Returning otters to undersea world failing in their absence

In this photo taken Monday, March 26, 2018, eel grass is seen in the foreground with sea otters in the distance at the Elkhorn Slough in Moss Landing, Calif. Along 300 miles of California coastline, including Elkhorn Slough, a wildlife-friendly pocket of tidal salt marsh and rich seagrass in the curve of Monterey Bay, southern sea otters under state and federal protection as a threatened species have rebounded from as few as 50 survivors in the 1930s to more than 3,000 today. (AP Photo/Eric Risberg)

In this photo taken Monday, March 26, 2018, a sea otter dives to the bottom of its exhibit at the Monterey Bay Aquarium in Monterey, Calif. California sea otters, once thought wiped out by the fur trade, are booming again in a federally-protected enclave of Northern California coast. But outside that sanctuary, a new study finds, a chain of unintended bad consequences has followed man’s removal of otters as a top predator of the sea, and is preventing the furry creature’s return to its former range from Baja California north. (AP Photo/Eric Risberg)

In this photo taken Monday, March 26, 2018, a sea otter is seen at the Monterey Bay Aquarium in Monterey, Calif. California sea otters, once thought wiped out by the fur trade, are booming again in a federally-protected enclave of Northern California coast. But outside that sanctuary, a new study finds, a chain of unintended bad consequences has followed man’s removal of otters as a top predator of the sea, and is preventing the furry creature’s return to its former range from Baja California north. (AP Photo/Eric Risberg)

In this photo taken Monday, March 26, 2018, a sign warns motorists of sea otters at the Elkhorn Slough in Moss Landing, Calif. Along 300 miles of California coastline, including Elkhorn Slough, a wildlife-friendly pocket of tidal salt marsh and rich seagrass in the curve of Monterey Bay, southern sea otters under state and federal protection as a threatened species have rebounded from as few as 50 survivors in the 1930s to more than 3,000 today. (AP Photo/Eric Risberg)

In this photo taken Monday, March 26, 2018, sea otters are examined during their afternoon feeding at the Monterey Bay Aquarium in Monterey, Calif. California sea otters, once thought wiped out by the fur trade, are booming again in a federally-protected of Northern California coast. But outside that sanctuary, a new study finds, a chain of unintended bad consequences has followed man’s removal of otters as a top predator of the sea, and is preventing the furry creature’s return to its former range from Baja California north. (AP Photo/Eric Risberg)

In this photo taken Monday, March 26, 2018, sea otters are seen together along the Elkhorn Slough in Moss Landing, Calif. Along 300 miles of California coastline, including Elkhorn Slough, a wildlife-friendly pocket of tidal salt marsh and rich seagrass in the curve of Monterey Bay, southern sea otters under state and federal protection as a threatened species have rebounded from as few as 50 survivors in the 1930s to more than 3,000 today. (AP Photo/Eric Risberg)