Reproductive biology of the scalloped hammerhead shark Sphyrna lewini (Chondrichthyes: Sphyrnidae) off south-west Mexico
Published on 15 January 2011
Marcela Bejarano-Álvarez, Felipe Galván-Magaña and Rosa Isabel Ochoa-Báez
ABSTRACT:
The scalloped hammerhead shark Sphyrna lewini is the most important species in the artisanal shark fishery in the Gulf of Tehuantepec, Mexico. Knowledge about the reproductive biology of this species in the area is nonexistent, despite its being listed worldwide as endangered by the IUCN. To determine the basic reproductive biology of this shark would give important data for management or conservation plans for this species in Mexico. Samples were collected of 991 hammerhead sharks (342 females and 649 males), including juveniles (45 to 160 cm TL) and adults (170 to 288 cm TL), from September 2004 to June 2006. The sex ratio was 1F: 2M. The scalloped hammerhead was present year round in the study area with the greatest catch from May to July, the season when pregnant females were present. The females reached sexual maturity at 220 cm TL based on characteristics and measurements of reproductive organs. A histological analysis showed that testes in males are a diametric type and have compound spermatozeugmata in the seminal vesicles, indicating sexual maturity in males at 180 cm TL. We recorded 40 pregnant females, with 14 to 40 embryos per female. The births occurred in July and August with an embryo size of between 41 and 51 cm TL. The presence of neonates, juveniles, and pregnant females with embryos in an advanced development condition suggest that the coastal waters off Oaxaca are an important nursery area for the scalloped hammerhead shark.
aqua International Journal Volume 17, Issue 1