swarms apparently attract morv larger, vorwious animals and becornt*
the object of heavy predation. Thp shrimps would not be eaten by
baleen whales unless they made large homogeneous swarms of heavy
concentrations or patches. Elsewhere in the North Pacific fin whales
take both copepods itnd euph;riisiids, i t n t l si c4 u~hales feed diicfly OII
copepods. Although there W ~ L H 1 1 0 i n t l i c - i i t i o n tlliLt the stiLntling stoc:kn
of these food animals decreased, S ( ~ r y p s l p s s i r d i a was preferentially
eaten by the whales where it swarmed in restricted areas south of the
Gulf of Alaska. Sergia Zucens comprises the bulk of the diet of many
fishes occurring in Suruga Bay. The predation by fishes appears to
increase with increasing population density of the shrimps in swarms,
and i t becomes highest in early summer (Kosaka et aE., 1969). These
facts indicate that without considering the peculiar shoaling behaviour
of the species and their social life, discussion of the food chains and
biological productivity in the sea is not very valuable. The ecological
significance of the macroplankton and micronekton communities is
indeed different in this aspect from that of phytoplankton, which
shows relatively uniform di~tribution o v w broad areas and reflects
environmental effects within u relthtivoly short tinici.
VII. LIFN HISTORY
For estimates of the productivity of shrimps from field measurements, precision and accuracy of sampling are critical. If the general
features of the morphology, duration and mobility of each stage of
development from egg to adult were clarified, we could samplc thc:
species accordingly and estimate the true abunrlance of the arlirnitls in
the sea. Need for more information on the life history of inclividual
species should be emphasized to determine the principal laws in
various life phases of the species through its development and growth.
Our knowledge of the life history of pelagic shrimps is very scanty.
However, there are numerous sources of information on the biology
and ecology of shallow benthic forms, and these contributions arc very
useful for study of the pelagic species. The life history ant1 other
biological characteristics of the commercially important ponuc 1 i ( 1 iirc
reviewed in detail by Kurata ( 1 971). In this section data ohtainc:tl from
the study of three pelagic shrimps, A’erqiu lucms, Acules j(iponicun i t r ~ t l
Lzbcifer chacei Bowman, provide thc hasis for tlisounsion.
A . A‘pnc.un/i t u y
The ovaries of Sergia luccns and 8. challenyeri Hansen, lilte thost:
of all members of the genus Sergesks. are located beneath the heart,
the object of heavy predation. Thp shrimps would not be eaten by
baleen whales unless they made large homogeneous swarms of heavy
concentrations or patches. Elsewhere in the North Pacific fin whales
take both copepods itnd euph;riisiids, i t n t l si c4 u~hales feed diicfly OII
copepods. Although there W ~ L H 1 1 0 i n t l i c - i i t i o n tlliLt the stiLntling stoc:kn
of these food animals decreased, S ( ~ r y p s l p s s i r d i a was preferentially
eaten by the whales where it swarmed in restricted areas south of the
Gulf of Alaska. Sergia Zucens comprises the bulk of the diet of many
fishes occurring in Suruga Bay. The predation by fishes appears to
increase with increasing population density of the shrimps in swarms,
and i t becomes highest in early summer (Kosaka et aE., 1969). These
facts indicate that without considering the peculiar shoaling behaviour
of the species and their social life, discussion of the food chains and
biological productivity in the sea is not very valuable. The ecological
significance of the macroplankton and micronekton communities is
indeed different in this aspect from that of phytoplankton, which
shows relatively uniform di~tribution o v w broad areas and reflects
environmental effects within u relthtivoly short tinici.
VII. LIFN HISTORY
For estimates of the productivity of shrimps from field measurements, precision and accuracy of sampling are critical. If the general
features of the morphology, duration and mobility of each stage of
development from egg to adult were clarified, we could samplc thc:
species accordingly and estimate the true abunrlance of the arlirnitls in
the sea. Need for more information on the life history of inclividual
species should be emphasized to determine the principal laws in
various life phases of the species through its development and growth.
Our knowledge of the life history of pelagic shrimps is very scanty.
However, there are numerous sources of information on the biology
and ecology of shallow benthic forms, and these contributions arc very
useful for study of the pelagic species. The life history ant1 other
biological characteristics of the commercially important ponuc 1 i ( 1 iirc
reviewed in detail by Kurata ( 1 971). In this section data ohtainc:tl from
the study of three pelagic shrimps, A’erqiu lucms, Acules j(iponicun i t r ~ t l
Lzbcifer chacei Bowman, provide thc hasis for tlisounsion.
A . A‘pnc.un/i t u y
The ovaries of Sergia luccns and 8. challenyeri Hansen, lilte thost:
of all members of the genus Sergesks. are located beneath the heart,