12. PREDATORS AND PARASITES
350
Whales are not the only marine mammals to eat krill. As long ago
as 1903 Koefoed on the Norwegian research ship “ Michael Sars ” near
the Arctic island of J a n Mayen observed considerable numbers of
Meganyctiphanes norvegica on the surface near the ice (Damas and
Koefoed, 1909). These were considered to be important in the diet of
seals, especially the Greenland or harp seal, Phoca groenlandica Erxl.
Knipowitsch (1907) also observed very young harp seals feeding on
euphausiids in the Arctic seas bordering Russia. Stephensen (1933)
found only one specimen of Meganyctiphanes norvegica together with
many Thysanoessa inermis in the stomach of a seal of the same species
from Greenland waters and Sivertsen (1941) found this species feeding
on T . inermis and T . raschii in the White Sea. Dunbar (1941, 1942)
recorded a specimen of Meganyctiphanes norvegica in the stomach of
another species of seal, Phoca hispida, in the Canadian Arctic and
McLaren (1958), examining the food of this seal in the same area, found
them feeding on species of Thysanoessa. This seal also fed on T . inermis
in West Spitzbergen (Hartley and Fisher, 1936). Thus, although there
are several records of North Atlantic seals feeding on euphausiids, it
would appear that they are probably not of any outstanding importance
in their diet but are usually consumed along with other foods. Three
Antarctic seals probably do feed to some degree on euphausiids (Marr,
1962). The leopard seal has been found, on occasion, with fresh krill in
its stomach. The Weddell seal is not thought to consume euphausiids
directly from the water but to feed on organisms that do eat euphausiids
directly from the water ; the pups of the Weddell seal, however, immediately after weaning appear to have a transitional feeding period when
they do feed directly on the euphausiids, Euphausia superba and
E . crystallorophias. Crab-eater seals probably feed to a large extent on
E . crystallorophias in the shallow waters of the Ross Sea and on E.
superba farther offshore. Of all the Antarctic seals, the crab eater is
probably the only major predator of euphausiids.
Although the importance of euphausiids generally, and Meganyctiphanes norvegica in particular in the North Atlantic, as food for whales
has been emphasized, the predator that has been most frequently
mentioned in the literature is undoubtedly the herring, Clupea harengus
L. This, however, may be a measure of the economic importance of
this fish rather than of its predation on euphausiids. The extent to
which Meganyctiphanes norvegica, Thysanoessa raschii, and T . inermis
form part of the herring’s diet obviously depends on their local abundance and this was soon realized by even the earliest workers. Thus,
Norman (1886) reported Meganyctiphanes norvegica in the stomachs of
herring taken off the east coast of Scotland and Brook and Calderwood
350
Whales are not the only marine mammals to eat krill. As long ago
as 1903 Koefoed on the Norwegian research ship “ Michael Sars ” near
the Arctic island of J a n Mayen observed considerable numbers of
Meganyctiphanes norvegica on the surface near the ice (Damas and
Koefoed, 1909). These were considered to be important in the diet of
seals, especially the Greenland or harp seal, Phoca groenlandica Erxl.
Knipowitsch (1907) also observed very young harp seals feeding on
euphausiids in the Arctic seas bordering Russia. Stephensen (1933)
found only one specimen of Meganyctiphanes norvegica together with
many Thysanoessa inermis in the stomach of a seal of the same species
from Greenland waters and Sivertsen (1941) found this species feeding
on T . inermis and T . raschii in the White Sea. Dunbar (1941, 1942)
recorded a specimen of Meganyctiphanes norvegica in the stomach of
another species of seal, Phoca hispida, in the Canadian Arctic and
McLaren (1958), examining the food of this seal in the same area, found
them feeding on species of Thysanoessa. This seal also fed on T . inermis
in West Spitzbergen (Hartley and Fisher, 1936). Thus, although there
are several records of North Atlantic seals feeding on euphausiids, it
would appear that they are probably not of any outstanding importance
in their diet but are usually consumed along with other foods. Three
Antarctic seals probably do feed to some degree on euphausiids (Marr,
1962). The leopard seal has been found, on occasion, with fresh krill in
its stomach. The Weddell seal is not thought to consume euphausiids
directly from the water but to feed on organisms that do eat euphausiids
directly from the water ; the pups of the Weddell seal, however, immediately after weaning appear to have a transitional feeding period when
they do feed directly on the euphausiids, Euphausia superba and
E . crystallorophias. Crab-eater seals probably feed to a large extent on
E . crystallorophias in the shallow waters of the Ross Sea and on E.
superba farther offshore. Of all the Antarctic seals, the crab eater is
probably the only major predator of euphausiids.
Although the importance of euphausiids generally, and Meganyctiphanes norvegica in particular in the North Atlantic, as food for whales
has been emphasized, the predator that has been most frequently
mentioned in the literature is undoubtedly the herring, Clupea harengus
L. This, however, may be a measure of the economic importance of
this fish rather than of its predation on euphausiids. The extent to
which Meganyctiphanes norvegica, Thysanoessa raschii, and T . inermis
form part of the herring’s diet obviously depends on their local abundance and this was soon realized by even the earliest workers. Thus,
Norman (1886) reported Meganyctiphanes norvegica in the stomachs of
herring taken off the east coast of Scotland and Brook and Calderwood