Effects of scale and habitat distribution on the movement of the southern stingray Dasyatis americana on a Caribbean atoll

Abstract

The structure of animal movement paths at varying spatial scales allows insight into the importance of habitat distribution and their response to scale in heterogeneous landscapes. Home-ranging animals typically exhibit constrained random movements at large spatial scales, with small-scale orientation reflecting responses to sensory stimuli. The southern stingray Dasyatis americana is an abundant demersal elasmobranch found in coastal systems throughout the Caribbean, yet very little is known of its movement ecology. Twelve southern stingrays were manually tracked at Glovers Reef (Belize) for up to 32 non-continuous hours to evaluate movement structure and activity space. Response to spatial scale was analysed using fractal analysis, and domains of scale were compared to habitat spatial characteristics. Mean stingray activity space was relatively small (< 0.5 km 2) with daytime activity space significantly larger than nighttime activity space. Movement paths showed significant straightening correlated with increasing size in females. Stingray movement structure exhibited 2 distinct domains: at scales of <100 m, paths were more dispersed than a correlated random walk (CRW), and at scales >100 m, paths were more constrained than CRW, indicating directed movement at scales up to 100 m. Nearest neighbour spatial analysis of lagoon patch reefs showed mean spacing of 100 m (± 4.5), equivalent to orientation distance seen in rays. Random walk movements at large scales are consistent with a home-ranging animal; however, larger scale orientation than expected and patch reef spacing equalling 100 m suggests that patch reefs represent important spatial and ecological networks, strongly influencing stingray movement, habitat use, and dispersal.

Diet Reconstruction and Resource Partitioning of a Caribbean Marine Mesopredator Using Stable Isotope Bayesian Modelling

“…This variation may relate to ontogenetic diet shifts [45] , [46] , where growing predators feed on progressively larger prey items, or a completely distinct prey set [47] . Isotopic nitrogen values in stingray muscle and skin tissues showed positive correlations with size, however, stingrays tracked acoustically at GRA showed no expansion of activity space or habitat shifts with ontogeny [32] . This suggests that an increase in δ 15 N could be attributed to eating larger prey items rather than a diet shift, however greater sampling of consistent tissue type will be needed to confirm positive ontogenetic diet shifts.…”

“…This would suggest that diet variations recorded in D. americana are responses to different sampling period, however the Glovers Reef lagoon is a relatively stable environment with low flushing rates, limited wave action and stable sediments, and no variation with sampling month was observed at GRA within the sampled months. Given the high site fidelity of stingrays and restricted movement within the same base isotope system [32] , stark seasonal variations to diet are unlikely, however, more complete seasonal sampling will be necessary to more confidently assess this.…”

“…They are commonly found in shallow reef and lagoon habitats of coastal areas and offshore atolls, where they can reach extremely high densities [31] . D. americana shows very restricted movements and high site fidelity in areas characterised by sand flats, patch reefs and seagrass beds [32] . The diet of D. americana is relatively well characterised from six known stomach content studies [6] , [10] , [11] , [26] , [33] , [34] .…”

Prenatal stress from trawl capture affects mothers and neonates: a case study using the southern fiddler ray (Trygonorrhina dumerilii)

“…Compared to oviparous species, viviparous species are likely to be most vulnerable to reproductive disturbance, particularly those whose breeding habitats overlap with both commercial and recreational fisheries. Symptoms of stress observed in our study could therefore manifest in fisheries where frequent recaptures are possible, particularly in species that can exhibit high site-fidelity7475. For example, T. dumerilii frequently occupy areas in Port Phillip Bay that are extensively fished by both commercial and recreational hook-and-line fishers and it is not uncommon for repeat captures of an individual animal to occur within hours or weeks (L. Guida pers.…”

Dietary composition and prey selectivity of juvenile porcupine rays Urogymnus asperrimus

“…Although myliobatoids are often thought to mediate prey communities (Navia et al ., ; Vaudo & Heithaus, ; O'Shea, ), in tropical marine ecosystems trophic complexity is generally high and there are both strong and weak predator–prey interactions present (Connell et al ., ; O'Gorman et al ., ). The strength of an interaction is a measure of influence over one another (Tilley, ) and only if a predator displays a strong predator–prey interaction can it potentially have strong influences over its prey species. As U .…”