Shrimp Trawling Re-Suspending BP Oil?

Way back last autumn I had a nagging thought: once oil impacted areas of the Gulf were re-opened to fishing in the wake of the BP / Deepwater Horizon spill, would shrimp trawlers repeatedly churn up oil that had settled on the seafloor?

Google Earth panoramic image showing sediment plumes raised by bottom-trawl fishing for shrimp along the Louisiana coast. More images here.

As the federal government proceeds with a long and complicated legal and scientific process, the Natural Resources Damage Assessment, they are holding a series of public meetings to get input and comments from affected Gulf-area residents. At a meeting last week in Biloxi, Mississippi,

Vietnamese shrimpers said they have pulled up nets full of oil from the seafloor and have had to decide whether to report the oil to the Coast Guard, which would mean dumping their day’s catch, or pretend they don’t see the oil.

John Lliff, a supervisor with NOAA’s Damage Assessment Remediation and Restoration Program, said no one knows how much of the seafloor is covered in oil.

Until the oil totally disappears, it seems highly likely that this will continue. But we don’t have a clue how long the oil will linger, or what the impacts of this would be on the health of fishermen, the recovery of the Gulf ecosystem, or the safety of seafood.

Meanwhile, some of our politicians seem to be ignoring the fact that the world’s worst accidental oil spill happened here in our own back yard less than a year ago, and are intent on returning to business as usual without assuring the public that drilling is any safer than it was last April. Does anybody else see this as a recipe for another disaster?

BP / Gulf Oil Spill – Are Shrimpers Inadvertently Churning Up Oil?

There have been conflicting reports coming from coastal Lousiana since October 22, suggesting that large areas of East and West Bays near Southwest Pass are covered with long streamers of what appears to be weathered oil, possibly originating from the BP / Deepwater Horizon spill. Some of the local fishermen insist it’s oil; the Coast Guard thinks it’s an algal bloom. Samples taken by the Coast Guard are awating analysis. [UPDATE 10/28/10 10:00 am ET – LSU scientists confirm the substance is mostly algae with only trace amounts of oil]

Oil or algae? Photo of West Bay, Louisiana taken October 22. Source: Matthew Hinton via the Times-Picayune. Photo gallery here.

At SkyTruth we’re concerned that fishing activity could potentially stir up any oil that’s sitting on the seafloor, resuspending it in the water column. We don’t know if that’s what has happened near Southwest Pass. But we do know that bottom-trawling for shrimp in the Gulf routinely churns up the muddy seafloor, creating long sediment-laden plumes that trail for miles behind the trawlers and can be seen on satellite images. Check out our gallery of trawling images, and read more about it on this blog.

Google Earth image showing muddy plume of sediment raised by a shrimp trawler at work along the Louisiana coast. Image taken before the BP spill.

NOAA reports they haven’t yet found any signs of oil sitting on the Gulf seafloor. Other scientists claim they found inches-thick layers of oil on the seafloor on research cruises in September and “vast amounts” of oil on the seafloor in October. It seems reasonable to assume that if those scientists are correct, and if bottom-trawling for shrimp is occurring now in places where layers of oil are sitting on the seafloor, that oil will be disturbed by trawling.

We don’t know what the effects of that could be. It might help the oil biodegrade more quickly. But it will also repeatedly expose marine life, including commercially important species, to oil that would otherwise remain on the ocean floor.

This suggests to us that it’s very important to quickly, accurately and thoroughly survey the Gulf seafloor for residual oil, so we can let shrimpers know what areas to avoid for now.

Shrimp trawler working in mysterious substance floating in West Bay, Louisiana on October 23. Note plume behind the trawler. Source: Erika Blumenfeld via Trouthout.

Fishing The Line: Do Marine Reserves Improve Fishing?

Low-altitude air photo showing small boats “fishing the line” on the border of a protected area that is off-limits to fishing. Photo courtesy of Billy Causey, Florida Keys National Marine Sanctuary.

Here’s a blast from the past: a recap of one of the first projects SkyTruth ever conducted, a limited study of satellite imagery as a tool to demonstrate “fishing the line.” There is abundant anecdotal information that when an area of the ocean is closed to fishing, fish populations rebound and “spill over” into adjacent areas outside of the protected zone. Fishermen, who go wherever the most fish can be found, take advantage of spillover by fishing as close to the boundaries of the protected area as possible — fishing the line. Wherever we see an accumulation of fishing vessels close to the borders of a marine reserve or other area off-limits to fishing, conservationists argue that the fishermen themselves are demonstrating that the protected zone is doing a good job at increasing fish populations and improving the fishing opportunity.

But how do you actually go about showing this “fishing-the-line” phenomenon?

One way is to collect data on the locations of fishing vessels. The U.S. Coast Guard does this for certain fishing grounds, requiring all vessels to have a transponder on board that continually broadcasts data on the vessel’s position. This is called the Vessel Monitoring System (VMS). SkyTruth acquired VMS data for scallop fishing in the northwest Atlantic ocean, in the vicinity of George’s Bank off Cape Cod, Massachusetts. The aggregated data, plotted on a map that includes the boundaries of three areas that were closed to scallop fishing at that time, clearly showed vessels avoiding (or simply transiting through) those closed areas, and spending a lot of their fishing time congregated along the borders of those closed areas.

Aggregated VMS data showing fishing-vessel locations (colored points) and areas closed to fishing (blue polygons) in the northwest Atlantic Ocean in May, 1999.

We used this pattern to guide an analysis of archived satellite imagery to test whether fishing-the-line behavior could also be detected, and illustrated, using satellite images as the sole source of data on vessel locations. Thanks to a small research grant from American Oceans Campaign (now Oceana), SkyTruth was able to purchase, process and analyze three Radarsat satellite images taken in March and May of 1998, while the closure of Area 1 was in effect. Vessels typically appear on radar satellite images as very bright targets.

RADARSAT-1 satelite images used in this study.

 

The combined locations of vessels on the images was plotted on the map shown below. Although the pattern isn’t as obvious as in the VMS dataset (we were not able in this limited study to discriminate between fishing vessels and the many other types of vessel that transit the north Atlantic), possible fishing-the-line is apparent, particularly along the western boundary of the closed area.

Vessel locations in and around an area closed to fishing off Cape Cod.
Compiled by SkyTruth from radar satellite images.


As fisheries around the world struggle, many scientists claim that establishing more protected areas can be an effective tool to help those fisheries recover and move toward sustainability. With a little more work by SkyTruth, we may find that satellite images can help convince skeptical fisherman and managers to embrace protected areas.

Bottom Trawling: Sediment Plumes Visible From Space

I’m here in Boston at the annual meeting of the American Association for the Advancement of Science (AAAS). SkyTruth is part of a session looking at the impacts of commercial fishing on the oceans, specifically a technique called bottom-trawling. The trawlers drag heavy nets back and forth on the seafloor, flattening what’s in their path and, where the ocean floor is muddy, sending big billowing clouds of sediment into the water. The amazing thing is this phenomenon is actually visible from space: a trawler, with its nets deployed, leaves a long and persistent trail of sediment in it’s wake, not unlike a jet contrail:

We’ve built a public image gallery showing the sediment plumes generated by trawlers in the Gulf of Mexico, using both Google Earth and Landsat satellite images. We’ve also put together a virtual tour of this issue for Earth users. Today we took part in a press conference on this work; tomorrow we’ll give a talk at the symposium. You can download our presentation here (mostly pictures, not a lot of words — just the way we like it at SkyTruth).

But don’t stop there: send us your Google placemarks and other image examples showing the impacts of trawling, other fishing techniques, and other forms of human impact to our oceans. Email us (info@skytruth.org) or submit a comment on this blog posting. We’ll compile the submissions, credit the contributors, and post the results.