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|Posted: Tue Jan 18, 2011 2:55 am Post subject:
|good points allrounder!
Surley the fact is, that there are not enough bigger fish left to be caught to make it worthwhile the skippers going out? this leads us to a negative loop where smaller fish are being landed as you said, before they have had chance to breed.
Because we have caught all the larger fish, the younger fish are having a chance to breed as there are theoreticaly no larger males to have to compete with. This means that natural "selection of the biggest fish" no longer occurs as females are breeding with in theory "teenage fish". The whole life cycle of the fish becomes shorter, adults mature erlier, and the adult of the species becomes smaller!
Ive got some data about 1962 and 1991 where newfoundland stocks of cod declined 99%. the body size variation declined by 55% (smaller fish)
Larger females that are also being caught are of huge value to stocks. Larger females generaly produce larger and more healthy eggs so the offspring have a higher chance of survival.
If the largest sizes are selected, then there is an aparent reduction in egg volume, larval size a hatching, growht rate, feed rate etc..So the more older females present, the higher the recruitment of young fish, and the more successfull breading. now the females are breading younger, there is less recruitment.
same goes for old school whaling! if the males were bigger, and they only took the biggest fish - then the male population will fall way faster than the female equalling a very low reproduction rate!
it may be a good idea then to only bring back the fish that are in the middle age group, although all the larger fish will die when netted anyway, and god knows what the implications of doing that would be!