Estudio sobre la influencia de los factores de temperatura del agua, dureza del sustrato y abundancia de presas en la distribución espacial de crías de Squatina squatina en su área de cría (playa de Las Teresitas, Tenerife)

Abstract

The angel shark (Squatina squatina) is one of the most endangered species in the world, actually being at the top one hundred (Dulvy et al., 2014), catalogued as critically endangered by the IUCN in 2006. The decline on its population began just over 10 years ago, mainly caused by a large fishing pressure over its original range. Other factors such as habitat loss caused by humans or certain change in some features of their ecology make them even more vulnerable. At present they can only be found in areas of the southern Mediterranean and the Canary Islands. Elasmobranches nursing areas are considered essential habitats for survival ("Essential Fish Habitat" EFH) or critical habitats (Beck et al., 2001). It has recently been discovered that the beach Las Teresitas (Tenerife, Canary Islands) are nursing areas for S. squatina (Escánez et al., 2013) In this project we have studied different factors, both biotic and abiotic, that might be influencing the distribution of juveniles. The aim of this study is to determine if these factors are significantly important and influential in the spatial distribution along the nursery area. Samples have been taken following the seasonal visual census methodology or "fixed point" method (Bortone et al., 1989; Falcon et al., 1996) which consisted on the collection of data of abundance potential prey, the substrate hardness and the water temperature at different distances from where the juvenile shark was. On the one hand, the results and their analysis (Kruskal-Wallis test) for the factors of water temperature and substrate hardness revealed no significant difference, concluding that none of them is decisive in the distribution of juveniles. On the other hand, the analysis of the abundance of prey does not give such a concise answer. Although the Kruskal-Wallis test suggests a non significant difference, several graphical representations of the data show a downward trend in the number of dams with increasing distance to breeding. In addition, this fact seems to be accentuated with high value of abundance of prey (5 or more ind.). These results lead to further discussions as to where new issues can be addressed in the future. Different strategies focused on the methodology used, with modifications and alternatives to continue the research