Estimating surplus production and maximum sustainable yield from biomass data when catch and effort time series are not available

In order to describe a simple method of estimating maximum sustainable yield (MSY), we first demonstrate that the parameters of the two well-known surplus production models of Schaefer and Fox can be expressed in terms of fishing mortality that yields maximum sustainable yield (FMSY), annual yield and mean biomass. If FMSY is known, or alternatively, is assumed to be some specified function of a known natural mortality rate, it thereby becomes possible to estimate MSY and describe the surplus production function even when the data are limited to one year of estimates for catch and mean biomass. The method is compared to other simple methods for estimating MSY and its potential application is discussed. (Résumé d'auteur

Oxygen: A Fundamental Property Regulating Pelagic Ecosystem Structure in the Coastal Southeastern Tropical Pacific

Background: In the southeastern tropical Pacific anchovy (Engraulis ringens) and sardine (Sardinops sagax) abundance have recently fluctuated on multidecadal scales and food and temperature have been proposed as the key parameters explaining these changes. However, ecological and paleoecological studies, and the fact that anchovies and sardines are favored differently in other regions, raise questions about the role of temperature. Here we investigate the role of oxygen in structuring fish populations in the Peruvian upwelling ecosystem that has evolved over anoxic conditions and is one of the world's most productive ecosystems in terms of forage fish. This study is particularly relevant given that the distribution of oxygen in the ocean is changing with uncertain consequences. Methodology/Principal Findings: A comprehensive data set is used to show how oxygen concentration and oxycline depth affect the abundance and distribution of pelagic fish. We show that the effects of oxygen on anchovy and sardine are opposite. Anchovy flourishes under relatively low oxygen conditions while sardine avoid periods/areas with low oxygen concentration and restricted habitat. Oxygen consumption, trophic structure and habitat compression play a fundamental role in fish dynamics in this important ecosystem. Conclusions/Significance: For the ocean off Peru we suggest that a key process, the need to breathe, has been neglected previously. Inclusion of this missing piece allows the development of a comprehensive conceptual model of pelagic fish populations and change in an ocean ecosystem impacted by low oxygen. Should current trends in oxygen in the ocean continue similar effects may be evident in other coastal upwelling ecosystems

Illex argentinus

The Argentinean short-finned squid, Illex argentinus, is distributed along the shelf and slope in the western South Atlantic from 22° to 54°S. Since 1977 catches by a local and an international fleet increased by two orders of magnitude from c. 7 000 to > 700 000 t y-l. The species is associated with the Subtropical Convergence of the Brazil and Falkland (Malvinas) Currents. Three or four stocks are identified: the summerspawning stock (SSS), the south patagonic stock (SPS), the Bonaerensis-northpatagonic stock (BNS) and the southern Brazil stock (SBS), which may be a northern continuation of the BNS. Surveys of the shelf and adjacent oceanic waters from 29° to 54°S have covered most of the year. Mature and spawned specimens, and rhynchoteuthion paralarvae of I. argentinus, have been found in summer over the northern Patagonian Shelf and in winter and spring from 29° to 38°S, mainly off the Río de la Plata and along southern Brazil. Evidence suggests that the SPS, which supports the major fishery, makes a spawning migration northward to the confluence of the Brazil and Falkland (Malvinas) Currents, and paralarvae are subsequently carried to the confluence. The life span of I. argentinus is c. one year. Females grow faster and reach a larger size than males, and there is evidence that within a cohort, specimens hatching in warmer conditions have higher overall growth rates. Mantle length at maturity ranges from 142 to 250 mm for males and from 195 to 330 for females. Squid from the SSS are the smallest at maturity and those from the SPS are the largest. Potential fecundity could be as high as 750 000 in the largest females if spawning is intermittent and all eggs that attain a major axis of >0.05 mm at first maturity undergo complete vitellogenesis and are released. Crustacea are the major prey of I. argentinus in the southern part of the species range and fish increase in importance towards the north. It is preyed on by the most abundant demersal fishes of the patagonian Shelf. Off Argentina and Uruguay Merluccius hubbsi is a major competitor with I. argentinus for Engraulis anchoita as well as being predator and prey at different ontogenetic stages. In southern Brazil it is preyed upon by various species of tuna and the serranid Polyprion americanus. Future research should focus on the biology of the early ontogenetic stages, on gene flow among stocks and on the impact of the fishery for I. argentinus on other commercial species

The northern Humboldt Current System: Brief history, present status and a view towards the future

Support for the conference, the special issue and this paper came from the Institut de Recherche pour le Développement (IRD), the Instituto del Mar del Perú (IMARPE), the Food and Agriculture Organisation of the United Nations (FAO), the International Council for the Exploration of the Sea (ICES), the North Pacific Marine Science Organization (PICES), the Global Ocean Ecosystem Dynamics (GLOBEC) program, the Integrated Marine Biogeochemistry and Ecosystem Research (IMBER) program, the European network of excellence EUR-OCEAN, the Centre National d’Etudes Spatiales (CNES, France), the Peruvian Consejo Nacional de Ciencia, Tecnología e Innovación Tecnológica (CONCYTEC), the French Ministère des Affaires Étrangères (MAE), the French Embassy in Peru, and the Alliance Française of Lima, the National Aeronautics and Space Administration (NASA, USA), and the David and Lucile Packard Foundation. The 300 participants in the conference are warmly thanked as are the large number of reviewers. J.T. Pennington served as the copy editor and Shannon Boedecker supported the editorial office. Figures in this paper were prepared by Dorota Kolber and Reiko Michisaki.Consejo Nacional de Ciencia, Tecnología e Innovación Tecnológica - Concyte