Spatial structure in Pacific sardine stocks
This research exposes bias in current Pacific sardine assessments and develops a spatially structured model that provides more accuracy and points toward changes in harvest rules.
André Punt, University of Washington, School of Aquatic and Fishery Sciences
Kevin Hill, NOAA-NMFS, Southwest Fisheries Science Center
Richard Methot, NOAA Fisheries, Northwest Fisheries Science Center
Using a spatially explicit model based on the 2010 sardine stock assessment, WSG-funded researchers studied the effects on population estimates driven by seasonal migration, spatial recruitment patterns, and the availability of fish-length data. Furthermore, they crosschecked the sensitivity of their findings against the 2011 assessment and acoustic trawl surveys.
The Pacific sardine, one of the most abundant fish species in the California Current, constitutes the second-largest federally managed fishery on the West Coast. Furthermore, this species is an important food source for many valuable and protected species.
Traditionally, sardine stocks have been assessed using a simple model. This has led to biased results. In 2008 the fishing industry challenged the assessments, and the Pacific Fisheries Management Council (PFMC) is now reevaluating its sardine harvest rules. More precise and accurate assessments are urgently needed.
The analyses showed that spatially aggregated stock assessment methods can be biased when populations are spatially structured, especially when temperature affects migration. Results also indicated that a spatially structured assessment method can reduce this bias. Researchers presented their results to the PFMC and are scheduled to lead a discussion of possible adjustments in harvest parameters at an upcoming Council meeting.
This model has been tailored to the Pacific sardine but could be modified to represent almost any mobile coastal fish stock. The simulation framework used to evaluate estimation performance could be easily modified to evaluate harvest control rules.
Kuehne L (2011) West Coast sardines become focus in the science of space. Fishermen’s News. August 2011.