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Blacktip shark Carcharhinus limbatus presence at fishing piers in South Carolina: association and environmental drivers

Journal of Fish Biology

March 2019
94(3)

DOI:10.1111/jfb.13917

Authors:

Kelsey Martin

Texas A&M University – Corpus Christi

Derek P. Crane

Coastal Carolina University

Neil Hammerschlag

Shark Research Foundation

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We tagged 12 Carcharhinus limbatus with acoustic transmitters and monitored their presence at five piers along the north‐east coast of South Carolina, USA in 2016 and four piers in 2017 using acoustic receivers. Data were analysed with pier association indices (PAI), mixed models and fast Fourier transformation analyses to identify potential factors related to residence time and presence at piers and any cyclical patterns in visits to piers. While the majority of monitored C. limbatus were infrequently detected at piers, three (25.0%) were highly associated with piers (PAI ≥ 0.50). Of the C. limbatus that were detected after initial capture, three (25.0%) recorded detection events only at the pier where they were tagged and two individuals (16.7%) recorded at least one detection event at all monitored piers. The best‐fit model explaining C. limbatus residence time at piers included terms for pier location and diel cycle (wi = 0.88), whereas the best fit model explaining presence–absence of C. limbatus at piers included terms for tidal height, diel cycle, barometric pressure and angler count (wi = 0.98). Carcharhinus limbatus did not appear to display cyclical patterns in their visits to piers. Along the north‐east coast of South Carolina, association of C. limbatus with piers is a phenomenon for a proportion of mature individuals, but continued research is necessary to understand if this behaviour is driven by attraction to and feeding on angler discards or increased foraging opportunities resulting from the attraction of potential prey to the physical structure provided by piers.

All piers in the Grand Strand, South Carolina in 2016 prior to Hurricane Matthew. Black circles indicate sites that were monitored with a receiver either in 2016, 2017, or both. Black squares indicate piers that were not monitored with an acoustic receiver. SC Private Pier, Sea Cabin Private Pier; MBSP Pier, Myrtle Beach State Park Pier; Ave., Avenue

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Receiver coverage by date 2016–2017 at piers monitoring Carcharhinus limbatus activity. Gaps represent absences in coverage for that location. MBSP, Myrtle Beach State Park Pier; 2nd Ave., 2nd Avenue Pier; *, piers monitored by the South Carolina Department of Natural Resources

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Timeline of detections for each Carcharhinus limbatus detected with an acoustic receiver in the Grand Strand, South Carolina. Black triangles indicate the release date for each individual

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Proportional use of piers (Pier 14 in north, GCP in south) for each Carcharhinus limbatus (transmitter tag number) detected by acoustic receivers post‐release. Bar thickness is equivalent to the proportion of days with a detection event at that location divided by the total number of days with a detection event for each individual. For each individual, an asterisk above the bar indicates that the shark was tagged at the corresponding pier on the y‐axis. Ave., Avenue; MBSP, Myrtle Beach State Park; GCP, Garden City Pier

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Spectral density graphs generated from the fast Fourier transformation analyses for each Carcharhinus limbatus with greater than 200 detections by acoustic receivers in the Grand Strand, South Carolina

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REGULAR PAPER

Blacktip shark Carcharhinus limbatus presence at fishing piers in

South Carolina: association and environmental drivers

Kelsey L. Martin

| Dan C. Abel

| Derek P. Crane

| Neil Hammerschlag

| Erin J. Burge

Burroughs and Chapin, Center for Marine and

Wetland Studies, Coastal Carolina University,

Conway, South Carolina, USA

Department of Marine Science, Coastal

Carolina University, Conway, South

Carolina, USA

Department of Biology, Coastal Carolina

University, Conway, South Carolina, USA

Rosenstiel School of Marine and Atmospheric

Science, University of Miami, Miami,

Florida, USA

Correspondence

Kelsey L. Martin, Coastal Carolina University,

Conway, SC, 29528, USA.

Email: kelsey.martin@tamucc.edu

Funding information

Financial support for this project was provided

by the Coastal Marine and Wetland Studies

graduate program at Coastal Carolina

University and Essex County Turtle Back Zoo.

Support in the form of acoustic telemetry

equipment was provided by the Ocean

Tracking Network and Myrtle Beach State

Park.

We tagged 12 Carcharhinus limbatus with acoustic transmitters and monitored their presence at

five piers along the north-east coast of South Carolina, USA in 2016 and four piers in 2017

using acoustic receivers. Data were analysed with pier association indices (PAI), mixed models

and fast Fourier transformation analyses to identify potential factors related to residence time

and presence at piers and any cyclical patterns in visits to piers. While the majority of monitored

C. limbatus were infrequently detected at piers, three (25.0%) were highly associated with piers

(PAI ≥0.50). Of the C. limbatus that were detected after initial capture, three (25.0%) recorded

detection events only at the pier where they were tagged and two individuals (16.7%) recorded

at least one detection event at all monitored piers. The best-fit model explaining C. limbatus resi-

dence time at piers included terms for pier location and diel cycle (w

= 0.88), whereas the best

fit model explaining presence–absence of C. limbatus at piers included terms for tidal height, diel

cycle, barometric pressure and angler count (w

= 0.98). Carcharhinus limbatus did not appear to

display cyclical patterns in their visits to piers. Along the north-east coast of South Carolina,

association of C. limbatus with piers is a phenomenon for a proportion of mature individuals, but

continued research is necessary to understand if this behaviour is driven by attraction to and

feeding on angler discards or increased foraging opportunities resulting from the attraction of

potential prey to the physical structure provided by piers.

KEYWORDS

acoustic telemetry, blacktip shark, Carcharhinus limbatus, fishing piers, South Carolina

1|INTRODUCTION

Coastal man-made structures, such as fishing piers, bridge pilings and

docks, attract and support a wide variety of fishes (Barwick et al.,

2004; Burchmore et al., 1985). Smaller fish congregate around these

physically complex structures, which disrupt predator foraging effi-

ciency (Glass, 1971; Savino & Stein, 1989) while providing cover for

predatory fishes to ambush prey (Able et al., 2013). The concentration

of fishes around man-made structures provides coastal sharks, which

are commonly observed around piers, with foraging opportunities

(Ellis & Musick, 2007).

The blacktip shark Carcharhinus limbatus (Valenciennes 1839) is

one of the most commonly observed shark species around fishing

piers along the north-east coast of South Carolina, USA (K. Martin

personal observation, June 2016). Carcharhinus limbatus migrates sea-

sonally in the western north Atlantic Ocean (Castro, 1996; Kajiura &

Tellman, 2016) and from May until early November, they are one of

the most commonly caught large coastal shark species in North Caro-

lina (Thorpe et al., 2004), South Carolina (Ulrich et al., 2007) and the

southern Georgia and north-east Florida waters (Trent et al., 1997).

Despite the seasonal abundance of C. limbatus and individuals com-

monly being observed near fishing piers, no scientific studies to date

have specifically examined the association of C. limbatus, nor any

other shark species, with coastal fishing piers.

Associative behaviour, which can be defined as the association

between an animal and. inanimate objects or topographic structures

(Fréon & Dagorn, 2000), has been studied using acoustic telemetry for

a variety of shark species (Chapman et al., 2015; Espinoza et al., 2011;

Heupel et al., 2010; Heupel & Hueter, 2002; Kock et al., 2013; Lowe

et al., 2006). In adult sharks, this behaviour is advantageous for feeding,

mating, pupping, or resting (Speed et al., 2010). In north-east South Car-

olina, sharks are commonly observed feeding on discarded fish and

Received: 17 September 2018 Accepted: 30 January 2019

DOI: 10.1111/jfb.13917

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