Completed Manuscript Describing the Simulated Response
of a Pelagic Ecosystem to Climate Forcing

Current Status of Accomplishment or Milestone: Manuscript submitted to the Canadian Journal of Fisheries and Aquatic Sciences (CJFAS) in September, 2002. Comments from referees received in February, 2003, and revised manuscript resubmitted to the Editors in March 2003. Currently, we are waiting for the Editors of CJFAS to indicate whether the manuscript will be accepted for publication.

Background: This manuscript uses a published ecosystem model (Olson and Watters 2003) to consider how physical forcing might affect animals that are targets of or bycatches in pelagic tuna fisheries.

Purpose of Activity/Goal of Project: Inform other researchers about ongoing ecosystem research at the Pacific Fisheries Environmental Laboratory.

Description of Accomplishment and Significant Results: We used a model of the pelagic ecosystem in the eastern tropical Pacific to explore how climate variation at El Niño-Southern Oscillation (ENSO) scales might affect animals at middle and upper trophic levels. We developed two physical-forcing scenarios: 1) physical effects on phytoplankton biomass; and 2) simultaneous physical effects on phytoplankton biomass and predator recruitment. We simulated the effects of climate-anomaly pulses, climate cycles, and global warming. Pulses caused oscillations to propagate through the ecosystem; cycles affected the shapes of these oscillations; and warming caused trends. We concluded that biomass trajectories of single populations at middle and upper trophic levels cannot be used to detect bottom-up effects, that direct physical effects on predator recruitment can be the dominant source of interannual variability in pelagic ecosystems, that such direct effects may dampen top-down control by fisheries, and that predictions about the effects of climate change may be misleading if fishing mortality is not considered. Predictions from ecosystem models are sensitive to the relative strengths of indirect and direct physical effects on middle and upper trophic levels.

Problems: Long delays in receiving comments from the referees and evaluations from the Editors of the CJFAS.

Key Contact: George Watters (831-648-0623, gwatters@pfeg.noaa.gov)