JAS 1999 Quarterly Rpt. sidebar
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(Quarterly Report for Jul-Aug-Sep 1999)
Fish Use of Eelgrass and Kelp Habitats
Auke Bay Laboratory (ABL) Habitat Program
staff sampled eelgrass (Zostera marina) and kelp (e.g., Laminaria) habitats
near Sitka, Alaska, to document their value as essential fish habitat. High value
habitats are designated Habitat Areas of Particular Concern and receive
special consideration during permit reviews of shoreline development.
Fish were sampled monthly by beach seine from
April through September 1999 at two subsites of each habitat at four sites. Vegetation was
characterized by determining percent cover and biomass. Fish species diversity was
higher at eelgrass (25-34 species) than at kelp (16-27 species) sites. Eelgrass sites also
had greater monthly mean fish abundance (2,877 fishes versus 2,117 fishes), although
abundance at kelp sites in May and June was higher than at eelgrass sites, largely due to
high abundance of pink (Oncorhynchus gorbuscha) and chum (O. keta) salmon
fry.
Abundance and use differed between habitats.
Chum and pink salmon fry dominated both types of habitat in April and May and persisted in
kelp sites through June. Young-of-the-year Pacific herring (Clupea harengus
pallasi) were the most numerous species in eelgrass sites in July and persisted
through August, but were not found in kelp. In August and September, young-of-
the-year shiner perch (Cymatogaster aggregata) and juvenile Pacific cod (Gadus
macrocephalus) dominated both habitat types. In general, if a species occurred in both
habitats, it was more abundant in eelgrass. Exceptions were higher numbers of salmon
fry and white spotted greenling (Hexagrammos stelleri) in kelp relative to eelgrass
communities.
Results from this study help to define the
role of eelgrass and kelp habitats as essential fish habitat and enable habitat managers
to ensure their conservation during shoreline development.
By Pat Harris.
Residence Time
of Juvenile Rockfish in Eelgrass/ Kelp Habitats
Movement of age-1+ black (Sebastes
melanops), copper (S. caurinus), dusky (S. ciliatus), quillback (S.
maliger), and yellowtail (S. flavidus) rockfishes was investigated in Sitka
Sound to determine residence time in eelgrass and kelp habitats, areas of possible high
value as Essential Fish Habitat. Movement of juvenile rockfish between eelgrass and
kelp habitats within four small semi-enclosed bays was investigated by mark-recapture
methods. Two soft-bottom eelgrass and two cobble-bottom kelp sites in each bay were
sampled monthly with a beach seine from April to September 1999. Fish were marked
with injected elastomer tags to distinguish month and site. Fish held in the
laboratory showed no tag loss or handling mortality. Because of difficulty
distinguishing juveniles, rockfish were pooled into three species groups:
copper/quillback, black/yellowtail, and dusky rockfish.
A total of 1,747 age-1+ rockfish were
captured, of which 1,189 were tagged, and 161 were recaptured. The recapture rate
was similar for all species groups: copper/quillback (14%), black/yellowtail (12%), and
dusky (13%). Recaptured fish showed little movement from the original tagging site
or between habitat types. Only 6% of recaptures were caught more than 30 m from
their tagging location. Only three recaptures changed habitat types.
Recaptures in later months were composed of fish tagged from several earlier
periods, indicating residence of up to 4 months.
Results show that juvenile rockfish move into
shallow eelgrass and kelp habitats in May and remain in the same local area throughout
late spring and summer. Because of the extended residence of juvenile rockfish
in particular habitat types in summer, research will next focus on linkages between
habitat and rockfish growth and survival. This information will further assess the
relative value of eelgrass and kelp as essential habitat for juvenile rockfish.
By Mike Byerly.
Habitat Assessment for Tatitlek
Harbor
Habitat Program staff conducted a fish
habitat assessment at proposed harbor construction sites at Tatitlek, Prince William
Sound, Alaska, in July 1999. The proposed site for harbor construction,
Tatitlek Cove, has a lush eelgrass meadow, which is designated as a Special
Aquatic Site under the Clean Water Act. Principal concerns are the potential impacts
including the cumulative effects of harbor construction on eelgrass and fish habitat in
the Tatitlek area.
The objective of the habitat assessment study
was to characterize fish and habitat in the project area in order to provide perspective
on the relative value as fish habitat of alternative construction sites. Six beaches in
the Tatitlek area were sampled with a seine to determine use by fish and crab species.
Submerged aquatic vegetation along the shoreline in the Tatitlek area was surveyed
by skiff and with a remotely operated vehicle (ROV).
Beach seining showed that eelgrass beds had
higher species diversity (9-15 species) than non-eelgrass sites (5-9 species) and also had
greater fish abundance (mean, 277 fishes and crabs) than non-eelgrass sites (mean, 77
fishes and crabs). Eelgrass assemblages were dominated by juvenile Pacific cod
(53-196 cod per seine haul), with lesser catches of lingcod (Ophiodon elongatus)
and other species. Non-eelgrass sites were dominated by tubesnouts (Aulorhynchus
flavidus) and juvenile Pacific cod. Skiff and ROV surveys found eelgrass along an
estimated 80% of the shoreline in the Tatitlek area. Eelgrass occurred in all
suitable enclosed areas, as well as in some marginal areas that were exposed to wind and
waves. Relatively few locations had bare substrate or non-eelgrass (e.g.,
Laminaria) vegetation.
The site of proposed harbor construction in
Tatitlek Cove was typical of other eelgrass habitats in the area, with high species
diversity and fish abundance. An alternative construction site south of Tatitlek
Cove (South Point) had predominantly filamentous algae and Laminaria, and fish
assemblages there were less diverse and less abundant than in Tatitlek Cove. South
Point, however, was one of the few sites in the study area that contained Laminaria,
which may be important for biodiversity. Because eelgrass was ubiquitous in the study
area, the cumulative effects of harbor construction in Tatitlek Cove are not a major
concern.
By Mike Murphy.
Habitat Areas
of Particular Concern
ABL staff assisted the North Pacific Fishery Management Council in
analyses for the Draft Environmental Assessment/ Regulatory Impact Review for Habitat
Areas of Particular Concern (HAPC). Specifically, they reported on the description and
distribution of coral in the Gulf of Alaska and Bering Sea and on the impacts of fishing
on coral. Corals had previously been identified as HAPC. In the draft report, the Council
proposed options for management measures to reduce adverse impacts on HAPC. The
options are:
Status quo. No additional fishery management actions to protect HAPC
from fishing impacts would be taken.
Reclassify some living substrate HAPC as a prohibited species.
This would specifically prohibit retention of all coral, sponges, kelp, rockweed and
mussels.
Establish no fishing zones in areas of Gorgonian coral abundance.
Note that both options 2 and 3 can be adopted.
ROV Observations of Essential Fish Habitat in Southeast Alaska
Figure 1. Rockfish observed via a video-equipped ROV inhabited areas with complex habitat
such as bedroock walls and boulder piles.
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Information is limited on the nearshore
habitat of many commercially important groundfish species in Alaska, especially during
their larval and juvenile stages. Many groundfish species utilize shallow (<70 m deep),
nearshore areas during their early life. Information is needed by managers to
protect and conserve those habitats that are essential to maintain healthy fisheries.
In 1999, the ABL used a remotely operated
vehicle (ROV) equipped with a video camera to study the association between habitat and
fish assemblages in nearshore waters of Southeast Alaska. Approximately 100 ROV dives were
conducted in a variety of habitat types from southern Southeast Alaska near Craig to
northern Southeast Alaska near Sitka and in inside waters near Juneau. Important
commercial species observed included 6 species of rockfishes (Sebastes spp.),
Pacific cod, longcod, and walleye pollock (Theragra chalcogramma). Most
rockfish were in areas with complex habitat, such as bedrock walls and boulder piles, with
numerous cracks and overhangs for cover (Figure 1 above), whereas areas with not much
relief, such as basin bottoms, were void of rockfish. Juvenile rockfish were often
seen in shallower water than adults were, particularly in areas with vegetation, such as
eelgrass meadows, Laminaria beds, and Nereocystis forests.
Distribution of rockfish differed between
outside and inside waters and between southern and northern Southeast Alaska. For
example, juvenile yelloweye rockfish (Sebastes ruberrimus) were seen in outside
waters between Craig and Sitka but not in inside waters near Juneau. Similarly, most
lingcod were seen in outside waters near Sitka, whereas few were observed in inside
waters. Quillback rockfish were ubiquitous, occurring in both inside and outside waters
between Craig, Sitka, and Juneau.
We observed some distinct associations
between fish assemblages and habitat in nearshore waters of Southeast Alaska. For
example, juvenile rockfish, lingcod, and Pacific cod were often in shallow water
areas with vegetation (e.g., eelgrass, Laminaria), whereas juvenile yelloweye
rockfish were only in high-relief, vertical wall-habitat. Distribution of fish
between northern and southern and inside and outside waters of Southeast Alaska was
patchy, especially with few fish observed in inside waters near Juneau. Differences
in physical and biological factors, such as salinity, temperature, food, and cover likely
account for the presence or absence of some species among our study sites. Information on
fish assemblages and habitat will help managers identify and protect those habitats in
nearshore areas susceptible to impacts from shoreline development.
By Scott Johnson
Juvenile Salmon
Surveys In Eastern Bering Sea
The Ocean Carrying Capacity program conducted
a survey of juvenile salmon in the eastern Bering Sea from 2 to 12 September 1999.
The survey began 30 nmi east of Cape Seniavin, near Port Moller, and extended
southwestward to Cape Mordvinof, east of Unimak Pass. Surface trawls were made along
eight transects spaced 30 nmi apart; each transect began near the coast and extended to 60
nmi offshore or farther if large numbers of juvenile salmon were encountered at offshore
stations. Co-investigators in the study included scientists from the University of
Alaska.
Our results indicate a much broader offshore
distribution of juvenile sockeye salmon (O. nerka) than that from
our previous survey in July 1999. During July 1999, juvenile sockeye salmon were
encountered nearshore (less than 10 nmi offshore) and were distributed northeastward
of Port Moller. During September 1999, most of the juvenile sockeye salmon were
encountered southwestward of Port Moller to 60 nmi east of Unimak Pass and were
distributed from nearshore environment to 60 nmi offshore and further (80 nmi offshore)
along the 50 fathom shelf break.
The expanded distribution of juvenile sockeye
salmon encountered during September 1999 may have been the result of increased sea surface
temperatures. During July 1999, juvenile sockeye salmon were only encountered when
sea surface temperatures were 6EC or more; sea surface temperatures in offshore waters
during July were 4E-5EC. During September 1999, sea surface temperatures had
warmed considerably; nearshore sea surface temperatures were 10E-10.5EC, while offshore
surface water temperatures were 8.5E-9.5E C.
Increased sea surface temperatures may also
have lead to rapid increase in growth. During July 1999, juvenile sockeye salmon
were generally small in size, ranging in length from 80-105 mm near the coast to 105-115
mm off Port Moller. During September 1999, juvenile sockeye salmon lengths near the
coast ranged from 105 to 140 mm, while lengths of juvenile sockeye salmon encountered at
offshore locations ranged from 190 to 240 mm. Analyses of plankton, stomach contents,
freshwater age, and scale growth data collected during both surveys will be done to shed
additional light on the growth and migration characteristics of juvenile sockeye salmon
emigrating from Bristol Bay.
By Steve Ignell.
SASPop Up and
Running
Biologists from the ABLs Marine Salmon
Interactions Program accepted the completion report for development of the Statewide
Escapement Survey Database by the Alaska Department of Fish and Game (ADF&G).
The project, initiated in FY95 though a grant developed by the ABL and funded by
NOAAs Enviromental Services Data and Information Management Program (ESDIM),
has been funded with $370,000 in ESDIM grants over the last four fiscal years, as
well as an equivalent amount of in-kind funding from the ADF&G. The project has
created a geo-referenced salmon and escapement data system, the Status of Alaska Salmon
Populations Geographic Information System (SASPop GIS), incorporating over 1.5 million
escapement observations from almost 4,000 streams throughout Alaska. The
system includes digitized, statistical area maps defining fishing districts and escapement
locations and identification of several hundred streams statewide for which survey data
exists, but which have not been previously identified in the Alaska Anadromous Water
Catalog. This information will allow the inclusion of these anadromous streams in
the catalog, so that they will be afforded the regulatory protection of the Anadromous
Stream Act. The data system will be an invaluable tool for both research and
management, providing new capabilities for assessing the trends and status of Alaska
salmon populations and examining salmon production in relation to landscape and watershed
scale habitat alterations. Now that the system is operational, the ADF&G will
maintain it with annual updates from regional escapement surveys.
By Alex Wertheimer.
Stock
Identification of Salmon Samples from the Vessel Ying Fa
Samples of chum and sockeye salmon seized
from the stateless fishing vessel Ying Fa were analyzed to determine their region
of origin using genetic stock identification (GSI), otolith marks, parasite analysis, and
scale data. Based on GSI, the chum salmon samples originated in Russia, 86%; Japan,
2%; western Alaska, 2%; Alaska Peninsula and Kodiak Island, 8%; and British Columbia, 2%.
Origins of the sockeye salmon sample were not so clear because there was some
disagreement between the parasite data and the GSI and scale data. Results of
parasite analysis suggested the sample was nearly all of Alaskan origin, with at least 15%
coming from Bristol Bay. The GSI analysis indicated that 30% of the sockeye salmon
originated in Russia and 70% in North America. The scale analysis showed that 97% of
the sockeye salmon sample were ocean age 3, whereas the return to Bristol Bay in 1999 was
approximately 70% ocean age 2 fish.
By Richard Wilmot.
Migration of Yukon
River Chum Salmon
A total of 892 Yukon River fall chum salmon
were tagged with radio transmitters during the 1999 field season. Locations and
migration rates are being determined through radio-telemetry monitoring. As of the
end of September 1999, 508 fish (57%) were in the U. S. portion of the main-stem Yukon
River, and 44 fish (5%) had crossed the border into Canada. In the Porcupine River
system, 115 fish (13%) had crossed the border into Canada, and 22 fish (2%) were in the U.
S. portion of the river. The Chandalar River in the U.S. portion of the drainage continues
to be one of the major spawning destinations, with 203 tagged fish (23%) currently
located.
By Richard Wilmot.
Forage Fish Diet
Study
The role of forage fishabundant,
schooling fishes that transfer energy from primary or secondary producers to higher
trophic levelsis being examined in coastal Alaska and ecosystems worldwide. In
Prince William Sound (PWS), the Exxon Valdez (EVOS) Oil Spill Trustee Council,
between 1994 and 1997, sponsored the Alaska Predator Ecosystem Experiment (APEX), a
multi-disciplinary ecological research program undertaken by a consortium of natural
resource agencies and academic institutions to assess forage fish populations and their
trophic interactions with one another and with jellyfish, seabirds, and marine mammals.
One component of APEX is the Forage Fish Diet
Study, conducted as a cooperative project of the ABLs Marine Salmon Interactions and
Habitat Investigations Programs. Stomachs were examined from 14 forage species (>
5,100 specimens) caught mainly in midwater trawls, purse seines, and beach seines, and
representing nine sampling periods during 1994-96. Food habits data were used in
conjunction with prey field samples to examine diet, prey partitioning and preference,
diet overlap, and potential competition between forage species. A final report
of the Forage Fish Diet Study, published in 1999 by the EVOS Trustee Council,
describes monthly and interannual diet composition and overlap between 14 forage fish
species; compares young-of-the-year Pacific herring and pollock feeding in allopatric and
sympatric aggregations in summer and autumn 1995; and compares feeding of juvenile
herring, sand lance, and pink salmon in allopatric and sympatric aggregations in summer
1996. These data were also used with another APEX component to examine the potential
competition between four zooplanktivorous jellyfish species (Aurelia, Cyanea, Aequorea,
and Pleurobrachia) and the four forage species and have been an important data
component in the development of bioenergetic models and energy flows between trophic
levels in the PWS marine ecosystem.
By Molly Sturdevant.
Sablefish
Longline Survey Completed
The AFSC has conducted an annual longline
survey of sablefish and other groundfish off Alaska from 1987 to 1999. The survey is
a joint effort involving the ABL and the Resource Assessment Conservation Engineering
(RACE) Division. Beginning in 1996, biennial sampling of the Aleutian Islands region
and eastern Bering Sea was added.
In 1999, 73 stations were sampled in the Gulf
of Alaska and 16 stations were sampled in the eastern Bering Sea from 28 May to 5
September. Sixteen kilometers of groundline were set each day, containing 7,200
hooks baited with squid. The survey vessel was the chartered fishing vessel
Ocean
Prowler. Catch rates on the survey are critical for the determination of the
annual Allowable Biological Catch of sablefish. The surveys sablefish
abundance index for all regions combined increased 9.8% in numbers and 4.7% in weight from
1998 to 1999, following decreases of 5.7% in numbers and 5.8% in weight from 1997 to 1998.
Approximately 4,633 sablefish, 603 shortspine thornyhead (Sebastolobus alascanus),
and 188 Greenland turbot (Reinhardtius hippoglossoides) were tagged and released
during the survey. Length-weight data and otoliths were collected from approximately
2,451 sablefish. During the survey a surface gill net was deployed to sample
juvenile sablefish (ages 0 and 1). The net was set at 35 different stations
and caught juvenile sablefish as well as other fish species, especially juvenile and adult
salmon. Sperm (Physeter macrocephalus) and killer (Orcinus orca) whales took
fish from the longline at several stations as in previous years.
By Michael Sigler.
Sablefish Longline
Hook Spacing Experiment
The effect of hook spacing has been measured
for sablefish in two experiments. The purpose of both experiments was to test
an assumption of how to interpret longline fishery catch rates. The fishery
catch-per-skate is assumed to be an index of relative abundance. For example, a 10%
difference in catch rate reflects a 10% difference in relative abundance. This
assumption would be wrong if increasing the hook spacing increased the fishing power of
each hook. Most (about 70%) sablefish longline fishermen currently use 1-m
hook spacing, but the spacing differs between vessels and may change with time.
The first experiment was conducted in Chatham
Strait near Tenakee Inlet during 4-13 July 1986 from the NOAA ship John N. Cobb.
Circle hooks (size equivalent to 13/0) baited with herring were used. Three
hook spacings were tested: 1, 2, and 4 m; all three hook spacings were tested in each set.
The second experiment was conducted 25-26 July 1999 in the Gulf of Alaska off Icy
Bay aboard the chartered fishing vessel Ocean Prowler. Circle hooks (size 13/0)
baited with squid were used. Four hook spacings were tested: 0.5, 1, 2, and 4
m. For both experiments, catch-rate-per-hook increased as hook spacing increased.
For both the 1986 and 1999 experiment,
catch-rate-per-hook increased as hook spacing increased to an asymptote at 4-m spacing.
Catch-per-hook for 1-m spacing, the most common spacing currently in the
fishery, was about half that for the 4-m spacing. These results imply that fishery
catch rates should be standardized by longline set to account for differences in hook
spacing.
By Michael Sigler.
Stock Assessment of
Slope Rockfish and Pelagic Shelf Rockfish in Gulf of Alaska
Updated stock assessments of slope rockfish
and pelagic shelf rockfish in the Gulf of Alaska will be completed during the first
quarter of FY 2000. The results of the recently completed triennial trawl survey will be
included in the updated stock assessments. The most recently completed assessment of
Pacific ocean perch (Sebastes alutus), a member of the slope rockfish
assemblage, used an age-structured model and estimated exploitable biomass at 228,190
metric tons (t) and determined the stock is increasing. The assessments of most other
species of slope rockfish and pelagic shelf rockfish in the Gulf of Alaska rely on biomass
estimates provided by trawl surveys. The most recently completed assessments
indicate the following stock levels and stock trends; Shortraker (S.
borealis) and
rougheye (S. aleutianus) rockfish exploitable biomass 65,380 t, trend unknown;
northern rockfish (S. polyspinis) exploitable biomass 65,380 t, trend unknown;
other slope rockfish, exploitable biomass 103,710 t, trend unknown; pelagic shelf rockfish
exploitable biomass 54,220 t, trend unknown.
Age-structured
Model of Northern Rockfish in Gulf of Alaska
The northern rockfish, S. polyspinis, is
one of the most abundant and commercially valuable members of its genus in Alaska waters,
second only to Pacific ocean perch, S. alutus. The stock assessment of northern
rockfish in the Gulf of Alaska used to recommend catch levels has relied almost entirely
on biomass estimates provided by trawl surveys. An age-structured analysis of
northern rockfish population dynamics has been suggested as a way to improve the stock
assessment. Preliminary results were presented at the Gulf of Alaska Groundfish Plan
Team meeting held in September 1999, and a report will be included in the NPFMC Stock
Assessment and Fishery Evaluation Report. The model will be updated with additional
data and further evaluated prior to application and determination of the status of the
northern rockfish stock. The value of the model at this stage is the feature
of incorporating several disparate fisheries and survey data sources in the analysis.
In particular, the model provided a subjective framework for evaluating the effect
of the different data components on the estimated population and suggested a rationale for
determining an appropriate level of confidence in apparently inconsistent data components.
By Jon Heifetz.
Rockfish Adaptive
Sampling Experiment
A cooperative study between the ABL and the
Juneau Center for Fisheries and Ocean Science, University of Alaska Fairbanks was
conducted 13-29 June 1999 aboard the chartered factory trawler Unimak in the Gulf
of Alaska. This was the second year of a 2-year study to improve survey techniques
for assessing abundance of slope rockfish using adaptive sampling. Partial funding for
both years was provided by the Sea Grant - NOAA Partnership Program. The study
focused on three commercially important species of slope rockfish, Pacific ocean perch,
shortraker rockfish, and rougheye rockfish. For 1998, contrary to expectations,
adaptive sampling results showed only modest gains in the precision of abundance estimates
when compared with random sampling. These results appeared highly dependent on the
stratification pattern used. For 1999, the number of strata were reduced. Although final
analyses have not been completed, the larger sample size (165 hauls) and lack of
stratification of the 1999 study area appeared to improve the precision of adaptive
sampling abundance estimates for Pacific ocean perch. However, for abundance estimates of
shortraker/rougheye rockfish the 1999 results did not appear to show a marked advantage
for adaptive sampling over random sampling.
By Jon Heifetz.
Sablefish
Assessment
A preliminary revision of the sablefish
assessment was presented to the Plan Teams in September 1999. The revision consisted
mainly of the addition of about 20 years of historical data and the addition of
contemporary fishery catch rates. Also included in the model were 1) a Bayesian
analysis that incorporated prior probabilities for natural mortality and survey
catchability into parameter estimation, 2) a decision analysis using the posterior
probability from the Bayesian analysis to determine what catch levels likely will reduce
abundance, and 3) an alternate method of apportioning Allowable Biological Catch (ABC)
that adds fishery catch rate data to the survey data currently used to apportion the ABC.
The final assessment will be completed in November after further external review. The
abundance of sablefish is considered low but stable.
By Mike Sigler.
Effects of Trawling
on Soft-bottomed Marine Ecosystem
ABL staff completed a research cruise on 24
August to study the effects of bottom trawling on the seafloor near Kodiak Island.
This was the final cruise of the 2-year study to make observations of the seafloor
in areas open to bottom trawling and adjacent areas which have been closed to bottom
trawling since 1986. Cruises during both years were supported by the ADF&G vessel
Medeia, and the research submersible Delta was used to make in situ observations of the
seafloor. Study objectives were to compare nontrawled zones and trawled zones to
determine if changes have occurred to 1) infaunal species abundance and diversity; 2)
abundance of fish and invertebrate populations, and 3) substrate characteristics,
including grain-size composition and total organic carbon content.
During the August 1999 cruise, one of two
sites investigated in 1998 was revisited, and a third site 25 km south of the Trinity
Islands was investigated. Ten 3,000-m long transects were completed at each site,
and 60-70 sediment samples were collected per site. Experimental trawl sampling was
also conducted at each site to collect animals observed from the submersible for
definitive identification and to estimate relative species composition. An
epibenthic camera sled designed by Ken Krieger (ABL) and Brad Stevens of the AFSCs
Kodiak Laboratory was successfully tested as a potential tool for collecting benthic video
data in future studies on soft-bottomed marine habitat. Digital camera capabilities are
being developed for the sled used in studies concerning fishing impacts and
essential fish habitat. Several submersible dives were also made in
shallow areas of Albatross Bank to investigate the uniqueness of that area as a potential
Habitat Area of Particular Concern.
Video footage is currently being analyzed for
counts of fish and invertebrates in the trawled and nontrawled zones and should be
completed by October 2000. Infaunal composition, grain size composition, and organic
carbon content analyses from the 1998 sediment samples are completed and analysis of
the 1999 samples will be completed by January 2000.
By Robert Stone.
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