Carl G. Meyer

Movement Patterns, Habitat Utilization, Home Range Size and Site Fidelity of Whitesaddle Goatfish, Parupeneus Porphyreus, In a Marine Reserve

Suitability of small (< 1 km2) marine reserves for protecting a commercially important endemic Hawaiian goatfish, Parupeneus porphyreus, was examined by quantifying goatfish habitat use, home range size and site fidelity in an existing marine reserve (Coconut Island in Kaneohe Bay, Hawaii). Five goatfish equipped with acoustic transmitters were tracked for up to 93 h each over 3–14 days. Daytime habitat use patterns of two of these fish were continuously monitored for one month using a fixed hydrophone hardwired to an onshore computer. Acoustically tagged fish showed consistent diel patterns of behavior, refuging in holes in the reef by day and moving over extensive areas of sand and coral rubble habitat at night. Remote monitoring of daytime habitat use by two goatfish revealed that the same daytime refuge was used by both fish for at least one month (the battery life of the transmitters). Home ranges of all fish were within the boundaries of the Coconut Island reserve suggesting that even small areas containing suitable habitat can make effective reserves for this species. A relatively low abundance of reproductive size P. porphyreus at Coconut Island in comparison with deeper areas may indicate an ontogenetic shift to deeper habitat in this species.

Movement patterns, home range size and habitat utilization of the bluespine unicornfish, Naso unicornis (Acanthuridae) in a Hawaiian marine reserve

SynopsisWe quantified bluespine unicornfish, Naso unicornis, movement patterns, home range size and habitat preferences in a small Hawaiian marine reserve. Bluespine unicornfish were site-attached to home ranges situated within the reserve boundaries and their movements were aligned with topographic features. Two different diel movement patterns (‘commuting’ and ‘foraying’) were observed. Commuters made crepuscular migrations of several hundred meters between daytime foraging areas and nighttime refuge holes. Foraying fish did not partake in crepuscular migrations and utilized refuge holes both day and night. Two bluespine unicornfish were also nocturnally active. There was little direct evidence of dispersal from the reserve but differences in bluespine unicornfish abundance and size among reef habitat zones were consistent with ontogenetic habitat shifts. The influence of habitat topography on bluespine unicornfish movements suggests that gross habitat characteristics could be used to predict reef fish movements. This could provide a simple method for setting marine reserve boundaries at sites for which empirical fish movement data are unavailable.

Scales of orientation, directed walks and movement path structure in sharks

1. Animal search patterns reflect sensory perception ranges combined with memory and knowledge of the surrounding environment. 2. Random walks are used when the locations of resources are unknown, whereas directed walks should be optimal when the location of favourable habitats is known. However, directed walks have been quantified for very few species. 3. We re-analysed tracking data from three shark species to determine whether they were using directed walks, and if so, over which spatial scales. Fractal analysis was used to quantify how movement structure varied with spatial scale and determine whether the sharks were using patches. 4. Tiger sharks performed directed walks at large spatial scales (at least 6-8 km). Thresher sharks also showed directed movement (at scales of 400-1900 m), and adult threshers were able to orient at greater scales than juveniles, which may suggest that learning improves the ability to perform directed walks. Blacktip reef sharks had small home ranges, high site fidelity and showed no evidence of oriented movements at large scales. 5. There were inter- and intraspecific differences in path structure and patch size, although most individuals showed scale-dependent movements. Furthermore, some individuals of each species performed movements similar to a correlated random walk. 6. Sharks can perform directed walks over large spatial scales, with scales of movements reflecting site fidelity and home range size. Understanding when and where directed walks occur is crucial for developing more accurate population-level dispersal models.

Sharks can detect changes in the geomagnetic field

We used behavioural conditioning to demonstrate that sharks can detect changes in the geomagnetic field. Captive sharks were conditioned by pairing activation of an artificial magnetic field with presentation of food over a target. Conditioned sharks subsequently converged on the target when the artificial magnetic field was activated but no food reward was presented thereby demonstrating that they were able to sense the altered magnetic field. This strong response provides a robust behavioural assay that could be used to determine how sharks detect magnetic fields and to measure detection thresholds.

Seasonal cycles and long-term trends in abundance and species composition of sharks associated with cage diving ecotourism activities in Hawaii

Shark cage diving is both popular and controversial, with proponents citing educational value and non-extractive use of natural resources and opponents raising concerns about public safety and ecological impacts. Logbook data collected 2004–2008 from two Oahu (Hawaii) shark cage diving operations were analysed to determine whether such voluntary records provide useful insights into shark ecology or ecotourism impacts. Operators correctly identified common shark species and documented gross seasonal cycles and long-term trends in abundance of Galapagos ( Carcharhinus galapagensis ), sandbar ( Carcharhinus plumbeus ) and tiger sharks ( Galeorcerdo cuvier ). Annual cycles in shark abundance may indicate seasonal migrations, whereas long-term trends suggest gradual exclusion of smaller sandbar sharks from cage diving sites. Numerically dominant (> 98%) Galapagos and sandbar sharks are rarely implicated in attacks on humans. Negligible impact on public safety is supported by other factors such as: (1) remoteness of the sites, (2) conditioning stimuli that are specific to the tour operations and different from inshore recreational stimuli and (3) no increase in shark attacks on the north coast of Oahu since cage diving started. Tracking studies are required to validate logbook data and to determine whether sharks associated with offshore cage diving travel into inshore areas used for in-water recreation.

Diet, resource partitioning and gear vulnerability of Hawaiian jacks captured in fishing tournaments

Stomach content, capture method and capture location data were collected for 401 carangids captured during three annual 1-day fishing tournaments held at a coastal bay in Hawaii. Blue jack (Caranx melampygus), white jack (Caranx ignobilis) and island jack (Carangoides orthogrammus) were the most common species, accounting for 83.5, 8.5 and 5.2% of tournament catches, respectively. Geographical area fished consisted of a sheltered bay and the adjacent seaward coastal reef beyond. Area of capture and fishing method influenced species and size of fish captured. Small ( 500 mm) C. melampygus were captured outside Kaneohe Bay. Trolling (towing a surface lure) accounted for 80% of C. melampygus, 76% of C. orthogrammus and 55% of C. ignobilis captured. Differential vulnerability to trolling may be related to interspecific differences in diet; captured C. melampygus had fed primarily on fish whereas C. orthogrammus had consumed both fish and benthic crustaceans, and C. ignobilis had eaten mainly benthic crustaceans. Differences in diet may indicate resource partitioning between these sympatric and closely related species. For C. melampygus there was a consistent relationship between prey size and predator size. When conducted under scientific scrutiny, fishing tournaments can provide synoptic data on diet and gear vulnerability that would otherwise be very difficult to obtain.

Effects of food type on diel behaviours of common carp Cyprinus carpio in simulated aquaculture pond conditions

In order to better understand behaviour patterns of common carp Cyprinus carpio in aquaculture ponds, their diel grazing, swimming, resting and schooling behaviours were observed in six 1 m(2) tanks under simulated pond conditions. Each tank was fertilized to stimulate natural food production before starting experiments, and then stocked with three C. carpio. Fish behaviours were compared among three treatments: (1) tanks with plankton only, (2) tanks with plankton and benthic macroinvertebrates and (3) tanks with plankton, benthic macroinvertebrates and artificial feed. Overall C. carpio grazed more frequently during daytime than at night and exhibited the reverse pattern for non-feeding swimming behaviour. A significant negative relationship (r(2) = 0.99, P < 0.01, n = 48) was observed between total per cent grazing time and total per cent swimming time. Fish dispersed to graze individually during daytime but schooled at night and did not display any agonistic behaviours. Diel variations in the vertical swimming behaviour of C. carpio were related to food types available. In tanks containing plankton only, fish grazed in the water column, whereas when benthic macroinvertebrates were present, they spent more time near the tank bottom. Resting behaviour was only seen in tanks with artificial feed and even then was rare (2-5% of total time). Results suggest that C. carpio growth and feed utilization efficiency in semi-intensive aquaculture systems could be optimized by using a combination of plankton, benthic macroinvertebrates and artificial feed, and feeding fish twice per day (at c. 0730 and c. 1630 hours).

Transintestinal Expulsion of Surgically Implanted Dummy Transmitters by Bluefin Trevally—Implications for Long-Term Movement Studies

Abstract The feasibility of long-term acoustic monitoring of coral reef fish movements was evaluated by quantifying transmitter retention times for captive bluefin trevally Caranx melampygus and detection patterns of transmitter-implanted free-ranging bluefin trevally. Wax-coated dummy transmitters (9 × 22 mm; 3.6 g) were surgically implanted into the gut cavity of four captive bluefin trevally. The fish retained the dummy transmitters for 17–22 months, but at the end of the study transintestinal expulsion was in progress in one individual. Five bluefin trevally captured at Honokohau, Hawaii, were surgically implanted with long-life (1-year) coded transmitters and released. Their movements were monitored with the use of 27 underwater receivers deployed along a 115-km stretch of coastline. The five bluefin trevally were detected by the receivers over periods ranging from 1 to 173 d (mean, 60 d), and their movements spanned up to 10.2 km of coastline. Daily movements were consistent with those observed by p...

Site fidelity and movements of sharks associated with ocean-farming cages in Hawaii

Sharks are found in association with main Hawaiian Island ocean fish farms more frequently and at higher densities than is typical for coastal Hawaiian waters. Sharks attracted to fish farms could potentially threaten human water users, interact negatively with other fisheries, and seasonal migrations could be disrupted if individuals become entrained around farms throughout the year. We hypothesised that smaller coastal species would reside near farms, whereas more wide-ranging species would associate with farms only for short periods. We utilised passive acoustic telemetry to monitor the movements and behaviour of sandbar (Carcharhinus plumbeus) and tiger (Galeocerdo cuvier) sharks adjacent to two open ocean fish farms in Hawaii. Approximately half the tagged sandbar sharks showed site fidelity to the farms, with some individuals being detected repeatedly for 2.5 years. Sandbar sharks moved seasonally to the west coast of Oahu, suggesting that fish farms are not disrupting natural seasonal cycles in this species. Tiger sharks tagged near the cages were more transient, and showed much shorter residence times although some individuals returned sporadically to the cages over the 3-year period. Ocean fish cages appear to aggregate sandbar sharks, but are only ‘visited’ by tiger sharks. Although threats to public safety are probably minimal, the ecological effects of aggregating top-predators are still unknown.

Five Tags Applied to a Single Species in a Single Location: The Tiger Shark Experience

Five different types of tags were used to monitor the horizontal and vertical movement patterns of tiger sharks and to document site fidelity. Sonic tracking experiments gave insight into the fine-scale movement patterns of the sharks for periods of up to 50 h whereas long-lived, acoustic pingers and automated, anchored data loggers (listening posts) provided data regarding the long-term periodicity and frequency of return of tiger sharks. These electronic recaptures were compared with the rate of traditional recaptures of sharks tagged with standard dart tags and recaptured with fishing gear. In the most recent phase of research, archiving tags capable of downloading stored data via sonic modem technology (CHAT tags) were implanted in sharks. The characteristics of data derived from these tags were compared with data acquired by active sonic tracking. A single pop-up satellite tag was provided to the shark tracking project by the manufacturer. This tag was attached with a saddle fitted around the anterior edge of the dorsal fin of a shark. Again, the active sonic tracking data were used to evaluate the veracity of the data acquired form the satellite tag. Data from these various sources are beginning to paint a consistent picture of tiger shark home range size and site fidelity in the Hawaiian archipelago.