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Resource Ecology and Ecosystem Modeling - Models

Ecosystem Modeling

Program scientists work on single-species, multispecies and ecosystem models that incorporate predation interactions and bioenergetics.  Below are some examples of the types of models that are presently being worked on.

1) Multispecies fish stock assessment models that include predation

We have developed a multispecies virtual population analysis and forecasting (MSVPA and MSFOR) for the eastern Bering Sea (Livingston and Jurado-Molina, 2000) and incorporated uncertainty estimation through the creation of a new Bayesian multispecies model (MSM; Jurado-Molina et al. 2005). These models include predation interactions among several commercially important groundfish stocks and also predation by external predators (arrowtooth flounder and northern fur seal) on these stocks. Available results include estimation of predation mortalities produced by predators on prey species, and the annual consumption of prey by predators.

References:
Jurado-Molina J., P. A. Livingston and J. N. Ianelli. 2005. Incorporating predation interactions to a statistical catch-at-age model for a predator-prey system in the eastern Bering Sea. Canadian Journal of Fisheries and Aquatic Sciences. 62(8): 1865-1873.

Livingston, P.A. and Jurado-Molina J. 2000. A multispecies virtual population analysis of the eastern Bering Sea. ICES Journal of Marine Science 57: 294-299.

2) Ecosystem mass-balance and simulation models

Ecosystem level models have been developed for the eastern and western Bering Sea (.pdf, 4.3MB) and are under final development for the Gulf of Alaska and Aleutian Islands. Current models include separate accounting dynamics for over 120 species or species groups and include simulation of multiple gear and fishing methods and age-structured simulation of major commercial fish. Bayesian Synthesis techniques are being implemented to better estimate the relative impacts of predation, climate and fishing on marine populations, and methods of linking these simulation models to climate and lower-trophic level production are under development (Aydin et al. 2005).

References:
Aydin, K., GA. McFarlane, JR. King, BA. Megrey, and KW. Myers. 2005. Linking oceanic food webs to coastal production and growth rates of Pacific salmon (Oncorhynchus spp.), using models on three scales. Deep-sea Res, II. 52: 757-780

3) Single-species stock assessment models that include predation.

So far we have developed two of these models: one for EBS pollock (Livingston and Methot 1999) and one for GOA pollock (Hollowed et al, 2000). We are planning on doing one for Aleutian Islands Atka mackerel in the near future. The idea of these models is that we can better examine the sources and time trends of natural mortality for these predators. We have learned that not only is natural mortality at younger ages much higher than adults but that it varies across time depending on time trends in predator stocks. This has given us better ideas of what influences predation has on fish recruitment over time and helps us to separate predation and climate related effects on recruitment. We can better show the demands of other predators such as marine mammals for a commercially fished stock and how it might influence the dynamics of that stock (although there is need for more progress in modeling the effects on marine mammals). These models will be updated periodically.

Results: Pollock cannibalism and predation on pollock by Pacific cod and northern fur seals were added to a Bering Sea pollock population model. Results indicated cannibalism was the dominant source of predation mortality, particularly of juvenile pollock and predation mortality varied on a year-to-year basis. Cannibalism appears to explain a large portion of the declining recruitment seen during periods of high adult pollock biomass (Figure 1) although the largest recruitment outliers from the estimated stock-recruitment relationship appear to be years with anomalous oceanographic conditions.

Current Model Work: The GOA pollock model is being updated in 2003-2004 to include two new years of groundfish food habits data and to address questions of arrowtooth flounder influence on pollock population dynamics.

References:
Hollowed, A., J. N. Ianelli, and P. Livingston. 2000. Including predation mortality in stock assessments: A case study for Gulf of Alaska pollock. ICES J. Mar. Sci 57(2):279-293.

Livingston, P.A. and R.D. Methot. 1998. Incorporation of predation into a population assessment model of eastern Bering Sea walleye pollock. P. 663-678. In: Fishery Stock Assessment Models. Alaska Sea Grant College Program Publication AK-SG-98-01. 1037p.

4) Bioenergetic Models

Bioenergetic modeling of groundfish is important to quantify the relationship between fish growth, prey availability, and physical factors on the amount of food consumed by groundfish.  A bionergetic model of walleye pollock has been developed for the eastern Bering Sea (Buckley and Livingston, 1994; 1996).

PROGRESS REPORTS OF VARIOUS MODELING PROJECTS:

       A spatial model of upper-trophic level interactions in the eastern Bering Sea – SEBSCC Project Final Report(.pdf, 109KB)

       SEBSCC Modeling Project 1998 Status Report(.pdf, 78KB)

       CIFAR Modeling Project on Ecosystem Analysis and modeling of eastern and western Bering Sea living marine resources 1998 Status Report(.pdf, 58KB)


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