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

TitleDemography and movement patterns of leopard sharks (Triakis semifasciata) aggregating near the head of a submarine canyon along the open coast of southern California, USA
Publication TypeJournal Article
Year of Publication2013
AuthorsNosal AP, Cartamil DC, Long JW, Luhrmann M, Wegner NC, Graham JB
JournalEnvironmental Biology of Fishes
Volume96
Pagination865-878
Date Published2013/07
Type of ArticleArticle
ISBN Number0378-1909
Accession NumberWOS:000319611600006
KeywordsAcoustic telemetry; bay; behavior; elasmobranch; elkhorn slough; fidelity; fishes; food-habits; ginglymostoma-cirratum; home-range; Marine reserve; reef shark; scalloped hammerhead sharks; Sexual segregation; Shark aggregation; site; sphyrna-lewini; Wave height
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 (a parts per thousand currency sign2 m for 71.0 % and a parts per thousand currency sign10 m for 95.9 % of time), with some dispersing to deeper (max: 53.9 m) and cooler (min: 12.7 A degrees 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.

DOI10.1007/s10641-012-0083-5
Short TitleEnviron. Biol. Fishes
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