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Demografía del tiburón tollo Carcharhinus falciformis (Bibron, 1839) y del tiburón zorro Alopias spp. en aguas de Galápagos, Ecuador.

Year: 2015
Type: dissertation
Abstract: The objective of this study is to provide demographics data for the Thresher Shark (Alopias spp.) and the Silky Shark (Carcharhinus falciformis) based on age analysis estimated through growth marks deposited in the vertebrae of 300 individuals. The sharks were obtained from an illegal fishing boat seized on July 2011 in the Galapagos Islands. The boat “Fer Mary I” contained seven species of sharks, of which 79.95% were Alopias spp. and 11.08% Carcharhinus falciformis. Females were predominant in both species (1M: 2H). We found a relationship within male and female of 1.5M: 1F in silky sharks and 1M: 2F in thresher sharks. To estimate the age, we used four methods: silver nitrate, X -rays, acrylic resin and histopathological plates. The best method to determine the age for Alopias spp. was through X-rays due to the ease of reading. For Carcharhinus falciformis the four methods had similar results. The age groups found in the Alopias spp. Samples were: for females from 5 to 21 years (mode in 6). For males: between 6 to 19 years, mode in 18. For Carcharhinus falciformis: the groups to age for females were from7 to 15 with mode in 10. For males: between 5 to 19 years, mode 5. For Alopias spp. the age ranged from 5 - 21 years with a mode of 6 for females and 6 -19 with a mode of 18 for males. For Carcharhinus falciformis the age ranged from7 - 15 with a mode of 10 for females and 5 - 19 with a mode of 5 for males. In Alopias spp. there were more adults (63%) than young, whereas in Carcharhinus falciformis there was a higher percentage of juveniles (59.26%). No significant difference in size was found between males and females. The relationship between the radius of the vertebrae and body length (LC &LD) in Silky shark (Carcharhinus falciformis) was straight (r2 = 0.78) for LC and (r2=0.70) for LD, indicating that both variables grow proportionally; whereas thresher sharks (Alopias spp.) appear to grow independently considering growth layers in vertebrae and body size: LC:(r2=0.198) LD: (r2=0.26). The relationship between the radius of the vertebrae and body length (LC & LD) in Silky shark (Carcharhinus falciformis) was linear (r2 = 0.78) for LC and (r2=0.70) for LD, indicating that both variables grow proportionally; whereas thresher sharks (Alopias spp.) appear to grow independently considering growth layers in vertebrae and body size: LC: (r2=0.198) LD: (r2=0.26).
Language: Spanish
Open Access status: green
OpenAlex ID: W2204955925
Cites: 42
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Related to: 10