Size at onset of maturity of spiny lobsters Panulirus homarus homarus at Mambrui, Kenya

Abstract

The size at onset of sexual maturity of the scalloped spiny lobster Panulirus homarus homarus captured off Mambrui, Kenya, was estimated from ovary condition, presence of external eggs and/or spermatophore remains (berry method), and presence of well developed ovigerous setae (setal method). The predictive utility of morphometric relationships between carapace length (CL), pleopodal exopodite length (exopod length) and second leg length were assessed by fitting linear regressions to lobsters categorised as immature and mature, and comparing the intersect values with other estimates of functional maturity. The smallest female with mature ovaries was 52mm CL, compared with the smallest specimens of 50mm with ovigerous setae and 54mm with external eggs. Logistic curves indicated that 50% maturity was reached at 52.6mm (setal method) or 63.4mm (berry method) during the main breeding season. Female exopod lengths suggested that functional maturity was reached at 50.5mm and male leg lengths increased significantly upon reaching 57.5mm. The analyses indicate that measurements of female exopods and male second leg length can be used as cost-effective methods to estimate size at functional maturity of P. homarus homarus in Kenyan waters, and that these indices can augment estimates based on the presence of external eggs and ovigerous setae.