New Zealand Journal of Marine and Freshwater Research abstracts
Spatial and temporal variation in the growth rate of elephantfish
(Callorhinchus milii)
MALCOLM P. FRANCIS
National Institute of Water & Atmospheric
Research Ltd
P. O. Box 14-901
Wellington, New Zealand
Abstract Growth rate estimates were obtained for elephantfish
using length-frequency and tag-recapture data from the east coast of South
Island during 1966-88. Elephantfish hatch from egg cases at about 10 cm fork
length (FL) during May-July. Females grow faster than males after their first
year and growth is fastest in summer. In 1966-68, elephantfish in Pegasus Bay
grew faster than in Canterbury Bight, resulting in modal length differences
that were maintained for the first 3 years of life. This suggests there are at
least two distinct juvenile nurseries. Maximum observed lengths were 76 cm FL
for males and 97 cm FL for females. Length-frequency analyses identified 5-8
male age classes and 8-9 female age classes, but longevity probably exceeds
these values. Growth rates of 0+ elephantfish in Pegasus Bay in 1983-84 and
Canterbury Bight in 1988 were 33-56% greater than in 1966-68. The faster growth
rate meant male age at maturity was 4+ in the 1960s and 2+ to 3+ in the 1980s.
If female length at maturity was the same in the 1980s as in the 1960s, then
female age at maturity would have been 5+ to 6+ in the 1960s and 4+ to 5+ in
the 1980s. The increased growth rates and earlier maturity may have led to an
increase in elephantfish stock productivity between the 1960s and 1980s.
Keywords elephantfish; Callorhinchus milii; growth;
length-
frequency
analysis; tagging; maturity; MULTIFAN; GROTAG
New Zealand Journal of Marine and Freshwater Research, 1997: Vol. 31:
9-23
0028-8330/97/3101-0009 $2.50/0 (c) The Royal Society of New Zealand
PDF file of entire paper: medium quality (1047K); (scanned from paper original: notes about this process)
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