Visit WPSU's Marine Fisheries & Aquaculture Series [1] and read about the problems with overfishing. This PBS documentary is a must see. You may be able to get it from your local library. If not you could buy it (it's a great thing to show to your classes). I've also collected a few youtube links with interesting shorts on related topics.
Click on the links below. I have provided some guidance about what to focus on, but these are excellent resources, so you are encouraged to read beyond my suggestions.
See the grading rubric [8] for specifics on how this assignment will be graded.
Links
[1] http://www.pbs.org/emptyoceans/
[2] https://www.e-education.psu.edu/earth540/sites/www.e-education.psu.edu.earth540/files/2006-11-13_Oceans_of_NothingTime_and_Science.pdf
[3] https://www.e-education.psu.edu/earth540/sites/www.e-education.psu.edu.earth540/files/Boris_Worm_MAR19_2007.pdf
[4] https://www.youtube.com/watch?v=b-Zhlprs_Ew
[5] https://www.youtube.com/watch?v=a2Ubw6bgMKA
[6] http://www.pewenvironment.org/our-focus/ocean-1080/fisheries-1082
[7] https://www.greenpeace.org/usa/oceans/issues/overfishing-destructive-fishing/
[8] https://www.e-education.psu.edu/earth540/grading_rubric_problemsets