Ichthyoplankton sampling design to monitor marine fish populations and communities

The ability to assess, model, predict and manage the impacts of climate change and other anthropogenic stressors on marine ecosystems depends on having adequate ecological time series. Unfortunately the development of ecological time series considerably lags those for the physics and chemistry of the oceans. Ichthyoplankton time series are proposed here to fill this gap in ocean observations. Marine fish species spanning a wide range of families, habitats, feeding guilds, and trophic levels broadcast large numbers of their reproductive products into the open waters. For a limited period, the larvae generally reside in the upper 200 m of the water column, where they may be quantitatively sampled with plankton nets. Larval abundance provides a relative index for adult spawning stock biomass, enabling diverse fish communities to be monitored quantitatively by relatively simple means. Recent analyses of the ichthyoplankton time series extending back to 1951 from the California Cooperative Oceanic Fisheries Investigations (CalCOFI) program indicate that non-commercial as well as commercially-exploited taxa have experienced dramatic change in recent decades. The CalCOFI data set is re-sampled here to show that a reduced sampling program-one based on a few stations along a single transect (cf >50 stations along 6 transects for CalCOFI) or one based on a shorter time series-can, within limits, obtain similar single-species and multivariate patterns of abundance. Ichthyoplankton survey programs may thus provide the basis for a global system of ocean ecological observations in addition to their primary use today for fisheries stock assessment.