Deep Sea News folks aren’t exactly famous for their love of dolphins (if you haven’t read Dr. M.’s “10 reasons why dolphins are a**holes“, well, you haven’t lived!). But truth be told, our contrarian stance is more about “charisma fatigue” and a rejection of the new-agey woo-woo that seems to surround our flippered friends, than anything substantive about Tursiops (bottlenose) and other dolphin genera. When there’s science to be had, though, you can bet the #DeepSN team will be all about it. And so here I am writing about dolphins at Deep Sea News, for SCIENCE! Wonders will never cease…
Dolphins are trying to tell us something. Not in clicks and whistles, but in tissues and organs. This post has nothing to do with dolphin intelligence and interspecies communication, it’s about what happens when nature loses its complex balance of host-pathogen stability and tips over into a disease outbreak. Right now, dolphins are dying in substantial numbers along the US East Coast. Authorities call this a UME, or Unusual Mortality Event, a bland but descriptive acronym if ever there was one. A UME is a specific situation defined by the Marine Mammal Protection Act, wherein the number of dying dolphins (or any marine mammal) rises significantly above “the usual” rate. Once a UME is declared, the government frees up money for additional research and intervention to address the issue. So what exactly is the problem?
In early summer, more dead dolphins than usual began washing up on beaches in Virginia, Long Island and New Jersey. Over the course of the summer and fall, sick and dead dolphins continued washing up and eventually the strandings spread to Delaware, Maryland, North Carolina, South Carolina, Georgia and even Florida. In an average year in this region, about 300 dolphins strand but so far in 2013 there have been over 1200 (I wouldn’t be surprised if we hit 1400 by EoY). This extensive geographic range includes several different dolphin stocks, both coastal resident animals and more migratory stocks that move over great distances in open waters. Dolphins are still washing up at the time of writing, and this UME has become one of if not the biggest dolphin UME ever.
The overwhelming majority of dolphins tested to date have been positive for cetacean morbillivirus, a virus in the same group as the human measles virus. This is a specific agent that seems to pose little risk to other animals or to people, but which is evidently lethal to dolphins. The rate of positive antibody tests from UME dolphin blood samples is a very strong circumstantial case for a morbillivirus epizootic (a large-scale disease outbreak among animals). Its unlikely that we will ever have stronger evidence than that, because to fulfill, for example, Koch’s postulates in this case would be kind of unethical!
It’s not an unprecedented epizootic, however. There was another dolphin UME on the Atlantic coast in 1987-88 that killed over 700 bottlenose dolphins, which was also (later) attributed to morbillivirus. In fact, it was that event in part that lead to the UME provisions in the Marine Mammal Protection Act in the first place.
Why do these things happen? The short answer is that we don’t really know. From a disease ecology point of view, natural ecosystems are staggeringly complex, so much so that trying to nail down a single cause is probably futile. It may be meaningless anyway, because with multiple age/size classes of multiple stocks affected in multiple habitats along an extensive stretch of coastline, the only things that may be common among all these cases could well be the host and the pathogen! Its entirely possible, indeed likely, that significant differences exist in the underlying stressors that made the dolphins susceptible to both infection by the pathogen and the disease that results when they fail to fight it off.
Perhaps the most important lesson to be learned here is simply that something is profoundly out of whack right now. Dolphins are apex predators and we know from studies like the long-running HERA project that they are excellent sentinels of coastal ocean health. They bioaccumulate toxins from lower in the food web with ruthless efficiency and, as mammals like us, they express disease in ways that resonate with human health. For example, check out this paper about multi-drug resistant E. coli in dolphins in Florida. Where do you think they got that from huh? Yep, probably us, possibly from hospital effluent.
Regarding morbilivirus, which they did NOT get from us, it may be that these epizootics are cyclical or sporadic, only time will tell. But for the next little while at least the stranding response networks on the east coast are going to be working overtime.
If you have questions about the dolphin UME, especially if you live in the affected areas and are worried about risks to your health or that of your pets, I strongly recommend this NOAA/NMFS page loaded with Frequently Asked Questions about the current outbreak.