Causes and contrasts in current and past distribution of the white shark (Lamniformes: Carcharodon carcharias) off southeastern South America

Abstract

Abstract:The great white shark is a cosmopolitan temperate marine species which is rare in Argentina, Uruguay, and Brazil today. Several publications include the white shark as inhabiting Patagonian waters. However, there is no recent or fossil record of the white shark south of S 38° 30´ in the southwestern Atlantic. A tooth found in Quaternary sediments at Pehuencó (S 38° 56´), southern Buenos Aires province, is the southernmost occurrence of the species in the southwestern Atlantic. The occurrence of C. carcharias in the Buenos Aires province is another confirmation that the Argentine biogeographic province extends to the south of the Río de la Plata. The present extremely scarce record indicates that there are not permanent living populations in the South American Atlantic coast but occasional transient individuals. However, the abundant fossil and archaeological record suggests that it was much more common in southwestern Atlantic during the late Pleistocene and Holocene than today. This drop in abundance is here mostly attributed to the massive extermination of pinnipeds and cetaceans during the XIX th and XX th centuries. Patagonian waters, where marine mammals are relatively abundant even today, might be too cold for the species which is mostly encountered between 15-23°C. Besides, another important predator, the killer whale, which also feeds on marine mammals, is frequently found in these waters. Consequently, available evidence suggests that unrestricted hunting of pinnipeds and cetaceans also decimated another animal, a fish. Keywords:Carcharodon carcharias, white shark, Argentina, Atlantic, pinniped, cetacean, biogeography. Resumen: Causas y contrastes en la distribución presente y pasada del tiburón blanco (Lamniformes:Carcharodon carcharias) costa afuera de Sud América sudoriental. El tiburón blanco es una especie cosmopolita en mares templados y que es rara actualmente en Argentina, Uruguay y Brasil. Varias publicaciones incluyen a tiburón blanco como habitando aguas patagónicas. Sin embargo, no hay registro actual o fósil al sur de S 38° 30´ en el Atlántico sudoccidental. Un diente hallado en sedimentos cuaternarios en Pehuencó (S 38°5 6'), sur de la provincia de Buenos Aires es el registro más austral en el Atlántico sudoccidental. El registro actual de C. carcharias en la provincia de Buenos Aires es otra confirmación de que la provincia biogeográfica Argentina se extiende al sur del Río de la Plata. El extremadamente escaso registro actual indica que no hay poblaciones permanentes en la costa atlántica sudamericana sino individuos aislados. Sin embargo, el abundante registro fósil y arqueológico sugiere que fue mucho más común durante el Pleistoceno tardío y el Holoceno. La disminución de la abundancia es aquí principalmente atribuida al exterminio masivo de pinípedos y cetáceos en los siglos XIX th y XX. th Las aguas patagónicas, donde todavía hay abundancia de mamíferos marinos podrían ser demasiado frías para la especie, que es más frecuente entre 15° y 23 °C. Por otra parte, la orca, que ...

A tale that never loses in the telling: Considerations for the shifting ethnobaseline based on artisanal fisher records from the southwestern Atlantic

“…This study allowed for the retrieval and addition of two more records of the presence of the white shark Carcharodon carcharias in Brazilian waters (Figure 4), previously reported as rarely occurring on the Atlantic coast of South America (Gadig and Rosa 1996;Cione and Barla 2008;Amorim et al 2018), but confirmed by the fisher survey concerning records, containing both information and photographic evidence. The oldest account, concerning the capture of a C. carcharias in 1968, was reported by a 76-year-old fisher who reported a size of 11 m and 6 ton.…”

“…The white shark C. carcharias is an emblematic species in the popular imagination, rare in Brazilian waters and with only a few dozen occurrences recorded along the coast, with Rio de Janeiro being the northernmost area of South American occurrences (Gadig and Rosa 1996;Cione and Barla 2008). The oldest record reported by fishers was from 1968, with the specimen being called an anequim-boto, followed by another more recent incident, in 2010.…”

First occurrence of the giant shark Carcharocles megalodon (Agassiz, 1843) (Lamniformes; Otodontidae) at Buenos Aires Province, Argentina

“…These specimens are found mixed on the same beaches with other marine vertebrates coming from more recent Holocene beds (e.g. Cione, 1983;Cione & Barla, 2008). However, the age of the specimens described here is uncertain because the geology of the marine platform is rather complex and includes a succession of diverse stratigraphic units.…”

“…Possibly some of the above-mentioned stratigraphical units, such as DS5 or DS4, may be correlated to the sandy beds informally known as the "Puelchense" (see Parker et al, 2008). The "Puelchense" beds are partially correlated with Miocene-Pliocene beds close to Paraná city based on its fossil record (see discussion in Cione & Barla, 2008) and belong to a subterranean aquifer that extends along a large portion of the subsoil of Buenos Aires Province, up to the Mar de Ajó locality (see also Auge et al, 2002). The "Puelchense" beds yielded several fossils studied by Carlos Rusconi in the 1930s during the extraction of sand destined for construction (Rusconi, 1933;1934;Cione & Barla, 1999;Chimento, 2012).…”

Future Research Directions on the “Elusive” White Shark

“…New molecular tools such as environmental DNA (eDNA) sequencing, which uses filtered water samples to noninvasively identify species from trace DNA, can contribute toward understanding movement patterns of large migratory marine fauna such as sharks and cetaceans at species and community level (Larson et al, 2017;Bakker et al, 2017;Baker et al, 2018), and pinpointing habitat use by endangered sawfishes (Simpfendorfer et al, 2016). For instance, although white sharks appear to be exceptionally rare in South American waters, archeological and historical evidence suggest resident populations may have been extirpated by intense fishing (Cione and Barla, 2008;Amorim et al, 2017). Fisher interviews, aerial surveys, and eDNA surveys around pinniped colonies could be used to determine if white sharks persist in areas in South America where they were previously documented as well as other areas.…”