NORTHWESTERN HAWAIIAN ISLANDS CONNECTIVITY STUDIES

Movements of Top Predators along the Hawaiian Archipelago

Top predators play a keystone role in many ecosystems and in the Northwestern Hawaiian Islands Marine National Monument (NWHIMNM). This role is filled by sharks (primarily Galeocerdo cuvier, Carcharhinus galapagensis, Carcharhinus amblyrhynchos and Triaenodon obsesus) and large teleost fishes (primarily Caranx ignobilis). 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 archipelago (and between the Main Hawaiian Islands and the Northwest Hawaiian Islands). We are using acoustic and satellite telemetry to quantify the movements of top predators in the NWHIMNM and address three questions relevant to management zoning:

Do 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?

Transmitter and receiver deployments

To date we have equipped 122 top predators with surgically implanted acoustic transmitters (Table 1) and stationed 19 underwater receivers among eight NWHIMNM atolls, reefs and pinnacles to detect movements of these animals (Table 2). We have also deployed a receiver at Johnston Atoll to detect predator movements between the NWHIMNM and this location.

Table 1. Acoustic transmitter deployments in the NWHIMNM by species.
Species Name	Hawaiian Name	Common Name	Number Equipped with Transmitters
Aprion virescens	Uku	Green Jobfish	28
Caranx ignobilis	Ulua aukea	Giant Trevally	32
Caranx melampygus	Ōmilu	Bluefin Trevally	2
Carcharhinus amblyrhyncos	Manō	Grey Reef Shark	6
Carcharhinus galapagensis	Manō	Galapagos Shark	38
Galeocerdo cuvier	Manō	Tiger Shark	15
Triaenodon obesus	Manō lālākea	Whitetip Reef Shark	1
TOTAL			122

Table 2. Acoustic receiver deployments in the NWHIMNM and Johnston Atoll.
Location	Number of Acoustic Receivers Deployed
Kure Atoll	3
Midway Atoll	3
Pearl and Hermes Reef	4
Maro Reef	2
French Frigate Shoals Atoll	5
Mokumanamana	1
Nihoa	1
Johnston Atoll *	1
TOTAL	20

Figure 1. SPOT tag attached to dorsal fin of tiger shark. Photo by Jill Zamzow. (Click on the image to open a larger version.)

Figure 2. Tiger shark with PAT tag. Photo by Jill Zamzow. (Click on the image to open a larger version.)

In addition to our acoustic transmitter deployments, we have also equipped nine sharks (five tiger sharks and four galapagos sharks) with satellite transmitters to provide information on shark movements in areas not equipped with acoustic receivers. We are using two types of satellite transmitters; (1) Fin mounted SPOT tags (Figure 1), and (2) Pop-up archiving tags (PAT tags – Figure 2). SPOT tags transmit the shark’s location to the Argos satellite array whenever the dorsal fin breaks the surface of the water. PAT tags collect and store temperature, depth and light intensity data as the shark swims, and then detach from the animal on a preprogrammed date and time. The released PAT tags float to the surface where they transmit archived data to the Argos satellite array.

Acoustic monitoring results

Figure 3. Spawning color dimorphism in ulua from school at Rapture Reef (FFS Atoll). Photo by Jill Zamzow. (Click on the image to open a larger version.)

Figure 4. Ulua school at Rapture Reef (FFS Atoll), May 23, 2006. Photo by Jill Zamzow. (Click on the image to open a larger version.)

In May 2006, we downloaded data from our receivers stationed at FFS, and now have a 12 month time-series of acoustic monitoring data for this location. Between May 2005 and May 2006, our receivers recorded 192,070 detections of 32 top predators that were equipped with acoustic transmitters at FFS during 2005. Our data suggest that most of these animals are site-attached to FFS, but wide ranging within this location. Several of these species exhibit well-defined patterns of movement and habitat use. For example, ulua were site-attached to small (<4 km²) daytime home ranges within FFS atoll from which they made monthly excursions of up to 29 km during summer, to reach a spawning site (Rapture Reef) on the south side of the atoll. These summer spawning migrations have a lunar rhythm, with ulua aggregating at Rapture Reef during the full moon and last quarter of the lunar cycle. On May 23, 2006 (nine days after the full moon), we sighted a large school of ulua containing individuals with characteristic dark spawning coloration while SCUBA diving at Rapture Reef (Figures. 3 and 4).

Figure 5. Geographic track of tiger shark #67152 equipped with SPOT tag at FFS atoll on May 26, 2006. Red points = geographic fixes from SPOT tag, dashed blue line = nominal path between fixes, red star = capture location. (Click on the image to open a larger version.)

Satellite telemetry results

Since May 2006, we have received 1,526 transmissions from 8 SPOT-equipped sharks, yielding 229 estimates of geographic position. The SPOT data show that while most sharks have remained at FFS, 2 tiger sharks have moved North to submerged banks located approximately 100 km North of FFS atoll (e.g., Figure 5). Preliminary data from released PAT tags have provided unprecedented insight into the depth profiles of tiger and galapagos sharks, revealing that these animals range from the surface to depths of 680m in the waters around FFS.

Invited Presentations

Sharks of the NWHI Talk at Hanauma Bay. On April 27, 2006 Carl Meyer gave a formal presentation on the sharks of the NWHI to a full house of 60 at the Hanauma Bay Education Center. This presentation concluded a series of public lectures on the NHWI held at Hanauma Bay Nature Preserve and co-sponsored by the NWHI Reserve.

Project Publications

Meyer CG, Holland KN, Papastamatiou YP (In Press) 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.

Papastamatiou YP, Meyer CG, Maragos JE (In Press) Sharks as cleaners for reef fish. Coral Reefs.

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