Rep16 - Bering Sea - Process

## Process-Oriented Studies

The goal of any process study is the development of strong, testable hypotheses and the design of field/laboratory experiments to repudiate these hypotheses. The results of these studies should be used to augment or modify retrospective and monitoring studies, but they also will provide needed input, particularly biological rates, for modeling studies. The development and use of appropriate new technologies (rapid discrete and continuous sampling, and non-invasive techniques such as optical counters, acoustics, and remote sensing) is strongly encouraged and should be incorporated into any field sampling program. Moreover, U.S. GLOBEC encourages coordination with other U.S. and international research programs presently conducting process studies in the Bering Sea to further our advancement of knowledge and avoid duplication of effort.

Process studies should be focused on the key species and factors which lead to the production and control of these species. Process studies will ideally be conducted over several years to examine interannual variability and will include both a Eulerian-frame (fixed grid or moorings) and a Lagrangian-frame (tracking a patch or water parcel) approach.

Field studies will be conducted to examine the processes at the critical periods when they most influence zooplankton production and should occur at the appropriate temporal and spatial scales to elucidate the controlling mechanisms. Process studies fall into two broad space/time categories: small- and meso-scale. Meso-scale (10-100 km) processes include distribution and movements of plankton in relation to features that are stable (fronts) or predictable (eddies, ice extent, "cold pool") from year to year. Variability in large-scale physical forcing may be expected to affect the location and/or intensity of these features in different climatic regimes.

Meso-scale process studies will entail physical measurements from satellites, shore- or ship-based observations, and drifter/mooring-based sensors. Biological observations would involved repeated at-sea sampling or enumeration of zooplankton and their food or predators. Emphasis should be placed at "pulse points" that could be expected to vary the most interannually or in some way reflect the status of the Bering Sea ecosystem.

Small-scale studies (1 m-10 km) will examine elements that affect individual survival including diel vertical migrations, predator-prey interactions, growth, and mortality. These studies should utilize repeated sampling at one location or tracking a population for a period of time to allow continuous or repeat sampling. Some behavioral and physiological components may require controlled experiments using either ships, floating mesocosms, or shore laboratories.

Six cruises are recommended:

1. An early spring cruise (March-April). Process-oriented studies conducted during this cruise will examine meso-scale physical and biological conditions leading to the initiation of the spring bloom, and will provide an estimate of the timing and magnitude of the spring bloom. Vital rates of key primary and secondary producers will be monitored. Moorings and drifters will be deployed.

2. A mid- to late-spring cruise (May). Process-oriented studies will be devoted to studies of small-scale patchiness of zooplankton in relation to physical conditions, food concentrations and predator distributions throughout the diel cycle. Zooplankton collections will be taken during this cruise to examine growth and egg production rates for comparison to available laboratory-derived rates. Comparative samples will be collected inside and outside of the cold pool. Zooplankton food dependencies and feeding rates will also be determined.

3. A broad-scale cruise, conducted in the summer (June-July). This cruise will examine the abundance and distribution patterns of zooplankton in relation to predators and prey. Vertical and horizontal distributions of zooplankton and their predators and prey will be collected. Concurrent measurements of physical conditions will occur using ADCP and CTD casts. In some years cooperation with NMFS may augment this research effort.

4. A cruise dedicated to the main run of Bristol Bay sockeye salmon (end of June). Process-oriented work will focus on the food habits and growth samples of returning salmon in relation to prey availability.

5. Summer predator surveys (June-August). Meso-scale studies of prey selectivity and diel consumption rates of important predators will be examined to estimate predation mortality of the key species. Fine scale studies of the mechanisms attracting or concentrating zooplankton in some areas (fronts, eddies, vertical stratification) will be examined. The impact of large concentrations of predators (schools, flocks) on depleting food resources will be addressed. Regions near the Pribilof Islands are recommended as survey sites to facilitate studies of sea birds and marine mammal food habits. Surveys near Unimak Pass and the outer 200 km shelf/slope are recommended to examine salmon feeding behavior. Secondary study sites could be determined by coordination with the broad-scale cruise.

6. Fall cruise to retrieve moorings and conduct hydrographic surveys.