Current trends in the assessment and management of stocks

The assessment and management of small pelagic fish (SPF) stocks is particularly difficult and uncertain because their short life expectancy, characteristic aggregative behavior, rapid response to climate and environmental signals and large and variable natural mortality make them less tractable through traditional population dynamic models and assumptions. In this review we summarize the assessment and management approaches applied in 29 SPF stocks or management units (12 anchovy, 10 sardine, 4 herring, and 3 sprat). The review demonstrates that the assessment and management of SPF varies substantially in its approach and performance between stocks and regions. Most stocks have a scientific assessment program in place and a management approach that generally takes into account assessment results, but in some stocks management practices deviate substantially from scientific advice and in some, assessment and management processes are largely disconnected. It is concluded that only properly tailored scientific assessment and management programs can provide the speed of response and the flexibility of management that highly variable SPF demand. The most effective monitoring programs are based on fishery-independent surveys (daily egg production or/and hydroacoustics), while analyses based on catch per unit effort offer limited value. Most assessments, defined as what management uses to base its decisions on, rely on catch-at-age or yield per recruit models. Harvest strategies range from those driven by harvest control rules to those derived from outputs of best assessment runs. Some stocks use operating models based on age-structure model outputs or forward VPA(1). On the issue of scientific uncertainty some practitioners propose reducing it through additional science and measures, while others promote the development of management procedures robust to uncertainty. This difference is particularly evident in relation to the value of recruitment forecasts. Other identified uncertainties include fishing versus natural mortality estimates and fleet catchability estimates. Regarding governance it is suggested that adaptive management practices applied by independent governance structures capable of interacting at ecological, social and economic levels need development for effective stewardship and governance. The review also addresses recent concerns over managing stocks that may be subject to productivity regimes or regime shifts, and whether two-level management strategies are required to address short- and long-term resource variability. The straddling nature of some stocks adds complexity to management procedures, and it is feared that this could be accentuated by climate-driven changes in stock distribution. Finally, SPF should be managed under ecosystem considerations, to protect their value as forage species to other fish, mammals and birds, and thus to respect the integrity of ecosystems. While the Ecosystem Approach is yet to be successfully applied to the management of any SPF, this may be the single most important driving force in influencing future assessment and management policies.