Northern California Current:
Fisheries and Ecosystem Modeling

The Nature Conservancy and the Science for Ecosystem-based Management Initiative (SEMI) of the Northwest Fisheries Science Center, National Oceanic and Atmospheric Administration (NOAA) Fisheries, have been examining the relationships between marine ecoregional planning and fisheries modeling. The goal of SEMI is to research the ecological interactions and processes necessary to sustain ecosystem composition, structure and function in the environments in which fish and fisheries exist. Understanding the factors that sustain the ecosystem provide the scientific underpinnings needed to inform ecosystem-based management of groundfish in the Pacific Northwest. The goals and objectives of SEMI dovetails with ecoregional planning that attempts to identify a set of high priority areas which, if conserved and effectively managed, will protect a representative subset of the marine biodiversity in an ecoregion.

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The common threads of ecosystem-based management approaches involve taking a more holistic view of managing resources in the context of their environment. For marine fisheries, this implies greater consideration of the interactions between climatic and oceanographic processes, the connections and interactions between fished and unfished populations in the ecosystem, and the role of humans as both predators and competitors in such ecosystems. To address this approach we have adopted an Ecopath model of the Northern California Current (NCC) that emphasizes mid-trophic level predators, in particular commercially important groundfish.

The NCC ecosystem is part of the larger shelf, slope and offshore regions of the California Current System (CCS). Along the coast of the CCS there are changes in physical and biological characteristics at major promontories including Point Conception, Cape Mendocino and Cape Blanco. The model of the NCC was constructed to improve our understanding of the relationships among physical, ecological and human (fisheries) processes in shaping the trajectories of commercially important populations of fish and shellfish. In particular, the Ecopath model evaluates how conceptual and statistical relationships between climate and the commercially important biota in this ecosystem. Being roughly the same geography as the Pacific Northwest ecoregional assessment this model has allowed us to examine the relationships between biodiversity planning and fisheries modeling.

The region modeled is the area between the nearshore and the continental slope from Cape Flattery to Cape Mendocino to a depth of approximately 1,280 meters (typically 20-80 kilometers offshore). This represents the limits of available data from continental slope surveys and the approximate limits of most historical and contemporary fishing effort for trawl and fixed gear.

Features of the Ecopath Model

The final Ecopath model includes 63 components: 21 of which are commercially significant species or stocks of fish or shellfish, eight of which are aggregations (at the genus or family level) of commercially significant groups (e.g. salmon, skates), 11 of which are functional groups of top predators (seabirds and marine mammals), four of which are either producers (phytoplankton) or detritus (benthic, pelagic, fisheries offal), with the remaining 19 representing broad aggregates of zooplankton, benthic fauna, and non-commercial fishes. As such, the model emphasizes detail for mid-trophic level predators, in particular commercially important groundfish, for which considerably more data tend to be available.

This model incorporates information over a 42 year timeline (1960 – 2002). Changes in biomass indicate whether a particular species is in “good” condition. A number of commercially important species including salmon, shrimp, sardine, and many flatfish show increased biomass over this time period; an observation consistent with recent record runs of salmon , catches of shrimp and crab, and production of forage fish. Many marine mammals (harbor seals, sea lions, and baleen whales) have increased in abundance as well. However much of the upper-middle level of the food web, in particular groundfish, have decreased, representing the observation that a very significant fraction of this low-turnover biomass has been removed by fishing.

A range of climate effects were explored, here called forcing functions. The indices include upwelling wind indices, indices of wind derived from southward transport, the Pacific Decadal Oscillation index. The results demonstrate that adding some of the climate indices as a forcing factor improve the “fit” of the model, or conditions that exist in real time. This is consistent with the observation that climate forcing has been shown to be a critical factor in determining the productivity and dynamics of many individual species in this ecosystem.

From this Ecopath model we can project these trophic and climatic interactions over time (Ecosim) and through space (Ecospace). This case study has focused on the Ecospace component of the Northern California Current model and its relationships to biodiversity conservation planning.

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