The natural rate of lipofuscin accumulation in an eyestalk ganglion was determined from microtagged European lobsters, Homarus gammarus, of known age, recaptured from the Yorkshire fishery (United Kingdom). This calibration, in combination with supporting data from shorter-lived astacideans (freshwater crayfish), was used to age wild lobsters from the fishery. A unique perspective of age-at-size in a clawed-lobster population was obtained, which circumvented some difficulties associated with conventional methods for estimating generalized growth and natural mortality. The exceptional ages attained by some of the largest lobsters (males: average 31 years, maximum 42 ± 5 years; females: average 54 years, maximum 72 ± 9 years) are explained by ageing theory, indicate natural mortality rates, M, of 0.15 and 0.08 for males and females, respectively, and point to the existence of an offshore refuge. Age-at-size is highly variable: at least seven year-classes enter the fishery at 85 mm carapace length. This limits resolution of annual cohorts in size compositions, complicates development of recruitment indices, and may explain past size composition stability. The new age-length data suggest potential selective fishing impacts and past early recruitment variations. The study highlights the need for age data in order to obtain accurate crustacean stock assessments.
As a discipline, marine historical ecology (MHE) has contributed significantly to our understanding of the past state of the marine environment when levels of human impact were often very different from those today. What is less widely known is that insights from MHE have made headway into being applied within the context of present-day and long-term management and policy. This study draws attention to the applied value of MHE. We demonstrate that a broad knowledge base exists with potential for management application and advice, including the development of baselines and reference levels. Using a number of case studies from around the world, we showcase the value of historical ecology in understanding change and emphasize how it either has already informed management or has the potential to do so soon. We discuss these case studies in a context of the science–policy interface around six themes that are frequently targeted by current marine and maritime policies: climate change, biodiversity conservation, ecosystem structure, habitat integrity, food security, and human governance. We encourage science–policy bodies to actively engage with contributions from MHE, as well-informed policy decisions need to be framed within the context of historical reference points and past resource or ecosystem changes.
Historically, hatcheries in Europe and North America attempted to contribute to the conservation and enhancement of clawed lobster stocks, but lacked monitoring programmes capable of assessing success. In the 1990s, this perspective was changed by the results of restocking and stock enhancement experiments that inserted microwire tags into hatchery-reared juvenile European lobsters (Homarus gammarus) before release. This allowed recapture in sufficient numbers to prove that lobsters had survived and recruited to the mature fishable stock. However, evidence of recruitment still failed to answer key questions about the ultimate ecological and economic benefits. As a result, a growing number of lobster stocking ventures remain hindered by a lack of clear evidence of the effects of their stocking schemes. This review evaluates these experiments and related studies on other fished species, summarizes key findings, and identifies data and knowledge gaps. Although studies of fitness in cultured lobsters provide some of the most encouraging results from the wider field of hatchery-based stocking, the limitations of physical tagging technology have significantly hindered appraisals of stocking impacts. We lack basic knowledge of lobster ecology and population dynamics, especially among prerecruits, and of the impact of stocking on wild lobster population genetics. We advocate the use of genetic methods to further our understanding of population structure, rearing processes, and stocking success. We also recommend that more focused and comprehensive impact assessments are required to provide a robust endorsement or rejection of stocking as a viable tool for the sustainable management of lobster fisheries.
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