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Title: Population dynamics of post-larval and juvenile sprat, Sprattus sprattus (L.) and herring, Clupea harengus L.
Author: Matisa, M.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1993
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Morphometric and meristic characters for distinguishing between clupeid fish stocks were examined on specimens of post-larval and juvenile sprat and herring entering the Loughor Estuary. Temperature was the major factor influencing arrival and departure time of sprat and herring to and from the estuary. Their arrival time is species-specific. Post-larval herring arrived during May every year, when most of them had not completed metamorphosis, as compared with sprat, which arrived during July and mostly had completed metamorphosis. A temperature higher than 13oC is favourable for herring and higher than 15oC is favourable for sprat. High catches of both species were obtained at the temperature ranging from 13o to 23.5oC in 1990, 1991 and 1992. Maximum catches of herring occurred in June and July but of sprat from July to August, and extended to October. The catches decreased and ceased altogether during late summer or early autumn when the temperature dropped below 11oC. Sprat overwinter in the Bay, but not as herring. Size distributions of 0-group sprat and herring showed increasing length with one mode, throughout the summer months of 1990, 1991 and 1992. Age, growth and mortality estimations of juvenile sprat and herring were based on micro-structure of the sagittal otoliths. Ring deposition rate in sprat was 0.78 rings/d and in herring 1.1-1.3 rings/d. Growth in the otolith micro-structure of both species was positively influenced by temperatures between 7o and 15oC, and negatively influenced at temperatures higher than 15oC. Growth in weight of juvenile sprat and herring were an allometric function of length. Growth rates estimated from three different models (length-at-capture, daily rings and backcalculated lengths) ranged from 0.05 to 0.36 mm/d in sprat and from 0.22 to 0.46 mm/d in herring. However, the growth rate estimations using different models were significantly different as compared within years.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available