Genetic attributes unique to the Prince William Sound (PWS) population, that either pre-existed or emerged in the years following the Exxon Valdez oil spill (EVOS), may help explain the lack of recovery in the PWS stock following the 1993 collapse, and may also illuminate the causes of the collapse. Diseases are key variables that help explain the population dynamics of PWS herring since the 1990s decline. The contribution of the EVOS to the PWS decline is more controversial. However, recent studies have shown that herring embryos are sensitive to fitness impacts at very low concentrations of oil, these low-level exposures can affect fitness and natural selection from pollutants can quickly drive complex genetic change in exposed populations. Are there connections that link the PWS herring collapse and lack of recovery with disease impacts and the oil spill?
Conspicuous events that coincided with the dramatic PWS collapse include the Exxon Valdez oil spill four years previous, and the emergence of disease. Researchers test hypotheses concerning the effects of oil exposure, the effects of disease challenge, and their potential interactive effects, on herring health and fitness. Researchers will test predictions and hypotheses by reconstructing genome-wide genetic change through time (over the past 30 years) in PWS fish and compare this to population genetic change through time in two reference site populations (Sitka Sound and Togiak Bay). Furthermore, a series of laboratory-based experiments will test for population differences in their response to oil exposure in early life and subsequent resilience to pathogen exposures. Physiological measurements and patterns of genome-wide gene expression will serve to reveal similarities and differences in mechanisms of response to these stressors between PWS and reference population fish.
To date, the researchers have completed the first draft of a reference genome assembly for Pacific herring. Experimental design and first steps for lab studies involving oil exposure on live herring were developed and are underway. This experiment involved exposing three different populations of Pacific herring to a broad range of low concentrations of oil during development, including populations from Sitka Sound, Prince William Sound, and Puget Sound. The animals from these exposure experiments have hatched and are currently in their grow-out phase. Pathogen exposure experiments with these animals are being conducted early in 2019. These studies should provide novel insights into the causes and consequences of recent dramatic demographic changes in PWS fish, potentially inform novel intervention strategies, and provide modern genomic resources for management and conservation of Pacific herring.