A new study by marine biologists reports that seals can essentially act as ‘smart sensors’ for monitoring fish populations in the ocean’s eerily dim ‘twilight zone.’ Over the past 60 years, marine biologists at UC Santa Cruz have monitored the behaviour of northern elephant seals that journey to nearby Ano Nuevo Natural Reserve.

With the seals gathering on the beach by the thousands to breed and moult, generations of researchers have been able to amass more than 350,000 observations on over 50,000 seals.

Roxanne Beltran is next in line to lead the project, and her new study being published on February 14 as the cover story for Science reports that seals can essentially act as “smart sensors” for monitoring fish populations in the ocean’s eerily dim “twilight zone.”

This is the layer of water between 200 and 1,000 meters below sea level, where sunlight penetration all but stops, and which today’s ocean monitoring tools cannot easily reach.

Ships and floating buoys only allow measurements of a tiny fraction of the ocean, while satellites can’t measure below the surface where fish occur.

Importantly, this zone holds the majority of the planet’s fish biomass. Because this is also where the seals feed, seals whose foraging success is tracked can provide a previously impossible way to measure the availability of fish populations across a vast ocean.

This, Beltran said, represents a significant discovery because humans are considering harvesting these fish populations to satisfy humanity’s ever-increasing need for protein-rich foods.

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