Complex sentence: The dolphin-safe movement in the U.S. was led by environmental and consumer groups in response to the use of total encirclement, wherein dolphin pods were surrounded with the tuna they were catching and the dolphins were given no chance to escape before the nets were lifted.
Split into simpler sentences: The dolphin-safe movement in the U.S. was led by environmental and consumer groups in response to the use of total encirclement netting. With this method, fishermen surrounded dolphin pods along with the tuna they were catching and the dolphins were given no chance to escape before the nets were lifted.