Early Life Survival
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.
Photo Credit: Olav Ormseth
Photo Credit: Olav Ormseth
Regional and 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. The stomach contents of predatory fish are analyzed to document their level of predation on the focal species. Another component of the project (Controlling Mechanisms for Nutrients, Plankton and Larval Fishes) is collecting oceanographic data that will be integrated with the fish data to understand the environmental conditions at the time of sampling.
Acoustic sampling using echosounders provides information about aggregations of fish and zooplankton at depth. Mid-water trawls are used to collect specimens of the fish or zooplankton to determine species composition. Acoustic data provides information about patterns in fish and zooplankton distribution in the water column and may provide clues about the environmental conditions that these species prefer, and where predation is most likely to occur.
The abundance and distribution of seabirds and marine mammals is being documented during offshore cruises as well in order to estimate how these predators may affect the survival of larval groundfish in their first year of life.
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.
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.