The first study ever done of the effects of bottom trawling on mud seafloors off the West Coast of North America suggests alarming environmental changes. The study by Mark Hixon of Oregon State University and Brian Tissot of Washington State University found that trawling not only reduces fish numbers, but also severely alters communities of organisms inhabiting these deep-sea habitats. Their research compared trawled to untrawled areas 600 to 1,200 feet deep off the southern Oregon coast, comprising thousands of square miles. They found nearly 20 percent fewer fish in the trawled areas, and 30 percent fewer fish species. Certain seafloor dwellers, including sea pens and crabs, were six times more abundant in areas that had not been trawled. Furthermore numerous scavenging species in trawled areas largely replaced the marine life common on undisturbed seafloors. This report is the first to examine the effects of a common fishing practice on a vast ocean floor ecosystem off Washington, Oregon, and California -- the mud flats that dominate more than 75 percent of the outer continental shelf.
Imagine bulldozing entire landscapes to collect a few rabbits and gophers. That's what bottom trawlers do in pursuit of sole, lingcod, rockfish and other common seafood staples, by dragging large nets along the seafloor and scooping up everything in their path. It's estimated that trawlers drag nets across every square inch of the bottom of the continental shelves every two years, trawling some regions many times a season.
Regulations, including gear modifications and closed areas, have actually steered trawl fisheries toward the mud seafloors, keeping them out of rock or coral areas, because trawls cause less environmental damage on mud. But the long-term implications of fishing with this technology over such a broad area are a concern, say Hixon and Tissot.
Wonder what's down there? Read about some Alvin dives in the current MoJo article Gone. And you may remember Mark Hixon's fascinating work on BOFFFs (big-old-fat-female-fish) reported in The Fate of The Ocean (Mar/Apr 2006).