Well, what about gill nets? It might be not the usual solution but they might work.
You should use several nets with mesh size that allows fish to go through. Cormorants might end their miserable lives there...

I'm not sure about the righ mesh size but I've seen a lot of pics with birds died in gill nets.

I don't know much about law things in your country but this could work wll in Latvia. I was simply fishing my trout (I CAN DO THAT) and it's not my fault that these birds managed to die in the net...

I've heard that those cannons are the solution but only without close neighbours... they won't tolerate the sound for a long time.

ADDED:

I did some searching and found a lot of articles about the way of killing cormorants (look above):

http://www.ifs.tas.gov.au/news/illegal-gill-net-retrieved-from-wayatinah-lagoon

The net contained dead cormorants...

http://news.mongabay.com/2013/1118-seabirds-die-by-gillnets-solution.html

The birds most likely to be affected by gillnets are those that hunt underwater, such as penguins, loons and cormorants

http://www.seaturtle.org/PDF/ForsellDJ_1999_USFWSTechReport.pdf

http://www.fish2fork.com/en-GB/news-inde...-calculate.aspx

Static nets, including gill nets, in the Baltic and the North Sea are estimated by the EU to kill between 90,000 and 200,000 seabirds annually, including grebes, sea ducks, cormorants and auks.

So, it's a real solution for your case. Think about it...

Last edited by Grundulis; 02/19/14 04:05 AM.