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| Author(s): |
Camila Marion
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Instituto Oceanográfico (IO/DIDC) |
| Defense date: | 2015-05-20 |
| Examining board members: |
Lucy Satiko Hashimoto Soares;
June Ferraz Dias;
Otto Bismarck Fazzano Gadig
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| Advisor: | Lucy Satiko Hashimoto Soares |
| Abstract | |
Dasyatis guttata is the most abundant stingray in Todos os Santos Bay (TSB, Northeast of Brazil), with fisheries landings up to 900t per year. It is also one of the most important nekton components of the TSB. Despite such an economic and ecological importance, there is no information about spatiotemporal dynamic, ecology and biology of the species, and information about the importance of this bay for this species. The aim of the present study was to describe the use of this bay by Dasyatis guttata in its life cycle, that is, if this bay is used for reproduction, growth and feeding, and to investigate the relation of the fisherman\'s biological and ecological traditional knowledge on this stingray with those obtained in this study and available in the literature. Landings survey of D. guttata was carried out monthly in two localities of TSB, between January 2012 and January 2013. The total landed weight and the site of the captures in the TBS were registered in each survey. Biometric data, reproductive and digestive organs and about five vertebras centrum were obtained during the landings. Ethnobiological questionaries were applied for describe the environmental and biological perception of the fisherman in relation of TSB and D. guttata. Several temporal and spatial data were taken and used as predictor variables to verify the species distribution and abundance pattern. Results indicated a relationship between the D. guttata abundance and the local capture, tide and season. The females (31 - 105 cm Disc Width, DW) was significantly bigger than males (16.5 - 78 cm DW). Taken both sexes together, one fashion was verified between 43.5 e 52.5 cm DW. There were significant differences in proportion between male and female, being the females more numerous than males. Spatial variation of DW class was verified, with greater proportions of small-sized individuals in Northwest of TSB, suggesting a nursery area there. The females (L50=60.4) reached the first maturity with a size larger than that for males (L50=41.9). Reproduction is continuous throughout the year. Summer and spring are the most important mating and breeding season, as revealed by the higher proportion of gravid females, the biggest embryos, and highest median values of gonadosomatic and hepatossomatic relations. Uterine fecundity was 3.5 embryos/birth and the ovarian fecundity was 2.7 oocyte/birth. Dasyatis guttata is a generalist mesopredator, feeding upon a wide range of prey items, and mostly on the crustaceans Thalassinidea and Alpheidae. The ranking importance of these food items changed significantly with season and ray size. There are negative allometry between the weight and DW, indicating that, in TBS, the species gains proportionally smaller mass with increasing in DW. Females attained sizes larger than males and exhibited lower growth coefficients than those of males (females: DW∞=169.8, k=0.03; males: DW∞=80.3, k=0.07). The fishermen\'s ethnobiological knowledge was consistent with that from literature and obtained here. The information generated in this study contributes to a better understanding of the role of D. guttata in BTS and could be used in ecological and fisheries modeling. They are available for the use in fisheries-related institutions for the development of fishery management plans and conservation of the species in BTS. (AU) | |
| FAPESP's process: | 11/12660-0 - "FUNCTION OF TODOS OS SANTOS BAY IN LIFE CICLE OF RAYS AND SKATES" |
| Grantee: | Camila Marion |
| Support Opportunities: | Scholarships in Brazil - Doctorate |