So not only do salmon shark have to keep swimming so as to avoid sinking, they need to do so to avoid freezing as well.[1] Apparently doing so (swimming) helps it maintain its temperature. Very cool.
- The National Science Foundation. "How Hot Tuna (and Some Sharks) Stay Warm" Press Release 05-187, 2005-10-27. http://www.nsf.gov/news/news_summ.jsp?cntn_id=104543&org=NSF&from=news