NOAA Technical Memorandum NMFS-AFSC-29

Estimation of Salmonid 

Bycatch in the 1989 Japanese

Squid Driftnet Fishery

by

Steven E. Ignell, Laura J. Simon, and Michael L. Dahlberg

U.S. DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

National Marine Fisheries Service

Alaska Fisheries Science Center
NOAA Technical Memorandum NMFS

The National Marine Fisheries Service’s Alaska Fisheries Science Center

uses the NOAA Technical Memorandum series to issue informal scientific

and technical publications when complete formal review and editorial

processing are not appropriate or feasible. Documents within this series

reflect sound professional work and may be referenced in the formal

scientific and technical literature.

The NMFS-AFSC Technical Memorandum series of the Alaska Fisheries

Science Center continues the NMFS-F/NWC series established in 1970 by

the Northwest Fisheries Center. The new NMFS-NWFSC series will be used

by the Northwest Fisheries Science Center.

This document should be cited as follows:

Ignell, S. E., L. J. Simon, and M. L. Dahlberg. 1994. Estimation of

salmonid bycatch in the 1989 Japanese squid driftnet fishery. U.S.

Dep. Commer., NOAA Tech. Memo. NMFS-AFSC-29, 45 p.

Reference in this document to trade names does not imply endorsement by

the National Marine Fisheries Service, NOAA.
NOAATechnical Memorandum NMFS-AFSC-29

Estimation of Salmonid

Bycatch in the 1989 Japanese

Squid Driftnet Fishery

by

Steven E. Ignell, Laura J. Simon, Michael L. Dahlberg

Auke Bay Laboratory

Alaska Fisheries Science Center

11305 Glacier Highway

Juneau AK 99801-8626

U.S. DEPARTMENT OF COMMERCE

Ronald H. Brown, Secretary

National Oceanicand Atmospheric Administration

D. James Baker, Under Secretary and Administrator

National Marine Fisheries Service

Rolland A. Schmitten, Assistant Administrator for Fisheries

January 1994
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iii

ABSTRACT

Salmonid (Oncorhynchus spp.) bycatch data from the 1989

U.S., Canada, and Japan monitoring program for Japanese squid

driftnet vessels were analyzed. Sampling effort was 

consistently less than expected by proportionate sampling

between 170°E and 180° long., especially during the first part

of the month when capture of salmonids would most likely

occur. Salmonid incidence (the proportion of monitored

operations encountering salmonids) was highest at the western

and eastern boundaries of the fishery.

Fishing-effort data for the bycatch calculations were

divided into three categories: a portion-represented by.

observer data, an unrepresented portion that could be

estimated by extrapolation of sampled data, and an

unrepresented portion thatcould not be estimated. The

observers reported a catch of 79 salmonids in 57 monitored

operations (4% of total fishing effort). For the estimated

portion (81% of total fishing effort), a bycatch estimator

based on an extension of Aitchison's delta distribution

produced a bycatch estimate of 2,648 salmonids. Although the

unestimated portion of Japanese fishing effort is small,

salmonid bycatches there may have been significant; a Republic

of Korea research vessel operating in an unsampled portion of

the fishing area and using 37 tans of driftnet caught

13 salmonids. This represents over 16% of the total salmon

observed in 1,427,225 tans through the monitoring program.

The problem of unestimated strata may be unique to

migratory species like salmonids which are found only within a

small portion of the total fishing area. In addition, the

warm ocean conditions of 1989 probably displaced salmonids

northward, restricting the amount of fishing area intersecting

salmonid waters, and inducing some of the estimation problems

associated with our data.

V

CONTENTS

INTRODUCTION . . . . . . . . . . . . . . . . .

ANALYSIS OF OBSERVER SAMPLING EFFORT . . . . .

Data Collection . . . . . . . . . . . . .

Analytic Methods . . . . . . . . . . . . .

Results . . . . . . . . . . . . .

Distribution of Sampling Effort . . .

ANALYSIS OF SALMONID INCIDENCE . . . .

Analytic Methods . . . . . . . . .

Results . . . . . . . .

Model Fitting . . . .

Trends in Incidence Rates . .

SALMONID BYCATCH ESTIMATION

Analytic Approach . .

Results . . . . . . .

CONCLUSIONS . . . . . . . .

ACKNOWLEDGMENTS . . . . . .

CITATIONS .

TABLES . .

FIGURES . .

APPENDIX .

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INTRODUCTION

In 1989, the United States, Canada, and Japan established

a monitoring program aboard Japanese squid driftnet vessels

operating in the North Pacific Ocean. This program was

intended to secure information on the catch of neon flying

squid (Ommastrephos bartrami) and the incidental take 'of

salmonids (Oncorbynchus spp.) and other fishes... [and] to

secure information on incidental take of marine mammals,

seabirds, and other marine species of mutual interest.1

The

program was designed to provide initial data on the variability of bycatch rates in the fishery.2

The 1989 data would be

used to design a 1990 observer program to obtain fishery-wide

bycatch estimates.

The need for immediate information on levels of bycatch

in these fisheries led scientists from the participating

nations to develop bycatch estimates based on 1989 data rather

than waiting for 1990 data. Despite the limited amount of

monitoring effort in 1989, expansion of observer data to

provide fishery-wide bycatch estimates was theoretically

feasible, given certain assumptions. Validity of these

assumptions depends on estimation methodology. If the

assumptions are false, an evaluation of possible estimation

biases is required.

Methodology for estimating the number of salmonids caught

in the 1989 Japanese flying squid driftnet fishery is developed and evaluated in this paper. First, the distribution of

observer sampling effort relative to the reported fishing

effort is examined. Second, the temporal and spatial patterns

of salmonid incidence' are evaluated. Finally, a salmonid

bycatch estimator is developed and applied.

1

Annex to the 2 May 1989 letter from Kazuo Shima, Councillor to the

Fisheries Agency of Japan, to Richard Smith, Deputy Assistant Secretary,

U.S. Department of State.

2

The reader should note that a U.N. sponsored moratorium on large-scale

driftnet fishing was implemented beginning in 1993.
2

ANALYSIS OF OBSERVER SAMPLING EFFORT

Data. Collection

The 1989 monitoring program was implemented in two parts

(Int. North.Pac. Fish. Comm. 1990): 1) a July-August program

to collect data on the incidental catch of salmonids and other

species near the recently modified northern boundary of the

fishery, and 2) a June-December program to collect. data

fishery-wide. The July-August program consisted of

22 Japanese, 5 Canadian, and 4 U.S. observers aboard

22 driftnet vessels. The July-December program consisted of

5 U.S. and 810 Japanese observers aboard 10 driftnet vessels.

Canadian and U.S. observers were always paired with Japanese 

observers; 'thus, vessels included in the program were either

monitored by a single Jgpanese observer or jointly by Japanese

and North American observers.

Distribution of sampling effort was not controllable.

Although the Fisheries Agency of Japan (FAJ) randomly selected

vessels from each fishing port to host the observers, the

-observers exerted no influence over areas fished. The vessels

fished in accordance with directions from the fishing master

(Int. North Pac. Fish. Comm. 1990).

The observers monitored driftnet operations 5 days at a

time, resting each 6th day. For each observed fishing operation, they recorded the month, day, latitude, longitude, sea

surface temperature, number of standardized effective tans.

(50 m of driftnet) deployed; and the bycatch counts of various

species. Observers monitored retrieval operations from an

unobstructed vantage point, usually atop the pilot house or on

the bridge wing. Because retrieval operations commonly lasted

up to 12 h, one of every four net sections was randomly

selected for a work break. Total catch by species was

recorded on standardized data forms. Catch and: fishing effort

for the entire fleet was provided by the FAJ and summarized by

10-day periods and by 1o latitude by 1o longitude statistical

areas.

Analytic Methods

Distribution of observer monitoring 'effort relative to

fishing effort by the fleet was examined. Fishing and
3

observer effort data were stratified by time and area: nine

approximately 10-day periods (1-10, 11-20, and 21 to end of

month) in June, July, and August and between-10 and 13 areas

depending on the time. If observer effort were proportional

to fleet effort in the stratum, then the expected observer.

effort for the jth area in the ith period is computed as

where Obs is the number of operations observed and FE is the

number of operations fished.

These statistical areas were formed from a combination of

1) five longitudinal categories--four 10o intervals between

170°E and 15O°W long. and one 5° interval between 15O°W and

145°W long.; 2) three latitudinal categories for July and

August data east of 17O°W long.--within 1o

, between 1o and 2°,

and more than 2° south of the northern boundary; and 3) two

latitudinal categories for areas not covered in 2)--one above

and one below the 1o line of latitude south of the northern

fishing boundary (Fig. 1). Data from the July-August and

June-December programs were combined.

The statistical areas were designed to divide observer

and fishing effort data into strata reflecting possible

differences in salmonid densities. For example, near the

southern limit of salmonid distribution, a 2°C change in ocean

temperatures--the expected monthly temperature change for a

given latitude near the northern boundary of the squid fishing

area--can lead to a marked change in salmonid abundance (Ogura

and Takagi 1987). Selection of 10-day periods in the analyses

were thus used-to minimize these changes.

Results

Observers monitored 1,402 Japanese squid driftnet operations from June through October 1989, observing the retrieval

of 1,427,225 tans (71,361 km) of driftnet. These observations

represent a 4.17% coverage of fishing operations and a 4.15%

coverage of deployed tans (Fisheries Agency of Japan 1990).

Although the program called for the monitoring of 32 driftnet
4

vessels, data from only 27 vessels proved useful (Int. North

Pac . Fish. Comm. 1990).

Distribution of Sampling Effort

The observer sampling effort was generally not proportional to reported commercial fishing effort (Fig. 2;

Table 1) as , observer effort was relatively more intense in

the summer months. Deviations from proportional effort were

related to longitude. Sampling effort was consistently

greater than expected between 160°W and 150°W long. near the

northern boundary, and between 170°W and 16O°W long. in the

southern portion of the fishery. Sampling effort was less

than expected between 170°E and 180° long. for both

latitudinal categories (Table 2).

The deviations also differed by time period between and

within strata (e.g.; compare figures in Appendix Fig. 1). For

the northern strata defined by 170°E-180° long. and 170-160°W

long., sampling effort increased, by period; for adjacent

strata located east of these two strata, sampling effort

decreased by period (Figs. 3, 4). Within the extreme northwestern stratum (northern 1o

, latitude of 170°E-180° long.);

observed vessels were east of the fleet average toward the

first of the month; toward the end of the month, they were

located similarly (Fig. 5).

Differences between reported fishing effort and observed

effort may be affected by the experimental design of the

observer monitoring program. Observer placement was randomized over vessels, not over time and area. Vessel movements.

are nonrandom; vessels may fish in an area for an extended

period, or move great distances to fish in a new area.

ANALYSIS OF SALMONID INCIDENCE

Analytic Methods

Consider a random variable Yi, such that Yi = 1 if.

salmonids are present and Yi = 0 if salmonids are absent in,,

the ith fishing operation. Assume that Yi is distributed

binomially. The likelihood function for a set of N driftnet

operations is, then,
5

Using the logit function,

and fitting a linear predictor composed of a p-dimensional

vector of independent variables (X1, X2,..., Xp), leads to the

familiar logistic regression model where the conditional

probability of salmonid incidence is-given as

The independent variables used in the analyses consisted of

spatial factors (latitude and longitude), month, time period,

and sea surface temperature. Model parameters Bi of the

linear predictor were estimated by the method of maximum

likelihood.

Model selection employed a stepwise regression algorithm.

Design variables for categorical variables were constructed

using "reference cell coding," where the lowest group of a

categorical variable serves as a referent group (Table 3).

Model significance was assessed by likelihood ratio statistics

which are formed from the logarithm of the ratio of two

likelihoods (hereafter called the deviance). For a particular

step, the deviance provides a test for whether the term

entered (or removed) at that step significantly improves model

prediction. Model adequacy was assessed by the Hosmer

goodness-of-fit test (Hosmer and Lemeshow 1989), which

compares the observed and predicted frequencies within strata

defined by a grouping of the 'estimated probabilities.

Results

Only 57 of the 1,402 (i.e., 4.07%) observed operations

encountered salmonids, resulting in a total observed catch of

79 salmonids during the 1989 monitoring program. 'As a result,

the frequency distribution of salmonid bycatch rates was

highly skewed, largely composed of zeros and ones (Fig. 6).
Catches of salmonids were sporadic in location (Fig. 7,

for example) but generally highest at the western and eastern

boundaries of the fishery (Tables 4, 5). The area of greatest

incidence was between 145°W and 150°W long., where 22% (12/55)

of the fishing operations located in the upper 1o latitude of

the monitored fishery encountered salmonids. East of 180°

long. (180°-170°W), 42 of the 44 operations encountering

salmonids were within the northern 1o

West of 180° long.

latitude of the fishery.

(180°-170°E), the incidence rate (the

proportion. of monitored operations encountering salmonids)

decreased more gradually with distance from the northern

boundary. For example, if we consider the area 1o

or more

below the northern boundary,. 8 of 222 driftnet operations west,

of 180° long. encountered salmonids, as compared with 2 of 

476 operations eastward, an 8.6-fold increase over the

incidence rate eastward (Table 4).

Model Fitting

Based on these results, we divided, the data-into two

sections --west and east of 180° long.?-and fit separate

logistic regression models to each set of data. This division

eliminated the need to include interaction terms; such as

longitude x latitude, thereby enabling a 'more straightforward

interpretation of -parameter coefficients. For each section,

regression models were first fit to the entire data set.

Regions south of the northern boundary with very low incidence

rates were then removed and the model refitted to clarify

'relationships among factors affecting the incidence measure. 

For data. east of 180° longitude, two covariates were

selected by the stepwise algorithm--longitude and distance

from the northern boundary. The Hosmer test indicated that

the model performed satisfactorily '(Table 6). Coefficients

for the three longitude design variables, were negative. This

means that for a given distance from the northern boundary of

the fishery, the likelihood of salmonid incidence in strata

west of 150°W long. was less than that from 145-150°W long.

The other estimated coefficients in the model indicate that

salmonid incidence was greatest 'during July and August, least

during. September ‘and October, and least one or more-degrees

south of the northern' boundary (Table 6).
7

When data were constrained further to within 0-1o of the

northern boundary, both month and longitude entered into the

model. Estimated coefficients for longitude were similar to

those for the full data set; salmonid incidence was greatest

during July and August and along the eastern portion of the

fishery. 

For data west of 180° long., only one variable (month)

was selected by the stepwise algorithm (Table 7). Salmonid

incidence was greatest in July, and greater in June than

August. When restricted to data 0-20 south of the northern

boundary, period replaced month in the regression mode-l.

Trends in Incidence Rates

The logistic model indicated that the probability of

salmonid incidence in the areas observed in the 1989 squid

fishery was small. Areas of greatest probability were west of

180° long. or along the northern boundary east of 180° long.

The incidence rates were related to time period west of 180°

long., but not eastward. East of 180° long., salmonid

incidence was least from 17O°W to 160°W long. and greatest

from 145°W to 15O°W long.; salmonid incidence there usually

varied by month, never by 10-day period within month, and

always by longitude and the distance from the northern

boundary. Incidence rates for some months (e.g., July and

August) and for some areas (e.g., 160-170°W long., and

170°W-180° long.), however, were similar.

Results from these models could be affected by the

distribution of sampling effort in some areas. For example;

salmonid incidence west of 180° long. was low during August.

There was no observer coverage, however, reported along the

northern boundary of this stratum during the first two periods

of the month. In other months, salmonid incidence west of

180° was highest during the first of the month; thus the low

August incidence is probably affected by these sampling

patterns. This possibility is supported further by analyses

of research vessel data which show that this area typically

exhibits a high probability of salmonid incidence during early

August (Ignell 1989).
8

SALMONID BYCATCH ESTIMATION

Analytic Approach

Assume each fishing operation is independent and selected

at random. Also, assume that the fishing operations can be

stratified into i regions and periods with relatively

homogeneous rates of salmonid bycatch. Assume, within each

stratum i that there is a pi proportion of zero salmonid

bycatch rates, and that nonzero salmonid bycatch rates are

distributed log-normally.

Under the above assumptions, Pennington's (1983)

extension of Aitchison's (1955) delta-distribution methodology

can be used to construct a bycatch estimator that treats

zeroes in the data- separately. Separate treatment: of zeroes

provides a more efficient bycatch estimator statistically.

The minimum-variance unbiased estimator of the mean, k, of the

delta distribution is

the number of nonzero values, 

the sample-size,

the sample mean of the natural logarithm of the

nonzero salmonid bycatch rates,

an infinite series (Pennington 1983),

the sample variance of the natural logarithm of

the nonzero salmonid bycatch. rates, and

the actual salmonid bycatch rate of the one

nonzero value.

The estimated variance of the mean k, varest(k), is

approximated by (Berrien et al. 1981)
For each observed stratum i of the squid fishery, an estimate

of the mean; ki, and variance of the estimated mean, varest(k,),

were derived. Weighting the estimated means ki by the amount

of fishing effort in each stratum i, (wi), and summing over

all strata, provides an estimate of the number of salmonids

incidentally caught in 1989. A 95%-confidence interval of the

total number of salmonids caught can be calculated by assuming

that this weighted sum of the ki is approximately normally

distributed with standard-error 

Sampled data were extrapolated into the unsampled cells

based on the results of the logistic regression analysis. We

used incidence data rather than catch rates because the mode

of the catches was one and because our efforts to develop a

regression model for catch per unit effort (CPUE) proved

unfruitful. Accordingly, the following guidelines--derived

from examinations of model statistics and parameter

coefficients--were established to guide this extrapolation:

1) For data along the northern boundary east of 180° long.,

first look for data from adjacent periods (period was not

significant for this region); 2)if there were no sampling in

the stratum for that month, use data from an adjacent

longitude stratum, but only if the parameter coefficientsfor

the two strata were similar (e.g.,, the two strata between

160°W and 180° long.); 3) for data east of 180° long. but at

least 1o south of the northern boundary, expand over time

period, or adjacent longitudinal strata; and 4) do not

extrapolate for data west of 180° long. (time period was
10 

important in the model, and observer effort was irregular

time and area),or for data in October (insufficient data

determine bycatch patterns).

by

to

Results

The observed data set was stratified into the same 10-day

periods and statistical areas as for the Chi-square analysis

of the sampling distribution. Because of the limited number

of positive values in each stratum (<8), we were unable to

test the assumption of log-normality of the data.

For each stratum containing observed fishing operations,

the mean salmonid bycatch rate (per 1,000 standardized

effective tans), ki, and its. standard error were estimated

(Table 8). Weighting each estimated stratum mean by the

number of 1,000 standardized effective tans in the stratum,

and summing over all strata,

2,635 salmonids (S.E.

provided an estimate of

=675.997) and a 95% confidence interval

of 1,310 to 3,959 salmonids.

Given the foregoing rules, we extended observer data into

28 -unsampled strata providing an estimate of 13.08 salmonids

(S.E. of 9.01) (Table 9): 'Combining these two estimates

yields a total estimate of 2,648 salmonids in 27,934,788 tans

of fishing effort (81%of total fishing effort).

For unsampled strata meeting none of the foregoing 

criteria, or when period of fishing exceeded the period of

sampling. (10 October), we did not estimate the salmonid

bycatch. The nonsampled regions represent 0.25% of the

fishing effort for June through August and 19% of the overall

effort. In some strata, however, salmonid catch would be

likely and perhaps even large. For example, between 1 and

10 August, none of the 20 fishing operations in the

northwestern block of the fishery (the 44,-45°N lat. and

170°E-180° long. block) were observed. Yet, we know that

salmonids were present then; a Republic of 'Korea (ROK)

research vessel3 caught 13 salmon on 5 August 1989 at

3

Cruise report of the ROK vessel Pusan 851, Daniel Cheng, NOAA, National,

Marine Mammal Laboratory, Seattle, Washington.
11

45°N lat. and 170°E. long. using 1.85 km of variable mesh-size

driftnet. This is equivalent to a bycatch rate of

351.4 salmon per 1,000 standardized effective tans, and it

occurred in an unsampled stratum containing 24,960 tans of

commercial fishing effort.

CONCLUSIONS

Observer monitoring effort was generally not proportional

to reported commercial fishing effort. Deviations from the

expected proportions varied by longitude and period, but they

were consistently less than expected between 170°E and 180°

long. 'Some (an unknown amount) of these deviations may be an

artifact of the experimental design of the observer monitoring

program as this was the first year of wide-scale sampling-of

the fishery.

Nonproportional sampling, however, is consequential only

if it results in fishing areas that are not represented by

sampling effort. This is most likely to occur in areas in

which expected observer effort is small. One of these areas

was the extreme northwest portion of the fishery; for some

periods, sampling effort was either absent or observed vessels

were spaced east of the fleet average (where salmonid catches,

would probably be lower).

Salmonid incidence was highest at the western and eastern

boundaries of the fishery. The area of greatest incidence was

between 145°W and 150°W long., where 22% of the monitored

fishing operations located in the upper 1o latitude of the

fishery encountered salmonids. When salmonids were

encountered, CPUEs were highest 'west of 180° long., even

though observer sampling effort there was generally located

south of sampling effort in the eastern portion of the

fishery. 

Fishing effort data for the bycatch calculations was

divided into three sections: a portion represented by

observer data, an unrepresented portion that could be

estimated by extrapolation of sampled data, and an

unrepresented portion that could not be estimated. For the

estimated portion (81% of total fishing effort), a bycatch

estimator based on an extension of Aitchison's delta
12

distribution--proposed by Pennington (1983)--produced -a

bycatch estimate of 2,648 salmonids.

Only a small part of the portion of the fishery that

could not be estimated is likely to have any significance in

terms of salmonid bycatch. For these data, the central

problem is how to extrapolate observer data from a sampled

region of low salmonid abundance to an unsampled region of

historical high abundance. Unsampled effort in this region

represents less than 1% of the total fishing effort; however,

on 5 August 1989, a ROK research vessel in one unsampled area

using 37 tans of driftnet caught over 16% of the total amount

of salmon observed in 1,427,225 tans of monitored fishing

effort. Thus, despite the extremely small amount of fishing

effort, bycatch in this region may be significant.

We note, however, that these estimation difficulties may

be unique to species like salmonids which are vulnerable to

only a small portion of the fishery and thus are more affected

by sampling variations. There is significant zonal:

variability in the density of salmon across the northern.

boundary of the squid driftnet area (Ignell. 1991). Salmonids

are most likely to be caught near the northwestern boundary of

the fishery during the first part of the month. Moreover, the

extent of thisvulnerability varies yearly, depending on ocean

conditions (Ignell 1989). Surface and subsurface temperatures

near the squid driftnet fishing area were warmer than normal

in 1989, and the subarctic frontal zone wasprobably displaced

northward that summer (Ignell 1990): Because of the role

ocean conditions play in determining salmonid distributions in

the North Pacific Ocean! salmonids were also probably

 displaced northward, restricting the amount of fishing area

intersecting salmonid-inhabited waters. These phenomena

probably induced some of the estimation problems encountered

in the 1989 data.

In conclusion, our estimation difficulties point out the

need to carefully consider some of the inherent problems of

sampling a highly skewed population. Such a population

 contains extreme values which, -although rare; can affect-the

results of even moderately large samples (Kish 1965). Many of

these effects (decreased precision, increased variance, and

invalidation of the normal approximation) are well known.'
13

From an applied perspective, however, the most crucial effect

is that a single sample generally provides a point estimate

that underestimates the true population mean, particularly as

in our case, where the sampling fraction is greater than the

expected probability of extreme events. In such cases, it is

good sampling practice to segregate these events (e.g., high

catch rates) in the sampling design, especially when concentrations of the events correspond to other factors such as

temperature or geographic area.

ACKNOWLEDGMENTS

We are indebted to Dr. Jerry Pella of the National Marine

Fisheries Service, Dr. Terry Quinn of the University of

Alaska, and -Dr. Bruce Lindsay of Pennsylvania State University

for advice regarding the statistical methodology. We also

thank Jim Murphy and Susan Fowler for assistance with the

figures.

CITATIONS

Aitchison, J. 1955. On the distribution of a positive random

variable having a discrete probability mass at the

origin. J. Am. Stat. Assoc. 50: 901-908.

Berrien, P. L., N. A. Naplin, and M. R. Pennington. 1981.

Atlantic mackerel, Scomber scombrus, egg production and

spawning population estimates for 1977 in the Gulf of

Maine, Georges Bank, and Middle Atlantic Bight.

P.-V. Reun. Cons. Int. Explor. Mer 178: 279-288.

Fisheries Agency of Japan. 1990. Catch and effort statistics

for the Japanese squid driftnet fishery in the North

Pacific in 1989. Int. North Pac. Fish. Comm. document,

44 p.

Hosmer, D. W., Jr., and S. Lemeshow. 1989. Applied logistic

regression. John Wiley and Sons, New York. 307 p.

Ignell, S. E. 1989. Annual variability in salmonid incidence

and near-surface ocean temperatures in the central North

Pacific Ocean, 1978-1988. (Document submitted to annual

meeting of the International North Pacific Fisheries
14

Commission, Seattle, September, 1989;) Auke Bay

Laboratory, Alaska Fisheries Science Center, NMFS, NOAA,

11305 Glacier Hwy., Juneau, AK99801-8626, 22 p.

Ignell, S. E. 1990. Diagnostic indices of oceanographic and

atmospheric conditions in the central North Pacific

Ocean. (INPFC Doc.) Auke Bay Laboratory, Alaska'

Fisheries Science Center, NMFS, NOAA, 11305 Glacier Hwy.,

Juneau, AK,99801-8626, 14 p. 

Ignell, S. E. 1991. Zonal variability in salmonid driftnet

catch rates in the central North Pacific Ocean, p. 89-95.

In J. E. Wetherall (editor),, Biology, oceanography, and

fisheries of the North Pacific transition zone and

subarctic frontal zone. U.S. Dep. Commer., NOAA Tech..

Rep. NMFS 105.

Int. North Pac. Fish. Comm. 1990. Final report of squid and

bycatch observations in the Japanese driftnet fishery for

neon flying squid (Ommastrephes bartrami), June -

December, 1989 Observer Program. (INPFC Doc:) Joint

report by the National Sections of Canada, Japan and the

United States. (Available from Driftnet Program

Coordinator, Alaska Fisheries Science Center, 7600 Sand

Point Way N.E., BIN C15700, Seattle, WA 98115-0070.),

111 p.

Kish, L. 1965. Survey sampling. John Wiley and Sons,

New York., 643 p.

Ogura, M., and K. Takagi. 1987. Differences in area of

distribution between salmon and flying squid based on

data collected by Japanese salmon 'research vesseles

[sic], 1983-1986. (INPFC Doc.) Fisheries Agency of

Japan, Tokyo, Japan 100, 21 p.

Pennington, M. 1983. Efficient estimators of abundance, for

fish and plankton surveys.., Biometrics 39: 281-286. 
15

Table 1. --Chi-square (x2

) tests of whether

observer effort is proportional to

fishing effort in the Japanese squid

driftnet defined fishery. Data are

stratified by statistical areas and

by time period for months with

significant observer effort.

x

2

 test

Period Month Days statistic P
Table 2.--Distribution of observer effort by time period and area compared to

the expected reported fishing effort of the Japanese squid driftnet

fishery. Minus signs = observer effort less than expected; + =

greater than expected; NA = no reported fishing effort; and 0 = no

observer effort.
17

Table 3. --Specification of the design variables

for the four categorical variables used

in the stepwise logistic regression.

analysis of salmonid incidence in the

Japanese squid driftnet fishery, 1989.
1 8

Table 4. --The number of Japanese squid driftnet operations

encountering salmonids stratified by longitudinal

stratum and time period, and distance from the northern

boundary of the fishery.
19

Table 5. --The number of Japanese squid driftnet operations

encountering salmonids stratified by longitudinal

stratum, month, and distance from the northern boundary

of the fishery.

Number of driftnet operations

with salmonids either present or absent
2 0

Table 6. --Output from the stepwise regression model. Data

are from monitored driftnet operations of the

Japanese squid driftnet fishery, 1989, -east of

180° longitude.

Data

Model statistics Maximum likelihood statistics

Deviance D.f. Hosmer p. Effect Level* Coeff. S.E.

-*

Levels of model effects are defined as follows.

Distance: (1) is 1-2°,

(2) is 2° or more south of the northern boundary.

Longitude: (1) is 150-16O°W,

(2) is 160-17O°W,

(3) is l70°W-180°.

Month: (1) is July,

(2) is August.

(3) is September-October;
21

Table 7,. --Output from the stepwise regression model. Data

are from monitored driftnet' operations of the

Japanese squid driftnet fishery, 1989, west of

180° long.

-Level of month effects are defined similar to those in Table 6.

Level (1) of time period is defined as monthly days 11-20, and level

(2.) of time period as monthly days 21 to end of month.
Table 8 .--Estimation based on Pennington's (1983) method using 1989 Japanese

strata with observed operations are shown. h

squid observer data.

Per =

Only

11-20, 3 = days 21-31).

period wit in the month (1 = days 1-10, 2 = days

Number of operations: n = total number; n

tions; and no = number of zero operations.

= number of nonzero operaA tan is a standardized effective tan (50 m long).
Table 9.--Estimation based on Pennington's (1983) method using 1989

Japanese squid driftnet observer data. Only unsampled strata

that were filled in with extrapolations of observed operations

are shown. A tan is a standardized effective tan.. NA = not

able to be estimated.

Figure 2. --Comparison of the distribution of commercial fishing effort and observer

monitoring effort by month for the Japanese squid driftnet fishery, 1989.
Figure 3. --Temporal and spatial variability in the- ratio of observed to expected

sampling-effort averaged over the fishing season for four longitudinal

strata located within 1o of the northern boundary of the Japanese squid

driftnet fishery. 
Figure 4. --The distribution of the ratio of observed to expected-sampling effort

(z-axis) for four longitudinal strata located within 1o of the northern 

boundary of the Japanese squid driftnet fishery (y-axis) and nine sequential

10-day periods (x-axis) from June through August 1989.
Figure 5. --Average longitude of observed vessels compared to the average longitude of

all fishing vessels located within 1o

between 170°E and 180° long.

latitude of the northern boundary and

in the Japanese squid driftnet fishery, 1989.
Figure 6. --Frequency distribution of the number of salmonids

observed caught in 1,402 monitored operations of

the 1989 Japanese squid driftnet fishery.

APPENDIX
THIS PAGE INTENTIONALLY LEFT BLANK
Appendix 1.--Distribution of observed and reported fishing effort in 1o

 by 2°

statistical areas for the 1989 Japanese squid driftnet fishery. Width and

height of rectangles are scaled to the percent of fishing effort and

observer effort, respectively,

1989.

located in the statistical area, 1-10 June










Appendix 1. --Continued. 21-30 September.

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AFSC28 MORTENSEN, D. G., and H. SAVIKKO. 1993. Effects of water temperature on growth of juvenile

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26 LOW, L-L. (coordinator). 1993. Status of living marine resources off the Pacific coast of the United

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25 KINOSHITA, R. K., A. GREIG, J. D. HASTIE, and J. M. TERRY. 1993. Economic status of the

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24 SINCLAIR, E. H. (editor) 1993. Fur seal investigations, 1991, 142 p. NTIS No. PB94-118171. 

23 PARKS, N. B., F. R. SHAW, and R. L HENRY. 1993. Results of a 1988 trawl survey of groundfish

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22 YANG, M-S. 1993. Food habits of the commercially important groundfishes in the Gulf of Alaska

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21 KINOSHITA, R. K., and J. M. TERRY. 1993. Oregon, Washington, and Alaska exports of edible

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20 REEVES, J. E. 1993. Use of lower minimum size limits to reduce discards in the Bristol Bay red

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19 SYRJALA, S. E. 1993. Species-specific stratification and the estimate of groundfish biomass in

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18 PELLA, J., M. HOFFMAN, S. HOFFMAN, M. MASUDA, S. NELSON, and L. TALLEY. 1993. Adult

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17 SEASE, J. L., J. P. LEWIS, D. C. MCALLISTER, R. L. MERRICK, and S. M. MELLO. 1993. Aerial

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and Aleutian Islands during June and July 1992, 57 p. NTIS No. PB93-226025. 

16 FISCUS, C. F. 1993. Catalogue of cephalopods at the National Marine Mammal Laboratory, 183 p. NTIS

No. PB93-226678.

15 KINOSHITA, R. K., A. GREIG, L. E. QUEIROLO, and J. M. TERRY. 1993. Economic status of the

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14 PEREZ, M. A., and W. B. MCALISTER. 1993. Estimates of food consumption by marine mammals

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13 BERGER, J. D. 1993. Comparisons between observed and reported catches of retained and

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