growth rates

Migration patterns, densities, and growth of Neritina snails in Rio Espiritu Santo and Rio Mameyes, northeastern Puerto Rico

PYRON, MARK; COVICH, ALAN P. 2003. Migration Patterns, Densities, and Growth of Neritina punctulata Snails in Rio Espiritu Santo and Rio Mameyes, Northeastern Puerto Rico.. Caribbean Journal of Science, Vol. 39, No. 3, 338-347, .

Abstract: 
Snail size-frequency distributions in Rios Espiritu Santo and Mameyes, which drain the Luquillo Experimental Forest, Puerto Rico, showed that Neritina punctulata with shell lengths greater than 30 mm were the most abundant size class at upstream sites. The highest densities for all size classes were at the downstream sites. Growth rates were 0.015 mm/day for a large cohort (¡«25 mm shell length) and 0.035 mm/day for a small (¡«15 mm shell length). Minimum longevity estimates range from 3 to 7 years. Size distribution data suggest that snails migrate upstream. An August mark-recapture study resulted in most snails remaining at the release site, and some moved downstream. The greatest upstream distance reached was 200 m in 12 weeks. In a May mark-recapture study, when snails were observed moving in aggregations, the greatest distance moved was 200 m in 27 days, suggesting seasonality in movements and reproduction. Movement rates of snails in aggregates in May were between 0.08 and 0.17 cm/s. All of the snails marked in May moved upstream, and none were observed downstream from, or at the release site. We suggest that upstream movements can be explained by snails avoiding increased predation in the downstream reaches of these rivers from fishes, crustaceans, and birds
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