Comparison of spatio-temporal variability in Fulton’s K and RNA:DNA ratio as condition indices of juvenile plaice and dab
De Raedemaecker, F.; Brophy, D.; O’Connor, I. (2011). Comparison of spatio-temporal variability in Fulton’s K and RNA:DNA ratio as condition indices of juvenile plaice and dab, in: 8th International Flatfish Symposium, 5-11 November 2011, Ijmuiden, The Netherlands.
In: (2011). 8th International Flatfish Symposium, 5-11 November 2011, Ijmuiden, The Netherlands. [S.n.]: [s.l.]. , more
The growing importance of defining high quality nursery grounds for juvenile fish as a result of changing nearshore environments has resulted in the use of different indicators for fish condition and growth. This field study aimed to compare and evaluate a morphometric (Fulton’s K condition factor) and biochemical (RNA:DNA ratio) condition index in juvenile flatfish to assess habitat quality in four sandy beach nursery grounds in Galway Bay, Ireland. Juvenile plaice (Pleuronectes platessa), and dab (Limanda limanda) were surveyed monthly from June - September in 2008 and 2009 using a 1.2 m beam trawl. Sediment samples were collected using Van Veen grabs for substrate characterization and physicochemical measures and predator densities were recorded. Gut content analyses revealed recent feeding history of both species. Generalized Additive Modelling (GAM) was used to investigate non-linear relationships between condition indices and habitat characteristics and diet features. The results of the study revealed a lack of correlation between the morphometric and biochemical condition indices of plaice and dab. Fish growth, indicated by RNA:DNA ratios and Fulton’s K, displayed considerable spatio-temporal variability. Site-related patterns in Fulton’s K for plaice and dab were consistent between years whereas RNA:DNA ratios displayed annual and interspecific variability among nursery habitats. This indicates a higher sensitivity of RNA:DNA ratios to short-term environmental fluctuations which is not apparent in Fulton’s K measurements of juvenile flatfish. Density of predators, sediment grain size and salinity were the most important predictors of both condition indices. Diet features did not contribute to the explained variability in the models predicting RNA:DNA ratios whereas certain prey groups significantly improved Fulton’s K of plaice and dab. These findings aid understanding of the biological and physical mechanisms promoting fast growth and high survival which will help to identify high quality nursery areas for juvenile plaice and dab.
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