12. PREDATORS AND PARASITES
367
Several invertebrates have been found to feed on euphausiids. I n
the North Atlantic, Hickling (1927) found that the squid, Ommastrephes
sp., fed at times exclusively on Meganyctiphanes norvegica as did another
squid, Loligo sp. Hjort and Ruud (1929) considered euphausiids to be
important as food of the squid, Gonatus fabricii. According to Marr
(1962) young Euphausia superba are eaten by the large Sagitta gazellae
Ritter-Zahony and the amphipod, Parathemisto gaudichaudi. Two
pelagic shrimps, a caridean Pasiphaea paci$ca Rathbun and a penaeid
Sergestes similis Hansen, feed primarily on euphausiids which Renfro
and Pearcy (1966) identified as Euphausiapaci$ca. Many other plankton
organisms, including medusae and copepods, probably feed on euphausiid larvae to a very considerable degree but no information is available
on the extent of their predation.
One important group of predators has not yet been mentioned,
namely sea birds. The predations, especially for the non-diving species,
are limited to the occasions when the euphausiids are swimming on the
surface. Thus Smith (1879), describing the swarming of Meganyctiphanes
norvegica in the Bay of Fundy, mentioned that in the autumn the
swarms were accompanied by immense flocks of gulls and that many
of these, especially the smaller ones, appeared to be feeding almost
exclusively on M . norvegica. Collett (1911-12) observed fin whales
feeding on a swarm of euphausiids while the sea birds waited for the
euphausiids to be swirled to the surface by the movements of the
whales. Einarsson (1945) also observed a swarm of euphausiids in
Faroese waters on which gulls, fulmars and puffins were feeding. The
fulmar probably depended on euphausiids and other plankton organisms
for iis food before man started the intense whaling operations and
fishing which involved large-scale gutting a t sea ; once this latter source
of food became available, in the last three hundred years or so, the
fulmar’s diet changed to scavenged materials and, for this reason or
some other, the populations of this species increased tremendously
(Fisher, 1952). Surface swarms of Thysanoessa raschii in the Barents
Sea were devoured by capelins from below and kittiwakes, Rissa
tridactyla (L. ), and herring gulls, Larus argentatus Pontopiddan, from
above (Zelikman, 1961a).
A detailed study of the feeding habits of sea birds on swarms of
Thysanoessa inermis in an inland fjord region of West Spitzbergen was
made by Hartley and Fisher (1936). They found that the kittiwakes,
fulmars (Fulmarus glacialis (L.)), and arctic terns (Sterna paradisea
Pontopiddan) fed almost exclusively on the euphausiids while the ivory
gulls ( Pagophila eburnea (Phipps)), Brunnich’s guillemots ( Uria
lomvia (L.)), Mandt’s guillemots ( U . qrylle mandtii = Cephus grylle (L.)),
367
Several invertebrates have been found to feed on euphausiids. I n
the North Atlantic, Hickling (1927) found that the squid, Ommastrephes
sp., fed at times exclusively on Meganyctiphanes norvegica as did another
squid, Loligo sp. Hjort and Ruud (1929) considered euphausiids to be
important as food of the squid, Gonatus fabricii. According to Marr
(1962) young Euphausia superba are eaten by the large Sagitta gazellae
Ritter-Zahony and the amphipod, Parathemisto gaudichaudi. Two
pelagic shrimps, a caridean Pasiphaea paci$ca Rathbun and a penaeid
Sergestes similis Hansen, feed primarily on euphausiids which Renfro
and Pearcy (1966) identified as Euphausiapaci$ca. Many other plankton
organisms, including medusae and copepods, probably feed on euphausiid larvae to a very considerable degree but no information is available
on the extent of their predation.
One important group of predators has not yet been mentioned,
namely sea birds. The predations, especially for the non-diving species,
are limited to the occasions when the euphausiids are swimming on the
surface. Thus Smith (1879), describing the swarming of Meganyctiphanes
norvegica in the Bay of Fundy, mentioned that in the autumn the
swarms were accompanied by immense flocks of gulls and that many
of these, especially the smaller ones, appeared to be feeding almost
exclusively on M . norvegica. Collett (1911-12) observed fin whales
feeding on a swarm of euphausiids while the sea birds waited for the
euphausiids to be swirled to the surface by the movements of the
whales. Einarsson (1945) also observed a swarm of euphausiids in
Faroese waters on which gulls, fulmars and puffins were feeding. The
fulmar probably depended on euphausiids and other plankton organisms
for iis food before man started the intense whaling operations and
fishing which involved large-scale gutting a t sea ; once this latter source
of food became available, in the last three hundred years or so, the
fulmar’s diet changed to scavenged materials and, for this reason or
some other, the populations of this species increased tremendously
(Fisher, 1952). Surface swarms of Thysanoessa raschii in the Barents
Sea were devoured by capelins from below and kittiwakes, Rissa
tridactyla (L. ), and herring gulls, Larus argentatus Pontopiddan, from
above (Zelikman, 1961a).
A detailed study of the feeding habits of sea birds on swarms of
Thysanoessa inermis in an inland fjord region of West Spitzbergen was
made by Hartley and Fisher (1936). They found that the kittiwakes,
fulmars (Fulmarus glacialis (L.)), and arctic terns (Sterna paradisea
Pontopiddan) fed almost exclusively on the euphausiids while the ivory
gulls ( Pagophila eburnea (Phipps)), Brunnich’s guillemots ( Uria
lomvia (L.)), Mandt’s guillemots ( U . qrylle mandtii = Cephus grylle (L.)),