First record of bottom-feeding behaviour in the whale shark (Rhincodon typus).

Despite being the world's largest fish, many questions remain regarding the ecology and behaviour of the whale shark (Rhincodon typus). We present the first direct evidence of whale sharks engaging in bottom-feeding behaviour and provide potential explanations for this foraging strategy. We suggest that whale sharks actively feed on benthic prey, either predominantly in deepwater environments or where the abundance of such prey exceeds that of planktonic food sources. We also highlight the potential for ecotourism and citizen science projects to contribute to our understanding of marine megafauna behavioural ecology.

First concurrent assessment of elemental- and organic-contaminant loads in skin biopsies of whale sharks from Djibouti.

The Gulf of Tadjoura (Djibouti) is an important site where the whale shark (Rhincodon typus Smith, 1828) aggregates seasonally. Because of the proximity to the port of Djibouti that is located along one of the busiest shipping areas in the world, whale sharks are potentially exposed to relatively high levels of trace elements and organochlorines. To assess their contamination status, concentrations of 15 trace elements, DDTs and PCBs were concurrently assessed for the first time in skin biopsies of 20 whale sharks. Additionally, 12 zooplankton samples were collected and analyzed for trace elements content. Concentration of As, Cu, Zn and Se were higher than in previous studies on this species. Whale shark samples exceeded the maximum allowable limits for foodstuffs for Cr, Pb Se, Cd and Zn. Results from this study suggests that Cr, Ni and Mo may biomagnify in this species. With regard to PCBs, the predominant congener were Tetra-CB, accounting for 41% of total PCBs and Penta-CB for 23%, while for DDTs, the predominant metabolite was DDE contributing for 51% of total compounds. The maximum residue limit for DDTs and for the ind-PCBs in fish set by U.S. EPA and by the EU regulation, respectively, was exceeded in 62% of whale sharks. Moreover, the p,p'DDE/ΣDDT ratios were higher than the critical value of 0.6, indicating possible recent inputs of technical DDTs in the area. This study suggests some concerns for the contamination status of whale sharks in Djibouti and, since major threats for this species include bycatch and illegal fisheries, highlights some level of risk from the exposure to elemental- and organic-contaminant via shark consumption.

Oceanic adults, coastal juveniles: tracking the habitat use of whale sharks off the Pacific coast of Mexico.

Eight whale sharks tagged with pop-up satellite archival tags off the Gulf of California, Mexico, were tracked for periods of 14-134 days. Five of these sharks were adults, with four females visually assessed to be pregnant. At least for the periods they were tracked, juveniles remained in the Gulf of California while adults moved offshore into the eastern Pacific Ocean. We propose that parturition occurs in these offshore waters. Excluding two juveniles that remained in the shallow tagging area for the duration of tracking, all sharks spent 65 ± 20.7% (SD) of their time near the surface, even over deep water, often in association with frontal zones characterized by cool-water upwelling. While these six sharks all made dives into the meso- or bathypelagic zones, with two sharks reaching the maximum depth recordable by the tags (1285.8 m), time spent at these depths represented a small proportion of the overall tracks. Most deep dives (72.7%) took place during the day, particularly during the early morning and late afternoon. Pronounced habitat differences by ontogenetic stage suggest that adult whale sharks are less likely to frequent coastal waters after the onset of maturity.

Mark-recapture with multiple, non-invasive marks.

SUMMARY: Non-invasive marks, including pigmentation patterns, acquired scars, and genetic markers, are often used to identify individuals in mark-recapture experiments. If animals in a population can be identified from multiple, non-invasive marks then some individuals may be counted twice in the observed data. Analyzing the observed histories without accounting for these errors will provide incorrect inference about the population dynamics. Previous approaches to this problem include modeling data from only one mark and combining estimators obtained from each mark separately assuming that they are independent. Motivated by the analysis of data from the ECOCEAN online whale shark (Rhincodon typus) catalog, we describe a Bayesian method to analyze data from multiple, non-invasive marks that is based on the latent-multinomial model of Link et al. (2010, Biometrics 66, 178-185). Further to this, we describe a simplification of the Markov chain Monte Carlo algorithm of Link et al. (2010, Biometrics 66, 178-185) that leads to more efficient computation. We present results from the analysis of the ECOCEAN whale shark data and from simulation studies comparing our method with the previous approaches.