Scripps Study Finds Plastic in Nine Percent of ‘Garbage Patch’ Fishes

SEAPLEX researchers estimate tens of thousands of tons of debris annually ingested by fish in middle ocean depths of North Pacific Ocean

Scripps Institution of Oceanography / University of California, San Diego

The first scientific results from an ambitious voyage led by a group of graduate students from Scripps Institution of Oceanography at UC San Diego offer a stark view of human pollution and its infiltration of an area of the ocean that has been labeled as the “Great Pacific Garbage Patch.”

Matt Durham, Jim Leichter and Pete Davison deploy a Matsuda-Oozeki-Hu Trawl at the North Pacific Subtropical Gyre during SEAPLEX.

Two graduate students with the Scripps Environmental Accumulation of Plastic Expedition, or SEAPLEX, found evidence of plastic waste in more than nine percent of the stomachs of fish collected during their voyage to the North Pacific Subtropical Gyre. Based on their evidence, authors Peter Davison and Rebecca Asch estimate that fish in the intermediate ocean depths of the North Pacific ingest plastic at a rate of roughly 12,000- to 24,000 tons per year.

Their results were published June 27 in the journal Marine Ecology Progress Series.

During the SEAPLEX voyage in August 2009, a team of Scripps graduate students traveled more than 1,000 miles west of California to the eastern sector of the North Pacific Subtropical Gyre aboard the Scripps research vessel New Horizon. Over 20 days the students, New Horizon crew and expedition volunteers conducted comprehensive and rigorous scientific sampling at numerous locations. They collected fish specimens, water samples and marine debris at depths ranging from the sea surface to thousands of feet depth (See SEAPLEX Oceanographic Equipment).

Of the 141 fishes spanning 27 species dissected in the study, Davison and Asch found that 9.2 percent of the stomach contents of mid-water fishes contained plastic debris, primarily broken-down bits smaller than a human fingernail. The researchers say the majority of the stomach plastic pieces were so small their origin could not be determined.

“About nine percent of examined fishes contained plastic in their stomach. That is an underestimate of the true ingestion rate because a fish may regurgitate or pass a plastic item, or even die from eating it. We didn’t measure those rates, so our nine percent figure is too low by an unknown amount,” said Davison.

Researchers collected confetti-sized flecks of plastic during the expedition.

Rather than a visible “patch” or “island” of trash, marine debris is highly dispersed across thousands of miles of the North Pacific Subtropical Gyre. The debris area cannot be mapped from air or space, so SEAPLEX researchers collected samples in 132 net tows (130 of which contained plastic) across a distance of more than 2,375 kilometers (1,700 miles) in an attempt to find the boundaries of the patch. The region, a “convergence zone” where floating debris in water congregates, is generally avoided by mariners due to its calm winds and mild currents. The North Pacific Subtropical Gyre has been understudied by scientists, leaving many open questions about marine debris in the area and its long-term effects on the marine environment.

“This study clearly emphasizes the importance of directly sampling in the environment where the impacts may be occurring,” said James Leichter, a Scripps associate professor of biological oceanography who participated in the SEAPLEX expedition but was not an author of the new paper. “We are seeing that most of our prior predictions and expectations about potential impacts have been based on speculation rather than evidence and in many cases we have in fact underestimated the magnitude of effects. SEAPLEX also clearly illustrates how relatively small amounts of funding directed for novel field sampling and work in remote places can vastly increase our knowledge and understanding of environmental problems.”

SEAPLEX was supported by the UC Ship Funds program, Project Kaisei/Ocean Voyages Institute and the National Science Foundation.

Headlines with misconceptions about the "Great Pacific Garbage Patch"

As a scientist, it can be pretty frustrating to see these misconceptions repeated and repeated for years on end. That’s why the SEAPLEX team has done our best to accurately relay our observations from our own voyage to the North Pacific Central Gyre, and to refer people to reliable sources such as the NOAA Marine Debris Program’s FAQ. But I suspect the persistence of these misconceptions is why Oregon State University oceanographer Angelique White stated in a press release last week that the Great Pacific Garbage Patch is “grossly exaggerated.”

Since that press release and the ensuing media coverage, I’ve received many requests for clarification. If there’s no garbage patch, what the heck were we measuring back in 2009? But actually there’s no conflict between Dr. White’s statements and SEAPLEX findings. In this blog post, I’ll explain a few of the key points from the OSU press release.

“…it is simply inaccurate to state that plastic outweighs plankton, or that we have observed an exponential increase in plastic.”

Reports that plastic outweighs plankton stem from a 2001 study by Moore et al., published in Marine Pollution Bulletin. Most oceanographers, including myself, do not think that comparing the dry weight of plankton and plastic is a helpful way of understanding what is going on in the ocean. The reasons for this are somewhat technical, but you can read about them in this blog entry, which I wrote a year before I starting doing my own research on plastic in the North Pacific. I believe that this method is no longer much used – in a recent post at the Plastic Pollution Coalition’s blog, Marcus Eriksen of Algalita Marine Research writes “…it’s important to describe plastic to plankton ratios as an anecdote, but not worth quantifying.” Read his whole blog entry for the anti-plastic activist take on Dr. White’s press release.

As for an exponential increase in plastic, there is evidence that plastic debris increased from the 1960s and 1970s to the 1980s and 1990s. For example, a study by Robards et al. (1997) found more plastic in the stomachs of Arctic and subarctic seabirds in the late 1980s than between 1969-1977. After the mid-1980s, the trend becomes unclear. The only study of which I am aware that has measured this is Gilfillan et al. (2009). Using archived samples, they measured plastic in the California Current (not the gyre itself) in 1984, 1994, and 2007, and did not detect a significant increase.

“The studies have shown is that if you look at the actual area of the plastic itself, rather than the entire North Pacific subtropical gyre, the hypothetically “cohesive” plastic patch is actually less than 1 percent of the geographic size of Texas.”

In order to understand this, I emailed Dr. White directly, and she was happy to explain her calculations. First, remember that the vast majority, more than 90%, of the plastic found in the NPG are tiny – less than the size of your pinky fingernail. These pieces are spread out over the surface making them very hard to see with the naked eye. Mostly, the ocean just looks like ocean. In fact, here’s a photo I took smack in the middle of the “Eastern Garbage Patch” this fall:

But when you tow a fine-meshed plankton net through this same area, there are thousands of tiny plastic crumbs. They’re just really small, and fairly spread out on the surface of the ocean. Here’s a photo of the highest plastic densities I’ve ever seen in three trips to the Gyre, measured from a small boat on a glassy calm day. This is an area about the size of a dining room table.

So how can we reconcile finding plastic over 1,700 miles on SEAPLEX with Dr. White’s calculation that the “Great Pacific Garbage Patch” is just 1% of the state of Texas? There’s actually no conflict at all. Dr. White was looking at the area of the ocean’s surface covered by solid plastic, not where plastic pieces could be found. She calculated the area that would be covered by plastic if all tiny pieces were squished together into a solid “island.” Since the pieces are so small, that’s not very much area.

Many of the SEAPLEX scientists are considerably more concerned about the environmental impacts of these tiny pieces than we would be over a few larger pieces, or even a huge plastic island. There are many reasons for this, including toxins and the potential for such pieces to be ingested, but I think one of the most underrated impacts is the introduction of hard surfaces to an ecosystem that naturally has very few of them. Microbes, plants, and animals that live on hard surfaces are very different than those that live floating freely in the ocean, and adding all that plastic is providing habitat that would not naturally exist out there. To read more about our research, check out our webpage, or for a brief summary, this video podcast.

“If we were to filter the surface area of the ocean equivalent to a football field in waters having the highest concentration (of plastic) ever recorded…the amount of plastic recovered would not even extend to the 1-inch line.”

Once again, over 90% of the plastic pieces in the North Pacific Gyre are very small. There is no island, and the pieces are spread over the ocean’s surface. This photo of plastic and plankton collected on SEAPLEX represents an Olympic-sized swimming pool area of ocean (about 600 square meters).

A single manta tow from SEAPLEX. The plastic is the colorful bits floating on top - the fluffy beige and dark stuff in the rest of the jar is plankton.

When we painstakingly pick all that plastic out of the plankton samples, it is indeed a very small volume, only partially filling a container about the size of a nail polish jar (20 mL). However, in that tiny jar may be thousands and thousands of tiny pieces, collected in just 15 minutes of slowly towing a net along the ocean surfaces. Right now we don’t know what impact those pieces are having on the marine ecosystem, but we do know there are a lot of them, and that they can be found over a remarkably vast swathe of the North Pacific.

“Most plastics either sink or float,” White pointed out. “Plastic isn’t likely to be evenly distributed through the top 100 feet of the water column.”

This is true. Though we did find a few pieces of plastic at depth, most of the plastic that we observed on SEAPLEX was right on the ocean’s surface. Plenty of plastic debris has been found resting on the seafloor closer to shore – for example, one study conducted off central California found 6,900 pieces of debris per km2 (Watters et al 2010). I am not aware of any studies that have looked for plastic on the seafloor of the North Pacific Central Gyre – it’s pretty deep out there and considerable time and funds would be required.

Conclusion

Widespread misinformation, as is so common regarding plastic in the North Pacific, serves no one – not activists trying to ban plastic bags, not plastic manufacturers trying to develop ocean-degradable products, not groups developing methods to stop plastic pollution. Our role as scientists is to find out truths about the world, and to interpret and explain them. Debating what the data actually mean is a crucial part of the scientific process.

I think it is fantastic that so many groups and members of the public are passionate about what is happening in an obscure part of the ocean more than 1,000 miles away from any land. But the flip side of this interest is that the healthy scientific debate is going to be more public than usual. This is nothing to fear – in fact, I think it is a great window into how science is done. And I believe that this debate will ultimately be critical to finding a feasible solution to plastic pollution, whether than solution is based on land, at sea, or in legislative change.

Sources

Brief daily updates about cruise activities were posted here, along with a fine selection of pretty pictures. And I’m always a big fan of science ship fashion – the combination of orange hardhat/workvest and blue-and-yellow boots is TOTALLY going to be the next big thing. (Though can I get a work vest designed to actually fit female anatomy? Please?)

Manta net towed off the Okeanos Explorer. Image courtesy of NOAA Okeanos Explorer Program.

Washing down the manta net dressed in my finest. Image courtesy of NOAA Okeanos Explorer Program.

We were able to sail under the Golden Gate Bridge. We looked very, very pretty if I do say so myself.

Hello internets! I am back from a month of sailing from Hawaii to California on the tall ship SSV Robert C. Seamans. The Seamans is run by the Sea Education Association, where undergraduate and high school students can learn oceanography, maritime history, and seamanship aboard one of two gorgeous tall ships, one in the Atlantic, one in the Pacific. (The Southern Fried Scientist is an alumnus – anyone else out there?). The SEA vessels are well-equipped for research (PDF) with all the standard tools of oceanography – CTD, ADCP, winch & hydraulic J-frame, and so on – though it definitely is more challenging to maneuver under sail than by burning tons and tons of diesel fuel.

I was on board as a visiting researcher, continuing my work on the impact of plastic debris on zooplankton in the North Pacific Central Gyre. I did as many plankton tows as time allowed at the surface of the water, filtered lots of seawater to look for plastic particles too small to be caught by the net, and tested live zooplankton to see if they were ingesting plastic. I don’t know what the results are yet – in order to make the most of my time at sea, I just preserved samples as fast as possible, and will go through them now that I am back at the lab. (Also, looking in a microscope at sea makes me hurl.)

Doing a plankton tow off the SSV Seamans. That's me in the purple jacket. Roberto Meléndez took this photo from way up the foremast.

I was totally off the grid while at sea, so instead of trying to capture the full experience, I’m going to do a couple of posts on selected awesome moments and fantastic critters. If you want to know more, just ask in the comments – I can answer there or as an additional post. You can also check out SEA’s excellent Plastic blog for more on science under sail.

Awesome Moment #1

The cruise track was great for my work – we had to sail right through the north-center section of the gyre – but not so great for sailing. After we lost the trade winds north of Hawaii, we experienced very little wind until we got into the westerlies not far from California. I’m used to motoring around and it didn’t bother me much, but of course a tall ship is meant to sail, so the sailors (students as well as staff) all pined away for the wind.

It was flat, glassy calm for about two weeks, forcing us to motor along. Photo by Wei Xin.

The lack of wind did produce one glorious, wonderful moment – SWIM CALL! Swimming is strictly forbidden in the US research fleet due to a tragic incident with a white shark, so I’d never been swimming in the open sea before. (No, I was not worried about sharks. We had people acting as lookouts, visibility was amazing, and shark attacks are vanishingly, vanishingly rare.)

Conditions had to be exactly right to assure everyone’s safety, but we were lucky and the captain decided that the flat calm sea and lack of shark sightings meant that we’d be able to swim. Here I am paddling about, nothing between me and the giant isopods of the abyssal plain except 4000 meters of water.

Swimming in the middle of the Pacific. It was GLORIOUS. Photo by Roberto J. Meléndez.

Next: ATTACK OF THE PTEROPODS!!!

[cross-posted at Deep Sea News]

The romance of the sea, at least in my mind, is tied to the Age of Sail. This might be because of the inherent beauty of tall ships, or maybe because of a wee bit obsession with Patrick O’Brian’s “Master and Commander” novels (all 20 books, plus the glossary, plus the recipe book…), or maybe because I’ve always wanted to sing a shanty while actually hauling on a rope. This summer, I’ll finally get my chance.

I’ll be sailing from Hawaii to California with Sea Education Association aboard the SSV Robert C. Seamans. (I wrote about their plastic debris cruise in the Atlantic a couple weeks ago). The primary mission of the cruise is student education, but they are very kindly letting me come aboard as a visiting researcher. In fact, I type to you from aboard the Seamans at the dock in Honolulu.

I’ll be continuing the research I started last summer on SEAPLEX, further exploring the impact of plastic debris on marine life in the North Pacific Subtropical Gyre. Since we think the highest concentrations of plastic are on the very surface of the ocean, I’ll be studying with surface-dwelling (neustonic) zooplankton to see if they are interacting with the plastic debris. And I’ll be continuing my studies of the fouling community – the animals that grow directly on the plastic.

So far life on the Seamans is much like life on any research vessel preparing for a cruise – there’s a lot of securing and adjusting and last-minute runs to Home Depot. But as soon as we leave the dock on Wednesday morning, I’m going to get to learn the proper way to haul on a rope and scrub the deck. I’m very, very excited.

I don’t know what the internet situation will be, but if possible I will post updates from our journey across the Pacific. You can also follow the ship’s Twitter feed @SEA_Seamans. See you all in four weeks!

This blog has been silent for the past few months, since the SEAPLEX team has been holed up in our labs, processing samples as fast as our little fingers can go.  While at sea, we grabbed as many jars of plankton and water samples and fish as we could without doing much analysis. Now we are carefully going through them to understand the impact of plastic on the oceanic ecosystem.  You can get a glimpse into this process with Rebecca Tolin’s blog entry at Voice of San Diego.

While attending the Science Online 2010 conference in North Carolina, I was inspired to try to blog more on what we are actually doing in the lab. I know a lot of people wonder why results aren’t out yet, but turning a jar of plankton or a dead fish into data is really hard and time-consuming work. In the coming weeks, I will try to post photos and explanations of this not-so-glamorous but critically important side of ocean science.

I sent a list of corrections to the New York Times, and I am republishing them here as well. They are in the order they appear in the article. Because there are so many, I have kept each explanation brief, but please ask in the comments if you would like elaboration. Thanks to my SIO colleagues Kristen Marhaver and Mike Navarro for their suggestions!

In this remote patch of the Pacific Ocean, hundreds of miles from any national boundary, the detritus of human life is collecting in a swirling current so large that it defies precise measurement.

The gyre is not a current, but a lack of currents. Please see Pete’s explanation of convergence zones for more detail.

…an area of widely dispersed trash that doubles in size every decade and is now believed to be roughly twice the size of Texas.

There is no evidence for this. There certainly is a lot of trash, but there have been no measurements of either the trash’s total area or its growth rate.

But one research organization estimates that the garbage now actually pervades the Pacific, though most of it is caught in what oceanographers call a gyre like this one — an area of heavy currents and slack winds that keep the trash swirling in a giant whirlpool.

There is evidence for debris in some other areas of the Pacific, namely in the California Current, off Japan, and in the Alaskan Gyre, but there are few measurements from the southern hemisphere. A few studies have studied macrodebris – big stuff floating around or washed up on islands – but I am not aware of any microdebris studies there. And again, the gyre is defined by a LACK of currents, not “heavy currents.”

Scientists say the garbage patch is just one of five that may be caught in giant gyres scattered around the world’s oceans.

This is a very poor description of oceanic circulation. There are five major gyres, but lots of minor ones (e.g., the Alaskan Gyre). There is no evidence for all five major oceanic gyres containing large amounts of trash – only the North Atlantic and North Pacific have been studied. It certainly could be the case, but we don’t know yet.

Millions, billions, trillions and more of these particles are floating in the world’s trash-filled gyres.

As above, there is no evidence for all gyres being filled with trash. Also, though I realize writing is trying to be poetic, we do not know how many particles there are, but there may not be “trillions.”

Scientists…say that fish tissues contain some of the same chemicals as the plastic. The scientists speculate that toxic chemicals are leaching into fish tissue from the plastic they eat.

This is highly misleading. Fish tissues may contain pollutants, but no current evidence that they contain chemicals transferred from ingestion of plastic. There is only one study of this kind, and it was done on birds in the laboratory. To be fair, the article did say “speculate,” but it should have been clearer on the current state of the science.

Fish that feed on plankton ingest the tiny plastic particles.

We do not know if significant numbers or important species of fish are ingesting plastic. We are studying this now, and it continues to be unclear.

The researchers say that when a predator — a larger fish or a person — eats the fish that eats the plastic, that predator may be transferring toxins to its own tissues, and in greater concentrations since toxins from multiple food sources can accumulate in the body.

There is no current evidence of this, particularly since food species of fish (e.g., tuna) do not inhabit the gyre. The gyre is a biological desert – it is an area of very low productivity and there are very few large fish there. Top predators certainly do accumulate toxins like methylmercury, but that is not related to plastic ingestion.

“I saw much higher concentrations of trash in the Pacific garbage patch than in the Sargasso,” Ms. Monteleone said, while acknowledging that she might not have found the Atlantic gyre.

The Sargasso Sea is in the North Atlantic Gyre, and nearly synonymous with it, so I don’t know what this means. It might be possible to be in part of the North Atlantic Gyre without seeing the seaweed Sargassum, but it is impossible to be in the Sargasso Sea without being in the North Atlantic Gyre.

Water samples from February contained twice as much plastic as samples from a decade ago.

This is a very difficult claim to make without controlling for the medium- and small-scale variation of plastic abundance. Even in the same year, some areas have little plastic and some areas have a lot of plastic. Without controlling for these variations, the increase in plastic can’t be measured accurately.

—-

*If you’re interested in how the story was funded, I recommend checking out Hoshaw’s fundraising page at Spot.us, as well as Megan Garber’s critical article at the Columbia Journalism Review and John Zhu’s thoughtful blog post.

He writes:

The past two weeks of the SEAPLEX cruise have been spent far offshore in oligotrophic (nutrient-poor) water. In the California Current closer to shore, the nutrients required for plant growth are present in the surface water. This cold, nutrient-rich water has been recently upwelled from the deep by the action of winds blowing south along the coast. The growth of phytoplankton near the surface depletes the nutrients as the water warms up. Primary productivity is a measure of the rate of growth of phytoplankton. It is typically measured in grams of carbon per square meter per day. The carbon comes from photosynthesis as the plants change CO2 to O2 with energy from the sun. The winds eventually push the warmer, nutrient-depleted surface water offshore to the west. The position of the SEAPLEX trawls has been marked on a satellite map of annual primary productivity from our study area in the image below.

Phytoplankton are consumed by zooplankton, which are in turn eaten by larger predators. Changes in the pattern of food availability delineate pelagic habitat changes, and are reflected in the communities of animals that live there. The amount of available food also determines the quantity of animals (biomass) that can be supported in the habitat.

We have been collecting very small volumes of zooplankton and fish at Stations 2, 3, and 4 that correspond to the low productivity of the habitat we are sampling in comparison to Station 1 in the California Current. We have also been catching different species of animals that reflect the new habitat that we are sampling. This is clear in the photo below.

We separate the fish from the zooplankton at sea before preservation because two groups of animals are often studied by different scientists.  From the map, annual primary productivity at Station 1 is ~1 gram of carbon per square meter in comparison to ~0.3 grams of carbon per square meter at Station 4. We would expect a ratio of ~3.3 in the catch volume (assuming that the standing stock of animals is equal to annual growth). It can be seen that Station 1 had roughly four times the zooplankton volume and twice the fish volume as were found at Station 4. This is pretty close to our expectations.

Map of primarpy productivity in the Eastern North Pacific Ocean.   The SEAPLEX cruise track is overlayed on the map.  Station 1 is in the California Current region, an area of high primary productivty.  Stations 2, 3, and 4 are in the North Pacific Gyre, an area of low primary productivity.

Samples collected on the SEAPLEX cruise.  The samples were divided into zooplankton (left) and fish (right).  The jars in the back are from one trawl at station 1 in the California Current.  The jars in the front are from a similar trawl (same duration, same speed, same net, etc.) from Station 4 in the North Pacific Gyre.

He writes:

Pop quiz! What’s the largest migration on Earth? Is it the wildebeest of the African plains, or perhaps a marine bird like the sooty shearwater seasonally migrating from New Zealand to North America, or maybe the migration of the gray whales from Baja California to Alaska? In fact it is none of these. The largest migration on Earth, in terms of total biomass migrating, or number of individuals migrating, is the daily migration of plankton and small fishes from depth to the surface and back again. This phenomenon is called diel vertical migration, or DVM for short, and is by far the largest migration on Earth. Each night, plankton and small fishes (aka micro-nekton) come to the surface from a depth of a few hundred meters. They come to the surface to feed on phytoplankton and on other zooplankton. Before day breaks these same zooplankton will descend again to the depths, usually 200 to 800 meters (656 to 2625 feet) below the surface.

Let’s consider a specific case of a copepod 2.5 millimeters (0.1 inches)in length that migrates 350 meters (1148 feet). Three-hundred and fifty meters? I hear you scoffing! Granted it doesn’t sound like a long distance. However, when you realize that 350 meters equals about 140,000 body lengths for a migrating copepod, then you realize that this is equivalent to me walking from downtown San Diego to Santa Barbara every evening for dinner, and then walking back. And migrating plankton do this every day of the year–roughly equivalent to me walking around the world, more than twice, every year! Literally trillions of individual animals participate in this nightly mass migration. Also consider that a significant portion of the ocean’s biomass participates in this nightly migration, so we’re talking about hundreds of millions of tons of biomass. It quickly becomes clear that DVM is larger than all of the other great migrations combined.

Why do they do it? Well, it’s pretty clear that zooplankton and micro-nekton come to the surface layer (e.g. top 100 meters (328 feet) to feed. That’s where the phytoplankton are, and therefore, that’s where most of the food is. But this doesn’t explain why they descend with the coming day. Why spend all that energy moving up and down vast distances when you could simply stay at the surface and gorge on the
all-you-can-eat-buffet? The best answer is predators. During the day, light renders zooplankton and small fishes much more visible to their predators. DVM is an adaptive behavior that probably evolved independently in many taxa, or groups of zooplankton and fishes, over many, many generations. Several interesting corroborating observations support the light/predator hypothesis. First, during a solar eclipse, migrating zooplankton and fishes will start to migrate to the surface, only to turn around when the solar eclipse ends. Tricky! Second, when a parcel of water containing migrating zooplankton passes over a shallow seamount during the day, the zooplankton are unable to descend to darkness, and are consequently massacred by planktivorous fish. A total bloodbath. Finally, and most convincingly, is the observation that in those rare areas where predators are found predominantly at depth during the day, and at the surface at night, the local zooplankton prey will reverse their migration (e.g. reverse-DVM) in reaction to the new predation pressures. So, ultimately, we believe that DVM is driven by predation pressures. I guess I’d walk back to San Diego, too, if there was a strong possibility of me being eaten in Santa Barbara.

I hope you have all found this little diversion into the secret lives of critters interesting! I’ll leave you with a couple pictures from a recent manta net tow. This manta tow was remarkable in that we collected a huge number of zooplankters, and that the sample was composed mainly of only two species of small crustaceans. You can see in the pictures a clear, smaller copepod species, and also a beautiful iridescent blue amphipod. I’ve never seen this amphipod species before. When the cod-end from the manta net came up filled with what looked like blue paste, I was sure that we had captured a big blob of grease or waste. Instead, imagine our surprise when we saw these!

Contents from the cod end of one of today’s manta tows filled with blue amphipods.

Close up of the manta sample.  The small clear crustaceans are copepods.  The blue ones are amphipods.