MEPS 223:243-250 (2001)  -  doi:10.3354/meps223243

ABSTRACT: The aim of this study was to determine how climatic (North Atlantic Oscillation winter index, NAO, December through March), oceanographic (upwelling intensity, turbulence, water column stability and larval offshore transport) and biotic (adult abundance) factors affect recruitment success of Sardina pilchardus off the northwest coast of the Iberian peninsula. Annual sardine juvenile landings in the port of Vigo (Spain) from 1980 to 2000 were used as an indicator of sardine recruitment success. Ekman transport along the x-axis (Q_x) in February (Q_xF), from March to April (Q_xMA), from May to August over the preceding year (Q_xMJJA), and NAO explained 86% of the variance observed in catches of sardine juveniles. Due to the north-south orientation of the west coast of the Iberian peninsula, upwelling intensity and larval drift offshore are higher the lower the Q_x. Landings of sardine juveniles were higher in those years with moderate Q_xF, high Q_xMA, low Q_xMJJA and low NAO values. There was a dome-shaped relationship between sardine juvenile landings and Q_xF. Under both high and low Q_x conditions, the upper layer is strongly mixed. Therefore, the reduced recruitment success observed at both high and low Q_xF values could be due to a stratified upper layer in February enhancing primary production during the spring bloom and, hence, larval food availability. As March and April are the main spawning periods for sardine in this area, the reduced sardine recruitment success observed as Q_xMA decreased was probably due to the transport offshore of eggs and larvae. In this area the main upwelling season is from May to August. Therefore, the positive relationship between upwelling intensity from May to August and nutrient concentration in surface layers could explain why landings of sardine were higher when Q_xMJJA over the preceding year was lower. Finally, in years with low NAO sardine recruitment success was higher. When NAO is lower than average, the winter/spring temperatures are warmer and transport offshore is lower.

KEY WORDS: Sardine · Recruitment success · Larval transport offshore · Upwelling · NAO · Water column stability · Turbulence