(1) Parallel studies of fish distribution and the diet and activity of common seals were made to assess the relationship between the seals' winter feeding activity and the distribution and abundance of their prey. Echosounder and trawling surveys revealed that a large part of the fish biomass was sprat and small herring, while faecal analyses showed that > 90% of common seal prey (by weight) were clupeoid fish.
(2) During the day, clupeoids concentrated in trenches and holes more than 12 m deep. Radio-tagged seals were located regularly over these areas. At night, clupeoid shoals rose in the water column and became more dispersed. Diel changes in seal activity patterns suggest that seals fed more often during the day.
(3) Prey sizes were estimated from the size of otoliths retrieved from seal feaces. Estimated sizes of clupeoids taken by seals were similar to the sizes of fish caught in trawls, even though estimates were not corrected to allow for partial digestion of otoliths. This suggests that the rapid otolith digestion rates previously reported from captive seals may have been artificially high, or that the Moray Firth seals selected fish larger than those caught in trawls.
|Number of pages||12|
|Journal||Journal of Animal Ecology|
|Publication status||Published - Feb 1991|
- HARBOR SEALS