Genesis of mass migration of fish observed for first time

March 27th, 2009 - 4:49 pm ICT by ANI  

Washington, March 27 (ANI): Engineers at MIT (Massachusetts Institute of Technology), for the first time, have observed the initiation of a mass gathering and subsequent migration of hundreds of millions of fish.

The work, conducted using a novel imaging technique, “provides information essential to the conservation of marine ecosystems that vast oceanic fish shoals inhabit,” according to the research team.

It also confirms theories about the behavior of large groups of animals in general, from bird flocks to locust swarms.

Until now, those theories had only been predicted through theoretical investigations, computer simulations and laboratory experiments.

For example, the team found that once a group of fish reaches a critical population density, it triggers a kind of chain reaction resulting in the synchronized movement of millions of individuals over a large area.

The phenomenon is akin to a human “wave” moving around a sports stadium.

“As far as we know, this is the first time we’ve quantified this behavior in nature and over such a huge ecosystem,” said Nicholas C. Makris, leader of the work and a professor of mechanical and ocean engineering.

The resulting shoals of migrating fish can extend some 40 kilometers or approximately 25 miles across the ocean.

The researchers focused on Atlantic herring off Georges Bank near Boston during the fall spawning season.

They found that the formation and movement of large shoals of the fish constituted a kind of daily evening commute to the shallower waters of the bank where they spawn under cover of darkness.

Come morning, the fish head back to deeper water and disband.

The work was conducted using Ocean Acoustic Waveguide Remote Sensing (OAWRS).

OAWRS allows the team to take images of an area some 100 kilometers (approximately 62 miles) in diameter every 75 seconds, which is a vast improvement over conventional techniques such as fish-finding echo-sounders.

Both OAWRS and conventional methods rely on acoustics to locate objects by bouncing sound waves off of them.

With conventional techniques, survey vessels send high-frequency sound beams into the ocean.

In contrast, the new system uses much lower frequency sound that can travel much greater distances and still return useful information with signals far less intense.

According to Ron O’Dor, co-senior scientist of the Census of Marine Life (CoML), “OAWRS allows us to gather information such as geographical distributions, abundance and behavior of fish shoals and to better understand what constitutes healthy fish populations, which can be implemented by policymakers to better monitor and improve conservation of fish stocks.” (ANI)

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