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Size-spectra and assemblage traits of Mediterranean fish around settlement: a comparison of 6 sampling techniques

AutorDunand, A.
DirectorCatalán, Ignacio Alberto
Palabras claveSampling
Fish Larvae
Fecha de publicación12-dic-2012
EditorCSIC-UIB - Instituto Mediterráneo de Estudios Avanzados (IMEDEA)
Universidad de las Islas Baleares
ResumenSettlement is a process through which demersal littoral fishes go from a planktonic stage to a benthonic stage. Understanding this process is fundamental in order to evaluate recruitment processes and population dynamics. The analysis of settlement (pre-settlement phases including the pelagic stages that are about to migrate to the bottom, and post-settlement phases that have already been recruited to the bottom but don’t usually appear in conventional fishing gears) is rare in the Mediterranean Sea and data exist only for few species within the frame of very specific objectives. Locating settlement pulses is key to understand connectivity patterns and to spatially delimit/evaluate MPAs. Sampling of these phases requires specific methods whose design is more developed for tropical environments than temperate latitudes. In addition, pre-settled individuals often escape conventional plankton nets, making it necessary to develop innovative methods of sampling. The objective of this study was to compare six different methods of sampling in terms of species composition, capture efficiency, size-spectra and abundance in order to determine the best combination of techniques to assess settlement processes in temperate littoral species. We used three types of pelagic nets (bongo 40, beam trawl and WP2 ring of 80 cm) and two types of light traps (Quatrefoil and Ecocean C.A.R.E) to sample pre-settled individuals whilst a type of beam trawl of low impact for the bottom was evaluated to catch post-settled individuals. We obtained at least three replicates per sampling gear for each of two nights in May and June 2012, during the peak of the spawning season for summer species. Sampling was conducted in the Bay of Palma, characterized by large littoral fish populations and known to be an area of both high selfrecruitment (Basterretxea et al. 2012) and high recreational fishing pressure (Morales-Nin et al.2010). Individuals were identified and measured to the nearest 0.1 mm (SL). Our results show significantly different size-spectrum for each method, with a continuum of sizes from 2mm to 200mm SL with the smallest sizes taken by the bongo, followed by the ring net, the neuston net, the quatrefoil, the Ecocean and finally the beam trawl. Consistent differences were found in the two sampling periods. In general, the pelagic nets collected high abundance of presettlement stages, the light-traps caught post-larval stages about to settle, and the beam trawl sampled mainly larger juveniles but also recent settlers of key littoral species. These results prove that an optimal strategy for sampling key littoral species around settlement is possible by selecting the Ecocean C.A.R.E. for pre-settlers and beam trawl for post-settlers, which should guarantee further insight into recruitment processes in littoral fishes of temperate water.
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