1. The status of white-breasted cormorants Phalacrocorax carbo lucidus as possible
competitors with the fisheries of Lake Malawi was assessed. 2. Numbers of P. carbo
on the lake were estimated, from visual counts and photographs of resting sites taken at
last light, to be 10 000 individuals in 1979. 3. Observations were concentrated on a colony
of 5000+ birds on Boadzulu Island, in the south-east arm of the lake, the main area of
commercial fishing. The birds fished in a single large flock, in shallow water, at or near
the sandy or muddy bottom. 4. The birds' diet was assessed qualitatively and quantitatively
from examination of regurgitates and cast pellets recovered at the nests, of fish dropped
by the birds during their feeding activities, of the stomach contents of shot birds, and
from the amounts consumed by captive cormorants. The mean daily weight of fresh fish caught
by an adult, non-breeding cormorant was 250 g, rising to 293 g during the breeding season.
5. Annual fish consumption of the Boadzulu Island colony, including nestlings, was 491 t [tons],
of which 392.5 t came from the south-east arm of Lake Malawi. The entire white-breasted
cormorant population of Lakes Malawi and Malombe consumed 950 t year-1 [tons per year].
6. The standing stock of available prey in the areas fished by the Boadzulu birds was
126.3 kg ha-1 [kilograms per hectare]. This stock should be able to withstand indefinitely
the cormorant exploitation of 21.6 kg ha-1 year-1 [kilograms per hectare per year].
7. Available prey in the areas fished by the cormorants was estimated
from sample trawls. The birds took fish in rough proportion to their abundance. 8. The
average catch by man over the years 1979-87, in the south-east arm of Lake Malawi, of the
fish groups which formed the main prey of the cormorants, was 10417 t. The harvest by the
birds in the same area in 1979 represents 3.8% of this figure, or 14.9% of the 2634 t of
small demersal cichlids, the cormorants' preferred prey, in the catch. 9. But the cormorants
forage in areas which are not exploited by either commercial or traditional fishing, and most
of the demersal fish which are the cormorants' main prey have very restricted distributions
within the lake, so that only a few species with wide distributions are common in both
commercial fishing and cormorant feeding areas. The cormorants' harvest of fish species
common in commercial trawling is 70 t year-1. This is only 2.7% of the human harvest of
demersal cichlids. 10. It is concluded that the white-breasted cormorant has no significant
impact on the commercial or traditional fisheries at present carried out on Lake Malawi.