Page 16

3.55 r 3s
STANDARDIZED LPUE
3- <a 30
s
£25) NEFSC p25 &
= SURVEY INDEX =
> 24 F + 20 2
5 v ~
£15 His =
wi 3
2 1- ;10S
al

°
a
f
T
a

°o
No
@

4

°

80 82 84 86 88 90 92
Year

Figure 9. Trends in commercial standardized LPUE and NEFSC research vessel spring bottom trawl survey
biomass index (mean weight per tow) for Georges Bank cod, 1978-1992.

0.85 pt2
0.75 4 L410
So6- STANDARDIZED |
o Vv. 2
£ LPUE —+> te 8
= 0.574 =
= Z
20.44 fe og
Eos =
wes L, §
a 0.24 SS rs ae nn =
as ‘ -2
0.14 NEFSC SURVEY INDEX
(0) T T T T T T T 0

—t
82 83 84 85 86 87 88 89 90 91 92
Year

x

Figure 10, Trends in commercial standardized LPUE and NEFSC research vessel spring bottom trawl survey
biomass index (mean weight per tow) for Gulf of Maine cod, 1982-1992.

EZ Zz BEREREBEBEBEE BeBe uaa ue


Page 10

Table 5. Landings at age of Georges Bank cod (thousands of fish, metric tons) and mean weight (kilograms) at
age for the otter trawl subfleet, ages 2 -9+, 1978-1992

Year Age Total
2 3 4 5 6 7 8 9+
Number (000s)
1978 210 3530 1038 402 21 99 10 15 5325
1979 1748 391 2479 523 197 37 158 18 5551
1980 2508 3291 201 899 602 261 30 81 7873
1981 1704 2193 1161 95 377 177 51 54 5812
1982 5524 1552 965 669 60 237 56 50 9113
1983 2404 3512 720 493 379 41 105 100 7754
1984 921 2050 1772 292 241 225 16 131 5648
1985 3525 1228 610 844 162 92 97 58 6616
1986 765 2311 284 204 259 34 32 37 3926
1987 3591 624 868 109 106 96 25 25 5444
1988 1045 4051 648 787 125 70 57 30 6813
1989 1342 1876 2014 138 217 28 9 9 5633
1990 3621 2342 814 883 77 76 15 7 7835
1991 756 1641 1260 511 348 26 12 5 4559
1992 1577 725 343 459 109 76 5 9 3303
Metric Tons
1978 281 8705 3949 1807 95 687 64 186 15774

1979 3040 926 10506 2462 1454 332 1624 220 20565
1980 3830 7981 810 4929 4094 2054 327 1073 25098
1981 2648 5042 3794 610 2576 1496 525 836 17527
1982 7855 4212 3470 3564 412 2239 619 723 23094
1983 3572 8531 2415 2204 2339 318 1122 1433 21934

1984 1437 4815 6195 1487 1601 1949 153 1655 19293
1985 4977 2516 2389 4214 996 724 997 749 17563
1986 1122 5271 941 1101 1862 308 331 488 11424
1987 5092 1444 3370 592 804 820 236 304 12661
1988 1613 9362 1820 4000 801 534 493 357 18980
1989 2260 4210 6880 681 1438 244 86 99 15887
1990 5460 4967 2598 3984 450 614 153 70 18297
1991 1172 3971 4118 2423 2059 187 132 80 14141
1992 2427 1648 1193 2065 667 594 50 89 8733

Mean Weight (kilograms)
1978 1.338 2.466 3.804 4.496 4.530 6.936 6.366 12.421
1979 1.739 2.369 4.238 = 4.708 ~—7.383 8.969 :10.281 12.229
1980 1,527 2.425 4.031 5.483 6.801 7.869 10.897 13,247
1981 1.554 2.299 3.268 6.416 6.834 8.453 10.301 15,481
1982 1.422 2.714 3,596 5.327 6.863 9.447 11.054 14.460
1983 1.486 2.429 3.354 4.471 6.171 7.755 10.685 14.330
1984 1.560 2.349 3.496 5.091 6.644 8.663 9.592 12.634
1985 1.412 2.049 3.917 4.993 6.151 7.866 10.274 12.914
1986 1.467 = 2.281 3.314 5.396 7.188 9.064 10.339 13.189
1987 1.418 2.314 3.882 5.435 7.582 8.536 9.444 12.160
1988 1.544 2.311 2.809 5.082 6.406 7.629 8.643 11.900
1989 1684 2.244 3.411 4.934 6.628 8.714 9.532 11.000
1990 1.508 2.121 3.192 4.512 5.844 8.079 10.200 10.000
1991 1.550 2.420 3,268 4.741 5.916 7.202 10.971 16.000
1992 1.539 2.273 3.478 4.498 6.115 7.822 10.084 9.889

ZEEE Ea ee ee eee ee ee =


Page 1

ABSTRACT

Standardized effort series for Gulf of Maine and Georges Bank cod were estimated using
General Linear Models (GLM) incorporating year, area, quarter, and vessel tonnage class.
Landings and effort data included in the models were derived from interviewed trips using otter
trawl gear. Annual commercial landings per unit effort indices were computed for the
interviewed subfleets based on the standardized effort estimates. Annual landings at age
estimates corresponding to the effort subfleets were also derived as a basis for computing
landings per unit effort at age. y

For both cod stocks, standardized fishing effort increased throughout most of the 1980s.
Effort peaked in 1987 in the Gulf of Maine, declined through 1990 but increased again in 1991
and 1992. On Georges Bank, effort has increased continuously since 1978. Commercial
landings per unit effort (LPUE) for both stocks consequently declined through the mid-1980s.
LPUE increased sharply in the Gulf of Maine in 1989 and 1990, but declinedin 1991 and 1992.
On Georges Bank, commercial LPUE declined continuously through 1987, but increased
slightly between 1988 and 1991 before declining again in 1992.

. Comparison of standardized effort and LPUE trends from the GLM analyses with those
computed by various means in previous studies indicated good overall agreement, although
differences evident in the latter years may be due to recent changes in the degree of directivity
of the cod fisheries in both areas.

Landings at age estimates indicated a very strong 1987 year class in the Gulf of Maine which
supported a sharp increase in landings and LPUE in this region in 1989 and 1990. On Georges
Bank, recruitment was distributed more evenly among several year classes, particularly those
produced in 1983, 1985 and 1987. Age compositions of the otter trawl effort subfleets were
generally similar to the total landings at age estimates for each stock, although the otter trawl

fleets tended to take a slightly higher proportion of 2- and 3-year-old cod.

INTRODUCTION

At the 15th Northeast Regional Stock Assess-
ment Workshop (15th SAW), the Stock Assess-
ment Review Committee (SARC) noted that com-
mercial landings per unit effort (LPUE) at age
based on multigear landings derived by multiply-
ing the retransformed year factor obtained from a
General Linear Model (GLM) based on otter trawl
landings per day fished by the estimated total
multi-gear effort may not reflect actual standard-
ized fishing effort or the actual age composition of
otter trawl trips from which effort was derived.
Furthermore, it was suggested that this approach
may not capture changes in effort patterns for
other gears. It was recommended that standard-
ization of effort be conducted separately for indi-
vidual gears (NEFSC 1993).

In preparing the 1993 assessments for Gulf of
Maine and Georges Bank cod, we recomputed the
landings per day fished for the otter trawl subfleets
alone. Also, we reconstructed the landings at age
matrices based on landings that corresponded to
the otter trawl effort subfleet which was used to
compute the standardized annual effort. The
following report summarizes the methods used
to select landings, effort, and length and age

sample data, and presents both the results of the
GLM used to compute standardized effort for
each stock and comparisons between the annual
age compositions estimated for the entire fishery
and for the effort subfleets.

METHODS
DATA SOURCES

Landings and effort data for each stock were
obtained from the Northeast Fisheries Science
Center (NEFSC) Commercial Fisheries Database
(CFDBS) master files covering the period 1978-
1992 for Georges Bank cod and from 1982-1992
for Gulf of Maine cod. A data base that included
only records for interviewed otter trawl trips
(excluding shrimp trawls, pair trawls, etc.), inclu-
sive of valid tonnage classes that appeared in the
data consistently over time, was constructed for
each stock (statistical areas 521,522, 523/561,
524/562, 525, and 526 for Georges Bank codand
areas 511, 512, 513, 514, 515 for Gulf of Maine
cod).

Standardized fishing effort (days fished) was
derived for all interviewed trips that landed cod


1991. The discrepancy between LPUE and the
survey index suggests a substantial increase in
the degree of directivity in the Gulf of Maine cod
fishery during 1989-1991 as the 1987 year class
was targeted. The disparity evident in 1992
resulted from an increase in the mean weight of
1987 year class cod as they continued to domi-
nate the survey catches. The overall result of this
comparison indicates that LPUE may have over-
estimated abundance due to changes in directiv-
ity and that fishing effort was higher during
1989-1991 than indicated by the model.

REFERENCES

Gavaris, S. 1980. Use of a multiplicative model
to estimate catch rate and effort from com-
mercial data. Can. J. Fish. Aquat. Sci. 37:2272-
2275.

Granger, C. W., and P. Newbold. 1977. Forecast-
ing economic time series. New York: Aca-
demic Press.

Kimura, D. K. 1981. Standardized measures of
relative abundance based on modelling log
(c.p.u.e), and their application to Pacific ocean
perch. ICES J. Cons. 39:211-218.

Page 17

Kimura, D. K. 1988. Analyzing relative abun-
dance indices with log-linear models. No.
Am. J. Fish. Manage. 8:175-180.

Mayo, R. K., M. J. Fogarty, and F. M. Serchuk.
1992. Aggregate fish biomass and yield on
Georges Bank, 1960-87. J. Northw. Atl. Fish.
Sci. 14:59-78.

Mayo, R. K., L. O'Brien, and F. M. Serchuk. 1993.
Assessment of the Gulf of Maine cod stock for
1992. Woods Hole, MA: NOAA/NMFS/
NEFSC. Center Ref. Doc. 93-04.

NEFSC [Northeast Fisheries Science Center].
1993. Report of the 15th Northeast Regional
Stock Assessment Workshop (15th SAW):
Stock Assessment Review Committee (SARC)
Consensus Summary of Assessments. Woods
Hole, MA: NOAA/NMFS/NEFSC, Center Ref.
Doc. 93-06.

Robson, D. S. 1966. Estimation of the relative
power of individual ships, ICNAF Res. Bull.
3:5-14,

Serchuk, F. M., L. O'Brien, R. K. Mayo, and S. E.
Wigley. 1993. Assessment of the Georges
Bank cod stock for 1992. Woods Hole, MA:
NOAA/NMFS/NEFSC. Center Ref. Doc. 93-
05.


Page 14

Full EJ vs. Tuning Subset °

70

60 +
50 +
40};
30 -
205
10}

19884

40+
SO -
204+
10

40h
30 +
20 +
10 |-

PERCENT AT AGE

234567849
AGE

Figure 7. Continued.



Page 6

Table 1.

Georges Bank cod GLM effort standardization.

SAS General Linear Models Procedure

Dependent Variable: LNCPUEDF

Source DF Sum of Squares Mean Square F Value Pr>F
Model 27 28516.42490940 1056. 16388553 675.36 0.0001
Error 52179 81599.90019330 1.56384561
Corrected Total 52206 110116,32510271
R-Square cv. Root MSE LNCPUEDF Mean
0.258966 -646.8736 1.25053813 -0,19332033
Source DF Typel SS Mean Square F Value Pr>F
YEAR 14 10439.97027882 745.71216277 476.85 0.0001
AREA 5 5174.90711295 1034.98142259 661.82 0.0001
QTR 3 3745.70569133 1248,56856378 798.40 0.0001
TONCLASS 3 5672.12786313 1890.70928771 1209.01 0.0001
DEPTHCD 2 3483.71396317 1741.85698159 1113.83 0.0001
Source DF ‘Type I SS Mean Square F Value Pr>F
\
YEAR 4 13140.20128030 938.58580574 600.18 0.0001 \
AREA 5 7474.17955441 1494.83591088 955.87 0.0001 \
QTR 3 2875.21677184 958.40559061 612.85 0.0001
TONCLASS 3 5933.08867445 1977.69622482 1264.64 \
DEPTHCD 2 3483.71396317 . —1741.85698159 1113.83 |
fo 29% i \
Parameter Estimate T for HO: Pr> ITI StdErrorof " Retransformed =|
Parameter=0 Estimate ...... Estimate )
INTERCEPT 0.724000592 iB 25.20 0.0001 0.02872607 wes oP?
AREA 522 -0.445165897 B -28.67 0.0001 0.01552672 0.640795
523 -0.018132063  B 0.3872 0.02097022 0.982247
524 -0.744920018  B 0.0001 0.01828704 0.474852
525 -0.857301608 BB 0.0001 0.02348380 0.424422
526 -1.204446759 iB 0.0001 0.02009898 0.299918
521 0.000000000 «iB : : 1.000000
QTR 1 -0.059039765  B 0.0001 0.01522176 0.942778
3 -0.596095117. BB 0.0001 0.01542695 0.551024
4 -0.434279166 = B 0.0001 0.01617803 0.647816
2 0.000000000 BB : . 1.000000
TONCLASS 31 -0,783352144 BB 0.0001 0.02474775 0.457012
32 -0.543263442 B 0.0001 0,01619049 0.580926
4l 0.417412098-B 0.0001 0.01331944 1.518163
33 0.000000000-~&B : : : : 1.000000
DEPTHCD 1 0.729218401 B 46.49 0.0001 * 0.01568675 2.073714
2 0.375635575 BB 24.34 0.0001 « 0.01543178 1.459090
3 0.000000000 «iB . ‘ : 1,000000

Table 2, Nominal and standardized (GLM) Georges Bank cod landings (metric tons), effort (days: fished) and

BEeeeteerrTrEeEBtBtESe &ss<.<=-

laridings per day fished (LPUB) oy” Godelteed Gt somefat TEMG Sern,
“GSA Landings (mt) Nominal Standaidized
Year Total Subfleet_ __ Effort LPUE Effort LPUE «Raised Effort
1978 26579 18776 8078 508272637" ~—«210079
1979 32645 20584 9847 7788 2.643 12394
1980 40053 25213 10217 8600 2.932 13661
1981 33849 18340, 9149 8113 2.260 14977
1982 39333 23292. 8859 2.629 14961
1983 36756 22072 10456 2111 17412
1984 32915 19669 12495 1574 20912
1985 26828 18012 14892 1.209 22190
1986 17490 11572 ~~ 11884 0.978. 17883
1987 19035 12731 18791 0.923 20822
1988 26310 19010, 16911 1.124 23407
1989 25097 15557 15407 1.010 24849
1990 28193 18358 14836 1.237 22791 |
1991 24175 14173, 14917 0.950 25447
1992 16855, 8786 12845 0.684 24642 fl
v “Vv V



AREA 511—Tonclass (CPUE mt/days) on Year AREA 514—Tonclass (CPUE mt/days) on Year .
Diemond=T23 Star=T24 Squere=T25 THangie=T31 Plus =T32 X= 733 Dot=T41 Crs = T42 Diemond=723 Ster=T24 Square<T25 Ttangie< 731 Pius =T82 X=TS8 Dot=T41 Crce= Tay

oo «4 & 8 7 8 8 mo M w 2 8 &@ & 8 & 8 @ 0 4
Year Year
AREA 512—Tonclass (CPUE mt/days) on Year AREA 515—Tonclass (CPUE mt/days) on Year

Dlemond=T23 Star=T24 Square=T25 Ttangie=T3! Plus =T32 X=T83 Dot=T41 Croe=T42  Dlamond=T23 Stars T24 Square=T25 Tangle TS! Plus =T&2 X= TE Dot=T41 Crcie = Ta

2 8 &@ & 86 8 B&B 8 0 Hf a2 8 8 8S 68 BF 88 8 0
Year Year .

AREA 513—Tonclass (CPUE mt/days) on Year
Dimond=T23 Star=T24 Square=T25 THangle=T31 Pius =T82 X=T83 Dot= Tat Cece =T42

2 8 & 8 8 & 8 8 OM S 2
Year

Figure 2. Trends in log, CPUE of Gulf of Maine cod by vessel tonnage class, 1982-1992.


| Page 2

AREA 621 —Tonclass (CPUE mt/days) on Year AREA 524—Tonciass (CPUE mt/days) on Year
Dienond=T23 Star=T24 Square=T25 THange=T3t Pus=T32 X=T33 Dot=Tét Crcie = T42 Diemond=T23 Star=T24 Square=T25 THangie=T3t Pius =T82 X= 133 Dot= 41 Croe=T42

73 80 & 62 & & 6 8 G7 Bw OM B
Year Year

AREA 522-Tonclass (CPUE mt/days) on Year AREA 525 —Tonclass (CPUE mt/daya) on Year
re Stara T24 Square=T25 Thange=TS! Pus= 782 X=783 Dot=T4t Cree T42 — Diemond=T23 Star To ‘Squere= 725 Thangie= 781 Plus =T82 X=T83 Dot=T41 Crcia= 42

2

7a 7) 8 St G2 83 GF 8 8 87 8 HO MH
Year . Year

| AREA 523—Tonclass (CPUE mt/days) on Year AREA 526—Tonclass (CPUE mt/days) on Year
lOlenond=T23 Star=T24 Squere=T25 Tangie= 731 Pas =T82 X= 733 Dot T4t Crote = 142 ‘Diamond = T23 Sern T24 ‘Square =T25 Thange=TS1 Plus =T82 X=T33 Dot=Tét Croe= 142,



mao EE OmmEElUlUElll DTCC a a es ee ee ee

PERCENT AT AGE

Figure 8.

Page 15

Full MB vs. Tuning Subset

60 7
| 50 + |
1982 | 50 F 1988 |
3OF 7
20 |
10

40

PERCENT AT AGE

234567 8 9

~s AGE

2345 678 9

AGE

Percent age composition of Gulf of Maine cod from the full landings at age matrix and the effort subfleet
landings at age martix for ages 2-9+, 1982-1992,


LANDINGS AT AGE ESTIMATES

Numbers landed at age were estimated by
applying quarterly commercial age-length keys
to the quarterly commercial numbers landed at
length by market category using NEFSC BIOSTAT
software. Market category samples were com-
bined to three categories: small, medium, and
large. Length frequency samples were reviewed,
mis-coded market category samples were re-
coded and very small sublegal size fish that
appeared to be mis-coded were eliminated from
the analyses. Age-length samples were also
reviewed and perceived outliers were either moved
within the age-key or eliminated from the key.

RESULTS

EFFORT STANDARDIZATION

Results from the GLM analysis for the Georges
Bank and Gulf of Maine cod stocks are given in
Tables 1-2 and 3-4, respectively. In both analy-
ses, the five-factor model accounted for approxi-
mately 22 to 26% of the total sums of squares.
For each data set, year, area, tonnage class,
quarter, and depth effects were highly significant
(P < 0.01). In general, the contribution of the
interaction terms to the model sums of squares
was minimal. Coefficients for the area, quarter,
tonnage class, and depth effects, retransformed
and converted to linear scale, are given in Tables
l and 3. Relative to the chosen standard statis-
tical area (521), cod catch rates on Georges Bank
are lower in all other areas; but in general, rates
are approximately twice as great on Northern
Georges Bank (SA 521-523) (Table 1). Such a
pronounced difference in standardized cod catch
rates by area is not as apparent in the Gulf of
Maine, where area coefficients are nearly equal
(Table 3). Tonnage class coefficients for both
Georges Bank and Gulf of Maine analyses gener-
ally increase with vessel size. Vessel classes 33
and 41 exhibit an almost twofold increase in
fishing power over those smaller vessels on
Georges Bank, while in the Gulf of Maine vessel
classes 33 and 41 exhibit two to four times
greater fishing power. Standardized cod catch
rates were higher in shallower depths and in the
first two quarters of the year for the Georges Bank
and Gulf of Maine analyses.

Because effort standardization procedures
differed here from those used in earlier cod as-
sessments, we compared our standardized effort

Page 5

series with those of Serchuk et al. (1993) for the
Georges Bank cod stock (Figure 3) and Mayoet al.
(1993) for the Gulf of Maine cod stock (Figure 4).
These authors computed U. S. fishing effort for
the Georges Bank and Gulf of Maine cod stocks
in two different ways: 1) from an average LPUE
across tonnage classes weighted by tonnage class
landings termed ‘calculated’, and 2) from a five-
factor GLM in which year coefficients were used
to adjust nominal effort relative to a standard
year termed ‘standardized’. The standardized
subfleet effort derived from our present analysis
differed from the earlier series in that, although
year was included in the model as a factor, the
year coefficients themselves were not used ex-
plicitly as a multiplier with the other factor's
coefficients, nor were subsequent years adjusted
relative to the base year. We then computed
annual U. S. fishing effort for each stock by
raising the estimated subfleet effort by the ratio
of subfleet landings to total U. S. landings in each
year (Tables 2 and 4). On Georges Bank, the effort
subfleet generally accounted for about 50 to 60%
of the total U. S. landings whereas in the Gulf of
Maine, the subfleet often accounted for only 25 to
30% of the total U. S. landings. This is due, in
part, to the large amount of gillnet catch in this
area.

Effort trends in each of the series were similar
for both the Georges Bank and Gulf of Maine cod
stocks. On Georges Bank (Figure 3), total U. S.
standardized effort has increased almost con-
tinuously since 1978, whereas the subfleet effort
declined after 1988. This decline in the subfleet
effort is the likely result of a lower proportion of
trips being included in the subfleet analysis in
recent years. Hence, our raised standardized
effort series provides a more complete view of
trends in actual fishing effort. Our standardized
effort series Suggests that the ‘calculated’ effort of
Serchuk et al. (1993) provided a more consistent
indicator of overall effort’than that given by their
‘standardized’ effort series. “

The various effort series for the Gulf of Maine
cod stock appear to be.more consistent than
those for Georges Bank, although the subfleet
effort is considerably less than the total effort
estimated by each of the previous methods (Fig-
ure 4). The ‘calculated’ and ‘standardized’ effort
series computed by Mayo et al. (1993) are consis-
tent with the trends indicated by our standard-
ized effort estimates. Each series indicates a
peak in effort in 1987, followed by a decline. The
raised standardized effort increases again after
1990 while the ‘standardized’ series computed by
Mayo et al. (1993) indicated an increase after
1989.


Northeast Fisheries Science Center Reference Document 94-12

Estimation of Standardized
Otter Traw] Effort, Landings
per Unit Effort, and
Landings at Age
for Gulf of Maine
and Georges Bank Cod

by

R. K. Mayo, T. E. Helser, L. O'Brien,
K. A. Sosebee, B. FE. Figuerido,
and D. Hayes"

NOAA/National Marine Fisheries Service
Northeast Fisheries Science Center
Conservation and Utilization Division
Woods Hole, MA 02543

May 1994


Page 8

40) STANDARDIZED
-Serchuk et al.

—“, pon’ \ we
~ Moy .
a 30° CALCULATED
=) were - Serchuk et al.
Bo fey ~*~ STANDARDIZED - RAISED
wh
o
s
a10

STANDARDIZED - SUBFLEET

78 80 82 84

86 88 90 92

Year

Figure 3. Fishing effort estimated for Georges Bank cod from Serchuk et al. (1993) and from the GLM

standarization procedure, 1978-1992.

405

(0)

oe CALCULATED .
- Mayo et al. a

STANDARDIZED - RAISED

\ STANDARDIZED
- Mayo et al.

STANDARDIZED - SUBFLEET

82 83 84 85

86 87 88 89 9
Year

91 92

%

Ms
Figure 4, Fishing effort estimated for Gulf of Maine cod from Mayo et al. (1993) and from the GLM standarization

procedure, 1982-1992.

We also compared our LPUE series with those
obtained by Serchuk et al. (1993) and Mayo et al.
(1993) for the Georges Bank and Gulf of Maine
cod stock, respectively. Our standardized LPUE,
computed by dividing the standardized effort
series into landings, was quite similar to the
‘calculated’ LPUE obtained by Serchuk et al.
(1993) for the Georges Bank cod stock (Figure 5),

except in the earlier years when our standardized
LPUE index peaks more distinctly, However, the
sharp decline in the Serchuk et al. ‘standardized’
LPUE compared to their ‘calculated’ LPUE and
our standardized LPUE explains the large differ-
ence in total effort estimated by this index (Figure
3). Although Serchuk et al. (1993) conclude that
their ‘calculated’ series may be underestimating



a aa ae)

Page 7
Table 3. Gulf of Maine cod GLM effort standardization.
SAS General Linear Models Procedure
Dependent Variable: LNCPUEDF
Source DF Sum of Squares Mean Square F Value Pr>F
Model 24 10042.42776453. 418.43449019 271.01 0.0001
Error 22417 34610.87206235 1,54395646,
Corrected Total 22441 44653.29982688
R-Square cv. Root MSE LNCPUEDF Mean
0.224898 -116.8327 1,24256045 -1,06353847
Source DF Type ISS Mean Square F Value Pr>F
YEAR 10 4172.47634712 417.24763471 270.25 0.0001
AREA 4 213.43028101 53.35757025 34.56 0.0001
QTR 3 1091.33076950 363.77692317 235.61 0.0001
TTONCLASS 4 2804.09441832, 701.02360458 “454,04 0.0001
DEPTHCD 3 1761.09594858 587.03198286 380.21 0.0001
Source DF TypeINss Mean Square F Value Pr>F
YEAR 10 3864.47552921 386,44755292 250.30 0.0001
AREA 4 337.52113256 84.38028314 54.65 0.0001
QTR 3 1077.53586173 359.17862058 232.64 0.0001
TONCLASS 4 3365.93344569 841.48336142 545.02 0.0001
DEPTHCD 3 1761.09594858 587.03198286 380.21 0.0001
PArameter . Estimate T for HO: Pr> {Tl Std Error of Retransformed
: Parameter=0 Estimate Estimate
INTERCEPT -0.966438423  B -22,.51 0,0001 0,04293803
AREA 511 0.352862172  B 6.04 0.0001 0.05840734 1.425565
512 0.093390087  B 2.64 0.0083 0.03535865 1.098576
513 0.282590501 B 11.13, 0.0001 0.02540134 1.326990
515 -0.026414709 B -0.84 0.4026 0.03155861 0.974416
514 0,000000000 _B . . . 1,000000
QTR 1 -0.450275482  B -17,99 0.0001 0.02503570 0.637652
3 -0.555648751 B -23.76 0.0001 0.02338944 0.573857
4 -0.471084150 B -20.69 0.0001 0.02276910 0.624487
2 0,000000000 B . . . 1.000000
TONCLASS 31 0.470024146 B 18.66 ‘ 0.0001 0.02519506 1.600541
32 0.854568967  B 33.24 0,0001 0,02571061 2.351138
33 0,896470299 B 32.09 0.0001 0.02793882 2.451894
4l 1301746565 B 43.24 0.0001 0,03010851 3.677377
25 0.000000000 B . . ” . 1.000000
DEPTHCD 1 0.593978838 B 18.13 0.0001 0,03275947 1,812153
2 0.324741394 B 12.86 0.000f 0.02525790 1.384114
4 -0.636948746 B -24.01 0.0001 0.02652370 0.529090
3 0.000000000 B + : oe 1,000000

Table 4, Nominal and standardized (GLM) Gulf of Maine cod landings (metric tons), effort (days fished) and

landings per day fished (LPUE) You
U. S. Landings (metric tons) Nominal Standardized

Year Total Subfleet Effort LPUE Effort LPUE = Raised Effort
1982 13582 3395 3158 1.075 4953 0.686 19799
1983, 13981 3698 3791 0.975 5782 0.640 21845
1984 10806 2423 3798 0,638 5495 0.441 24503
1985 10693 3012 5294 0.569 8489 0.355 30121
1986 9664 2794 5568 0.502 8745 0.320 30200
1987 7527 1708 5100 0.335 7836 0.218 34528
1988 7958 2060 4753 0.433 7994 0.258 30845
1989 10397 - 2316 3524 0.657 6125 0.378 27505
1990 15154 4916 4053 1.213 7663 0.641 23641
1991 17781 5432 4737 1.147 8829 0.615 28912
1992 10891 2777 4978 0.558 8003 0.347 31386



Page 4

between 1978 and 1992. Factors incorporated in
the effort standardization analyses were year,
quarter, depth zone, statistical area, and tonnage
class. To reduce the number of levels of each
factor and to provide a more balanced statistical
design, depth zones and tonnage classes appear-
ing infrequently in the data set were either elimi-
nated or combined. Levels within a given factor
were eliminated when that level was not repre-
sented well in the levels of the other factors
included in the analysis.

An example of this is shown in Figure 1 for the
Georges Bank fleet, where tonnage classes 23-25
and 42 are not represented in all years in each
statistical area. As such, these levels of the
tonnage class factor were eliminated from further
analysis. Similarly, tonnage classes 23-24 and
42 were eliminated as levels in the tonnage class
factor for the Gulf of Maine cod analysis (Figure
2). Levels within a factor were combined when
reasonably well represented in the levels of other
factors and an initial GLM analysis (which in-
cluded all levels within a factor) indicated little or
no difference in the estimated parameters. The
combinations resulted in three levels for the
depth factor and four levels in the tonnage class
factor in the Georges Bank analysis, and four
levels of depth and five levels of tonnage class in
the Gulf of Maine analysis.

A standard category was chosen for each
factor in both Georges Bank and Gulf of Maine
cod analyses. In the Georges Bank analysis, year
= 1978, quarter = 2, tonnage class = 33 and
statistical area = 521; in the Gulf of Maine analy-
sis, year = 1982, quarter = 2, tonnage class = 25
and statistical area = 514.

The age composition of the landings corre-
sponding to the effort subfleets from Georges
Bank and the Gulf of Maine was estimated and
used with standardized effort estimates to calcu-
late a LPUE at age index. Landings from Georges
Bank were restricted to areas 521-526, tonnage
class (TC) vessels 31-33, and 41, and depth zones
less than 183 m. Landings from the Gulf of Maine
were restricted to areas 511-515, TC vessels
25,31-33, and 41 in depth zones less than 274 m.

EFFORT STANDARDIZATION

Relative harvesting efficiency varies mark-
edly among different vessel size classes, seasons,
and areas. To account for these differences, we
standardized nominal fishing effort using a gen-
eral linear model approach (e.g. Robson 1966;
Gavaris 1980; Kimura 1981, 1988) based on the

multiplicative model:

Uyramn = Bi Pra TBYE yen

where Ujen, is the CPUE for the i year, jTM
statistical area, k** quarter, 1“ ton. class, m”
depth, and n" observation; By Yo 5, and p,,
represent year, area, quarter, ‘tonnage class and
depth effects respectively, q is the catchability
coefficient, B represents mean population biom-
ass and €,,,,,, is a log-normally distributed ran-
dom error term with mean 1.0 and constant
variance. Because the population biomass is not
directly known, the term qB is replaced by the
mean CPUE (1) and all coefficients are estimated
relative to an arbitrarily defined standard (de-
scribed previously). Least squares estimates of
the model coefficients were made under the con-
straints:

Zlog.o.=Zlog B=Zlog.y,=Zlog §=Zlog p,,=0
for the linearized model:

108.Uyjiamn = 108,H + logo, + log.B, + log.y, + log.3, +
108.Py, OBL pamn *

In this model, the year coefficient (a,) absorbs
both changes in cod abundance and technologi-
cal improvements in fleet efficiency over time.
These factors could be separated in future analy-
ses by incorporating an independent measure of
abundance, such as the NEFSC bottom trawl
survey index, as a covariate in the model as
described by Mayo et al. (1992).
Retransformation of the model coefficients to
linear scale was made after correction for bias
following Granger and Newbold (1977). We tested
for interactions among all main effects in the
model, and foiind several interactions to be sta-
tistically significant. In each case, however, the
proportion of variance explained by the interac-
tion terms was small relative to the miain effects
(< 9%). Accordingly, we considered only main
effects models in subsequent analyses. The large
number of degrees of freedom in the model in-
creased the probability of detecting significant
interactions, but the practical significance of
these interactions seems to be minor.
Standardized effort for each area-quarter-
tonnage class-depth category was estimated by
multiplying the sum of the nominal effort for that
cell by the product of the retransformed GLM
coefficients for each factor. The estimated stan-

dardized effort was then accumulated over all ©

categories to provide annual estimates.





Page iv
Figure 7.

Figure 8.

Figure 9.

Figure 10.

Percent age composition of Georges Bank cod from the full landings at age

matrix and the effort subfleet landings at age martix for ages 2-9+, 1978-1992 .......... 13
Percent age composition of Gulf of Maine cod from the full landings at age

matrix and the effort subfleet landings at age martix

for ageS 2-9+, 1982-1992 .2.cccsseres eerste renee recs steeereseeete nen eens eee 15
Trends in commercial standardized LPUE and NEFSC research vessel

spring bottom trawl survey biomass index (mean weight per tow)

for Georges Bank Cod, 1978-1992 ...scscssccescsssersersseessseeesesnernsesneestserersee seers eeeeeeene 16
Trends in commercial.standardized LPUE and NEFSC research vessel

spring bottom trawl survey biomass index (mean weight per tow)

for Gulf of Maine cod, 1982-1992 ..c.cceccccseseneeteeenscnsetereterseeteeneerenrenreeeseeiereiseiees 16

rd

SBEEBEEE EES ES


Page 11

Table 6. Landings at age of Gulf of Maine cod (thousands of fish, metric tons) and mean weight (kilograms) at
age for the otter trawl subfleet, ages 2-9+, 1982-1992

Year Age Total
2 3 4 5 6 7 8 oF
Number (thousands)
1982 449 446 272 131 16 20 15 20 1369
1983 337 777 298 148 87 6 17 8 1678
1984 222 300 296 79 37 21 4 12 971
1985 137 422 289 179 36 20 9 6 1098
1986 42 707 = 232 68 44 9 7 10 1119
1987 71 179 250 55 17 10 2 5 589
1988 139 470 231 89 14 3 3 1 950
1989 125 469 292 78 17 12 1 4 998
1990 99 1439 705 110 46 5 6 9 2419
1991 197 410 1374 220 40 11 6 2 2260
1992 144 167 133 496 50 14 1 4 1009
Metric Tons
1982 538 750 753 617 107 177 149 293 3383
1983 398 = 1225 692 527 503 37 174 124 3680
1984 237 509 771 276 220 185 37 163 2399
1985 170 714 791 773 195 158 95 100 2996
1986 52 1229 651 300 267 67 74 122 2764
1987 93 291 783 259 110 91 20 60 1705
1988 154 797 515 456 64 26 33 15 2059
1989 162 777 817 327 94 105 ll 65 2358
1990 118 2230 1463 456 355 60 73 153 4908
1991 224 573 3221 879 288 109 75 48 5416
1992 211 302 336 1495 258 135 15 45 2798

Mean Weight (kilograms)

1982 1.198 1.681 2.767 4.710
1983 1.181 1.576 2.322 3,561
1984 1.069 1.697 2.604 3.500
1985 1.244 1.692 2.737 4.319
1986 1.245 1.739 2.808 4.416
1987 1.304 1.623 3.131 4.702
1988 1.110 1.696 2.228 5.118
1989 1.298 1.657 2.799 4.187
1990 1.192 1.550 2.075 4.146
1991 1.189 1.897 2.344 3.995
1992 1.468 1.806 2.530 3,014

6.698 8.835 9.955 14.650
5.783 6.210 10.256 15.500
5.935 8.831 9.351 13.583
5.422 7.903 10.521 16.667
6.063 7.487 10.605 12.200
6.485 9.075 9.756 12.000
4.559 8.708 10.889 14.638
5.504 8.771 11.085 16.250
7.717 12.000 12.167 17.000
7.191 9.873 12.474 24.000
5.161 9.652 14.952 11.250

1990 was consistent with changes in estimated
fishing mortality during that period, suggesting
that both standardized effort series best reflect
conditions in the fishery.

LANDINGS AT AGE ESTIMATES

The effort subfleet landings at age and mean
weight at age matrices with sum of products for
Georges Bank and Gulf of Maine cod are listed in
Tables 5 and 6, respectively. The full landings at
age matrices for each stock are listed in Tables 7
and 8, respectively. Percentage age composition
of the landings (ages 2-9+) from each stock for the

full and subfleet components are presented in
Figures 7 and 8. Although differences in percent-
age age composition between the full landings at
age and the otter trawl ‘effort subfleet do not
appear to be substantial for either stock, younger
cod, particularly at age 2, appear in higher pro-
portions in the otter trawl effort subfleet. Differ-
ences in seasonal weighting of the quarterly age
composition estimates are likely to have oc-
curred when the fixed gear landings were elimi-
nated from the subfleet data set. Despite these
differences, the overall similarity between the
two sets of age compositions implies that gill net
and other gear are selecting age classes in similar
proportions as the otter trawl gear. Therefore,


Za mE Hw ES SS Le Lee eee ee

Page 13

Full MB vs. Tuning Subset ;

60 19787
50 |

40 | 4

PERCENT AT AGE

60 |-
50 }-
40 |-
30 |-
20

234567889
AGE

PERCENT AT AGE

50
40
30
20
10

30
20
10

50
40
30
20
10

60
50
40
30
20
10

60
50
40

30 |-

20
10

1983

2345 67 8 9

AGE

Figure 7. Percent age composition of Georges Bank cod from the full landings at age matrix and the effort subfleet
landings at age martix for ages 2-9+, 1978-1992.


Page iii

TABLE OF CONTENTS

Abstract
Introduction .
Methods
Data sources.
Effort Standardization...
Landings at Age Estimates
Results
Effort Standardization...
Landings at Age Estimates
Discussion
Literature Cited

List of Tables

Table 1. Georges Bank cod GLM effort standardization
Table 2. Nominal and standardized (GLM) Georges Bank cod landings (metric tons),
effort (days fished) and landings per day fished (LPUE) .
Table 3. Gulf of Maine cod GLM effort standardization
Table 4. | Nominal and standardized (GLM) Gulf of Maine cod landings (metric tons),
effort (days fished) and landings per day fished (LPUE) ......ssssscsssreerneter resets eseesseseess 7
Table 5. Landings at age of Georges Bank cod (thousands of fish, metric tons) and
mean weight (kilograms) at age for the otter trawl subfleet,
ages 2 -9+, 1978-1992
Table 6. Landings at age of Gulf of Maine cod (thousands of fish, metric tons) and
mean weight (kilograms) at age for the otter trawl subfleet,
ages 2 -9+, 1982-1992 :
Table 7. Total commerical landings at age of Atlantic cod (thousands of fish)
from Georges Bank and South, ages 1-10+, 1978-1992...
Table 8. Total commercial landings at age of Atlantic cod (thousands of fish)
from the Gulf of Maine, ages 2-10+, 1982-1992

il

12

12

List of Figures

Figure 1. Trends in log, CPUE of Georges Bank cod by vessel tonnage class, 1978-1992 ..
Figure 2. Trends in log, CPUE of Gulf of Maine cod by vessel tonnage class, 1982-1992
Figure 3. Fishing effort estimated for Georges Bank cod from Serchuk et al. (1993)

and from the GLM standarization procedure, 1978-1992 ......ssscssseeseretenerreetenseetesees 8
Figure 4. Fishing effort estimated for Gulf of Maine cod from Mayo et al. (1993)
and from the GLM standarization procedure, 1982-1992 ......sscsseserereeteteretereeees 8

Figure 5. Landings per unit effort (LPUE) estimated for Georges Bank cod

from Serchuk et al. (1993) and from the GLM

standardization procedure, 1978-1992 ....ccccsesssseeeetesseenetectenetecsteretssteressenreeeent ees 9
Figure 6. Landings per unit effort (LPUE) estimated for Gulf of Maine cod

from Mayo et al. (1993) and from the GLM

standardization procedure, 1982-1992 w..sccesssereeenesseersneresssrereserssereaenreenr sey 9


Sa
The Northeast Fisheries Science Center Reference Documents are a series of informal reports
produced by the Center for timely transmission of results obtained through work at the various
NEFSC labs. The documents are reviewed internally before publication, but are not considered formal
literature, The National Marine Fisheries Service does not endorse any proprietary material, process,
or product mentioned in these reports. To obtain additional copies of this report contact, Information
Services Unit, Northeast Fisheries Science Center, Woods Hole, MA 02543 (508-548-5123, ext. 260).

The correct citation for the document is: Mayo, R. K., T. E. Helser, L. O'Brien, K. A. Sosebee, B.
F. Figuerido, and D. Hayes. 1994. Estimation of standarized otter trawl effort, landings per unit
effort, and landings at age for Gulf of Maine and Georges Bank cod. NOAA/NMFS/NEFSC: Woods
Hole, MA. NEFSC [Northeast Fisheries Science Center] Ref. Doc. 94-12.



mm Hi UL lee

i a a a a a a || |

Page 9

CALCULATED
- Serchuk et al.

3.55
STANDARDIZED

3

3 é

225

2

= 2

2 ee

w ‘.

4 1 a ys
0.5 STANDARDIZED
TM | + Serchuk et al.
ce) a

78 80 82

T ee I

84 86 88 90 92

Year

Figure 5. Landings per unit effort (LPUE) estimated for Georges Bank cod from Serchuk et al. (1993) and from
the GLM standardization procedure, 1978-1992.

1.25
CALCULATED ;
1- -Mayo et al.~,
ost S STANDARDIZED
- Mayo et al.

LPUE (mt/ day fished)
o °o
b a
f f

°
iy
1

STANDARDIZED

) T T ,

T ET T 1
82 83 84 85 86 87 B88 89 90 91 92

Year

Figure 6. Landings per unit effort (LPUE) estimated for Gulf of Maine cod from Mayo € et al. (1993) and from the

GLM standardization procedure, 1982-1992.

effort due to recent changes in fleet directivity,
our standardized series suggests that the sharp
decline in the year effect in their model may have
been influenced by factors not considered explic-
itly, resulting in an overestimate of fishing effort
throughout most of the 1978-1991 period.

In the Gulf of Maine, each of the LPUE series
was quite similar except for the sharp increase in

the ‘calculated’ LPUE after 1989 (Figure 6). This
trend is inconsistent with the standardized indi-
ces given in the present study and those com-
puted by Mayo et al. (1993). This rather large
increase accounts for the relatively low estimates
of total ‘calculated’ effort in the most recent years
(Figure 4). Further, Mayo et al. (1993) noted that
a substantial increase in 1991 effort compared to


Page 12

Table 7. Total commerical landings at age of Atlantic cod (thousands of fish) from Georges Bank and South, ages

1-10+, 1978-1992

Year Age

1 2 3 4 5 6 7 8 9 10+
1978 2 393 7748 2303 830 131 345 47 40 15
1979 34 1989 900 4870 1212 458 77 253 4 48
1980 89 3777 5828 500 2308 1076 445 87 167 10
1981 27 3205 4221 2464 235 1406 417 123 130 62
1982 331 9138 3824 2787 2000 281 673 213 71 83
1983 108 4286 8063 2456 1055 776 95 235 100 65
1984 81 1307 3423 3336 840 516 458 44 171 121
1985 134 6426 2443 1368 1885 412 218 203 21 97
1986 156 1326 4573 797 480 627 87 72 47 29
1987 26 7473 1406 2121 279 252 270 63 38 24
1988 10 1577 8022 1012 1497 244 161 197 50 47
1989 oO 2088 2922 4155 331 541 82 43 50 18
1990 7 4942 5042 1882 2264 229 245 36 17 38
1991 52 1525 3243 3281 1458 1088 126 70 23 23
1992 70 4177 2170 1038 1482 404 309 34 33 10

Table 8. Total commercial landings at age of Atlantic cod (thousands of fish) from the Gulf of Maine, ages 2-10+,

1982-1992

Year Age

2 3 4 5 6 7 8 9 10+
1982 1380 1633 1143 633 69 91 61 4l 37
1983 866 2357 1058 638 422 47 61 23 24
1984 446 1240 1500 437 194 74 19 15 28
1985 407 1445 991 630 128 78 32 4 22
1986 84 2164 813 250 177 39 24 20 12
1987 216 595 1109 277 66 51 9 8 ll
1988 160 1443 953 406 43 9 17 1 3
1989 337 1583 1454 449 81 35 6 3 12
1990 205 3425 2064 430 157 27 30 10 32
1991 344 934 4161 851 143 41 30 6 2
1992 313 530 484 2018 202 ° 62 7 12 3

both the full and the subfleet landings at age are
representative of the fishery, and either matrix is
applicable for calibrating the VPA.

DISCUSSION

Inclusion of the year effect in the GLM effort
standardization models accounts for changes in
cod abundance over time but does not allow
separation of the confounding effect of increasing
efficiency due to improvements in technology.
Inclusion of an independent measure of stock
abundance as a covariate in the GLM as illus-
trated by Mayo et al. (1992) would allow for such
an adjustment. The impact of the covariate on
the resulting standardized LPUE indices may be

inferred by comparison of trends in abundance
as illustrated by the commercial LPUE and the
NEFSC bottom trawl survey weight per tow indi-
ces;ie., the greater the divergence between trends,
the greater the adjustment to the standardized
LPUE. These comparisons, are provided in Fig-
ures 9 and 10. *

On Georges Bank, there appears to be rea-
sonable correspondence between the two series
suggesting that there would be no appreciable
impact of including the index as a covariate in the
GLM. In the Gulf of Maine, however, agreement
between the two series, while quite good between
1982 and 1988, deteriorates in the last four
years. This period corresponds to the recruit-
ment and rapid decline of the very large 1987 year
class, particularly as it became fully recruited in

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