Biology Reference
In-Depth Information
By applying the hierarchical classification scheme (Dizon et al., 1992) for defining stocks
for management purposes, Secchi et al., (2003
a
) comprehensively reviewed the genotypic,
phenotypic, population response and distributional data and proposed that the franciscana
distribution range be divided into four areas. The range limits for each area were defined as
provisional Franciscana Management Areas (FMA)(Figure 2), as follows: FMA I - coastal
waters of Espírito Santo and Rio de Janeiro states (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; FMA III - coastal waters of Rio
Grande do Sul State and Uruguay; and FMA IV - coastal waters of Argentina, including the
provinces of Buenos Aires, Rio Negro, and Chubut. It is not meant to apply new management
dogmas to these stocks, rather, it is strongly recommended that limits and sub-structuring of
these FMAs be constantly reassessed as new data become available.
Combining all information on bycatch from fleet monitoring programs and interviews
along the species' range resulted in an annual bycatch estimate of about 110 (min: 44;
max:176) franciscanas for FMA I; 279 (min: 63; max: 497) for FMA II; 1,245 (min: 562;
max: 1,778) for FMA III and; 405 (min: 241; max: 567) for FMA IV (Ott et al., 2002; Secchi
et al., 2003
b
; Di Beneditto, 2003). These results might represent an underestimate of the
actual bycatch for several reasons. For example, there are captures in other non-monitored
types of fisheries such as gillnetting (Secchi et al., 1997) and shrimp trawling (Cappozzo et
al., 2000) and fishermen generally tend to under report bycatch (Lien et al., 1994, Hall, 1999).
Also, bycaught dolphins may fall from the net before or during the hauling-in process
(Bravington & Bisack, 1996) and some small fishing villages may not have been monitored,
especially in the central and northern portions of the species' range (
e.g.
Bertozzi & Zerbini,
2002). Nevertheless, these values together with information on population dynamics can be
useful as baselines for modeling the potential effects of fishing bycatch on the viability of the
species on a local basis.
Bearing in mind the uncertainty on abundance and the between area variation in the
quality data on bycatch rates and population dynamics (see Secchi's chapter), Secchi (2006)
projected the four management units 25 years into the future based on a stage-structured
matrix model (
e.g.
Caswell, 2001) using a variety of scenarios of fishing effort. Because there
were estimates of franciscana density and abundance only for FMA III and IV, 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 modeled 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 & Barbosa, 2003). The modeling exercise described above is
considered to underestimate the risk of franciscana decline. The most recent data on bycatch
(
e.g.
Rosas et al., 2002; Bordino & Albareda, 2005; Secchi et al., 2004; IWC, 2005) indicate
that the numbers caught annually in FMAs II and IV are roughly twice as high as the values
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