108
MALCOLM R. CLARKE
0. pteropus from Madeira and indeed from the whole area studied in
the eastern North Atlantic (Clarke, 1965a) contrasts markedly with
the situation found in the Caribbean and the West African Coast
from Cape Verde Islands to 1325's (Adam, 1952, 1960c, 1962) where
there are both males and females of all sizes. At present, therefore,
it appears that the 0. pteropus in the eastern North Atlantic migrate
into the region from the West Atlantic or from the South (Clarke, 1965a).
Ovaries and nidamental glands of 0. pteropus at Madeira indicate that
egg laying has either recently taken place or is imminent and spermatophores on the buccal membranes show that mating has taken place
(Clarke, in preparation); it therefore seems likely that this migration
is for spawning.
0. pteropus reaches Madeira a t about the same time as the northmoving 22°C mean surface isotherm and nearly all catches of this
species from R.R.S. Discovery I1 were made south of the isotherm.
The southern limit of 0. pteropus seems to be 13"25'S (Adam, 1952)
which is coincident with the southern limit of the 25°C isotherm.
I n assessing the distribution of 0. pteropus and 0. caroli the author
has ignored all records which do not include sufficient details for him
to be confident of the identification.
0. caroli and 0. pteropus are the dominant near-surface forms
where they occur. They can usually be seen within an hour of stopping
a ship at night except on bright moonlight nights when they are less
frequently seen, apparently because they tend to stay at greater depths
(Baker, 1957b, 1960). Something of the depth range of 0. caroliis known
from photographs taken with a deep-sea camera which is triggered by
any pull on a baited hook (Baker, 1957a) and twice, tentacles have
been caught in water bottles when they reversed thus giving a
precise depth of capture (Clarke, unpublished). These records show that
0. caroli extends down to a t least 1490 m below the surface (Table 11)
and, as most of the photographs were taken during dark hours, it is
evident that the whole population does not migrate to the surface a t
night. 0. pteropus has been recorded from 3 160 m with a non-closing
net (Voss, 1956b).
There can be no doubt that 0. caroli and 0. pteropus are present in
enormous numbers in their areas of distribution as shown by their
regular appearance a t the surface a t night. Both species form shoals
of less than about fifty individuals consisting of similarly-sized individuals; each squid being no more than two or three body lengths from
its neighbours. Shoals become smaller as individuals grow in size.
These animals are extremely strong and rapid swimmers and specimens identified as 0. bartrami have been known to leap out of the water,
MALCOLM R. CLARKE
0. pteropus from Madeira and indeed from the whole area studied in
the eastern North Atlantic (Clarke, 1965a) contrasts markedly with
the situation found in the Caribbean and the West African Coast
from Cape Verde Islands to 1325's (Adam, 1952, 1960c, 1962) where
there are both males and females of all sizes. At present, therefore,
it appears that the 0. pteropus in the eastern North Atlantic migrate
into the region from the West Atlantic or from the South (Clarke, 1965a).
Ovaries and nidamental glands of 0. pteropus at Madeira indicate that
egg laying has either recently taken place or is imminent and spermatophores on the buccal membranes show that mating has taken place
(Clarke, in preparation); it therefore seems likely that this migration
is for spawning.
0. pteropus reaches Madeira a t about the same time as the northmoving 22°C mean surface isotherm and nearly all catches of this
species from R.R.S. Discovery I1 were made south of the isotherm.
The southern limit of 0. pteropus seems to be 13"25'S (Adam, 1952)
which is coincident with the southern limit of the 25°C isotherm.
I n assessing the distribution of 0. pteropus and 0. caroli the author
has ignored all records which do not include sufficient details for him
to be confident of the identification.
0. caroli and 0. pteropus are the dominant near-surface forms
where they occur. They can usually be seen within an hour of stopping
a ship at night except on bright moonlight nights when they are less
frequently seen, apparently because they tend to stay at greater depths
(Baker, 1957b, 1960). Something of the depth range of 0. caroliis known
from photographs taken with a deep-sea camera which is triggered by
any pull on a baited hook (Baker, 1957a) and twice, tentacles have
been caught in water bottles when they reversed thus giving a
precise depth of capture (Clarke, unpublished). These records show that
0. caroli extends down to a t least 1490 m below the surface (Table 11)
and, as most of the photographs were taken during dark hours, it is
evident that the whole population does not migrate to the surface a t
night. 0. pteropus has been recorded from 3 160 m with a non-closing
net (Voss, 1956b).
There can be no doubt that 0. caroli and 0. pteropus are present in
enormous numbers in their areas of distribution as shown by their
regular appearance a t the surface a t night. Both species form shoals
of less than about fifty individuals consisting of similarly-sized individuals; each squid being no more than two or three body lengths from
its neighbours. Shoals become smaller as individuals grow in size.
These animals are extremely strong and rapid swimmers and specimens identified as 0. bartrami have been known to leap out of the water,