CHANGES IN THE QUEEN CONCH (STROMBUS GIGAS L.) POPULATION STRUCTURE AT BANCO CHINCHORRO, QUINTANAROO, MEXICO, 1990-1997

摘要

Changes in the queen conch population structure from 1990-1997 were analyzed. Density and length-frequency data were collected in four fishing sites within Banco Chinchorro, using four random sample units of 100 m~2. All conchs contained in the sample unit were measured for shell length and returned to the bottom. Von Bertalanffy's growth parameters, natural mortality, and total mortality were calculated. There was a significant decrease in conch density over the years. The highest density (2.651 conchs m~(-2)) occurred in 1992 at Cayo Norte and lowest occurred in 1994 (0.108 conchs m~(-2)) and 1997 (0.006 conchs m~(-2)) at Isla Che. There were significant differences in mean shell length (SL) between years. In 1994 mean SL was 229.30 +- 2.07 mm; in 1997 mean SL was only 128.30 +- 3.23 mm and 99.31% of conchs were lesser than 200 mm SL. No significant differences in the L_∞ were detected from 1990-1997, but K had higher values in 1997 (K = 0.45) indicating presence of a juvenile population, with a higher natural mortality (M = 1.06). Conch stock at Banco Chinchorro is overexploited and if the levels of harvesting continue the fishery is predicted to collapse in a short period. A total ban of five years is proposed and more conservative management measures are recommended in order to maintain a sustainable conch fishery.