Hawaiian monk seals, which are critically endangered, inhabit the Papahānaumokuākea Marine National Monument and the Hawaiian Islands. For the first time we have identified the algal toxin ciguatoxin, the cause of ciguatera fish poisoning syndrome, in Hawaiian monk seals. We developed an experimental model using mice to determine the effect of ciguatoxin on seal foraging behavior. We will use the model to evaluate the potential impact of ciguatoxin on the recovery of the Hawaiian monk seal.
Why We Care
We have determined that Hawaiian monk seals, whose population is estimated at 1,100–1,200, are exposed to significant levels of ciguatoxin. Ciguatoxin is produced by marine algae (e.g., Gambierdiscus toxicus) common on coral reefs and accumulates in fish species that are then consumed by marine mammals and humans. Ciguatera fish poisoning, the human disease caused by ciguatoxin, affects thousands of people every year worldwide in the form of acute gastrointestinal and neurological illness with persistent symptoms resembling chronic fatigue syndrome. Ciguatoxin can similarly poison seals and could pose management challenges for Hawaiian monk seals, whose population has been dwindling at four percent annually due to poor foraging success and additional environmental and human factors.
What We Did
Working with the Hawaiian Monk Seal Research Program, monk seals were sampled throughout the Hawaiian Islands, including in the Papahanaumokuakea Marine National Monument (PMNM). We developed methods to detect the presence of toxin in blood, and used analytical chemistry techniques to identify the chemical signature for Pacific ciguatoxin (ciguatoxin conger 3C). This represented the first identification of ciguatoxin in any marine mammal, and was present in the blood of 19 percent of 53 monk seals ranging across the entire Hawaiian archipelago.
The amount of toxin found in blood was comparable to that which would elicit toxic symptoms in a laboratory rat. Next, we conducted toxicokinetic modeling (how fast a chemical enters an animal and what happens to it when inside) in laboratory rats and determined that 75 percent of the toxin in a meal is absorbed and has a mean residence time in blood of 82 hours. This research indicates that Hawaiian monk seals are exposed to significant levels of ciguatoxins that could pose a threat to their recovery from being a critically endangered species.
To address the extent of ciguatoxin exposure in Hawaiian monk seals, we are developing new methods to analyze a large data set of monk seal dried blood specimens that have been archived over the last decade on blood collection cards. This will allow a spatial and temporal understanding of the Hawaiian monk seal exposure to ciguatoxin.
To address the potential impact of ciguatoxin exposure on Hawaiian monk seal foraging behavior, we have developed a mouse model to determine the effect of ciguatoxin on foraging behavior, and will work in conjunction with the NMFS Monk Seal Foraging Program to see how ciguatoxin exposure interacts with the stress of competing predators to affect feeding success in juvenile monk seals.