A new study about the importance of collective memory for fish migration was just published in the Journal of the Royal Society Interface
Giancarlo De Luca, Patrizio Mariani, Brian R. MacKenzie, and Matteo Marsili
Fishing out collective memory of migratory schools
J. R. Soc. Interface June 6, 2014 doi:10.1098/rsif.2014.0043 1742-5662
Removal of experienced individuals from a fish school can make the group to collapse. A new modeling framework has been used to study group formation processes in migratory fish and results suggest that collective memory is an essential element for schooling formation and migration. Moreover, intensive fishing targeting a migratory predator species and their preferred prey can reduce both populations to a point at which migration to the destination sites is abruptly stopped. In such case even if the prey population is recovered the school may not be able to migrate there any more.
You can read the article here: Journal of the Royal Society Interface.
The Scientist Magazine also has a story about the study.