Feeding habitat of the whale shark Rhincodon typus in the northern Gulf of Mexico determined using species distribution modelling

Abstract

Whale shark Rhincodon typus is a globally distributed species, but there is a lack of knowledge pertaining to their biology, seasonal occurrence, and distribution in the northern Gulf of Mexico (NGOM). Understanding critical habitat for whale sharks is essential on both a regional and global basis for proper management because of their large migratory range. The goal of the present study was to describe the regional distribution of whale shark feeding aggregations in the NGOM by exploiting a presence-only dataset collected as a part of a volunteer sighting survey. Whale shark aggregations have been documented in large numbers in the NGOM since 2003, and species distribution models provide a unique approach to analyzing these presence data. We used maximum entropy and ecological niche factor analysis, 2 algorithms designed for predicting species distribution based only on presence data, to analyze data for the summer period in 2008 and 2009. Cohen's kappa (kappa) and the 'area under the receiver operating characteristic curve' (AUC) were used to evaluate model performance with an external testing dataset. Kappa values ranged from 0.28 to 0.69, and AUC values ranged from 0.73 to 0.80, indicating that the predicted distribution had a fair to substantial agreement with the testing data. Distance to continental shelf edge, distance to adjacent petroleum platforms, and chlorophyll a were the variables most strongly related to whale shark sightings, likely due to an association of these variables with high food availability. Suitable habitat was predicted along the continental shelf edge, with the most suitable habitat predicted south of the Mississippi River Delta. The spatial distribution of suitable habitat is dynamic; therefore, a multi-year study is underway to better delineate temporal trends in regional whale shark distribution and to identify consistent areas of high suitability. Presenceonly habitat models are a powerful tool for delineating important regional habitat for a vulnerable, highly migratory species.

<b>The seasonal occurrence of the Whale Shark <I>Rhincodon typus</I> (Smith, 1828) (Orectolobiformes: Rhincodontidae) along the Odisha coast, India</b>

“…The southern part of the Odisha coast becomes more productive with periodic phytoplankton and ciliate blooms and these were mainly attributed to local coastal upwelling (Choudhury & Panigrahy 1989;Panigrahy & Gouda 1990;Sasamal et al 2005;Mohanty et al 2007;Sahu et al 2016). Chlorophyll a and phytoplankton concentration have been used successfully to predict the seasonal occurrence of these Whale Sharks in the northern Gulf of Mexico (McKinney et al 2012). During the present study fish eggs were found to be dominant in the plankton sample; however, it cannot be ascertained that the abundance of fish eggs might be the reason for the occurrence of the Whale Shark in the region during February-March.…”

Horizontal Movements, Migration Patterns, and Population Structure of Whale Sharks in the Gulf of Mexico and Northwestern Caribbean Sea

“…The dynamic physical processes associated with shelf edges generate upwellings of nutrient-rich water to the surface [15], that can result in localized increases in planktonic biomass [100]–[102]. A correlation between whale shark distribution and proximity to the shelf edge has been described for the northern GOM [7], [103] and may be related to pulses of productivity associated with these areas.…”

Environmental influence on the seasonal movements of satellite-tracked ocean sunfish Mola mola in the north-east Atlantic

“…Overall, sunfish tracked outside the Mediterranean experienced a SST range from 13 to 23 °C. This thermal envelope was found to be warmer for individuals that entered the Mediterranean (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)Figs. 3,4).…”

“…The aggregation of marine pelagic vertebrates in areas dominated by steep thermal gradients such as tidal and shelf-break fronts, upwelling regions, mesoscale eddies and oceanic fronts has also been documented widely [for review, see 16]. Chlorophyll a was also found to influence the distribution and migration of marine predators such as loggerhead turtles and albacore tuna (Thunnus alalunga) [17] and whale sharks (Rhincodon typus) [18]. Hence, the importance of these oceanographic features is likely due to improved foraging opportunities [19].…”