C. Rohner, A. Armstrong, S. Pierce, C. Prebble, E. Cagua, J. Cochran, M. Berumen, A. Richardson
Journal of Plankton Research, 37, pp. 352-362, (2015)
Large planktivores require high-density prey patches to make feeding energetically viable. This is a major challenge for species
living in tropical and subtropical seas, such as whale sharks Rhincodon typus.
Here, we characterize zooplankton biomass, size structure and taxonomic
composition from whale shark feeding events and
background samples at Mafia Island, Tanzania. The
majority of whale sharks were feeding (73%, 380 of 524 observations),
the most common behaviour being active surface
feeding (87%). We used 20 samples collected from immediately adjacent to
sharks and an additional 202 background samples for
comparison to show that plankton biomass was ∼10 times higher in
where whale sharks were feeding (25 vs. 2.6 mg m−3). Taxonomic analyses of samples showed that the large sergestid Lucifer hanseni
(∼10 mm) dominated while sharks were feeding, accounting for ∼50% of
identified items, while copepods (<2 mm) dominated background
samples. The size structure was skewed towards
larger animals representative of L.hanseni in feeding samples.
Thus, whale sharks at Mafia Island target patches of dense, large,
zooplankton dominated by sergestids.
Large planktivores, such as whale sharks, which
generally inhabit warm oligotrophic waters, aggregate in areas where
can feed on dense prey to obtain sufficient energy.