Age and growth of two sharpnose shark species (Rhizoprionodon lalandii and R. porosus) in subtropical waters of the south-western Atlantic

Abstract

The age and growth of subtropical populations of the Brazilian and Caribbean sharpnose sharks (Rhizoprionodon lalandii and R. porosus respectively) were determined by combining direct and indirect ageing methods, maximising the use of available information. Using vertebrae ageing for R. lalandii, the theoretical maximum length L∞ and growth coefficient k were 661.9mm and 1.14 year–1 for males and 751.7mm and 0.59 year–1 for females. Vertebrae were not sampled for R. porosus. Values of L∞ and k from electronic length–frequency analyses (ELEFAN) were 762mm and 0.71 year–1 for male R. lalandii, 791mm and 0.67 year–1 for female R. lalandii, 1040mm and 0.41 year–1 for male R. porosus and 1165mm and 0.31 year–1 for female R. porosus. Growth during the first year of life in relation to birth size was 80.3% for R. lalandii and 55% for R. porosus. Both species exhibit rapid growth, primarily in the first year of life. The growth estimates for R. lalandii and R. porosus are even faster than those reported in previous studies from tropical populations.