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estimated to be as high as 1,500 to 2,000 animals (Brownell & Ness, 1970; Pilleri, 1971).
Large mesh-size nets targeting sharks were responsible for about 70 to 90% of the captures
(
e.g.
Praderi, 1997; 2000). The depletion of the target shark species led to a drop of 25% in
the fishing effort using these nets from the 1960s and 1970s to the early 1980s. Since the mid
1990s, only 20% of the fishery targets sharks (Praderi, 1997). Changes in the Uruguayan
coastal fishery may be beneficial to the recovery of the franciscana from the intense bycatch
pressure of the past (Praderi, 1997). However, an uncontrolled increase in fishing effort closer
to shore using small mesh-sized nets to catch bony fishes, with an associated high rate of
franscicana bycatch, in adjacent areas of southern Brazil is likely to have offset or nullified
any recovery.
The gillnet coastal fishery in southern Brazil
emerged in the 1940s and increased greatly
during the 1980s. Throughout this time, vessels increased in size and engines became more
powerful, which allowed for longer trips and the use of larger nets (Haimovici et al., 1997).
The first information regarding franciscana bycatch, however, was published only in the
1980s (
e.g.
Pinedo, 1986; Praderi et al., 1989). This information was based on the number of
animals found washed ashore in southern Brazil. Strandings of franciscanas were also
published later for the coast of São Paulo State, southeastern Brazil (
e.g.
Pinedo, 1994; Santos
et al., 2002). It is well known that stranding data greatly underestimate the magnitude of the
bycatch (Secchi et al., 1997) as only a small fraction of the bycatch is washed ashore (Prado
et al., 2007). Incidental mortality of franciscanas based on the monitoring of fishing
operations started in the late 1980s (Lodi & Capistrano, 1990) and have been conducted
systematically in several places along the Brazilian coast. Incidental catches occur mostly in
coastal gillnets set at the bottom for sciaenid fish and at the surface for sharks and other fish
(Ott et al., 2002; Secchi et al., 2003
b
). Estimated annual mortality of franciscanas in coastal
gillnet fisheries off Brazil range from several hundred up to more than one thousand in the
Rio Grande do Sul State coast (Moreno et al., 1997; Secchi et al., 1997; 2004; Kinas & Secchi
1998; Ferreira, 2009); tens to hundreds along the coast of Santa Catarina, Paraná and São
Paulo states altogether (
e.g.
Cremer et al., 1995; Bertozzi & Zerbini 2002; Rosas et al., 2002)
as well as for the Rio de Janeiro and Espirito Santo state coasts together (Di Beneditto &
Ramos, 2001; Di Beneditto, 2003; Freitas-Neto & Barbosa, 2003).
In Argentina, most of the franciscana bycatch occurred in inshore gillnets targeting
croakers (Sciaenidae fish) and sharks (
Galeorhinus galeus
,
Mustelus
spp.,
Eugomphodus
taurus
,
Squatina argentina
) in waters less than 20 m deep (Corcuera et al., 1994, Crespo et
al., 1994). In the mid 1980s, based on information provided by fishermen, annual mortality of
franciscana was estimated to be at least 340-350 animals (Perez-Macri & Crespo, 1989). Data
collected over several years, from the mid 1980s and early 1990s, resulted in estimated annual
mortality of around 230 and 240 franciscanas in the northern and southern Buenos Aires
Province, respectively (Corcuera, 1994; Corcuera et al., 1994, 2000). In the late 1990s, the
estimates of overall mortality of the species in the entire Buenos Aires Province was around
450 to 500 dolphins/year based on interviews (Cappozzo et al., 2000; Corcuera et al., 2000).
Research carried out onboard artisanal fishing boats off Cabo San Antonio, however, has
shown that annual by-catch was much higher than previous estimates obtained from
interviews (Bordino & Albareda, 2005). Since most of the available data on by-catch
estimates (
e.g.
Corcuera, 1994; Corcuera et al., 1994; Cappozzo et al., 2000) were obtained
from interviews, it is likely that the total annual by-catch for Argentina is considerably
underestimated. Gillnet fishing effort has decreased in some important fishing ports due to the
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