Assortative interactions and leadership in a free-ranging population of juvenile lemon shark Negaprion brevirostris

Abstract

For marine predators there is a paucity of studies on social behaviour, and even fewer studies have quantified interactions between individuals. In the present study, we looked at the social structure and leadership of free-ranging juvenile lemon shark Negaprion brevirostris in a known aggregation site, Bimini, the Bahamas. Observations of these sharks were made from towers placed in a mangrove inlet, where clear, shallow, protected waters made it possible to record group compositions of externally colour-code tagged wild juvenile lemon sharks. Thirty-eight different individual sharks were observed to use the area over a 2 yr period. Results show repeated social interactions suggestive of active partner preference. In addition, we found that group structure was mostly explained by body length, and possibly by preference for relatives but not by sex. Finally, we observed that some sharks led more groups than others and that those lead individuals were usually larger than those following them. This study quantifies the social structure of a free-ranging shark population and provides novel insights into the social behaviour of juvenile sharks.

Diet shift and site-fidelity of oceanic whitetip sharks Carcharhinus longimanus along the Great Bahama Bank

“…Gallagher et al (2014) reported oceanic whitetip swimming in 'nose-to-tail' formation at CI during spring and speculated that this could be related to courtship (Gallagher et al 2014). However, this be havior was observed in all-female groups, and other studies have observed similar behavior in immature sharks (Guttridge et al 2011).…”

Deep danger: intra-specific predation risk influences habitat use and aggregation formation of juvenile lemon sharks Negaprion brevirostris

“…This area has been the location for a series of studies investigating aspects of juvenile lemon shark behavioural ecology. The sharks use the area daily and are regularly observed to aggregate at and around the high tide (Guttridge et al 2010(Guttridge et al , 2011. …”

“…1b). Over a 2 yr period, a total of 58 juvenile lemon sharks (n = 25 females, n = 33 males; TL = 79 ± 12.3 cm, mean ± SD) were caught every 3 to 4 mo (some repeatedly) through seine and gill netting (Guttridge et al 2011). Briefly, all sharks were sexed, measured (pre-caudal, total length), tagged with a passive integrated transponder (PIT, Destron Fearing ® ) and colour-code tagged through the first dorsal fin (T-bar anchor tag, Floy Tag ® ) to enable individual identification using mono-, bi-or tri-coloured tags.…”

“…This was to ensure that water surface and light levels did not affect clear identification of sharks. Preliminary observations over the full tidal cycle revealed that no sharks used the area over the low tide period because AS regularly dried out, thus preventing access (Guttridge et al 2011). Observers arrived at mid-tide before the sharks and left once the last shark had departed the area, usually 6 to 8 h later.…”

“…20 to 30) of juvenile lemon sharks (<1.1 m TL) have been documented to use mangrove-inlets and channels that are only accessible between mid-tides over the high (Franks 2007, Guttridge et al 2011. At one of these sites (Aya's Spot) sharks have been observed daily to interact in social groups following and resting in shallow water (0.2 to 0.9 m depth), often within mangrove edge habitat (Guttridge et al 2011). A shallow channel entrance, interspersed with mangrove prop roots, precludes access to larger predatory sharks, such as sub-adult conspecifics (>1.3 m).…”