Biological parameters, ecology and population trends of the Mediterranean endemic skate, Raja polystigma, in the Balearic Islands |
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Francesca Ferragut-Perello, Maria Valls, Miquel A. Cortes-Pujol, Sergio Ramirez-Amaro, Beatriz Guijarro, Francesc Ordines |
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Elasmobranchs
are a vulnerable group that has been overexploited for almost half a
century in the Mediterranean. However, few elasmobranch species have
been assessed because information on their basic biological parameters
is lacking for most species. Raja polystigma is a poorly studied
endemic skate in the Mediterranean. The aim of this work is to determine
some basic life history parameters of this skate in the Balearic
Islands. Data were collected from commercial catches and during MEDITS
surveys. Total length varied from 17 to 59 cm for both sexes, with a
higher proportion of females than males. Allometric and morphometric
relationships differed between sexes, females being heavier for a given
size. Females matured at a larger size than males (L50 47.7
cm and 38.4 cm, respectively). Potential fecundity ranged between 11 and
45 yolked oocytes per female, and spawning was observed mainly during
winter and spring. Persistent hotspots of adults and juveniles were
detected on the shallow shelf off the northwest of Mallorca and east of
Menorca, with adults being found mainly in the shallow and juveniles in
deeper areas. Time series of abundance and frequency of appearance
showed stable trends throughout the study period (2003-2018). |
Keywords: speckled ray; biology; reproduction and condition; diet; fecundity; distribution; population indicators; western Mediterranean |
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