US GLOBEC Newsletter 14: Coastal Gulf of Alaska

| GLOBEC Studies in the Coastal Gulf of Alaska by Hal Batchelder
Also in This Issue .... LTOP in the NEP Zooplankton in OR Coastal Zone El Niño Affects Marine Nekton GLOBEC Studies in the CGOA GoMex Workshop - Summary Cod & Climate Change Program Notes From the Field .... Sea Scallop Fishery Closures
The U.S. GLOBEC Northeast Pacific Program (NEP) comprises sub-programs in the California Current System (CCS) and in the Coastal Gulf of Alaska (CGOA). The question of phase relationships between the production of marine populations in the CCS and CGOA in relation to climatic forcing is central to the NEP efforts. The NEP program emphasizes studies on the biology and ecology of juvenile salmon, the dominant euphausiids, on several large copepods, and forage fish (salmon prey) in coastal regions of the North Pacific, and how these populations are controlled by physical and biological processes at large- to meso-scales. Process-oriented studies are slated to begin in 2000 in the California Current System (see also USGLOBEC Newsletter 13: Northeast Pacific Program Moves Forward). Process studies in the Coastal Gulf of Alaska are planned to start in 2001. Here, the overall goals of the Coastal Gulf of Alaska studies are described. An announcement of opportunity for U.S. GLOBEC studies in the CGOA will be released this fall. The Northeast Pacific CGOA study will focus on the continental shelf, but - where appropriate - also encompasses the processes and phenomena of the larger oceanic boundary region that affect the CGOA. Process studies in 2001 and 2003 will focus on the effects of nearshore transports and cross-shelf exchange on the population dynamics of the target organisms in the northern Gulf of Alaska. Emphasis is on understanding the conditions that favor rapid growth and survival of juvenile pink salmon, so [the study] will involve examining both bottom up (productivity) and top-down (predation) processes. Where feasible (where timing and geography overlap), parts of the field and LTOP programs may be carried out in coordination with other research programs in the region. Links to other programs currently underway [that have] important connections to GLOBEC goals and objectives are provided in the accompanying sidebar.
On-Line Resources Provided by U.S. GLOBEC and Related Programs in the North Pacific The GLOBEC NEP web site The Pacific Component of Canada GLOBEC The Ocean Carrying Capacity Program of the US National Marine Fisheries Service and the North Pacific Anadromous Fisheries Commission Fisheries Oceanography Coordinated Investigations (FOCI) The North Pacific Marine Science Organization (PICES) Climate Change & Carrying Capacity (CCCC) Program California Cooperative Oceanic Fisheries Investigations (CalCOFI) The Exxon Valdez Oil Spill (EVOS) Trustee Council and SEA Program
U.S. GLOBEC research in the NEP began in 1997, with integrated, multi-investigator, interdisciplinary programs of modeling, retrospective analysis, and pilot-scale monitoring (henceforth referred to as the Long-Term Observation Program or LTOP). Synthesis and new understanding of the large-scale and meso-scale forcing and responses in the NEP ecosystem will require integration of observations, models, and field experiments from the CCS and CGOA; the design of observational programs, experiments, and process studies that will enable such comparisons between these two NEP ecosystems is critical to the success of the overall program. Ultimately, the U.S. GLOBEC effort in the Northeast Pacific has an overall goal of improving predictability and management of living marine resources of the region through improved understanding of ecosystem interactions, and the coupling between the physical environment and living resources. PROGRAM GOALS: The over-arching goals of the Northeast Pacific (NEP) studies are: To determine how biological processes and characteristics of zooplankton populations are affected by mesoscale features and dynamics in the NEP, and To quantify the biological and physical processes that determine growth and survival of juvenile salmon in the coastal zone. Within the overall goals outlined above, the NE Pacific / CGOA process-oriented field program has four general goals: To determine how changing climate, especially its impacts on local wind forcing, freshwater runoff, mixed layer depth, and basin-scale currents, affect spatial and temporal variability in mesoscale circulation and vertical stratification. To quantify how physical features in the Coastal Gulf of Alaska impact zooplankton biomass, production, distribution, and the retention and exchange of zooplankton between coastal regions and oceanic waters, with particular emphasis on the targeted euphausiid and copepod species (see below). In turn, how do the zooplankton distributions influence the distributions of higher trophic level organisms (fish, seabirds, marine mammals)? To quantify the importance of (a) local primary and secondary production, and (b) imported secondary production (e.g., cross-shelf import of large-bodied zooplankton [copepods and euphausiids] from deeper offshore waters in spring) for providing rapid growth and/or high survival of juvenile pink salmon in coastal waters of the Gulf of Alaska. To determine the extent to which high and variable predation mortality on juvenile pink salmon in the coastal region of the Gulf of Alaska is responsible for large interannual variation in adult pink salmon populations, and the factors responsible for the variable predation intensity. Toward these ends, the Northeast Pacific field program has planned two years (2001, 2003) of intensive study in the Coastal Gulf of Alaska. The geographic domain of the study is centered on the coastal shelf region SW of Prince William Sound (off Seward, AK), but generally extends from approximately Shelikof Strait (in the west) to Yakutat Bay (in the east; approx. 143°-155°W). This is a major corridor for juvenile salmon migrations in the CGOA, both for pink salmon exiting from Prince William Sound, and for pink, sockeye and chum salmon from SE Alaska stocks. Three-dimensional mesoscale surveys (via ship, drifter, mooring and satellite observations) and process studies will be conducted over a seven-month period (ca. April - October) in each of the two intensive, process-study years. Mesoscale surveys of physical conditions and biological distributions in spring and fall will augment the less spatially-extensive LTOP observations, which will occur during all years (2001-2004) of the study. The surveys will provide the short-term spatial context for the focused process studies, and will provide 3-dimensional data to supplement the predominantly 2-dimensional LTOP data. Key target species for U.S. GLOBEC process-oriented field studies in the CGOA are euphausiids, calanoid copepods (Neocalanus, Calanus), and juvenile pink salmon. The most abundant euphausiids on the shelf in the Gulf of Alaska are Euphausia pacifica, Thysanoessa spinifera, T. inermis, and T. raschii. Of these, T. inermis is the most abundant in spring and summer, while T. raschii is distributed more inshore. Euphausia pacifica and T. spinifera are also common species in the CCS studies of the NEP, and are important subjects of study for developing comparisons between the two regions. The primary focus of process studies will be on: Physical (e.g., stratification intensity; transport patterns in space and time; effect of freshwater runoff in buoyancy-driven flow; downwelling-favorable winds) and biological (e.g., prey and predator abundance, distributions, and productivity) factors influencing the population dynamics and vital rates of juvenile pink salmon and other target taxa in the coastal region, and The importance of bottom-up (primary and secondary production processes) and top-down (predation) processes in controlling juvenile salmon survival. Physical variability in the marine environment (e.g., number and distribution of fronts, mesoscale eddies, vertical stratification and mixed layer depth) may have an impact on salmon growth and survival through either bottom-up, top-down or both mechanisms simultaneously. Structure of the CGOA Research Program The large range of spatial and temporal scales of important forcing processes and responses in the NEP requires a nested sampling approach (and some associated trade-offs), which is reflected in the descriptions of the LTOP, mesoscale surveys, and process-studies below: Long-Term Observation Programs (LTOP) Long-Term Observation Programs have been established by U.S. GLOBEC at two NEP sites: one along the Gulf of Alaska (GAK) transect extending offshore from Seward, AK, and the second encompassing several offshore extending transects off Newport and Coos Bay, OR, and off Northern California. In both regions, the programs are sampling ocean physics, nutrients, and biology at approximately bimonthly intervals (LTOP projects are described on the NEP web site). Although GLOBEC focuses on zooplankton and juvenile salmon in the NEP, we encourage sampling of phytoplankton, nutrients, and higher trophic levels. The LTOPs provide the fundamental seasonal description of the physical, chemical and biological environment required to complement the mesoscale surveys and process studies. Moreover, U.S. GLOBEC LTOPs, in conjunction with observations at other sites by other programs (Canada GLOBEC, CalCOFI, Ocean Carrying Capacity (OCC), and EVOS) will document the low-frequency, large amplitude signals (e.g., regime shifts, El Niños) that occur at the largest spatial scales in the Pacific. Mesoscale surveys (described below) conducted 2-3 times during spring to fall during process-study years will provide the spatially-resolved 3-dimensional data required to evaluate how well local LTOP data generalize to a broader region. Data from the mesoscale surveys will be used to bridge the gap between the low spatial (2-D), but annual and long-term coverage of the LTOPs, and the intensive, but spatially-limited process-studies. LTOP projects may make use of multi-disciplinary moorings, long-term drifter deployments, and analysis of satellite data, in addition to seasonal ship observations. There is a continuing need for long-term mooring and drifter-based observations and interpretation of regional satellite data, which provide the broadest temporal (moorings, drifters) and spatial (satellites) resolution and coverage. LTOP activities in other regions of the CGOA (e.g., Shelikof Strait or SE Alaska) might be considered if the observations are deemed critical to understanding the connection between large-scale atmospheric and ocean forcing and ecosystem responses, particularly of the target organisms. Three-Dimensional Mesoscale Surveys Ship surveys are needed to determine the distribution and abundance of the target species in relation to their physical and biological environment during the period of euphausiid recruitment and juvenile salmon entry into the ocean, and during the period of possible onshore transport of large, oceanic copepods (March to September). Surveys would be desirable in April (period when large calanoid copepods are advected onshore), July, and September-October. The latter two periods correspond with the anticipated times of juvenile salmon trawling (see following paragraphs). The ship-based mesoscale sampling should encompass the nearshore Alaska Coastal Current region (driven primarily by freshwater input distributed along the coast, along with downwelling-favorable winds), and extend offshore beyond the shelf-edge break, to investigate potential exchanges of shelf and deep ocean waters. High priority will be given to proposals that would survey a region extending from approximately Kodiak Island to Yakutat Bay, i.e., about 500-600 km alongshore, and extending from nearshore to 200-250 km offshore. The fundamental importance of the mesoscale studies is to provide the basis for comparisons of population processes and their coupling to the physical structure and variability of the environment. The mesoscale studies will provide a regional context for the in situ process studies (described below), and provide data for evaluating the environment for juvenile salmon. Mesoscale studies will complement and be complemented by LTOP characterizations and descriptions of the physical and biological conditions of the nearshore and offshore ocean environment. Surveys will provide data required to evaluate coupled circulation-ecosystem models being developed for the NEP study sites, and for assimilation of data into these models. It is anticipated that the mesoscale surveys will be conducted at a given site only in years of process-studies, and that three mesoscale surveys per year focused on critical periods in the life history of the target species (April, July, Sept.-Oct.) will be done. Mesoscale surveys will augment, and must coordinate with LTOP observations and salmon trawling, as appropriate. Trawling and gillnet sampling of juvenile salmon and multifrequency hydroacoustic assessment of both salmon and zooplankton has been conducted in the summers of the past three years as part of a pilot LTOP program on the GAK line. Trawling for juvenile salmon in the broader region described above is a critical addition to the CGOA component of the NEP program, since it will help to identify potentially critical regions supporting the rapid growth and/or high survival of salmon in the coastal corridor. Trawl spatial surveys will document habitat utilization by juvenile salmon, and their competitors and predators, in relation to physical dynamics and structures, and provide samples for dietary and genetic studies. Salmon sampling in this region will complement existing efforts (e.g., Ocean Carrying Capacity coastwide surveys) at larger spatial scales. Sampling is planned at the time of ocean entry of pink salmon from Prince William Sound (July) and at the end of the first summer in the ocean (approx. September-October). These cruises would also collect salmon from other source regions that are transported through the coastal corridor, and will be useful for examining (a) trophic relationships in the nearshore ecosystem, and (b) genetic structure / stock identity of the salmonids. Highest priority will be given to salmon sampling in the field during process-study years, but contingent on the availability of funding and perceived program needs, salmon sampling in "off" years might be supported as well.
Research Questions for Process Studies in the CGOA: What is the time-dependent three-dimensional circulation associated with the buoyancy-driven coastal current, and the fronts associated with this feature in the CGOA ?? How do mesoscale transport processes affect the recruitment, vital rates, and other measures of population dynamics of the target species ?? What are the exchange rates, due to frontal processes, of water properties and the target species between the coastal corridor and offshore waters ?? What are the consequences for individual and population growth rates of these exchanges ?? How do biological and physical processes interact to control cross-shelf exchange of target organisms ?? Does strong seasonal variation in freshwater input and buoyancy-driven nearshore flow cause frontal movement, and what are the effects on the exchange of water and organisms across the fronts ?? How does distribution, growth and survival of juvenile pink salmon (assessed using otolith marked fish) depend on the timing and intensity of cross-shelf import of large zooplankton (e.g., copepods and euphausiids), either directly (as salmon prey) or indirectly (as alternative prey for juvenile salmon predators) ?? How are salmon distributed in relation to mesoscale physical features, and what are the mechanisms responsible for the observed patterns ?? What are the dominant predators, how are they distributed, and what are their feeding rates and impacts on juvenile salmon during the period they transit the coastal zone of the CGOA ??
Process Studies Buoyancy-driven coastal currents, such as the Alaska Coastal Current, are often relatively narrow, fast, seasonal, and typically have a strong front along their seaward edge. Thus, they may act as a rapid conduit for alongcoast flow and as a barrier for cross-shore transport. The conduit along the coast is potentially a major route for many of the salmon stocks entering the ocean in the NEP. Mesoscale features are important to biological processes in many other regions, and the eddies which occur in this region are likely to be important to production processes and in modifying residence times in the CGOA. Detailed investigations of mechanisms linking biological response to physical forcing at the meso- and other scales is the goal of process-study cruises. Specifically, the physical and biological processes that control the population dynamics of the target species will be examined in process studies. Process studies will occur during the spring-setup and productive summer seasons (March - October), preferably in conjunction with other program activities (mesoscale surveys, fish trawling). From previous studies on the ecosystem of Prince William Sound, it is known that many fishes of the pelagic food web (salmon, herring, pollock) rely directly on zooplankton (copepods and euphausiids) and each other as prey. Moreover, there may be ecologically significant indirect effects, such as the import of oceanic zooplankton to the nearshore providing an alternative prey field to otherwise piscivorous species, reducing the mortality on some of the fish species. The continental shelf outside Prince William Sound is identified for detailed process studies because it is a region that has a large influx of hatchery released juvenile pink salmon. The thermal marks carried by these salmon provide advantages in tracking mortality of the juveniles in their first summer nearshore. It is strongly suspected, but not certain, that most of the "surviving" juvenile salmon entering the coastal ocean are swept westward in the general transport of the Alaska Coastal Current. A large fraction of the juvenile salmon do not survive, but the exact agent of their mortality is not known. A goal of the CGOA process studies will be to track the progression of an entering cohort in the western flow, and identify the agents of mortality (starvation, vagrancy, predation by birds, mammals, other fish, etc.). The exchange of physical and biological properties across the frontal zones associated with the coastal buoyancy flows, and downwelling-favorable winds, can influence the supply of nutrients for primary production, the retention (loss) of the target species and their prey in (from) the coastal zone, and interactions between the target species, their prey, and their predators; this will be studied in process-oriented cruises. Cross-frontal exchange is influenced by physical processes which determine the location, deformation, and movement of the front including tides, winds, seasonal heating / cooling, offshore forcing, and freshwater runoff, and by biological characteristics and behavior which may enhance or minimize exchange. Fronts often are regions of aggregation for marine plankton, both because of physical processes such as divergence or convergence and biological responses such as enhanced production or behavior (i.e., depth-keeping swimming). Such aggregations of plankton may provide an enhanced food source for predators, including juvenile salmon. Fine-scale description of the physical and biological fields comprising fronts may reveal aggregations of phytoplankton and zooplankton associated with specific physical (e.g., density, temperature) structures. Determination of the population structure of target organisms within the study area is further identified as an area of critical research. Because of the movement and migratory patterns of juvenile salmon, process studies of pink salmon may require work outside the domain highlighted above, perhaps to regions extending further to the west (beyond Kodiak Island) to ensure success. Proposals that focus on geographical locations outside the principal study area should closely consider the availability of complementary sampling programs to provide a broader geographical context for their studies. Proposers should recognize that process studies that address relevant issues within the specific region described above will have higher funding priority than projects aimed at peripheral goals or targeted at other geographic regions. Proposers seeking additional information concerning related NEP programs should contact the U.S. GLOBEC Northeast Pacific Coordinating Office. Modeling The research conducted during the CGOA study will result in a significant archive of data concerning abundance and distribution of the target species, source regions, vital rates, and trophic interrelationships. Inverse modeling will provide specific estimates of population vital rates. These archives and tools will provide significant opportunities for hypothesis testing concerning biophysical processes. The program is expected to progress toward a data-assimilative capability, wherein LTOP and mesoscale survey data are incorporated into coupled biophysical models. In addition, process-oriented model studies are encouraged. The field research supported by U.S. GLOBEC on euphausiids, copepods, and salmon in the CGOA, together with already funded research in the CCS, provide opportunities for larger (basin) scale modeling of coupled biological / physical dynamics. We are soliciting additional modeling proposals that complement existing projects (described on the GLOBEC NEP web site), that provide additional breadth to the program by examining responses at additional trophic levels, and that explore processes in other targeted regions of the northeast Pacific. Proposals responding to this request for additional modeling activities in the NEP may deal with either the CGOA, the CCS, or both. Priority will be given to projects that complement or significantly augment ongoing modeling efforts - for example, evaluating the impact of other prey (e.g., forage fish) on salmon survival and distribution. Retrospective / Comparative Analyses A number of retrospective projects in the NEP were funded by earlier RFPs (see summaries on the NEP web site). Projects proposing retrospective analysis should document or address population variability of key species (see U.S. GLOBEC Report No. 17) in NEP ecosystems on several different time and space scales. These studies should also examine linkages between physical and biological processes on these different scales. NEP retro-spective analysis should attempt to test the core GLOBEC NEP hypotheses relating to the linkage between climate and ocean variability and population variability. Previous U.S. GLOBEC reports (see especially U.S. GLOBEC Report Nos. 11 and 15) review some of the kinds of data sets and research approaches suitable for examining links between climate variability, ocean physics and marine animal populations in the NEP. Other research approaches and examination of other existing data sets may be appropriate for retrospective analyses provided that they address the critical NEP GLOBEC mandates highlighted above. With the funding of the CGOA field work in this notice, U.S. GLOBEC will have funded ecosystem studies in the Northwest Atlantic (a tidally and event dominated shelf bank), in the California Current (wind-driven upwelling and advective system), and the CGOA (a buoyancy-driven downwelling system). Comparative studies among these coastal ecosystems and with others (Benguela, North Africa, Bering Sea, California Bight, Southern Ocean) across the globe are feasible and could be undertaken. Moreover, recent studies of Calanus in the North Atlantic and of Euphausia superba in the Southern Ocean provide opportunities for broader, global-scale comparisons of biophysical / population dynamics among congeneric systems. This summary of GLOBEC NEP's CGOA research program represents a combined effort. As coordinator of the NEP program, I am grateful to those scientists from academic and government institutions across the U.S. who contributed their expertise and time to the development of the research program for the Northeast Pacific. Last updated: 14 October, 1999 Please address any comments, suggestions or questions to: GLOBEC Webmaster