Zijlstra M. & Van Eerden M.R. (1995) Pellet production and the use of otoliths in determining the diet of Cormorants Phalacrocorax carbo sinensis: Trials with captive birds. ARDEA 83 (1): 123-131

In a feeding experiment with two separated captive Cormorants, production of pellets and otoliths and wear of otoliths was investigated. It was found that Cormorants produce one pellet a day containing only undigested remains from the day before. With regard to fish species offered, a great variation in proportions of otoliths recovered was found. The recovery rate of otoliths (about 52%) was highest for the larger size classes of Ruffe. Although the calculated mean wear of otoliths from small and large size classes did not differ significantly in absolute terms, the recalculated fish mass did. The results differ strongly from field experiences. It is hypothesised that experiment induced stress causes severe otolith wear in feeding trials with captive Cormorants, making this type of research unfit for calibration of the use of otoliths in diet studies.