Validated sampling, measuring and ageing techniques were developed to facilitate a study of the population dynamics of larval and young-of-the-year juvenile bass. Drag seines were proven non size-selective when used for sampling juveniles. Repeated measurements of larvae and juveniles, following death and during preservation, indicated that their lengths decreased. Accordingly, conversion factors were calculated to permit live lengths to be determined from measurements of preserved length. Bass eggs were incubated from fertilization at 15 temperatures from 6.8-20.6<SUP>o</SUP>C, and a system to age eggs by reference to developmental stage and temperature was developed. Laboratory reared bass larvae, exposed to temperature and photoperiod regimes similar to those encountered by wild larvae, deposited growth increments on their sagittal otoliths at a rate not significantly different from one per day following mouth opening. In order to permit egg fertilization (birth) dates to be back-calculated from increment counts, relationships between environmental temperature and the time from fertilization to mouth opening were determined experimentally. Larvae, of 5.0-11.0 mm notocord length and 10-45 days old, were captured during ichthyoplankton surveys in the Bristol Channel in May 1989. Their distribution and growth was reported, and hypotheses for their recruitment to estuarine nursery habitats proposed. Back-calculated birth dates of juveniles recruiting to three sites in South Wales during 1988 and 1989 were not significantly different, suggesting they originated from the same larval populations. Growth rates at different sites, and for cohorts at the same site but with early, mid or late season birth dates were rarely significantly different in 1988 or 1989. However, comparison on growth in 1988 and 1989 indicated that it was significantly faster at all sites in 1989. This was attributed to consistently higher water temperatures in 1989. The effects of birth date and growth rate on subsequent overwintering mortality were discussed.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:637424 |
| Date | January 1991 |
| Creators | Jennings, S. |
| Publisher | Swansea University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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