New Insights Into the Seasonal Movement Patterns of Shortfin Mako Sharks in the Gulf of Mexico

Kesley J Gibson,Tara S Topping,Matthew K Streich,Gregory W Stunz

doi:10.3389/fmars.2021.623104

Kesley J Gibson, Tara S Topping + Show 2 more

Open Access

https://doi.org/10.3389/fmars.2021.623104

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Abstract

Highly mobile apex predators such as the shortfin mako shark (mako shark;Isurus oxyrinchus) serve an important role in the marine ecosystem, and despite their declining populations and vulnerability to overexploitation, this species is frequently harvested in high abundance in both commercial and recreational fisheries. In 2017, the North Atlantic stock was deemed overfished and to be undergoing overfishing and was recently listed in CITES Appendix II. Effective management of this species can benefit from detailed information on their movements and habitat use, which is lacking, especially in the Gulf of Mexico, a potential mating and parturition ground. In this study, we used satellite telemetry to track the movements of mako sharks in the western Gulf of Mexico between 2016 and 2020. In contrast to previous studies that have primarily tagged juvenile mako sharks (&gt;80% juveniles), ∼80% of sharks tagged in this study (7 of 9) were presumed to be mature based on published size-at-maturity data. Sharks were tracked for durations ranging from 10 to 887 days (mean = 359 days; median = 239 days) with three mature individuals tracked for &gt;2 years. Mako sharks tagged in this study used more of the northwestern Gulf of Mexico than reported in previous movement studies on juveniles, suggesting potential evidence of size segregation. While one mature female remained in the Gulf of Mexico over a &gt;2-year period, predominantly on the continental shelf, two mature males demonstrated seasonal migrations ∼2,500 km from the tagging location off the Texas coast to the Caribbean Sea and northeastern United States Atlantic coast, respectively. During these migrations, mako sharks traversed at least 12 jurisdictional boundaries, which also exposed individuals to varying levels of fishing pressure and harvest regulations. Movement ecology of this species, especially for mature individuals in the western North Atlantic, has been largely unknown until recently. These data included here supplement existing information on mako shark movement ecology and potential stock structure that could help improve management of the species.

Highlights

Migratory species often fill the role of apex predator in marine ecosystems, but many populations are declining globally which can have cascading effects on lower trophic levels (Estes et al, 2011; Dulvy et al, 2014; Hammerschlag et al, 2019)
From 2016 to 2020, nine shortfin mako sharks were tagged with SPOT tags off the coast of Texas (5 M, 4 F; Table 1)
Most mako sharks tagged in this study were mature based on size-at-age information with females in this study representing some of the largest females reported in satellite telemetry studies to date (e.g., Loefer et al, 2005; Abascal et al, 2011; Musyl et al, 2011; Rogers et al, 2015; Campana et al, 2016; Byrne et al, 2017; Vaudo et al, 2017; Francis et al, 2019; Nasby-Lucas et al, 2019)

Summary

Introduction

Migratory species often fill the role of apex predator in marine ecosystems, but many populations are declining globally which can have cascading effects on lower trophic levels (Estes et al, 2011; Dulvy et al, 2014; Hammerschlag et al, 2019). Conservation and rebuilding of these declining species can benefit from species-specific knowledge on movements and habitats needed to complete their life cycles (Hays et al, 2019) One such species is the shortfin mako (Isurus oxyrinchus; hereafter mako shark), which are pelagic, fast-swimming, sharks found in tropical and temperate waters circumglobally. In 2018, the Shortfin mako was listed as endangered globally on the International Union for Conservation of Nature (IUCN) Red List due to their declining populations (Rigby et al, 2018)

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