Expert Report

Dynamic Changes in Marine Ecosystems: Fishing, Food Webs, and Future Options (2006)

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Recent scientific literature has raised many concerns about whether fisheries have caused more extensive changes to marine populations and ecosystems than previously realized or predicted. In many cases, stocks have been exploited far beyond management targets, and new analyses indicate that fishing has harmed other species--including marine mammals, seabirds, sea turtles, and sea grasses--either directly through bycatch or habitat damage, or indirectly through changes in food-web interactions. Several scientific papers suggest that fishing has affected food web interactions and altered the structure of marine ecosystems, although these conclusions have been debated. This report concludes that ecosystem-level effects of fishing are well supported in the scientific literature, including changes in food-web interactions and productivity of important fisheries, and that food-web interactions should be evaluated in future fisheries management decisions.

Key Messages

  • A variety of new regulatory mechanisms and institutions ought to be considered to help implement ecosystem-based management approaches.
  • Assessing historical data can continue to lead to new insights about former species abundances and interactions.
  • Both fishing down the food web (sequential depletion) and fishing through the food web (sequential addition) are occurring.
  • Combining biological and spatial data will allow both large-scale population trends and changes at finer scales to be monitored and understood.
  • Currently, fisheries data are fragmented and dispersed, which is slowing the use of these data in comprehensive analyses.
  • Ecosystem-level effects of fishing are evident.
  • Effects of fisheries removals can cascade through marine ecosystems.
  • Existing laws and agency structures will need to be examined against a wider mandate to implement an ecosystem approach to management.
  • Food-web and other ecosystem models currently exist that provide useful tools for policy screening.
  • Future protocols for ecosystem-based fisheries management will place new demands on social and economic analyses to determine tradeoffs and make strategic decisions.
  • Greater knowledge of food-web interactions, including interactions at lower trophic levels, will be essential to improving ecosystem and food-web models.
  • Large declines in overall abundance of many stocks are evident even though the scientific debate continues regarding the magnitudes and implications of the declines.
  • Managing fisheries within an ecosystem context will require accounting for food-web interactions and trophic effects and making tradeoffs between species or among fisheries and other uses.
  • More extensive use of food-web and other ecosystem simulation analyses are needed to explore possible consequences of different candidate harvesting strategies under alternative scenarios representing the state and dynamics of marine ecosystems.
  • Owing to their inherent complexity and associated uncertainties, ecosystem models are unlikely to provide numerical tactical advice on fisheries regulations.
  • Realizing that there is a theoretical limit to the productivity that can be taken from the oceans and that we may currently be at or approaching that limit, food-web interactions will become increasingly important in future fisheries management decisions.
  • Regime shifts caused by physical forcing, fishing, or both do occur.
  • Scenario analyses and the corresponding management actions are best applied in an iterative and adaptive process. A diverse cross-section of constituents may be needed to weigh the varied ecosystem values and uses involved in model-based scenario analysis.
  • Single-species MSY policies are unlikely to be sufficient for future management because these measures do not take into account species interactions and food-web effects nor do they consider nonconsumptive ecosystem services.
  • The development of new ecosystem and food-web models will be a highly interactive process that will require input from many disciplines.
  • The shifting baselines phenomenon does occur.
  • Various management institution options are available that change the race-to-fish incentives for fishermen, and encourage stewardship in single-species systems.