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Temporal variability in key life history traits of Atlantic herring (Clupea harengus) in the Gulf of Maine
Analysis of otolith, body length, body weight, and gonad weight data from Maine’s Department of Marine Resources fishery dependent Atlantic herring (Clupea harengus) database suggests a downward trend and variation in size-at-age and life history traits of herring in the Gulf of Maine for the years 1978-2011. Modeling was conducted to evaluate the changes in the size-at-age, and the interrelationships between growth and maturation, fitting three models to the herring data. Two models showed an overall decline in life history parameters, however all three revealed substantial variations over time. The Weight-Length model revealed a variable, but overall decline to the allometric factor, along with a narrowing of the weight and length range. Results suggest herring gravitated towards a more attenuated shape and a decrease in the availability of larger and smaller fish. The Von Bertalanffy growth model expressed a variable decline in the maximum attainable length and weight, and omega for both of these growth parameters revealed potential stress on the herring population in 1996. These results support the decrease in size and a declining growth potential. Results from Lysack’s maturation model however, expressed a surprising result. While the length at 50% maturity fluctuated to some degree, overall it revealed a decrease for the available years, but the age at 50% maturity showed an overall increase. The catch depth data of the herring samples showed using the Kruskal-Wallis test, that the mean annual depths were significantly different. Further analysis will be applied to look for spatial trends in the locations of larger sized herring versus smaller, and tests for changes in fishing areas over time to see if this has biased the data. Future analysis will include application of the coefficient of variation and principal component analysis to test the statistical strength of the herring data, and the use of a general additive model to look for links to environmental variables like ocean temperature and salinity
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