the cormorants are eating fish that have been artificially introduced by people.
This very well may be the case in many instances. However I know that it is not the case in the 3 locations near me where cormorants are booming. One is a public park that has a 2 acre pond and a 4 acre wetland/swamp. Another is a lake, perhaps 20 acres, that is semiprivate. The third is the south eastern end of barnegat bay.
The pond/swamp is stocked with small trout for a local fishing derby once a year, however I fish there frequently and know that the stocked fish are "fished out" extremely rapidly. Those that remain are poorly suited to the depth & water conditions. The local pickerel population certainly makes short work of those remaining. Within 3 weeks of the derby no trout are ever seen from again until the following stocking. I feel that these stocked trout are such a short term affair that they have no long term "draw" for additional predators.
The private lake is not stocked at all, and except for the original forming of it (1930's?) it never was. The lake is spring fed and has one tiny tributary feeding it as well- no stocked fish upstream. The lake has what I'd judge to be a very healthy diversity of type and size fish. Cormorants are arriving and hitting it pretty heavily the past 2 years. It is inland approx 40 miles in the mountains, so these are likely not transient/spillover ocean cormorants.
The third, The barnegat bay, isnt stocked. However there are several ecological changes in recent decades. Its not a static ecosystem.
My point is that for these 3 local ecosystems, the cormorants arent feeding on stocked fish. The cormorants are, nonetheless, expanding into these ranges.
My central qustions is, what are some natural predators that are lagging behind this recent boom? I'm not for shooting cormorants just because they make a meal out of the fish I aim to C/R. However, if there are some natural predators that could be encouraged locally, this might help to minimize a significant change to the local ecosystem (as well as maintain the good fishing action for me and the boys !).
Thanks in advance for reasoned responses.