Life-history traits as growth, age at first maturity, reproduction and condition as well as the size distribution of the commercial and the discarded catch, have been studied for the blue whiting, Micromesistius poutassou, from the NW Mediterranean. This is a species of commercial interest in the area. In the last decade its landings remained at very low levels and the stock has not shown signs of recovery. Samplings were conducted monthly in the northern Catalan coast on board a commercial bottom trawler, from October 2016 to October 2018. The results showed a high variability in the size at age. The size at first maturity was around 18 cm for both sexes that is achieved when the species completes its first year of life, that is, the spawning season following its birth. Females and males showed different growth curves, with females reaching higher sizes than males. From 25 cm TL females became dominant in the population. The readings of lapilli otoliths of very young individuals (from 42 to 87 days old) allowed an accurate estimate of the growth parameters. The diameter of the first annual ring in *Manuscript including abstract Click here to view linked References the sagitta otoliths was defined for the NW Mediterranean (9.8±0.74 mm). The diameter of the observed two false annual rings were also provided. This study has also shown a close relationship between reproduction, condition and stomach fullness trends, which, in turn, have been observed to be related with the changes in the species growth during the year. Finally, the study allowed knowing the very high amount of blue whiting discards. The main component of catches (in numbers) corresponded to discarded individuals, and, in addition, the minimum landing size implemented in the study area is smaller than the size at first maturity.
This study analyses the trophic ecology of the horse mackerel (Trachurus mediterraneus) juveniles associated with two jellyfish species, Rhizostoma pulmo and Cotylorhiza tuberculata, in the NW Mediterranean. The aim was to know whether the natural diet composition of the hosted fish could be influenced by the jellyfish species and to explore if the fish could feed on the host jellyfish. Samplings were carried out off the coast of Barcelona in summer 2011 at depths of up to 10 m. Juveniles associated with C. tuberculata showed a higher feeding incidence and number of ingested prey than those associated with R. pulmo. The relative importance of the different prey varied depending on the jellyfish species with which fish were associated. In juveniles associated with C. tuberculata, the diet was similar to the composition of the ambient zooplankton, with the cladocera Evadne spp. and Calanoida copepods as the most important prey. However, juveniles associated with R. pulmo fed mainly on Calanoida and Harpacticoida copepods. These differences could be related to the depth-associated behaviour of each jellyfish species, with R. pulmo particularly making deeper living plankton accessible to the horse mackerel juveniles. The presence of nematocyst cells in the juvenile gut contents suggests that they fed on the host jellyfish, either directly on the jellyfish tissue or accidentally when they remove the prey captured by the jellyfish oral arms. Our results provide a better understanding of the associations between jellyfish and juvenile fish which can have important effects on fish population dynamics.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.