Repeated, long-distance migrations by a philopatric predator targeting highly contrasting ecosystems.

James S E Lea,Gonzalo R Mucientes,Guy M Harvey,David W Sims,Nicolas E Humphries,Bradley M Wetherbee,Neil Burnie,Choy Aming,Mahmood S Shivji,Nuno Queiroz,Lara L Sousa

doi:10.1038/srep11202

Abstract

Long-distance movements of animals are an important driver of population spatial dynamics and determine the extent of overlap with area-focused human activities, such as fishing. Despite global concerns of declining shark populations, a major limitation in assessments of population trends or spatial management options is the lack of information on their long-term migratory behaviour. For a large marine predator, the tiger shark Galeocerdo cuvier, we show from individuals satellite-tracked for multiple years (up to 1101 days) that adult males undertake annually repeated, round-trip migrations of over 7,500 km in the northwest Atlantic. Notably, these migrations occurred between the highly disparate ecosystems of Caribbean coral reef regions in winter and high latitude oceanic areas in summer, with strong, repeated philopatry to specific overwintering insular habitat. Partial migration also occurred, with smaller, immature individuals displaying reduced migration propensity. Foraging may be a putative motivation for these oceanic migrations, with summer behaviour showing higher path tortuosity at the oceanic range extremes. The predictable migratory patterns and use of highly divergent ecosystems shown by male tiger sharks appear broadly similar to migrations seen in birds, reptiles and mammals, and highlight opportunities for dynamic spatial management and conservation measures of highly mobile sharks.

Highlights

Is because temporal change in the density of a population at a specific geographic location is a function of births and deaths and of movements, including migration[2]
The satellite tracks are the longest reported for individual tiger shark movements to date throughout their distribution
This apex marine predator displays remarkable plasticity in ecosystem use, accomplished by extensive, seasonal migrations between insular, coral reef ecosystems in winter and temperate oceanic, potentially foraging areas in summer. These round-trip migrations span over 7,500 km annually, with individuals displaying marked philopatry to overwintering areas. These migrations are partial in nature: the five sharks that remained close to Bermuda over winter were all juveniles, whilst all migrants were large males, with the exception of the single mature female tracked

Summary

Introduction

Is because temporal change in the density of a population at a specific geographic location is a function of births and deaths and of movements, including migration[2]. The tiger shark Galeocerdo cuvier (Péron & Lesueur, 1822) is an interesting and suitable species to investigate migratory patterns because it is one of the largest predatory sharks, reaching up to ~5.5 m in length and ~600 kg in mass, and is found circumglobally in tropical and warm temperate coastal/ pelagic waters[22] It is captured in commercial fisheries, and is listed as ‘near threatened’ in the Red List of the International Union for Conservation of Nature (IUCN)[23]. In this study we use long-term satellite tracking of tiger sharks to determine movement patterns across multiple years, including examination of whether a large, marine predator with high intraspecific variability in diet and vertical habitat use shows any predictable migratory behaviour

Methods

Results

Conclusion