SOME QUANTITATIVE ASPECTS OF REPRODUCTION AND GROWTH OF THE RED ABALONE, Haliotis rufescens SWAINSON

Reproduction and growth of a laboratory‐held population of red abalone, Haliotis rufescens , collected at Mendocino, California, were studied at the Telonicher Marine Laboratory, Trinidad, California. Specimens were continuously supplied with and consumed bull kelp fronds, Nereocystis luetkeana . Following induction of artificial spawning, specimens were sacrificed at 15‐day intervals to histologically describe and record the timing of gonadal phases, and to measure gonadal growth. A modified Gonad Bulk Index (GBI tc ) detected temporal changes in gonad volume and was highly correlated with defined stages of ovarian development. For specimens sexually mature when collected, viable gametes were spawned again 75 to 90 days following artificial spawning. Some specimens were spawned 3 times during a one‐year period. The laboratory regime increased somatic growth and fecundity, and reduced the minimum size at spawning relative to equivalent sized specimens from the field. Estimated fecundities for laboratory‐conditioned specimens averaged 260% greater than for field‐conditioned specimens. The minimum size at spawning for laboratory‐conditioned specimens was less than that for field‐conditioned specimens. The ratio of spawners to non‐spawners for specimens less than 100 mm long was significantly higher for laboratory‐conditioned specimens. Laboratory‐conditioned specimens less than 100 mm long had fecundities comparable to field‐conditioned specimens up to 140 mm long. The criterion of gonadal phases developed for laboratory specimens was compared to a field population from the collection area and indicated an annual gametogenic cycle. About 120 days are required for the completion of a reproductive cycle for red abalone in the field. Natural spawning occurred from April through July, with a peak in May. There was no evidence of partial spawning.