Settlement and Recruitment Processes in Fish Species of Interest for Recreational Fisheries

[eng] The processes that regulate the settlement phase in marine fish species, passing from pelagic larvae to juveniles associated with the benthos, are complex and play a key role in the population dynamics. Examples of these processes are the duration of the pelagic larvae stage, metamorphosis, the orientation towards their adult habitat, adaptation to different predatory field or changes in feeding. While these processes are widely studied in coral reef fishes, knowledge of these early life stages is still scarce for temperate regions. In the Mediterranean Sea, these fish species are subjected to high anthropogenic pressure, either due to pollution, environmental physical alterations or direct exploitation by fishermen. More concretely in the Balearic Islands, Spain, the pressure of recreational fisheries is high enough to be considered as a not negligible stress factor on fish population dynamics and this recreational activity has been steadily increasing for the last years. Furthermore, the recreational fisheries are locally concentrated in areas around towns, normally close to small bays where other environmental stressors are particularly acute. This thesis evaluates some of the effects of this anthropogenic interaction with the fraction of the fish community that is not directly affected by recreational fishing, i.e. recruits or juveniles, through a series of field collected datasets, laboratory experiments and the use of other indirect indicators of fish fitness such as otoliths. In the field based chapters, we first describe the sequential use of Posidonia oceanica seagrass meadows as nursery habitats by a wide range of juvenile fish, and how this transient community has changed in the last half century. A key example is the increase in abundance of juvenile Diplodus annularis in shallow seagrass meadows. We then describe and apply a method based on stereoscopic video-filming to better understand the nursery function of P. oceanica meadows. This work generates new potential for further studies ...