| Top Predator Movements in the Northwestern Hawaiian Islands |
| Principal Investigators: Carl Meyer & Kim Holland |
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| Project Overview |
Figure 1. Galapagos sharks (Carcharhinus galapagensis) school at Midway Atoll. Photo: Kevin Flanagan. |
Top predators play an important role in ecosystems by influencing prey behavior and shaping communities through trophic cascades. In the Papahanaumokuakea Marine National Monument (Northwestern Hawaiian Islands), this role is filled by sharks (primarily tiger sharks, galapagos sharks, grey reef sharks and whitetip reef sharks) and large fishes (primarily giant trevally). Science-based management of the fish resources of the Hawaiian Archipelago requires that we know whether key species are site attached to specific areas and, if not, how frequent and extensive are their movements. If the populations of key species are “tied” to individual atolls or islands, different management options may be available than if significant numbers of individuals move between atolls or, indeed, move throughout the Hawaiian archipelago. We are using acoustic and satellite telemetry to quantify the movements of top predators captured in Monument waters. |
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| Research Questions |
We are addressing three broad questions about top predator movements:
- Which top predators move across open-ocean between atolls?
- How extensive are their intra-atoll movements?
- Do top predators exhibit predictable patterns of movement and habitat use?
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| Study Species |
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| We are quantifying the movements of 4 shark and 3 teleost species: |
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| Tiger Shark |
| (Galeocerdo cuvier) |
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| Grey Reef Shark |
| (C. amblyrhynchos) |
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| Galapagos Shark |
| (C. galapagensis) |
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| Whitetip Reef Shark |
| (Triaenodon obesus) |
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| Giant Trevally |
| (Caranx ignobilis) |
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| Green Jobfish |
| (Aprion virescens) |
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| Hawaiian Grouper |
| (Hypothordus quernus) |
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| Methods |
To date we have captured 394 top predators in Monument waters and surgically implanted them with small ultrasonic transmitters. We are remotely monitoring the movements of these sharks and fishes by using underwater receivers stationed around every island in the Monument and around 4 Main Hawaiian Islands. Our receiver array stretches over 2,500km from Kure Atoll to Hawaii Island and listens continually for the presence of sharks and fishes equipped with coded pulse acoustic transmitters (within a detection range of up to 1000m). Receivers are periodically retrieved by divers and downloaded to find out which predators have visited, when they came and how long they stayed at each location. In 2006 we also ‘triple-tagged’ 8 sharks (galapagos and tiger) with both acoustic and satellite transmitters. The satellite transmitters provide information on shark movements in areas outside the detection range of our underwater listening stations, and reveal how deep these sharks typically swim.
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Figure 2. A captured tiger shark (Galeocerdo cuvier) is rolled over to facilitate transmitter implantation. Photo Luiz Rocha |
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| Results |
| Tiger sharks are the most wide-ranging top reef predator in Monument waters, routinely swimming hundreds of kilometers along the Hawaiian Archipelago and out into open ocean. Grey reef and galapagos sharks occasionally cross open ocean between islands but are generally resident at a single island. Ulua (giant trevally) and uku (green jobfish) are resident at their ‘home’ atolls where they exhibit well-defined patterns of movement with distinct diel, seasonal & lunar rhythms. All top predators range widely within individual atolls, although for most fish these movements are excursions away from core areas where they spend most of their time. For example, during summer full moons ulua from all across French Frigate Shoals swim up to 30 km to a spawning aggregation site on the southwest side of the atoll. Individual ulua return to the same spawning sites in successive years. |
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Figure 3. Inset: Overview of tiger shark satellite (SPOT) track (red line) from French Frigate Shoals (FFS) to Pearl and Hermes Reef (PHR) within the Papahanaumokuakea Marine National Monument (shaded area). Boxes indicate regions of track shown in detail in top and bottom panels. Top Panel: Concentration of SPOT detections at FFS between 5/26/06 and 7/7/06, and route taken after departure from FFS on 7/8/06. Bottom Panel: Detail of SPOT detections associated with submerged banks and seamounts surrounding Lisianski and Laysan islands. |
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| Ongoing Predator Research in the Northwestern Hawaiian Islands |
| We now have multi-year data sets from many of our tagged predators and are currently using this information to identify broad, functional groups of predator movement patterns. We are increasingly focusing on predator vertical (depth) behavior using a combination of satellite (PAT) tags and pressure sensitive acoustic transmitters. Quantifying the vertical range of sharks and large predatory teleosts is key to understanding trophic links between deep (mesophotic) and shallow reef habitats. Knowing how deep fish such as giant trevally typically range will help us to understand whether deep foraging behaviour by critically endangered Hawaiian monk seals helps seals to avoid competition with other reef predators. |
| At French Frigate Shoals (FFS) atoll we are quantifying the movements of large sharks around monk seal pupping sites (small, sandy islets within the atoll lagoon) to help determine the numbers and species of sharks preying on seal pups at these locations. In 2009 we captured and acoustically tagged 68 Galapagos sharks and 39 tiger sharks at locations inside and outside the atoll. To detect the movements of these tagged sharks, we deployed a total of 24 underwater monitoring receivers at FFS, of which 18 were deployed at monk seal pupping islets (Trig, Tern, East, Gins & Round islands). These receivers will remain in situ for at least 2 years to collect information on which tagged sharks visit seal pupping sites, how frequently they visit and how long they remain in the vicinity of these sites. The receiver array will also provide information on shark use of other atoll habitats. In 2010 we recovered, downloaded and redeployed these receivers, and found that during the first year of monitoring, 9 (13.2%) tagged Galapagos sharks and 19 (48%) tagged tiger sharks had visited the shallows surrounding the two top pupping islets (Trig and Big Gin islands). |
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| Project Publications |
| Dale JJ, Stankus AM, Burns MS, Meyer CG. (2011) The Shark Assemblage at French Frigate Shoals Atoll, Hawai'i: Species Composition, Abundance and Habitat Use. PLoS ONE 6(2): e16962. doi:10.1371/journal.pone.0016962. |
| Dale JJ, Meyer CG, Clark CE. (2011) The ecology of coral reef top predators in the Papahanaumokuakea Marine National Monument. Journal of Marine Biology. 2011:1-14. doi:10.1155/2011/725602. |
| Meyer CG, Papastamatiou YP, Holland KN. (2010) A multiple instrument approach to quantifying the movement patterns and habitat use of Tiger (Galeocerdo cuvier) and Galapagos sharks (Carcharhinus galapagensis) at French Frigate Shoals, Hawaii. Marine Biology. 157:1857–1868. DOI: 10.1007/s00227-010-1457-x |
| Meyer CG, Clark CE, Dale JJ. (2010) Unusual surface schooling behavior by bullethead parrotfish (Chlorurus sordidus). Coral Reefs. 29:881. DOI:10.1007/s00338-010-0657-7 |
| Meyer CG, Papastamatiou YP, Holland KN (2007) Seasonal, diel and tidal movements of green jobfish (Aprion virescens, Lutjanidae) at remote Hawaiian atolls: Implications for Marine Protected Area design. Marine Biology. 151: 2133-2143. |
| Meyer CG, Holland KN, Papastamatiou YP (2007) Seasonal and diel movements of giant trevally (Caranx ignobilis) at remote Hawaiian atolls: implications for the design of Marine Protected Areas. Marine Ecology Progress Series. 333: 13-25. |
| Papastamatiou YP, Meyer CG, Maragos JE (2007) Sharks as cleaners for reef fish. Coral Reefs. 26 (2): 277 |
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