|
Resource
Ecology &
|
Yellowfin sole: | 302 |
Walleye pollock: | 10,306 |
Sablefish: | 3,700 |
Atka mackerel: | 1,989 |
Pacific whiting: | 1,913 |
Northern rockfish: | 1,240 |
Light dusky rockfish: | 186 |
Total production
figures were 19,636 with 4,524 test ages and 148
examined and determined to be unreadable.
OSCURS Model
As part of the NMFS Rotational Assignment Program,
Jim Ingraham visited the Southwest Fisheries Science
Center’s Pacific Fisheries Environmental
Laboratory (PFEL) from November to March in order to
collaborate on the implementation of the Ocean
Surface Current Simulations (OSCURS) model on PFEL’s
Live Access Server (LAS). The OSCURS numerical
model is a research tool that allows oceanographers
and fisheries scientists to perform retrospective
analyses of daily ocean surface currents over the
last several decades anywhere in the North Pacific
Ocean and Bering Sea in a 90-km oceanwide grid from
Baja California to China and from 10ºN to the
Bering Strait. OCSURS is used to measure the
movement of surface mixed-layer water (trajectory)
over time, as well as the movement of what was in or
on the water. Ocean surface currents affect
organisms suspended and swimming in the water by
determining their drift and affecting their
destinations. OSCURS has also gained
visibility as an accidental debris tracker to
analyze accidental at-sea events.
Investigation of events such as spills of
cargo containers loaded with thousands of long-term
floating objects such as shoes, plastic
bathtub toys, professional hockey gloves, thongs, or
computer monitors have been used to fine-tune the
OSCURS model and has drawn much public interest.
The upgraded OSCURS model software has been
implemented on a separate version of PFEL’s LAS,
available on the internet at http://las.pfeg.noaa.gov/las_oscurs.
Users can input a location in the North
Pacific and a start and ending time (1967–present),
and get a plot or listing of the predicted daily
trajectory. Input to the model are daily
values of gridded sea level pressure from the Fleet
Numerical Meteorology and Oceanography Center’s
6-hourly 1 X 1 degree global files. Prior to
implementation on the LAS, a pressure extract was
sent from PFEL by ftp each month to REFM. OSCURS
has now been updated to read netCDF pressure files
created as part of PFEL’s monthly data processing.
This facilitated implementation on the LAS and
also increased the speed of data access. This
automatic updating of the pressure fields makes the
previous months data available only a few days after
that month ends. Future development will
include an improved user interface, extension of the
input data back farther in time, and integrating the
OSCURS LAS with PFEL’s primary LAS. Monthly
current charts of the North Pacific is one of the
newly derived products. Other products will be
designed in response to user requests. Contact
Jim Ingraham (206-526-4241, or Lynn deWitt
(831-648-0936 ).
Interannual variability of ocean currents can affect
survival of both suspended and swimming marine
species. Implementation of OSCURS on PFEL’s
LAS will provide access to a greater number of
researchers in fisheries and related fields and
could serve as a public relations tool for educators
and the general public.
By James Ingraham.
Resource Ecology and
Ecosystems Modeling Program
Stomachs collected totaled 486 from the eastern
Bering Sea and 1,106 from the Gulf of Alaska.
Laboratory analysis was performed on 1,618
groundfish stomachs from the eastern Bering Sea and
715 from the Washington-Oregon-California region.
Nine observers returned groundfish stomach samples
during the quarter.
Climate Forcing Effects on
Trophically-linked Groundfish Populations
Commercially important groundfish populations in the
eastern Bering Sea are connected to each other
through the food web and act either as predators,
prey, or both in the system. Some species,
such as walleye pollock (Theragra chalcogramma),
are dominant in terms of biomass and may also
dominate trophic dynamics. In addition to
having different trophic roles, the recruitment
patterns of these species are variable and may be
related to climate forcing on either interannual or
interdecadal time scales. We examined the
possible future effects of four levels of fishing
mortality (F30%, F40%,
F50%, and no
fishing) on trophically-linked species under two
different scenarios of future climate regimes using
both single-species and multispecies forecasting
models of the eastern Bering Sea. We used the
eight-species system developed in the multispecies
virtual population analysis (MSVPA) of the eastern
Bering Sea by Livingston and Jurado-Molina.
Four species, walleye pollock, Pacific cod,
Greenland turbot (Reinhardtius hippoglossoides),
and yellowfin sole (Pleuronectes asper)
played the role of both predator and prey. Two
species, rock sole (Lepidopsetta bilineata)
and Pacific herring (Clupea pallasi), were
considered only as prey. Two species,
arrowtooth flounder (Atheresthes stomias) and
northern fur seal (Callorhinus ursinus), were
considered “other predators,” whose populations
are not estimated within the model but are provided
externally from other sources. The
multispecies forecast model includes predation
interactions and uses as input the predator-prey
suitabilities which were derived from MSVPA.
Monte Carlo simulations for each level of fishing
mortality and each assumption on mean recruitment
level associated with each regime shift were
performed using the single-species and multispecies
forecasting models. We took a simple approach
for recruitment by assuming that the climate regime
shift produced a change in the variability and mean
level of this parameter. Two hypotheses were
examined. One hypothesis was that the eastern
Bering Sea is still responding to the 1977 climate
regime; the second hypothesis was that the species
are responding to a possible new regime shift that
occurred in 1989. Mean and variance in recruitment
for each species used in the forecast models were
calculated from historical recruitment estimates
corresponding to a particular regime shift. The
ratio of spawning biomass in the forecast of year
2015 relative to the starting year of 1998 was used
as indicator of performance. The temporal
trend of the median spawning biomass ratio of
pollock was also tracked in the long term.
In the single-species context, fishing mortality in
conjunction with the regime shift assumption was the
most important factor driving the dynamics of the
species. The regime shift assumption produced
important effects in only three species in a
single-species context. The three species,
Pacific cod, Greenland turbot, and rock sole, were
the species in which the regime shift assumption
changed the mean (Pacific cod and rock sole) or had
a larger change in the variance of recruitment
(Greenland turbot). The observed changes in
spawning stock biomass (SSB) ratios of these species
were a direct result of the changes in recruitment
assumptions for the two regime shift
scenarios. Thus, forecasts of single-species
dynamics can be influenced if regime shifts changes
in recruitment can be estimated and incorporated
into the projections.
In the multispecies scenario, the results showed
greater complexity. Fishing was an important factor
driving the dynamics of all species. An increase in
fishing mortality produced a decrease in the mean
spawning biomass in the majority of the species. For
Pacific herring, in which fishing mortality was held
constant at the 20% harvest rate policy presently
used in its management, an opposite trend was
observed. This tendency was due to predation
interactions. As the fishing mortality
of Pacific herring predators increased, their
abundance decreased, producing a reduction in
Pacific herring predation mortality and thus an
increase in its mean SSB ratio. This shows how
fishing changes on predator populations in
combination with predation interactions have the
potential to cause unintended changes in prey
populations.
The cumulative frequency distributions of some
species’ SSB ratios were also affected by
predation. Within a no-fishing scenario, the
single-species simulation of both assumptions of
climate regime shift suggested an increase in the
spawning biomass of most species. Different
results were seen in the multispecies forecasts,
which included predation interactions. For
walleye pollock, the multispecies no-fishing
simulation suggested an increase in the SSB ratio in
the medium-term projections. However, this
increase was smaller than the multispecies
simulations of the F40%
and F50% levels of
fishing mortality. These differences are due
to the cannibalistic interactions that increase the
complexity of the dynamics of walleye pollock.
If predation interactions are taken into account in
models of walleye pollock, the absence of fishing
mortality produces an increase in the survival of
adult walleye pollock and consequently an increase
in the predation mortality of juvenile pollock. This
result is also seen in our simulations (Figure 1
above) in which the initial effect of a no-fishing
regime on pollock in the multispecies forecast is a
strong build-up of adult biomass and the depression
of juvenile pollock biomass. Therefore,
results of the multispecies forecast suggest that
cannibalism is an important factor influencing the
amplitude and frequency of biomass oscillations in
walleye pollock in this model. The lack of an
explicit stock recruitment function in generating
recruitment values in this model is also likely
responsible for the strong depression of juveniles
at high, adult walleye pollock stock sizes.
Future refinements for this model should
include derivation of functional stock-recruitment
relationships for walleye pollock under different
climate regimes. However, there are not yet
enough historical observations of stock and
recruitment to derive these for different climate
regimes.
For rock sole, predation interactions were also
important. The multispecies forecast of the
no-fishing level under the 1989 regime shift
assumption predicted a decreasing spawning biomass
ratio compared with the no-fishing scenario under
the 1977 regime shift assumption, which predicted an
increasing biomass ratio. The decreasing trend
of the spawning biomass ratio is likely due to
increased predation mortality caused by an increase
in the population of rock sole’s predators
(walleye pollock and Pacific cod) when fishing is
stopped, together with the reduced recruitment in
rock sole assumed under the 1989 regime relative to
the 1977 regime. The single species forecast
for rock sole under the 1989 regime shift scenario
predicted an increased SSB trend. Thus,
predation interactions can influence not only the
magnitude of population change but also the
direction of change.
The displacement of the frequency distributions
produced by the different combination of assumptions
of climate regime and fishing mortality in the
single-species and multispecies forecasts
produced an overlap of some cumulative frequency
distributions of the SSB ratio of some species such
as Pacific cod and rock sole. In
the case of Pacific cod, a more conservative policy
(F40%) under
recruitment assumptions of a 1989 regime shift could
produce similar effects to those produced by a less
conservative policy (F30%)
under the assumptions of the 1977 regime shift in
the medium term (Figure 2 below).
In the case of walleye pollock, there was overlap
among scenarios in the cumulative frequency
distributions in both the medium-term and the
long-term multispecies projections. For this
species, the addition of strong cannibalistic
interactions in combination with fishing and changes
in recruitment variability produce oscillations in
the medium term that have a different amplitude and
frequency for each scenario. There is overlap
at various short and long time intervals of the
median biomass estimates from different scenarios.
Discriminating among environment, predation,
and fishing effects on this species will continue to
be a challenge. Similarly, the design of
multispecies or ecosystem-based management
strategies that attempt to balance human and
predator needs for walleye pollock are complicated
by these cannibalistic interactions that are
confounded with fishing and environmental factors.
In summary, the effects of fishing, predation
interactions, and climate could be considered
similar because they produce changes in the SSB
ratios of species of the same order of magnitude.
The effect of fishing is always to reduce the
biomass of the target species in single-species
forecasts. On the other hand, the effects of
predation and fishing in multispecies forecasts
cannot be generalized and depend on the species, the
complexity, and magnitude of the predation
interactions and the species’ position in the food
web and its response to climate variability.
The MSVPA and the multispecies forecast models are a
first step in taking a more holistic approach in
providing advice for fisheries management.
However, some aspects in this approach can be
improved. The incorporation of climate regime
shifts in the model will require a better
understanding of the mechanisms involving changes in
physical environment and their effects on
recruitment success during a particular climate
regime. The recognition of the 1977 regime
shift was made in the early 1990s, and there is a
belief that this event was not exceptional but the
latest in a sequence of regime shifts. Therefore, it
is necessary to develop a reliable way to identify
regime shifts based on biological and physical
indices. Monitoring these indices in the
North Pacific and the Bering Sea ecosystems might
allow for an earlier identification of regime
shifts. This identification, in combination
with a sufficient number of stock and recruitment
data points in different regimes, will allow a more
detailed functional specification of recruitment of
the Ricker or Beverton-Holt form for each regime
shift. Long-term monitoring is required in
order to recognize and quantify the effects of
regime shifts on marine ecosystems. This
recognition and the improved understanding of
the influence of multispecies interactions will help
resource management better adapt to current or
future environmental conditions.
By Pat Livingston.
Socioeconomic Assessments
Program:
Alaska Marine Sport Fishing Economic Survey
The Center received $95,000 from the NMFS
Headquarters to estimate the economic value of
sport halibut fishing trips in Alaska, including
estimating attributes of a recreational fishing trip
and how those attributes affect participation rates.
The attributes include fish size, number of
fish caught, and harvest regulations. A key
component of the research will be estimating the
value of fish that are caught and retained versus
fish that are caught and released. Todd Lee is
responsible for directing the project, designing the
study and angler questionnaire, and completing the
econometric analysis. The survey will be
administered through a contracted survey research
firm.
Alaska Halibut Charter Boat
Operator Economic Survey
In cooperation with the Pacific States Marine
Fisheries Commission (PSMFC), the AFSC is engaged in
a project to collect economic data from halibut
charter boat operators. The purpose of the
survey is to provide information about the economic
performance of the halibut charter fleet. It is
expected that the survey will be repeated every few
years. The project will provide baseline data that
can be used to evaluate some of the economic effects
of management proposals, such as an IFQ program and
guideline harvest levels, if and when they take
effect.
By Joe Terry.