Patterns of movement and grouping of gray reef sharks, Carcharhinus amblyrhynchos, at Enewetak, Marshall Islands
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.
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Document Type: Research Article
Publication date: 1986-01-01
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