Marine Fisheries Review 1992: Vol 54 Iss 4

45 Pages·1992·14.3 MB·English

“\¢, Marine Fisheries
Naor REVIEW
7)
WDof *
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On the cover: One of the
types of vessels used in the North
Pacific yellowfin sole fishery. NMFS photo.
54(4), 1992
Articles
Yellowfin Sole, Pleuronectes asper, of the Eastern Bering Sea: Thomas K. Wilderbuer, Gary E. Walters,
Biological Characteristics, History of Exploitation, and Management and Richard G. Bakkala
Potential Impact of PCB’s on Bluefish, Pomatomus
saltatrix, Management Peter J. Eldridge and G. Malcolm Meaburn — 19
Status, Constraints, and Opportunities for
Salmon Culture in the United States: A Review James L. Anderson and Sofia U. Bettencourt 25
Shortraker Rockfish, Sebastes borealis,
Observed from a Manned Submersible Kenneth Krieger 34
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Yellowfin Sole, Pleuronectes asper, of the Eastern
Bering Sea: Biological Characteristics,
History of Exploitation, and Management
THOMAS K. WILDERBUER, GARY E. WALTERS, and RICHARD G. BAKKALA
Thomas K. Wilderbuer and Gary E. Walters are Introduction In this paper, we describe the life
with the Alaska Fisheries Science Center, Na- history characteristics of eastern Bering
tional Marine Fisheries Service, NOAA, 7600
Sand Point Way NE, Seattle, WA 98115. Rich- Yellowfin sole, Pleuronectes asper, Sea yellowfin sole, the history of its
ard G. Bakkala, a retired fisheries biologist, was of the family Pleuronectidae (Fig. 1), exploitation and long-term trends in
formerly with the NMFS Alaska Fisheries Sci-
ence Center. is the second most abundant flatfish in abundance, the current condition of the
the North Pacific Ocean and is the most resource, and the methods used for es-
abundant species of groundfish in the timating biomass and yields with two
eastern Bering Sea after walleye pol- forms of catch-at-age models and a
ABSTRACT—Yellowfin sole, Pleuro- lock, Theragra chalcogramma. Yellow- yield-per-recruit model.
nectes asper, is the second most abundant
fin sole inhabits continental shelf wa-
flatfish in the North Pacific Ocean and is The Eastern Bering
most highly concentrated in the eastern ters of the North Pacific Ocean from
Sea Environment
Bering Sea. It has been a target species in off British Columbia, Can., (about lat.
the eastern Bering Sea since the mid-1950’s, 49°N) to the Chukchi Sea (about lat. One of the factors contributing to
initially by foreign distant-water fisheries 70°N) in North American waters, and the high abundance of yellowfin sole
but more recently by U.S. fisheries. Annual
south along the Asian coast to about in the eastern Bering Sea is the expan-
commercial catches since 1959 have ranged
from 42,000 to 554,000 metric tons (t). lat. 35°N off the South Korean coast in sive nature of the continental shelf of
Yellowfin sole is a relatively small flatfish the Sea of Japan (Fig. 2). It is by far this region (Fig. 3). The eastern Bering
averaging about 26 cm in length and 200 g most abundant in the eastern Bering Sea shelf, which is 1,200 km long and
in weight in commercial catches. It is Sea, where current biomass has been >500 km wide at its narrowest point,
distributed from nearshore waters to
depths of about 100 m in the eastern Bering estimated at between 1.9 and 2.6 mil- is the widest continental shelf outside
Sea in summer, but moves to deeper water lion metric tons (t) or more. the Arctic Ocean (Coachman, 1986).
in winter to escape sea ice. Yellowfin sole
is a benthopelagic feeder. It is a long-
lived species (>20 years) with a cor-
respondingly low natural mortality rate es-
timated at 0.12.
After being overexploited during the
early years of the fishery and suffering a
substantial decline in stock abundance, the
resource has recovered and is currently in
excellent condition. The biomass during the
1980's may have been as high as, if not
higher than, that at the beginning of the
fishery. Based on results of demersal trawl
surveys and two age structured models, the
current exploitable biomass has been esti-
mated to range between 1.9 and 2.6 mil-
.
liinovne sti.i gAaptperdo pruinadteer ah arrvaensgte sotfra ptoesgsiiesb lew erree- en~s)t s teT e
cruitment levels. The recommended harvest SMei yoF%fa ME E ECED
level was calculated by multiplying the yield Mi
uy fe P 0
derived from the F,, harvest level (161 g
at F = 0.14) by an average recruitment py
value resulting in a commercial harvest of
276,900 t, or about 14% of the estimated
exploitable biomass. Figure 1.—Yellowfin sole, Pleuronectes asper.
54(4), 1992
Distribution
i Fishing areas
GULF OF
Tartar Strait ALASKA
Vancouver Is.
Peter The
Great Bay ~
} }
160° 140°
Figure 2.—Overall distribution and areas of commercial fishing for yellowfin sole (from Bakkala, 1981).
In the Atlantic Ocean, only the North between central shelf water above and sonal variation in temperature from
Sea continental shelf approaches its Aleutian Basin water below. This do- near freezing (—1.5°C) in winter to av-
breadth. main differs from the rest of the shelf erage air temperatures (10°C) in sum-
The eastern Bering Sea shelf is es- by having both significantly higher mer. Flushing time for the coastal do-
sentially a large, featureless plain that mean and subtidally variable flows main is about 6 months.
deepens gradually from the shore to (Coachman, 1986), resulting in a more Properties of the oceanographic
about 170 m at the shelf break. How- rapid flushing of these waters (perhaps fronts and domains in the eastern
ever, there are two zones of enhanced on the order of 2-3 months) than those Bering Sea divide the shelf into dis-
gradients near the 50 and 100 m of the other two domains. The main tinct production regions (Alexander,
isobaths (Askren, 1972), related to feature of the central shelf domain is 1986; Walsh and McRoy, 1986). Over
fronts separating the shelf region into its two-layered vertical structure, with the outer shelf, a large portion of the
three oceanographic domains. These are a surface layer 10-40 m in depth over- annual primary production is advected
the coastal, central, and outer shelf do- laying a relatively homogeneous layer off the shelf or channeled into a pe-
mains which are separated by the in- of cold bottom water (<0°—3°C). Flush- lagic food web which supports the large
ner and middle shelf fronts at 50 and ing in the central domain is extremely population of semidemersal pollock and
100 m; the outer shelf domain is sepa- slow, taking >1 year and perhaps as other species in this region. This leads
rated from the oceanic waters of the much as 2 years. The coastal domain to a relatively low biomass of
Aleutian Basin by the ocean break front is a product of direct mixing of fresh- macrobenthos on the outer shelf do-
between the 150 and 200 m isobaths. water runoff and saline water, and has main and reduced abundances of
The domains are defined by tempera- a tendency toward homogeneity due to benthic feeding groundfish. On the cen-
ture and salinity values, vertical struc- the shallowness of the domain and wind tral shelf, however, where the abun-
ture, and seasonal changes in these and strong tidal mixing. Because of dance of pelagic grazers is low, practi-
properties (Schumacher et al., 1983). these features there is ready heat ex- cally all of the primary production
The outer shelf domain represents a change between the water column and settles to the sea floor, providing a
zone of lateral water mass interaction the atmosphere, resulting in a large sea- macrobenthic infaunal biomass 10
Marine Fisheries Review
ied
A, GULF OF ANADYR
62°) Pr tugts F (iat,
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ST LAWRENCE
ft ra <p if Pr @ ISLAND
oino l ft 23 4 ai a NACVAAPREI N
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NUNIVAK
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KAMCHATKA
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© PRIBILOF
ALEUTIAN BASIN NOS
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ISLAND ge
! A
a eee ee eee1 68°E L I72L °w ~ 176°E 180° ~1T6°W i=72 °w 168°w ae | 1ea.ee we
Figure 3.—The Bering Sea: About half is abyssal plain exceeding depths of 3,500 m and the other half is continental
shelf of depths less than 200 m (Kinder, 1981—from a figure prepared by Noel McGary for the atlas by Sayles et
al., 1979).
times greater than on the outer shelf cussed later, winter offshore migrations (Fadeev, 1965; Bakkala et al., 1982;
(Haflinger, 1981) and an abundant food of yellowfin sole are believed to be re- Wakabayashi'). Results of cohort analy-
source for benthic feeders such as yel- lated to avoidance of this ice cover. sis indicate that the exploitable biomass
lowfin sole and other species. declined sharply from an estimated 1.2
History of Exploitation
Seasonal ice cover is another char- million t in 1960 to <500,000 t in 1963.
acteristic of the eastern Bering Sea Yellowfin sole was the first target As a result, catches also declined to a
shelf. Ice begins to intrude into the species of distant-water fleets from Ja- range of 48,000—167,000 t over the next
northern Bering Sea in November. pan and the U.S.S.R., which initiated decade. There was a further decline in
When it reaches its southern maximum fisheries for groundfish in the eastern catches to generally <100,000 t annu-
in March-April, ice coverage may be Bering Sea during the middle and late ally from 1972 to 1982 because of the
as great as 80%. The intruding ice is 1950’s. Catches were processed for fish absence of a U.S.S.R. target fishery for
completely melted by early July meal. These fisheries intensified dur- yellowfin sole in most of those years.
(Niebauer, 1983). There are large year- ing the early 1960’s with a peak catch Since 1982, the improved condition of
to-year deviations in the amount of ice of 554,000 t in 1961; during the 4-year
cover, on the order of hundreds of ki- period of 1959-62, catches averaged 'Wakabayashi, K. 1975. Studies on resources of
lometers, which have been found to be 404,000 t (Table 1). It is generally rec- yellowfin sole in the eastern Bering Sea. I. Bio-
correlated with either wind fields or ognized that this level of exploitation logical characteristics. Unpubl. manuscr., 8 p.,
of Far Seas Fish. Res. Lab., Fish. Agency Jpn.,
storm tracks (Niebauer, 1983). As dis- was more than the stock could sustain 1000 Orido, Shimizu 424.
54(4), 1992
Distribution
Table 1.—Annual catches of yellowfin sole in the eastern Bering Sea in metric tons'
from 1954-91. The winter distribution of adult yel-
Other U.S. US. lowfin sole in the eastern Bering Sea is
non-U.S. joint domestic centered in three locations (Fig. 4). All
Year Japan R.O.K.? fisheries ventures fisheries Total
are at depths of 100-270 m along the
1954 12,562 12,562
1955 14,690 14,690 shelf edge and upper slope. The major
1956 24,697 24,697 group is located just north of Unimak
1957 24,145 24,145
1958 39,153 44,153 Island near the end of the Alaska Pen-
1959 123,121 185,321 insula. Concentrations are so dense that
1960 360,103 456,103 a research vessel caught over 25 t dur-
1961 399,542 553,742 ing a half-hour tow (Bakkala et al.,
1962 281,103 420,703
1963 20,504 85,810 1982). A smaller group is located west
1964 48,880 111,177
of the Pribilof Islands, and a still
1965 26,039 53,810 smaller group is located just south of
1966 45,423 102,353
1967 60,429 162,228 the Pribilof Islands. A fourth group,
1968 40,834 84,189 consisting almost entirely of juveniles
1969 81,449 167,134
<6 years old is found on the inner shelf,
1970 59,851 133,079 sometimes under ice cover.
1971 82,179 160,399
1972 34,846 47,856 Beginning in April or early May, the
1973 75,724 78,240
1974 37,947 42,235 three adult groups begin a migration
onto the inner shelf. This was shown
1975 59,715 64,690
1976 52,688 56,221 specifically during a spring research
1977 58,090 58,373 survey in 1976 (Smith and Bakkala,
1978 62,064 69 138,433
1979 56,824 1,919 99,017 1982). At that time, portions of the yel-
lowfin sole population were followed
1980 61,295 16,198 9,623 87,391
1981 63,961 17,179 16,046 97,301 as the ice retreated during a particu-
1982 68,009 10,277 17,381 95,712
1983 64,824 21,050 22,511 108,385 larly cold year. Japanese tagging stud-
1984 83,909 34,855 32,764 159,526 ies (Wakabayashi, 1989) have shown
1985 59,460 33,041 126,401 227,107 that each group moves into a specific
1986 49,318 7,632 151,400 208,597 location (Fig. 4). The Unimak Island
1987 TANT 694 179,613 o 181,428
1988 213,323 9,833 223,156 group moves into Bristol Bay, the east-
1989 151,501 1,664 153,165 ernmost portion of the Bering Sea. The
1990 69,677 10,907 80,584
1991 84,482 84,482 two Pribilof Islands groups move far-
ther north to the vicinity of Nunivak
‘Catches from data on file at NMFS Alaska Fisheries Science Center, 7600 Sand Point
Way N.E., Seattle, WA 98115. Island. Since these areas are for feed-
?Republic of Korea. ing and spawning, it was originally
3A dash indicates fishing, but any catches of yellowfin sole were not reported.
thought that at least two stocks existed.
However, further examination of the
the resource has again allowed higher dance, Pacific halibut, Hippoglossus tagging results and genetic studies us-
catches; these have exceeded 200,000 stenolepis; Greenland turbot, Rein- ing electrophoretic techniques (Grant
t in recent years. Since the early 1960's, hardtius hippoglossoides; and arrow- et al., 1983) now leads to a concensus
yellowfin sole catches have been tooth flounder, Atheresthes stomias, oc- that there is only one stock.
mainly utilized for human consump- cupy both continental shelf and The summer distribution of yellow-
tion. Based on results of cohort analy- continental slope waters. The four re- fin sole extends over the inner and
sis and catch-at-age data, annual ex- maining species, which are the most middle shelf to a depth of approxi-
ploitation rates for exploitable ages abundant and primarily occupy conti- mately 100 m (Fig. 5). However, above
7-17 of yellowfin sole have ranged nental shelf waters, are yellowfin sole, lat. 61°N the density decreases drasti-
from 4 to 11% and have averaged 8% Alaska plaice, Pleuronectes quadrituber- cally. The summer surveys by the
since 1977. culatus; rock sole, Pleuronectes bilin- NMFS Alaska Fisheries Science Cen-
eatus; and flathead sole, Hippoglussoides ter (AFSC) cover the significant por-
Biological Characteristics
elassodon. The latter three species play tions of the distribution. During the
Yellowfin sole is one of 16 species of major roles in the ecology of yellowfin summer, yellowfin sole is closely as-
flatfish in the eastern Bering Sea. Nine sole. As might be expected in a com- sociated with the two next most abun-
of these species have very low abun- plex of this sort, fish size is inversely dant flatfish species, rock sole and
dance and make up only 1-2% of the related to abundance, with yellowfin sole Alaska plaice. Estimated abundances of
biomass of the total flatfish complex. being the smallest and most abundant the latter two species in 1990 were 1.6
Three large species of moderate abun- species in the eastern Bering Sea. million t and 0.5 million t, respectively,
4 Marine Fisheries Review
the upper eye which provide them with
more downward vision than yellowfin
Major area sole (Zhang, 1987). Livingston et al.
Wo: Wintering
S : Spawning (1986) found that while bivalves were
F : Feeding dominant in the stomach contents of
WY. vnimak group yellowfin sole during the spring, sum-
WAS Pribilof-west 94 mer proportions of bivalves dropped
E===2 Pribilof-southg considerably and_ polychaetes,
Major migration route echiurids, euphausids, and crangonid
mame Spring
<> Summer and shrimp were most important. Although
£222}>unceratuatiunm n Tanner crabs, Chionoecetes sp., were
only a small part of the stomach con-
tents, the large yellowfin sole popula-
tion is a significant predator on this
valuable resource.
Daily ration estimates for yellowfin
sole were made by Livingston et al.
(1986) using both stomach content
weight information and bioenergetic
calculations. Values obtained were
0.12% body weight and 0.40% body
weight respectively. Based on gross
conversion efficiency, the latter value
is considered most accurate.
The primary predators on yellowfin
sole are two abundant gadids, Pacific
cod, Gadus macrocephalus, and wall-
eye pollock, the Pacific halibut, and
Figure 4.—Schematic diagram showing seasonal migration and distribu- four species of cottids (Brodeur and
tion of yellowfin sole by wintering group in the eastern Bering Sea (from Livingston, 1988; Wakabayashi, 1986).
Wakabayashi, 1989). On a much smaller scale, sea birds and
marine mammals also consume yellow-
fin sole.
based on survey data. This compares described as opportunistic. Feeding The yellowfin sole plays an impor-
with the survey estimate of 2.4 million studies in different areas at different tant part in the ecosystem of the east-
t for yellowfin sole. Although the dis- times of the year (Livingston et al., ern Bering Sea (Fig. 7). The prey items
tributions overlap almost totally, the 1986; Wakabayashi, 1986) describe a consumed by such a large fish popula-
center of abundance for yellowfin sole wide variety of prey items ranging from tion represent a significant portion of
is located between that of rock sole to strictly benthic bivalve siphons to small the prey available to potential competi-
the south and Alaska plaice to the pelagic fish. In general, feeding during tors. In turn, the yellowfin sole itself
north. Yellowfin sole is found as far winter is very slight to none. Feeding contributes a significant input to the
north as the Chukchi Sea; however, begins during the spring migration to diet of the predators and represents a
their numbers are very small (Alverson the major feeding and spawning large portion of the resource.
and Wilimovsky, 1966) and the maxi- grounds. Wakabayashi (1986) found
mum size was reported to be less than four major groups in the diet of yel- Growth and
20 cm. lowfin sole. Over 65%, by weight, of Natural Mortality
During the summer, adults are found the yellowfin sole stomach contents col-
in almost all areas of the shelf at depths lected during the summers of 1970 and The yellowfin sole is a slow grow-
less than 100 m (Fig. 6). However, the 1971 consisted of polychaetes, bi- ing, long-lived flatfish. Although
juveniles located in the shallow waters valves, amphipods, and echiurids. Al- lengths seldom exceed 400 mm, ages
during the winter remain in waters pri- though these categories were also im- above 25 are not uncommon. Lengths
marily less than 50 m during the portant to the potential competitors, at age are similar for males and
summer. rock sole and Alaska plaice, the rela- females during the juvenile years
tive proportions of each prey were quite (Fig. 8), but females slightly outgrow
Feeding and Predators
different for yellowfin sole than for the males as they near the onset of sexual
Yellowfin sole is characterized as a other species. Alaska plaice and rock maturity. There is considerable variabil-
benthopelagic feeder. It could also be sole have heads that are indented at ity in length at age for both sexes. How-
54(4), 1992
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54(4), 1992
PACIFIC COD cu
WALLEYE POLLOCK PREDATORS
PACIFIC HALIBUT
YELLOWFIN Possible
EELPOUTS ComMPETITORS
SOLE
ROCK SOLE
i
AMPHI Popa
OPHIUROIDEA POLYCHAETA BIVALVIA EUPHAUSIACEA
FISHES DECAPODA. MACRURA BRACHYURA
(Crustacea)
Figure 7.—Schematic diagram of interspecific feeding relationships with reference to yellowfin sole on the conti-
nental shelf of the eastern Bering Sea. Arrows indicate flow of matter. Bold-faced and underlined species are key
ones for yellowfin sole; minor species are excluded (from Wakabayashi, 1986).
ever, these data are combined from vir- M for yellowfin sole as 0.25 and for females. Wakabayashi (1989) re-
tually the entire distribution on the shelf Wakabayashi’ derived the same value ported 50% maturity in 1973 to occur
and therefore does not reflect possible using the methods of Alverson and at 13 cm for males and 25 cm for fe-
growth differences due to environmen- Carney (1975). Bakkala et al.* believed males. He suggested that the lower
tal variations from south to north. this value to be too high. Using a simu- abundance in 1973 was responsible for
Based on data gathered in 1988, the lation based on cohort analysis, they the decrease in size at maturity. Males
parameters for the von Bertalanffy found that an M of 0.12 provided the and females reached 50% maturity at
equation are as follows: best fit to available data. That value about ages 5 and 9, respectively. Al-
has been used subsequently and is used though the sample size was only about
to L., (mm) k in analyses reported in this paper. 1,500 fish, results of a study during the
1990 AFSC survey showed the size at
Males 1.63 352 0.16 Maturity and Spawning
50% maturity to be 20.3 cm for males
Females 2.44 376 0.17 Fadeev (1970) reported that during and 28.8 cm for females. Because the
1959-64, when the population was estimate of exploitable biomass (2 mil-
The length-weight relationships for
sharply decreasing from a high level, lion t) is now equal to or greater than
males and females are very similar
50% maturity was reached at a length that of either of the past studies, there
(Fig. 9). From 1987 data, the param-
of 16-18 cm for males and 30-32 cm appears to be a relationship of in-
eters for the relationship, Weight (g) =
creasing size at maturity with popula-
a-Length (mm)” are:
"Wakabayashi, K. 1975. Studies on resources of tion abundance. In summary, the size
the yellowfin sole in the eastern Bering Sea. II. at maturity has varied over time as
a b Stock size estimated by the method of virtual
population analysis and its annual changes. follows:
Males 8.955-10° 3.0426 Unpubl. manuscr., 22 p., of Far Seas Fish. Res.
Lab., Fish. Agency Jpn., 1000 Orido, Shimizu Year(s)/source Males Females
Females 5.783-°10° 3.1231 424.
*Bakkala, R., V. Wespestad, T. Sample, R. Narita, 1959-64, Fadeev 16-18 cm 30-32 cm
R. Nelson, D. Ito, M. Alton, L. Low, J. Wall, and (1970)
It is to be expected that the natural R. French. 1981. Condition of groundfish re-
mortality (M) of such a slow-growing, sources of the eastern Bering Sea and Aleutian 1973, Waka- 13 cm 25cm
long-lived specics would be relatively Islands region in 1981. Unpubl. rep., 152 p., of bayashi (1989)
Alaska Fish. Sci. Cent., 7600 Sand Point Way
low. However, Fadeev (1970) estimated N.E., Seattle, WA 98115. 1990, this paper 20.3 cm 28.8 cm
Marine Fisheries Review