ON THE SUBJECT OF CORMORANTS

by Geoff Hogan, Springvale, P E.I.

Anyone birdwatching along the shore this fall or just driving across the Hillsborough Bridge or near the Summerside waterfront will likely have noticed the presence of cormorants. It is the time of year when cormorants are dispersing from the summer breeding colonies and, in the case of the Double- crested CormOrant (Phalacrocorax auritus), preparing for migration south. You will also likely have noticed that there are more cormorants than you remember before. The reason is, of course, that in the past few years cormorants on P E.I. have under- gone a substantial population increase. Whereas the last thorough census in 1978 revealed six colonies on the Island, by 1983 there were eleven. Interestingly,

a similar increase in cormorants has been occurring elsewhere such as the Great Lakes (C. Weseloh, pers. comm.). Both of our species, the Great (3, carbo) and Double-crested cormorants, have shown a population increase.

There are several possible factors that may explain this increase, although it is difficult to say with certainty which factor is most important. Earlier in this century cormorants were widely persecuted along the east coast (and else- where) to such an extent that Double-crested Cormorants were extirpated along the coast of Maine and New England as a breeding species and Great Cormorants were thought to have been completely extirpated as a breeding species in North America (Bent 1922, Erskine 1972, Lewis 1929). However, both species returned to their former range to nest and by mid-century appeared to have reached a peak. Pop— ulation growth since then has been less rapid ... until recently. As a result, the increase may simply be a delayed recovery to their original population level. Another possibility may be that reproductive potential has improved since the reduction of harmful pesticides (lg DDT) in our environment. Like many species high on the food chain cormorants in some areas were adversely affected by such pesticides. In addition, growing populations elsewhere may be adding new recruits to our own population. Whatever the reason, cormorants evidently find P.E.I. to their liking.

While both species of cormorants are seen most often on salt or brackish water, Double-crested Cormorants will also visit freshwater ponds to feed. It is the feeding habits of cormorants that is the subject of concern to fishermen in particular. Cormorants feed upon a variety of fish and have been widely persecuted for this reason. 0n the contrary, certain naturalists maintain that cormorants keep fish stocks healthy by removing the weak and diseased and that they are, in fact, beneficial because they feed upon certain fish species that prey upon young lobsters. Birdwatchers enjoy cormorants for esthetic reasons as P.E.I. offers some of the best opportunities to view nesting cormorants in the Maritimes.

But what do they eat? There have been numerous studies to date on the feeding habits of cormorants, often in response to fishermen's complaints that the birds are a threat to the fishery (Lewis 1929, Madsen and Sparck 1950, Men- dall 1936, Robertson 1974, Ross 1973, Scattergood 1950, Traverner 1915 and others). All of these studies have shown the same result ....Cormorants rarely prey upon economically important species and, except in unnatural situations

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