288
THE BIOLOGY OF EUPHAUSIIDS
these variations in the development of euphausiids are probably directly
related to food and temperature, as are probably the rates of growth of
the older stages, and until the effects of different combinations of food
and temperature on the growth rates of individuals are known quantitatively only broad pictures of the growth rates can be obtained from
statistical analyses of the wild populations. Consequently, Sheard does
not attempt to fit equations to his data (Fig. 109) as Mauchline does
(Fig. 108). An examination of the data in these two figures shows that
the fitting of a single regression line is of limited value because there
appear to be changes in the rates of development between different
groups of the data. Nevertheless, a regression line has a practical value
in converting one set of measurements to another, for comparative
purposes, as long as it is remembered that considerable variation exists
and therefore any supposed differences between two sets of comparable
data have to be examined with care.
This is especially true in equating length, volume and weight
measurements in a species. When the gonads mature, the body weight
relative to length increases, the carapace tending to swell. The swelling
of the carapace causes an increase in the body volume which likewise
changes in relation to length at sexual maturity. The relationship,
however, of body weight to body volume remains relatively more
constant. Ponomareva (1963) has published tables relating body length
to average weights in Thysanoessa longipes, T . inermis, T . raschii, and
Euphausia paci$ca at different times of the year and in different sea
areas. She found insignificant variations in weight correlated with
changing seasons, and similar variations were found between the sexes.
Ponomareva found that gravid females with eggs in the ovaries at
stage I V (see Chapter 4) were 30mg in Thysanoessa longipes and
40 mg in T . inermis heavier than spent females of the same body length,
but from an examination of the data which she presents this must refer
only to the largest females of these species. There is considerable
variation in the weights of any one species when similar sizes are
compared in her tables of weight against length of euphausiids from the
Sea of Japan, the Bering Sea, and the Sea of Okhotsk. She presents
comparable figures for winter, spring and summer. If her data are
plotted, then individuals of T . inermis, T . longipes and Euphausia
pacijica of the same body length are heavier in the Bering Sea than in
the Sea of Japan but the different seasonal times of sampling in these
two areas make inferences from these data unreliable. No reliable data
comparing weightllength relationships of euphausiids in different sea
areas at different seasons are yet available because detailed knowledge
of the states of sexual maturity of individuals in the samples must be
THE BIOLOGY OF EUPHAUSIIDS
these variations in the development of euphausiids are probably directly
related to food and temperature, as are probably the rates of growth of
the older stages, and until the effects of different combinations of food
and temperature on the growth rates of individuals are known quantitatively only broad pictures of the growth rates can be obtained from
statistical analyses of the wild populations. Consequently, Sheard does
not attempt to fit equations to his data (Fig. 109) as Mauchline does
(Fig. 108). An examination of the data in these two figures shows that
the fitting of a single regression line is of limited value because there
appear to be changes in the rates of development between different
groups of the data. Nevertheless, a regression line has a practical value
in converting one set of measurements to another, for comparative
purposes, as long as it is remembered that considerable variation exists
and therefore any supposed differences between two sets of comparable
data have to be examined with care.
This is especially true in equating length, volume and weight
measurements in a species. When the gonads mature, the body weight
relative to length increases, the carapace tending to swell. The swelling
of the carapace causes an increase in the body volume which likewise
changes in relation to length at sexual maturity. The relationship,
however, of body weight to body volume remains relatively more
constant. Ponomareva (1963) has published tables relating body length
to average weights in Thysanoessa longipes, T . inermis, T . raschii, and
Euphausia paci$ca at different times of the year and in different sea
areas. She found insignificant variations in weight correlated with
changing seasons, and similar variations were found between the sexes.
Ponomareva found that gravid females with eggs in the ovaries at
stage I V (see Chapter 4) were 30mg in Thysanoessa longipes and
40 mg in T . inermis heavier than spent females of the same body length,
but from an examination of the data which she presents this must refer
only to the largest females of these species. There is considerable
variation in the weights of any one species when similar sizes are
compared in her tables of weight against length of euphausiids from the
Sea of Japan, the Bering Sea, and the Sea of Okhotsk. She presents
comparable figures for winter, spring and summer. If her data are
plotted, then individuals of T . inermis, T . longipes and Euphausia
pacijica of the same body length are heavier in the Bering Sea than in
the Sea of Japan but the different seasonal times of sampling in these
two areas make inferences from these data unreliable. No reliable data
comparing weightllength relationships of euphausiids in different sea
areas at different seasons are yet available because detailed knowledge
of the states of sexual maturity of individuals in the samples must be