Resource Ecology and Ecosystem Modeling - Overview of Activities
Overview of Activities
- Field collection and laboratory
analysis: The program performs annual collection of groundfish stomachs in the eastern
Bering Sea and biennial collections in the Gulf of Alaska and
the Aleutian Islands and West Coast regions. About 15,000 stomachs
are collected and analyzed annually. The groundfish food habits database contains over 400,000 records of
data from about 147,000 stomachs collected since 1981, including
historical collections off the west coast.
- Species level data analysis
includes groundfish diet composition by season, size, and area. Various methods for
estimating daily ration are used including detailed bioenergetic models of growth and
consumption. Estimates of total annual predation on commercially important prey species by
groundfish are produced and compared with marine mammal and bird consumption. Cooperative
work with process-oriented field programs provides insight into predator functional
feeding responses.
- Multispecies data analysis focuses
on identifying physical and biological factors influencing diet overlap and competition
among groundfish and other ecosystem components. Multivariate statistical analysis, diet
overlap indices, and analysis of food web characteristics are used to identify feeding
guilds and important habitat features. Ecosystem implications of current fishing, discard,
and processing practices have been examined using data on consumption of discards by
marine predators and rates of energy flow to the detritus. Indices of ecosystem
status,
e.g. species diversity, are also developed along with research
focused on the development of indices showing the links between
climate and fish production.
- Diverse modeling approaches are
being used to quantify and understand predator/prey interactions. Predators (including
mammals) have been incorporated into single-species catch-at-age models. Static energy
balance models have been parameterized for different time periods. A multispecies virtual
population analysis of eastern Bering Sea groundfish is being parameterized and tested. A
dynamic upper-trophic level model of predation on juvenile pollock in the eastern Bering
Sea is currently being planned with links to outputs of other agency modelling efforts
such as physical transport models, individual-based models of juvenile
pollock, and lower
trophic level models of phytoplankton-zooplankton production.
- Seabird-fishery interactions are being quantified and fishing
gear improvements to reduce seabird incidental catch are being
evaluated. Standardized reporting, education, and outreach
are important activities in understanding and reducing the
incidental catch of seabirds in groundfish fisheries.
Future Directions
Improve short-term yield
predictions.
Current
stock assessments predict on a single-species basis the short-term effects and yield
obtained due to fishing pressure. However, these short-term projections tend to be based
on fairly uncertain stock-recruitment relationships. Predation data will be incorporated
into single-species stock synthesis models of Gulf of Alaska pollock and Bering Sea crab
stocks in order to include pre-recruit mortality and to reduce recruitment uncertainty due
to this mortality in our assessment process.
A multispecies virtual
population analysis model where species are linked by predation has been parameterized for
the eastern Bering Sea. We will be able to compare mortalities, abundances, and
recruitments of fish populations obtained from this model with the single-species models
currently being used for each species. New insights will be obtained on how production of
commercially important species is affected by multispecies interactions.
Improve long-term yield
predictions.
Because
most predation mortality occurs at young ages, the effects of multispecies interactions
need to be assessed in the long-term. Strategic assessment of long-term consequences of
various fishing strategies on the multispecies groundfish complex can be made through
multispecies yield-per-recruit models and forecasting with results of the multispecies
virtual population analysis model. These models will allow us to evaluate the effects of
different fishing strategies on the total yield from the groundfish complex as a whole.
All predictions that rely on
specifying spawner-recruit relationships can benefit from more research on reducing
uncertainty in spawner-recruit relationships. Environmental and biological effects are
often confounded in spawner-recruit data. More explicit spawner-recruit models that
include both environmental and biological effects in their parameterization need to be
developed.
|