Jensen is a fisheries scientist and aquatic (marine and freshwater) ecologist. His research focuses on evaluating the ecological and management factors that make fisheries sustainable through global comparisons of fisheries; the effects of climate change on lake and river ice; ecology of Mongolian lakes and rivers; ecology and fishery management of tuna and marlin; and understanding how fishing and environmental changes impact fish populations. 

Jensen was a postodoctoral researcher at the U. of Washington and completed his Ph.D. at U. of Wisconsin. He grew up along the Delaware River in upstate New York.