Age, Growth and Maximum Size of Antarctic Notothenioid Fish - Revisited
31
from other methods. These prerequisites have rarely been met. However,
scale circuli analysis has been the method most commonly applied, in
particular to nototheniids [1,15].
Length compositions of a number of channichthyids and nototheniids
exhibit distinct peaks at the lower end of their range which show little
overlap between modes. The position of these modes is consistent with
little variation between years. Shifts in these modes have been followed
within a year, clearly indicating that they represent age classes. Despite its
potential to estimate growth and its inter-annual variation in a number of
species in their first 3-4 years, this method has thus far only been utilized
to estimate age in Champsocephalus gunnari from South Georgia and Iles
Kerguelen [17,18].
Growth has also been independently checked against age estimates from
otolith readings by measurement of the growth increments of marked and
recaptured fish, such as in N coriiceps [12,19] and T bernacchii [20].
The Reliability of Age Estimates
The correct detennination of age is crucial for any growth estimate.
However, only few of the age estimates for Antarctic fish are scientifically
validated. For example, comparative age detenninations by five
investigators on the same set of scales of Gobionotothen gibberifrons
from South Georgia revealed considerable differences between readers
ranging from 1-3 years in scales offish 10 cm long to 6-13 years in fish of
33 cm length ([1]: Fig. 38).
Numerous such examples are available from the scientific literature and
from comparative age readings within the BIOMASS and CCAMLR age
detennination workshops [21-25]. They clearly demonstrate the high
degree of subjectivity still inherent in age detenninations of Antarctic fish
which means that the possibility of bias caused by the expectation that
Antarctic fish grow slowly may have influenced the results.
To date, age estimates have been validated for only a few species, with
N coriiceps, juvenile N rossii, T bernacchii, and C. gunnari among
them, all of which, with the exception of T bernacchii, occur in lesserAntarctic/subAntarctic waters. It is important to bear this in mind for the
following discussion on growth of Antarctic fish.
Maximum Ages
Maximum ages reported for small sized (20-23 cm) nototheniids, for
example Lepidonotothen larseni, L. nudifrons or Patagonotothen
guntheri, in lesser-Antarctic/subAntarctic waters were 8-10 years ([1] for
review). Similar-sized (20-30 cm) high-Antarctic nototheniids, such as
31
from other methods. These prerequisites have rarely been met. However,
scale circuli analysis has been the method most commonly applied, in
particular to nototheniids [1,15].
Length compositions of a number of channichthyids and nototheniids
exhibit distinct peaks at the lower end of their range which show little
overlap between modes. The position of these modes is consistent with
little variation between years. Shifts in these modes have been followed
within a year, clearly indicating that they represent age classes. Despite its
potential to estimate growth and its inter-annual variation in a number of
species in their first 3-4 years, this method has thus far only been utilized
to estimate age in Champsocephalus gunnari from South Georgia and Iles
Kerguelen [17,18].
Growth has also been independently checked against age estimates from
otolith readings by measurement of the growth increments of marked and
recaptured fish, such as in N coriiceps [12,19] and T bernacchii [20].
The Reliability of Age Estimates
The correct detennination of age is crucial for any growth estimate.
However, only few of the age estimates for Antarctic fish are scientifically
validated. For example, comparative age detenninations by five
investigators on the same set of scales of Gobionotothen gibberifrons
from South Georgia revealed considerable differences between readers
ranging from 1-3 years in scales offish 10 cm long to 6-13 years in fish of
33 cm length ([1]: Fig. 38).
Numerous such examples are available from the scientific literature and
from comparative age readings within the BIOMASS and CCAMLR age
detennination workshops [21-25]. They clearly demonstrate the high
degree of subjectivity still inherent in age detenninations of Antarctic fish
which means that the possibility of bias caused by the expectation that
Antarctic fish grow slowly may have influenced the results.
To date, age estimates have been validated for only a few species, with
N coriiceps, juvenile N rossii, T bernacchii, and C. gunnari among
them, all of which, with the exception of T bernacchii, occur in lesserAntarctic/subAntarctic waters. It is important to bear this in mind for the
following discussion on growth of Antarctic fish.
Maximum Ages
Maximum ages reported for small sized (20-23 cm) nototheniids, for
example Lepidonotothen larseni, L. nudifrons or Patagonotothen
guntheri, in lesser-Antarctic/subAntarctic waters were 8-10 years ([1] for
review). Similar-sized (20-30 cm) high-Antarctic nototheniids, such as