Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Parameters
• Instruments
• Deployments
• Project Information
• Program Information
• Funding

GLOBEC 2000: Factors Affecting the Distribution of Juvenile Salmon in the Gulf of Alaska
J. Helle (NMFS/AFSC, Auke Bay Laboratory)
E. D. Cokelet (Pacific Marine Environmentla Laboratory),
E. V. Farley, Jr. (NMFS/AFSC, Auke Bay Laboratory),
A. B. Hollowed (NMFS/AFSC),
P. J. Stabeno (Pacific Marine Environmental Laboratory)

"Remarkable changes in atmospheric, oceanic and biological conditions have occurred in recent decades in the North Pacific Ocean including declines in the marine survival of some salmon stocks. Fishery scientists generally agree that in the first few months after leaving freshwater, salmon survival and growth are linked to oceanic variability. The purpose of this research is to focus National Marine Fisheries Service studies on the GLOBEC region, augment oceanographic measurements and determine what biological and physical factors influence the distribution of juvenile salmon. Three general hypotheses are explored in this proposal: (1) juvenile salmon prefer the buoyancy-driven Alaska Coastal Current (ACC) at the head of the Gulf of Alaska, (2) they associate with oceanic temperature, salinity, current and prey fields, and (3) they migrate landward of Kodiak Island in the ACC rather than seaward in the Alaskan Stream. Annual, summer cruises aboard a chartered fishing vessel will catch juvenile salmon on 10 transects between Yakutat Bay and Kodiak Island. The vessel will be outfitted with a thermosalinograph to measure sea-surface temperature and salinity, and with an Acoustic Doppler Current Profiler (ADCP) - each operating continuously for fine-scale resolution. Modeled tidal currents will be removed from ADCP measurements to reveal the mean flow fields. At each trawl site, temperature and salinity profiles will provide water-column properties, and bongo-net hauls will give zooplankton distributions. Stomach samples from juvenile salmonids will be analyzed in the laboratory for diet composition and compared with zooplankton distributions. Analysis of salmon otoliths for hatchery thermal marks and Genetic Stock Identification techniques will be used to determine the home stream of hatchery and wild stocks in the Gulf of Alaska and their distribution with respect to oceanographic regimes. Retrospective analysis of catch per unit effort versus oceanographic and prey factors will reveal what affects the distribution of pink, chum, coho and sockeye salmon in the study region. Proxies for bio-physical factors will be developed and compared with salmon-run size."(project proposal)

Data Collection Details:
Types: CTD profiles, ADCP profiles of ocean current, juvenile salmonid catch statistics from trawls, salmonid stomach samples analyzed for diet composition, salmonid otolith analyses, Genetic Stock Identification, zooplankton distributions from bongo-net hauls
Platform: Chartered fishing vessel
Spatial extent: 10 transects perpendicular to the coast between Yakutat Bay and Kodiak Island
Temporal extent: ~2 weeks each July-August of 2001-2004.

Fish samples were collected with a 198-m-long mid-water rope trawl with hexagonal mesh wings and body, and a 1.2-cm mesh liner in the codend (Fig. 2, Table 1). The rope trawl was towed at 3.5 to 5 kt, at or near surface, and had a typical spread of 40-m horizontally and 14-m vertically. All tows lasted 30 minutes and covered 1.5 to 2.8 nautical miles. All fish sampling was done during daylight hours. Sometimes this meant that salmon trawls preceded CTD casts. For reference, sunrise occurred at 06:04 ADT and sunset at 22:27 ADT on 1 August 2003 at 58o N. Alaska Daylight Time (ADT) is 8 hours earlier than Greenwich Mean Time (GMT).

Station map from the GP0108 cruise report.

Salmon and other fishes were sorted by species and counted. Standard biological measurements including fork length, body weight and sex. Scale samples from a preferred area (to document age and growth) were taken from subsamples of all salmon species. Subsamples of juvenile pink (Oncorhynchus gorbuscha), chum (O. keta), and sockeye (O. nerka) salmon were frozen whole for laboratory analyses of food habits, otolith hatchery thermal marks (pink and chum salmon), and genetic analysis (chum salmon). Tissues and otoliths were also saved from immature and maturing chum salmon to determine stock distribution and migration of these salmon. All other fish species were counted; juvenile rockfish (Sebastes spp.) and sablefish (Anoplopoma fimbria) were frozen whole for laboratory analyses.

Program in a Nutshell

Goal: To understand the effects of climate variability and climate change on the distribution, abundance and production of marine animals (including commercially important living marine resources) in the eastern North Pacific. To embody this understanding in diagnostic and prognostic ecosystem models, capable of capturing the ecosystem response to major climatic fluctuations.

Approach: To study the effects of past and present climate variability on the population ecology and population dynamics of marine biota and living marine resources, and to use this information as a proxy for how the ecosystems of the eastern North Pacific may respond to future global climate change. The strong temporal variability in the physical and biological signals of the NEP will be used to examine the biophysical mechanisms through which zooplankton and salmon populations respond to physical forcing and biological interactions in the coastal regions of the two gyres. Annual and interannual variability will be studied directly through long-term observations and detailed process studies; variability at longer time scales will be examined through retrospective analysis of directly measured and proxy data. Coupled biophysical models of the ecosystems of these regions will be developed and tested using the process studies and data collected from the long-term observation programs, then further tested and improved by hindcasting selected retrospective data series.

U.S. GLOBEC (GLOBal ocean ECosystems dynamics) is a research program organized by oceanographers and fisheries scientists to address the question of how global climate change may affect the abundance and production of animals in the sea.

The U.S. GLOBEC Program currently had major research efforts underway in the Georges Bank / Northwest Atlantic Region, and the Northeast Pacific (with components in the California Current and in the Coastal Gulf of Alaska). U.S. GLOBEC was a major contributor to International GLOBEC efforts in the Southern Ocean and Western Antarctic Peninsula (WAP).