Biology Reference
In-Depth Information
Detailed information regarding each fishing trip was recorded such as the total number of
days per trip, number of fishing days, number of castings, and fishing sites. Total captures per
species, abundance of each species, gender, and size of dolphins captured were also recorded.
The authors interviewed the fishing crew at the ports of Vigia and Bragança after they
returned from their fishing excursions. Here, at port, they recorded the number, gender, and
age group of dolphins caught (released alive or dead at sea) as well as dolphin carcasses
aboard the vessels. Captured dolphins (carcasses) were categorized into three age groups.
Those equal to or greater than 1.6 m in total length were considered adults. Dolphins with
lengths of 1.3 m to 1.6 m were recorded as young, while those less than 1.3 m were calves.
Since the data on dolphin bycatches were obtained from fishermen, it is normal to find a
large variance among them. That is the sort of bias and risk one takes by working with
fishermen and information collected from them. As a measure to reduce this bias, fishermen
were asked multiple forms of the same question and only those answers that were consistently
given were analyzed and included in this chapter.
A descriptive bycatch data analysis was completed that described the
S. guianensis
bycatch frequency subdivided by gender, age group, monthly census, and fishing fleet
stratum. Significant differences in the total number of dead dolphins (in each period) between
strata, were detected via a
Z
test for two averages. And, significant differences of the data
between two periods were detected through the use of a
t-
test. The significance differences in
the total number of dead dolphins between strata, per gender and age group were established
through an analysis of variance (ANOVA Type Two). A simple linear regression analysis was
carried out to determine the relationship between dolphin bycatch and fishing effort.
R
ESULTS
Fishing fleet activity area
.
Artisan fishing boats that relied on drifting gillnets to collect
fish in the Amazonian estuary sailed approximately between coordinates 4
o
N; 1
o
S and 47
o
;
51
o
W (Fig. 1). This is an area that encompasses 90,000 square kilometers.
Net types used and targeted fish species
. Thread gauge and mesh size varied according
to depth, time of year (season) and fish species (Table 1). When targeted fish species resided
in deeper depths, driftnets were designed for sinking and lowered to deeper waters
.
When the
sea water flowed into the estuary during the summers, the most commonly captured fish
species were: gillbacker sea catfish (
Arius parkeri),
weakfish (
Cynoscion acoupa
), crucifix
sea catfish (
Arius proops
) and fat snook (
Centropomus parallelus
). However, during the
winters an influx of freshwater from the Amazon river pushed against the sea water and the
targeted species changed to piramutaba (
Brachyplatystoma vaillantii
) and dourada
(
Brachyplatystoma flavicans
).
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