A Synthesis of the Ecology, Human-Related Threats and Conservation Perspectives for the Endangered Franciscana Dolphin

Abstract

The franciscana is endemic to subtropical coastal waters of Brazil, Uruguay, and Argentina, and is the only living species of the family Pontoporiidae. It is regarded as the most endangered cetacean in the western South Atlantic. Five management units are recognized (Franciscana Management Areas, FMAs – sensu Secchi et al., 2003a), with abundance estimates ranging from a few hundred to around 15,000 dolphins. Low reproductive potential and short life span make this species highly susceptible to current non-natural removal rates. Bycatch in gillnet fisheries occurs in high levels since the 1960s in Uruguay and 1980s in Brazil and Argentina. Although other threats exist, such as habitat degradation that includes physical (noise) and chemical pollution, depletion of fish stocks and climate change, incidental mortality in gillnets is currently the greatest threat to franciscanas. Fishing-related mortality ranges from approximately 100, in FMA I, to more than 1,000 in FMA III, and exceed from near two (in FMA IV) to more than five times (in FMA III) the maximum allowed sustainable mortality rate, based on potential biological removal (PBR) approach. These numbers indicate that the species is unlikely to cope with the current levels of bycatch and that urgent and extreme reduction on fishing practice and effort are required to avoid collapse of the franciscana and to lower its risk of extinction. Current mortality levels and projected declines resulted in the listing of the franciscana as “Vulnerable” in the IUCN Red List. Recent fisheries regulations were implemented in areas with extensive bycatch in Brazil and were expected to improve the species’ conservation status. There is evidence, however, that this regulation is insufficient to reduce fishing-related mortality to sustainable levels due to either or both lack of compliance and inadequate regulation strategies. Here we provide a comprehensive review on the franciscana ecology and threats and discuss perspectives for its conservation.

Identifying priority areas using a multispecies approach for the conservation of marine megafauna vulnerable species

“…The intense shing effort is the main threat to P. blainvillei (Secchi et al 2003a(Secchi et al , 2021 Several studies have demonstrated that, among various methods used to reduce incidental catches (e.g. modi cation of shing gear, limitation of mesh size/length of nets), MPAs has proven to be effective tools for the conservation of megafauna threatened by incidental catches (e.g.…”

“…The Franciscana is endemic to the coastal waters of Brazil, Uruguay and Argentina and due to incidental catches in gillnet sheries is possibly the cetacean species most impacted in the Western South Atlantic Ocean (Secchi et al 2003a(Secchi et al , 2021, classi ed as Vulnerable -VU by the International Union for Conservation of Nature (IUCN) red list (Zerbini et al 2017). Bycatch have been recorded throughout its distribution range (Secchi et al 1997, Ott et al 2002, however, the coast of Rio Grande do Sul (RS) is where the incidental mortality rate of this species is highest (Ott et al 2002, Secchi et al 2003a.…”

Large groups of Atlantic spotted dolphin (Stenella frontalis) in a coastal bay from southeastern Brazil

“…While studies have been conducted on many aspects of the biology and ecology of this species (Azevedo et al, 2010; Bisi et al, 2013; Bittencourt, Barbosa, Santos‐Neto, et al, 2020; Caballero et al, 2013; Di Beneditto et al, 2001; Di Tullio et al, 2016; do Amaral et al, 2015; Dorneles et al, 2010; Lavandier et al, 2019; Leonel et al, 2012; Lima et al, 2016; Lopes et al, 2012; Méndez‐Fernandez et al, 2018, 2020; Moreno et al, 2005), information about habitat use, abundance, and behavior are scarce in SWAO. In southeastern Brazil cetaceans face several threats, such as chemical and noise pollution, habitat degradation, and bycatch (Bittencourt, Barbosa, Bisi, et al, 2020; Di Beneditto, 2003; Moreno et al, 2005; Oliveira‐Ferreira et al, 2021; Secchi et al, 2021), and Atlantic spotted dolphins are frequent in this region (Bisi et al, 2013; Moreno et al, 2005).…”

Guidelines to merge stranding databases: the case of franciscana (Pontoporia blainvillei) in the extreme South of Brazil

“…The franciscana, Pontoporia blainvillei (Gervais and d'Orbigny, 1844), is considered the most threatened dolphin species in South America (Secchi et al, 2021), and is classified as vulnerable (VU), with decreasing population trend by the International Union for Conservation of Nature (IUCN, 2022). Franciscanas, the only living representative of the Pontoporiidae family, are endemic to the waters of the Southwest Atlantic Ocean (Secchi, 2010), and occurs from the coast of Espírito Santo (ES) (~18º S), in Brazil, to Chubut (~42º S), province of Argentine Patagonia (Bastida et al, 2007).…”

“…Aerial surveys and data on fisheries bycatch indicate that franciscanas are more common in shallow waters, up to the isobaths of 30 or 50 m depending on the region, and may occur less frequently beyond these depths (Danilewicz et al, 2010;Secchi et al, 2021). The franciscana's habitat and diet overlap with the coastal gillnet fishing area in the southern coast of Rio Grande do Sul state (RS), Southern Brazil, and with the commerciallyvalued species such as whitemouth croaker (Micropogonias furnieri) and striped weakfish (Cynoscion guatucupa) (Secchi et al, 1997;Rodríguez et al, 2002;Danilewicz et al, 2009;Haimovici & Cardoso, 2016;Bassoi et al, 2021), respectively.…”