356
THE BIOLOGY OF EUPHAUSIIDS
and Thysanoe,ssa inermis form the food of whales in the North Pacific.
Thysanoessa raschii, an inshore species, has only been recorded as
important to whales in the Bering Sea but is probably more important
in the North Atlantic coastal areas. The whales in the North Atlantic
probably have a more varied diet than those in the Antarctic and no
euphausiid in the North Atlantic is as important to the whales as
Euphausia superba is to those in the Antarctic. Meganyctiphanes
norvegica is probably the most important northern species but
Thysanoessa inermis, a considerably smaller species, is also largely
preyed on.
I n the North Atlantic, Meganyctiphanes norvegica has been reported
as the most important euphausiid in the diets of whales in the seas near
Ireland (Lillie, 1910; Burfield, 1913; Hamilton, 1916)) off southwest
Norway (Collett, 1911-12), and off Iceland (Saemundsson, 1937). In
recent years, the fin whale, Balaenoptera physalus, is the species most
frequently taken by whalers in northern seas. It feeds on fish and
euphausiids but prefers the latter when a choice is available (Jonsgkd,
1966). It eats the same species of euphausiids as the blue whale,
consuming the different species present in swarms indiscriminately.
Hjort and Ruud (1929) found that Meganyctiphanes norvegica was the
most abundant species of euphausiid off the coast of More, Norway, in
summer but that Thysanoessa inermis was commonest in this area in
winter. Consequently, it is not surprising that they found that the fin
whales in this area were living mainly on T . inermis or herring in early
spring but from mid May until mid August they lived exclusively on
Meganyctiphanes norvegica. One of the authors has seen the stomach
of a fin whale packed solely with M . norvegica at the former whaling
station a t West Loch Tarbet in the Island of Harris in the Outer
Hebrides.
Hjort (1927) and Ruud (1927) believed that the distribution of
M . norvegica on the slopes of the coastal banks of Iceland, the Faroes,
the Shetlands, and the North Sea towards the Norwegian Channel
influenced the migrations of whales along the slopes and Ruud (1932)
drew attention to the accumulations of krill as the primary stages in a
food chain involving whales and men or, as Ingebrigtsen (1929) put it :
“ The cause of the great fluctuations in the occurrence of finbacks at
Bear Island and Spitzbergen in our time must be sought in the great
variations in the supply of food, i.e. krill and copepods.” Ingebrigtsen
was in no doubt as to the beneficial effect of krill on its baleen predators :
“ The blue whale was found to be rather thin in its spring migration
towards the north, but increased well in weight during the summer after
having feasted on krill.”
THE BIOLOGY OF EUPHAUSIIDS
and Thysanoe,ssa inermis form the food of whales in the North Pacific.
Thysanoessa raschii, an inshore species, has only been recorded as
important to whales in the Bering Sea but is probably more important
in the North Atlantic coastal areas. The whales in the North Atlantic
probably have a more varied diet than those in the Antarctic and no
euphausiid in the North Atlantic is as important to the whales as
Euphausia superba is to those in the Antarctic. Meganyctiphanes
norvegica is probably the most important northern species but
Thysanoessa inermis, a considerably smaller species, is also largely
preyed on.
I n the North Atlantic, Meganyctiphanes norvegica has been reported
as the most important euphausiid in the diets of whales in the seas near
Ireland (Lillie, 1910; Burfield, 1913; Hamilton, 1916)) off southwest
Norway (Collett, 1911-12), and off Iceland (Saemundsson, 1937). In
recent years, the fin whale, Balaenoptera physalus, is the species most
frequently taken by whalers in northern seas. It feeds on fish and
euphausiids but prefers the latter when a choice is available (Jonsgkd,
1966). It eats the same species of euphausiids as the blue whale,
consuming the different species present in swarms indiscriminately.
Hjort and Ruud (1929) found that Meganyctiphanes norvegica was the
most abundant species of euphausiid off the coast of More, Norway, in
summer but that Thysanoessa inermis was commonest in this area in
winter. Consequently, it is not surprising that they found that the fin
whales in this area were living mainly on T . inermis or herring in early
spring but from mid May until mid August they lived exclusively on
Meganyctiphanes norvegica. One of the authors has seen the stomach
of a fin whale packed solely with M . norvegica at the former whaling
station a t West Loch Tarbet in the Island of Harris in the Outer
Hebrides.
Hjort (1927) and Ruud (1927) believed that the distribution of
M . norvegica on the slopes of the coastal banks of Iceland, the Faroes,
the Shetlands, and the North Sea towards the Norwegian Channel
influenced the migrations of whales along the slopes and Ruud (1932)
drew attention to the accumulations of krill as the primary stages in a
food chain involving whales and men or, as Ingebrigtsen (1929) put it :
“ The cause of the great fluctuations in the occurrence of finbacks at
Bear Island and Spitzbergen in our time must be sought in the great
variations in the supply of food, i.e. krill and copepods.” Ingebrigtsen
was in no doubt as to the beneficial effect of krill on its baleen predators :
“ The blue whale was found to be rather thin in its spring migration
towards the north, but increased well in weight during the summer after
having feasted on krill.”