from the NMFS fall 2002 survey, the NMFS spring 2003 survey
and the DFO spring 2003 surveys were presented. The NMFS fall 2002
survey catch per tow index of cod increased markedly from 2001 and
is the highest observed value in the time series. The high survey
index appeared to be due to a “year effect” from several high catches
including one catch of over 600 kg that accounted for about 60% of
the overall estimate. The DFO spring 2003 survey index showed a substantial
decline from 2002, while the NMFS spring 2003 survey index was similar
that in spring 2002. This was the first time that current year NMFS
spring survey indices were available for inclusion in the assessment
analysis. Recruitment estimates from all three surveys were relatively
low.
Based on the 2003 VPA, the adult (age 3+) biomass of Eastern Georges
Bank cod declined from the recent high in 2001 (18,000 t) to about
13,000 t at the beginning of 2003. Fishing mortality for fully recruited
ages (4-6) ranged between 0.20 and 0.32 during the past five years,
above the Fref of 0.18. Assuming a catch in 2003 of
about 2,800 t (equal to the 2002 catch), the yield in 2004 at Fref was
projected to be 1,300 t and would generate only a small improvement
in adult biomass.
TRAC Discussion
Discarding is not technically allowed in the Canadian fishery as all
fish are supposed to be landed. However, if more than 15% of the catch
(by number) is less than 43 cm (16.9 in), an area can be closed to
fishing under the “small fish protocol”. In the US fishery, cod below
the minimum size of 22 inches (56 cm) cannot be landed or possessed
at sea. Prior to August 2002, the US minimum size for cod was 19 in
(48 cm). Discarding of cod in the US fishery is primarily due to catches
of undersized fish, whereas discarding in the Canadian fishery may
occur as a consequence of the disparate TACs for cod and haddock. The
current assessment does not account for any discarding, which may affect
the perception of stock status.
1. The TRAC recommends that discard estimates in both US and
Canadian fisheries be explored for potential inclusion in the next
assessment.
Comparison of age-length keys between the two countries revealed
some differences. Cod otoliths are prepared for ageing differently
in each country. This difference in methodology may contribute to
the observed differences in age compositions.
2. The TRAC recommends that age comparisons be done on otoliths
prepared with the same methodology. The TRAC also recommends that
an ageing workshop on gadids (cod and haddock) be held within the
next year.
Comparison of at-sea and on-shore length frequency samples indicate
generally good correspondence for otter trawl, longline, and gill net
gear, with some notable exceptions. While these exceptions may indicate
that discarding is occurring, the differences may also be explained
by spatial coverage of observed vs. unobserved trips. Also, when the
Canadian longline fishery is directing for haddock, a smaller hook
size is employed which may incidentally catch small cod.
The Canadian longline industry survey index for cod has shown an
increasing trend since 1999, with a substantial increase in the 2002
weight per tow index. Age 4 is the first fully recruited age in
this survey, and the increase in the 2002 index appears to be due
to the
recruitment pulse of the 1998 year-class.
Mean weights-at-age of cod in the DFO 2003 survey declined for all
ages. There has been a noticeable increase of slower growing cod in
the Eastern Georges Bank landings (as detected by otoliths) that may
be contributing to the decline in mean weight. Differences between
beginning year and mid-year mean weights indicate a decrease in weight
by mid-year. This has been previously been observed in pollock and
is attributed to loss of weight after the spawning season. In the
projections, variability in mean weights is accounted for by using
average mean weight-at-age values (from the most recent three years).
NMFS spring and fall surveys exhibit relatively high sampling variability
compared to the DFO spring survey. However, this does not affect
the perception of stock abundance as the calibration of these surveys
within the VPA ADAPT framework appears to be suitable.
A retrospective pattern is evident in the current assessment and
is similar to that observed in the 2002 assessment. Generally, the
more abundant younger ages are underestimated and the older ages are
overestimated, although the 1998 year-class in the 2003 assessment
is larger than previously estimated. This retrospective pattern needs
to be explored further. Possible causes may be related to the US closed
areas and the lack of discards in the catch-at-age.
Working paper:
Van Eeckhaute, L., and S. Gavaris. 2003. Determination
of Discards of Georges Bank cod by comparing observed and unobserved
species compositions. Working Paper 2003/14.
The analysis explored a potential approach for estimating discards
in the Canadian fishery. Although misreporting of cod as another
species is not a problem with mandatory dockside monitoring, a potential
for
discarding exists when there is a large difference in the cod and
haddock TACs, which occurred during the late 1990s.
Observer coverage of about 10% or greater is needed in the Canadian
fishery to obtain a good estimate of the landings multiplier used to
derive discarded catch. Multipliers that were less than unity or were ‘too
large’ were not included in this preliminary analysis. Either bootstrapping
the model residuals or using the standard error of the landings multiplier
to estimate confidence intervals would provide objective criteria to
determine the feasibility of each landings multiplier. This would
be a one-sided test since a multiplier less than one would indicate
no discarding and therefore be excluded from the analysis. Landings
multipliers less than unity could, however, provide information on
the variability of parameters greater than one.
This method may potentially be applied ‘in reverse’ to the US 5Z
data to determine if estimates of discards agree with the direct estimates
of discard derived from the sea sample data.
3. The TRAC recommends future analysis of discarding
since 1995 when more limiting cod quotas were implemented in the
Canadian fishery.
Eastern Georges Bank Haddock (WP 2003/12)
Working Paper:
Van Eeckhaute, L., S. Gavaris, and J. Brodziak. 2003. Assessment of Haddock
on Eastern Georges Bank. Working Paper 2003/12.
Summary
The input data to the assessment were presented and included the Canadian
and USA commercial catches, the catch at age matrices, length and age
sample summaries, and results of between reader and inter aging precision
tests. Canadian CPUE was not used in the calibration but was presented. The
three research vessel survey time series used in the calibration were
described, and survey data were reviewed on abundance at age, distribution
by age group(s), and adult biomass and recruitment trends. The NMFS
2003 spring survey, which is not usually available until the following
year’s assessment, was available for inclusion in this year’s assessment. Overall,
the surveys indicated that biomass/abundance increased during the mid
1990s, and that the 2000 year-class is strong but the 2001 and 2002
year-classes are weak. Weights-at-age in both the surveys and commercial
fisheries showed no obvious trends. Weights-at-length from the DFO
survey, used as a measure of condition, have fluctuated without trend.
The ADAPT formulation in 2003 was much the same as in the 2002 assessment
with a few minor changes relating to the inclusion of the 2003 NMFS
spring survey (in previous assessments, only the previous year’s
survey was available) and the estimation of population size at the
beginning
of April 2003 (assuming a catch of 0 for the 1st quarter),
rather than at the beginning of the year (i.e., January 1st). The
diagnostics (residual and retrospective patterns, and the standard
error and bias on the final year abundance estimates from bootstrap
analyses) were deemed to be acceptable.
The assessment results indicated that adult biomass (age 3+) has
steadily increased since 1993 and was about 78,000 t at beginning
of 2003, which is at the lower range of the 1930 to 1950s historical
level
when productivity was higher. The fully recruited (4+) F has been
below Fref =0.26 since 1995. Several years of improving
recruitment and increased survivorship (due, in part, to reduced
exploitation) has contributed to the increased abundance of the stock.
The stock
is now at a level where recruitment success is more likely than when
spawning stock biomass was depressed.
A projection to the beginning of 2005, assuming a catch of 8,000
t in 2003, indicated that a combined Canada/US yield of 8,000 t in
2004 resulted a very low risk of exceeding Fref, a negligible
chance of biomass decline, and a low risk of the biomass falling below
the median 2005 rebuilding biomass of 65,000 t.
TRAC Discussion
Catch Data
Eastern Georges Bank haddock catches in 2002 were dominated by the
1998 year-class at age 4. The 1996 year-class also comprised a substantial
fraction of the catch. The expansion of haddock age structure continued
in 2002 and an increasing abundance of older age fish was evident in
the fishery. Canadian fishery catch-per-unit-effort has increased
since 1993.
Canadian fishery length and age sampling in 2002 provided an accurate
characterization of the Canadian catch, which accounted for nearly
88% of the total 2002 Eastern Georges Bank haddock catch. Length and
age sampling in the USA fishery was much lower than in the Canadian
fishery, similar to the pattern in recent years. Sampling intensity
of the USA fishery should be increased in the future.
Survey Data
DFO and NMFS research surveys all show a strong 2000 year-class. For
example, the catch per tow of haddock in the NMFS autumn 2002 survey
was the highest since 1976, with the index dominated by the 2000 year-class. Survey
data consistently show that older haddock are now more abundant than
in previous years.
Abundance and biomass indices of haddock in the DFO and NMFS autumn
surveys show similar trends in recent years. The NMFS spring survey
suggests a more moderate increase in haddock biomass.
Canadian survey data show no trends in condition index (weight-at-length)
during recent years. Haddock growth rates appear stable.
Assessment Model
An analytical assessment of Eastern Georges Bank haddock was conducted
using a sequential population analysis model. The model formulation
was the same as in the 2002 assessment, except that NMFS 2003 spring
survey data were available for inclusion in the tuning.
Assessment results were consistent with the 2002 assessment results. Bias-corrected
bootstrap estimates were used for inference. Residual patterns from
the tuning indices were similar to those in the 1998 benchmark assessment.
There was no persistent pattern in retrospective analyses in the
Eastern Georges Bank haddock assessment. The strength of the 2000
year-class was lower in the retrospective analyses. This year-class
now appears to be stronger than estimated in the 2002 assessment.
Stock Status
The TRAC agreed upon the assessment and results. Haddock biomass
is the highest in over 30 years. The 2000 year class now appears larger
than both the 1975 and 1978 year-classes, but the 2001 year-class is
well below-average and preliminary estimates of the 2002 year-class
are low. Despite the weak 2001 and 2002 year-classes, recruitment
generally appears to be improving. Fishing mortality has been below
Fref =0.26 since 1995 and survivorship of recent year-classes
has been relatively high.
Projections
Deterministic and stochastic projections were conducted for Eastern
Georges Bank haddock. The TRAC agreed that use of a two-state stock
recruitment model with a spawning biomass cutpoint of 40,000 t was
appropriate for Eastern Georges Bank haddock. This is the same approach
used in stochastic projections by USA scientists of the entire Georges
Bank haddock stock.
Sources of Uncertainty
1. USA fishery
catch-at-age data have low precision due to low sampling intensity.
2. The 2002
year-class appears to be weak.
3. Cautious interpretation of the probability of a biomass increase
from 2004 to 2005 is warranted due to the dominance of the strong
2000 year-class.
Georges Bank Yellowtail Flounder
Working Paper:
Stone, H.H., and C.M. Legault. 2003. Assessment of Georges Bank (5Zhjmn)
yellowtail flounder for 2003. Working Paper 2003/13.
Summary
Input data for the 2003 assessment of Georges Bank yellowtail flounder
were reviewed and information presented for both Canada and the USA
on commercial fishery landings, catch size composition, port and sea
sampling results, and catch- and weight-at-age. The Canadian fishery
in 2002 was comprised mainly of fish in the 32-41 cm size range, while
the USA fishery proportionally captured slightly larger fish (34-44
cm). The 2000 year-class (age 2) and the 1999 year-class (age 3) occurred
in equal proportions in the 2002 catch, with age 2 fish dominant in
Canadian catches during the 2nd half of the year, and age 3 fish dominant
in USA catches during the first half of the year. Although not used
in the VPA calibration, a standardized catch rate series for Canadian
mobile gear was updated and compared to the DFO spring survey biomass
index for stratum 5Z2 (Canadian portion of the Bank < 90m). Canadian
mobile gear catch rates increased in 2002.
Abundance and biomass indices from DFO spring and NMFS spring and
fall surveys were presented and discussed, along with the spatial distribution
of survey catches and survey size composition data, by sex and sampling
strata (e.g.., 5Z2/5Z4). All three groundfish surveys indicated a
decline in abundance since 2000, but survey indices are still relatively
high compared to the mid 1990s. The 1999 year-class (age 3) was dominant
in the 2002 DFO and NMFS spring surveys, but not in 2003 at age 4. The
2000 year-class at age 2 was relatively abundant in the NMFS 2002 fall
survey and also at age 3 in the 2003 DFO and NMFS spring surveys. Abundance
indices of age 1 yellowtail in the NMFS sea scallop survey index increased
again in 2002.
The VPA (ADAPT) and surplus production model (ASPIC) formulations
were the same as used in the 2002 assessment. Retrospective analyses
using the updated ADAPT results indicated a more pronounced retrospective
pattern than in previous assessments, and showed a strong tendency
to underestimate F on ages 4 and 5, and to overestimate spawning stock
biomass (SSB) and age 1 recruitment. The impact of this pattern on
abundance and F was apparent back to 1994. The trajectories of F,
SSB and recruitment are now considerably different from those in the
2002 assessment. There are several large negative residuals in the
2003 DFO and NMFS spring survey indices (ages 5-6+) and in the NMFS
2002 fall survey (ages 4-6+) (i.e., the model predicts higher abundance
for these ages), and concern was expressed that these may significantly
affect the estimates of current abundance.
Overall, results from the current assessment showed lower abundance
and higher Fs for the same age groups than the values provided in the
2002 assessment. Age 1+ VPA population biomass (38,300 t) in 2003
was lower than that predicted in last year’s assessment (58,000 t)
and considerably lower than the total biomass estimated from the surplus
production model (64,000 t). Similarly, the estimated 2003 adult (age
3+) biomass of 26,000t is much lower than that forecasted from the
2002 assessment (40,000 t). Although recruitment has improved since
the mid-1990s - with several good year-classes from 1997 onward - estimates
of abundance are much lower than in last year’s assessment. The 1997
year-class is now estimated to be only of moderate strength (age 1
abundance of 28 million fish vs. 59 million fish estimated last year),
while the 2000 year-class (the strongest since 1980) is now estimated
to be 48 million fish at age 1 vs. 62 million at age 1 in the 2002
assessment. While the proportion of older fish (age 4+) in the population
is increasing, younger fish (ages 1 and 2) still predominate. Fishing
mortality (age 4+ ) since 1994 is now higher than previously estimated
but declined to below Fref =0.25 in 2002. Exploitation
on age 3 has also decreased to Fref, but has not followed
the same trend as age 4+. Catches at Fref in 2004 was projected
to be 7,900 t. The 2001 and 2000 year-classes are expected to contribute
about 58% of the total yield in 2004 and constitute 49% of the total
stock biomass. At the projected Fref yield of 7,900 t
in 2004, adult biomass is expected to increase from 32,500 t in 2004
to 33,300 t in 2005.
TRAC Discussion
The updated ADAPT calibration, configured in the same way as in the
most recent benchmark assessment (Neilson and Cadrin 1998), suggests
that previous assessments were optimistic. Revised estimates of 1997-2001
SSB are now less than one-third of the estimates obtained in recent
assessments. Revised estimates of the 1997-2001 Fs are more than three
times greater than estimates from past assessments. A retrospective
pattern has been apparent since the 1990s, but the magnitude of inconsistency
in the 2003 update is much greater. The most recent survey abundance
values produced large, negative calibration residuals at older ages,
balanced by several years of large positive residuals in preceding
years.
Several sensitivity analyses were conducted to investigate potential
sources of the retrospective pattern. Four alternative ADAPT configurations
were run assuming a “flat-topped” partial recruitment schedule (i.e.,
estimating 2003 F for only age 4 and assuming the same F for ages 5
and 6+), assuming a dome-shaped PR, truncating the catch at age (age
1 to age-5+), artificially increasing discards of age 1 and 2 fish,
and removing the age-6+ calibration series. All seven alternative
configurations had similar retrospective patterns, with large 2003
residuals at older ages (age 6+). Additionally, sensitivity analyses
were completed using a range of assumed Ms (from 0.1 to 1.0). The
results showed reduced retrospective patterns with increased M values
to M=0.7, with a reversal of the retrospective pattern (overestimated
F) when M was between 0.7 and 1.0.
An exploratory application of a statistical
catch at age model (ASAP: Legault and Restrepo 1999) was applied to
further investigate the retrospective pattern. The model emulated
the ADAPT configuration, except that constant selectivity was assumed,
observation error in catch at age was included, and the underlying
population processes were calculated forward from age 1 (rather than
backward from age-6+). The results indicated that allowing for errors
in the catch-at-age (ASAP) produced a closer fit to the survey trends
(i.e., the negative 2003 residuals at older ages persisted, but were
not as large as those from ADAPT). However, there was a noticeable
pattern of negative catch residuals at older ages (i.e., the model
expected a relatively greater abundance of older fish in the catch).
Several possible reasons for the retrospective pattern were considered:
The ADAPT VPA calibration assumes that
older fish (age 6+) are fully vulnerable to the fishery. The possibility
of Closed Area II offering a refuge for these fish was discussed. Length
distributions from several sources inside and outside Closed Area
II were examined. In all years, length distributions from the Canadian
survey were similar inside and outside, except in 2002 when the Closed
Area stations had more large fish. Monthly length frequencies from
a 2002 Closed Area II access study (C. Glass, personal communication;
Manomet Center for Conservation Sciences 2003) were compared to both
fishery and survey length frequencies in 2002. The size (mode) from
fishery samples outside the Closed Area was smaller, with relatively
more 33-38 cm fish in the fishery samples and relatively more fish
greater than 38 cm in the Closed Area samples. However, the 20 min
tows in the Manomet study may have had a lower selectivity for small
yellowtail than in the fishery because the meshes may have been relatively
unclogged in comparison to commercial tows (which typically are several
hours in duration). The relative frequencies of medium and large
fish (>41cm) were very similar among the fishery, survey, and
access study samples. Overall, there was no compelling evidence
of a refuge effect for larger yellowtail in Closed Area II.
The difficulty in determining the age
of older fish using scales, and the potential for underaging older
fish were also discussed as possible reasons for the retrospective
pattern. It was noted that catch-at-size has gradually increased
in recent years, but catch-at-age of older fish has not. Size at
age in the surveys increased in the mid- 1990s, but not in recent
years. Eight published studies on the scale method of aging yellowtail
were reviewed including validation studies and quality control information. Yellowtail
can be reliably aged with the scale method to age 7, but determination
of older ages may be problematic (Walsh and Burnett 2003). Regarding
the aging of yellowtail by the Northeast Fisheries Science Center,
it was reported that: (1) age determinations from scales are considered
reliable up to age 6; (b) processing methods and ageing protocols
have been consistent since the 1960s; and (3) the shift in size
at age observed in the mid 1990s does not coincide with a change
in age readers. The TRAC noted that there are several other processes
that can produce a shift in size at age (e.g., natural variability,
poor sampling, borrowed age-length keys, fishing patterns, etc). Therefore,
there is no evidence of systematic underaging of fish from age 1
to age 6.
Other reasons for underestimating age
compositions were discussed as possible causes of the retrospective
pattern. Non-representative sampling resulting from low sampling
intensity or small sample sizes may generate different proportions
of older fish in the catch vs. the population. The use of USA commercial
age samples and NEFSC fall survey age samples to characterize the
age composition of the Canadian commercial catch may result in an
under representation of the proportion of old fish in the population. The
application of NEFSC spring survey age-length keys to the DFO spring
survey yellowtail catches may also bias the estimation of survey
catch at age because of potential spatial patterns in demographics. Such
spatial patterns are suggested by the general increase in proportion
of male yellowtails in the Canadian fishery. The mean length of
fish sampled from the USA fishery is larger than that in the Canadian
fishery. Observations from the Closed Area II access study (Manomet
Center for Conservation Sciences 2003) suggest that yellowtail seasonally
disperse, and a recently developing autumn fishery along the southern
edge of Closed Area II may be associated with a seasonal shift in
yellowtail distribution that was not apparent historically. Differences
in biological characteristics among spatial groups may bias the estimation
of age composition. However, the available data are insufficient
to evaluate sampling error as a potential source of the retrospective
pattern.
Sexually dimorphic growth was also discussed
as a possible source of underaging fishery and survey catches. Canadian
survey and fishery data are characterized by both sex and age, whereas
USA fishery and survey data are not. Previous comparisons of catch
at age estimates using pooled-sex and separate sex age-length keys
produced only minor differences that were insufficient to explain
the retrospective pattern. Sensitivity analyses suggest that the
assumption of M=0.2 may produce the retrospective pattern, if M is
actually greater than this. Natural mortality (M) has been assumed
to be 0.2 based on yellowtail tag returns (Lux 1969), relationships
of Z to effort (Brown and Hennemuth 1971), and the age of the oldest
individual sampled from the stock (age 14). However, different
size and age distributions by sex suggest that males may have a
higher
natural mortality rate than females.
Underestimation of catches was the final
potential source of the retrospective pattern that was discussed. USA
yellowtail catches, by stock area, are prorated according to vessel
trip reports and may underestimate the portion of yellowtail landed
from Georges Bank. However, other USA stocks of yellowtail have
similar retrospective patterns, suggesting that catch is not overestimated
everywhere simultaneously. There is also considerable uncertainty
in discard estimates. However, sensitivity analyses suggest that
discards would have to be severely underestimated to produce the
observed retrospective pattern.
Given the magnitude of the retrospective inconsistency, the TRAC
concluded that there is substantially greater uncertainty in the assessment
in 2003 than in previous years. Although there is obvious need for
a revised benchmark assessment, such a revision was not possible at
this meeting. The TRAC agreed that stock status should be based on
survey observations and the range of results from the current benchmark
assessment methods (i.e., the 2002 ADAPT solution, the 2003 ADAPT solution
and the 2003 ASPIC solution) to communicate the uncertainty in stock
status determination. To meet the term of reference, the TRAC agreed
to use the 2003 ADAPT results to perform projections, with the understanding
that results are highly uncertain. For example, using the 2003 ADAPT
result, the projected 2004 catch at Fref is 7900 t (Stone
and Legault 2003). Considering the great uncertainty in the assessment,
a status quo catch strategy (6100 t) may be reasonable.
Due to the large
retrospective pattern seen in this assessment and the divergence with
the production model results, a benchmark assessment is recommended
for Georges Bank yellowtail flounder.
In addition to
examining changes in model formulation and alternative models, this
benchmark should consider topics such as closed area impacts, sexual
dimorphism in growth and natural mortality rates, movements within
and among management areas, catch estimation and alternative methods
to estimating catch at age in recent years.
4. The TRAC
recommends that a benchmark assessment be conducted for Georges Bank
yellowtail flounder in 2005.
References
Brown, B.E. and R.C. Hennemuth. 1971. Assessment of the yellowtail
flounder fishery in Subarea 5. ICNAF Res. Doc. 71/14, 57 pp.
Legault, C.M. and V.R. Restrepo. 1999. A
flexible forward age-structured assessment program. ICCAT Coll. Vol.
Sci. Pap. 49(2): 246-253.
Lux, F.E. 1969. Landings per unit of effort, age composition, and
total mortality of yellowtail flounder, Limanda ferruginea (Storer),
off New England. ICNAF Res. Bull. 6: 47-52.
Manomet Center for Conservation Sciences. 2003. Collaborative program
to assess possible temporal access to Closed Area II: Targeting yellowtail
flounder without significant bycatch of cod and haddock. Interim Summary
Report to NMFS.
Neilson, J.D. and S.X. Cadrin. 1998. 1998 Assessment of Georges
Bank (5Zjmnh) Yellowtail Flounder. Canadian Stock Assessment Secretariat
Res. Doc. 98/67.
Walsh, S.J. and J. Burnett (Eds.). 2002. The Canada-United States
yellowtail flounder age reading workshop. 28-30 November 2000, St.
John’s, Newfoundland. NAFO Sci. Coun. Studies 35: 1-59.
Working Paper:
Stone, H.H. 2003. Update on Georges Bank
Yellowtail Flounder Tagging Studies. Working Paper 2003/15.
Results from Canadian yellowtail flounder tagging studies on Georges
Bank were presented. In 1999, 2,155 yellowtail were released in the “Yellowtail
Hole,” and in 2002, 452 were released in Closed Area II near the international
boundary. Of 108 recaptures with location information from the Yellowtail
Hole releases in 1999, nearly all (106) were caught in the Yellowtail
Hole over a three-year period from 2000-2002. One fish moved to the
northeast peak of Georges Bank, and one moved to the northern edge
in USA waters. Eight yellowtail flounder recaptures were reported
from the Closed Area II releases. All were from Canadian yellowtail
directed trips in the Yellowtail Hole area during August and September
2002. Results from these studies support earlier tagging experiments
by Royce and Lux and indicate that yellowtail on Eastern Georges Bank
undertake limited movements with a possible seasonal component. They
are also capable of transboundary movements in both directions.
Appendix I. List of Participants
|
Participant |
Affiliation/Address |
Telephone |
E-Mail |
|
Chris J. Allen |
DFO, Science, Ottawa, Ontario Canada |
613-990-0105 |
allenc@dformpo.gc.ca |
|
Jon Brodziak |
NMFS, NEFSC Woods Hole, MA USA |
508-495-2365 |
Jon.Brodziak@noaa.gov |
|
Steve Cadrin |
NMFS, NEFSC Woods Hole, MA USA |
508-495-2335 |
Steven.Cadrin@noaa.gov |
|
Claude d’Entremont |
Industry Representative, (mobile gear) Canada |
902-762-2522 |
claude@inshore.ca |
|
Stratis Gavaris |
DFO, Science St Andrews, NB Canada |
506-529-5912 |
GavarisS@mar.dfo-mpo.gc.ca |
|
Chris Glass |
Manomet CCS
Manomet, MA USA |
508-224-6521 |
glasscw@monomet.org |
|
Jorgen Hansen |
DFO Management Canada |
902-426-9046 |
HansenJ@dfo-mpo-gc.ca |
|
Bette Hatt |
DFO Science, St Andrews, NB Canada |
506-529-5920 |
hattB@mar.dfo-mpo.gc.ca |
|
Joseph Hunt |
DFO Science, St Andrews, NB Canada |
506-529-5893 |
huntJJ@mar.dfo-mpo.gc.ca |
|
Larry Jacobson |
NMFS, NEFSC, Woods Hole, MA USA |
508-495-2317 |
Larry.Jacobson@noaa.gov |
|
Chris Legault |
NMFS, NEFSC Woods Hole, MA USA |
508-495-2025 |
Chris.Legault@noaa.gov |
|
Ralph Mayo |
NMFS, NEFSC Woods Hole, MA USA |
508-495-2310 |
ralph.mayo@noaa.gov |
|
Steve Murawski |
NMFS, NEFSC Woods Hole, MA USA |
508-495-2303 |
Steve.Murawski@noaa.gov |
|
Loretta O’Brien |
NMFS, NEFSC Woods Hole, MA USA |
508-495-2273 |
Loretta.O’Brien@noaa.gov |
|
Bill Overholtz |
NMFS, NEFSC Woods Hole, MA USA |
508-495-2256 |
William.Overholtz@noaa.gov |
|
Heath Stone |
DFO Science, St Andrews NB, Canada |
506-529-5880 |
Stoneh@mar.dfo-mpo.gc.ca |
|
Lou Van Eeckhaute |
DFO Science, St Andrews NB, Canada |
506-529-5938 |
van-eeckhauteL@mar.dfo-mpo.gc.ca |
|
Evan Walters |
Industry Representative Canada |
902-637-3276 |
stifa@klis.com |
|
Susan Wigley |
NMFS, NEFSC Woods Hole, MA USA |
508-495-2359 |
Susan.Wigley@noaa.gov |
Appendix II. Terms of Reference.
Remit
Transboundary Resource Assessment Committee
Aquarium Conference Center, NEFSC, Woods Hole
27 – 29 May 2003
Stock Assessments
For the following resources:
Eastern Georges Bank Cod
Eastern Georges Bank Haddock
Georges Bank Yellowtail
Using the benchmark assessments, report on the status of the stocks,
updating results for the latest information from fisheries and research
surveys and characterize the uncertainty of estimates.
Estimate the 10th percentile, median, and 90th percentile
rebuilding biomass path for a at the beginning of each year from 2004
to 2008, assuming that the stocks are exploited at fishing mortalities
of 018 (cod), 0.26 (haddock) and 0.25 (yellowtail flounder) respectively.
For a range of values for total catch in 2004, estimate the risk
that
the 2004 fishing mortality rate would exceed 0.18 (cod), 0.26
(haddock) and 0.25 (yellowtail flounder) respectively
the biomass at the beginning of 2005 would be lower than the
respective B2005reb
the biomass at the beginning of 2005 would not achieve a 0%,
10%, and 20% increase compared to the beginning of 2004.
Appendix
III. Agenda
Agenda
Transboundary Resource Assessment Committee
Aquarium Conference Center, NEFSC, Woods Hole
27 – 29 May 2003
27 May 2003 – Tuesday
08:30 – 09:00 Welcome and Introduction
09:00 – 12:00 Cod 5Zjm
12:00 – 13:00 Lunch
13:00 – 16:30 Haddock 5Zjm
28 May 2003 – Wednesday
08:30 – 12:00 Yellowtail Flounder 5Zhjmn
11:00 – 12:00 Report Preparation
12:00 – 13:00 Lunch
13:00 – 16:30 Further considerations and Report Review
29 May 2003 – Thursday
08:30 – 12:00 Further considerations and Report Review
12:00 – 13:00 Lunch
13:00 – 16:00 Further considerations and Report Review
16:30 Adjournment
Appendix IV. Pre-Assessment
Consultation
Yarmouth
28 April 2003
Minutes
The Transboundary Resource Assessment Committee will review assessments
of Eastern Georges Bank cod and haddock and of Georges Bank yellowtail
flounder during 27-29 May 2003 with respect to fisheries management
advice for the 2004 fishing year.
The purpose of the meeting was to review survey and fishery observations
in relation to what they indicate about stock status and how they can
be interpreted. DFO science staff presented summaries of available
information as a starting point for discussion. As Canada and USA move
towards consistent management of these transboundary resources, it
is necessary to harmonize, to the extent possible, the respective fishing
seasons to ensure that management measures in both countries are based
on a common assessment. The recent developments and the anticipated
evolution of the process were discussed.
The following points were raised during discussion.
Eastern Georges Bank Cod
A discrepancy between the size composition of landed samples and
samples taken at sea by observers raised concerns about the possibility
of discarding, but no corroborative accounts were offered by participants.
Further exploration was warranted to determine if the disparity might
be due to differences in location of fishing. It was noted that observer
coverage on fixed gear was only 5% where the target was 10%.
It was noted that port samplers would avoid taking a sample from
a landing where discarding or high-grading was suspected. This diminishes
the utility of comparing port samples and sea samples for the purpose
of detecting potential discarding.
An observation was made that difference in the size composition
of landings was not apparent in the historical plant records. The size
of fish landed by the longline fishery appeared to be relatively consistent
in past years. This is in contradiction to observations in the assessment
of strong and weak year-classes passing through the fishery. An examination
of the longline fishery length composition over time should be undertaken
to investigate this observation.
The variability in trawl catches was questioned and it was suggested
that differences in trawl performance may be influential. It was noted
that a rigorous protocol was followed during all survey operations
to ensure comparability over time. The use of trawl monitoring equipment
(Scanmar) has been employed experimentally to investigate the consistency
of trawl performance but it cannot be deployed on a routine basis due
to operational constraints.
Tides, full moon, and other factors are thought to influence catchability.
However, these factors introduce random effects and should not bias
abundance trends.
Feeding behaviour and fish are following the feed can also affect
catchability. The Georges Bank survey is conducted during the same
time of year each year to control for seasonal differences in behaviour.
Further, it is conducted during spawning when feeding is not an issue.
Shifts in spawning condition during the NMFS spring survey will
be investigated.
Declines in weight at age have been noted for this cod stock as
well as other cod stocks and some haddock stocks (not Georges Bank
haddock). Hypotheses about ecosystem effects such as competition
for feed do not appear to explain the patterns as it was noted that
herring
abundance is increasing.
The longline survey weights at age will be examined for trends.
Some movement between the Georges Bank and Browns Bank is evident
but cannot be quantified at this time. The tagging project, currently
in progress, may give information on population structure.
The longline survey showed an increase in both numbers and weights
in 2002, however some boxes were dropped this year compromising the
comparison of results with previous years. Fishermen who conducted
the survey noted there were valid reasons for dropping these boxes
because of damage to their equipment.
The benefits of area/season closures and quota management measures
were questioned. It was noted that that there has been an increase
in biomass however we’re not seeing recruitment. The underestimation
of recruitment by the DFO survey was questioned but it was noted that
the DFO age 1 index was not used in the assessment.
Eastern Georges Bank Haddock
A request was made for calculation of the rate at which biomass
is increasing.
Georges Bank Yellowtail Flounder
Age determination of yellowtail flounder remains an issue. Participants
asked if collaboration had been made with Newfoundland on aging.
Scientists from St. Andrews and Woods Hole had collaborated on methodology
at
the recent workshop in St. John’s Newfoundland.
Approaches to reduce the bycatch of skates should be investigated.
Participants
|
Name |
Affiliation |
Fax |
e-mail or Tel. # |
|
Claude d'Entremont |
Inshore Fisheries Ltd. |
902-762-3464 |
inshore@inshore.ca; 902-762-2522 |
|
Jorgen Hansen |
Marine House - DFO |
|
902-426-9046 |
|
Denny Morrow |
NSFPA |
902-742-1620 |
fishpackers@klis.com; 902-742-6168 |
|
Michael O’Connor |
NSP |
902-634-4926 |
michael.oconnor@highlinerfoods.com; 902-634-5200 |
|
Ron Wolkins |
SWFRA |
902-745-2632 |
swfra@auracom.com |
|
B. d’Entremont |
Acadian Fish |
902-762-3316 |
902-762-2700 |
|
Aaron d’Entremont |
Acadian Fish |
902-762-3316 |
acadian@ns.sympatico.ca; 902-762-2700 |
|
Adlai Cunningham |
Sea Star Seafood |
902-745-2129 |
902-745-2925 |
|
Daniel J. Fleck |
DFO, C&P, Barrington |
902-637-2944 |
fleckd@mar.dfo-mpo.gc.ca; 902-637-2851 |
|
Susan d’Entremont |
SFMGFA |
902-762-0935 |
sue-rejean@ns.sympatico.ca; 902-762-0177 |
|
Rejean d’Entremont |
Fisherman |
902-762-0935 |
sue-rejean@ns.sympatico.ca; 902-762-0177 |
|
Aldric C. D’Eon |
Inshore Fisheries Ltd. |
|
902-762-3400 |
|
Wilson d’Entremont |
Fisherman – Little Island Fisheries Ltd. |
|
902-762-3260 |
|
Brian Lowe |
Fisherman |
|
902-745-3428 |
|
Darrell Bass |
Fisherman |
|
902-745-0335 |
|
Roger Atwood |
Fisherman |
|
902-637-2764 |
|
Russell W. Atkinson |
Fisherman |
902-745-0313 |
902-745-2541 |
|
Jean Guy d’Entremont |
Inshore Fisheries Ltd. |
902-762-3464 |
jean.guy@ns.sympatico.ca; 902-762-2522 |
|
Sandy d’Entremont |
Fisherman |
|
902-663-2385 |
|
Derek d’Entremont |
Little Island Fisheries Ltd. |
902-762-3479 |
902-762-3402 |
|
Ray Belliveau |
Charlesville Fisheries |
902-762-3158 |
902-762-2405 |
|
Evan Walters |
SFIFA |
902-637-3270 |
sfifa@klis.com |
|
Francois B. d’Entremont |
Fisherman |
|
902-762-3322 |
|
Peter Comeau |
DFO Science, BIO |
902-426-1506 |
902-426-5418, comeaupa@mar.dfo-mpo.gc.ca |
|
Heath Stone |
DFO Science, SABS |
506-529-5862 |
StoneH@mar.dfo-mpo.gc.ca; 506-529-5880 |
|
Bette Hatt |
DFO Science, SABS |
506-529-5862 |
HattB@mar.dfo-mpo.gc.ca; 506-529-5920 |
|
Joseph Hunt |
DFO Science, SABS |
506-529-5862 |
HuntJJ@mar.dfo-mpo.gc.ca; 506-529-5938 |
|
Lou Van Eeckhaute |
DFO Science, SABS |
506-529-5862 |
Van-EckhauteL@mar.dfo-mpo.gc.ca;
506-529-5893 |
|
Stratis Gavaris |
DFO Science, SABS |
506-529-5862 |
GavarisS@mar.dfo-mpo.gc.ca; 506-529-5912 |
Appendix V. List of Working Papers for the
Seventh TRAC
1. Hunt, J.J. and B. Hatt. 2003. Population status of eastern
Georges Bank cod (unit areas 5Zjm) for 1978-2004. Working Paper 2003/11.
37 pp.
2. Van Eeckhaute, L. and S. Gavaris. 2003. Determination of Discards
of Georges Bank cod by comparing observed and unobserved species compositions. Working
Paper 2003/14. 7 pp.
3. Van Eeckhaute, L., S. Gavaris, and J. Brodziak. 2003. Assessment
of Haddock on Eastern Georges Bank. Working Paper 2003/12. 28 pp.
4. Stone, H.H. and C.M. Legault. 2003. Assessment of Georges Bank
(5Zhjmn) Yellowtail Flounder for 2003. Working Paper 2003/13. 76
pp.
5. H.H. Stone. 2003. Update on Georges Bank Yellowtail Flounder
Tagging Studies. Working Paper 2003/15. 15 pp
