Overview
This aspect of the project is testing the central hypothesis that early life survival is the primary factor that determines the year-class strength of marine groundfishes in the Gulf of Alaska. This project focuses on five commercially and ecologically important groundfish species: Pacific cod, pollock, Pacific ocean perch, sablefish, and arrowtooth flounder. Year-class strength determines how many adult fish are available for commercial fisheries, therefore the results of this project are important to fisheries managers and Alaska’s economy.
Surviving the gauntlet
The “gauntlet” refers to the obstacle course that fish swim during their first year of life as they attempt to travel from offshore areas where they are spawned to nearshore nursery areas. Factors that may affect their survival include habitat quality both offshore and nearshore (for example, water temperature, salinity), the strength and direction of the currents, and whether or not they settle into nursery areas that are suitable for them.
Regional & Seasonal Comparisons
This project compares the central Gulf of Alaska (Kenai peninsula and Kodiak Island area) to Southeast Alaska because these regions differ from one another, and examining these differences may provide clues about why certain species survive better in one area over another. The central Gulf of Alaska has a broad continental shelf, a high degree of oceanographic variability, and large demersal fish biomass. Southeast Alaska has a much narrower continental shelf, lower demersal fish biomass, and higher species diversity.
The project is also examining seasonal differences in the factors that affect fish survival. Field sampling is conducted in spring, summer, and fall in all regions. The physical and biological characteristics of the Gulf of Alaska change between seasons, and these seasonal differences may affect fish survival and recruitment.
Data Collection & Sampling
Samples are collected both offshore and in nearshore bays in both of the regions described above. Samples are also collected in the area of the Gulf of Alaska that lies between these two regions, near Kayak Island and Yakutat. To see maps of the sampling sites, please visit the Study Region page under the About the Project menu.
The Surviving the Gauntlet component of the project is primarily collecting fish samples offshore. Samples of the larval fish that are the main focus of this study are collected, and juvenile and adult fish are being collected as well to better understand the abundance and distribution of marine predators that may eat the focal fish during their first year of life. Read More
Fish Bioenergetics
Some of the fish collected offshore are being brought back to the NOAA Auke Bay Lab so that bioenergetics studies can be done on them. These studies attempt to understand how much food a fish needs in order to survive and how growth rates change based on available prey. This information will help the modeling team to build models that accurately simulate fish growth rates and calculate their chances of survival.
Fish Habitat
In order to determine if fish are likely to settle in suitable nursery areas, the scientists need information about the habitat characteristics of potential nursery areas. They have been compiling information about habitat characteristics in nearshore bays along the Gulf of Alaska coast. This is important because fish species have different habitat type preferences. For example, some fish may survive best in rocky areas while others will survive better where they can hide among seagrasses.
The modeling team needs to know how much of each habitat type is available in each area in order to estimate the probability that fish will settle in areas that are suitable for them. Their oceanographic models will simulate how many fish of each species will be transported to a given area, and the habitat information will be used to estimate how many fish are likely to survive there.
Overview
This aspect of the project focuses on the physical and biological oceanography that influences the survival of the five focal groundfish species (Pacific cod, pollock, Pacific ocean perch, sablefish, and arrowtooth flounder) during their first year of life. Oceanographers are testing the hypothesis that cross-shelf and along-shelf transport of nutrients and plankton differs in the central and southeast Gulf of Alaska and that the mechanisms controlling primary production differ as a result. They are also testing the hypothesis that the food webs leading to larval and juvenile fish differ between these regions.
Cross-shelf transport
Cross-shelf transport is the process by which nutrient-rich water from the deep ocean basin is carried by currents or upwelling into the shallower waters over the continental shelf. Nutrients collect in deeper waters when organisms die and sink to the sea floor. When they are brought up into shallower waters, nutrients act as the fertilizer that planktonic algae need to grow. When these planktonic plants are exposed to sunlight in the presence of nutrients, they can grow very quickly in what is known as a plankton bloom and form the base of the marine food web. This project will contribute to our understanding of the processes controlling when and where these blooms occur and how that influences the food web in the Gulf of Alaska.
Along-Shelf Transport
Along-shelf transport is the movement of water along the coast over the continental shelf. In the Gulf of Alaska, coastal water typically flows counter-clockwise, northward along the coast of Southeast Alaska, westward along the central Gulf of Alaska coast, and southwest as it moves past Kodiak Island toward the Aleutian Island chain. This project is describing this movement of water and how it changes both seasonally and inter-annually to better understand how currents may affect the transport of zooplankton and larval fish from their offshore spawning areas to nearshore nursery areas. It is also providing information about the transport of iron, zooplankton, and fish off of the continental shelf into the deeper waters of the basin.
Data Collection & Sampling
Iron sampling is conducted aboard the oceanographic vessels as well. Iron is necessary for primary production to occur, and iron is typically input into coastal Gulf of Alaska waters via terrestrial freshwater runoff. Understanding the processes that concentrate iron in the ocean, such as eddies (circular currents), will further our understanding of primary production and allow us to better predict when and where plankton blooms are likely to occur.
Satellite-tracked drifters are deployed from the oceanographic vessels to illustrate the actual movement of water around the Gulf of Alaska. Researchers watch the movement of these drifters over time to learn about the passive transport of larval fish and how their trajectories may change based on climatic conditions. Read More
Overview
Ecosystem modeling is being used to determine which environmental conditions have the greatest effect on the survival of the five groundfish species that are the focus of this study (walleye pollock, Pacific cod, Pacific ocean perch, sablefish and arrowtooth flounder). A series of models is used to examine the effects of oceanography, current patterns, nutrient availability, food availability, predator interactions, and various combinations of these factors on how these fish survive under different conditions. This information will help managers to predict fish survival and therefore predict more accurately the number of fish that should be available to support the ecosystem and commercial fisheries in the future. Historic data is used to develop the models and field data provides information about current conditions and is used to test the predictive power of the models.
Oceanographic Models
Regional Oceanographic Modeling Systems (ROMS) are used to model the oceanography that transports larval fish from areas offshore where they were spawned to nearshore nursery areas. Factors like water temperature, salinity, wind, and current patterns determine if fish are transported to appropriate nursery areas and how they grow and survive.
Nutrient Phytoplankton Zooplankton (NPZ) Models
Nutrient Phytoplankton Zooplankton (NPZ) models examine the effects of varying levels of nutrients, phytoplankton, and zooplankton in the water column, which provides information on the productivity of the system, and the availability of prey, under different environmental conditions.
Individual Based Models (IBM)
Individual Based Models (IBM) developed for each of the five focal groundfish species provide information about the basic life history and behavior of these fish as they grow from eggs to larvae and juveniles and are transported from spawning to nursery areas. Information about the typical depth at which the fish spend time during a given life stage, and the time that elapses between stages, is included the models. The IBM, NPZ, and ROMS models are nested so that the oceanography determines the location of a given fish at a particular time, the NPZ model determines the productivity at that location, and the IBM determines if the habitat is suitable for the fish during that stage of its life cycle. The combination of these environmental conditions determines fish survival.
Overview
Retrospective analyses allow us to put the data collected during this short-term study into context by examining patterns in historical data collected over the past few decades. Examining long-term patterns allows us to ask informed questions about the possible environmental drivers of fish survival and recruitment in the Gulf of Alaska.
Further Details
Studying patterns in data collected in the same manner over long periods of time (called time-series) allows us to see how much things typically change over time and also allows us to identify points in time when changes are out of the ordinary. For example, natural variability may cause a measurement like water temperature to be a little higher in some years and a little lower in other years, and that variation may not be enough to cause effects on fish survival. We need to know how much change is natural in order to identify years when changes are extreme. If we can identify extreme years, we may be able to find a link to fish survival. Ultimately we are trying to identify a few environmental measurements that can be monitored to predict fish recruitment, which allows scientists to better predict future abundances and managers to set more appropriate quotas for fisheries. Read More
Overview
This component of the project is testing several hypotheses about forage fish in the Gulf of Alaska and the role that they may play in affecting the survival of the five focal groundfish species during their first year of life. Forage fish are the fish that many large fish, seabirds, and marine mammals eat. They include fish like herring, capelin, and sandlance that do not grow to large sizes as adults. Forage fish also include the juvenile stages of larger fish, including the five focal groundfish species.
Forage fish may eat the eggs and larval stages of the groundfish that are the focus of the Gulf of Alaska Project. Forage fish often congregate in nearshore bays, and most of the sampling for this part of the project is conducted in coastal bays. In the central Gulf of Alaska samples are collected in Kiliuda Bay, Izhut Bay, Barren Islands, Chugach Bay, Port Dick, and Aialik Bay. In southeast Alaska sampling is conducted in Torch Bay, Islas Bay, Salisbury Sound, Shelikof Bay, St. Lazaria, and Whale Bay. (To see the locations of these bays on a map, please visit the Study Region page under About the Project.) Field sampling is conducted in spring, summer, and fall to examine seasonal differences.
Hypotheses
- Variability in forage fish populations is driven by climate and the availability of plankton prey.
- Physical and biological oceanographic conditions regulate forage fish populations throughout the Gulf of Alaska and the mechanisms vary by region.
- The habitat needs of fishes vary with life stage and season, leading to variability in interspecies interactions.
- Competition among species results in reduced nutritional condition for all species, especially in areas or at times when prey availability is low.
Data Collection & Sampling
Fish sampling is conducted in a variety of ways, including beach seining, beam trawling, jigging, and collecting underwater video footage. Acoustic sampling is conducted in deeper waters of the bays to document fish and zooplankton aggregations at depth.
Diet studies are being conducted on some of the sampled fish to describe the relationships among forage fish community members, their prey such as zooplankton, and predators higher up the food chain. Several methods are being used for these diet analyses, including stomach content, stable isotope and fatty acid analyses. The nutritional condition of forage fish community members is also being examined.
Spatial and Temporal Comparisons
This project compares forage fish communities in both space and time. Spatial comparisons are done by region (central vs. southeast Gulf of Alaska), and habitat type (water characteristics, wave action, bottom type, vegetation, predators). Temporal variability is compared interannually and on decadal time scales as well as seasonally. Seasonal comparisons examine differences between spring, summer, and fall seasons, and also biologically-important factors such as community structure and behavior (e.g., spawning periods).
