Manta birostris , predator of the deep? Insight into the diet of the giant manta ray through stable isotope analysis

Abstract

The characterization of diet for the giant manta ray Manta birostris has been problematic given their large-scale movement patterns and the difficulty in obtaining stomach contents from this species. The large majority of existing information is based on observational data limited to feeding events at the sea surface during daylight. Recently discovered aggregation sites for the giant manta ray off mainland Ecuador are some of the most accessible to date and provide a unique opportunity for researchers to gather much needed information on this elusive species. To assess how important surface zooplankton is to giant manta ray diet, we conducted stable isotope analysis (15N and 13C) on M. birostris muscle and surface zooplankton. Trophic position estimates placed M. birostris overall at a secondary consumer level of approximately 3.4 but there was large variation in δ15N and δ13C values among individuals. Manta birostris muscle tissue δ13C values were also not consistent with this species feeding predominantly on surface zooplankton and suggest that the majority of dietary intake is of mesopelagic origin. Given the conservative life history and fisheries pressure on large planktivores, knowledge of their trophic role and foraging strategies is essential to better understand their ecology and develop effective conservation measures.

Enhancing insights into foraging specialization in the world's largest fish using a multi‐tissue, multi‐isotope approach

“…There is evidence that R. typus make regular deep dives, including in excess of 1000 m where they may encounter temperatures as low as 4°C (Wilson et al 2006). Both R. typus and the planktivorous reef manta ray Mobula alfredi have been shown to perform reverse diurnal migrations, which may be linked to stochastic feeding on abundant mesopelagic zooplankton layers (Gleiss et al 2013, Tyminski et al 2015, Burgess et al 2016, Stewart et al 2016). In addition to thermoregulation, returning to surface waters post-dive would aid in more efficient assimilation of prey consumed at depth.…”

Southernmost record of the Giant Manta Ray Mobula birostris (Walbaum, 1792) in the Eastern Pacific

“…Thus, we suggest that M. birostris was preying on P. monodon. Even though the observed individual was seen with its cephalic fins closed at 16 m deep, suggesting a non-feeding behavior (Ari & Correia, 2008) and recent work has found that M. birostris mainly feeds on deep-water zooplankton (Burgess et al, 2016;, the possibility that this muninid crustacean could be a prey of Mobula spp. shall not be completely discarded as few studies have determined that zooplankton, shrimps, crabs and small fishes are key items on giant manta rays diet (Bigelow & Schroeder, 1953;Couturier et al, 2012;Rohner et al, 2017).…”

Interactions between Manta birostris and Sotalia guianensis in a World Heritage listed Brazilian estuary

“…and has been attributed to mating displays, parturition, removing attached remoras, playing and communicating (Rayner, ; Medeiros et al ., ). Based on the observations here, sequential breaches by M. birostris above schools would disrupt and disorientate individuals thereby increasing the chances of predation, although it remains uncertain if teleosts are a dietary component (Burgess et al ., ). If teleosts are targeted by M. birostris , then the arrival of S. guianensis and competition for the same prey would represent amensalism.…”

“…Despite its global distribution and status as the world's largest batoid, the ecology and biology of M. birostris remain poorly understood and are based on opportunistic observations (Luiz et al, 2009;Medeiros et al, 2015;Burgess et al, 2016). Their diet is thought to comprise predominantly zooplankton (Burgess et al, 2016); differences in the relative spatio-temporal abundances of which probably affect M. birostris distributions (Luiz et al, 2009).…”

“…Despite its global distribution and status as the world's largest batoid, the ecology and biology of M. birostris remain poorly understood and are based on opportunistic observations (Luiz et al, 2009;Medeiros et al, 2015;Burgess et al, 2016). Their diet is thought to comprise predominantly zooplankton (Burgess et al, 2016); differences in the relative spatio-temporal abundances of which probably affect M. birostris distributions (Luiz et al, 2009). Specifically, the wet summers (typical rainfall >2500 mm year −1 ) in southern Brazil produce high levels of suspended organic material and nutrients in estuaries which support zooplankton and their predators (Possatto et al, 2016) and might explain why M. birostris is most frequently observed in the PEC from January to April (Medeiros et al, 2015).…”