Whale shark foraging on baitfish off Djibouti
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Whale shark foraging on baitfish off Djibouti G. Boldrocchi 1
&
R. Bettinetti 1
Received: 14 September 2018 / Revised: 6 December 2018 / Accepted: 14 December 2018 # Senckenberg Gesellschaft für Naturforschung 2019
Abstract In the Gulf of Tadjoura, Republic of Djibouti, whale sharks (Rhincodon typus Smith, 1828) are known to feed on a wide variety of zooplankton organisms. However, for the first time in this area, seven juvenile whale sharks were filmed feeding on a school of baitfish (anchovies). During the event, zooplankton samples were collected and biomass was calculated. Results support the hypothesis that when dense patches of zooplankton are not available in the Gulf of Tadjoura, whale sharks remain in the area and feed on alternative energy-rich prey, such as baitfish, to meet their energetic demands. Keywords Filter-feeders . Feeding ecology . Bait-ball . Gulf of Aden
Introduction The whale shark (Rhincodon typus Smith, 1828) is a suction filter-feeder that inhabits all oceans from tropical to temperate latitudes (Colman 1997). Several studies on its preferences indicate that whale sharks congregate in coastal habitats to feed on dense patches of zooplankton organisms (Colman 1997; Compagno 2001; Stevens 2007; Rowat and Brooks 2012). Preys include copepods (Clark and Nelson 1997), krill (Gunn et al. 1999; Wilson et al. 2001; Taylor 2007), crab larvae (Meekan et al. 2009), sergestids (Rohner et al. 2015), fish spawn (Heyman et al. 2001; De la Parra Venegas et al. 2011), gelatinous zooplankton, and chaetognaths (Rowat et al. 2007; Taylor 2007). Recent studies indicate that whale sharks feed on a wider foraging range, including demersal and deep-water macrozooplankton, and fishes (Duffy 2002; Borrell et al. 2011; Rohner et al. 2013; Marcus et al. 2016). In Djibouti, whale sharks aggregate on a regular basis from October to February (Rowat et al. 2007, 2011; Rezzolla and Communicated by S. Lluch-Cota Electronic supplementary material The online version of this article (https://doi.org/10.1007/s12526-018-00934-8) contains supplementary material, which is available to authorized users. * G. Boldrocchi [email protected] 1
Department of Theoretical and Applied Sciences, University of Insubria, Via Valleggio 11, 22100 Como, Italy
Storai 2010), using this area as a feeding ground during those months (Boldrocchi et al. 2018). The whale shark occurrence might be related to an increase in zooplankton biomass due to the southwestern monsoon upwelling (Boldrocchi et al. 2018). In Djibouti, whale sharks have been observed targeting dense patches of copepods chaetognaths, salps and mantis shrimp larvae (Rowat et al. 2007; Rezzolla and Storai 2010). In the present note, we provide the first observation of whale sharks feeding on a school of baitfish (anchovies) at the beginning of the aggregation period.
Material and methods On 16 October 2017 in the Gulf of Tadjoura (11°34.596′ N 42°47.468′ E) at 11:30 a.m., seven whale sharks were filmed and photographed feeding on a school of anch
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