Fish populations of the Avon‐Heathcote Estuary

Abstract

Breeding seasons and sizes at first maturity for nine species of fish in the Avon‐Heathcote Estuary, Christchurch, New Zealand, were: sand flounder, Rhombosolea plebeia, mid‐winter to spring at 200 mm+; yellow‐bellied flounder, Rhombosolea leporina, winter and spring at 260 mm+; common sole, Peltorhamphus novaeieelandiae, did not breed in the estuary but reached first maturity at 220 mm +; yellow‐eyed mullet, Aldrichetta forsteri, spawned twice a year, winter and summer, at 220 mm +; kahawai, Arripis trutta, bred outside the estuary at 520–540 mm +; spotty, Pseudolabrus celidotus, spring to autumn at 200 mm for males and 160 mm for females; cockabully, Tripterygion nigripenne, spring and early summer at 52–57 mm +; common bully, Gobiomorphus basalis, spring and early summer at 45–50 mm+; and globefish, Speroides richei, spring to autumn at 147 mm + for males and 120 mm + for females. The successive stages in gonad development are described for these species.

In pelagic species, e.g., flatfish and kahawai, x² analyses showed that for most months females are more numerous than males, and that migration is of major importance. In (littoral species, e.g., common bully and cockabully, there is a 1 : 1 sex ratio in the breeding season, but this ratio subsequently breaks down.

The Avon‐Heathcote estuary was used mainly as a nursery area by juvenile fish, although some species, such as sand flounder, yellow‐bellied flounder, yellow‐eyed mullet, and cockabully spawned in the estuary.

Notes

Part 1: General ecology, distribution and length‐frequency. N.Z. Journal of Marine and Freshwater Research 6 (4): 570–601.

Present address: Fisheries Division, Department of Agriculture, G.P.O. Box 192B, Hobart, Tasmania.