Seasonal variation in abundance of the Indian mackerel,Rastrelliger kanagurtaCuvier (Pisces: Scombridae) along the Zanzibar coast of East Africa

摘要

Purse-seine catches of the mackerel,Rastrelliger kanagurtaCuvier along the west coast of Zanzibar revealed seasonal patterns of abundance associated with monsoon winds. Low catches were obtained during the south-east monsoons while the north east monsoons were characterised by high catches. The largest sizes of mackerel were caught between June and August with a mixture of large and smaller ones between September and March. Mackerel in spawning condition were common between June and September with immature ones between September and January. The variations in mackerel abundance, size composition, and maturity of the fish are discussed in relation to seasonal changes, fish migrations, recruitment and food supply.