Search

Whale sharks are known to feed primarily on zooplankton all over the world; however, recent findings suggest that they also prey on fish using behaviors that have not been fully described. Here, we provide detailed evidence of whale sharks interacting with schools of anchovy on four occasions in Bahia de Los Angeles, Baja California, Mexico. Three of these were predatory interactions in multi-species feeding frenzies, and one was a non-predatory interaction. In predatory interactions, whale sharks exhibited two types of feeding behaviors: (1) stationary suction-feeding, a previously described behavior for whale sharks, and (2) lunge-feeding, which has not been previously described in whale sharks, but has been observed among other large filter feeders, such as rorqual whales. The whale sharks moved simultaneously around the school of anchovy, lunging simultaneously or one after another into the school, with 66% (N = 17) of these lunges occurring in the same direction. In the non-predatory interaction, whale sharks exhibited "sit-and-wait" behavior. The evidence presented here, along with previous observations, suggests that whale sharks may change their feeding strategy from suction to lunge-feeding when other predators corner schooling fish. [ABSTRACT FROM AUTHOR]

Tourists approaching wild animals can potentially cause disturbance as a result of the perceived predation risk. Risk effects arise when prey alter their behaviour in response to predators. This response may carry costs through its impact on fitness-related activities such as foraging. We recorded behavioural responses of whale sharks Rhincodon typus to experimental vessel and swimmer approaches. We simulated the disturbance caused by ecotourism in the foraging site of this planktivorous fish in Bahia de Los Angeles, Gulf of Baja California, Mexico. Stress-related behaviours (vigilance, change of direction, diving and acceleration) were more common directly after both types of disturbance than before, in particular after approach by a swimmer. Individuals were more likely to be vigilant when they were new to the bay, but we did not find evidence of within-season behavioural habituation. Sharks were 24% more likely to forage before human stimuli than after. Our study highlights negative effects of vessel and swimmer approaches on whale shark behaviour, with a short-term increase in stress-related behaviours potentially carrying energetic costs, combined with a decrease in food intake following the disturbance. Our results indicate concerns about the impact of ecotourism on large fish species. An important next step would be to determine whether these short-term behavioural responses to the perception of predation risk negatively affect fitness. Among other guidelines, we recommend preventing swimmers from approaching if whale sharks stop feeding when a vessel approaches. [ABSTRACT FROM AUTHOR]

Mercury and selenium were measured for first time in the endangered species whale shark (Rhyncodon typus) from two areas of the Gulf of California, Bahía Los Angeles (BLA) and Bahía La Paz (LAP) using dermal biopsies of seventy specimens. Additionally, nineteen zooplankton samples from LAP were analysed. Concentrations (ng/g, wet weight (ww)) in biopsies of BLA ranged from 1 to 40 for Hg and 100 to 680 for Se; while in LAP varied from 1 to 9 for Hg and 11 to 850 for Se. A positive correlation was found for Hg in BLA males biopsies with length. Hg and Se concentrations in the zooplankton from LAP were 1.6 ± 1.8 and 770 ± 930 ng/g, respectively. Hg biomagnification factor ranged from 0.8 to 5.3 in sharks. A molar excess of Se over Hg was found in the biopsies and the zooplankton., (Copyright © 2019. Published by Elsevier Ltd.)

The present study analyses whale shark Rhincodon typus stranding in the Gulf of California, Mexico, reported by the public, scientists, authorities and artisanal fishermen. A total of 14 strandings were documented during the period 2001-2018. The total length of R. typus ranged from 350-1,102 cm, with a sex ratio of 3.5:1 (males: females). This study highlights potential stranding areas, the need for better stranding protocols to assist R. typus recovery and the importance of samples from dead animals for scientific research., (© 2018 The Fisheries Society of the British Isles.)