REVIEW OF THE SYSTEMATICS AND ECOLOGY OF OCEANIC SQUIDS
257
ran through the netting (P. M. David personal communication).
Some of the mass was retained and close examination has shown it to
be an oegopsid species but further identification has not proved
possible.
It is difficult to account for the scarcity of oegopsid egg masses
when one considers the great numbers of adults present in the ocean.
One possibility is that the gelatinous nature causes them to break up
in a net and be lost through the meshes. If this were the case, one
might expect small pieces to be retained not infrequently and to be
identified in the catches on more occasions than they are. The explanation that the eggs are laid on the continental slope at depths in excess of
say 1 000 m has much to recommend it. First, no nets are fished very
near to the bottom on the continental slope; secondly many of the
squids in Sperm whale stomachs, which are thought to feed on the
slope about 1 000 m are gravid and probably actively spawning; and
thirdly the fact that Todarodes paci$cus lays its egg mass on the
bottom, probably on the slope.
XXIV. GROWTH, SIZE AND FORM
Growth rate and duration of life has been studied for very few
oceanic squid species. The ommastrephids Illex illecebrosus (Fig. 11,
p. 121 based on Squires) I . coindeti (Fig. 12, p. 124 based on MangoldWirz 1963), Todarodes sagittatus (Fig. 18, p. 138 based on Fridriksson,
1943 and Clarke, unpublished) and T . pacijicus (Fig. 18 based on
Katoh, 1959), have been studied in some detail while the work on
other oegopsids such as Gonatus fabricii and Todaropsis eblunae can
only be regarded as very preliminary (see pp. 155 and 126). All the four
species studied in detail appear to reach maturity after about one
year but nothing is known about the earlier stages so that, although
improbable, one cannot rule out a two year growth to maturity.
Regarding length of life it would seem that three years may be a
maximum for these species.
Study of growth has relied on finding year groups in size distributions of large samples or on detecting changes in the mode or mean of
a sample from month to month. Each method has a serious disadvantage; the sampling technique seriously biases the distribution of
the sample (two types of gear or two variations in the use of the same
gear can produce a bimodal size distribution which may be interpreted
as showing two year groups); migrations of the population may
suggest accelerated or decelerated growth if smaller or larger individuals
enter or leave the sampling area at different times. Both these errors
would be avoided if a method of age determination could be found.
I*
257
ran through the netting (P. M. David personal communication).
Some of the mass was retained and close examination has shown it to
be an oegopsid species but further identification has not proved
possible.
It is difficult to account for the scarcity of oegopsid egg masses
when one considers the great numbers of adults present in the ocean.
One possibility is that the gelatinous nature causes them to break up
in a net and be lost through the meshes. If this were the case, one
might expect small pieces to be retained not infrequently and to be
identified in the catches on more occasions than they are. The explanation that the eggs are laid on the continental slope at depths in excess of
say 1 000 m has much to recommend it. First, no nets are fished very
near to the bottom on the continental slope; secondly many of the
squids in Sperm whale stomachs, which are thought to feed on the
slope about 1 000 m are gravid and probably actively spawning; and
thirdly the fact that Todarodes paci$cus lays its egg mass on the
bottom, probably on the slope.
XXIV. GROWTH, SIZE AND FORM
Growth rate and duration of life has been studied for very few
oceanic squid species. The ommastrephids Illex illecebrosus (Fig. 11,
p. 121 based on Squires) I . coindeti (Fig. 12, p. 124 based on MangoldWirz 1963), Todarodes sagittatus (Fig. 18, p. 138 based on Fridriksson,
1943 and Clarke, unpublished) and T . pacijicus (Fig. 18 based on
Katoh, 1959), have been studied in some detail while the work on
other oegopsids such as Gonatus fabricii and Todaropsis eblunae can
only be regarded as very preliminary (see pp. 155 and 126). All the four
species studied in detail appear to reach maturity after about one
year but nothing is known about the earlier stages so that, although
improbable, one cannot rule out a two year growth to maturity.
Regarding length of life it would seem that three years may be a
maximum for these species.
Study of growth has relied on finding year groups in size distributions of large samples or on detecting changes in the mode or mean of
a sample from month to month. Each method has a serious disadvantage; the sampling technique seriously biases the distribution of
the sample (two types of gear or two variations in the use of the same
gear can produce a bimodal size distribution which may be interpreted
as showing two year groups); migrations of the population may
suggest accelerated or decelerated growth if smaller or larger individuals
enter or leave the sampling area at different times. Both these errors
would be avoided if a method of age determination could be found.
I*