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.
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.
Courtesy: Jamal Moss
Data Collection and Sampling
Field sampling for this aspect of the project involves sampling fish in the nearshore bays listed above to describe the forage fish community structure. Basic oceanographic information is collected at the same time, and that allows analysis of how the fish community varies with changing environmental conditions. The scientists note the habitat type in each area where sampling is conducted and look for patterns in the habitat associations of the different fish species. Knowledge of the degree of overlap in habitat type preferences among fish species will allow the researchers to analyze how the habitat needs of fish influence their spatial distribution and potentially lead to competition or predation.
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.
Photo Credit: Ashley Hovis
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).