Whale Shark (Rhincodon typus) Seasonal Occurrence, Abundance and Demographic Structure in the Mid-Equatorial Atlantic Ocean

Abstract

Whale sharks are generally associated with environmental factors that drive their movements to specific locations where food availability is high. Consequently, foraging is believed to be the main reason for the formation of whale shark aggregations. Feeding aggregations occur mainly in nearshore areas and are composed primarily of immature individuals. Conversely, aggregations of mature adults are rarely observed, and their occurrence is correlated with oceanic environments. Despite an increase in the number of whale shark studies, information on mating and parturition grounds is still lacking. In the present work, we assessed the ecological and behavioural aspects of the whale sharks that visit the archipelago of São Pedro and São Paulo (ASPSP), located ~1,000 km off the coast of Brazil in the equatorial Atlantic Ocean. Forty-nine whale sharks were recorded from February 2005 to May 2014. The estimated mean ± SD size was 8.27 ± 2.52 m (range: 2.5–14.0 m) with no significant differences in size across the year. The maturational stages were classified by size as immature (<8.0 m; 32.56%) and mature (>9.0 m; 46.51%); with almost half of the observed animals being mature specimens. The majority of sightings occurred between February and June. During this period, the ocean current weakens and the waters are enriched by eggs and larvae of fishes and invertebrates that attract marine life to forage. At the same time, evidence of reproductive activity in adult females (i.e. swollen abdomen and bite marks on the pectoral fins), and the potential mating behaviour exhibited by one male, suggest that the ASPSP area might also have a role in whale shark reproduction. Irrespective of its use for feeding or reproduction, this insular habitat serves as a meeting point for both juvenile and adult whale sharks, and may play an important ecological role for the species.

Ensemble modeling of the potential distribution of the whale shark in the Atlantic Ocean

“…Under existing climate projections, this key area, as well as the São Pedro and São Paulo archipelago (Brazil), is also predicted as relevant future sites by our models. These findings provide support to our methods and results, as our data did not include presences in these regions, although their importance is documented in the literature (Macena & Hazin, ). For this reason, the methodology used in the present study could be a useful tool to model other vulnerable marine species.…”

Seasonal aggregation and diel activity by the sicklefin devil ray Mobula tarapacana off a small, equatorial outcrop of the Mid‐Atlantic Ridge

“…Despite M. tarapacana being sighted in the SPSPA virtually year‐round, the conventional and acoustic tagging suggest that the tagged individuals may not remain in the vicinity of the archipelago for a long time (mean = 16.73 days). Tagged M. tarapacana remained in the vicinity of SPSPA for a few weeks only; the same kind of short‐stay behaviour around the SPSPA, with partial purpose of feeding, was also found in the migratory R. typus (Macena & Hazin, ). The low rate of detections by acoustically‐tagged M. tarapacana over several consecutive months cannot be interpreted exclusively as if they had migrated away from the region, given the constraints in tag retention and in the detection range of the receivers.…”

Long-Term Photo-Identification Reveals the Population Dynamics and Strong Site Fidelity of Adult Whale Sharks to the Coastal Waters of Donsol, Philippines

“…Such male bias is consistent with coastal aggregations from across the globe Rowat et al, 2007Rowat et al, , 2009Riley et al, 2010;Ramírez-Macías et al, 2012a,b;Himawan et al, 2015;Rohner et al, 2015b) and with others from within the Philippines (Araujo et al, 2014. Adult-dominated sites remain a rarity, namely at Darwin's Arch in the Galapagos Islands (ECU), Gorda Banks in Baja California (MEX), at an offshore aggregation in Qatar (QAT), and at St Helena Island (GBR) in the South Atlantic, and at a newly identified area in the mid-equatorial Atlantic off Brazil (Ramírez-Macías et al, 2012b;Acuña-Marrero et al, 2014;Clingham et al, 2016;Macena and Hazin, 2016;Robinson et al, 2016). Whale sharks at Donsol are uncharacteristically larger than those found elsewhere in the Philippines (e.g., 5.2 m mean total length in the Bohol Sea, Authors, unpub.…”

“…Few aggregations dominated by adults have been identified to date, namely the Galapagos Islands (Acuña-Marrero et al, 2014), St. Helena Island (Clingham et al, 2016) and the Revillagigedo Islands off Baja California (Ramírez-Macías et al, 2012b), and a large proportion of adults has been reported at an offshore aggregation in Qatar (Robinson et al, 2016) and in the mid-equatorial Atlantic off Brazil (Macena and Hazin, 2016). Some evidence exists that adults spend most of their time in the open ocean (Ramírez-Macías et al, 2017), which might explain why coastal sites tend to be juvenile dominated.…”