Trophic inference in two sympatric sharks, Sphyrna lewini and Carcharhinus falciformis (Elasmobranchii: Carcharhiniformes), based on stable isotope analysis at Malpelo Island, Colombia

Abstract

Background. Elasmobranchs can play important roles in marine communities. But, relatively little is known about their diet, and movement. Sphyrna lewini (Griffith et Smith, 1834) consumes fishes, cephalopods, rays, and crustaceans. Carcharhinus falciformis (Müller et Henle, 1839) feed on fishes, cephalopods, crustaceans and sea turtles. To date, there are no studies available on the trophic ecology of sharks in Malpelo Island. The aim of this study was to describe the trophic ecology of S. lewini and C. falciformis, using stable isotope analysis of δ 13 C and δ 15 N, to better understand the role of both shark species in the Malpelo Island ecosystem. Material and methods. In January, February, and November 2013, specimens of Sphyrna lewini and Carcharhinus falciformis illegally caught at Malpelo Island were confiscated at the port of Buenaventura, Colombia. For each shark specimen, total length and sex were registered. Samples of muscle tissue were taken from the nape of all specimens. Each muscle sample was lyophilized for 24 h and analysed with lipid and urea extraction and without extraction. For each shark specimen, a subsample of ~1.0 mg was used for isotopic analysis. Results. A total of 14 Sphyrna lewini (Griffith et Smith, 1834) and 12 Carcharhinus falciformis (Müller et Henle, 1839) were analysed. δ 13 C values were similar between S. lewini (-16.3 ± 0.1‰) and C. falciformis (-16.5 ± 0.1‰). Sphyrna lewini showed a wider trophic niche than C. falciformis, with low trophic overlap (5%) between the two species. The δ 15 N values of S. lewini (15.9 ± 0.11‰) were higher than those of C. falciformis (14.9 ± 0.09‰). In C. falciformis, δ 13 C values were similar in both sexes (-16.5 ± 0.1‰), while δ 15 N values were significantly different between males (14.6 ± 0.1‰) and females (15.0 ± 0.1‰). The trophic position of S. lewini was 5.25 ± 0.12, and that of C. falciformis, 5.48 ± 0.18, which suggests that both shark species occupy a high position in the marine food chain. Conclusion. Both shark species co-occur at Malpelo Island, but they do not share food resources and feeding areas, and they probably feed far from the island, using it as a resting and cleaning area. This indicates the need for more research to increase biological and ecological knowledge of both species, particularly within marine protected areas and their influence areas throughout the Colombian Pacific.

Feeding behavior and trophic interaction of three shark species in the Galapagos Marine Reserve

“…In this study, no differences were observed in the foraging habitats among the three shark species. The δ 13 C values (between −17.2 and −16.2) indicate an oceanic/pelagic foraging strategy, consistent with what was previously reported in various studies conducted in the coasts of Ecuador, Colombia, Chile and Mexico ( Polo-Silva et al, 2013 ; Hernández-Aguilar et al, 2015 ; Estupiñán Montaño et al, 2017a ; Estupiñán Montaño et al, 2017b ; Klarian et al, 2018 ). Spatial variation in δ 13 C values of predators can be partly explained by differences in the isotopic composition of primary producers, which are the main energy suppliers for the food web ( Goericke & Fry, 1994 ; Pancost et al, 1997 ).…”

“…With regards to the feeding behavior of C. falciformis , both isotopes showed no intersexual difference, which suggests that both sexes exploit similar prey and foraging habitats. Dietary studies conducted on the eastern Pacific Ocean has reported fish of the Scombridae family and squid as the species’ main prey ( Duffy et al, 2015 ; Estupiñán Montaño et al, 2017a ; Estupiñán Montaño et al, 2017b ). Other authors have found males of C. falciformis to be more active than females, undertaking vertical migrations in the evening to complement their diet with squid and rest there at night ( Compagno, Dando & Fowler, 2005 ).…”

“…It has been shown, however, that when there is a lower diversity of prey in the environment, these sharks tend to be more selective in choosing them ( Cabrera-Chávez-Costa, Galván-Magaña & Escobar-Sánchez, 2010 ; Filmalter et al, 2010 ). Other authors have described this shark as a specialist consumer, because despite feeding on a wide food spectrum, a large proportion of its diet is made up of a limited number of prey types ( Duffy et al, 2015 ; Estupiñán Montaño et al, 2017a ). This may explain to some extent the great variability in δ 15 N values observed in this study.…”

“…Several studies have shown that the pelagic thresher shark and blue sharks have a broad diet (e.g., cephalopods, crustaceans, pelagic and benthic fish), and their feeding behavior can vary depending on seasonal conditions, marine productivity and abundance of resources ( Polo-Silva et al, 2013 ; Hernández-Aguilar et al, 2015 ; Klarian et al, 2018 ). While the silky shark is considered a piscivorous predator, consuming mainly fishes of the Scombridae family ( Duffy et al, 2015 ; Estupiñán Montaño et al, 2017a ).…”

Description and characterization of the artisanal elasmobranch fishery on Guatemala’s Caribbean coast

“…Similarly, for the capture of rays, longlines were more frequently used Fishing gears used to catch Chondrichthyan fish landed in this study. Data were grouped according to the following authors: a. Compagno [28], b. Compagno [29], c. Estupiñan-Montaño et al [42], d. Estupiñan-Montaño et al [43], e. Estupiñan-Montaño et al [44], f. Estupiñan-Montaño et al [45], g. Carpenter [46] and Ebert [47].…”