It appears that the slow moving cow shark may have been accidentally cut in the throat area while the angler was attempting to cut the dogfish free. It appears to be a minor injury and we do see the cow shark slowly turn and begin swimming off when the video ends.
Here's a brief description of the Cow shark from sharksavers.org (click link for additional information):
Cow sharks are little known because they spend most of their lives in deep, cold oceans beyond the reach of divers. However, there are times during the year when some species spend time in shallow waters to feed and give birth. Cow sharks are unusual in that they have six, and in some species, seven pairs of gills. They have wide heads, small eyes, and a heavily-built body.Photo is a video screenshot
Video posted by Walter W and is one minute in length.