Cost-benefit analysis of ecosystem modeling to support fisheries management.

Mathematical and statistical models underlie many of the world's most important fisheries management decisions. Since the 19th century, difficulty calibrating and fitting such models has been used to justify the selection of simple, stationary, single-species models to aid tactical fisheries management decisions. Whereas these justifications are reasonable, it is imperative that we quantify the value of different levels of model complexity for supporting fisheries management, especially given a changing climate, where old methodologies may no longer perform as well as in the past. Here we argue that cost-benefit analysis is an ideal lens to assess the value of model complexity in fisheries management. While some studies have reported the benefits of model complexity in fisheries, modeling costs are rarely considered. In the absence of cost data in the literature, we report, as a starting point, relative costs of single-species stock assessment and marine ecosystem models from two Australian organizations. We found that costs varied by two orders of magnitude, and that ecosystem model costs increased with model complexity. Using these costs, we walk through a hypothetical example of cost-benefit analysis. The demonstration is intended to catalyze the reporting of modeling costs and benefits.

Growth and survival of Azolla filiculoides in Britain. II. Sexual reproduction.

Sporulation in the floating fern Azolla filiculoides Lam. is both frequent and widespread in Britain and might therefore play a greater part in the population dynamics of the species than has been suggested by earlier reports. In laboratory experiments, increasing plant density and/or phosphorus supply resulted in increased sporulation. It was estimated that a thick mat of 8 kg m2 fresh biomass can produce 380000 microsporocarps and 85000 megasporocarps per m2 . Light and temperatures >10°C were necessary for sporocarp germination. Sporocarps could survive exposure to both low temperatures (5°C for at least 3 months) and sub-zero temperatures (-10°C for at least 18 d). Sporocarps were found to survive storage in water for 3 yr and to germinate from mud samples collected in the field. In laboratory culture, sporeling growth and survival were optimal at 15°C. There is some evidence that A. filiculoides might have adapted to the British climate since its introduction.

Growth and survival of Azolla filiculoides in Britain I. Vegetative production.

Azolla filiculoides Lam. causes serious weed problems in Britain, but its long-term survival might be limited by winter death. The aim of this study was to establish the low temperature responses and limitations of A. filiculoides sporophytes. In the laboratory, normal vegetative growth was shown to continue at 5°C. Reddening of plants was a response to low temperature and high light conditions which could be prevented by shading. Adult plants died after short (18 h) exposure to -4°C but survived sub-zero temperatures >-4°C. Evidence was found of seasonal changes in chill tolerance, but not in freeze tolerance. In outdoor culture, plants survived encasement in ice and air temperatures to -5°C. Additional evidence suggested that natural populations can readily survive air temperatures much lower than this. Microclimatic effects are likely to be responsible for this discrepancy between laboratory and outdoor culture results. Three phenotyes were identified; survival, colonizing and mat forms.