MEPS 257:303-309 (2003)  -  doi:10.3354/meps257303

ABSTRACT: Recently, winter upwelling events off western Iberia have become more frequent. This may affect the production and survival of sardine eggs and larvae through increased offshore transport. By analysis of RNA:DNA ratios, we investigated the impact of winter upwelling events on the larval condition of Sardina pilchardus larvae as a function of oceanographic conditions and food availability. Larvae were collected on a research cruise off northern Portugal in February 2000. Environmental parameters such as wind, water temperature, salinity, microzooplankton biomass and daily egg production of the calanoid copepod Calanus helgolandicus were also measured. The mean RNA:DNA ratios were relatively high, indicating that almost all larvae collected were in good condition. This was in agreement with the high microzooplankton biomass and high daily egg production of the copepod C. helgolandicus recorded during the same period. No adverse effects of upwelling causing offshore transport of larvae into poor feeding areas could be demonstrated because of the presence of a stratified warm plume with consequent high food production.

KEY WORDS: RNA:DNA ratios · Sardina pilchardus · Fish larvae · Microzooplankton biomass · Daily egg production