Size structure and reproductive variation of the spiny lobster Panulirus homarus over a relatively small geographic range along the Dhofar coast in the Sultanate of Oman

Abstract

This paper reports variations in size structure, size at sexual maturity, and reproductive potential in the Panulirus homarus population sampled from commercial catches at three sites: Shuwamiyah, Sudh and Mugsyl along the Dhofar coast in the Sultanate of Oman. The size structure of the lobster population showed significant variation (P < 0.001) among the three sites. Size at sexual maturity, based on the presence of spermatophores or an ovigerous condition, indicated variation within the population. Females mature at a smaller size at Shuwamiyah than they do at Sudh and Mugsyl. The relationship between the number of eggs (E) and carapace length (L, in mm) of female lobsters is expressed by E = –249322 + 8942L (r2 = 0.95; n = 11) over the size range 65–95 mm carapace length. Length frequency, size at sexual maturity, and fecundity were used to estimate the index of reproductive potential (IRP) of each 5-mm size class. The size class with the highest IRP varied among the three sites. The variation in size structure and size at sexual maturity was explained by fishery exploitation and by different oceanographic and ecological conditions caused by seasonal upwelling in the study region.