Someone threw all the marbles in the air and they haven't landed yet. We wont know anything till they start landing. The fish dont know anything about Brexit so will can still go and catch them, we will still be paying our licence fees and obeying the close season, the same rules etc for some time to come.
Regarding the EU legislation, I don't think its reliable to compare this with our own legislation before we joined the EU, that was 40+ years ago, we have all become more aware of environmental issues, more knowledgeable how to deal with it, it is much more in the public consciousness than it ever was back then. Its been a world wide progressive thing of which we would have been part of in or out of the EU.
Its not as if we would still be in the same place as we were 50 years ago if the EU had never existed.
It has helped that countries have come together to help these issues for sure and the EU has helped facilitate that but we are not leaving Europe or the world, just the EU.
Some environmental legislation is better done home grown anyway, some Eu countries don't have meadows, chalk streams or even a sea, we will understand these things a lot better. It must have been hard for some of their representatives to vote on legislation on things they had never heard of or seen in their lives. They probably had to use Wikipedia before voting.