Differences in the length-age relationship of the snail Astraea undosa (Wood, 1828) between two localities of Tortugas Bay, Baja California Sur, Mexico

The differences in basal diameter (DB), age and DB-age of the snail Astraea undosa in two zones of Tortugas Bay (Mexico) were studied from November 1996 to November 1997. Age was determined by counting the opercular growth marks. The age groups were annual. The interval size was of 49 to 118 mm DB in snails of 2 to 12 years of age. Monthly frequency distributions of the DB and of age between zones were significantly different, except for the age distributions of November 1996, and June and November 1997. The legal minimum catch size (90 mm DB) is reached in one zone at 5 years and in the other at 9 years, on average, indicating a different growth pattern between zones. The differences in DB-age between zones were significant at 4 years of age. To promote a rapid growth of the snails from the slowgrowth zone, we suggest moving individuals of ≥63 mm DB to better growth zones.