Seasonal trends in whale sharkRhincodon typussightings in an established tourism site in the Gulf of California, Mexico

Abstract

The number of individual whale shark Rhincodon typus sightings registered October 2015-March 2018 in Bahia de La Paz, Mexico, ranged from 73 to 129 animals per season (total 1662), with the majority of them identified as males. Density plot maps showed high correlations in sightings between sample seasons and revealed potential hotspot areas. Our study provides an essential baseline of information for the management of whale shark conservation and the associated touristic activities in the region.

Habitat suitability ofRhincodon typusin three localities of the Gulf of California: Environmental drivers of seasonal aggregations

“…The bathymetry and slope of this area has the potential to increase the presence of prey through upwelling events, making this an important foraging site for whale sharks (Ketchum et al, 2013;Whitehead et al, 2019bWhitehead et al, , 2020. In contrast, the cold water conditions of La Niña during 2017/2018 could have favoured the habitat suitability of the whale sharks in several parts of BLP, which could explain an observed decrease in whale shark sightings for the southern area (CPC, 2019;Whitehead et al, 2019b). As the conditions for prey availability increase due to higher CHLOa and therefore habitat suitability, the presence of whale sharks was expanded to different localities of BLP.…”

“…Although fisheries do not seem to affect the presence of whale sharks in the area, there are other phenomena that could alter its distribution and therefore use in ecotourism activities, such as pollution or climate change (Pierce & Norman, 2016; Wilson et al ., 2001). Analysis of the current occurrence in the aggregation sites of whale sharks could provide a solid baseline for future studies regarding the changes of global environmental conditions (Páez‐Osuna et al ., 2016; Whitehead et al ., 2019b). In the present study, we provide general insights about the effect of climate variability at some of the most important aggregation sites for this endangered species in terms of CHLO a and SST, which could affect the whale shark's prey.…”

“…In this regard, the effects of invasive anthropogenic activities should be considered, as our results evidenced a high preference of this species to coastal and shallow areas where some fishing resources such as shrimp, sardines or other elasmobranchs occurs (Lluch‐Cota et al ., 2007; Petatán‐Ramírez et al ., 2019). Although the rate of interactions between the whale sharks and fisheries has not been studied, several affectations such as lacerations and even the death of some individuals have been reported (Whitehead et al ., 2019b,c). Interactions with fisheries, along with the study of the whale shark's distribution during the next decades, should be considered in future research, since oceanographic conditions will shift according to climate change predictions (Hoegh‐Guldberg & Bruno, 2010; Lluch‐Cota et al ., 2007; Páez‐Osuna et al ., 2016).…”

“…Records were obtained from biological data repositories (http://gbif.org, http://obis.org) and published scientific literature. Sightings from scientific surveys were reported between 1996 and 2018 for BLA (Nelson & Eckert, 2007; Peregrín Tovar, 2014) and BLP (Fossi et al ., 2017; Ketchum et al ., 2013; Pancaldi et al ., 2019; Whitehead et al ., 2019b), while occurrence records from NAY were obtained during the period 2013–2019 (Ramírez‐Macías et al ., 2015, 2016; Whitehead, unpublished data). These records were obtained during multiple scientific or tourist surveys, in which a standardization according to the sampling effort was not possible, thus the records of occurrence were driven by the different sampling efforts in known distribution areas.…”

“…Polygons represent the minimum training presence for the prevalence of whale sharks F I G U R E 3 Response curves for environmental factors in the Maxent model of whale sharks in the Gulf of California using occurrence records from 1996 to 2018. Higher logistic output indicates better environmental conditions for whale shark presence FISH aggregation site of BLA, mean values for each environmental factor were obtained from June to November (Nelson & Eckert, 2007;Peregrín Tovar, 2014), for BLP from October to March (Whitehead et al, 2019b) and for NAY from November to March (Ramírez-Macías et al, 2015, 2016. In this regard, environmental factors such as bathymetry (m) and slope (percentage rise) were also included (Hacohen-Domené et al, 2015;McKinney et al, 2012).…”