252
MALCOLM R. CLARKE
which suggests that connection between the two was severed sufficiently
long ago to allow the isolated populations to evolve to the species level
of differentiation. A bipolar distribution within the oegopsids is
perhaps shown by Gonatus fabricii which is not clearly distinguishable
from the southern G. antarcticus; they may well be forms of the same
species. I n addition, the Antarctic Crystalloteuthis glacialis differs very
little from C . beringiana from the North Pacific. Dosidicus gigas is
rather curious in being found in the eastern Pacific off Central and
South America and in the western Pacific off Australia, but it has not
been recorded off New Zealand; however, the limits of distribution are
poorly known.
Several species of the Ommastrephidae are known to migrate
annually into inshore waters but few specimens are in spawning
condition when caught inshore. Illex illecebrosus and I . coindeti
seem to move into shallower water after food during adolescence
while Todarodes paci$cus and T . sagittatus apparently move on to the
continental shelf prior to spawning on the continental slope. Ommastrephes pteropus females apparently migrate into the eastern North
Atlantic and leave the males further south or west; this migration is
probably for spawning. Other species known to migrate annually are
Gonatus fabricii, Thysanoteuthis rhombus and Abralia veranyi. Where
data is available (Illex illecebrosus, Todarodes paci$cus) migrations
are intimately related to movement of water masses.
The little evidence we have on tolerance of oceanic squids to
environmental factors (e.g. Todarodes pacijicus, Bathyteuthis abyssicola,
Watasenia scintillans) suggests that they are able to live in a wide
range of temperature and salinity a t least for brief periods. A few
species are rather limited to particular latitudes (e.g. Gonatus fabricii,
Spirula spirula) and in these species possibly temperature throughout
the year is the principal factor in limiting their distribution,
XXII. DEPTH
The extensive use of non-closing nets makes analysis of the depth
range of oceanic squids extremely difficult. Additional inaccuracy
arises because depth gauges have been used infrequently and most
depths have been calculated from the length of warp out and the
warp angle, a method giving only a very approximate idea of the
depth. It is not always clear whether authors are quoting soundings
or depths of net. Here, only the depths of the shallowest and the
deepest hauls which have caught a species have been noted. While
these depths, in most cases, give an over-estimate of the depth a t
which a species lives, they do give us a few indisputable facts which
MALCOLM R. CLARKE
which suggests that connection between the two was severed sufficiently
long ago to allow the isolated populations to evolve to the species level
of differentiation. A bipolar distribution within the oegopsids is
perhaps shown by Gonatus fabricii which is not clearly distinguishable
from the southern G. antarcticus; they may well be forms of the same
species. I n addition, the Antarctic Crystalloteuthis glacialis differs very
little from C . beringiana from the North Pacific. Dosidicus gigas is
rather curious in being found in the eastern Pacific off Central and
South America and in the western Pacific off Australia, but it has not
been recorded off New Zealand; however, the limits of distribution are
poorly known.
Several species of the Ommastrephidae are known to migrate
annually into inshore waters but few specimens are in spawning
condition when caught inshore. Illex illecebrosus and I . coindeti
seem to move into shallower water after food during adolescence
while Todarodes paci$cus and T . sagittatus apparently move on to the
continental shelf prior to spawning on the continental slope. Ommastrephes pteropus females apparently migrate into the eastern North
Atlantic and leave the males further south or west; this migration is
probably for spawning. Other species known to migrate annually are
Gonatus fabricii, Thysanoteuthis rhombus and Abralia veranyi. Where
data is available (Illex illecebrosus, Todarodes paci$cus) migrations
are intimately related to movement of water masses.
The little evidence we have on tolerance of oceanic squids to
environmental factors (e.g. Todarodes pacijicus, Bathyteuthis abyssicola,
Watasenia scintillans) suggests that they are able to live in a wide
range of temperature and salinity a t least for brief periods. A few
species are rather limited to particular latitudes (e.g. Gonatus fabricii,
Spirula spirula) and in these species possibly temperature throughout
the year is the principal factor in limiting their distribution,
XXII. DEPTH
The extensive use of non-closing nets makes analysis of the depth
range of oceanic squids extremely difficult. Additional inaccuracy
arises because depth gauges have been used infrequently and most
depths have been calculated from the length of warp out and the
warp angle, a method giving only a very approximate idea of the
depth. It is not always clear whether authors are quoting soundings
or depths of net. Here, only the depths of the shallowest and the
deepest hauls which have caught a species have been noted. While
these depths, in most cases, give an over-estimate of the depth a t
which a species lives, they do give us a few indisputable facts which