In relation to the 'over the top fine', it might be worth considdering that this is the most likely species to become extinct within its natural habitat the UK in the near future - very likely within the next 20 years. Not only that but this chap could have introduced signal pluage - which has been known to destroy whole populations and completely irradicate the natives from huge streaches of river systems.
Thats why the fine is per individual animal, it makes it nesesairily proportional and actually could have been significantly higher if the book was fully thrown at him (up to
£5K per Crayfish i believe, but have not checked).
Its as often decent people who are not fully informed as uncaring numpties who cause these types of mishaps. A simply enquiry to the EA would have prevented his prosecution and that trapping ANY crayfish is licencable is very well known and freely available in public information, so sorry i thinks its a very reasonable fine and nice to see the law actually being enforced.