CHAPTER 12
PREDATORS AND PARASITES
The predators of euphausiids are numerous, ranging from birds,
seals and whales to fish and invertebrates. Man also may become a
notable predator in the future because investigations of economic
methods of catching and ways of processing krill for human consumption are being made a t present. The literature on predation of euphausiids is immense and in many cases it is difficult to decide whether the
euphausiids form a significant portion of the diet or whether the record
of their occurrence in the stomach contents should be treated as an
isolated instance. For example, McLaren (1958) states that the ringed
seal, Phoca hispida Schreber, feeds predominantly on Themisto
libellula (Mandt), Mysis oculata Fabr., polar cod (Boreogadus saida
= Gadus saida Lepechin) and species of Thysanoessa but it is difficult
to estimate just how important the euphausiids actually are in the
diet. Consequently, in this chapter consideration is given mainly to
predators known to feed to a large extent on euphausiids although mention will be made of other organisms that feed to a lesser extent on
them. No effort, however, is made to review the whole literature on
predators because, as will be shown, most larger marine predatory
organisms seem, a t some stage of their life history, to feed directly on
euphausiids or on organisms which in turn feed on euphausiids. Many
predators, of course, probably eat euphausiids by accident rather than
by design, catching them along with more important food organisms.
The baleen whales are undoubtedly among the most important
predators of euphausiids and they will be considered first. The most
extensive and recent works on the diets of these whales, mostly in the
Antarctic and North Pacific, are those of Nemoto and his colleagues a t
the Whales Research Institute, Tokyo (Kakuwa et al., 1953; Mizue,
1951a,b; Mizue and Murata, 1951; Nasu, 1966; Nemoto, 1957, 1959,
1962b, 1963b, 1964; Nemoto and Kasuya, 1965; Nemoto and Nasu,
1958; Nishimoto et al., 1952; Nishiwaki, 1959, 1960; Nishiwaki and
Hayashi, 1950; Nishiwaki and Oye, 1951; Ohno and Fujino, 1952;
Omura, 1950, 1958, 1962; Omura and Sakiura, 1956). The work of this
Institute also involves investigations of whaling grounds, their hydrographical and biological characteristics, and studies of the biology of
361
12'
PREDATORS AND PARASITES
The predators of euphausiids are numerous, ranging from birds,
seals and whales to fish and invertebrates. Man also may become a
notable predator in the future because investigations of economic
methods of catching and ways of processing krill for human consumption are being made a t present. The literature on predation of euphausiids is immense and in many cases it is difficult to decide whether the
euphausiids form a significant portion of the diet or whether the record
of their occurrence in the stomach contents should be treated as an
isolated instance. For example, McLaren (1958) states that the ringed
seal, Phoca hispida Schreber, feeds predominantly on Themisto
libellula (Mandt), Mysis oculata Fabr., polar cod (Boreogadus saida
= Gadus saida Lepechin) and species of Thysanoessa but it is difficult
to estimate just how important the euphausiids actually are in the
diet. Consequently, in this chapter consideration is given mainly to
predators known to feed to a large extent on euphausiids although mention will be made of other organisms that feed to a lesser extent on
them. No effort, however, is made to review the whole literature on
predators because, as will be shown, most larger marine predatory
organisms seem, a t some stage of their life history, to feed directly on
euphausiids or on organisms which in turn feed on euphausiids. Many
predators, of course, probably eat euphausiids by accident rather than
by design, catching them along with more important food organisms.
The baleen whales are undoubtedly among the most important
predators of euphausiids and they will be considered first. The most
extensive and recent works on the diets of these whales, mostly in the
Antarctic and North Pacific, are those of Nemoto and his colleagues a t
the Whales Research Institute, Tokyo (Kakuwa et al., 1953; Mizue,
1951a,b; Mizue and Murata, 1951; Nasu, 1966; Nemoto, 1957, 1959,
1962b, 1963b, 1964; Nemoto and Kasuya, 1965; Nemoto and Nasu,
1958; Nishimoto et al., 1952; Nishiwaki, 1959, 1960; Nishiwaki and
Hayashi, 1950; Nishiwaki and Oye, 1951; Ohno and Fujino, 1952;
Omura, 1950, 1958, 1962; Omura and Sakiura, 1956). The work of this
Institute also involves investigations of whaling grounds, their hydrographical and biological characteristics, and studies of the biology of
361
12'