Growth and morphometric relationships of the bean clam Donax punctatostriatus Hanley, 1843 in a sandy beach of southern Sinaloa, Mexico
Esqueda-González, María del Carmen
Michel-Morfin, Jesús Emilio
There have been no published studies of the genus Donax in the eastern tropical Pacific. This work describes the morphometric relationships, growth and mortality of the bean clam Donax punctatostriatus Hanley, 1843 in the sandy beach of Isla de la Piedra, south of Mazatlán Bay, Mexico. Direct collections by hand were performed during 20 monthly sample periods (November 2008 to June 2010) in the intertidal zone of the beach. A total of 2,324 clams of different sizes were removed from the sand, then measured and weighed in the laboratory. The length range of the shells was 2.78-25.64 mm (mean = 12.61 ± 4.04 mm). The length-weight relationship of the total sample indicated isometric growth (a = 0.0002 g; b = 3.0 g mm-1, R2= 0.97); there was positive allometric growth in the recruits (<6.99 mm) (b = 3.4) and in juveniles (b = 3.2); in adults there was negative allometric growth (b = 2.6). Negative allometry of the length/width (log Wd = -0.239 + 0.922 log L) and height/width (log Wd = -0.054 + 0.900 log H) ratio of adults is consistent with a more compressed form of their shell, which assists rapid burying behavior in the sand. The maximum-recorded size of an empty shell (39 mm) was used to set the value of L∞ and to estimate K with the Shepherd (SLCA) method. The average growth rate during the life cycle was 0.43 mm yr-1. Values of L∞ between 29.16 and 34.22 mm were estimated with the Powell-Wetherall method using different class intervals. The mortality coefficient estimated with various methods was variable (0.84-1.15 yr-1). The growth of the clam is rapid and the mortality high, probably because of the characteristics of the habitat, in a subtropical region with high hydrodynamics and sediment transport.