Comparative Use of a Caribbean Mesophotic Coral Ecosystem and Association with Fish Spawning Aggregations by Three Species of Shark

Understanding of species interactions within mesophotic coral ecosystems (MCEs; ~ 30–150 m) lags well behind that for shallow coral reefs. MCEs are often sites of fish spawning aggregations (FSAs) for a variety of species, including many groupers. Such reproductive fish aggregations represent temporal concentrations of potential prey that may be drivers of habitat use by predatory species, including sharks. We investigated movements of three species of sharks within a MCE and in relation to FSAs located on the shelf edge south of St. Thomas, United States Virgin Islands. Movements of 17 tiger (Galeocerdo cuvier), seven lemon (Negaprion brevirostris), and six Caribbean reef (Carcharhinus perezi) sharks tagged with acoustic transmitters were monitored within the MCE using an array of acoustic receivers spanning an area of 1,060 km2 over a five year period. Receivers were concentrated around prominent grouper FSAs to monitor movements of sharks in relation to these temporally transient aggregations. Over 130,000 detections of telemetered sharks were recorded, with four sharks tracked in excess of 3 years. All three shark species were present within the MCE over long periods of time and detected frequently at FSAs, but patterns of MCE use and orientation towards FSAs varied both spatially and temporally among species. Lemon sharks moved over a large expanse of the MCE, but concentrated their activities around FSAs during grouper spawning and were present within the MCE significantly more during grouper spawning season. Caribbean reef sharks were present within a restricted portion of the MCE for prolonged periods of time, but were also absent for long periods. Tiger sharks were detected throughout the extent of the acoustic array, with the MCE representing only portion of their habitat use, although a high degree of individual variation was observed. Our findings indicate that although patterns of use varied, all three species of sharks repeatedly utilized the MCE and as upper trophic level predators they are likely involved in a range of interactions with other members of MCEs

Acoustic array located along the southern edge of the Puerto Rico-Virgin Islands platform.

<p>Red circles represent locations of acoustic receivers. Minimum convex polygons (MCP) for three species of sharks quantified by acoustic tracking are indicated for all tiger sharks (blue line, 887 km²), lemon sharks (yellow line, 863 km²) and Caribbean reef sharks (green line, 8 km²).</p

Acoustic receiver locations within two FSA sites south of St. Thomas, USVI.

<p>Boundaries of the Hind Bank Marine Conservation District (MCD) and the Grammanik Bank fishing area closure are shown. Receivers were aggregated within the Hind Bank MCD along a general boundary of MCD East and MCD West. Each red circle represents the location of a receiver</p

Average Residence Index for lemon sharks at the FSA site during grouper spawning season (gray) and non-spawning season (white) between 2007–2011.

<p>Sample size indicates the number of sharks detected each year. Bars represent mean and standard error.</p

Average Residence Index on a monthly basis (number of days detected at the FSA site as a proportion of the total number of days in the month) between 2007-2011for a) lemon sharks (n = 6); b) tiger sharks (n = 10); and Caribbean reef sharks (n = 2).

<p>The gray background represents the grouper spawning season and the white background is non-spawning months. Bars represent mean and standard error.</p

Average absence values for three species of sharks within MCE habitat monitored by the acoustic array.

<p>Absence value = average number of consecutive days not detected within the acoustic array for tiger (8.4 days), lemon (10.6 days), and Caribbean reef sharks (35.3 days). Bars represent means ± standard error.</p

Detections on receivers as proportion of total detections on all receivers for lemon sharks during grouper spawning season and non-spawning season 2007–2011.

<p>Red arrows represent Grammanik Bank, Hind Bank MCD and El Seco spawning sites (right to left).</p

Sharks tagged with acoustic transmitters, number of detections on acoustic receivers comprising the mesophotic reef receiver array and track details.

<p>Sharks tagged with acoustic transmitters, number of detections on acoustic receivers comprising the mesophotic reef receiver array and track details.</p

Average presence values for three species of shark within MCE habitat monitored by the acoustic array.

<p>Presence values (days) = average number of consecutive days detected on any receiver within the acoustic array for tiger (1.8), lemon (2.2), and Caribbean reef sharks (25.2). Bars represent means ± standard error.</p