Free Content Patterns of movement and grouping of gray reef sharks, Carcharhinus amblyrhynchos, at Enewetak, Marshall Islands

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Abstract:

Over a 4-year period, free-ranging sharks were studied by ultrasonic telemetry and direct underwater observation. Twenty-six intermittent multi-day trackings were conducted, of from 2–6 (x = 3.5) days of contact, and with overall durations of 2–23 days. Three transmitter attachment methods were used and evaluated: 1) dorsal-fin mount, 2) body-cavity insertion and 3) self-ingestion in bait. Observed activity spaces of the telemetered sharks ranged in area from 0.19 km2 to 53 km2 (x = 4.2 km) and in length from 300 m to 16 km (x = 3.6 km). Movement patterns suggested that: 1) sharks tagged near the ocean reefs were generally nomadic, moving relatively long distances along the reefs and 2) sharks tagged on lagoon reefs or pinnacles had a more home-ranging pattern with different day and night areas, often returning day-after-day to the tagging site. The overall daytime mean rate of movement was 1.7 km/h, while the nighttime rate was significantly higher at 3.3 km/h. Observed daytime grouping patterns were of the following three intergrading types: 1) polarized schools–seen close to bottom over level areas, 2) loose aggregations–usually near ocean-reef dropoffs and 3) lone individuals–usually over shallower reefs and lagoon pinnacles.

Document Type: Research Article

Publication date: January 1, 1986

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  • The Bulletin of Marine Science is dedicated to the dissemination of high quality research from the world's oceans. All aspects of marine science are treated by the Bulletin of Marine Science, including papers in marine biology, biological oceanography, fisheries, marine affairs, applied marine physics, marine geology and geophysics, marine and atmospheric chemistry, and meteorology and physical oceanography.
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