Environmental and parental influences on the body size of N.E. Atlantic herring, Clupea harengus, larvae.
Morley, S. A. (1998). Environmental and parental influences on the size of herring
larvae. Ph.D. thesis submitted to the University of Liverpool for the degree of Doctor
Investigations were carried out into the effects of mean egg dry weight and
incubation temperature on the size of larvae from four N.E. Atlantic herring stocks
(Buchan, Manx, Clyde and Celtic Sea).
Hatching characterisitics (length, weight and yolk volume) of Buchan, Manx
and Clyde herring were investigated. The time of hatching was inversely related to
incubation temperature, although there was some variation between experiments in
the date of peak hatching. The total length of larvae increased through the hatching
period. In all experiments mean egg dry weight per female was strongly related to the
average length, weight and yolk volume of larvae at hatching. The same regression
model could be applied to all stocks. There were, however, stock-specific responses
of hatching characteristics to incubation temperature although a reduction in length at
hatching at higher temperatures was the most consistent response. Development at
low temperature resulted in a modification of the length-weight relationship; larvae
of the same weight were longer at lower temperatures. Both the increase in length of
larvae during the hatching period and the variation in the timing of peak hatching
have implications for the comparison of larvae hatching at different temperatures.
The otoliths of Manx herring larvae [from "large" (> 0.33mg mean dry
weight) and "small" «0.2Smg mean dry weight) eggs] were marked with either
alizarin complexone or calcein so that larvae from pairs of large and small egg
batches could be reared under identical conditions (at both 10 and I3.S0C) and
relative growth monitored. Within each rearing tank large eggs generally produced
larger larvae at hatch (length and weight) with higher growth rates (both weight and
length specific). There were significant differences both between eggs from different
females and between rearing tanks that confounded the comparisons between rearing
temperatures. Fultons Condition factor is not thought to be a good measure of
nutritional condition of herring larvae smaller than ISmm total length but may be
used as a relative measure of body reserves (ReF) and give an indication of ability to
withstand periods of poor feeding. This is indicated by a period of high mortality of
larvae hatched from small eggs at 10°C, which corresponded with the time period
when these larvae had the lowest body reserves.
Video recording of the foraging behaviour of laboratory reared herring larvae
was used to investigate differences between the feeding strategies of groups of larvae
of the same size but different ages, i.e. fast and slow growers. Slow growing larvae
searched larger areas, thus expending more energy, than fast growing larvae, but
there was no difference in food acquisition. The difference in behaviour tended to
increase through development A simple energetics calculation suggested that
approximately 50% of the difference in growth rate could be explained by the extra
swimming costs of slower growing larvae.
The size of Celtic Sea and Manx herring eggs were experimentally reduced in
order to investigate if the volume of yolk in each egg determines the size of hatching
larvae. Length at hatch was determined by the volume of yolk in each egg but body
weight was not. The development and chemical composition of embryos and larvae
needs to be investigated in a further series of experiments.
All results are discussed in terms of the influence of larval size on survival.