In his youth Greenberg experienced a catastrophic ecosystem destruction. The pond he had spent many years of his young life fishing at was suddenly stripped bare of fish either due to an especially cold winter, or the chemicals added to the water to control algal blooms. I have not experienced any sort of similar profound event but I have witnessed many ponds and streams decline from when I was much younger. The fish are noticeably smaller and harder to catch than they were 10 years ago.
At this point in the book I believe the Paul Greenberg would have said that worldwide fisheries are in a state of decline. At this point all he knew was that the ponds and ocean waters he had fished as a child had severely declined, so I think its safe to assume that he would think that worldwide fisheries are declining as well.
I believe that at the end of the book he will become more pessimistic about the future of the worlds fisheries. I think this because he is going to start with the idea that fisheries are declining and then continue to find evidence of more and more declining fisheries. Even though many fish populations are considered stable it is natural for humans to focus on the surface level negative news instead of the more in depth positive stories. That’s why headlines saying “2/3rds of world fish stocks fully exploited” are so common. The author is also not a scientist or expert in the field, so i am not sure that he will put in the effort to examine fisheries issues as deep as a scientist would.