Some improvements to your text:
Dear Dr. Burkholder,
My name is Paula Suleiman and I completed the undergraduate course in Biological Sciences at Universidade Federal de Viçosa in 2011. In 2013, I obtained the master’s degree in Ecology and Natural Resources at the same institution.
I have been researching the feeding habits of Trichiurus lepturus in Rio de Janeiro, Brazil, since 2011. Now *I intend to further develop my knowledge during my PhD degree study with the isotopic composition of this species and its food items, in association with local ecological knowledge of the local fishermen, for a better **understanding of the alimentary and ecological patterns of the species. My interest is based on the lack of the information about this subject in the Rio de Janeiro state.
In my master's degree research, I will utilize the muscle of Trichiurus lepturus and its feeding items from Rio de Janeiro for the isotopic analyses and I will compare the assimilation of each item with the results obtained for stomach contents analysis.
For the information of local ecological knowledge I will use the methods of social research: interview with questionnaire, diary of camp, maps, figures, and observation of the participants.
I have been following your research, and I know that you are a specialist in isotopic composition of marine organisms. I am aware that you have been working in this area with isotopic composition with sea turtles in Australia, for this reason, I would like to have the opportunity of doing an internship in your laboratory for a period.
Certainly, this opportunity will be of great importance for my research, besides that I believe that it can be foundation for the start for future collaboration because your experience and recognition in this area, without a doubt, will be very appreciated.
I look forward to hearing from you.
*"Develop" in this context implies something else.
**Is this what you mean: "for a better understanding of the alimentary and ecological patterns of the species"?
(If I 'm not mistaken, you've posted this same text in this forum some time ago).