Related to my recent posts, it looks like the marine mammal die-offs in the Pacific continue. A new story reports a die-off of right whales off Argentina. As with the sea lion die-off off Central California, a shortage of food (this time copepods) and possibly marine toxins are implicated.
Information sent today from Promed-Mail indicates that domoic acid is indeed implicated in the sea-lion die-off in California. Domoic acid is a neurotoxin produced by certain algal blooms that can bioaccumulate as it moves up trophic chains. Fisheries and Oceans Canada has a terrific resource page with extensive references on domoic acid. The report on the die-off comes from Southern California via the Ventura County Star, but it seems likely that it is related to the Central California die-off I wrote about last week. Also implicated — as I suggested last week — is a shortage in fish resulting from the El Niño warmed Pacific waters.
I just read this story about the alarming number of dead sea lions showing up around Monterey Bay in Central California. We were just down at Moss Landing State Beach and saw for ourselves evidence of this die-off. The sea lion had a couple of bites taken out of it but its unclear whether they were pre- or post-mortem.
A likely candidate for the cause of this excess mortality is food shortages due to unusually warm waters from the recent El Niño conditions, though no one has yet (to my knowledge) ruled out infectious disease, domoic acid, red tide, or any of the other possible causes of such die-offs.
Crocodiles have been dying in large numbers on the Olifants River in Kruger National Park, the crown jewel of the South African Parks System. The article rather casually states that the die-off is attributable to environmental pollutants:
There is growing consensus that the croc die-off is a result of a confluence of low level toxins, which has lead to endocrinal [sic] abnormalities (that is, hormonal changes) in croc tissues.
As the moderator for the promedmail wrote, however, it would be nice to have some specific details explaining why this consensus is apparently growing:
The article does not specify chemicals, pesticides, or heavy metals, or their amounts, yet the article boldly states, “Long term exposure to these and other toxins may well be conspiring towards the crippling condition suffered by Olifants River crocodiles.” So apparently, the specifics of the chemicals, pesticides and/or heavy metals are known. It would be much more beneficial to publish what has been found and the levels of those alleged toxins, then those doing research or having experience in the area would be able to suggest a possible solution.
It certainly seems possible, particularly given the diversion of water from the Olifants River and from new mining operations in Mozambique, but it would still be nice to have some more details. One of the striking features of the dead crocs is the fact that they have hardened yellow fat deposits in their tails. The article suggests that cause of death is pansteatitis, a disease caused by excessive consumption of unstabilized polyunsaturated fatty acids (often found in rotting fish). There is no evidence of correspondingly large fish die-off, which could complete the causal story. How the environmental contamination story fits in with pansteatitis seems an important missing link in understanding this problem.
Cattle that eat threadleaf groundsel can die of a disease that induces hard yellow liver, providing more suggestive evidence that an environmental poison might be responsible for the croc die-off. Maybe…?
This is a disturbing story, the resolution of which I will follow closely.