Demography and movement patterns of leopard sharks (Triakis semifasciata) aggregating near the head of a submarine canyon along the open coast of southern California, USA
Environmental Biology of Fishes
By: D.C. Nosal, D.C. Cartamil, J.W. Long, M. Luhrmann, N.C. Wegner, and J.B. Graham
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Abstract
The demography, spatial distribution, and movement patterns of leopard sharks (Triakis semifasciata) aggregating near the head of a submarine canyon in La Jolla, California, USA, were investigated to resolve the causal explanations for this and similar shark aggregations. All sharks sampled from the aggregation site (n=140) were sexually mature and 97.1 % were female. Aerial photographs taken during tethered balloon surveys revealed high densities of milling sharks of up to 5470 sharks ha-1. Eight sharks were each tagged with a continuous acoustic transmitter and manually tracked without interruption for up to 48 h. Sharks exhibited strong site-fidelity and were generally confined to a divergence (shadow) zone of low wave energy, which results from wave refraction over the steep bathymetric contours of the submarine canyon. Within this divergence zone, the movements of sharks were strongly localized over the seismically active Rose Canyon Fault. Tracked sharks spent most of their time in shallow water (≤2 m for 71.0 % and ≤10 m for 95.9 % of time), with some dispersing to deeper (max: 53.9 m) and cooler (min: 12.7 °C) water after sunset, subsequently returning by sunrise. These findings suggest multiple functions of this aggregation and that the mechanism controlling its formation, maintenance, and dissolution is complex and rooted in the sharks' variable response to numerous confounding environmental factors.
Suggested Citation
Nosal, D., Cartamil, D., Long, J., Luhrmann, M., Wegner, N., Graham, J., 2013, Demography and movement patterns of leopard sharks (Triakis semifasciata) aggregating near the head of a submarine canyon along the open coast of southern California, USA: Environmental Biology of Fishes, v. 96, no. 7, p. 865-878, https://doi.org/10.1007/s10641-012-0083-5.
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Demography and movement patterns of leopard sharks (Triakis semifasciata) aggregating near the head of a submarine canyon along the open coast of southern California, USA |
| Series title | Environmental Biology of Fishes |
| DOI | 10.1007/s10641-012-0083-5 |
| Volume | 96 |
| Issue | 7 |
| Publication Date | September 21, 2012 |
| Year Published | 2013 |
| Language | English |
| Publisher | Springer |
| Publisher location | Amsterdam, Netherlands |
| Contributing office(s) | St. Petersburg Coastal and Marine Science Center |
| Description | 14 p. |
| Larger Work Type | Article |
| Larger Work Subtype | Journal Article |
| Larger Work Title | Environmental Biology of Fishes |
| First page | 865 |
| Last page | 878 |
| Country | United States |
| State | California |
| County | San Diego |
| Other Geospatial | La Jolla Shores Beach |