Jaime Mendo

Management of the Peruvian bay scallop (Argopecten purpuratus) metapopulation with regard to environmental change

1. This paper sets out to: (1) review previous ecological studies and analyse recent trends of the Peruvian bay scallop fishery in order to better understand and to model the species’ temporal and spatial (meta) population dynamics along the South Pacific coast; (2) develop a fisheries model to protect the stock from overexploitation and optimize the annual yield of the pulse fishery in Independence Bay, the centre of the scallop diving fishery in Peru. 2. Natural stock fluctuations are very pronounced in this species and are positively correlated with the El Nino–Southern Oscillation (ENSO). During such an event, habitat conditions for the Peruvian bay scallop are improved either regionally or locally, such that populations proliferate and larval production and dispersal are greatly increased. Extinct beds and new habitats are recolonized during these periods (producing a strong pulse of metapopulation biomass), although most become extinct very shortly thereafter. 3. For management purposes, two considerations are fundamental: (1) heavy overfishing or extinction of the main scallop source populations would endanger the metapopulation as a whole; (2) rates of growth and survival greatly increase (and with them the potential yield of the scallop stock) locally over an El Nino cycle in a way that can be roughly estimated from past experience, including the most recent El Nino event (1997–1998). 4. We suggest a fisheries management regime capable of adapting to natural changes and propose a procedure for calculating both the optimal yield and the respective fishing effort under normal upwelling and El Nino scenarios, considering changes in the size at first capture (Lc) and fishery mortality (F). Copyright

Population dynamics of the oyster Crassostrea rhizophorae from the Ciénaga Grande de Santa Marta, Colombia

Abstract Growth parameters, instantaneous mortality rates ( Z , F and M ), yield per recruit and biomass per recruit of the oyster Crassostrea rhizophorae were estimated using the FiSAT package, based on shell length frequency data of 2551 individuals. Von Bertalanffy growth parameters and total mortality were estimated using the ELEFAN I program and the catch curve method, respectively. Paulys and M = 2 K empirical equations were used to estimate natural mortality. Values found are L ∞ = 149 mm, K = 0.9 year −1 , φ′ = 4.3 and t 0 = −0.05 year −1 , respectively. Age at entry is too low because of the harvest of small oysters attached to the adults shells. Total, natural and fishing mortalities were estimated at 5.16, 2.0 and 3.16 year −1 , respectively. The exploitation rate (0.6) and fishing mortality indicate that oyster is slightly overexploited due mainly to the harvest method used by fishermen rather than to the increase of effort itself. Yield per recruit could be substantially improved by returning shells to the environment.

Chapter 28 - Scallop Fishery and Culture in Peru

Abstract This chapter discusses the biology, ecology and aquaculture of the scallop, Argopecten purpuratus , in Peru. Of several scallop species, this is the only one exploited and cultured in Peru. During the last three decades, this resource has become one of the most important molluscs in Peru in terms of export value with volume greatly fluctuating since the onset of the export business in the early 1980s. The impact of El Nino on the population of A. purpuratus is discussed by regions in Peru, being favourable in central and southern Peru and detrimental in northern Peru. Conversely, the scallop production in northern Peru is augmented during cold years. Since most of the scallop production is dependent on seed extraction from natural banks, the use of artificial collectors and the production of larvae in hatcheries is proposed and discussed.