Twilight zone management challenges

Other than a few fisheries that include the harvest of Antarctic krill, the fishing industry has not yet seen mesopelagic species as a commercial option.

Bonnie Waycott

Some twilight zone fish have already been harvested historically in Antarctica and some other regions. The future development of a fishery for mesopelagic fish may hinge upon growth in the downstream fishmeal or fish oil markets, but the difficulties of designing and implementing rules for conservation and management should not be underestimated,’ Porter Hoagland said.

‘Climate change impacts on the ocean such as warming, deoxygenation and acidification will introduce additional uncertainty in a system that’s already difficult to predict. This argues for an adaptive approach to sustainable management but data to inform such an approach in the case of mesopelagic stocks are thin, costly to obtain and stocks may already be adjusting to climate change in unexpected ways.’

Deep sea imaging equipment deployed from research vessel Henry B Bigelow

The mesopelagic zone could become overfished if it was economically feasible to harvest fish there, and if government subsidies on vessels or operations increase economic feasibility.

Some mesopelagic fisheries could take place in areas beyond national jurisdiction, with no explicit regulation of stocks. In those areas, fishing may not violate international law but could be considered unregulated, within one of the definitions of IUU (Illegal, Unreported or Unregulated) fishing.

Longarm Octopus

‘Although there is a general duty in the UN Convention on the Law of the Sea (Art. 192) for states to protect and preserve the marine environment, in the presence of significant uncertainty over stock sizes and ecological linkages, this would be problematic to monitor and enforce,’ Porter Hoagland said.

Human history is replete with examples of the over-exploitation of unregulated fish stocks, and where twilight zone fish occur within national exclusive economic zones, the potential for overfishing is also significant. The OTZ Project is guided by a goal of developing scientific knowledge of the mesopelagic so that its resources can be used sustainably.’

Longray Fangjaw

Because the mesopelagic is perpetually dark, constantly changing and encompassing almost the entirety of the open ocean, exploration has historically been hampered. But despite the difficulties of reaching and studying the mesopelagic, new technologies are now providing unprecedented access to once inaccessible places.

Researchers at WHOI will be using autonomous robots, remotely operated vehicles, autonomous floats and profilers and deep-ocean sensors and samplers to address key questions about mesopelagic biomass and biodiversity, food web dynamics, animal life history and behaviour and carbon cycling and climate conditions.

Meolpelagic shrimp

Another area requiring further research is the degree to which pelagic species, including swordfish, tunas and sharks, rely on the mesopelagic. Limited information suggests that ecosystems there are important feeding areas for pelagic species and may be an important food source for non-commercial, protected species such as whales, seals and Antarctic penguins.

It’s also important to find out how commercial harvests of mesopelagic fish would affect the sequestration of carbon in an environment where critical mesopelagic processes could be affected by rising ocean temperatures, stratification of surface waters, reductions in dissolved oxygen and increased acidification. Such a changing environment could also affect potentially available stocks of mesopelagic fish. Many additional questions need to be addressed to understand the extent to which this would occur.

Nealotus tripes

Interest in fishing in the mesopelagic continues, however. In 2017, a Directorate of Fisheries representative in Norway gave a presentation at the North Atlantic Seafood Forum, calling for research into the various fish and invertebrates of the mesopelagic and describing them as ‘an important, almost untapped source for marine feedstuffs’ to support fish farming.

The OTZ project offers an unprecedented opportunity to transform how people relate to a relatively unknown and unexplored ecosystem so that we become better stewards, conserving newly discovered resources rather than overexploiting them.

More information is available here and data produced as part of the project will be made widely available to interested parties, helping to accelerate scientific exploration, public engagement and policy decisions.