A massive surgeonfish aggregation creates a unique opportunity for reef sharks

Weideli, Ornella C.; Mourier, Johann; Planes, Serge

doi:10.1007/s00338-015-1290-2

Cited by 10 publications

(7 citation statements)

References 3 publications

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“…Smaller sharks have also been spotted in aerial surveys, either specifically targeting them [ 55 , 56 ], or incidentally during marine mammal surveys [ 57 ]. Occasionally, massive schools of elasmobranchs have been documented from aerial photographs [ 58 , 59 ] and in some instances, aggregations have been correlated with the presence of prey [ 60 , 61 ].…”

Section: Discussionmentioning

confidence: 99%

Quantification of Massive Seasonal Aggregations of Blacktip Sharks (Carcharhinus limbatus) in Southeast Florida

Kajiura

Tellman

2016

PLoS ONE

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Southeast Florida witnesses an enormous seasonal influx of upper trophic level marine predators each year as massive aggregations of migrating blacktip sharks (Carcharhinus limbatus) overwinter in nearshore waters. The narrow shelf and close proximity of the Gulf Stream current to the Palm Beach County shoreline drive tens of thousands of sharks to the shallow, coastal environment. This natural bottleneck provides a unique opportunity to estimate relative abundance. Over a four year period from 2011–2014, an aerial survey was flown approximately biweekly along the length of Palm Beach County. A high definition video camera and digital still camera mounted out of the airplane window provided a continuous record of the belt transect which extended 200 m seaward from the shoreline between Boca Raton Inlet and Jupiter Inlet. The number of sharks within the survey transect was directly counted from the video. Shark abundance peaked in the winter (January-March) with a maximum in 2011 of 12,128 individuals counted within the 75.6 km-2 belt transect. This resulted in a maximum density of 803.2 sharks km-2. By the late spring (April-May), shark abundance had sharply declined to 1.1% of its peak, where it remained until spiking again in January of the following year. Shark abundance was inversely correlated with water temperature and large numbers of sharks were found only when water temperatures were less than 25°C. Shark abundance was also correlated with day of the year but not with barometric pressure. Although shark abundance was not correlated with photoperiod, the departure of the sharks from southeast Florida occurred around the vernal equinox. The shark migration along the United States eastern seaboard corresponds spatially and temporally with the spawning aggregations of various baitfish species. These baseline abundance data can be compared to future studies to determine if shark population size is changing and if sharks are restricting their southward migration as global water temperatures increase.

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Section: Discussionmentioning

confidence: 99%

Quantification of Massive Seasonal Aggregations of Blacktip Sharks (Carcharhinus limbatus) in Southeast Florida

Kajiura

Tellman

2016

PLoS ONE

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“…Fish spawning aggregations are known to be targeted by sharks [13,16] but were believed to only represent occasional opportunistic supplements. Our work demonstrates the potentially high importance of grouper spawning aggregations in the maintenance of local inverted pyramids in pristine marine areas.…”

Section: Spawning Aggregations and Reef Shark Residencymentioning

confidence: 99%

Extreme Inverted Trophic Pyramid of Reef Sharks Supported by Spawning Groupers

et al. 2016

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The extent of the global human footprint [1] limits our understanding of what is natural in the marine environment. Remote, near-pristine areas provide some baseline expectations for biomass [2, 3] and suggest that predators dominate, producing an inverted biomass pyramid. The southern pass of Fakarava atoll-a biosphere reserve in French Polynesia-hosts an average of 600 reef sharks, two to three times the biomass per hectare documented for any other reef shark aggregations [4]. This huge biomass of predators makes the trophic pyramid inverted. Bioenergetics models indicate that the sharks require ∼90 tons of fish per year, whereas the total fish production in the pass is ∼17 tons per year. Energetic theory shows that such trophic structure is maintained through subsidies [5-9], and empirical evidence suggests that sharks must engage in wide-ranging foraging excursions to meet energy needs [9, 10]. We used underwater surveys and acoustic telemetry to assess shark residency in the pass and feeding behavior and used bioenergetics models to understand energy flow. Contrary to previous findings, our results highlight that sharks may overcome low local energy availability by feeding on fish spawning aggregations, which concentrate energy from other local trophic pyramids. Fish spawning aggregations are known to be targeted by sharks, but they were previously believed to play a minor role representing occasional opportunistic supplements. This research demonstrates that fish spawning aggregations can play a significant role in the maintenance of local inverted pyramids in pristine marine areas. Conservation of fish spawning aggregations can help conserve shark populations, especially if combined with shark fishing bans.

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“…Alfred manta, Mobula alfredi ) [23]. Less observed, but equally spectacular are the foraging events on FSA by subtropical and tropical reef-associated requiem sharks (Carcharhinidae), including lemon sharks ( Negaprion brevirostris ; Poey 1868) [24], grey reef sharks ( Carcharhinus amblyrhynchos ; Bleeker 1856) [14, 25], and blacktip reef sharks ( Carcharhinus melanopterus ; Quoy and Gaimard 1824) [26]. During these periods, sharks may become vulnerable to the same types of gear used for target aggregating fish (Rhodes pers.…”

Section: Introductionmentioning

confidence: 99%

Grouper (Epinephelidae) spawning aggregations affect activity space of grey reef sharks, Carcharhinus amblyrhynchos, in Pohnpei, Micronesia

Rhodes¹,

Baremore²,

Graham³

2019

PLoS ONE

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Fish spawning aggregations (FSA) act as biological hotspots that concentrate food and nutrients across a broad trophic spectrum. In Pohnpei (Federated States of Micronesia), 20 female grey reef sharks ( Carcharhinus amblyrhynchos ) were acoustically tagged at two multi-species grouper (Epinephelidae) FSA to examine the likelihood that these mesopredators utilize FSA as a seasonal food source. Both FSA sites are within small-scale MPAs, thus providing a secondary opportunity to examine their conservation potential during these ephemeral events. Shark movement and residency was gauged against known spatial and temporal grouper reproductive patterns using an array of 15 and 50 acoustic receivers at Ant Atoll and Pohnpei (Island), respectively. Activity space was investigated using Kernel Density estimates of individual sharks, and residency indices (RI) were analyzed based on daily and monthly occurrence at the array. Three distinct residency patterns were identified: transient, semi-transient, or resident (Daily RI <0.40, >0.40 to 0.80, or >0.80, respectively). Generalized linear mixed models (GLMMs) were used to identify biological and environmental factors influencing shark activity space, including month, temperature, shark size, spawning month, and residency pattern. Findings revealed significant changes in average monthly residency indices and kernel densities during spawning months in support of an opportunistic foraging strategy around FSA. Monthly residency was higher during spawning months among semi-resident and transient sharks, while average monthly activity space was concentrated around FSA. Best-fit models for the GLMM indicated that activity spaces were most influenced by month and grouper spawning month. Seven of 20 sharks demonstrated inter-island movement and wide variations in individual movement and spatial requirements were shown. The concentration of sharks and groupers at unprotected FSA sites increases their vulnerability to fishing and supports the need for combined area and non-area management measures to effectively protect these species.

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A massive surgeonfish aggregation creates a unique opportunity for reef sharks

Abstract: International audienc

Cited by 10 publications

References 3 publications

Quantification of Massive Seasonal Aggregations of Blacktip Sharks (Carcharhinus limbatus) in Southeast Florida

Quantification of Massive Seasonal Aggregations of Blacktip Sharks (Carcharhinus limbatus) in Southeast Florida

Extreme Inverted Trophic Pyramid of Reef Sharks Supported by Spawning Groupers

Grouper (Epinephelidae) spawning aggregations affect activity space of grey reef sharks, Carcharhinus amblyrhynchos, in Pohnpei, Micronesia

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