Seamounts In Hawaii Decimated By Trawling Showing Signs Of Recovery Thanks To Federal Protections

Deep-sea corals and sponges provide habitat and refuge for many other animals living on or near the seafloor, like tiny anemones, brittlestars (pink), crinoids or “sea lilies” (yellow), and a basket star (brown). Papahānaumokuākea National Marine Monument/Flickr

Following decades of federal protection, once nearly depleted seamounts found in the waters of Hawaii are showing signs of recovery, according to a study published in Science Advances.

Papahānaumokuākea National Marine Monument is one of the most biologically diverse oceanic ecosystems in the world, home to many flora and fauna unique to the Hawaiian Island chain. As industrial fisheries expanded across the world during the 1960s and 1980s, the underwater mountain chain was devastated by overfishing and trawling so dramatically that images taken more than 30 years later still show vast stretches of barren seafloor scarred by fishing practices.

However, “This is a good story of how long-term protection allows for recovery of vulnerable species,” study author Amy Baco-Taylor said in a statement.

Previous trawling in these slow-growing deep-sea sponge and coral environments led scientists to believe that there was “not much hope” for the seamounts’ recovery. The practice involves dragging heavy nets along the seabed in order to capture fish, wreaking havoc on other animals who thrive along the seabed.

But there’s hope. Researchers studying the ocean depths of the Hawaiian-Emperor Seamount Chain say they are “surprised” by some of the species beginning to make a comeback in recent years.

“Contrary to expectations, these results show that, with long-term protection, some recovery of seamount deep-sea coral communities may be possible on 30- to 40-year time scales,” wrote the authors in their study, adding that allowing bottom-contact fishing in these areas could cause future harm to fragile ecosystems that likely rely on remnant populations for recovery.

A commensal brittle star on a deep-sea pink coral photographed at Salmon Bank in the Northwestern Hawaiian Islands. Papahānaumokuākea National Marine Monument/Flickr

Seven seamounts – underwater mountains that don't reach the surface – were surveyed over four research cruises in 2014 and 2015. Researches used a combination of autonomous underwater vehicles and human-occupied submersibles to explore sites along the chain and photograph the seamounts between 300 and 700 meters (984 to 2,300 feet) below the surface. In all, more than half a million images were captured, many of which showed trawling scars along the seafloor with baby coral growing within them, as well as coral growing from broken fragments that were entangled in fishing nets and left on the seafloor, indicating that the growth happened after fishing had been banned in the area almost 50 years ago when the US claimed the region as part of its Exclusive Economic Zone, halting foreign fishing fleets from trawling in the area. Then-president George W. Bush included the seamounts in a national monument in 2006, protecting it from further human disturbance.

“People started realizing how vulnerable seamounts were relatively recently, so seamounts in other locations have only been protected for 5 to 15 years,” Baco-Taylor said. “Establishment of the US EEZ in this region has provided protection for these sites for close to 40 years, providing a unique opportunity to look at recovery on longer time scales.”

Scientists also found pristine areas that had not been touched by fishing, leading them to believe that these intact ecosystems likely play a role in the rehabilitation of devastated ones. However, an expected lack of resilience in vulnerable marine ecosystems presents a challenge for understanding the ecology of these regions and setting standards for fisheries management. The authors note that conservation efforts need to incorporate a better understanding of how these systems might recover over long periods of time and how external forces might influence them.

The deep-sea gorgonian coral Iridogorgia magnispiralis. Individuals of this species can attain sizes approaching 6 m, thereby making them the largest deep-sea coral known to date. Papahānaumokuākea National Marine Monument/Flickr

  

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