Weir fishing grossly underreported, Google Earth reveals

A University of British Columbia Ph.D. student has developed a technique for estimating catches from small-scale fishing using satellite images, and discovered just how grossly underreported such catches are in the Persian Gulf.

Cheap, simple technique could provide more accurate fishing statistics worldwide

Using Google Earth satellite images, Dalal Al-Abdulrazzak counted visible weirs and estimated there were about 1,900 in the Persian Gulf. (Google Earth/University of British Columbia)

The amount of fish caught by small-scale fisheries using traps called weirs may be six times higher than officially reported in the Persian Gulf, suggest estimates made using images from Google Earth.

"We should realize what's being reported to the UN is likely an underestimate. That has implications for fisheries management," said Dalal Al-Abdulrazzak, a Ph.D. student with the University of British Columbia Fisheries Centre in a phone interview Tuesday about the results of the study she led.

Al-Abdulrazzak, who is currently working on ocean governance with the United Nations in New York, added that more effort needs to be made to improve the quality of fishing statistics. She said that is especially true in the case of small-scale fisheries that often go underreported because governments think studying them isn't worth the trouble.

"Nobody actually thinks they have a large impact, but they do."

She added that weir fishing can be particularly damaging to marine ecosystems because it tends to scoop up juvenile fish from their nursery grounds in shallow waters, long before they have a chance to spawn.

Al-Abdulrazzak grew up in Kuwait, where she often saw weirs in shallow, intertidal waters along the coasts.

The semi-permanent traps, made of bamboo and wire mesh, have a long "wing" that juts out into the water, guiding fish toward a tennis-court sized enclosure called a yard and eventually into pockets where they become trapped. Fishermen collect the fish once a day during low tide.

The weirs were such a common sight that Al-Abdulrazzak was surprised to see the low official catch numbers from weir fishing reported to the United Nations.

She decided to look for weirs in satellite imagery and see if she could come up with her own estimate. She chose Google Earth as the source of those images because the images are free, accessible, and easy to use, and she hoped to develop a technique that could be used in many different countries – "especially for developing countries where they don't have resources to allocate toward fisheries monitoring or improving data collection."

Al-Abdulrazzak said it took her about four months of patient sifting through satellite images and careful counting to estimate a total of 1,900 weirs in the Persian Gulf. She then asked fisheries scientists in the Middle East what average annual fish catches were per weir.

Based on that information, she estimated that weirs in Kuwait, Saudi Arabia, Qatar, the United Arab Emirates, Iran, and Bahrain scoop up about 31,000 tonnes of fish a year, plus or minus 10,000. That is about six times higher than the 5,260 reported to the United Nations Food and Agriculture Organization in 2005.

No reported catches in 3 countries

Al-Abdulrazzak acknowledged that her figure is a rough one, but said it is far better than what currently exists – officially, Saudi Arabia, Qatar and Iran reported no weir fishing catches at all.

"And my estimates are huge," she added. "My estimate is more likely to be closer to the truth."

The results suggest it's not that hard to improve on existing catch statistics, she said, and she hopes more countries will make the effort.

"I was able to do it with very few resources and just access to the internet and a little bit of patience... I'm hoping that this will gain some momentum and more people will start using this technique."

While Al-Abdulrazzak's study, published Tuesday in the ICES Journal of Marine Science, focused on the Persian Gulf, she noted that weirs are used for fishing "practically worldwide."


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