Bycatch of franciscana dolphins Pontoporia blainvillei and the dynamic of artisanal fisheries in the species' southernmost area of distribution

Abstract

In Argentina, the franciscana dolphin is one of the most vulnerable cetaceans regularly entangled in coastal artisanal fishery nets. The aim of this paper is to estimate the species' incidental mortality on the Southern coast of Buenos Aires province through interviews with the captains of artisanal fishing vessels, in the period 2006-2009. Franciscana bycatch was reported for gillnets and shrimper gear all year round but it occurred more frequently between October and February, at 5 km offshore and 10-20 m depth. The estimated mean annual incidental mortality was 107 dolphins (CI 95% = 87-129), 92 caught in gillnets (CI 95% = 73-112) and 15 in shrimpers' gear (CI 95% = 8-25) with a capture per unit effort of 0.029 dolphins per km of gillnet (CI 95% = 0.023-0.036) and 0.022 per shrimpe r's net (CI 95% = 0.012-0.035). Annual fluctuations were due to differences in the number of gillnetting fishing days. If mortality estimates for the Northern coast are also taken into account, values attain a maximum of 360-539 dolphins bycaught in the entire Buenos Aires province, representing 2.5-3.7% of the species' abundance in Argentina. This will inevitably lead to the decline of franciscana dolphin populations in the near future unless alternative fishing grounds are identified and alternative gearadopted.

Survival Estimates of Bycatch Individuals Discarded From Bivalve Dredges

“…Despite the relatively large number of studies on bycatch and discarding (see reviews by BROADHURST et al, 2007;NEGRI et al, 2012), there is a lack of knowledge regarding the survival of bycatch species after discarding. Accordingly, the main objective of the present study was to quantify the survival of damaged individuals of the most abundant and susceptible bycatch species (Polybius henslowii, Dicologlossa cuneata and Trachinus vipera) after sorting and discarding operations onboard commercial bivalve dredge vessels.…”

“…Accordingly, our ability to assess the status of a stock depends, in part, on our knowledge of the fate of discards. Additional mortality caused by discarding may hamper the sustainable use of marine resources, especially if this is not taken into account in stock assessment (CROWDER; MURAWSKI, 1998;RIJNSDORP et al, 2007) and when long and precise time-series of discard estimates are lacking (AARTS; POOS, 2009 BROADHURST, 2000;BROADHURST et al, 2007;NEGRI et al, 2012). On the other hand, studies of the estimation of discard mortality are scarce (KAISER; SPENCER, 1995;PRANOVI et al 2000).…”

Biological parameters of franciscana dolphins,Pontoporia blainvillei, by-caught in artisanal fisheries off southern Buenos Aires, Argentina

“…Dolphins were accidentally caught in gillnets and shrimper gears all year round at 0.1 -30.0 km offshore and 11-50 m depth. The sample survey took place during an incidental mortality estimation project carried out by the authors (Negri et al, 2012). A description of the fishing area, gear and effort can be found at Negri et al (2012).…”

“…Nowadays, it is estimated that more than 400 dolphins per year are incidentally caught in fishing gillnets in the Buenos Aires province (Bordino & Albareda, 2004;Cappozzo et al, 2007;Negri et al, 2012). Because of high by-catch levels, the species has been classified as 'vulnerable' by the International Union for the Conservation of Nature (IUCN) (Secchi, 2006;Reeves et al, 2012).…”

Patterns of population structure at microsatellite and mitochondrial DNA markers in the franciscana dolphin (Pontoporia blainvillei)

“…Its distribution, restricted within the 30 m isobaths from the coast, is comprised between Itanúas (18°25′ S), Brazil, and Golfo San Matías (41°10′ S), Argentina (Crespo, 2009;Crespo, Pedraza, Grandi, Dans, & Garaffo, 2010;Pinedo, Praderi, & Brownell, 1989;Secchi, Danilewicz, & Ott, 2003). Due to its reduced movement patterns and to anthropogenic impacts, it is the most threatened small cetacean on the southwestern Atlantic Ocean; it is particularly susceptible to high incidental bycatch mortality throughout its distribution (Bordino, Mackay, Werner, Northridge, & Read, 2013;Bordino, Wells, & Stamper, 2008;Bordino et al, 2002;Cappozzo et al, 2007;Crespo, Corcuera, & Lopez Cazorla, 1994;Crespo et al, 2010;Di Beneditto, 2003;Negri, Denuncio, Panebianco, & Cappozzo, 2012;Secchi, 2010;Secchi et al, 1997Secchi et al, , 2003. Based on a projected species abundance decline of more than 30% over three generations (36 years;Taylor, Chivers, Larese, & Perrin, 2007), the franciscana dolphin was classified as "Vulnerable" by the International Union for Conservation of Nature (IUCN) in 2008 (Reeves et al, 2012).…”