FISHERY ACTIVITY IMPACT ON THE SOTALIA POPULATIONS FROM THE AMAZON MOUTH - Biology, Evolution and Conservation of River Dolphins Within South America and Asia - page 226

Table 2. Number of fishing trips with drift gillnets completed by the artisan fishing fleet
across months and years in the Amazonian Estuary. The data are displayed by strata
(stratum 1 = S1; stratum 2 = S2).

1996 1997 1999 2000 2001

S1 S2 S1 S2 S1 S2 S1 S2 S1 S2

Jan 29 12 21 14 25 12 34 8

Feb 7 6 15 8 20 8 34 10

Mar 11 6 17 18 13 10 23 23

Apr 4 3 20 8 34 25

May 18 5 33 16

Jun 16 8 20 11

Jul 12 14 26 15

Ago 38 30 15 10

Set 18 18

Oct 104 17 44 18

Nov 113 30 33 17

Dec 86 19 57 28

Total 303 66 47 24 57 43 314 176 219 118

Bycatch . The monthly bycatch of S. guianensis in the Amazon estuary had great
variability both within and among years, with consistently greater values in stratum two
compared to stratum one. (Table 3). The total number of S. guianensis in bycatches per month
and strata ranged from 3 to 230. In 2000, stratum two had the maximum number of S.
guianensis caught in one year (1,245 individuals). It is very important to remember that the
final bycatch value should reflect all fishing trips, including those that received no bycatch.
Table 4 shows the mean and the standard deviation of bycatch for each time period and
stratum. There was a significant difference between means of bycatch/fishing excursion (df =
755; t c = -2.41; P = 0.01) and the means of bycatch/fishing trips with bycatch (df = 179 t c =
2.07; P = 0.04) of periods. There was a significant difference between means of
bycatch/fishing trips between strata of the first ( P = 0.05; Zt = 1.96; Zc = -4.68) and second
( P = 0.05; Zt = 1.96; Zc = -12.73) periods.
Bycatch distribution . Bycatch distribution was only described for the first sampling
period. According to fishermen, 703 (66%) of a total of 1,063 dolphins captured in bycatch
were sexed. The average percent of male and females dolphins caught per bycatch were 46.37
and 53.63 respectively. Out of a total of 147 trips with bycatch, 23% only caught females and
12% only caught males. Forty-two percent of the bycatches contained both sexes and in the
remaining bycatches (23%), gender was not determined (Table 5).
In relation to age, the most vulnerable group was the adults (dolphins longer than 1.6 m)
with a total of 753 accidentally caught out of a total of 132 trips. A total of 202 young
specimens (between 1.3 and 1.6 m long) were caught in 52 trips and 49 calves (smaller than
1.3 m long) were caught in 28 trips. It was not possible to determine the size of 59 dolphins
caught in 4 trips because the fishermen did not record the data or the dolphin carcasses were
returned to the water. In 147 trips presenting bycatch, 53% only caught adults; 7% only
young dolphins; 0.7% caught calves; 18% caught both adults and young; 8% had adults and
calves; and 10%, multiple sized (more than 2 sizes) dolphins (Table 5). Calf bycatches were