Deep space may be the final frontier, but we already know more about the orbits of stars
around the supermassive black hole at the center of the Milky Way then we do about the
behavior of the colossal squid and other creatures that live deep in the oceans here at home.
In fact, water deeper than a kilometer covers more than 60% of the planet, which means we
know very little about the most common environment on Earth. There, creatures odd and tasty have
learned to survive in constant darkness, near-freezing cold, and extreme pressure, all of which mean
there’s very little available oxygen, food, or companionship.
Surviving in this environment requires some extraordinary adjustments. One-thousand meters
down, the pressure is over 100 times what we experience at the surface, or enough to
compress the air in a soccer ball to the size of a ping pong ball – and a half. Unlike most
fish, the ones that live in these depths don’t have gas-filled cavities like swim bladders,
which would collapse under the extreme pressure. In fact, super deep-water fish often have
minimal skeletons and jelly-like flesh because the only way to combat the extreme pressure
of deep water is to have water as your structural support.
Until recently we left deep water fish alone, but as coastal fisheries became depleted,
fishermen went further out to sea, where they found a lot of large tasty fish. As they caught
(and depleted) the ones near the surface, they simply fished deeper.
Fishing deep is a game changer, though. Because these fish are remarkably well adapted to
the pressures of the depths, they are remarkably unfit to deal with modern fishing pressures.
Cold temperatures and lack of food means that fewer fish live in the deep, and those that
do, grow slowly – which means they also reproduce slowly. For example, the Orange roughy [Hoplostethus
atlanticus] live out their long lives – often more than a century – 500 to 1500 m below
the ocean’s surface. At their best they can only replace 6% of their population each
year, while shallow-water fish like cod, mackerel, and herring replace half of their entire population
in the same time. When commercial fishing for orange roughy took off in the 1980s, the
catch was astoundingly good – but within 25 years, most nets came up empty.
If you think about it, we’re basically mining the oceans, which means it’s rough going both
for orange roughy and other slow-growing but delicious denizens of the deep, as well as
for the fishermen whose livelihoods depend on them. If we could only learn to harvest
fish at the same rate as they replace themselves, it would benefit fish, fishermen, AND our
future cuisine. Because, while we can always mine asteroids for minerals and precious metals,
as far as we know, there aren’t any fish in space – so we should probably be protective
of the ones that we have here!