Neritina snails upstream migrations at the intersection of Rio Mameyes with road PR Route 3 (bridge 1771)

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Data set ID: 



This data set includes N. virginea densities and sizes from two channels in lower Rio Mameyes under PR Route 3 bridge during the upstream migration season Aug-Dec 2000. Microhabitat use (near-bed water velocities and depth) within both channels is also included. Massive migrations in long trails occurring on the sloped concrete embankment of the main channel were also documented during 99 weeks. Individual size from migratory aggregations was measured during selected dates.

Date Range: 
2000-05-09 00:00:00 to 2002-06-30 00:00:00

Publication Date: 

2011-03-16 00:00:00



Additional Project roles: 

Name: Eda Melendez-Colom Role: Data Manager
Name: Frederick Scatena (In Memorium) Role: Associated Researcher


Snails on and under rocks were counted within 0.5 x 0.5 m quadrats (n=10) placed on the streambed on a weekly basis. Sampling quadrats were placed ˜1 m apart across the main channel (MC), and in five pairs along the side channel (SC). At SC, one quadrat of each pair was placed on the thalweg and another on the shallow part. In addition, a random sample of individuals was collected from each quadrat to measure shell size. Shell size was measured as aperture width (straight line running along the columnella from the base of the operculum to the shell shoulder on body whorl). Total length (TL, perpendicular to AW) is related to aperture width (AW) but cannot be measured in individuals with broken outer lips (TL=1.24AW+0.04, r2=0.98). Individuals were divided into the following size groups: <4.00 mm (spats), 4.00-6.00 mm (early juveniles), 6.00-8.00 mm (late juveniles), and >8.00 mm (adults). This grouping was based on preliminary field observations indicating distinctive behavior relative to individual size (cf., Pyron and Covich 2003). Spats had small and smooth, dark-brown shells, and were usually found underneath rocks. Juveniles exhibited greenish coloration with a variable pattern of axial lines or small yellow “tongues.” These juveniles were very mobile and were commonly found on the sides of rocks. Adults exhibited the same coloration as juveniles, but moved randomly and were more common on the top of rocks. Sexual maturation was not considered for the grouping because it may be variable in tropical neritids, and it is not easy to determine in small sized individuals. Each sampling date was classified as either a migration or non-migration event. Migratory events were readily identified becausetdsmall individuals were abundant and aggregated into dense clusters or long trails that persistently moved upstream. All massive migrations appeared a few of days after spates (>2 m3td/s) and increased snail density 2 to 10 times (200 - 800 ind.m-2td) over values observed during non-migration periods (20 - 100 ind.mtd-2). Near-bed water velocity was measured at 2 cm above the streambed using a Marsh-McBirney flowmeter. Each velocity measurement was averaged over 30 s and 3 to 5 measurements were made at each point. Ten points every 1 m were sampled across MC. Paired sampling points (thalweg vs. shallow) were measured in five cross sections along SC. Snail density, size, cohort percent and occurrence of massive migrations were correlated to discharge regime descriptors calculated using data from USGS gage 50066000 located 50 m upstream of Route 3 bridge.



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