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Marine Mammal Physiology: Requisites for Ocean Living
degradation of the environment they live. Many contaminants bioaccumulate in the food
sources of marine mammals. These immunosuppressive chemicals are stored in marine
mammal blubber and tissues, often having a negative impact on the overall health of the
individual, and on the population as a whole.
13.7.1 Population example: Neoplasia
Neoplasia is rare in marine mammals, except for two distinct populations: beluga whales
living in St. Lawrence estuary in Canada, and California sea lions along the California
coast. Belugas living in the highly polluted St. Lawrence Estuary have a high prevalence
of cancer, as well as high levels of PCBs in their tissues. Tumors were found in 27% of
the dead belugas studied from this estuary between 1983 and 1999 (Martineau et al. 2002).
In California sea lions, 18% of stranded adults along the central California coast are diagnosed with urogenital carcinoma, the highest among a pinniped species. Three factors are
known to play a role in the development of cancer in this species: (1) presence of otarine
herpesvirus-1, which has been found in 100% of tumors tested; (2) immunosuppressive
contaminants such as PCBs, which are frequently elevated in tissues from animals with
urogenital carcinoma; and (3) a genetic predisposition, as sea lions with cancer appear to be
more genetically similar than those without cancer (Gulland et al. 1996; Ylitalo et al. 2005).
13.7.2 Population example: Viral infections
Morbillivirus is a genus that includes measles, canine distemper virus, rinderpest virus,
and marine morbilliviruses. Marine morbilliviruses, including phocine distemper virus
(PDV) and the cetacean morbilliviruses (CeMV), cause explosive outbreaks of disease
(Kennedy 1990). Morbilliviruses cause immunosuppression, and after they debilitate an
animal, secondary infections such as fungal or bacterial disease are often seen. In addition, high contaminant levels have been associated with animals infected with morbillivirus, suggesting that the immunosuppression caused by a high contaminant load could
make animals even more susceptible to infection (Hall et al. 1992). Animals that survive
the outbreak do have immunity for the virus, but it does not last for the lifetime of the
animal. As immunity wanes, and younger animals that are unexposed enter the population, a threshold is reached that allows the population to be susceptible to a large outbreak.
Outbreaks of marine morbilliviruses killed an estimated 18,000 harbor seals in Europe
in 1988, several thousand striped dolphins (Stenella coeruleoalba) in the Mediterranean from
1990 to 1992, and two outbreaks in 1987 to 1988 and 2013 to 2014 on the U.S. Atlantic coast
have killed more than 2500 bottlenose dolphins combined (Kennedy 1990; Aguilar and
Raga 1993; Lipscomb et al. 1994). Such large numbers have the potential to severely affect a
population, especially if that population is small and relatively isolated.
13.8 Difficulties of diagnosis
Veterinarians use many of the same techniques to diagnose disease in marine mammals
as they would in dogs or cats, or as a physician would diagnose disease in a human. Sterile
swabs are used to collect samples for bacterial culture; tests such as polymerase chain
reaction (PCR) and enzyme-linked immunosorbent assays (ELISAs) are used to screen for
diseases; blood tubes are used in the analysis of white and red blood cells.
These tests have caveats when used on marine mammal patients, though. Many marine
organisms are difficult to recognize, especially in a laboratory that is used to working
Marine Mammal Physiology: Requisites for Ocean Living
degradation of the environment they live. Many contaminants bioaccumulate in the food
sources of marine mammals. These immunosuppressive chemicals are stored in marine
mammal blubber and tissues, often having a negative impact on the overall health of the
individual, and on the population as a whole.
13.7.1 Population example: Neoplasia
Neoplasia is rare in marine mammals, except for two distinct populations: beluga whales
living in St. Lawrence estuary in Canada, and California sea lions along the California
coast. Belugas living in the highly polluted St. Lawrence Estuary have a high prevalence
of cancer, as well as high levels of PCBs in their tissues. Tumors were found in 27% of
the dead belugas studied from this estuary between 1983 and 1999 (Martineau et al. 2002).
In California sea lions, 18% of stranded adults along the central California coast are diagnosed with urogenital carcinoma, the highest among a pinniped species. Three factors are
known to play a role in the development of cancer in this species: (1) presence of otarine
herpesvirus-1, which has been found in 100% of tumors tested; (2) immunosuppressive
contaminants such as PCBs, which are frequently elevated in tissues from animals with
urogenital carcinoma; and (3) a genetic predisposition, as sea lions with cancer appear to be
more genetically similar than those without cancer (Gulland et al. 1996; Ylitalo et al. 2005).
13.7.2 Population example: Viral infections
Morbillivirus is a genus that includes measles, canine distemper virus, rinderpest virus,
and marine morbilliviruses. Marine morbilliviruses, including phocine distemper virus
(PDV) and the cetacean morbilliviruses (CeMV), cause explosive outbreaks of disease
(Kennedy 1990). Morbilliviruses cause immunosuppression, and after they debilitate an
animal, secondary infections such as fungal or bacterial disease are often seen. In addition, high contaminant levels have been associated with animals infected with morbillivirus, suggesting that the immunosuppression caused by a high contaminant load could
make animals even more susceptible to infection (Hall et al. 1992). Animals that survive
the outbreak do have immunity for the virus, but it does not last for the lifetime of the
animal. As immunity wanes, and younger animals that are unexposed enter the population, a threshold is reached that allows the population to be susceptible to a large outbreak.
Outbreaks of marine morbilliviruses killed an estimated 18,000 harbor seals in Europe
in 1988, several thousand striped dolphins (Stenella coeruleoalba) in the Mediterranean from
1990 to 1992, and two outbreaks in 1987 to 1988 and 2013 to 2014 on the U.S. Atlantic coast
have killed more than 2500 bottlenose dolphins combined (Kennedy 1990; Aguilar and
Raga 1993; Lipscomb et al. 1994). Such large numbers have the potential to severely affect a
population, especially if that population is small and relatively isolated.
13.8 Difficulties of diagnosis
Veterinarians use many of the same techniques to diagnose disease in marine mammals
as they would in dogs or cats, or as a physician would diagnose disease in a human. Sterile
swabs are used to collect samples for bacterial culture; tests such as polymerase chain
reaction (PCR) and enzyme-linked immunosorbent assays (ELISAs) are used to screen for
diseases; blood tubes are used in the analysis of white and red blood cells.
These tests have caveats when used on marine mammal patients, though. Many marine
organisms are difficult to recognize, especially in a laboratory that is used to working