10. GROWTH, MATURITY AND MORTALITY
285
the relationship of carapace length to total length and found that it
varied ; total length was measured from the posterior face of the eye
notch. The ratio of total length to carapace length varies in sexually
immature animals from 4.03 to 4.87 in males and from 3.87 to 4.58 in
females, whereas the ranges of these ratios in sexually mature animals
with ripe gonads are 4.12 to 4.91 in males and 3-86 to 4.33 in females.
These results are shown graphically in Fig. 108. The length of the
carapace relative to total length increases when the gonads ripen and
cause swelling of the cephalothorax. I n practice, however, although
these changes in the proportions of the body take place, mean factors
were used successfully to convert carapace measurements to total length
measurements. Carapace lengths of immature males were multiplied
by 4.33, of mature males by 4.27, of immature females by 4.27, and of
mature females by 4.05.
The relationships of abdomen length and telson length respectively
to carapace length were also examined in Meganyctiphanes norvegica
and linear relationships obtained (Fig. 108). The amount of scatter
present in the measurements of telson length are indicative of damage
to the telson. On the other hand, Lasker (1966) obtained a linear
relationship between total length and uropod length in Euphausia
paci$ca although the relationship in the smallest animals, less than
5 mm total length, did not conform to that of those over 5 mm and up
to 18 mm. Sheard (1953) studied, in Nyctiphanes australis, the relationships of total length to the abdomen length, the carapace length, and
the width of the third segment of the antennule and he divided total
length into its constituent parts, namely lengths of the cephalothorax,
the abdominal segments 1 to 6, and the telson. He points out that
various assumptions have to be made in these studies. First, individuals
of a species at comparable stages of morphological development are
considered to be of the same age, and second, that if measurements of
total length or parts of the body of individuals a t the same stage of
development are made then the length frequencies are distributed
normally about the mean. These assumptions are not justified in the
case of euphausiids and larval stages of decapod Crustacea (see Chapter
4). The sequence of larval stages of a species of euphausiid is different
in different geographical areas and often in the same geographical area
a t different times. Consequently, two larvae a t the same stage of
morphological development may have different life histories, that is
have passed through different numbers of moults and taken different
lengths of time to attain that stage of development. Consequently,
their growth rates are different but in a statistical analyses of a heterogeneous population it would be impossible to describe these. Basically,
285
the relationship of carapace length to total length and found that it
varied ; total length was measured from the posterior face of the eye
notch. The ratio of total length to carapace length varies in sexually
immature animals from 4.03 to 4.87 in males and from 3.87 to 4.58 in
females, whereas the ranges of these ratios in sexually mature animals
with ripe gonads are 4.12 to 4.91 in males and 3-86 to 4.33 in females.
These results are shown graphically in Fig. 108. The length of the
carapace relative to total length increases when the gonads ripen and
cause swelling of the cephalothorax. I n practice, however, although
these changes in the proportions of the body take place, mean factors
were used successfully to convert carapace measurements to total length
measurements. Carapace lengths of immature males were multiplied
by 4.33, of mature males by 4.27, of immature females by 4.27, and of
mature females by 4.05.
The relationships of abdomen length and telson length respectively
to carapace length were also examined in Meganyctiphanes norvegica
and linear relationships obtained (Fig. 108). The amount of scatter
present in the measurements of telson length are indicative of damage
to the telson. On the other hand, Lasker (1966) obtained a linear
relationship between total length and uropod length in Euphausia
paci$ca although the relationship in the smallest animals, less than
5 mm total length, did not conform to that of those over 5 mm and up
to 18 mm. Sheard (1953) studied, in Nyctiphanes australis, the relationships of total length to the abdomen length, the carapace length, and
the width of the third segment of the antennule and he divided total
length into its constituent parts, namely lengths of the cephalothorax,
the abdominal segments 1 to 6, and the telson. He points out that
various assumptions have to be made in these studies. First, individuals
of a species at comparable stages of morphological development are
considered to be of the same age, and second, that if measurements of
total length or parts of the body of individuals a t the same stage of
development are made then the length frequencies are distributed
normally about the mean. These assumptions are not justified in the
case of euphausiids and larval stages of decapod Crustacea (see Chapter
4). The sequence of larval stages of a species of euphausiid is different
in different geographical areas and often in the same geographical area
a t different times. Consequently, two larvae a t the same stage of
morphological development may have different life histories, that is
have passed through different numbers of moults and taken different
lengths of time to attain that stage of development. Consequently,
their growth rates are different but in a statistical analyses of a heterogeneous population it would be impossible to describe these. Basically,