Seamounts In Hawaii Decimated By Trawling Showing Signs Of Recovery Thanks To Federal Protections
After years of federally mandated protection, scientists see signs that this once ecologically fertile area known as the Hawaiian-Emperor Seamount Chain is making a comeback.
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.
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.
Depleted seamounts near Hawaii recovering after decades of federal protection
Florida State University
For decades, overfishing and trawling devastated parts of an underwater mountain range in the Pacific Ocean near Hawaii, wrecking deep-sea corals and destroying much of their ecological community.
But now, after years of federally mandated protection, scientists see signs that this once ecologically fertile area known as the Hawaiian-Emperor Seamount Chain is making a comeback.
Because of the slow growing nature of the corals and sponges that live on seamounts, "It's been hypothesized that these areas, if they've been trawled, that there's not much hope for them," said Florida State University Associate Professor of Oceanography Amy Baco-Taylor.
"So, we explored these sites fully expecting to not find any sign of recovery," she said. "But we were surprised to find evidence that some species are starting to come back to these areas."
Baco-Taylor and a team from Florida State and Texas A&M University published their findings today in the journal Science Advances. The overall understanding that a trawled seamount could recover is a game changer in terms of fishing management. Scientists and policymakers regularly debate whether protected areas could be reopened for fishing.
"This is a good story of how long-term protection allows for recovery of vulnerable species," Baco-Taylor said.
The Hawaiian-Emperor Seamount Chain is a mostly underwater mountain range in the Pacific Ocean. From the 1960s through the 1980s, the area was a hotbed for fishing and a practice called trawling, where fishermen use heavy nets dragged along the seafloor to capture fish. In the process, the nets scrape other animals off the seafloor as well.
The practice of trawling has devastated seamounts around the world and scientists have generally believed that an ecological recovery was unlikely. However, in the case of the Hawaiian-Emperor Seamount Chain, there is a glimmer of hope.
Baco-Taylor, her doctoral student Nicole Morgan and Texas A&M Associate Professor Brendan Roark led four research cruises out to the central and north Pacific Ocean to investigate the ecological communities of the region.
They specifically wanted to examine whether there was any recovery of life on the seamount chain because unlike other submerged mountain chains around the world, this one had been federally protected from fishing and trawling for decades.
In 1977, the United States claimed the region as a part of the U.S. Exclusive Economic Zone, which prevented foreign fleets from trawling the area. In 2006, then President George W. Bush included the area as part of the Papahānaumokuākea Marine National Monument, further protecting it from 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 U.S. 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."
Through the four research visits, scientists sent an autonomous underwater vehicle and used a human-occupied submersible to explore sites along the chain and to photograph the seamounts roughly 300 to 700 meters below the surface.
The team analyzed 536,000 images. In them, they could not only see the remnant trawl scars on the seafloor, they also saw baby coral springing up in those areas. They could also see coral regrowing from fragments on fishing nets that were left on the seafloor.
"We know the stuff growing on the net had to come after this practice stopped in the area," Morgan said.
Most importantly, they found evidence of a few precious areas that were not harmed by the trawling. These untouched areas are crucial to further populating the seamounts with a variety of fauna, researchers said.
It's too early to say how long it took for the new coral to arrive and whether the area will return to its former glory. Scientists are still analyzing coral samples to determine the age and diversity of species in the area.
Roark, who frequently collaborates with Baco-Taylor, said this study and the ongoing work provides critical knowledge for policymakers examining the effectiveness of protecting these areas.
"This is a high impact paper that bears directly on fishery management issues in the Northwest Hawaiian Islands and is timely relative to some changes the current administration is thinking about with respect to opening up marine monuments for more fishing," Roark said.