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(Bassoi, 1997; Bastida et al., 2000 - Danilewicz et al., 2002). For instance, stomach contents
of franciscanas from Rio Grande do Sul, southern Brazil contained discarded fishing gear
such as pieces of nylon net (17% of 36 stomachs), cellophane, and plastic fragments (6%)
(Bassoi, 1997). The rate of debris ingestion by franciscanas varies spatially with higher values
observed in northern Argentina, where cellophane, fishing debris, and plastic were found in
45%, 32% and 16% of the stomachs. Fishing-related debris were more often found in
stomachs of franciscanas collected in estuarial waters while, in contrast, cellophane debris
were more abundant (100% greater) in marine animals (Bastida et al., 2000). The frequency
of marine debris seems lower in animals found to the north of Rio Grande do Sul State,
though no assessment has been made so far (Danilewicz et al., 2002). Regardless if the
ingestion occurs directly or indirectly through the prey, the effects of such debris ingestion on
the health status of individual franciscanas have not been determined, and the population-
level implications are uncertain but should not be ignored.
Chemical pollution:
Coastal oil spills have affected other marine species (
e.g.
penguins
and pinnipeds) but there is no evidence that they also affect franciscanas. On the other hand,
trace elements and organochlorines have been documented in the tissues of franciscanas along
its distribution range. O'Shea et al. (1980) were the first to analyze the concentration of
organochlorine in franciscanas incidentally killed in fisheries off Uruguay. Only a decade
later, the presence of these pollutants in tissues of franciscanas were investigated in Argentina
(
e.g.
Borrell et al., 1995, 1997). More recently levels of organochlorine contamination were
compared between samples of franciscana from southern Brazil and Buenos Aires Province,
with higher concentration found in the latter (Castello et al., 2000). Concentrations of DDTs
and PCBs in the three countries were considered low and not regarded as a threat to the
species. Comparatively, the concentrations of DDTs in Brazil and Argentina were lower than
in Uruguay. A wide range of organochlorine residues have been discovered in the blubber of
franciscanas from the Brazilian coastal waters (Kajiwara et al., 2004). In contrast to the lower
residue levels of CHLs, HCB, HCHs, and heptachlor epoxide, the concentrations of DDT's
and PCB's are surprisingly, the highest compared to those of north Atlantic dolphins, possibly
reflecting high levels of industrialization or poor ecological enforcement in Brazil (Kajiwara
et al., 2004).
With regard to trace elements, Seixas et al. (2008) found that the concentrations of
selenium (Se), total mercury (Hg) and organic mercury (OrgHg) were higher in the livers and
kidneys of franciscanas from Rio Grande do Sul than Rio de Janeiro, Brazil. For both areas
the values were of the same order of magnitude as those reported in earlier studies with the
same species from Brazil (Lailson-Brito et al., 2002; Kunito et al., 2004; Seixas et al., 2007)
and Argentina (Marcovecchio et al., 1994; Gerpe et al., 2002). Franciscana livers showed
higher concentrations of mercury, zinc, and copper relative to concentrations in other organs,
whereas their highest cadmium concentrations were mostly found in kidneys (Marcovecchio
et al., 1990; Gerpe et al., 2002; Lailson-Brito et al., 2002; Kajiwara et al., 2004, Seixas et al.,
2008). Hepatic cadmium concentrations were low in franciscanas from both Rio de Janeiro
and Rio Grande do Sul states (Lailson-Brito et al., 2002; Dornelles et al., 2007
b
). Hepatic
cadmium accumulates in franciscanas through their feeding upon loliginid squids because this
squid family is known to contain relatively low levels of cadmium (Dornelles et al., 2007
a
).
The concentrations of these heavy metals seem to be positively correlated with age (
e.g.
Seixas et al., 2008). For example, mercury is an exogenous and harmful metal (no benefit at
any concentration), which accumulates in the tissues of higher food web organisms (such as
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