Activity and habitat use of two species of stingrays (Myliobatiformes: Potamotrygonidae) in the upper Paraná River basin, Southeastern Brazil

Abstract

The life history of freshwater stingrays (Potamotrygonidae) under natural conditions has been poorly documented. In this study, we investigated the period of activity and the habitat use of two species of the genus Potamotrygon in the upper Paraná River basin, Southeastern Brazil. Potamotrygon falkneri and P. motoro are similar to each other as far as the analyzed behavior is concerned. Individuals of both species segregate according to their size, and in function of the depth and period of the day. Younger individuals inhabit mostly sandy beaches and places that are no deeper than four meters throughout the whole day. Bigger stingrays realize bathymetric migrations, alternating their position between places deeper than eight meters during the day, and shallow areas at night. Individuals of intermediate size inhabit transition environments that have greater habitat diversity. Both species presented mostly nocturnal habits, especially regarding their feeding behavior. The behavioral patterns observed seem to go through ontogenetic variations and probably change throughout the year, between dry and wet seasons.Informações sobre o modo de vida das raias de água doce (Potamotrygonidae) sob condições naturais são escassas. Neste trabalho, estudamos o período de atividade e as formas de uso do habitat de duas espécies do gênero Potamotrygon na bacia do alto rio Paraná, no Sudeste do Brasil. Potamotrygon falkneri e P. motoro apresentaram comportamento muito semelhante, com nítida segregação espacial dos indivíduos em função do seu tamanho, da profundidade e do período do dia. Juvenis estiveram associados a praias arenosas e locais com profundidades abaixo de quatro metros ao longo de todo o dia. Raias de grande porte realizaram migrações batimétricas, alternando sua posição entre locais com profundidade superior a oito metros durante o dia e áreas mais rasas à noite. Indivíduos com tamanho intermediário ocuparam ambientes de transição, com maior heterogeneidade ambiental. Ambas as espécies apresentaram atividade, especialmente alimentar, predominantemente noturna. Os padrões comportamentais estudados parecem sofrer variações ontogenéticas e é provável que se alterem ao longo do ano, entre períodos de seca e cheia.

Nocturnal and crepuscular behavior in elasmobranchs: a review of movement, habitat use, foraging, and reproduction in the dark

“…For example, how behaviors during dark periods may differ according to individual life-stage or energetic condition, and behaviors in perpetually dark habitats. It is possible that juvenile elasmobranchs may reduce nocturnal activities to lower predation risk from larger conspecifics that actively forage during dark periods (Hammerschlag et al 2010). Individuals may also base their foraging decisions on body condition and health, as individuals in poor energetic condition may opt to assume increased predation risk in exchange for access to food resources and increases in probability of hunting success under low light conditions (Brown and Kotler 2004).…”

Proposal of a non-lethal visual census method to estimate freshwater stingray abundance

“…The advantage of nocturnal observation is that it permits the observer to see and quantify the number of neonates and juveniles, that during the day, stay in the deeper parts of their habitat, and adults that migrate at night towards the beaches on shore from the deeper waters of the main channel. This has been shown for P. motoro and P. falkneri in the upper Paraná River basin by Garrone Neto & Uieda (2012).…”

Geographic distribution of the short-tailed river stingray (Potamotrygon brachyura): assessing habitat loss and fishing as threats to the world’s largest obligate freshwater elasmobranch

“…An abiotic factor that affects the abundance of benthic organisms in the RdlP is the percentage of sand in the sediments (Rodrigues Capítulo et al 2002). This same factor is usually an important determinant of the abundance of many Potamotrygon species (Shibuya et al 2009;Garrone-Neto and Uieda 2012). An alternative hypothesis is that percentage of sand, rather than benthic fauna abundance itself, determines the congruence between the distribution of P. brachyura and the benthic fauna.…”