From: Allison Winter, ENN
Published November 27, 2013 09:10 AM

Google Earth Improves Estimates of Fish Catches

The basic idea of a fish trap is that when a fish swims inside through it's opening, it cannot get out, therefore trapping the fish and making it easier for populations to collect a decent catch. People around the world use different kinds of fish traps depending on the local conditions and behavior of the fish they are trying to catch. One type of fishing trap known as weirs that jut out from coastlines is now facing scrutiny as Google Earth images reveal the traps be snaring six times as many fish than what is officially reported.


Using satellite imagery from Google Earth, University of British Columbia researchers estimated that there were 1,900 fishing weirs along the coast of the Persian Gulf during 2005 and that they caught approximately 31,000 tonnes of fish that year. The official number reported by the seven countries in the region to the United Nation's Food and Agriculture Organization was 5,260 tonnes.

Fishing weirs are semi-permanent traps that take advantage of tidal differences to catch a wide variety of marine species. The basic purpose is to capture fish by limiting their movement without greatly impeding water flow. In the case of intertidal weirs (like those found in the Persian Gulf), fish swimming parallel to shore at high tide encounter the "wing" and invariably try to escape by swimming into deeper water, eventually entering a smaller enclosure where they are captured by receding tides. Weirs are mostly used in Southeast Asia, Africa and parts of North America, and can be more than 100 metres long.

"This ancient fishing technique has been around for thousands of years," says Dalal Al-Abdulrazzak, a PhD student with the UBC Fisheries Centre's Sea Around Us Project and the study's lead author. "But we haven't been able to truly grasp their impact on our marine resources until now, with the help of modern technology."

The study shows the potential for using remote-sensing approaches, such as satellite imagery, to validate catch statistics and fisheries operations in general.

"Time and again we've seen that global fisheries catch data don't add up," says Daniel Pauly, principal investigator with the Sea Around Us Project and the study's co-author. "Because countries don't provide reliable information on their fisheries' catches, we need to expand our thinking and look at other sources of information and new technologies to tell us about what’s happening in our oceans."

Because global fisheries are overexploited, viewing fishing practices from space using publicly available resources such as Google Earth will help mitigate gaps in catch reporting.

Read more at the University of British Columbia.

Read the complete study at ICES Journal of Marine Sciences.

Fishing weir image credit: Google Earth, via the University of British Columbia.

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