Ontogenetic feeding ecology of the scalloped hammerhead shark Sphyrna lewini in the Colombian Eastern Tropical Pacific

Abstract

Changes in feeding habits during ontogeny show that organisms can present shifts in foraging behavior during their life cycle, which can alter local trophic dynamics. Therefore, describing diet across species ontogeny clarifies the ecological niche and ecosystem role of marine predators. In this study, diet tracers (stable isotope analysis) were analyzed in 16 scalloped hammerhead sharks Sphyrna lewini, using δ13C and δ15N values of collagen in vertebral cross-sections to reconstruct diet across their ontogeny. Our results suggest that S. lewini occupies a broad isotopic niche due to the consumption of prey belonging to different trophic levels (δ15N: 7.6-13.0‰) of the food chain in both coastal and oceanic zones (δ13C: -17.2 to -14.1‰) during their lifetime. Accordingly, ontogenetic changes in diet and habitat use were suggested by differences in δ13C and δ15N across age groups, indicating high consumption of coastal prey at 0-2 yr, oceanic prey at ~2-4 yr, a shift to high coastal prey at >4 yr, and a shift to high coastal prey, along with the consumption of prey from multiple trophic levels through feeding ontogeny (estimated trophic position: 2.9-6.5). This study showed migration from coastal to oceanic zones in juvenile S. lewini, and their return to coastal habitats as adults, potentially related to the use of coastal zones (i.e. mangroves) in the Eastern Tropical Pacific, both as important feeding areas for neonates and as feeding and breeding grounds for adults.

New insights into the trophic ecology of the scalloped hammerhead shark, Sphyrna lewini, in the eastern tropical Pacific Ocean

“…These oceanic islands have high productive ecosystems, offering large amounts of different prey and protection, and they also represent key habitats in the important migratory corridor (which includes coastal areas and these oceanic hotspots) for several large predators in the ETP (Peñaherrera-Palma et al 2018). These findings are consistent with previous studies reporting the residency time of neonate S. lewini in coastal nursery areas (~ 2 years; Zanella et al 2019), when they start to move towards oceanic areas, confirming the ontogenetic shift in their habitat use and feeding preferences around the 2-year mark (Zanella et al 2019;Estupiñán-Montaño et al 2021b).…”

“…For example, the results for 2.7-3.6 years female sharks indicate that they might migrate to oceanic areas of the ETP, where they can consume prey of low trophic levels. These results are supported by the alignment between the isotopic composition of 2.7-3.6 years female individuals and the isotopic values of prey of Malpelo and Galapagos systems (Malpelo's crustaceans: δ 13 C = -19.2‰ and δ 15 N = 11.6‰; Malpelo's teleosts: δ 13 C = -18‰ and δ 15 N = 12.7‰ [Estupiñán-Montaño et al 2021b] and Galapagos' small teleosts: δ 13 C = -16‰ and δ 15 N = 10.9‰ [Páez-Rosas et al 2012]), after the application of shark-specific muscle TDF (Hussey et al 2010). These oceanic islands have high productive ecosystems, offering large amounts of different prey and protection, and they also represent key habitats in the important migratory corridor (which includes coastal areas and these oceanic hotspots) for several large predators in the ETP (Peñaherrera-Palma et al 2018).…”

“…According to this reasoning, female individuals might use the high-energy contents of high trophic level prey to expand their size and thereby provide a larger body cavity for reproductive organs (Klimley 1987;Hoyos-Padilla et al 2014) and thereafter reduce the energy invested in reproductive organ development to a level that is sufficient to maintain their basal metabolism until mating (Gerritsen 1984;Klimley 1987). The high nitrogen levels and protein contents of such prey (e.g., Dosidicus gigas: 78.3-78.5% of protein; Ochoa-Tepelta 2014) would be useful for the synthesis of yolk, maximizing their reproductive success (Estupiñán-Montaño et al 2021b). This is consistent with our results, which show an increase in δ 15 N values until 9 years, particularly for age classes of 3.7-4.5 and 5-6.5 years (Fig.…”

“…Despite the great variety of prey found by SCA, S. lewini is considered a specialist predator (Estupiñàn-Montaño et al 2009;Torres-Rojas et al 2013), which uses different habitats (Estupiñán-Montaño et al 2009;Rosende-Pereiro et al 2020). However, studies with stable isotope analysis (SIA) in S. lewini muscle tissues (Loor-Andrade et al 2015;Li et al 2016;Rosende-Pereiro et al 2020) suggest that the species is a generalist predator (Torres-Rojas et al 2013;Estupiñán-Montaño et al 2017;, revealing certain specializations (Loor-Andrade et al 2015;Li et al 2016) demonstrating that individual specimens can occupy several trophic positions with a high degree of dietary plasticity (Torres-Rojas et al 2013;Estupiñán-Montaño et al 2017, 2021b.…”

“…In particular, the information about feeding preferences, dietary ontogeny, trophic position, and habitat use of S. lewini can improve our understanding of its role in the various food webs that the species occupies throughout its life cycle, allowing the design of better management plans and MPAs for the populations of this species. This scientific knowledge will allow the identification of both essential foraging areas for the early stages of S. lewini and of critical habitats for its adult stages about their reproductive aspects (Estupiñán-Montaño et al 2021b). Therefore, it is crucial to better understand the connections between coastal and offshore populations, to assess the importance of S. lewini in both ecosystems (Jordán and Scheuring 2002;Dambacher et al 2010;Navia et al 2010) and to develop local, regional, and international management strategies.…”