Spatial and temporal variation in the growth rate of elephantfish (Callorhinchus milii)

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