Interação com a pesca: implicações na conservação da toninha, Pontoporia blainvillei (Cetacea, Pontoporiidae) no litoral do estado de São Paulo, SP / Fisheries interactions: implications on the conservation of franciscana, Pontoporia blainvillei (Cetacea, Pontoporiidae) in the coastal area of São Paulo state

Carolina Pacheco Bertozzi

The scope of this study is to investigate the interactions of gillnet fishing and the accidental captures of the Pontoporia blainvillei, as well as the implications of this activity in species conservation. Therefore, fishing activities are described and analyzed, accidental captures are evaluated, mortality is estimated and some aspects of population structure are studied, such as growth and age estimates, besides criteria estimates of reproduction variables in franciscana dolphin accidentally caught on the coast of the State of São Paulo. Continuous monitoring of the fishing boats in Praia Grande County, from July 1999 to December 2008 allowed both the chronological evaluation of accidental catching and capture per unit effort. Five different types of gillnets and one of trawl net for shallow areas were used by the fishing boats in Praia Grande, of which four types of gillnets registered catching. A total number of 91 franciscana dolphins were accidentally captured and the values of catch per unit effort (CPUE) indicate that "boeira" surface nets and "bottom thick" demersal nets are responsible for the highest capture numbers during autumn and winter time. The use of drift nets was observed along the coast of the São Paulo State where a total of 1,192 boats have used such nets. Through the systematic monitoring of four fishing communities, the total fishing effort concerning drift nets, in the State of São Paulo, was 4,684,981 km per fishing day. This value was then multiplied by the catch per unit of average fishing (0.00008 Franciscana dolphins/km x fishing day), which resulted in an estimate mortality of 372 dolphins between June 2004 and April 2005. Estimated age of captured animals varied from 0 to 14 years, 80.0% ranged between 0 and 3 years. Age distribution among female dolphins was from 0 to 7 years, while among male dolphins it was from 0 to 14 years. The maximum asymptotic lenght, estimated according to the von Bertalanffy model and adjusted to the length and age data, was of 117.5 cm for males and 135.6 cm for females. The estimated growth rate for males (0.859) was higher than for females (0.779). No significant difference regarding length, weight, and width between the gonads of the same animal was noticed, confirming the symmetry hypothesis. The average values of the gonads macroscopic measures, as well as both the Testicular (TIM) and Ovarian (OIM) Index of Maturity were significantly different among mature, pubescent and immature individuals. There was a clear increase in value for mature individuals, which demonstrates the gonads size and weight increase as they reach maturity. Microscopic analysis of 45 testicles showed that 33.3% of males were immature, 15.6% pubescent, and 51.1% mature. Microscopic analysis of 42 female ovaries showed that 54.8% of females were immature, 4.8% pubescent, and 40.5% mature. Nine out of the total mature females captured were pregnant and presented a pregnancy corpus luteum of greater size. The maximum corpus albicans and corpus luteum numbers observed in mature female ovaries was three - 61.9% occurring in the left ovary. Both average length and average sexual maturity age for male individuals were estimated between 103.6 107.83 cm and 1.31 1.48 years, respectively. For female individuals these numbers were 119 cm and 1.2 1.83 years, depending on the method used. The estimated pregnancy period was 10.22 months; the annual pregnancy rate was 0.56; the birth length was 72.05 cm; the fetal growth rate was 0.27 cm/day, and the reproduction interval was 1.77 year. The results obtained in the State of São Paulo indicate that drift nets affect mainly immature individuals of both sexes, from 0 to 2 years old. However, a significant percentage of mature adults have also been captured. Besides, no latitude pattern in the variables studied was confirmed.

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