Life History Characteristics, Reproductive Value, and Resilience of Pacific Herring (Clupea harengus pallasi)

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Abstract
The energy supply available for growth and reproduction (surplus energy), fecundity, and egg size increase with female size in British Columbia stocks of Pacific herring (Clupea harengus pallasi). Fecundity is directly proportional to body weight, whereas egg weight is a curvilinear function with a weight exponent of about 0.2. The reproductive rate, defined as the product of fecundity and egg weight, is, therefore, proportional to the 1.2 power of the body weight. In 1974, 1978, and 1980 the size-dependent fecundity and reproductive rates were remarkably constant among management divisions along the coast. There is no evidence at present that these rates respond significantly to natural variations in stock abundance or marine climate, in contrast, there were interannual and regional differences in surplus energy that appeared as differences in the growth rate. Cluster analysis of the average length at ages 3–7 indicated that herring returning to the same division to spawn were more alike than those between divisions. An approximate reproductive value was calculated for the Queen Charlotte Island stock from the foregoing information, assuming that the population was momentarily at equilibrium. For the suspected natural mortality rate (M = 0.45), the maximum reproductive value occurred quite late in the life span: between ages 9 and 10. in other stocks of Pacific and Atlantic herring (Clupea harengus harengus), with adequate time series, the growth rates and hence weight-at-age have increased by as much as 50% in response to a combination of fishing and adverse environmental changes which reduced population size. Concurrently the age at first maturity fell by as much as 2 yr. It is argued that the maximum growth response of a herring population roughly defines its ability to stabilize itself. If the maximum compensatory response is a 50% increase in weight at age, the population should be able to sustain an annual exploitation rate between 0.2 and 0.3. In principle, at this level of harvesting the population will be as resilient to a short run of unfavorable conditions as an unexploited stock

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