The main objectives
are:
1. To examine the viability of offspring from
recruit (first-time) female spawners compared to offspring from repeat (elder)
female spawners of Atlantic cod.
2. To examine variations in viability between
offspring of individual pairs of cod.
3. To analyse the demographic structure (age-,
sex- and maturity structure) of selected European cod stocks by means of
historical data sets.
4. Based on the results of objectives 1., 2. and
3., to evaluate the possible effects on
cod recruitment and implications for fishery management.
The first two points will be examined by
employing rearing experiments in large marine enclosures (mesocosms: 2500 &
4400 m3), and comparing measures of viability between individual
offspring originating from first-time and second-time spawning females. Such
differences will be compared with variation that occurs between parents within
each group.
Our null hypotheses
are:
1. H0A:
There is no difference in viability between the offspring of recruit and repeat spawners
2. H0B:
There is no difference in viability between the offspring of different
individual parents within each group.
The major viability measures are:
·
growth (length,
weight, otolith microstructure)
·
condition
(RNA/DNA of larvae, liver size (index), glycolytic enzymes of juveniles and
adults)
·
survival
(relative – between groups and individual mother fish, and absolute)
These measures will be
taken during the larval and juvenile stages, and until sexual maturation has
been reached. In addition, the fecundity and egg quality (dry weight,
fertilisation rate, energy content, fatty acid content) of each female will be
studied. The parental identity of offspring will be ascertained using DNA
microsatellite markers, which make it possible to link individual fish, sampled
at any stage in their lifespan, to their parents. The influence of the father
(the paternal effect) will be standardised by using elder males in both groups.
The investigation will improve our
understanding of the relative importance of individual genetic variation,
compared to maternal effects (recruit vs. repeat female spawners), on the
growth and survival of cod in the wild (and in aquaculture).
The size and age composition of cod stocks are
influenced by the fishery. If H0A turns out to be false, that is, if
the maternal effect is of significant importance; this information will
probably have significant implications for fishery management. We will examine
the demographic structure of selected European cod stocks, in particular sexual
differences in age, size and maturity in the spawning stock, by analysing data
sets that extend back several decades in history. This information will be
compared with our experimental results, to investigate how the composition of
the spawning stock affects recruitment. The results will be incorporated into
management models to study how they can be used to improve fishery management
strategies.