The pilot whale, harbor porpoise, and bottlenosed dolphin are all pelagic animals, which forage at a variety of depths.
The arrival of pelagic—mid-water—trawlers also coincides with the washing up of huge numbers of dead dolphins, porpoises and whales.
In 2002 and 2003, over 300 dolphins and porpoises were washed ashore and their carcasses could be seen on beaches.
I believe that it has been argued that harbour porpoises do not have a sufficiently identifiable breeding area.
Little research has been done internationally on the smaller cetaceans such as dolphins and porpoises.
I am aware of the concern that monofilament fishing nets may accidentally ensnare dolphins and porpoises.
Pair trawling for bass, in which two boats tow huge nets, causes hundreds of cetacean deaths: dolphins, porpoises and small whales.
In mediaeval language dolphins and porpoises were not distinguished, any more than whales were distinguished from fish.
