The effect of river discharge and winds on the interannual variability of the pink shrimp farfantepenaeus paulensis production in Patos Lagoon

Abstract

The Patos Lagoon estuary is an important environment for the life cycle of many species, including the pink shrimp Farfantepenaeus paulensis. This area acts as a nursery ground for the shrimp larvae, which are spawned in a coastal area and transported into the lagoon during spring and early summer (September to December). Harvesting of shrimp occurs from January to May, and yields have varied from around 1,000 to 8,000 tons year−1. This study is based on analysis of river discharge, pink shrimp catches, and wind velocity time series from 1964 to 2004. Negative correlation between pink shrimp catches and river runoff reflects the influence of discharge on the lagoon circulation and, consequently, on the intrusion of salt water and larvae. When river discharge is below average, landward currents forced by SW winds can enhance larval transport into the estuarine area, leading to an increase in pink shrimp captures. Above average river input would force a seaward flow that works as a barrier to ingress of larvae. This is unusual when compared to many other estuarine systems, and the main factor that accounts for this behavior is the morphology (choking) of Patos Lagoon. Interannual variability related to El Niño/Southern Oscillation events also influence pink shrimp production in this area. Low/high shrimp catches are related to El Niño(flood)/La Niña (drought) events. Wind can also impact production through its effect on the southward displacement of larvae from the spawning area. Long-term trends indicate an increase in river discharge around 20 m3 s−1year−1 and a decrease in shrimp catches on the order of 57 tons year-1.