On the Spawning of the Oval Squid Sepioteuthis lessoniana in the Coastal Waters off Kyoto Prefecture

From diving observations and spawning examination using artificial substrata settled on the sea bed at 5-50m depths in the sea off Kyoto prefecture, the spawning season and spawning grounds of the oval squid Sepioteuthis lessoniana were studied from April to July, 1991. With a rise in water temperature above 16°C in coastal waters, mature females migrated to the inshore spawning grounds in the middle of May to lay their eggs. The depth of spawnIng gradually descended during the spawning period to the 30-40m depth range in the middle of June. Samples of mature males and females were collected off Kyoto prefecture using set nets from May to July, 1991. All investigated females, including those without spermatophores embedded in the buccal membrane, had sperm in their seminal receptacles. The average number of spermatophores of males decreased during the spawning period. Judging from the maximum number of spermatophores of a male that embedded in the buccal membrane of a female, males may copulate repeatedly about 10 times during the spawning period.