NOAA Technical Memorandum NMFS-AFSC-39

U.S. DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

National Marine Fisheries Service

Alaska Fisheries Science Center

June 1994

Assessment of Gulf of Alaska

Sablefish and Other Groundfish

Species Based on the

1988 National Marine Fisheries Service

Longline Survey

by

H. H. Zenger, Jr., M. F. Sigler, and E. R. Varosi
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:

Zenger, H. H., Jr., M. F. Sigler, and E. R. Varosi. 1994. Assessment of

Gulf of Alaska sablefish and other groundfish species based on the 1988

National Marine Fisheries Service longline survey. U.S. Dep. Commer.,

NOAA Tech. Memo. NMFS-AFSC-39, 55 p.

 

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

National Marine Fisheries Service, NOAA.
NOAA Technical Memorandum NMFS-AFSC-39

Assessment of Gulf of Alaska

Sablefish and Other Groundfish

Species Based on the

1988 National Marine Fisheries Service

Longline Survey

by H. H. Zenger

1

 Jr., M. F. Sigler2, and E. R. Varosi3

1

Resource Assessment and Conservation Engineering Division

Alaska Fisheries Science Center

7600 Sand Point Way N.E., BIN C-l 5700

Seattle, WA 98115-0070

‘Auke Bay Laboratory

Alaska Fisheries Science Center

11305 Glacier Highway

Juneau AK 99801-8626

3

Alaska RegionalOffice

709 W. 9th Street, Room M 09 C

P.O. Box 21767

Juneau AK 99802-1767

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

June 1994
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iii

ABSTRACT

The Alaska Fisheries Science Center conducted the second

annual National Marine Fisheries Service (NMFS) longline survey

to study the abundance and biological condition of sablefish

(Anoplopoma fimbria) and other groundfish along the upper

continental slope of the Gulf of Alaska during the summer of

1988. This survey replicated the 1987 survey, with some

modifications to the sampling gear and a change in the bait from

Pacific herring (Clupea pallasi) to Atlantic squid (Illex spp.).

Sampled stations were the same as those used during the JapanU.S. cooperative longline survey which has been conducted in the

Gulf of Alaska from 1979 to 1988. In addition, 11 stations were

sampled in gullies. The most notable change in abundance during

the second NMFS survey was the decrease in sablefish and the

increase in giant grenadiers (Albatrossia pectoralis) in the

western Gulf of Alaska. Sablefish relative abundance was the

highest of any species, followed by grenadiers. Sablefish

abundance indices were highest in the 401-600 m depth interval

and grenadiers were most abundant in 801-1,000 m. Those two

species accounted for 83.1% of the total relative population

number (RPN) and 93.9% of the relative population weight (RPW).

Rockfish (Sebastes aleutianus and S. borealis), Pacific cod

(Gadus macrocephalus), and arrowtooth flounder (Atheresthes

stomias) together comprised 10.8% and 5.5% of the total RPN and

total RPW.
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V

CONTENT S

INTRODUCTION . . . . .

 MATERIALS AND METHODS .......... .

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Survey Area and Operations .

Data Collection . . . . . . .

Analytical Methods. . . . . .

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RELATIVE ABUNDANCE AND BIOLOGICAL CONDITION

Sablefish . . . . . . . . . .

Shortraker and Rougheye Rockfish

Thornyheads . . . . . .

Pacific Cod . . . . . .

Miscellaneous Species

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TABLES . .

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32
INTRODUCTION

Since 1979, annual longline surveys of sablefish (Anoplopoma

fimbria) and other groundfish species have been conducted

cooperatively by Japan and the United States. Initially the

survey sampled the upper continental slope of the Gulf of Alaska,

but it was later expanded to similar depths in-the Aleutian

Islands region (1980) and in the eastern Bering Sea (1982). This

research was conducted by Japanese and U.S. scientists using

Japanese commercial fishing vessels chartered by the Fisheries

Agency of Japan. The resultant data were analysed annually to

estimate the relative abundance of sablefish and other groundfish

(Sasaki 1987, Sigler 1987, Wakabayashi and Teshima 1987, Mito

1987, Sasaki and Teshima 1987).

In 1987 the National Marine Fisheries Service's (NMFS),

Alaska Fisheries Science Center (AFSC), initiated a similar

research program in the Gulf of Alaska using a chartered U.S.

longline vessel. The second annual (1988) NMFS longline survey

used the same station pattern, similar sampling gear, and was

conducted during the same season as the Japan-U.S. cooperative

longline survey in 1988. In addition, the NMFS longline survey

sampled 11 stations in gullies adjacent to the upper continental

slope (Figs. la and lb).

Three objectives guided the 1988 NMFS longline survey. The

first objective was to determine the relative abundance and size

composition of commercially important groundfish species found on

the upper continental slope of the Gulf of Alaska, including
2

sablefish, shortspine thornyhead (Sebastolobus alascanus),

rougheye rockfish (Sebastes aleutianus) and shortraker rockfish

(Sebastes borealis). The second objective was to determine the

relative abundance and size composition of other species caught

during the survey, such as Pacific cod (Gadus macrocephalus),

grenadiers (Macrouridae), arrowtooth flounder (Atheresthes

stomias), and other incidental species. The third objective was

to sample gullies on the continental shelf to compare catch rates

and size compositions from these deepwater shelf regions with the

adjacent slope.

The 1988 NMFS longline survey was conducted-jointly by two

components of the AFSC: the Resource Assessment and Conservation

Engineering Division in Seattle, Washington, and the Auke Bay

Laboratory in Juneau, Alaska.

MATERIALS AND METHODS

Vessel and Gear

Survey operations were conducted aboard the chartered 35 m

longline vessel Prowler. A description of the vessel, equipment,

and crew complement appear in Sigler and Zenger (1989). A

generalized diagram of longline gear is shown in Figure 2.

The total length of groundline set each day was 16 km

(8.6 nmi). It was composed of 160 sections of longline gear,

called skates, tied together; each skate was 100 m (55 fathoms)

long and contained 45 circle hooks (7,200 hooks total). The

Mustad No. 13/0 circle hooks were attached to 38 cm (15 in)
gangions that were secured to beckets tied into the groundline at

2 m (6.5 ft) intervals. Five meters (16 ft) of groundline were

left bare on the ends of each skate. Gangion, becket, and

groundline materials were medium lay No. 60 braided nylon, medium

lay No. 60 thread braided nylon (newer skates contained beckets i

of medium lay No. 72 braided nylon), and medium lay 9.5 mm (3/8

in) Goldline, respectively. Each end of the groundline was

attached sequentially to 366 m (200 fm) of Goldline, a 27 kg (60

lb) anchor, 92 m (50 fm) Goldline, a 16 kg (35 lb) piece of chain

(to dampen the effects of wave surge on the buoyline), 92 m of

9.5 mm polypropylene line, a buoyline made of 183-1,281 m (l00-

700 fm) Goldline, and at the surface, a buoy array and flag. The

groundline was weighted with 3.2 kg (7 lb) lead balls attached

with snaps to the end of each skate. Hooks were baited by hand

with chopped squid at a rate of about 5.5 kg (12 lb) per 100

hooks.

The standard Japanese survey gear was modified for the U.S.

survey to more closely match methods used in the U.S. commercial

fishery and to adapt to/differences between the Japanese and U.S.

commercial fishing vessels. The circle hooks used in the NMFS

longline survey replaced the "tara" (J-shaped) hooks that were

used in the cooperative longline survey. The U.S. survey gear

was set in two equal parts laid end to end because the Prowler

did not have a second line hauler to retrieve intermediate

buoylines. On the Japanese vessel used in the cooperative

survey, 160 skates were set in a continuous groundline with
4

buoylines, buoy arrays, and flags at each end and two buoylines

and buoy arrays in between.

The 1988 NMFS longline survey incorporated four changes

based on the experience gained from the first NMFS survey.

First, Atlantic squid (Illex spp.) was used for bait instead of

Pacific herring (Clupea pallasi); second, the gangions were

changed from No. 48 stiff lay braided nylon to No. 60 medium lay

braided nylon; third, 3.2 kg lead balls were snapped on at the

end of each skate of gear instead of a combination of lead balls

and clusters of seine weights; and fourth, Mustad 13/0 circle

hooks replaced Eagle Claw No. 7 circle hooks.

Survey Area and Operations

The upper continental slope from the Islands of Four

Mountains (lat. 52°45'N, long. 170°W) eastward to Dixon Entrance

(lat. 54°30'N, long. 133°00'W) was sampled at a rate of one

station per day (Fig. la) in 1987 and 1988. These correspond to

station numbers 62-108 of the Japan-U.S. cooperative longline

survey (Yoshimura and Sasaki 1987). In addition, three stations

(nos. 54-56) were sampled in Shumagin Gully, four (nos. 48-51) in

Shelikof Trough, one (no. 57) off Kodiak Island, one (no. 59) in.

Amatuli Gully, one (no. 60) in Spencer Gully, and one (no. 52) in

Ommany Trench (Figs. la and lb).

The survey was conducted from 6 July to 17 September 1988

and was divided into three legs of 23-24 days each. Leg 1 began

at the Islands of Four Mountains and sampled eastward to the
Shelikof Trough; leg 2 continued the survey eastward to near the

W-grounds; and leg 3 completed the sample pattern southward to

Dixon Entrance (Fig. lb).

The longline gear was set from shallow to deep depths and

was retrieved in the same order, except on infrequent occasions

when the groundline parted or wind and sea conditions dictated

that it be pulled from the opposite direction. Setting and

retrieval began at about 0630 and 0930 hours ADT, respectively,

and retrieval was completed at about 1900 hours. Soak time

ranged from 3 to 10 hours.

Data Collection

Fish species and hook condition were recorded as the

sampling gear was retrieved. Hook condition was classified as

baited, bare, or ineffective (missing, broken, or tangled). Time

and depth in meters were recorded when the first, last, and every

fifth skate came aboard and also when depth strata changed, where

strata l-8 were 0-100 m, 101-200 m, 201-300 m, 301-400 m, 401-600

m, 601-800 m, 801-1,000 m, and l,00l-1,200 m, respectively.

The lengths of sablefish, Pacific cod, grenadiers,

arrowtooth flounder, rockfish (Sebastes spp.), and thornyheads

(Sebastolobus spp.) were measured. Two species, sablefish and

Pacific cod, were sorted by depth stratum before sex and length

were determined. Subsamples of sablefish and Pacific cod were

measured when catches were large; otherwise all fish were

measured. Pacific halibut were not measured but were counted and
released at the rail.

Analytical Methods

Catches were stratified based on the recorded depth of every

fifth skate or the interpolated depth of the intervening four

skates. The number of fish caught per skate for each station was

adjusted for ineffective (e.g., lost or broken) hooks by the

following formula:

where Nc is the adjusted number of fish caught per skate by

species, N is the unadjusted number, M is the number of

ineffective hooks, and 45 is the number of hooks per skate. The

number of fish caught per skate was not adjusted for bait loss.

The average number of fish caught per skate or catch-per-uniteffort (CPUE) was calculated by species from the adjusted data

for each stratum of a station. The data for a given skate were

excluded in the CPUE computation when the number of ineffective

hooks was greater than five for that skate.

Relative population number (RPN, an index of abundance in

numbers) for each species or species group were computed from

CPUE by stratum (Sasaki 1985, Gulland 1969, Quinn et al. 1982).

The RPN values were determined for each stratum between 201 and

1,000 m and for the five International North Pacific Fisheries

Commission (INPFC) Gulf of Alaska statistical areas (Fig. la).
7

For depths less than 201 m or greater than 1,000 m, RPN was not

computed because those depths were sampled intermittently. The

CPUE for each stratum of a station was multiplied by the area

(km*) of the stratum (Table 1) and the resultant values were

averaged within the INPFC area to obtain an RPN for each stratum.

These RPN values were summed across strata to derive a total RPN

for each INPFC area and then summed across all INPFC areas to

calculate a grand total RPN for the Gulf of Alaska.

The abundance indices apply only to the portion of the

species' population resident on the upper continental slope. We

believe that the ranges of adult populations of sablefish,

rougheye and shortraker rockfish, and shortspine thornyhead are

largely encompassed by the survey area. Other populations such

as Pacific cod, Pacific halibut, rockfish species other than

rougheye and shortraker rockfish, grenadiers, and arrowtooth

flounder, are distributed over broader regions than those

surveyed and thus are only partially represented in abundance

estimates.

The depth intervals and areas used to calculate RPN for this

survey differ from those used to calculate RPN for the Japan-U.S.

cooperative surveys. Estimates from the cooperative surveys

(Sasaki 1987, Sigler 1987) included gullies and parts of the

continental shelf, even though only a small fraction of those

regions was surveyed. Thus, the cooperative survey RPN was

apparently overestimated at l00-1,000 m (Sigler 1987).
8

Length frequencies were computed to examine the size

compositions of each species. Relative population number

adjusted length frequencies (RPN-LF) by stratum and INPFC

were computed for the 201-1,000 m depth intervals by the

following method. For each stratum within a station, RPN was

allocated to each centimeter increment of the length frequency

based on the relative number (RPN) of fish caught at that

increment. The resultant RPN-LF by station and stratum was

averaged within the INPFC area to calculate an RPN-LF by stratum

and INPFC area. For sablefish and Pacific cod at depths of 101-

200 m, a catch-per-skate-weighted length frequency (CPUE-LF) was

computed for each INPFC area by the same procedure used to

compute RPN-LF. A CPUE-LF was calculated instead of an RPN-LF

because RPN was not estimated for those depths.

area

Relative population weights (RPW, an index of biomass) were

computed to assess relative biomasses of sablefish, Pacific cod,

grenadiers, arrowtooth flounder, rougheye and shortraker

rockfish, and shortspine thornyheads. For each species, the

appropriate length-weight equation (Table 2) was applied to RPNLF by stratum and INPFC area to compute corresponding RPWweighted length frequencies. These weighted length frequencies

were summed across lengths to calculate an RPW for each stratum

within an INPFC area. These RPWs were summed across strata to

calculate an RPW for each INPFC area and then across INPFC areas

to calculate a total RPW for the Gulf of Alaska.
9

Sebastes spp. were tallied as "rockfish" as they came aboard

and were identified to species when their lengths were measured.

As a result, the computation of RPN-LF and RPW for rougheye and

shortraker rockfish follows a modified procedure. We assume all

rockfish at depths greater

rockfish because those two

the rockfish caught during

than 201 m are rougheye and shortraker

species comprised nearly all (88%) of

the survey and were all caught below

201 m. Weighted length frequencies (RPN-LF) were calculated for

rougheye and shortraker rockfish for each station by allocating

the station's rockfish RPN to each centimeter increment of the

station's length frequency distribution based on the relative

numbers of each species caught at that increment. The resultant

RPN-LF by station were averaged within each INPFC area to

calculate an RPN-LF by INPFC area. An RPW then was calculated

for each species as described above.

The bootstrap method (Efron 1982, Efron and Tibshirani 1986)

was used to compute RPN confidence intervals. The method is

similar to that used by Sigler and Fujioka (1988). For our

application, stations were randomly sampled with replacement

within each INPFC area. A value denoted RPNi,k where i = INPFC

area and k = species was computed from the CPUE of the sampled

stations by the method of RPN calculation described above. The

RPNi,k were summed across area to compute RPNk*, the total for the

Gulf of Alaska. Sampling with replacement and the computation of

the RPNk* were repeated 1,000 times producing a bootstrap

distribution of 1,000 RPNk*.
10

Efron and Tibshirani (1986) outlined methods for setting an

approximate confidence interval from a bootstrap distribution for

a statistic of interest, here RPNk*. They considered the use of

the simplest method, the percentile method, to be correct if the

bootstrap distribution of the statistic of interest was described

by a normal distribution. Normality of the bootstrap

distribution was tested using the D'Agostino D Test (D'Agostino

and Stephens 1986) and in most cases the null hypothesis of

normality was accepted, thus justifying the use of the percentile

method. In the remaining cases where the null hypothesis of

normality was rejected, the bias-corrected percentile method

recommended by Efron and Tibshirani (1986) was applied.

RELATIVE ABUNDANCE AND BIOLOGICAL CONDITION

Sablefish

Longline survey catches indicated that sablefish was the

most abundant species of the groundfish population along the

upper continental slope both in numbers and weight; the RPN and

RPW for sablefish were 58.5% and 61.4% of their respective totals

for the Gulf of Alaska (Tables 3 and 4). By INPFC area, the

percentage of sablefish was the highest of any species, although

grenadiers closely followed sablefish in terms of RPW in the

Shumagin and Chirikof INPFC areas (Table 4). Sablefish ranked

first in all depth strata except depths 801-1,000 m, where the

percentage (RPN and RPW) of grenadiers was slightly higher

(Tables 5 and 6).
11

The RPN and RPW for sablefish were largest in the Kodiak

INPFC area and smallest in the Southeastern INPFC area (Fig. 3a,

Tables 7 and 8). By stratum, the sablefish RPN and RPW were

highest for the intermediate depths, 401-600 m and 601-800 m, and

lowest for the remaining three strata 201-300 m, 301-400 m, and

801-1,000 m (Fig. 3b, Tables 5 and 6).

The percentages of the overall RPN and RPW attributable to

sablefish were markedly lower in 1988 compared with 1987; in

1987 these percentages were 72.0% and 80.0%, respectively (Sigler

and Zenger 1989). In comparison, catch rates of grenadiers

increased in 1988 (24.6%, expressed as a percentage of the RPN

for the Gulf of Alaska, Table 3) compared with 1987 (8.53%). The

decreased sablefish proportion may be due to decreased sablefish

abundance, increased grenadier abundance, or an untested bait

effect. The INPFC area with the highest RPN and RPW for

sablefish changed from the Shumagin INPFC area in 1987 to the

Kodiak INPFC area in 1988.

Most of the male sablefish (72.6%) were medium sized,

ranging from 57 to 66 cm fork length (FL) and most of the female

sablefish (78.4%) were larger than 66 cm FL (Table 9, Fig. 4).

More males (5.5%) were smaller (less than 57 cm FL) than females

(1.9%). The percentage of small males and females has declined

since 1987, when they were 10.9% and 4.1%, respectively (Sigler

and Zenger 1989). For both sexes combined, the percentage of

large fish generally increased with depth, whereas the percentage

of medium-sized fish generally decreased with depth (Fig. 5).
The length compositions of fish sampled in the 101-200 m

depth range from previous Japan-U.S. cooperative longline surveys

were used to document the relatively strong 1977 and 1980 year

classes; modes at lengths less than 62 cm FL often were

associated with these two relatively strong year classes (Sigler

and Fujioka 1988). Length compositions from the NMFS longline

survey for 1987 and 1988 demonstrated similar length modes in the

Shumagin, Yakutat, and Southeastern INPFC areas, suggesting the

presence of a year class which was stronger than the adjacent

year classes and whose members were growing in length (Fig. 6).

Other reports have suggested that the 1984 year class may be

strong (Sigler 1987, McDevitt 1987, Sigler 1988, Sigler and

Zenger 1989), however the modal lengths from the NMFS longline

survey generally were greater than expected for 3-year-old fish

in 1987 and 4-year-old fish in 1988 (McFarlane and Beamish 1983),

and thus, we are uncertain if they represent the 1984 year class.

Alternatively, the progression of modes may be due to changes in

the distribution of fish rather than the growth of fish remaining

in a particular INPFC area.

Compared with the adjacent regions of the upper continental

slope, sablefish catch rates were higher for Shelikof Trough,

Albatross Bank, Amatuli Gully, and Spencer Gully and lower for

Shumagin Gully during 1988 (Table 10). These differences were

not significant however (P > 0.10, t-test, Snedecor and Cochran

1967).
13

Length frequency distributions for Shelikof Trough and the

adjacent upper slope region were not statistically different

(Fig. 7), whereas length frequencies from the other gullies and

Albatross Bank and their respective adjacent upper slope regions

were significantly different (P < 0.05, Kolmogorov-Smirnov

goodness of fit test, Zar 1984). Large sablefish (> 66 cm FL)

were much less abundant in Shumagin Gully compared with the

adjacent continental slope. The principal length frequency mode

for Spencer Gully was smaller than that of the adjacent upper

continental slope (Fig. 7). This suggests that in most cases,

the gully and slope populations are different.

Shortraker and Rougheye Rockfish

Rockfish was the third most abundant species group in number

and the fourth most abundant by weight (Tables 3 and 4). Their

RPN and RPW were highest at depths 201-400 m and in the Shumagin,

Yakutat, and Southeastern INPFC areas (Fig. 8). Shortraker

rockfish RPW was almost twice as high as that of rougheye

rockfish (Table 4). Shortraker rockfish RPW was greater than

rougheye rockfish abundance in the Shumagin, Kodiak, and Yakutat

INPFC areas. The difference was especially large in the Yakutat

INPFC area.

Rougheye rockfish RPW was almost twice as high as shortraker

rockfish RPW in 1987, whereas shortraker rockfish dominated by

weight in 1988. The change from 1987 to 1988 is primarily due to

decreased catches of rougheye rockfish in the Southeastern INPFC
14

area and increased catches of shortraker rockfish in the

Shumagin, Chirikof, Kodiak, and Yakutat INPFC areas (Fig. 9). In

1987, the RPN and RPW for rockfish were highest in the Yakutat

and Southeastern INPFC areas (Sigler and

1988, they were highest in the Shumagin,

Southeastern INPFC areas.

Zenger 1989), whereas in

Yakutat, and

Shortraker rockfish were generally larger than rougheye

rockfish (Figs. 10a and b), which helps to explain the striking

differences in their relative biomasses. For both species, sizes

were distributed over a relatively wide range. Shortraker and

rougheye rockfish lengths ranged from 35 to 80 cm FL and from 30

to 60 cm FL, respectively.

Thornyheads

Thornyheads were a relatively minor component of the survey

catches, comprising 2.8% of the Gulf-wide RPN for all species,

(Table 3) and 0.5% of the RPW (Table 4). Shortspine thornyheads

accounted for almost all of the thornyhead catch. The RPN and

RPW were highest in the Shumagin INPFC area and lowest in the

Southeastern INPFC area (Tables 3 and 4 and Fig. 11). The

thornyhead RPN was similar over the entire range of depths

sampled during the survey except in the deepest stratum, 801-

1,000 m, where the RPN was somewhat lower (Fig. 11). Fish in the

30-40 cm FL category dominated the thornyhead population in all

INPFC areas (Fig. 10c).
15

Thornyheads comprised 4.3% (Sigler and Zenger 1989) of the

Gulf-wide RPN in 1987 and 2.8% in 1988.

Pacific Cod

This survey did not adequately sample Pacific cod stocks in

the Gulf of Alaska. During the summer, Pacific cod are common on

the continental shelf in relatively shallow water, whereas

sampling occurred mostly on the upper continental slope or in

gullies at depths greater than 200 m. However, catch per unit

effort and size composition provide indices of abundance and

information on the biological condition of the stock.

Pacific cod ranked fourth in number and third by weight

(Tables 3 and 4). Pacific cod RPN and RPW were highest in the

Shumagin INPFC area, about four times as large as in the

Chirikof, Kodiak, and Yakutat INPFC areas (Fig. 12a). Catches of

cod were restricted mostly to depths less than 300 m (Fig. 12b).

The 1988 RPN increased slightly and the RPW remained the same

compared with the 1987 survey. The principal difference was that

the apparent center of cod abundance shifted more toward the

Shumagin INPFC area.

Male and female cod had similar size compositions (Figs. 13

and 14). A distinct mode at 55 cm, corresponding to age 3+

(Niggol 1982), indicated that the 1985 year class had recruited

to the adult population, and that it appeared to be slightly

smaller than the 1984 year class that recruited during the

previous year (Sigler and Zenger 1989).
16

Miscellaneous Species

Grenadiers were the second most abundant fish caught in the

survey in terms of both RPN and RPW (Tables 3 and 4). Grenadier

RPN was highest in the Chirikof and Shumagin INPFC areas, low in

the Yakutat INPFC area, very low in the Southeastern and Yakutat

INPFC areas, and increased with depth without exception (Fig.

15). The most common grenadier species was the giant grenadier,

(Albatrossia pectoralis). Another species, Pacific grenadier

(Coryphaenoides acrolepis), was caught less frequently. A mode

was present at 30 cm anal vent length (length from tip of snout

to vent) in the Shumagin, Chirikof, and Kodiak INPFC areas and at

18 cm and 26 cm in the Yakutat INPFC area (Fig. 16).

The grenadier RPN for the Gulf of Alaska increased by four

times from 1987 to 1988. This group comprised 8.5% of the Gulfwide RPN for all species in 1987, (Sigler and Zenger 1989) and

24.6% in 1988 (Table 5). Gross fluctuations in the apparent

abundance of grenadiers have been observed previously in the

Japan-U.S. cooperative longline survey (Sasaki 1987).

Arrow-tooth flounder was the fifth most abundant species in

terms of RPN and fourth in terms of RPW (Tables 3 and 4) and was

the most abundant flatfish in the Gulf of Alaska. Both RPN and

RPW were highest in the Shumagin INPFC area and lowest in the

Southeastern INPFC area. Fish from 50 to 65 cm FL dominated the

arrow-tooth population in the Yakutat, Kodiak and Southeastern

INPFC areas (Fig. 17). Modes were present at 62 cm FL in the

Shumagin INPFC area, 56 and 71 cm FL in Chirikof and Kodiak INPFC
17

areas, and 60 cm FL in the Yakutat and Southeastern INPFC areas

(Fig. 18).

Arrowtooth flounder comprised, 3.3% of the Gulf-wide RPN for

all species, a slight decrease from 4.6% in 1987. Their depth

distribution did not change from that of 1987, whereas their

length frequency distributions shifted; the major mode was at

70 cm FL in 1987 and 60 cm FL in 1988.

Pacific halibut were the seventh most abundant species

caught during the survey. This group comprised 1.8% of the

Gulf-wide RPN for all species (Table 3). RPWs were not estimated

for Pacific halibut. Pacific halibut were released rather than

hauled aboard to minimize handling and injury and as a result no

size measurements were taken. The PPNs for Pacific halibut were

similar in the Shumaginin Kodiak, Yakutat, and Southeastern INPFC

areas (Fig. 19) and was much lower in the Chirikof INPFC area.

The RPN was greatest at depths 201-300 m (Fig. 19) for all INPFC

areas; at this depth, Pacific halibut was the fourth most

abundant species caught. The proportion of Pacific halibut

compared with sablefish expressed in percent was highest at

depths of 201-300 m, and it decreased with depth: 1.5% at

201-300 m, 0.4% at 301-400 m, and it was not present at depths

greater than 400 m.

The proportion of Pacific halibut caught was similar in 1987

and 1988. The percentage of the Gulf-wide RPN attributable to

Pacific halibut decreased only slightly: from 2.0% in 1987

(Sigler and Zenger 1989) to 1.8% in 1988 (Table 3).
18

Skates (Order Rajiformes) were a relatively minor component

of the total catch (Table 3) and were not identified to species.

In 1988, skate abundance was similar to that observed in 1987.

Skates comprised 0.4% of the Gulf-wide RPN for all species (Table

5) compared with 0.3% in 1987 (Sigler and Zenger 1989). Length

was not recorded for skates, thus no RPW was calculated. Their

abundance was highest in the Shumagin INPFC area and at 201-300 m

in depth.

Forty-two other species or species groups were captured

during the survey. Twenty-nine of these actively took the baited

hooks (Table 11). The remaining 13 were incidentally snagged on

the bottom or in the water column and include jellyfishes, sea

anemones, tubeworms, sponges, sea cucumbers, Alaska false

jingles, skate egg cases, sea pens, sea squirts, scallops, coral,

and fucus.
19

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Efron, B., and R. Tibshirani. 1986. Bootstrap methods for,

standard errors, confidence intervals, and other measures of

statistical accuracy. Stat. Sci. 1:54-77.

Gulland, J. A. 1969. Manual of methods for fish stock

assessment. Part 1. Fish population analysis. St. Paul's

Press Ltd., Malta, Italy, 154 p.

McDevitt, S. A. 1987. Sablefish. In R. G. Bakkala, and J. W.

Balsiger (eds.). Condition of groundfish resources of

the eastern Bering Sea and Aleutian Islands Region in 1986,

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F/NWC-117.

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sablefish (Anoplopoma fimbria) in waters off western Canada.'

Proc. Int. Sablefish Symposium. March 29-31, 1983.

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Mito, K-i. 1987. Stock assessment of rockfishes and thornyheads

in the eastern Bering Sea and Aleutian Islands Region in

1987. Unpubl. manuscr., 10 p. Far Seas Fish. Lab.,

Fisheries Agency of Japan, 1000 Orido, Shimizu 424, Japan.

Niggol, K. 1982. Data on fish species from Bering Sea and Gulf

of Alaska. U.S. Dep. Commer., NOAA Tech. Memo. NMFS

F/NWC-29, 125 p.

Quinn, T. J., II., S.,H. Hoag, and G. M. Southward. '1982.

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Sasaki, T. 1987. Stock assessment of sablefish in the Bering

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20

Fisheries Agency of Japan, 1000 Orido, Shimizu 424, Japan.

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Seas Fish. Res. Lab.,

manuscr., 26 p. Far

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Highway, Juneau, AK 99801.

Sigler, M. F. 1988. Assessment of Gulf of Alaska sablefish

based on the Japan-U.S. cooperative longline survey, 1987.

In T. K. Wilderbuer (ed.), Condition of groundfish

resources of the Gulf of Alaska in 1988, p. 243-273. U.S.

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domestic longline survey-, 1987. U.S. Dep. Commer., NOAA

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Japan-U.S. joint longline survey by Fukuyoshi Maru No. 8 in

1986. Unpubl. manuscr., 21 p. (Document submitted to the

annual meeting of the International North Pacific Fisheries

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424, Japan.

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Prentice-Hall, Inc. Englewood Cliffs, NJ. 718 p.
21

Table 1 .--Area (km*) of the upper continental slope of the Gulf of Alaska by

International North Pacific Fisheries Commission (INPFC) statistical

area and depth.

Sources : Shumagin, Chirikof, and Kodiak INPFC areas and Yakutat INPFC area

from long. 147" to long. 144": E. Brown, Alaska Fisheries Science Center,

RACE Division, 7600 Sand Point Way NE., BIN C15700, Seattle, WA 98115, Pers.

commun., 1985. Yakutat INPFC area from long. 144" to long. 135" and

Southeastern INPFC area: R. Haight,

Laboratory,

Alaeka Fisheries Science Center, Auke Bay

11305 Glacier Highway, Juneau, AK 99801-8626, Pere. commun., 1986.

Table 2 .--Length-weight parameters used to calculate relative population

weight with the relationship, W = aLb. Length is expressed in

centimeters and weight is expressed in kilograms.
22

Table 3 .--Relative population number (RPN) eummed by International North

Pacific Fisheries Commieeion (INPFC) statistical area and expressed

as percentage of the total Gulf of Alaska RPN. SF = sablefish,

PC = Pacific cod, GR = grenadiers, HB = Pacific halibut,

ATF =

SK =

arrowtooth flounder, RF = rockfish, TH = thornyheads,

skateB, OS = other species. NMFS longline survey, 1988.

Table 4 .--Relative population weight (RPW) summed by International North

Pacific Fisheries Commission (INPFC) statistical area and expressed

as a percentage of the total Gulf of Alaska RPW. SF = sablefish,

PC = Pacific cod, GR = grenadiers, ATF = arrowtooth flounder,

RNF= rougheye rockfish, SRF =shortraker rockfieh,

TH = thornyheade. NMFS longline survey, 1988.
23

Table 5 .--Relative population number (RPN) summed by depth stratum and

expressed as a percentage of the RPN for the Gulf of Alaska.

SF = sablefish, PC = Pacific cod, GR = grenadiers, HB = Pacific

halibut, ATF = arrowtooth flounder, RF = rockfish, TH = thornyheads, SK = skates, OS = other species. NMFS longline survey,

1988.

Table 6 .--Relative population weight (RPW) summed by depth stratum and

expressed as a percentage of the RPW for the Gulf of Alaska.

SF = eablefieh, PC = Pacific cod, GR = grenadiers, ATF = arrowtooth flounder, RRF = rougheye rockfish, SRF = shortraker rockfieh, TH = thornyheade. NMFS longline Burvey, 1988.
Table 7 .--Relative population number by species, International North Pacific Fisheries Commission (INPFC)

statistical area and depth stratum. SF = sablefish, PC = Pacific cod, GR = grenadiers,

HB = Pacific halibut, ATF = arrowtooth flounder, RF = rockfish, TH = thornyheade, SK = skates,

OS = other species. Listed below each total RPN are the lower (L) and upper (0) 95% confidence

intervals. NMFS longline survey, 198B.

Species
Table 7 .--Continued.
26

Table 8 .--Relative population weight (RPW) by species, International North

Pacific Fisheries Commission (INPFC) statistical area, and depth

stratum. SF = sablefish, PC = Pacific cod, GR = grenadiers,

ATF = arrowtooth flounder, RRF = rougheye rockfish, SRF = shortraker

rockfish, TH = thornyheade. NMFS longline survey, 1988.

Depth (m) SF PC GR ATF RRF SRF TH
27

Table 8 .--Continued.
28

Table 9 .--Sablefish commercial size composition percentage for RPN-weighted

length frequencies by Internhtional North Pacific Fisheries

Commieeion (INPFC) etatietical area, depth stratum, and sex. NMFS

longline survey, 1988.
29

Table 9 .--Continued.
30

Table 10 .--Sablefish catch rates (sablefish per 100 hooks) for gullies and

adjacent upper continental slope regions. NMFS longline survey,

1988.
31

Table 11 .--Species captured infreqently during the 1988 NMFS longline survey

of the Gulf of Alaska.

Common Number of

Name Occurrences

Scientific

Name

Spiny dogfish

Yellow Irish lord

Lingcod

Walleye pollock

Unidentified starfish

Dover sole

Unidentified sculpins

Flathead sole

Weathervane scallop

True tanner crab

Pacific flatnoee

Unidentified brittlestare

Unidentified snails

Rock sole

Giant wrymouth

Unidentified basketetars

Octopus

Pacific sleeper shark

Searcher

Spinyhead sculpin

Spotted ratfish

Coho salmon

Blue shark

Broad snow crab

Chum salmon

Darkfin eculpin

Unidentified greenling

Pacific pomfret

404 Squalus acanthias

112 Hemilepidotus jordani

91 Ophiodon elongatus

75 Theragra chalcogramma

72 Aeteroidea

77 Microstomus pacificus

43 Cottidae

36 Hippoglossoides elassodon

23 Patinopecten caurinus

22 Chionoecetes tanneri

18 Antimora microlepis

17 Ophiuroidea

17 Gaetropoda

12 Lepidopsetta bilineata

9 Delolepis gigantea

8 Gorgonocephal us spp.

7 octopus spp.

6 Somniosus pacificus

5 Bathymaster signatus

5 Dasycottus setiger

4 Hydrolagus colliei

3 Oncorhynchus kisutch

2 Prionace glauca

2 Chionoecetes bairdi

1 Oncorhynchus keta

1 Halacocottus zonurus

1 Hexagrammidae

1 Brama japonica
Figure la.--Station locations for the 1988 NMFS longline survey of the Gulf of Alaeka and

boundaries of International North Pacific Fisheries Commission statistical areas.

Figure 2 .--Generalized description of longline fishing gear and longline hauling

equipment. Adapted from drawings by Charles R. Hitz, Alaska Fisheries

Science Center, Resource Asseesment and Conservation Engineering

Division, 7600 sand Point Way NE, BIN C15700, Seattle, WA 98115.
35

Figure 3.--Sablefish relative population numbers for the upper continental

slope of the Gulf of Alaska by: (a) International North Pacific

Fisheries Commission (INPFC) statistical area and (b) depth stratum.

Stratum codes: 3 = 201-300 m, 4 = 301-400 m, 5 = 401-600 m,

6 = 601-800 m, 7 = 801- 1,000 m. National Marine Fisheries

Service longline survey, 1988.
Figure a.-- Sablefish length frequencies weighted by relative population number of males (- )

and females (-). for the upper continental slope of the Gulf of Alaska, by International North Pacific Fisheries Commission statistical area and depth stratum,

Vertical dotted lines delineate small, medium, and large commercial sizes.

National Marine Fisheries Service longline survey, 1988.
Figure 4. --Continued.
38

Figure 5. --Percent of sablefish relative population number (RPN) by commercial

size category for depth intervals 3-7. Small-sized sablefish are less

than 57 cm fork length (FL); medium sablefish are 57-66 cm FL; and

large sablefish are greater than 66 cm FL. Stratum codes: 3=201-300

m, 4=301-400 m, 5=40l-600 m, 6=601-800 m, and 7=801-1,000 m.

National Marine Fisheries Service longline survey, 1988.
39

Figure 6.--Length frequencies of: (a) male sablefish and (b) female sablefish,

weighted by catch per unit effort (CPUE), for the 101-200 m depth

interval on the outer continental shelf of the Gulf of Alaska, by

International North Pacific Fisheries Commission statistical area.

National Marine Fisheries Service longline surveys, 1987 (-) and

1988 (-).

41

Figure 7. --Sablefish length frequencies from: (a) Shumagin Gully, 201-300

m, (b) Shelikof Trough, 201-300 m, (c) Albatross Bank, 201-400

m, (d) Amatuli Gully, 20 l-300 m, and (e) Spencer Gully, 401-

600 m (--); and equivalent ad

depths (-..). National Marine

1988.

jacent upper continental slope

Fisheries Service longline survey,
Figure 8. --Combined rougheye and shortraker rockfish relative population

numbers for the upper continental slope of the Gulf of Alaska

by: (a) International North Pacific Fisheries Commission (INPFC)

statistical area, and (b) depth stratum. Depth stratum codes:

3=201-300 m, 4=301-400 m, 5=401-600 m. 6=601-800 m, and

7=801- 1,000 m. National Marine Fisheries Service longline survey,

1988.
43

Figure 9.--Rougheye and shortraker rockfish relative biomass (relative

population weight, RPW) for the upper continental slope of the

Gulf of Alaska by International North Pacific Fisheries Commission

(INPFC) statistical area. National Marine Fisheries Service longline

surveys, 1987 and 1988.
44

Figure 10. --Length frequencies of: (a) rougheye rockfish, (b) shortraker rockfish,

and (c) thornyheads. weighted by relative population number, for the

upper continental slope of the Gulf of Alaska, by International North

Pacific Fisheries Commission statistical area. National Marine Fisheries

Service longline survey, 1988.
4 5

Figure lO.--Continued.
4 6

11. - -Thornyhead (Sebaslolobus spp.) relative population numbers for the

continental slope of the Gulf of Alaska by: (a) International North

Pacific Fisheries Commission (INPFC) statistical area and (b) depth

-stratum. Stratum codes: 3=201-300 m, 4=301-400 m, 5=401-600 m,

6=601-800 m, 7=801- 1,000 m. National Marine Fisheries Service

longline survey, 1988.
47

Figure 12.--Pacific cod relative population numbers for the upper continental

slope of the Gulf of Alaska by: (a) International North Pacific

Fisheries Commission (INPFC) statistical area and (b) depth stratum.

Stratum codes: 3=201-300 m, 4=301-400 m, 5=401-600 m,

6=601-800 m, 7=801- 1,000 m. National Marine Fisheries Service

longline survey, 1988.
Figure 13.--Pacific cod length frequencies weighted by relative population number

of males (-. .) and females (-), for the upper continental slope of the

Gulf of Alaska, by International North Pacific Fisheries Commission

statistical area. National Marine Fisheries Service longline survey, 1986.
49

Figure 14.--Pacific cod length frequencies weighted by catch per unit effort

(CPUE) of males (-..) and females (-), for the 101-200 m depth

stratum in the Gulf of Alaska, by International North Pacific Fisheries

Commission statistical area. National Marine Fisheries Service

longline survey, 1988.
Figure 15. --Grenadier relative population numbers for the upper continental

slope of the Gulf of Alaska by: (a) International North Pacific

Fisheries Commission (INPFC) statistical area and (b) depth stratum.

Stratum codes: 3=201-300 m, 4=301-400 m, 5=401-600 m,

6=601-800 m, 7=601- 1,000 m. National Marine Fisheries Service

longline survey, 1988.
Figure 16.--Giant grenadier length frequencies weighted by relative population

number for the upper continental slope of the Gulf of Alaska, by

International North Pacific Fisheries Commission statistical area.

National Marine Fisheries Service longline survey, 1988.
Figure

52

17.--Relative population numbers of arrowtooth flounder for the upper

continental slope of the Gulf of Alaska by: (a) International North

Pacific Fisheries Commission (INPFC) statistical area and (b) depth

stratum. Stratum codes: 3=201-300 m, 4=301-400 m, 5=401-600

m, 6=601-800 m, and 7=801-1,000 m. National Marine Fisheries

Service longline survey, 1988.
53

Figure 18.--Arrowtooth flounder length frequencies weighted by relative population

numbers, for the upper continental slope of the Gulf of Alaska, by

International North Pacific Fisheries Commission statistical area.

National Marine Fisheries Service longline survey, 1988.
54

lg.--Relative population numbers of Pacific halibut for the upper

continental slope of the Gulf of Alaska by: (a) International North

Pacific Fisheries Commission (INPFC) statistical area and (b) depth

stratum. Stratum codes: 3=201-300 m, 4=301-400 m, 5=401-600 m,

6=601-800 m, and 7=801- 1,000 m. National Marine Fisheries Service

longline survey, 1988.
55

Figure 20.- - Relative population numbers of skates (Rajiidae) for the upper

continental slope of the Gulf of Alaska by: (a) International North

Pacific Fisheries Commission (INPFC) statistical area and (b) depth

stratum. Stratum codes: 3=201-300 m, 4=301-400 m, 5=401-600

m, 6=601-800 m, 7=801-1,000 m. National Marine Fisheries Service

longline survey, 1988.
RECENT TECHNICAL MEMORANDUMS

Copies of this and other NOAA Technical Memorandums are available from the

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(web site: www.ntis.gov). Paper and microfiche copies vary in price. 

AFSC38 LOWRY, L. F., K. J. FROST, R. DAVIS, R. S. SUYDAM, and D. P. DEMASTER. Movements and

behavior of satellite-tagged spotted seals (Phoca largha) in the Bering and Chukchi Seas, 71 p. NTIS No.

PB94-180684.

37 BUCKLEY, T. W., and P. A. LIVINGSTON. 1994. A bioenergetics model of walleye pollock (Theragra

chalcogramma) in the eastern Bering Sea: Structure and documentation, 55 p. NTIS No. PB94-181831.

36 YANG, M-S., and P. A. LIVINGSTON. 1994. Variations in mean stomach content weights of walleye

pollock, Theragra chalcogramma, in the eastern Bering Sea, 32 p. NTIS No. PB94-178084.

35 PARKS, N. B., and F. R. SHAW. 1994. Relative abundance and size composition of sablefish

(Anoplopoma fimbria) in the coastal waters of California and Southern Oregon, 1984-1991. NTIS

number pending.

34 SAMPLE, T. M., and D. G. NICHOL. 1994. Results of the 1990 U.S.-U.S.S.R. cooperative bottom

trawl survey of the eastern and northwestern Bering Sea continental shelf, 183 p. NTIS No. PB94-

181849.

33 WEINBERG, K. L., M. E. WILKINS, R. R. LAUTH, and P. A. RAYMORE, JR. 1994. The 1989

Pacific west coast bottom trawl survey of groundfish resources: Estimates of distribution, abundance, and

length and age composition, 168 p. plus Appendices. NTIS No. PB94-173796.

32 PEREZ, M. A. 1994. Calorimetry measurements of energy value of some Alaskan fishes and

squids, 32 p. NTIS No. PB94-152907.

31 RONHOLT. L. L., K. TESHIMA, and W. D. KESSLER. 1994. The groundfish resources of the

Aleutian Islands region and southern Bering Sea 1980, 1983, and 1986, 351 p. NTIS No. PB94-

152915

30 LORENZ, J. M. 1994. Distribution and habitat of adult salmon in the Situk River, Alaska: Potential

impacts of flooding from Russell Fiord, 27 p. NTIS No. PB94-151859.

29 IGNELL, S. E., L. J. SIMON, and M. L. DAHLBERG. 1994. Estimation of salmonid bycatch in the

1989 Japanese squid driftnet fishery, 45 p. NTIS No. PB94-152105.

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

pink salmon (Oncorhynchus gorbuscha), 12 p. NTIS No. PB94-145349.

27 LOW, L-L. (coordinator). 1994. Status of living marine resources off Alaska, 1993, 110 p. NTIS No.

PB94-149846.

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

States for 1993, 90 p. NTIS No. PB94-133733.

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

groundfish fisheries off Alaska, 1992, 102 p. PB94-142759.

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