Abstract

Group behaviours are widespread among fish but comparatively little is known about the interactions between free-ranging individuals and how these might change across different spatio-temporal scales. This is largely due to the difficulty of observing wild fish groups directly underwater over long enough time periods to quantify group structure and individual associations. Here we describe the use of a novel technology, an animal-borne acoustic proximity receiver that records close-spatial associations between free-ranging fish by detection of acoustic signals emitted from transmitters on other individuals. Validation trials, held within enclosures in the natural environment, on juvenile lemon sharks Negaprion brevirostris fitted with external receivers and transmitters, showed receivers logged interactions between individuals regularly when sharks were within 4 m (∼4 body lengths) of each other, but rarely when at 10 m distance. A field trial lasting 17 days with 5 juvenile lemon sharks implanted with proximity receivers showed one receiver successfully recorded association data, demonstrating this shark associated with 9 other juvenile lemon sharks on 128 occasions. This study describes the use of acoustic underwater proximity receivers to quantify interactions among wild sharks, setting the scene for new advances in understanding the social behaviours of marine animals.

Highlights

  • Many animals across a diversity of taxa are recognized to form groups [1]

  • We investigate whether acoustic telemetry can be used to study grouping behaviours in sharks

  • The ARX receiver that functioned correctly (ARX #5, shark 365) recorded a total of 315 detections, over a period of 17 days in the Bone Fish Hole nursery area. These detections were from a total of 9 other juvenile lemon sharks, with detections on every day apart from two, and with up to 11 interactions per day of duration $60 seconds (Fig. 3)

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Summary

Introduction

Many animals across a diversity of taxa are recognized to form groups [1]. The durations of such groups can differ greatly; some may last for years, others just minutes or even a few seconds [2]. Shark behaviour is notoriously difficult to study especially when attempting to obtain accurate information on group composition [12,13]. For this reason, little systematic data is available on the structure and size of these groups, or the timing and frequency of interactions between individuals within them

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