Atlantic cod is a major target species for the European fishing fleet. All European cod stocks are under heavy fishing pressure or over-exploited. An effect of over-exploitation is a reduction in average age and size, with an increasing proportion of recruit spawners in the stock. Viability comparisons will be made between and within recruit female spawners and repeat female spawners. The investigation will improve our understanding of the relative importance of individual genetic variation compared to maternal effects on growth and survival of cod, and the result will be incorporated into management models to study how to improve fishery management strategies.
The basis of this project is to follow offspring from selected families of cod reared under identical and semi-natural conditions from hatching, through the larval and juvenile stages, to sexual maturity, and to compare their viability through these stages.
The main objectives are:
1) to examine the viability of offspring from recruit (first-time) female spawners compared to offspring from repeat (older) female spawners in 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 datasets
4) based on the results of the objectives achieved, 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 and 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 the 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:
1) growth (length, weight, otolith microstructure)
2) condition (RNA/DNA of larvae, liver size [index], glycolytic enzymes of juveniles and adults)
3) survival (relative - between groups and individual mother fish - and absolute)
These measures will be taken during the larval and juvenile stages, and until sexual maturity 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 older 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 compositions of cod stocks are influenced by the fishery. If H0a turns out to be false, that is if the maternal effect is of considerable 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 datasets that extend back several decades. This information will be compared with our experimental results, to investigate how the composition of the spawning stock affects recruitment.
Progress to Date
The final reports were submitted to the EU in April 2003.
Based on the present results from two years' experiments in two mesocosms, it can be concluded that there were no clear differences between the offspring of recruit and repeat spawners. However, there were significant differences in the survival and growth rates between offspring of different parents. Differences in growth rate appeared to be related to egg size, with larvae and juveniles from females that produced the largest and most energy-rich eggs having the highest growth rates. However, the spawners used were not representative of a natural population of recruit and repeat spawners, in the sense that the two groups were of similar body size but the eggs were largest in recruit spawners. In a natural population, repeat spawners generally produce larger eggs than recruit spawners. A more detailed discussion of the results, and implications for management, will be given in the final report.
FISHERIES AND AQUACULTURE
Scientist responsible for the project
Dr TERJE SVAASAND
Nordnesgaten 50 Box 1870
Norway - NO
Phone: +47 5523 6891
Fax: +47 5523 6379
||Institute of Marine Research
||01 January 2000
||1 589 578 €
|Total EC contribution
||1 057 102 €
|Web address of the project