Link between environmental anomalies, growth and condition of pilchard Sardina pilchardus larvae in the northwestern Mediterranean

Abstract

Relationships between environmental factors and the growth and condition of pilchard Sardina pilchardus (Walbaum) larvae were studied in November 1998 in the northwestern Mediterranean(NWM). Long-term growth of fish was assessed using otolith analysis and condition was assessed through histological and biochemical (RNA/DNA) indices. These measurements were conducted on larvae belonging to 2 station groups (A and B) previously defined through principal component analysis (PCA) on 7 environmental variables. Correlations between individual condition indices and environmental values at place of capture were also performed. Condition in environmental group A was significantly higher than in group B as assessed by both histological indices and RNA/DNA. Long-term growth, however, did not differ significantly between groups except for the otolith diameter vs. standard length (SL) relationship. The stations conforming to environmental group A were characterised by environmental ranges that would form a favorable habitat for larval success, including surface temperatures <19°C, relatively low stratification (maximum Brunt Väissälä, B-V, <0.8 cycles h-1) and mean potential food abundance >4500 nauplii(N) m-3 or >5500 of other microzooplankters (T-N) m–3. Apart from the good agreement found between histological and RNA/DNA results, each approach offered different information: histological indices detected the largest portion of unfit larvae at size-ranges ≤8 mm, whereas RNA/DNA best discriminated large larvae. The results from this study support the view that links exist between mesoscale anomalies, spawning intensity and growth or condition of pilchard larvae in the NWM.