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Feeding habits of Urotrygon microphthalmum (Myliobatiformes: Urotrygonidae) caught off northeastern Brazil

Abstract

The feeding habits of Urotrygon microphthalmum, a Critically Endangered (CR) species, were investigated through stomach contents analysis from specimens caught on bottom double rigged otter trawls in Pernambuco state, Brazil, between March of 2010 and March of 2012. A total of 338 stomachs were analyzed, and 31 food items were identified in the diet of U. microphthalmum. The species ingests mainly shrimps. The diets between males and females were not different, and an ontogenetic diet shift was not observed. The estimated species’ trophic level is 3.5, classifying it as a secondary order consumer.

Keywords:
Batoid; Diet; South Atlantic ray; Stomach contents; Trophic level

Resumo

Os hábitos alimentares de Urotrygon microphthalmum, uma espécie Criticamente Em Perigo (CR), foram investigados através de análise de conteúdo estomacal de espécimes capturados no arrasto duplo com portas no estado de Pernambuco, Brasil, entre março de 2010 e março de 2012. Um total de 338 estômagos foram analisados e 31 item alimentares foram identificados na dieta de U. microphthalmum. A espécie ingere principalmente camarões. A dieta entre machos e fêmeas não foi diferente e não foi observada mudança ontogenética na dieta. O nível trófico estimado da espécie é 3,5, classificando-a como consumidora de segunda ordem.

Palavras-chave:
Conteúdo estomacal; Dieta; Nível trófico; Raia; Raias

INTRODUCTION

Trophic ecology studies have long used stomach content analyses as an important tool in understanding the trophic position of species and their interactions (e.g., Bornatowski et al., 2014bBornatowski H, Navia AF, Braga RR, Abilhoa V, Corrêa MF. Ecological importance of sharks and rays in a structural foodweb analysis in southern Brazil. ICES J Mar Sci. 2014b; 71(7):1586–92. https://doi:10.1093/icesjms/fsu025
https://doi:10.1093/icesjms/fsu025...
; Navia et al., 2017Navia AF, Mejía-Falla PA, López-García J, Giraldo A, Cruz-Escalona VH. How many trophic roles can elasmobranchs play in a marine tropical network? Mar Fresh Res. 2017; 68(7):1342–53. https://doi.org/10.1071/MF16161
https://doi.org/10.1071/MF16161...
). These dietary data facilitate construction of network trophic interaction models, which are essential for predicting the possible effects of species presence or absence in an ecosystem (e.g., Bornatowski et al., 2014aBornatowski H, Braga RR, Abilhoa V, Corrêa MFM. Feeding ecology and trophic comparisons of six shark species in a coastal ecosystem off southern Brazil. J Fish Biol. 2014a; 85(2):246–63. https://doi:10.1111/jfb.12417
https://doi:10.1111/jfb.12417...
; Navia et al., 2016Navia AF, Cruz-Escalona VH, Giraldo A, Barausse A. The structure of a marine tropical food web, and its implications for ecosystem-based fisheries management. Ecol Model. 2016; 328:23–33. https://doi.org/10.1016/j.ecolmodel.2016.02.009
https://doi.org/10.1016/j.ecolmodel.2016...
).

Conventionally, small-bodied elasmobranchs (< 150 cm total length) are classified as mesopredators and are often consumed by large sharks and other predators (Ferretti et al., 2010Ferretti F, Worm B, Britten GL, Heithaus MR, Lotze HK. Patterns and ecosystem consequences of shark declines in the ocean. Ecol Lett. 2010; 13(8):1055–71. http://dx.doi.org/10.1111/j.1461-0248.2010.01489.x
http://dx.doi.org/10.1111/j.1461-0248.20...
; Vaudo, Heithaus, 2011Vaudo JJ, Heithaus MR. Dietary niche overlap in a nearshore elasmobranch mesopredator community. Mar Ecol Progr Ser. 2011; 425:247–60. https://doi.org/10.3354/meps08988
https://doi.org/10.3354/meps08988...
; Navia et al., 2017Navia AF, Mejía-Falla PA, López-García J, Giraldo A, Cruz-Escalona VH. How many trophic roles can elasmobranchs play in a marine tropical network? Mar Fresh Res. 2017; 68(7):1342–53. https://doi.org/10.1071/MF16161
https://doi.org/10.1071/MF16161...
), although this trophic niche may change according to size class, habitat use, behaviour, and ontogeny (Heupel et al., 2014Heupel MR, Knip DM, Simpfendorfer CA, Dulvy NK. Sizing up the ecological role of sharks as predators. Mar Ecol Prog Ser. 2014; 495:291–98. http://dx.doi.org/10.3354/meps10597
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; Roff et al., 2016Roff G, Doropoulos C, Rogers A, Bozec YM, Krueck NC, Aurellado E et al. The ecological role of sharks on coral reefs. Trends Ecol Evol. 2016; 31(5):395–407.https://doi.org/10.1016/j.tree.2016.02.014
https://doi.org/10.1016/j.tree.2016.02.0...
). Overall, mesopredators provide a crucial link between top predators and lower trophic levels in marine ecosystems and play an important role in ecosystem dynamics (Vaudo, Heithaus, 2011Vaudo JJ, Heithaus MR. Dietary niche overlap in a nearshore elasmobranch mesopredator community. Mar Ecol Progr Ser. 2011; 425:247–60. https://doi.org/10.3354/meps08988
https://doi.org/10.3354/meps08988...
; Bornatowski et al., 2014aBornatowski H, Braga RR, Abilhoa V, Corrêa MFM. Feeding ecology and trophic comparisons of six shark species in a coastal ecosystem off southern Brazil. J Fish Biol. 2014a; 85(2):246–63. https://doi:10.1111/jfb.12417
https://doi:10.1111/jfb.12417...
). The smalleye round ray Urotrygon microphthalmum Delsman, 1941 is a small batoid and occurs from Venezuela to Brazil. It is the only species of the family Urotrygonidae to inhabit Brazilian northeastern waters (Bigelow, Schroeder, 1953Bigelow HB, Schroeder WC. Sawfishes, Guitarfishes, Skate and Rays, Chimaeroids. New Haven: Sears Foundation of Marine Research; 1953. https://doi.org/10.2307/j.ctvbcd0f3
https://doi.org/10.2307/j.ctvbcd0f3...
; Almeida et al., 2000Almeida ZS, Nunes JS, Costa CL. Presencia de Urotrygon microphthalmum (Elasmobranchii: Urolophidae) en aguas bajas do Maranhão (Brazil) y notas sobre su biología. Bol Invest Mar Cost. 2000; 29:67–72.; Santander-Neto, Lessa, 2013Santander-Neto J, Lessa RPT. Hermaphroditic smalleyed roundray (Urotrygon microphthalmum) from north-eastern Brazil. Mar Biodiversity Rec. 2013; 6:e60. https://doi.org/10.1017/S1755267213000353
https://doi.org/10.1017/S175526721300035...
). According to McEachran, Carvalho, (2002)McEachran JD, Carvalho MR. Batoid Fishes. In: Carpenter KE, editor. The living marine resources of the Western Central Atlantic. Volume 1: Introduction, molluscs, crustaceans, hagfishes, sharks, batoid fishes, and chimaeras. Rome: Food and Agriculture Organization of the United Nations; 2002. p.508–30., individuals can grow up to a maximum of 300 mm total length. The species usually dwells in several environments such as estuaries, bays, inner platform shelves and islands, and is generally associated with muddy substrates (Piorski, Nunes, 2000Piorski NM, Nunes JLS. Dimorfismo sexual e tendência alométrica em Urotrygon microphthalmum Delsman, 1941 (Elasmobranchii: Urolophidae). Bol Lab Hidrobiol. 2000; 13(1):67–81. ).

Some basic aspects of the species’ biology have been studied in northern Brazil (Maranhão State) (Almeida et al., 2000Almeida ZS, Nunes JS, Costa CL. Presencia de Urotrygon microphthalmum (Elasmobranchii: Urolophidae) en aguas bajas do Maranhão (Brazil) y notas sobre su biología. Bol Invest Mar Cost. 2000; 29:67–72.; Piorski, Nunes, 2000Piorski NM, Nunes JLS. Dimorfismo sexual e tendência alométrica em Urotrygon microphthalmum Delsman, 1941 (Elasmobranchii: Urolophidae). Bol Lab Hidrobiol. 2000; 13(1):67–81. ; Costa, Almeida, 2003Costa CL, Almeida ZS. Hábito Alimentar de Urotrygon microphthalmum Delsman, 1941 (Elasmobranchii: Urolophidae) em Tutoia, Maranhão. Bol Lab Hidrobiol. 2003; 16(1):7–54. ). Almeida et al., (2000)Almeida ZS, Nunes JS, Costa CL. Presencia de Urotrygon microphthalmum (Elasmobranchii: Urolophidae) en aguas bajas do Maranhão (Brazil) y notas sobre su biología. Bol Invest Mar Cost. 2000; 29:67–72. reported that all females bigger than 239 mm in total length were mature and that males were fully mature from 219 mm. However, Santander-Neto et al. (2016)Santander-Neto J, Araújo MLG, Lessa RP. Reproductive biology of Urotrygon microphthalmum (Baitodea: Urotrygonidae) from North-East Brazil, tropical west Atlantic Ocean. J Fish Biol. 2016; 89(1):1026–42. https://doi.org/10.1111/jfb.12951
https://doi.org/10.1111/jfb.12951...
estimated that size at maturity for males and females were 187 and 198 mm of total length, respectively. The authors reported that mysids and cumaceans were predominant in the diet, and the species was deemed as an opportunistic feeder (Almeida et al., 2000Almeida ZS, Nunes JS, Costa CL. Presencia de Urotrygon microphthalmum (Elasmobranchii: Urolophidae) en aguas bajas do Maranhão (Brazil) y notas sobre su biología. Bol Invest Mar Cost. 2000; 29:67–72.; Costa, Almeida, 2003Costa CL, Almeida ZS. Hábito Alimentar de Urotrygon microphthalmum Delsman, 1941 (Elasmobranchii: Urolophidae) em Tutoia, Maranhão. Bol Lab Hidrobiol. 2003; 16(1):7–54. ).

Due to its small size, knowledge on much of U. microphthalmum biology is scarce and it has no commercial value as bycatch in trawl fisheries for prawn. Despite being globally categorized as Critically Endangered (CR) on the IUCN’s Red List (Pollom et al., 2020Pollom R, Charvet P, Faria V, Herman K, Lasso-Alcalá O, Marcante F et al. Urotrygon microphthalmum. The IUCN Red List of Threatened Species. 2020; e.T44598A2998129.https://dx.doi.org/10.2305/IUCN.UK.2020-3.RLTS.T44598A2998129.en
https://dx.doi.org/10.2305/IUCN.UK.2020-...
), the species was assessed in Brazil as Data Deficient (DD), meaning that there are not enough data on the species to assess its extinction risk (MMA, 2014Ministério do Meio Ambiente (MMA). Portaria 445, de 17 de dezembro de 2014. Brasil: Ministério do Meio Ambiente; 2014. Available from: https://www.ibama.gov.br/component/legislacao/?view=legislacao&force=1&legislacao=134521#:~:text=Ementa%3A,Extin%C3%A7%C3%A3o%20%2D%20Peixes%20e%20Invertebrados%20Aqu%C3%A1ticos.
https://www.ibama.gov.br/component/legis...
; ICMBio, 2016ICMBio. Avaliação do risco de extinção dos elasmobrânquios e quimeras no Brasil: 2010–2012. Itajaí, SC: Instituto Chico Mendes; 2016. Available from: http://www.icmbio.gov.br/cepsul/images/stories/biblioteca/download/trabalhos_tecnicos/pub_2016_avaliacao_elasmo_2010_2012.pdf
http://www.icmbio.gov.br/cepsul/images/s...
). This study aims to analyze feeding habits and trophic ecology using stomach contents of U. microphthalmum caught off the shore of Pernambuco, in northeast Brazil.

MATERIAL AND METHODS

Sampling. All analyzed specimens of Urotrygon microphthalmum were caught between March 2010 and March 2012 as by-catch of prawn-trawl operations. The target species of this fishery are white shrimp Litopenaeus schmitti (Burkenroad, 1936), seabob shrimp Xiphopenaeus kroyeri (Heller, 1862), pink shrimps Farfantepenaeus subtilis (Pérez-Farfante, 1967), and F. brasiliensis (Latreille, 1817). Fisheries operations occurred off the coast of Pernambuco, northeastern Brazil (08º11’43’’S 34º54’13’’W and 08º38’44’’S 35º01’24’’W) (Fig. 1).

FIGURE 1 |
Area of prawn-trawling fleet operation in: A) Jaboatão dos Guararapes; B) Barra de Sirinhaém.

The fishing gear used was twin bottom trawls. Each net was 10 m in length, 6 m at the mouth, and was formed by a 20 mm mesh in the body of the net and a 15 mm mesh in the bag. During operations, mean velocity of trawls was 3.7 km.h−1 (2 knots) which lasted 4 h in average. The fleet fishes daily in muddy and sandy bottoms but also with the presence of calcareous algae (Kempf, 1970Kempf M. A plataforma continental de Pernambuco (Brasil): Nota preliminar sobre a natureza do fundo. Trab Oceanogr Univ Fed Pernambuco. 1970; 9(11):111–24.; Manso et al., 2003Manso VAV, Corrêa ICS, Guerra NC. Morfologia e sedimentologia da Plataforma Continental Interna entre as praias Porto de Galinhas e Campos - Litoral sul de Pernambuco. Pesq Geoc. 2003; 30(2):17–25. https://doi.org/10.22456/1807-9806.19587
https://doi.org/10.22456/1807-9806.19587...
).

Care and use laws for experimental animals welfare were not applied in this study due to the nature of data collection from commercial fishing landings. Some of the specimens used in this study were deposited under the voucher number LBP 0255 (Laboratório de Biologia e Genética de Peixes, Instituto de Biociências, Universidade Estadual Paulista “Júlio de Mesquita Filho”, Botucatu). For each specimen the total length (LT, mm), total weight (WT, g), stomach weight (WS, g) and maturity level according to Santander-Neto et al., (2016)Santander-Neto J, Araújo MLG, Lessa RP. Reproductive biology of Urotrygon microphthalmum (Baitodea: Urotrygonidae) from North-East Brazil, tropical west Atlantic Ocean. J Fish Biol. 2016; 89(1):1026–42. https://doi.org/10.1111/jfb.12951
https://doi.org/10.1111/jfb.12951...
were recorded. All stomachs were fixed with a 4% formaldehyde solution buffered with sodium tetraborate for at least 24 h and preserved in 70% ethanol.

Feeding habits. Stomach contents were identified to the lowest taxonomic level according to Williams, (1965)Williams AB. Marine decapod crustaceans of the Carolinas. Fish Bull. 1965; 65:1–298., Nonato, (1976)Nonato E. Anelídeos Poliquetas. São Paulo: Instituto Oceanográfico da Universidade de São Paulo; 1976. , Melo, (1996)Melo GAS. Manual de identificação dos Brachyura (Carangueijos e Sirís) do litoral brasileiro. São Paulo: Editora Plêiade; 1996., Carpenter, (2002)Carpenter KE. The Living Marine Resources of the Western Central Atlantic. Volume 1: Introduction, Mollusks, Crustaceans, Hagfishes, Sharks, Batoid Fishes and Chimaeras. Rome: Food and Agriculture Organization of the United Nations; 2002., Costa et al., (2003)Costa RCC, Fransozo A, Melo GAS, Freire FAM. Chave ilustrada para identificação de camarões dendrobranchiata do litoral norte do estado de São Paulo, Brasil. Biota Neotrop. 2003; 3(1):1–12. Available from: https://old.scielo.br/pdf/bn/v3n1/a11v3n1.pdf
https://old.scielo.br/pdf/bn/v3n1/a11v3n...
, Grave et al., (2009)Grave S, Pentcheff ND, Ahyong ST, Chan TY, Crandall KA, Dworschak PC et al. A classification of living and fossil genera of decapod crustaceans. Raff Bull Zool. 2009; 21:1–109. Available from: https://lkcnhm.nus.edu.sg/wp-content/uploads/sites/10/app/uploads/2017/06/s21rbz1-109.pdf
https://lkcnhm.nus.edu.sg/wp-content/upl...
, Grave, Fransen, (2011)Grave S, Fransen CHJM. Carideorum Catalogus: The Recent Species of the Dendrobranchiate, Stenopodidean, Procarididean and Caridean Shrimps (Crustacea: Decapoda). Zool Meded. 2011; 85(9):195–589. Available from: https://repository.naturalis.nl/pub/403473
https://repository.naturalis.nl/pub/4034...
, and Souza et al., (2011)Souza JAF, Schwamborn R, Barreto AV, Farias ID, Fernandes LMG, Coelho PA. Marine and estuarine shrimps (Dendrobranchiata, Stenopodidea, and Caridea), of Pernambuco State (Brazil) and northeastern brazilian oceanic islands. Atlântica. 2011; 33(1):33–63. https://doi.org/10.5088/ATL.2011.33.1.33
https://doi.org/10.5088/ATL.2011.33.1.33...
. Each food item was weighed in a scale with a precision of 0.0001g. The fullness index was calculated as a ratio between stomach weight and the total weight of the predator (WT). The value obtained was then multiplied by 100 to demonstrate the amount of food ingested by the predator compared to its own body mass (Hureau, 1969Hureau JC. Biologie comparée de quelques poissons antarctiques (Nothotheniidae). Bull Inst Oceanogr. 1969; 68:1–44.).

A cumulative prey curve was constructed using the Shannon-Wiener method to evaluate whether the number of sampled stomachs was sufficient to describe the diversity of diet. The samples were randomized 50 times with the routine ‘sample-based rarefaction’ using EstimateS 7.5 software (Colwell et al., 2004Colwell RK, Mao CX, Chang J. Interpolating, extrapolating, and comparing incidence-based species accumulation curves. Ecol. 2004; 85(10):2717–27. https://doi.org/10.1890/03-0557
https://doi.org/10.1890/03-0557...
). Sample size was considered sufficient if the curves visually reached an asymptote (Magurran, 2004Magurran AE. Measuring biological diversity. Oxford: Blackwell Publishing; 2004. ). To assess the diet of U. microphthalmum, the following indexes were employed: Frequency of Occurrence (%FO), Percentage by weight and number (%W and %N, respectively) and Index of Relative Importance (IRI), where IRI = (%N + %W)*(%FO) (Pinkas et al., 1971Pinkas I, Oliphant MS, Iverson IK. Food habits of albacore, bluefin tuna and bonito in California Waters. Fish Bull. 1971; 152:1–105.; Zavala-Camin, 1996Zavala-Camin LA. Introdução aos estudos sobre alimentação natural em peixes. Maringá: EDUEM; 1996. Available from: https://docplayer.com.br/77288714-Introducao-aos-estudos-sobre-alimentacao-natural-em-peixes-download-free.html
https://docplayer.com.br/77288714-Introd...
; Cortés, 1997Cortés E. A critical review of methods of studying fish feeding based on analysis of stomach contents: application to elasmobranch fishes. Can J Fish Aquat Sci. 1997; 54(3):726–38. https://doi.org/10.1139/f96-316
https://doi.org/10.1139/f96-316...
; Lessa, Almeida, 1997Lessa RP, Almeida Z. Analysis of stomach contents of the smalltail sharks Carcharhinus porosus from Northern Brazil. Cybium. 1997; 21(2):123–33. Available from: https://sfi-cybium.fr/en/node/1774
https://sfi-cybium.fr/en/node/1774...
, 1998Lessa RP, Almeida Z. Feeding habits of the bonnethead sharks, Sphyrna tiburo, from nothern Brazil. Cybium. 1998; 22(4):383–94. Available from: https://sfi-cybium.fr/en/node/1702
https://sfi-cybium.fr/en/node/1702...
; Fonteles-Filho, 2011Fonteles-Filho AA. Oceanografia, biologia e dinâmica populacional de recursos pesqueiros. Fortaleza, CE: Expressão Gráfica; 2011.).

Diet niche breadth was estimated by Levin’s index (Bi): Bi=(ΣP2j)−1 where Pj is the fraction by mass of each food item in the diet j (ΣPj =1) (Krebs, 1999Krebs CJ. Ecological Methodology. Menlo Park, CA: Addison Wesley; 1999.). The values were standardized (BA) so that they ranged from 0 to 1 using the equation BA =(Bi−1) (N−1)−1, where N is the number of classes (Krebs, 1999Krebs CJ. Ecological Methodology. Menlo Park, CA: Addison Wesley; 1999.). Low values indicated diets dominated by few preys items (specialist predators), whereas higher values indicated generalist diets. The feeding strategy of U. microphthalmum was analyzed using the graphical method proposed by Cortés, (1997)Cortés E. A critical review of methods of studying fish feeding based on analysis of stomach contents: application to elasmobranch fishes. Can J Fish Aquat Sci. 1997; 54(3):726–38. https://doi.org/10.1139/f96-316
https://doi.org/10.1139/f96-316...
. Food items were grouped into categories following Ebert, Bizzarro, (2007)Ebert DA, Bizzarro JJ. Standardized diet composition and trophic levels of skates (Chondrichthyes: Rajiformes: Rajoidei). Environ Biol Fish. 2007; 80:221–37. https://doi.org/10.1007/s10641-007-9227-4
https://doi.org/10.1007/s10641-007-9227-...
.

A Bray-Curtis similarity matrix was built using standardized estimates of prey weights to test if there is an ontogenetic shift of diet for U. microphthalmum (Bornatowski et al., 2014aBornatowski H, Braga RR, Abilhoa V, Corrêa MFM. Feeding ecology and trophic comparisons of six shark species in a coastal ecosystem off southern Brazil. J Fish Biol. 2014a; 85(2):246–63. https://doi:10.1111/jfb.12417
https://doi:10.1111/jfb.12417...
). The reproductive parameters used here followed Santander-Neto et al., (2016)Santander-Neto J, Araújo MLG, Lessa RP. Reproductive biology of Urotrygon microphthalmum (Baitodea: Urotrygonidae) from North-East Brazil, tropical west Atlantic Ocean. J Fish Biol. 2016; 89(1):1026–42. https://doi.org/10.1111/jfb.12951
https://doi.org/10.1111/jfb.12951...
. Then, the data were analyzed using nonmetric multidimensional scaling (nMDS) followed by a one-way similarity analysis (ANOSIM). This test is analogous to analysis of variance (ANOVA), and was used to verify similarities (distance) within defined groups (factors) against similarities between groups, and also calculates the statistic R, which varies between −1 and +1 (Clarke, Gorley, 2006Clarke KR, Gorley RN. PRIMER v6: User Manual/Tutorial. Plymouth: PRIMER-E; 2006.). Analyses of percentage of similarity (SIMPER) were used to estimate the contribution of each prey category to ontogenetic differences in diets.

Trophic position. The trophic Level (TL) of U. microphthalmum was estimated by stomach contents following Ebert, Bizzarro, (2007)Ebert DA, Bizzarro JJ. Standardized diet composition and trophic levels of skates (Chondrichthyes: Rajiformes: Rajoidei). Environ Biol Fish. 2007; 80:221–37. https://doi.org/10.1007/s10641-007-9227-4
https://doi.org/10.1007/s10641-007-9227-...
. For that purpose, the TL was assessed both for the species overall and also for juvenile and adult maturation stages separately. The softwares EstimateS version 7.5.1 and R (R Development Core Team, 2021R Development Core Team. R: A language and environment for statistical computing. Vienna, Austria: R Foundation for Statistical Computing; 2021. Available from: https://www.R-project.org/
https://www.R-project.org/...
) were used to show the food items curve and three-dimensional graphic, respectively.

RESULTS

Feeding habits. A total of 338 stomachs of Urotrygon microphthalmum were analyzed. From this, 79 were removed from further analyses because they either contained only digested, unidentifiable material (n = 61) or were completely empty (n = 18) (emptiness index = 5.32%). Among the remaining stomachs, LT ranged between 94.15 to 298.1 mm and WT ranged between 5.34 and 148 g (Fig. 2). Length and Weight data showed a non-normal distribution (Shapiro-Wilk, W = 0.9598, p < 0.0001 and W = 0.9767, p = 0.0003, respectively).

FIGURE 2 |
Size classes frequency distribution of Urotrygon microphthalmum. Values in horizontal axis are the centre of size classes. F = females; M = males.

Of the remaining stomachs (n = 258), most of them showed one or two food items (58.68% and 25.48%, respectively). However, stomachs containing three (10.03%), four (5.01%) and five items (0.77%) were also observed. Fullness index had a maximum and medium value of 1.69 and 0.16, respectively. Nevertheless, fullness index values between 0.0001 and 0.1 comprised 56.48% of all analyzed stomachs. A predominance of items in the last stage of digestion was observed (69.8%). Across all stomach samples, 31 food items were identified in the diet (Tab. 1). The cumulative prey curve slope was reached at around 160 stomachs (Fig. 3). Urotrygon microphthalmum had a diet consisting predominantly of decapod crustaceans (82.9% IRI) and followed by Mysidacea (5.6% IRI) (Tab. 1). Urotrygon microphthalmum species feed primarily on shrimps.

TABLE 1 |
Frequency of occurrence (FO), Percentage frequency of occurrence (%FO), Number (N), Percentage by number (%N), Weight (W), Percentage by weight (%W), and Index of importance (IRI) of food items present in the diet of Urotrygon microphthalmum.

FIGURE 3 |
Prey accumulation curve of Urotrygon microphthalmum. Bold line represents mean values of Shannon-Wiener diversity index. Dotted lines represent standard deviation of the mean.

Similarity analysis between diets of juveniles (n = 52) and adults (n = 206) did not suggest an ontogenetic shift in the diet of U. microphthalmum (ANOSIM, R = 0.035, p = 0.147). Diets also did not differ between sexes (ANOSIM, R = 0.004, p = 0.151). The majority of smalleye round rays are decapod specialists and possess narrow niche widths (BA = 0.0144). Since the diet of males and females showed no statistical differences, all further analyses were conducted with the sexes grouped. The three-dimensional graphic showed a strong importance of unidentified decapods on the diet of U. microphthalmum. The species also demonstrated a low niche width and specialized foraging habits (Fig. 4).

FIGURE 4 |
Three-dimensional graphical representation of the percentage number, percentage weight, and percentage frequency of occurrence of the major taxa in the diet of Urotrygon microphthalmum. Food items grouping follow as proposed by Ebert, Bizzarro, (2007)Ebert DA, Bizzarro JJ. Standardized diet composition and trophic levels of skates (Chondrichthyes: Rajiformes: Rajoidei). Environ Biol Fish. 2007; 80:221–37. https://doi.org/10.1007/s10641-007-9227-4
https://doi.org/10.1007/s10641-007-9227-...
. DECA: Decapod crustaceans; OCRUST: Other crustaceans and unidentified crustaceans; EUPH: Euphasiids and mysids; FISH: Teleost fishes; AMPH: Amphipods and isopods; POLY: Polychaetes and other marine worms; MOLL: Molluscs (excluding cephalopods) and unidentified mollusks.

Trophic position. The trophic level calculated according to Ebert, Bizzarro, (2007)Ebert DA, Bizzarro JJ. Standardized diet composition and trophic levels of skates (Chondrichthyes: Rajiformes: Rajoidei). Environ Biol Fish. 2007; 80:221–37. https://doi.org/10.1007/s10641-007-9227-4
https://doi.org/10.1007/s10641-007-9227-...
for U. microphthalmum assumed a value of 3.5 (secondary consumer) for both juveniles and adults.

DISCUSSION

The 31 prey items seen in stomachs of Urotrygon microphthalmum in this study is more than twice as high as what was reported by Costa, Almeida, (2003)Costa CL, Almeida ZS. Hábito Alimentar de Urotrygon microphthalmum Delsman, 1941 (Elasmobranchii: Urolophidae) em Tutoia, Maranhão. Bol Lab Hidrobiol. 2003; 16(1):7–54. in northern Brazil (Maranhão). This may be due to many factors including difference in sample size, taxonomic categories and diversity of prey among the environments. Nevertheless, in the present study prey taxa number were closer to the 26 food items reported for the congeneric species Urotrygon rogersi (Jordan & Starks, 1895) in Colombia (Navia et al., 2010Navia AF, Cortés E, Mejía-Falla PA. Topological analysis of the ecological importance of elasmobranch fishes: A food web study on the Gulf of Tortugas, Colombia. Ecol Model. 2010; 221(24):2918–26. https://doi.org/10.1016/j.ecolmodel.2010.09.006
https://doi.org/10.1016/j.ecolmodel.2010...
, 2011Navia AF, Torres A, Mejía-Falla PA, Giraldo A. Sexual, ontogenetic, temporal and spatial effects on the diet of Urotrygon rogersi (Elasmobranchii: Myliobatiformes). J Fish Biol. 2011; 78(4):1213–24. https://doi.org/10.1111/j.1095-8649.2011.02931.x
https://doi.org/10.1111/j.1095-8649.2011...
).

Seventy-nine stomachs were discarded from dietary analysis, which was higher in proportion than the reported for U. rogersi (Navia et al., 2011Navia AF, Torres A, Mejía-Falla PA, Giraldo A. Sexual, ontogenetic, temporal and spatial effects on the diet of Urotrygon rogersi (Elasmobranchii: Myliobatiformes). J Fish Biol. 2011; 78(4):1213–24. https://doi.org/10.1111/j.1095-8649.2011.02931.x
https://doi.org/10.1111/j.1095-8649.2011...
). By comparing our results to the diet of U. microphthalmum from a previous study, there were differences both in the composition of the diet and the importance of given prey items. Decapods (mainly shrimps) were a more important contribution to the diets in our study, whereas mysids and cumaceans were the most abundant categories in prior studies (Almeida et al., 2000Almeida ZS, Nunes JS, Costa CL. Presencia de Urotrygon microphthalmum (Elasmobranchii: Urolophidae) en aguas bajas do Maranhão (Brazil) y notas sobre su biología. Bol Invest Mar Cost. 2000; 29:67–72.; Costa, Almeida, 2003Costa CL, Almeida ZS. Hábito Alimentar de Urotrygon microphthalmum Delsman, 1941 (Elasmobranchii: Urolophidae) em Tutoia, Maranhão. Bol Lab Hidrobiol. 2003; 16(1):7–54. ). Further comparisons between studies could not be done since only percent by number was estimated by the previous authors. These observed differences between diets of U. microphthalmum in these studies could be due to differences in the methodologies applied, the sample sizes or prey availability across locations. Although, our findings showed similar importance of preys as for U. rogersi in Colombia (Navia et al., 2011Navia AF, Torres A, Mejía-Falla PA, Giraldo A. Sexual, ontogenetic, temporal and spatial effects on the diet of Urotrygon rogersi (Elasmobranchii: Myliobatiformes). J Fish Biol. 2011; 78(4):1213–24. https://doi.org/10.1111/j.1095-8649.2011.02931.x
https://doi.org/10.1111/j.1095-8649.2011...
).

Dietary data in this study suggest that U. microphthalmum specializes on small crustaceans (including decapods and mysids) and small substrate-related fishes. When the most common food item of a predator’s diet is also a broad category with high abundance in the enviroment, the difference between generalized opportunism and feeding specialization can become quite difficult to infer (Yokota et al., 2013Yokota L, Goitein R, Gianeti MD, Lessa RPT. Diet and feeding strategy of smooth butterfly ray Gymnura micrura in northeastern Brazil. J Appl Ichthyol. 2013; 29(6):1325–29. https://doi.org/10.1111/jai.12213
https://doi.org/10.1111/jai.12213...
). With this issue in mind, Costa et al., (2015)Costa TLA, Thayer JA, Mendes LF. Population characteristics, habitat and diet of a recently discovered stingrayDasyatis marianae: implications for conservation. J Fish Biol. 2015; 86(2):527–43. https://doi:10.1111/jfb.12572
https://doi:10.1111/jfb.12572...
suggested to also evaluate prey availability and diversity in the study area when making a decision between opportunism vs. specialization.

Most teleostean individuals could not be identified to lower taxonomic levels due advanced levels of digestion, with only vertebrae, amorphous mass, and/or scales remaining. Nevertheless, in less digested preys by observing the shape of the body (leaf-like) it appears that at least some of non-identified teleosteans were in the family Cynoglossidae (tonguefishes) (Carpenter, 2002Carpenter KE. The Living Marine Resources of the Western Central Atlantic. Volume 1: Introduction, Mollusks, Crustaceans, Hagfishes, Sharks, Batoid Fishes and Chimaeras. Rome: Food and Agriculture Organization of the United Nations; 2002.). Several authors have demonstrated a relationship between sexual dimorphism in teeth and dietary differences across sexes in Batoid species (Kyne, Bennett, 2002Kyne PM, Bennett MB. Diet of the eastern shovelnose ray, Aptychotrema rostrata (Shaw & Nodder, 1794), from Moreton Bay, Queensland, Australia. Mar Fresh Res. 2002; 53(3):679–86. https://doi.org/10.1071/MF01040
https://doi.org/10.1071/MF01040...
; Morato et al., 2003Morato T, Solà E, Grós MP, Menezes G. Diets of thornback ray (Raja clavata) and tope shark (Galeorhinus galeus) in the bottom longline fishery of the Azores, northeastern Atlantic. Fish Bull. 2003; 101(3):590–602. Available from: https://spo.nmfs.noaa.gov/sites/default/files/10morato.pdf
https://spo.nmfs.noaa.gov/sites/default/...
; Scenna et al., 2006Scenna LB, García de la Rosa SB, Diaz de Astarloa JM. Trophic ecology of the Patagonian skate, Bathyraja macloviana, on the Argentine continental shelf. ICES J Mar Sci. 2006; 63(5):867–74. https://doi.org/10.1016/j.icesjms.2006.02.002
https://doi.org/10.1016/j.icesjms.2006.0...
). In these cases adult males have needle-like teeth that help them bite the pectoral fins of females. Despite U. microphthalmum showing tooth sexual dimorphism (Rangel et al., 2016Rangel BS, Santander-Neto J, Rici REG, Lessa RP. Dental sexual dimorphism and morphology of Urotrygon microphthalmum. Zoomorph. 2016; 135:367–74. https://doi.org/10.1007/s00435-016-0312-0
https://doi.org/10.1007/s00435-016-0312-...
), no differences between male and female diets were found. This result also aligns with findings for U. rogersi in Colombia (Navia et al., 2011Navia AF, Torres A, Mejía-Falla PA, Giraldo A. Sexual, ontogenetic, temporal and spatial effects on the diet of Urotrygon rogersi (Elasmobranchii: Myliobatiformes). J Fish Biol. 2011; 78(4):1213–24. https://doi.org/10.1111/j.1095-8649.2011.02931.x
https://doi.org/10.1111/j.1095-8649.2011...
).

Although ontogenetic shifts in diet are almost universal for fishes (Zavala-Camin, 1996Zavala-Camin LA. Introdução aos estudos sobre alimentação natural em peixes. Maringá: EDUEM; 1996. Available from: https://docplayer.com.br/77288714-Introducao-aos-estudos-sobre-alimentacao-natural-em-peixes-download-free.html
https://docplayer.com.br/77288714-Introd...
; Lessa, Almeida, 1997Lessa RP, Almeida Z. Analysis of stomach contents of the smalltail sharks Carcharhinus porosus from Northern Brazil. Cybium. 1997; 21(2):123–33. Available from: https://sfi-cybium.fr/en/node/1774
https://sfi-cybium.fr/en/node/1774...
; Wetherbee, Cortés, 2004Wetherbee BM, Cortés E. Food consumption and feeding habits. In: Carrier JC, Musick JA, Heithaus MR, editors. Biology of Sharks and their Relatives. CRC Press; 2004. p.223–44.), such a shift was not observed for U. microphthalmum. This may be due to habitat use by the species. From dietary data, U. microphthalmum seems to inhabit the same muddy areas throughout its entire life cycle, following the pattern shown by Knip et al., (2010)Knip DM, Heupel MR, Simpfendorfer CA. Sharks in nearshore environments: models, importance, and consequences. Mar Ecol Progr Ser. 2010; 402:1–11. https://doi.org/10.3354/meps08498
https://doi.org/10.3354/meps08498...
. However, Garrison, Link, (2000)Garrison LP, Link JS. Fishing effects on spatial distribution and trophic guild of the fish community in the Georges Bank region. ICES J Mar Sci. 2000; 57(3):723–30. https://doi.org/10.1006/jmsc.2000.0713
https://doi.org/10.1006/jmsc.2000.0713...
pointed out it is possible to have a change in trophic level within life stages even without an ontogenetic shift in diet, allowing a life stages within a given species to act like two species in an ecosystem due to differences in their trophic level. However the trophic level was equal between juveniles and adults of U. microphthalmum.

Trophic level assessed from stomach content analysis yielded a value of 3.5, which corroborates estimates by Jacobsen, Bennet (2013)Jacobsen IP, Bennett MB. A comparative analysis of feeding and trophic level ecology in stingrays (Rajiformes; Myliobatoidei) and electric rays (Rajiformes: Torpedinoidei). PLoS ONE. 2013; 8(8):e71348. https://doi.org/10.1371/journal.pone.0071348
https://doi.org/10.1371/journal.pone.007...
for the family Urotrygonidae. Thus, U. microphthalmum can be classified as a secondary consumer within the marine food chain. This consumer plays a fundamental role in energy transfer between benthic and demersal environments (Begon et al., 2006Begon M, Harper J, Townsend C. Ecology: from individuals to ecosystems. Oxford, UK: Blackwell; 2006.). Urotrygon microphthalmum feeds on detritivorous species, that can lead to a high energetic balance and would explain its fast somatic growth and early maturity (Santander-Neto et al., 2016Santander-Neto J, Araújo MLG, Lessa RP. Reproductive biology of Urotrygon microphthalmum (Baitodea: Urotrygonidae) from North-East Brazil, tropical west Atlantic Ocean. J Fish Biol. 2016; 89(1):1026–42. https://doi.org/10.1111/jfb.12951
https://doi.org/10.1111/jfb.12951...
).

ACKNOWLEDGEMENTS

Authors thank the Fundação de Amparo a Pesquisa do Estado de Pernambuco (FACEPE) for a PhD scholarship to JSN, Coordenação de Aperfeiçoamento Pessoal de Nível Superior (CAPES) for a MSc scholarship to DJVF; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) attributed Productivity Research grants to RL. Authors are grateful to Centro de Tecnologias Estratégicas do Nordeste (CETENE). The authors thank to Jeffrey Muehllbauer for reviewing English.

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ADDITIONAL NOTES

  • HOW TO CITE THIS ARTICLE

    Santander-Neto J, Freitas DJV, Bornatowski H, Lessa R. Feeding habits of Urotrygon microphthalmum (Myliobatiformes: Urotrygonidae) caught off northeastern Brazil. Neotrop Ichthyol. 2021; 19(4):e210039. https://doi.org/10.1590/1982-0224-2021-0039

Edited-by

Jennifer Wyffels

Publication Dates

  • Publication in this collection
    01 Dec 2021
  • Date of issue
    2021

History

  • Received
    4 Feb 2021
  • Accepted
    2 Aug 2021
Sociedade Brasileira de Ictiologia Neotropical Ichthyology, Núcleo de Pesquisas em Limnologia, Ictiologia e Aquicultura, Universidade Estadual de Maringá., Av. Colombo, 5790, 87020-900, Phone number: +55 44-3011-4632 - Maringá - PR - Brazil
E-mail: neoichth@nupelia.uem.br