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Title: Physical and biological factors affecting the distribution and abundance of juvenile flatfish in Swansea Bay
Author: Mig-Not, J.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1996
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A study of juvenile flatfish was undertaken in Swansea Bay to ascertain the distribution and abundance of plaice, dab, sole, flounder and brill, at five sites, across the Bay and to determine which factors had the greatest influence on the observed distribution. Swansea Bay was found to be a nursery area for 0-group plaice, dab, sole and brill but not for flounder, though these were observed in the freshwater streams draining into the Bay. Food was not considered to be a limiting factor. West Cross, in the more sheltered western part of the Bay was the most diversely and densely populated flatfish site. Partitioning of resources was promoted by the tidal migration used by flounder as a feeding strategy, night feeding of sole and the differing diet of brill from the other flatfish. Panjet dye-marking of the 0-group flatfish, showed no evidence of interchange of flatfish between inshore sample sites, but did show an offshore movement of the older flatfish. Tagging with mini-Petersen discs showed that all the III-group plaice had vacated the Bay, for deeper water. The growth rates and mean length after the first season of growth in plaice and dab were higher in Swansea Bay than in other British flatfish nursery areas, the high summer temperatures of 18-21oC being a contributing factor. A density-dependent effect occurred at West Cross, which was most pronounced when comparing the 1993 and 1994 year classes of plaice, dab and sole. The sedentary polychaete Lanice conchilega was an extremely important food source for 0-group plaice, dab and sole, and the mysid, Schistomysis spiritus for 0-group brill. A significant difference in diet was observed between sites for plaice, sole and flounder. Difference in the diet was significant between age groups of flounder, but all species, at the site where they were most abundant, showed an increase in niche breadth with age. Plaice, dab, sole and flounder were polychaete-crustacean feeders, and the older brill were piscivores.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available