Sustainable Lobster Fisheries Management: Reproductive Value As a Criteria

The American lobster (Homarus americanus) fishery in Atlantic Canada provides significant economic value, and has long been a mainstay of inshore fishers. In Newfoundland, the industry has undertaken a number of measures aimed at sustainable harvest, notably slot fisheries (adoption of a minimum and a maximum landing sizes), protected areas, and V-notching. We used reproductive value to evaluate the efficacy of these measures.  We estimated age-specific growth and mortality from catch-length data available from commercial fisheries and research surveys, taking into account size selectivity of fishing process.  Then, we combined age-specific mortality, growth rates, and a general size-fecundity model to estimate reproductive value. Reproductive value increased from 14,462 eggs at age of 7 or so, reached a peak of 220,950 eggs at age of 31, and then decreased. On average, an individual from age 21-32 contributes roughly 8 times more to the future generations than early ages. Estimated fishing mortality, F for fully recruited individuals is 0.3. By manipulating F associated with the conservation measures we found that total reproductive value was substantially increased, 32.6% for protected areas, 29.5% for slot fisheries (if maximum legal size = 127mm), and 19.2% for V-notching (if 50% of mature female lobster V-notched) .  Our study provided a framework to estimate age-specific vital rates and reproductive value from catch-length data for species, for which age information cannot be obtained from direct measurement.  Reproductive value, which combines the mortality and fecundity schedule to quantify the value of the individual to the population, can be more suited to evaluation of conservation strategies than standard assessment methods that focus on biomass and economic value.