4.13
The Distribution of Indian Ocean Euphausiids
E. BRINTON and K. GOPALAKRISHNAN
The present account includes charts of the distribution of 26 of approximately 36
species of Euphausiacea considered to have been representatively sampled during the
nOE. For the most part, these are the species occupying the upper strata of the sea.
Inasmuch as the Indian Ocean Standard Net (IOSN) typically fished from a depth of 200
meters to the surface, the species best represented in the samples are those having a) young
stages which regularly live above 200 m depth and b) adults which occupy nearsurface
waters at least during the night. Mention will be made of the more irregularly sampled
species, but plotting of their distributions will await completion of analysis of the full
complement of samples.
Charts are not included here of several of the widely ranging species - those which
appear throughout most of the tropical and subtropical waters of the Indian Ocean. This
presentation emphasizes the species ranges which are bounded within the ocean, and is
intended to illustrate what appear to be faunistic areas. Most of these distributions will
be non quantitative, though for 6 of the species estimates of abundance are given. Details
of the quantitative aspects of distribution, including the occurrences in space and time of
the many developmental stages, will be provided in a more definitive HOE euphausiid
atlas.
In order that some general features of seasonality may be considered, distributions
are plotted for 2 time periods, May - September (corresponding to the SW monsoon in the
northern half of the ocean) and November- March (corresponding to the NE monsoon
period). Data within a season, but for the several years of the expedition, are plotted
together.
More detailed consideration of seasonal change in distributions is probably not yet
justified for the ocean as a whole, in view of the limited temporal-geographical coverage
presented by even this extensive collection of samples. Time series are available from
waters east of South Africa, and west of Australia along 110 ° E. Thysanopoda euphausiids
sampled by the Isaacs-Kidd Midwater Trawl during the 6 cruises along 110° E, 1962-63,
have been the subject of an ecological study by ROGER (1966). Study of the IOSN
samples from the same cruises and from the South African cruises is not yet complete.
I. Material and Methods
The material upon which these charts are based was obtained by 16 of the vessels
participating in HOE.
The bulk of the samples are classified as standard. That is, they were obtained using
a net of 1 m 2 mouth opening and 0.33 mm mesh width (CURRIE, 1963; UNESCO, 1968)
hauled vertically from a depth of approximately 200 m. Though 0° wire-angle was rarely
attained, we assume, here, that a volume of approximately 200 m 3 of water was strained
The Distribution of Indian Ocean Euphausiids
E. BRINTON and K. GOPALAKRISHNAN
The present account includes charts of the distribution of 26 of approximately 36
species of Euphausiacea considered to have been representatively sampled during the
nOE. For the most part, these are the species occupying the upper strata of the sea.
Inasmuch as the Indian Ocean Standard Net (IOSN) typically fished from a depth of 200
meters to the surface, the species best represented in the samples are those having a) young
stages which regularly live above 200 m depth and b) adults which occupy nearsurface
waters at least during the night. Mention will be made of the more irregularly sampled
species, but plotting of their distributions will await completion of analysis of the full
complement of samples.
Charts are not included here of several of the widely ranging species - those which
appear throughout most of the tropical and subtropical waters of the Indian Ocean. This
presentation emphasizes the species ranges which are bounded within the ocean, and is
intended to illustrate what appear to be faunistic areas. Most of these distributions will
be non quantitative, though for 6 of the species estimates of abundance are given. Details
of the quantitative aspects of distribution, including the occurrences in space and time of
the many developmental stages, will be provided in a more definitive HOE euphausiid
atlas.
In order that some general features of seasonality may be considered, distributions
are plotted for 2 time periods, May - September (corresponding to the SW monsoon in the
northern half of the ocean) and November- March (corresponding to the NE monsoon
period). Data within a season, but for the several years of the expedition, are plotted
together.
More detailed consideration of seasonal change in distributions is probably not yet
justified for the ocean as a whole, in view of the limited temporal-geographical coverage
presented by even this extensive collection of samples. Time series are available from
waters east of South Africa, and west of Australia along 110 ° E. Thysanopoda euphausiids
sampled by the Isaacs-Kidd Midwater Trawl during the 6 cruises along 110° E, 1962-63,
have been the subject of an ecological study by ROGER (1966). Study of the IOSN
samples from the same cruises and from the South African cruises is not yet complete.
I. Material and Methods
The material upon which these charts are based was obtained by 16 of the vessels
participating in HOE.
The bulk of the samples are classified as standard. That is, they were obtained using
a net of 1 m 2 mouth opening and 0.33 mm mesh width (CURRIE, 1963; UNESCO, 1968)
hauled vertically from a depth of approximately 200 m. Though 0° wire-angle was rarely
attained, we assume, here, that a volume of approximately 200 m 3 of water was strained