From black box to blue box

Feb 19th 2004 | SEATTLE
© The Economist print edition

The American Association for the Advancement of Science (AAAS) has just held its annual meeting. One highlight was a session on new techniques for tracking marine animals

MAKING a living as a fisherman has never been easy. With the continual decline in fish stocks currently under way, it is becoming an even harder way to grind out a living. And it is not only fish that are disappearing, but marine fauna generally. In the past 20 years, for example, 90% of leatherback turtles and large predatory fish, such as sharks, have disappeared.

Where and how this is happening has been difficult to say, since the ocean is something of a black box. Things go in, and things come out, but what happens in between is hard to unravel. According to researchers presenting their work at the AAAS meeting in Seattle, Washington, this is now changing. Today, when many marine biologists swig their morning coffee and download their messages, they receive special e-mails from their research subjects. These messages, relayed by a satellite, tell them exactly where their animals have been. This has been made possible thanks to advances in underwater electronic tagging, and it is causing a revolution in marine biology.

One of the leading researchers in oceanic tagging is Barbara Block of Hopkins Marine Station in Pacific Grove, California. She tags bluefin tuna, which are commercially valuable animals that can reach 680kg (1,500lb) in weight, and swim at speeds of up to 80kph (50mph). So far, her group has tagged around 700 bluefin. Many of the tags are surgically implanted, a tricky thing to do while on board a moving boat. These tags archive their data in memory chips, and are eventually recovered when a fish is caught and butchered. (The tags carry a healthy reward.) Other tags, though, are fastened to the outside of a fish, and pop off at a pre-programmed time and date. They then broadcast their results to a satellite. Dr Block's work has shown that bluefin can migrate thousands of kilometres across the Atlantic, ignoring boundaries that have been set to protect stocks in the western Atlantic.

Thanks, and so long to all the fish

Tagging is also helping David Welch, the head of the Canadian government's salmon programme, to find out where and why large numbers of the fish are vanishing. He uses small acoustic tags (the size of a large multivitamin capsule) that are sewn into the body cavities of salmon. These tags broadcast their signals to microphones on the seabed.

Dr Welch can now track where an individual salmon spends its life and watch trends in an entire population. He was surprised to find that most salmon do not die as they leave the river and enter the sea, as previously believed. And he is finding that climatic fluctuations play an important role in determining population.

Dr Welch and his colleagues are planning to install a system of microphones stretching from the coast of Washington state to south-eastern Alaska. This could follow the movements of some 250,000 fish—collecting data on their direction of travel, speed, depth and position. If that works, the plan is to extend the system from Baja California in Mexico to the Bering Sea—a project that would involve about 1,000 underwater tracking stations.

Meanwhile, Andrew Read, a marine biologist at Duke University in North Carolina, is following 45 tagged loggerhead turtles. These animals must come to the surface to breathe. When they do so, the tags (which are glued to their shells) talk to the nearest convenient satellite.

Dr Read told the meeting that the tracking data he collects are now available online, to allow fishermen to follow the movements of turtles and, if they wish, to modify the deployment of their nets accordingly. Bill Foster, a fisherman from Hatteras, North Carolina, and Dr Read, proposed the project because the Pamlico Sound near Hatteras was closed to large-mesh gill nets (which are dragged behind a boat like a curtain) for four months a year because too many turtles were being caught by accident. Now, the fishermen are helping the researchers, and attaching tags to healthy turtles that are accidentally caught in their nets.

Together, all this work is beginning to fill in the map of marine “highways” used by particular species, and their preferred habitats. It is also showing where particular animals prefer to stay close to the surface, and where they prefer deeper waters. As in the case of Dr Read's turtles, this is helping scientists to devise ways of protecting rare species in an efficient manner, without interfering too much with the exploitation of common ones.

Larry Crowder, also at Duke University, has overlaid maps of marine highways for loggerhead and leatherback turtles in the Pacific on to those of “longline” fisheries, in which people catch prey on fishing lines that are several kilometres long. Turtles often take the bait on the hooks that these lines carry. Dr Crowder wants to identify the places of greatest danger to these turtles, in the hope that such places will be considered for protection. This need not, he says, mean a ban on fishing, but rather the use of different hooks, and other sorts of gear that are less damaging to turtles. It also turns out that turtles spend 90% of their time within 40 metres of the surface, so setting hooks deeper than this would reduce the chance of catching them accidentally.

Conservationists are now pushing the notion of “ocean zoning”. Like the land, parts of the sea—such as turtle highways—would be defined as sensitive, and subject to restrictions on how extractive industries operate. If this idea is ever to work, tagging data will be crucial. And because tagging data come in continually, this could mean that sensitive areas in the ocean could be flexible, changing in both time and space. Enforcing such zones might be difficult. But it would help fish, and other marine fauna, breathe a bit easier. And careful management might leave the fishermen on top as well.

Media Contact: Tim Lucas at 919-613-8084 or tdlucas@duke.edu