Resource partitioning between two young‐of‐year cownose rays Rhinoptera bonasus and R. brasiliensis within a communal nursery inferred by trophic biomarkers

Abstract

Aperfeiçoamento de Pessoal de Nível Superior -Brasil (CAPES) -Finance Code 001 for the Master scholarship.Although interspecific trophic interactions plays a principal role within elasmobranch communal nurseries, little is known over variation in foraging strategies adopted by young-of-year of sympatric species. To test the hypothesis of dietary resource partitioning between batoids within a communal nursery, we investigated two cownose ray species, Rhinoptera bonasus and R. brasiliensis, which occur in heterospecific groups, a strategy predicted to increase survival and foraging success. Using two biochemical tracers, fatty acids (FA) and stable isotopes (δ 15 N and δ 13 C), the combined effects of maternal investment and the formation of heterospecific groups implying competition for, or partitioning of available food resources were investigated. Through univariate and multivariate analyses of biochemical tracers in several tissues (fin clip, muscle, liver, red blood cells; RBC) and plasma, our results revealed significant interspecific differences in tracers between the two species. Total FAs ( P saturated FA, P monounsaturated FA and P polyunsaturated FA) and trophic biomarkers (i.e., docosahexaenoic acid, arachidonic acid, oleic acid and δ 15 N) were the principle tracers responsible for the differences detected. These data revealed that R. brasiliensis was less enriched in physiologically important essential FAs than R. bonasus. Our findings suggest that these congeneric species differ in maternal investment strategy and moderately partition food resources over relatively fine spatial scales within a single nursery habitat to limit competition. These results provide further knowledge on the foraging strategies adopted by batoids in communal nursery areas, information that is required for improving spatial conservation and management planning. K E Y W O R D S elasmobranch, fatty acids, life history strategy, maternal investment, stable isotopes, trophic ecology

Mercury concentrations and trophic relations in sharks of the Pacific Ocean of Colombia

“…Regarding the amplitude and overlapping patterns, only fin samples were considered since this tissue has been already employed in stable isotope and fatty acid analyzes in sharks (Every et al, 2016;Rangel et al, 2019), revealing feeding habits and habitat use over periods of time of more than a year due to its slow turn-over rate (Malpica-Cruz et al, 2012). Niche overlap of all species is not 100% in terms of trophic level (δ 15 N).…”

Trophic niche of Australian cownose rays (Rhinoptera neglecta) and whitespotted eagle rays (Aetobatus ocellatus) along the east coast of Australia

“…The trophic ecologies and resource use of elasmobranchs have been extensively explored and attributed to various intrinsic and extrinsic factors, including body size or ontogenetic stage (Ajemian & Powers, 2012; Heithaus et al ., 2013; Sommerville et al ., 2011), morphology (Yemişken et al ., 2018; Yick et al ., 2011), prey availability (Armstrong et al ., 2016; Frixione et al ., 2020; Stewart et al ., 2017), geographic location (Ajemian & Powers, 2012; Bird et al ., 2018) and resource partitioning or competition with co‐occurring species (Kinney et al ., 2011; Papastamatiou et al ., 2006; Rangel et al ., 2019; Raoult et al ., 2015). However, much of this existing research is biased towards sharks, with ray species considerably underrepresented in ecological studies, especially those involving trophic interactions or diet.…”

Trophic resources and mercury exposure of two silvertip shark populations in the Northeast Pacific Ocean

“…Various types of shark tissues have been used for ecological tracers analyzes, providing different time integration according to tissue turnover rate, from few months (plasma and liver) to approximately one year (muscle) (Sora Lee Malpica-Cruz et al, 2012). Generally sampled for genetic analyzes, fin clips have recently been employed in stable isotope and fatty acid analyses in sharks (Every et al, 2016;Rangel et al, 2019), revealing feeding habits and habitat use over long periods of time (i.e. more than a year) (Malpica-Cruz et al, 2012).…”