Cause(s) of developmental abnormalities among larvae from Puget Sound's once-largest herring population

Kerry Naish, University of Washington
$40,028

For unknown reasons the biomass of herring at Cherry Point, a region in north Puget Sound that served as spawning shoreline for Washington's once-largest herring stock, has decreased from approximately 15,000 mt in the early 1970s to 800 mt in 2000. We have recently determined that naturally-spawned herring eggs at Cherry Point produce larvae with significantly greater incidences of developmental abnormalities than do those from other populations of herring in Puget Sound. Although it is difficult to determine whether the developmental abnormalities caused, or rather were a consequence of, the biomass decline at Cherry Point, they may adversely affect the survival potential of larvae and prevent the stock from rebounding to healthy levels. We proposed to determine whether these developmental abnormalities result from site-related effects, possibly environmental contaminants, or non-site-related effects, possibly negative genetic consequences associated with a dramatic reduction in the effective population size. Site-related effects will be ascertained by employing a series of in situ herring egg bioassays using gametes from a healthy stock of herring in Puget Sound. Fertilized herring eggs will be incubated at different locations along the Cherry Point shoreline for several days, and then returned to the laboratory. Resulting larvae will be analyzed for developmental abnormalities and compared to larvae from laboratory and field controls. We will also test whether developmental abnormalities in the population have a genetic basis. We will conduct basic common-garden experiments in which reciprocal crosses between artificially spawned larvae from three different stocks will be raised together in the laboratory. The growth and development of within-site lines will be compared with each other and with between-site hybrid lines in attempt to answer two hypotheses. First, that the differences in development rates and birth defects are due to genetic differences between the stocks and second, that an increase in heterozygosity in the hybrid lines will result in a decrease in the observed abnormalities. Results from these experiments may be used for management purposes to possibly 1) prevent similar declines from occurring in other stocks, 2) facilitate recruitment of new cohorts back to the Cherry Point stock and 3) provide baseline data on sustainable genetic effective size thresholds in declining or threatened populations of herring.

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