In the decades prior to 1990 there was a robust Pacific herring population in Prince William Sound. Not only are these forage fish a key link in the complex food web of Prince William Sound, but they supported a lucrative early season commercial fishery that brought the communities of the Sound to life each spring. By 1993, that fishery had been closed and only briefly been reopened for two years. The current approximately 20,000 tonnes biomass is tiny compared to the peak value of 150,000 tonnes or the long-term average of around 65,000 tonnes.
The cause of this dramatic decline in this fishery is still hotly debated. Was it the 1989 Exxon Valdez Oil Spill, disease, climate change, predation, natural cycles, or some combination of these factors? While the question of the reason for the decline remains debated, it is more important to understand what is preventing the herring population from recovering.
Herring is an important source of energy transfer from lower food web levels (phytoplankton and zooplankton) to higher levels, such as birds, fish, whales and sea lions. Herring once supported a lucrative commercial fishery until species numbers declined dramatically in the early nineties. Researchers are working to discover why herring populations have remained low.
The goals of our research programs are to determine what is preventing the recovery of herring in the Sound, and to improve our ability to predict changes in the herring population. Much of our effort has been through two integrated research programs funded by the Exxon Valdez Oil Spill Trustee Council (EVOSTC), which oversees funds from a settlement between State/Federal government and Exxon. The PWS Herring Survey program occurred between 2009 and 2013. The Herring Research and Monitoring program began in 2012 and is continuing. Two draft syntheses have been submitted to EVOS. One was submitted in 2013, and focuses on examining the factors influencing survival in the first year of life of herring. The second was submitted in 2014 and includes lessons learned since 2013 and connects our knowledge of herring to environmental conditions.
Today, researchers from multiple institutions are working to determine why herring populations remain depressed. With funds from the Exxon Valdez Oil Spill Trustee Council, which oversees funds from a settlement between State/Federal government and Exxon, a group of research and monitoring projects were designed to improve predictive models of herring stocks through observations and research. Monitoring efforts include disease prevalence, enhanced adult biomass survey, juvenile biomass index survey,and condition of young of the year herring. A series of process studies will help improve our understanding of individual components of the herring life cycle. These studies include determining the age at first spawn, identifying population genetic structure, analysis of herring scales for growth patterns, intensive surveys of juvenile populations and conditions, analysis of fatty acids to determine migration distances, improving validation of acoustic measurements, disease related studies, acoustic tagging, development of nonlethal sampling methods, modeling of herring populations, data visualization, outreach, and synthesis. This work is complementary to the Gulf Watch Alaska program that examines other important environmental factors in the region. The purpose of this multi-faceted study is to:
The ASA model provides fisheries managers the estimated stock population. The disease and adult biomass surveys are designed to provide additional information to the ASA model. The juvenile biomass and condition surveys will lead to estimates of the number of new fish recruiting to the spawning biomass. We are examining when fish first spawn so the maturation function used by the model can be tested. We will examine the genetic stock structure to determine if there is one stock as assumed. We are also testing the ASA model and examining other stock dynamic models.
A synthesis is required in this program. The data management and visualization project will help gather the required information. Herring scale analysis will provide additional information about the growth of herring that can be connected to environmental conditions.
It is important to ensure we are properly interpreting the measurements we are making. We are conducting intensive sampling of juvenile herring distribution and condition to ensure proper timing of our sampling. Fatty acid analysis provides information on fish movement between sampling events. Acoustic validation efforts are designed to ensure proper interpretation of measurements. We are working to ensure proper timing of disease measurement as well.
Technological advances provide new tools for research and monitoring. We are using new acoustic and optical approaches to determine if they provide a non-lethal approach to sampling the fish. Acoustic tags are being implanted in fish to determine where they go after spawning. Disease research is leading towards the ability to determine populations at risk of disease outbreaks.
We are working to improve the input to the existing ASA model used by fisheries managers, while also conducting research that will lead to either new models or improvements to the existing one. We are ensuring the measurements that are being used are the best for the purpose, and we will continue to improve our efforts as our understanding and technology grows.DOWNLOAD PROJECT SUMMARY