I take a more simplistic view. All of the species being mentioned ( Ring billed Gulls, Common Tern, cormorants, herons) are all native species. Let them come to their own balance. I was opposed to shooting Great Horned Owls and Black Crowned Night Herons when they were identified as a possible cause for Common Tern decline in Vermont. Species have ebbs and falls. Let native species find their own carrying capacity. The environment changes and, therefore, the carrying capacity for a species changes. I find it incontiousable that we go in and oil eggs or shoot cormorants or gulls. Would we poison House Wrens because we find they are "responsible" for bluebird/phoebe declines or some other megafauna? If someone convinces me that cormorants are increasing because of some human perturbation of our environment, I might feel differntly.
I questioned the efforts made to enourage Bald Eagle nesting in Vermont. Historical records indicate that they were not a regular breeding specis in the state. Yet, they attracted a great deal of interest and attention. We need to look carefully, in my opinion, what species we feel need to be helped at the expense of others.