The influence of zooplankton communities on the feeding behavior of whale shark in Bahia de La Paz, Gulf of California

Variation of essential and non-essential trace elements in whale shark epidermis associated to two different feeding areas of the Gulf of California

The Gulf of California represents an important hotspot for whale shark (Rhincodon typus) aggregation. Anthropogenic activities and natural sources could expose sharks to high levels of trace elements (TEs). To determinate these levels in this endangered species, concentrations of As, Cd, Cu, Pb and Zn (in ng/g ww) were measured in 130 whale shark skin biopsies and 44 zooplankton samples collected from two areas of the Gulf of California, Bahía de Los Angeles (BLA) and Bahía de La Paz (LAP) during 2016-2018. For biopsies, Zn exhibited highest concentrations in BLA (2016-2017, 298 ± 406; 2017-2018, 1959 ± 2545) and at LAP (in 2016-2017, 595 ± 554; in 2017-2018, 2642 ± 1261). On the other hand, Cd (BLA 2016-2017, 3 ± 3; LAP 2016-2017, 4 ± 3; BLA 2017-2018, 17 ± 14; LAP 2017-2018, 13 ± 10) and Pb (BLA 2016-2017, 7 ± 7; LAP 2016-2017, 15 ± 32; BLA 2017-2018, 69 ± 76; LAP 2017-2018, 7 ± 5) showed lowest concentrations. Significant differences in TE concentrations between sites and periods occurred. Arsenic found in shark biopsies from La Paz suggested enrichment and/or increased bioavailability in this area. Sex alone was not a significant factor in TE concentration; nevertheless, a sex-dependent difference in correlation of TE concentration and size was noted (negative in males, positive in females). This indicates feeding strategies of whale shark may be sex and size segregated. During 2017-2018, zooplankton and sharks showed enrichment in all TEs. Essential elements were not biomagnified by sharks. Lead was biomagnified through zooplankton. Strong positive correlation between selected elements indicates that Zn, Cd and Pb follow the same metabolic route in the sharks' body.

Variability of Net Primary Productivity and Associated Biophysical Drivers in Bahía de La Paz (Mexico)

The use of information of net primary productivity (NPP) from remote ocean color sensors is increasingly common in marine sciences. The resulting information has been used to explain variations in productivity at different spatio-temporal scales and in the presence of climate phenomena, such as the El Niño Southern Oscillation, and global warming. Satellite remote sensing data were analyzed in Bahía de La Paz (BLP), Mexico, to determine the spatio-temporal variation in NPP. In addition, in situ hydrographic data were obtained to characterize the water properties in the bay. The satellite data agree with in situ measurements, validating the satellite observations over this region. The NPP generally presented seasonal variation with maximum values in winter-spring and minimum values in summer–autumn. The variance explained by NPP from the measured variables was ranked as Chl-a < DEN < SST < PAR < WSC. The highest NPP values generally occurred when subtropical subsurface (SsStW) water was relatively shallow. Due to divergence and mixing processes, this water provided nutrients to the euphotic zone, and consequently an increase in NPP and changes in plankton biomass were observed. The annual trends of the variation in hydrographic data with respect to that of remote sensing data were similar; however, it is necessary to increase the number of data validation studies. The remote sensing and in situ measurements allowed for the main biophysical variables that modulate NPP in different time scales to be identified. The satellite-derived NPP data classifies the BLP as a high productivity zone with 432 g C m−2 year−1. The use of satellite NPP data is satisfactory and should be incorporated into marine primary productivity studies.

The use of machine learning to detect foraging behaviour in whale sharks: a new tool in conservation

In this study we present the first attempt at modelling the feeding behaviour of whale sharks using a machine learning analytical method. A total of eight sharks were monitored with tri-axial accelerometers and their foraging behaviours were visually observed. Our results highlight that the random forest model is a valid and robust approach to predict the feeding behaviour of the whale shark. In conclusion this novel approach exposes the practicality of this method to serve as a conservation tool and the capability it offers in monitoring potential disturbances of the species.

Habitat suitability of Rhincodon typus in three localities of the Gulf of California: Environmental drivers of seasonal aggregations

The whale shark is an endangered species that usually feeds in coastal areas of highly productive seas such as the Gulf of California, Mexico. This study aims to describe the effect of sea surface temperature, chlorophyll a, bathymetry and slope on the habitat suitability of whale sharks in three important aggregation sites of the Gulf of California. A total of 2396 records of occurrence of whale sharks were obtained from international databases and scientific literature between 1996 and 2018. These records were used for the creation of a species distribution model using MaxEnt for each of the three aggregation sites. The concentration of chlorophyll a explained 71% of the habitat suitability, followed by bathymetry and slope with a combined 17%, and sea surface temperature constituting 10% of the model. Habitat suitability was related to areas where nontargeted fisheries may impact whale sharks through bycatch, entanglement and ship strikes. The implications for the conservation of whale sharks should be considered for management decisions in terms of marine protected areas, fishing refugees or bans, and other regulations regarding fisheries activities.