[MARMAM] Hemochromatosis in captive dolphins
naomi at awionline.org
Fri Sep 11 16:37:02 PDT 2015
A recent paper (Mazzaro et al. 2012) has come to my attention, regarding iron indices in dolphins:
The authors conclude that “Compared with those in managed collections, wild dolphins were 15 times more likely to have low serum iron (100 μg/dL or less), and this measure was associated with lower haptoglobin. In conclusion, bottlenose dolphins in managed collections are more likely to have greater iron stores than are free-ranging dolphins.” In addition, the authors note that a “25-y retrospective study of one population [the dolphins in the Navy Marine Mammal Program] demonstrated that 67% of dolphins [who had died] had excessive hepatic hemosiderin deposition at time of death, 92% of which had hemosiderin deposition in Kupffer cells; hemolytic anemia, anemia of chronic disease, and viral infections were not associated with hemosiderin deposition, and the primary hypothesis is that dolphins in managed collections may be susceptible to iron storage disease,” and “A total of 25% (28 of 115) of samples [from living dolphins] from managed collections had high serum iron (exceeding 300 μg/dL).” They point out that “determining why this situation occurs among some dolphin populations [presumably those in captivity] and not others [presumably those in the wild] may improve the treatment of hemochromatosis in dolphins.”
I was unaware of the prevalence of hemochromatosis and related indices in captive dolphins until some days ago, when it was brought to my attention that two dolphins in a facility in Finland are suffering from the disease. Mazzaro et al. (2012) conclude that the “primary hypothesis” is that captive dolphins may be more susceptible to the disease, but from my perspective, that hypothesis seems to be supported by the data in Mazzaro et al. (2012) itself (which looked at two separate captive populations, as well as two separate free-ranging populations). The next step, therefore, would be to consider hypotheses as to why captive dolphins are more susceptible to this disease than free-ranging dolphins – and also to ask the question of whether cetacean species other than bottlenose dolphins (in captivity or free-ranging) are susceptible to the disease or its related indices.
I have inquired with colleagues on this point and apparently no one is yet looking into these questions. There is some research ongoing with free-ranging dolphins regarding numerous health issues (including conditions related to iron indices) that may be associated with or exacerbated by climate change, oil spills and so on, but no one appears to be looking into the question as to why such a large percentage of captive dolphins suffer from some degree of hemochromatosis, a disease that can lead to diabetes, chronic pain, organ failure, etc. I know of at least one instance where a captive dolphin was euthanized as a result of suffering from hemochromatosis.
The first idea I had was that the inability of captive dolphins to dive deeply and the general lack of the need to breath-hold might make iron-based adaptations to breath-holding (i.e., greater amounts of hemoglobin and myoglobin) a liability in captivity, in terms of contributing to excessive iron loads. The fact that phlebotomy appears to be a relatively successful treatment for hemochromatosis in captive dolphins seems to bear this idea out. I am not a physiologist, but regardless of the likelihood of that etiology, it seems that this relatively recent discovery of what amounts to a significant welfare concern for captive dolphins should be a primary research question among public display facilities holding cetaceans. I am concerned that this does not appear to be the case and would welcome feedback from the marine mammal community, including anyone who can point me to evidence that I am wrong about the lack of ongoing research into this question.
NAOMI A. ROSE, PH.D.
Marine Mammal Scientist
ANIMAL WELFARE INSTITUTE
900 Pennsylvania Ave., SE
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