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Title: The biology and ecology of elasmobranch fish in the Bristol Channel and Irish Sea with emphasis on their feeding habits
Author: Ellis, J. R.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1995
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Biological observations on the elasmobranch assemblage of the Bristol Channel and Irish Sea have been made. Material was collected for a total of 18 species: Dalatias licha, Squalus acanthias, Squatina squatina, Lamna nasus, Cetorhinus maximus, Scyliorhinus canicula, S.stellaris, M.asterias, M.mustelus, Galeorhinus galeus, Prionace glauca, Raja brachyura, R.clavata, R. fullonica, R.microocellata, R.montagul, R.naevus and Dasyatis pastinaca. Data were most comprehensive for S.canicula, R.clavata and R.microocellata. Various aspects of the biology were studied, including morphometrics, dentition, spiral valves, clasper structure and abnormalities. Data on the population biology was collected, with particular reference to the species composition, length-frequency, sex ratio, distribution, catch per unit effort, growth, liver weight and the length-weight relationship. The reproductive biology of S.canicula was studied. Males and females reached 50% maturity at 52cm respectively. Fecundity increased with size and, from oocyte counts and egg-laying rates, was estimated to be in the range of 26-60 eggs per year. The egg-laying season was protracted and eggs were observed in the oviducts in all months of the year except in August and September. The eggs are deposited on a variety of algae and erect sessile invertebrates. The young hatch at a mean length of 100.5mm and at a mean weight of 3.07g. The major part of the research concentrated on the feeding ecology. The diets have been quantified and diet overlap and diet breadth assessed. Most species had relatively broad diets, although M.asterias and S.squatina appeared to be selective feeders, predating on brachyuran crabs and pleuronectiforms respectively. Most species consumed some commercially important species, however, one of the more important findings is that the Bristol Channel populations of both S.canicula and M.asterias predate heavily on Cancer pagurus.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available