This is a story some of you have heard before, others perhaps not. The sharper ones among you may identify errors in my narrative; if so, I invite you to correct them in the comments — after all, I’m a geologist. Not a biologist.
It’s a story about a small animal but one of the largest environmental contamination problems in the United States.
It’s a story that involves eagles, irresponsible industrial waste disposal, fish, feral pigs, organic chemistry, misguided human intervention, and even a Hollywood film production. It’s got it all.
The story has to do with manufacture of the pesticide DDT in the Los Angeles area and some of its effects on the environment. I used to go through a version of this story when I would give presentations to high school and middle school students about working in the environmental field to help them see how contaminants in the environment can have unexpected effects. I chose it because my experience includes working to investigate and clean up DDT contamination at multiple locations, and because I hoped the story had interesting appeal plus a cute protagonist, which never hurts in show biz.
Terrestrial and aquatic ecologists like to describe how the world’s ecology is interconnected. How harm to a species in one location may cause unanticipated effects far away (geographically or genetically) because the webs of nature are complex and often are only poorly understood. That’s one of the reasons why extinctions, even of a seemingly unimportant species in an obscure or remote place, are to be avoided if at all possible. Diversity is important to the resiliency and survival of life on Earth.
And brother, let me tell you: extinctions reduce diversity. Don’t get me wrong — extinctions are inevitable. It’s how the various kingdoms of life on Earth adapt to changing conditions. It’s when extinctions occur rapidly and not in response to changes in nature but to pressure from humans — that’s the kind of extinction that should be avoided.
This particular story is an example of where a persistent manmade chemical that is remarkably deadly to some species while causing little harm to others, can be taken up by a few low-trophic level species and then other higher level species, causing odd effects that may be unrelated to its chemical toxicity, until yet another species, that not only has little to no vulnerability to the contaminant, but may never even have been exposed to it, could be brought to the brink of extinction because of that chemical compound — a compound to which it likely never was exposed.
Clear enough? OK then — let’s get started.
Introduction to the Island Fox
The picture at the head of this story depicts an Island Fox (Urocyon littoralis). These little foxes live on the Channel Islands, an archipelago of eight islands west and northwest of Los Angeles.
The Island Fox is descended from the mainland gray fox, but is only about two-thirds the size of it. It’s not known how the gray fox arrived on the islands where it then evolved into the Island Fox. Some believe it rafted there from the mainland on debris, others think they may have been brought to the islands by indigenous people as pets or hunting companions thousands of year ago. Over time, the Island Fox population continued to evolve and now each of the six islands populated by the Island Fox contains its own subspecies, with minor differences in appearance and behavior between them.
Overall, they’re described as docile, easily tamed, and subsist on insects and fruit, with supplemental opportunistic consumption of small mammals such as mice, as well as lizards and eggs.
Among their other interesting traits, they have evolved the ability to rotate their paws slightly inward, allowing them to climb trees.
I’ll mention a bit more about their role in the terrestrial ecosystem of the islands they inhabit later on.
Now, about DDT...
DDT
DDT is an organochlorine pesticide: an organic compound that includes five chlorine atoms per molecule and has properties that make it useful as a pesticide.
It’s one of the first synthetic (that is, manmade) pesticides, originally having been synthesized in the late 1800s. But DDT had little use until its potent insecticidal properties were observed in the late 1930s.
DDT came into large scale production in the 1940s. It was used to control insect disease vectors during World War II. This was key, for example, to stopping a typhus epidemic in newly-liberated Naples, Italy in 1944 (by controlling infected lice) and helped facilitate the Allied advance north and the subsequent fall of Rome (by controlling malaria-carrying mosquitos in the Tiber River delta, through which Allied supply lines passed after landing at the Port of Ostia).
Over a decade before he met my Mom, my Dad was part of that movement north, after he and his company mates had been pinned down for weeks under German bombardment, having landed on the beach at Anzio.
So — it’s entirely possible I’m here today, writing this diary, because of DDT having saved Allied lives during that advance.
After all, it’s well documented across the span of history that disease is a bigger killer than weaponry during wartime; a relationship that in World War II finally was reversed, at least for American troops, because of widespread use of vaccines, antibiotics, and pesticides like DDT.
DDT’s use expanded after the war and was widely employed for agricultural purposes and general mosquito control purposes. I recall riding my Sears bike with my friends through the fog cloud behind the mosquito control truck that rolled down the tar-and-gravel roads of our housing area on the Great Plains Air Force base where our dads were stationed in the mid-1960s. Little kids aren’t the smartest people — you ever notice?
I didn’t know it at the time, of course, but a few years earlier, in 1962, Rachel Carlson broke new ground with her book Silent Spring, which warned of the dangers of widespread synthetic pesticide use. A decade after her book was published, in 1972, EPA banned most uses of DDT. Other countries followed suit. Today, DDT use is supported by the World Health Organization for indoor use only to control mosquitoes carrying malaria and sandflies carrying leishmania — consistent with the Stockholm Convention on Persistent Organic Pollutants.
Why indoor use only?
Well, that restriction is in place because of some of the negative aspects associated with DDT when it is released into the environment. DDT, like many large organic molecules, is “sticky.” It doesn’t dissolve very well in water. While some of it can evaporate and enter the atmosphere, it prefers to stick to soil and sediment, more specifically to small particles of organic carbon in soil and sediment.
That preference for absorbing to organic carbon in conjunction with its toxicity makes large synthetic molecules like DDT very persistent in the environment. While it can be degraded by bacteria in certain conditions, degradation is slow and DDT persists for decades, if not centuries or longer, when present in the environment in sufficient quantities.
You know another form of organic carbon that exists in the environment? Fats. Lipids.
It turns out that critters that ingest soil or sediment to get at microbes or the organic carbon, or plant life that grows in the soil/sediment, occupy a low trophic (feeding) level. If DDT is present in that soil or sediment, these organisms will pick up small quantities of it, where it is stored in their fat cells. As these little guys are eaten by other critters in the next trophic level, that DDT is absorbed by their fat cells too. DDT moves up the food chain to higher and higher trophic levels, with the concentration of DDT becoming greater and greater with each level. Wikipedia’s entry on DDT has a useful graphic illustrating this concept, which is called biomagnification.
That’s all well and good, but so what? Fish aren’t insects. Humans aren’t either. Why should the buildup of a pesticide like DDT be a problem?
The answer is that, like many contaminants, organisms exposed to DDT experience a dose-response relationship. Large doses, such as a worker at a plant producing or packaging DDT might experience, can cause large responses, such as nervous system effects, including dizziness, tremors, and seizures. But at the lower levels found in the environment, these kinds of effects would not occur. Instead, DDT exposure at low concentrations is linked to premature birth and DDT delivery to newborns via the essential fats in breast milk. Liver enzyme effects have been noted in the blood of exposed people and animals, and there also is an observed link to liver cancer. Accordingly, EPA has classified DDT as a probable human carcinogen. In short, DDT is not a good actor in the environment.
But let’s get back to our little fox, shall we?
DDT and the Island Fox
You might be wondering how DDT came to be in a place where it could end up affecting the Island Fox. Was it dumped on the islands?
Nope. I know of no evidence of that. In fact, it’s entirely possible that the Island Fox never was directly exposed to DDT at all.
Here’s how it worked. There was a large DDT manufacturer in the Los Angeles area called Montrose Chemical Corporation, located near Torrance. Montrose discharged wastewater to the LA County sewer system, and some of that wastewater contained DDT. It flowed through the treatment system (which was designed to remove turds but not DDT) and on to a l-o-n-g discharge outfall (White Point) far out into the ocean. EPA estimates that, from the late 1950s through the early 1970s, about 1,700 tons of DDT were discharged through this system. This would have been at the same time as Frankie Avalon and Annette Funicello were frolicking nearby in Beach Blanket Bingo and the Beach Boys were singing about California Girls.
Montrose’s discharge of wastewater to the LA County sewers created a vast area of DDT contamination in marine sediment that ultimately became known as the Palos Verdes Shelf, Operable Unit 5 of the Montrose Chemical Corporation Superfund Site.
(Side comment: I know I promised no politics, but I’ve been using EPA databases, records, documents, and hotlines for 40 years. I really hate the changes in EPA’s Internet-based resources that were implemented in early 2017 under the Trump Administration. If they were trying to hide information and make it difficult to find, they could hardly have done it more effectively. Thanks Pruitt. Thanks Trump)
Investigative work done in the 1980s that only recently has come to the attention of the general public, thanks to recent reporting by the LA Times, shows that not only was DDT waste discharged through the LA County sewers to the ocean but it’s now known that barges loaded with thousands of steel drums, or “barrels” of DDT production waste were dumped directly into the ocean.
From the LA Times article on the matter:
As many as half a million of these barrels could still be underwater right now, according to interviews and a Times review of historical records, manifests and undigitized research. From 1947 to 1982, the nation’s largest manufacturer of DDT — a pesticide so powerful that it poisoned birds and fish — was based in Los Angeles.
An epic Superfund battle later exposed the company’s disposal of toxic waste through sewage pipes that poured into the ocean — but all the DDT that was barged out to sea drew comparatively little attention.
Shipping logs show that every month in the years after World War II, thousands of barrels of acid sludge laced with this synthetic chemical were boated out to a site near Catalina and dumped into the deep ocean — so vast that, according to common wisdom at the time, it would dilute even the most dangerous poisons.
emphasis mine
In case you were worried that there’s a ticking time bomb of DDT waste currently ensconced within intact drums offshore of Los Angeles threatening to slowly corrode in salt water and eventually, at some point in the future, that DDT may leak out, well, you needn’t worry.
You see, the documents indicate they intentionally punctured the drums before they dumped them to make extra-sure their contents would leak out and be blissfully diluted by the vast waters of the Pacific Ocean. In other words, that particular horse has left the barn. The camel already is in the tent.
So, if you’ve been following this narrative thus far, you would know that, once DDT was discharged to the ocean, small aquatic creatures would take up the DDT as they lived their short lives, and they would be eaten by larger critters, and those guys by larger ones, until DDT rose up the food chain to the top predators, such as humans.
And, as it turns out, eagles. Bald Eagles specifically.
What in the heck does a Bald Eagle have to do with the Island Fox?
Quite a bit, actually.
Bald Eagles are an opportunistic predator. They’ll eat mammals, reptiles and carrion, but they especially like fish; usually over half their diet consists of fish. They’re also large and aggressive birds, capable of defending their range from other competing birds. Despite being much larger than the Island Fox, Bald Eagles don’t prey on them. They tend to go for the fish and carrion. It’s just how they roll.
For millennia these two predators co-existed on the Channel Islands. The Bald Eagle was the apex avian predator of carrion and aquatic life, and the Island Fox, despite its diminutive size, was the largest mammalian predator in the terrestrial ecosystem of the Channel Islands.
All was well.
Actually, no. It wasn’t. Alien species were introduced to the Channel Islands by humans. Pigs, goats, and sheep were brought to the islands by farmers. Some escaped and became feral, affecting the habitat in which the Island Fox lived and competing with the fox for food.
Keeping in mind this is California and Hollywood was just across the way, another non-native species brought to one of the islands, Santa Catalina Island specifically, was American bison, 14 of them, in fact. They were extras for a 1924 western. And, in true Hollywood fashion, their footage reportedly ended up on the cutting room floor and did not appear in the final print of the film. Tough luck, kiddos. You coulda been stars.
Even the pet or working dogs visitors brought with them carried diseases and parasites that harmed the heretofore isolated Island Fox. For example, canine distemper, brought to Santa Catalina Island in the 1990s by humans who visited the island in the company of their dogs, killed 90 percent of that island’s foxes in a 1998 outbreak.
So, in all truthfulness, not all was perfectly well. But what really set the table for disaster was DDT.
DDT and Eagles
It’s a well-known story. The fish that Bald Eagles in the Channel Islands prefer in their diet are known to contain DDT because unfortunately they were born, grew, and lived their lives within an aquatic food chain that contains DDT, thanks to we humans.
The DDT doesn’t exactly poison Bald Eagles, but it affects the way eagles process calcium, resulting in thin, brittle egg shells that crush under the weight of a brooding adult eagle. This has a drastic negative effect on reproductive success. With fewer and fewer eaglets to replace them, the Bald Eagles controlling the skies over the Channel Islands dwindled in number and eventually disappeared.
Gone.
Now, nature, as they say, abhors a vacuum, and the disappearance of the Bald Eagle over the Channel Islands left a niche that another bird eagerly exploited: the Golden Eagle.
Until they disappeared, Bald Eagles defended their range over the Channel Islands, keeping Golden Eagles away. Though the two birds are similar in size, Golden Eagles evidently did not pose a serious challenge to Bald Eagles in the islands.
But with Bald Eagles gone, of course Golden Eagles encroached. It’s nature’s way.
You may wonder: why weren’t they similarly decimated by DDT?
The answer has to do with diet.
Whereas Bald Eagles prefer fish, Golden Eagles prefer terrestrial prey: mammals, reptiles, even other birds. Consequently, DDT in the aquatic food chain had little effect on Golden Eagles.
Can you guess another terrestrial species the Golden Eagle began to prey upon once arriving in the Channel Islands?
That would be the Island Fox, which was about one-fourth the size of any self-respecting adult Golden Eagle.
Under stress from invasive species, from habitat changes those invaders caused, and from diseases introduced by visiting dogs, the fox faced what seemed to be its final challenge without its longstanding air defenses in place. With the Bald Eagle gone, the Island Fox had no protection from Golden Eagle predation.
Now, this wasn’t an immediate cause-and-effect. Nature is more complicated than that.
After all, the Bald Eagles began disappearing in the 1950s shortly after DDT deposition into the area’s waters began. And while Golden Eagles started moving into the island’s ecosystem way back then, they were uncommon visitors until the 1990s. Consequently, they didn’t take enough Island Foxes through predation to be a major problem until decades after the Bald Eagles declined.
Part of the reason for that is that when Golden Eagles arrived, they found two good-sized mammals that were active during daylight hunting hours to dine upon on the Channel Islands. One, yes, was the Island Fox, but the other was the tasty feral pig (or more specifically, feral piglets). Because pigs produce a large number of piglets annually, are capable of producing offspring year-round, and are only susceptible to predation until they grow too large to be taken by eagles, they were able to sustain the losses from predation while still thriving.
The fox, on the other hand, has comparatively low fertility, litters are small, and, unlike pigs, the Island Fox never grows to a size large enough to resist predation by Golden Eagles.
And so the situation existed: the Golden Eagles were living large, the pigs were doing well, and the Island Fox was dwindling in numbers over time.
Clearly, something had to be done.
A tough situation, but to really screw things up you need to bring in the humans
Well intentioned wildlife scientists of the National Park Service had an idea. Their field surveys told them that Golden Eagles were killing and eating a lot of piglets. And, while such abundant food was available the eagles would keep coming, with some nesting on the islands.
They reasoned that eradicating the feral pig population would discourage Golden Eagles from staying, which would provide a double benefit to the Island Fox because of less competition (from pigs) and less predation (from eagles that no longer would come and stay to eat the pigs).
Makes sense right?
Well, that plan was first tested on Santa Rosa Island in 1991, according to the controversial former Director of Channel Island National Park, Tim Setnicka.
Let’s see how the foxes did in the decade between 1994 and 2004:
Well, talk about unintended consequences, eh? Seems that just killing the pigs won’t do.
It turns out that the model of feral piglets luring Golden Eagles to the islands where they also hunted Island Foxes was a little too simplistic. Remember what I wrote at the beginning of this overlong story? Here it is:
...the webs of nature are complex and often are only poorly understood
What happened on the Channel Islands has been the subject of considerable study. The prevailing hypothesis seems to be that, while the invasive pigs did indeed cause habitat changes that disadvantaged foxes, their abundant piglets also provided a considerable quantity of food for recently-arrived Golden Eagles.
As long as piglets were available in quantity, foxes, while suffering some predation, were declining fairly slowly in population.
Remove the pigs, as was done on Santa Rosa, and there’s little for a hungry eagle to do but hunt and hunt and hunt Island Foxes.
And that’s what they did.
It gets better
A more holistic plan was needed, and that’s what was implemented beginning in 1999. Here’s how the National Park Service describes the plan:
In 1999, Channel Islands National Park began an island fox recovery program that included captive breeding and reintroduction of foxes, removal of resident golden eagles, re-establishment of bald eagles, and removal of non-native ungulates.
Ungulates would collectively include goats, sheep, and pigs, but it was the pigs that were the focus since foxes don’t graze on grasses to any great extent, unlike sheep and goats. Feral pig eradication on the islands was completed in 2007, under a controversial program involving a contractor from New Zealand.
Because the new and improved program didn’t just involve pig eradication but also focused on helping foxes breed and involved re-introducing their air defenses (i.e., the Bald Eagle), things have improved. Take a look:
Now, some of you may wonder, with all that DDT still lurking in the sediment at Palos Verdes Shelf why won’t this problem just re-occur? After all, the DDT is still there.
It’s possible, but in my opinion unlikely. Because DDT in wastewater discharge is much lower to nearly nonexistent compared to that occurrring in the 1950s and 1960s, there’s much less DDT loading to the aquatic system. It’s not zero — there still are low levels of DDT in storm water, for example, from erosion of soil and organic carbon that have DDT residues from historical uses in upland landscapes.
And the DDT in sediment, while still there, is slowly being buried by more recent, “cleaner” (with respect to DDT concentration) sediments. This process, called natural recovery by EPA, can (in certain favorable situations) be an important part of dealing with difficult, widespread contamination problems that may be financially infeasible to fully address by more active remediation approaches.
So disaster appears to have been averted. With care and monitoring, the Island Fox and Bald Eagle may continue to be the top predators in their respective areas of activity for the foreseeable future.
You can check out highlights from the Fraser Point Eagle Cam on Santa Cruz Island below: