Todd-Pearson, S., 2004.  Growth rate of the gastropod mollusk Hexaplex nigritus: implications for fishery management in the Gulf of California.  Gulf of California Conference, Tucson, AZ, June, 2004.

Hexaplex nigritus, commonly known as the black murex, is a commercially important species of gastropod in the northern Gulf of California. Effective management of this fishery requires that the species’ growth rate is known. I analyzed the δ18O content of samples of H. nigritus shell taken at varying distances from the shell’s growing edge in an approximately 16 cm long specimen from Bahia la Choya, Sonora, Mexico. δ18O values vary from 1.69 to –1.73 per mil and showed two cycles in the final 45.91 mm of the shell. Because δ18O varies inversely with the water temperature these δ18O cycles probably represent two years of growth. The average rate of growth in the final two years of life of this specimen is 21.30 mm/yr. This compares with an average growth rate of 35.43 mm/yr in Strombus gigas, a commercially harvested species in the Caribbean. The preliminary results from this research suggest that H. nigritus has a slower growth rate. This growth rate of H. nigritus indicates that the murex fishery is likely to be sustainable at levels somewhat lower than the fishery of Strombus gigas.