Scientists should not, according to this instructor while singling out DS and a student studying marine mammals as examples, pick a species that they “like” and then come up with a research question related to it. Author LF had a similar experience in graduate school, as she was also studying elasmobranchs. Both are/were perceived as “shark-huggers,” and felt pressure to defend their study organisms.
August Krogh (pictured), who codified it thus:
For many problems there is an animal in which it can be most conveniently studied.
However, convenience is not, and should not, be the sole arbiter of species that people study. In fact, Krogh himself mentioned this, in the very same article (my emphasis):
I want to say a word for the study of comparative physiology also for its own sake. You will find in the lower animals mechanisms and adaptations of exquisite beauty and the most surprising character(.)
Every person picks what they study for their own reasons. It might be the organism, it might be the question, it might be something else. None of those many reasons reasons is inherently better than any other. To pick on someone for doing science than a different reason you do is pompous.
Additional: Katie Pieper made this useful remark:
But the system must be well suited for the question.
Ferry LA, Shiffman DS. 2014. The value of taxon-focused science: 30 years of elasmobranchs in biological research and outreach. Copeia 2014(4): 743-746. http://dx.doi.org/10.1643/OT-14-044
Krogh A. 1929. The progress of physiology. American Journal of Physiology 90: 243–251. http://ajplegacy.physiology.org/content/90/2/243