Predator–prey landscapes of large sharks and game fishes in the Florida Keys

Abstract

Interspecific interactions can play an essential role in shaping wildlife populations and communities. To date, assessments of interspecific interactions, and more specifically predator-prey dynamics, in aquatic systems over broad spatial and temporal scales (i.e., hundreds of kilometers and multiple years) are rare due to constraints on our abilities to measure effectively at those scales. We applied new methods to identify space-use overlap and potential predation risk to Atlantic tarpon (Megalops atlanticus) and permit (Trachinotus falcatus) from two known predators, great hammerhead (Sphyrna mokarran) and bull (Carcharhinus leucas) sharks, over a 3-year period using acoustic telemetry in the coastal region of the Florida Keys (USA). By examining spatiotemporal overlap, as well as the timing and order of arrival at specific locations compared to random chance, we show that potential predation risk from great hammerhead and bull sharks to Atlantic tarpon and permit are heterogeneous across the Florida Keys. Additionally, we find that predator Lucas P. Griffin and Grace A. Casselberry share co-first authorship and contributed equally to this work.

Vertical space use and thermal range of the great hammerhead (Sphyrna mokarran), (Rüppell, 1837) in the western North Atlantic

“…These species and others ( e.g ., M. atlanticus and T. falcatus ; Griffin et al ., 2022) co‐occur within the horizontal and vertical distribution observed for the S. mokarran in this study; therefore, such high use of shallow depths may reflect targeting these prey species. Although it is not possible with these vertical space use data to confirm if the shallow depths occupied by these sharks were in shallow water versus deepwater (but at the surface), capture and pop‐off location of these tags and seasonal residency of S. mokarran to acoustic receiver arrays in the Florida Keys, Biscayne Bay and Bimini, The Bahamas, support the former (Griffin et al ., 2022; Guttridge et al ., 2017). The findings of this study align with previous research documenting predominant shallow depth use by S. mokarran ( e.g ., Drymon & Wells, 2017; Hueter & Manire, 1994) but across a broader scale.…”

“…Additionally, blacktip sharks Carcharhinus limbatus (J. P. Müller & Henle, 1839) form aggregations along the coastline in shallow waters during the winter months in Florida(Kajiura & Tellman, 2016;Doan & Kajiura, 2020). These species and others (e.g., M. atlanticus and T. falcatus;Griffin et al, 2022) co-occur within the horizontal and vertical distribution observed for the S. mokarran in this study; therefore, such high use of shallow depths may reflect targeting these prey species. Although it is not possible with these vertical space use data to confirm if the shallow depths occupied by these sharks were in shallow water versus deepwater (but at the surface), capture and pop-off location of these tags and seasonal residency of S. mokarran to acoustic receiver arrays in the Florida Keys, Biscayne…”

“…The extensive use of shallow depths could reflect habitat use as part of the species' foraging behaviour. Small‐bodied carcharhinid sharks, rays and M. atlanticus represent important prey for S. mokarran (Chapman & Gruber, 2002; Doan & Kajiura, 2020; Griffin et al ., 2022; Raoult et al ., 2019; Roemer et al ., 2016). The vertical range of PSAT‐equipped whitespotted eagle rays Aetobatus narinari (Euphrasén, 1790) was limited to depths of 26 m, with rays primarily occupying depths <10 m (Brewster et al ., 2021).…”

“…Guttridge et al (2017) revealed site fidelity and seasonal residency of S. mokarran in the waters of Bimini, The Bahamas, during the winter months, as well as long-distance return migrations in the summer to the southeastern U.S. coast. More recently, S. mokarran tracked in the Florida Keys in the U.S.A. showed varied movement behaviour with some individuals transiting the Gulf of Mexico and Atlantic using a migratory corridor, whereas others exhibited "stopover" behaviour, in response to predictable, seasonal spawning aggregations of game fish Atlantic tarpon Megalops atlanticus (Valenciennes, 1847) and permit Trachinotus falcatus (Linnaeus, 1758) (Griffin et al, 2022;Lowerre-Barbieri et al, 2021). These studies highlight the complexity of S. mokarran movement ecology, through different ecosystems throughout the year, and suggesting the species could be an important mobile link species (Heupel et al, 2015;Lundberg & Moberg, 2003;Raoult et al, 2020).…”

What acoustic telemetry can and can’t tell us about fish biology

“…The fine-scale co-occurrences of individuals, whether between conspecifics as mutually beneficial social affiliations, or between predator and prey species as direct interactions and displacements, are an important factor that can strongly influence population dynamics and/or spatial distributions of species (Morueta-Holme et al, 2016). The encounter rates of Atlantic tarpon (Megalops atlanticus) with predatory bull (Carcharhinus leucas) and great hammerhead (Sphyrna mokarran) sharks in the Florida Keys for instance, were elevated at specific locations and prior to spawning aggregation behaviour, a result identified using machine learning to quantify spatio-temporal overlap in multi-species AT tracking data (Griffin et al, 2022). To truly understand fine-scale interactions and associations, however, requires direct measurement rather than inference methods, and at a precise and known spatial scale (Aspillaga et al, 2021;Mourier et al, 2017).…”