I know that cormorants typically illicit a visceral negative reaction among sport fisherman and have read the negative affect they have on sport fishery's. I wanted to throw this up for discussion not necessarily to get a scientific response, but more of peoples opinions based on personal experience.
I like on a small lake (about 100 acres) surrounded by homes in a suburban environment. It is a catch & release fishery and doesn't get that much pressure despite the number of people who live on the lake (more So Cal anglers focus on saltwater fishing or stocked trout than largemouth bass). About a decade ago, the average bass I caught here was about 12" long & often were skinny. There are no shad in the lake and all of the bluegill were either under 3" long or over 10" long. Like many ponds & small lakes, I believe the lack of any harvesting stunted much of the bass population.
Now the bass population is very different. There still seem to be just as many numbers of fish, but the average size is closer to 14" and nearly every fish has a bit of a belly on them. Larger fish are showing up, 7 & 8 lb fish, good for a So Cal lake without Florida strain. The two differences I believe are instrumental between now & then are 1) the stocking of crayfish & 2) a pair of cormorants that have made this lake their home.
The crayfish are stocked 3 times a year, a natural method the HOA chose to fight off zebra mussels. Just 2 days ago, two of the bass I caught had crayfish antenna sticking up from their gullet. While I believe this increase of high protein forage has helped, I think the pair of cormorants have also helped by culling down the numbers of 6" - 10" bass. They are in effect the only "meat fishermen" on the lake, taking a fish or two a day and helping keep the fish population in a healthy balance.
Now I am fully aware that if a flock of 50 plus cormorants descended on the lake, it could be devastating. I think that the large human presence, between homeowners and pleasure boaters, keep other cormorants from joining in. In fact, the only time I see the cormorants fishing is at dawn, when I pretty much have the lake to myself. As the day progresses and people scurry about, the pair of birds retreat to a tall Eucalyptus tree until the next morning. I was original concerned that they were a nesting pair, but in the past few years, neither has made nor sat on a nest. Apparently they are just a couple of bachelors hanging out.
The HOA has a policy of harassing migratory waterfowl to keep them from making the lake a home, often chasing off the loud Canada geese. I haven't mentioned anything to them about the cormorants because I don't know if they are a positive or negative in these small numbers, although I am obviously leaning towards them being a plus.
Has anyone else had experiences with cormorants that would confirm or contradict what I believe to be occurring?