Growth processes in the two Scottish populations of powan, Coregonus lavaretus (L.) (Eateleosteia, Salmonidae)
Abstract
The powan, Coregonus lavaretus (L.) is endemic to only two
British waters, Loch Lomond and Loch Eck, Scotland. This
thesis describes the seasonal and longer term growth
processes of the two populations, concentrating on growth in
length back-calculated from scales, factors affecting
recruitment and mortality, reproductive cycles, and seasonal
deposition and mobilisation of storage products,
particularly lipid. The interrelationships of these cycles
is discussed. The populations differ in their diet and
duration of feeding, and it is shown that most of the inter-population differences in seasonal cycles of growth relate
to these feeding differences. The Loch Eck population is the
more variable. In addition to adult and immature powan, a
third category is identified, termed adolescents. These are
fish which are entering their first reproductive cycle.
Immature and adolescent fish are analysed separately and
compared with the adults. There are some differences in
seasonal cycles between the juveniles and adults, mainly in
relation to the presence or absence of the reproductive
cycle. A preliminary histological study of the ovaries of
adolescent females is carried out. Comparison of historical
data with the results of the present study shows that there
has been little change in the Loch Lomond powan in the past
200 years. Both lochs are coming under increasing human
pressure, and conservational measures urgently need to be
taken if the powan populations are to survive.
Type
Thesis, PhD Doctor of Philosophy
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