|Scientific Name:||Pontoporia blainvillei|
|Species Authority:||(Gervais & d'Orbigny, 1844)|
|Infra-specific Taxa Assessed:|
|Taxonomic Notes:||This species was listed in the 1996–2002 IUCN Red Lists under the family Platanistidae. Some authors prefer to place it rather in the family Iniidae.|
|Red List Category & Criteria:||Vulnerable A3d ver 3.1|
|Assessor/s:||Reeves, R., Dalebout, M., Jefferson, T.A., Karkzmarski, L., Laidre, K., O’Corry-Crowe, G., Rojas-Bracho, L., Secchi, E., Slooten, E., Smith, B.D., Wang, J.Y. , Zerbini, A.N. & Zhou, K.|
|Reviewer/s:||Brownell Jr., R.L. & Cooke, J.|
The species qualifies as VU under criterion A3d because a projected decline of more than 30% over three generations (36 years, Taylor et al. 2007) is suspected based on the results of a population simulation analysis (Secchi 2006) using actual and potential levels of fishing-related mortality (with bycatch defined as exploitation for purposes of applying the criteria). The rate of decline is probably underestimated because a period of only 25 years was considered and other sources of non-natural mortality were not incorporated into the analysis. The causes of the inferred population decline have not ceased and are likely increasing because of fishery expansion (causing higher bycatch and also potentially reducing prey base) and lack of mitigation actions.
|Range Description:||Franciscanas inhabit shallow coastal waters (and they sporadically enter the estuary of the La Plata River) of tropical and temperate regions of the western South Atlantic Ocean (Crespo 2002). They are found only along the east coast of South America (Brazil, Uruguay, and Argentina), from the northern Golfo San Matias, central Argentina (ca. 42°10'S), to Espirito Santo, southeastern Brazil (18°25'S) (Siciliano 1994; Crespo et al. 1998). The species is not distributed continuously throughout its range. Surveys (including beach surveys, museum specimens, and interviews with local people) indicate that franciscanas are extremely rare or absent in two areas of the northern parts of their range between Macaé (southern Rio de Janeiro State) and Ubatuba (northern São Paulo State) and in Espírito Santo State (Azevedo et al. 2002; Siciliano et al. 2002; Secchi et al. 2003). The reasons for these gaps are unclear, but because the species prefers shallow, turbid waters (Brownell 1989; Pinedo et al. 1989), water transparency and depth may be among the factors responsible (Siciliano et al. 2002).
The map shows where the species may occur based on oceanography. The species has not been recorded for all the states within the hypothetical range as shown on the map. States for which confirmed records of the species exist are included in the list of native range states.
Native:Argentina (Buenos Aires, Chubut, Rio Negro); Brazil (Espírito Santo, Paraná, Rio de Janeiro, Rio Grande do Sul, Santa Catarina, São Paulo); Uruguay
|FAO Marine Fishing Areas:||
Atlantic – southwest
|Range Map:||Click here to open the map viewer and explore range.|
Morphological and molecular data strongly support the existence of two main subpopulations of Franciscanas. Multivariate analysis of morphometric data revealed two subpopulations: a smaller form in the northern part of the species' range (north of 27°S) (those in the far north are of intermediate size) and a larger form in the coastal waters of southern Brazil, Uruguay and Argentina (south of 27°S) (Pinedo 1991). Analyses of a highly variable region of mitochondrial DNA (mtDNA) also supported these two geographic forms (Secchi et al. 1998). Ott (2002) and Lázaro et al. (2004) compared the mtDNA of Franciscanas from Uruguay and Argentina with those published by Secchi et al. (1998). These studies found support for the existence of a large southern population (composed of animals from Rio Grande do Sul, Uruguay and northern Argentina) that is clearly differentiated from animals in the waters off Rio de Janeiro. In addition, they revealed fixed genetic differences between the populations that suggest essentially no effective genetic exchange (see Secchi et al. 1998, Ott 2002, Lázaro et al. 2004). Ott’s results also clearly showed that individuals inhabiting Paraná and São Paulo waters belong to a genetically distinct subpopulation. This is consistent with morphological data showing that size is not clinal, with animals from Paraná and São Paulo being smaller than those in adjacent populations to the south and north of those States (e.g.. Kasuya and Brownell 1979, Di Beneditto and Ramos 2001, Barreto and Rosas 2006, Barbato et al. 2007) A pairwise analysis of haplotype distances between different geographic locations showed increasing differentiation in the haplotype frequencies with increasing distance, following an isolation-by-distance pattern (Lázaro et al. 2004). Furthermore, recent analysis indicated that haplotype frequencies of samples from Claromecó (in Argentina) were significantly different from those of the rest of the southern population (Ott 2002, Lázaro et al. 2004).
Secchi et al. (2003a) proposed four provisional management units (Franciscana Management Areas, or FMAs) with the following ranges: FMA I - coastal waters of Espírito Santo and Rio de Janeiro states, Brazil (note: confirmation of the hiatus in the Espírito Santo State with increased survey effort will require further division of this FMA); FMA II - São Paulo, Paraná and Santa Catarina states, Brazil; FMA III - coastal waters of Rio Grande do Sul State, southern Brazil and Uruguay; and FMA IV - coastal waters of Argentina, including the provinces of Buenos Aires, Rio Negro and Chubut.
There is no current abundance estimate for the species as a whole, but there is an estimate for the management stock inhabiting FMA III (hereafter referred as the RS/URU management unit). During aerial surveys of coastal waters of Rio Grande do Sul State in 1996 (Secchi et al. 2001), this stock’s abundance was estimated at 42,078 (95% CI 33,047–53,542). This extrapolated result must be used very cautiously, however, because it is based on a density estimate for only a small fraction of the coastline, representing approximately 0.7% of the possible range of the subpopulation (ca. 64,045 sq. km), and there is limited information on the distribution pattern of Franciscanas within their total range. This and other estimates of Franciscana density and abundance need to be interpreted cautiously as they could be either positively or negatively biased. The IWC Scientific Committee concluded, after reviewing the methods and limitations of Franciscana surveys through 2003–2004, that it was not appropriate to consider them as providing minimum estimates of abundance (IWC 2005a).
While the overall abundance of the species would seem relatively high, in most areas the gillnet mortality alone is not thought to be sustainable. Secchi (2006) projected the four management units 25 years into the future based on a stage-structured matrix model using a variety of scenarios of fishing effort. Because there were estimates of Franciscana density and abundance only for FMA III and IV (Secchi et al. 2001, Crespo et al. 2004), Secchi (2006) used the density estimated for FMA III and applied a correction factor based on the ratio of capture per unit of effort (CPUE) between the other areas and FMA III. This was assumed to represent a valid index of abundance because the unit of fishing effort is the same and the fishing gears are similar among management units. The corrected densities were multiplied by the entire area of both FMA I and II to obtain the estimate of total abundance. Uncertainty in the parameter estimates was incorporated through appropriate probability distributions. The scenarios considered most realistic (i.e. those that aimed to compensate for underestimation of the bycatch and that modelled environmental stochasticity) resulted in relatively high probabilities that each management unit would decline by at least 30% below its initial size with the exception of FMA I. However, it should be noted that estimates of bycatch in FMA I come from only one fishing village and it is known that bycatch occurs in other parts of this FMA (e.g. Freitas-Neto and Barbosa 2003).
The modelling exercise described above is considered to underestimate the risk of decline of Franciscanas. The most recent data on bycatch (e.g. Rosas et al. 2002, Bordino and Albareda 2005, A. Zerbini as summarized in IWC 2005b) indicate that the numbers caught annually in FMAs II and IV are roughly twice as high as the values used by Secchi (2006) in his projections. In addition, other sources of potential threat (risk factors, as described in the Threats section below) were not considered in Secchi’s study.
|Habitat and Ecology:||
Although sometimes described as a ‘river dolphin’, the Franciscana is not a freshwater species. Franciscanas apparently do not migrate, although seasonal inshore/offshore movements have been documented in some areas (Bordino et al. 1999, Bordino 2002). Predation by both large sharks and killer whales has been documented (Praderi 1985, Ott and Danilewicz 1996, Santos and Netto 2005).
Franciscanas are generally found in turbid waters < 30 m deep (Pinedo et al. 1989, Secchi and Ott 2000). Although they are found mainly in marine waters and only occasionally in estuaries, they are relatively common in the Uruguayan part of the La Plata River estuary (Praderi 1986). Franciscanas are primarily coastal, ranging no farther offshore than the 30 m isobath. Some sightings have been made in waters seaward of the 50 m isobath and 55 km offshore, but the density offshore is very low.
Franciscanas feed on several species of shallow-water fish (e.g., sciaenids, engraulids, gadids, and carangids), cephalopods, and crustaceans (Brownell 1989, Di Beneditto and Ramos 2001, Rodriguez et al. 2002, Danilewicz et al. 2002).
The main problem facing the species is incidental mortality in gillnet fisheries (there is no indication of direct exploitation of Franciscanas), which has been observed since at least the early 1940s (Van Erp 1969). In the 1960s, the bycatch in Uruguay alone was as high as 1,500–2,000 animals (Brownell and Ness 1969, Pilleri 1971). Current estimates total at least 2,900 animals per year in all four management stocks, combined (e.g., Ott et al. 2002, Secchi et al. 2003b), but the numbers used to get that total are thought to be underestimated to an unknown extent, primarily due to: (1) captures in other non-monitored types of fisheries (e.g., active gillneting, Secchi et al. 1997; shrimp trawling, Cappozzo et al. 2000); (2) under-reporting of bycatch by fishermen; and (3) dolphins captured sometimes falling from the net before or during haul-out (Secchi et al. 2003b). Bycatch is higher in FMA III with estimates being above 1,300 animals incidentally caught annually (Ott et al. 2002; Secchi et al. 2003b, 2004), followed by FMA IV: approximately 800 individuals (Bordino and Albareda 2005), FMA II: > 700 dolphins (Rosas et al. 2002, IWC 2004), and FMA I: > 110 Franciscanas (Di Beneditto 2003).
Stomach contents of Franciscanas from Rio Grande do Sul have included many kinds of debris: discarded fishing gear such as pieces of nylon net (17% of 36 stomachs), cellophane, and plastic fragments (6%) (Bassoi 1997). This problem has also been reported in northern Argentina, where cellophane, fishing debris, and plastic were found in 45%, 32% and 16% of the stomachs (Bastida et al. 2000; Danilewicz et al. 2002). The effects of such debris ingestion on health status of individual Franciscanas have not been determined, and the subpopulation-level implications are uncertain. However, debris could have a negative effect in at least some areas.
Other potential threats include various forms of habitat degradation (e.g. overfishing; destruction of benthic community and bycatch of small sciaenid fish – main Franciscana prey – by trawling) (e.g. Bassoi and Secchi 2000, Danilewicz et al. 2002, Rodríguez et al. 2002).
|Conservation Actions:||The species is listed in Appendix II of CITES. Measures are needed to reduce the level of bycatch of this species, and research is needed to monitor bycatch levels more accurately.|
|Citation:||Reeves, R., Dalebout, M., Jefferson, T.A., Karkzmarski, L., Laidre, K., O’Corry-Crowe, G., Rojas-Bracho, L., Secchi, E., Slooten, E., Smith, B.D., Wang, J.Y. , Zerbini, A.N. & Zhou, K. 2012. Pontoporia blainvillei. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 08 March 2014.|
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