cetaceans (in captivity). For the most part, deaths of marine mammals go 

 unobserved. In both cetaceans and pinnipeds the most debilitating bacterial 

 disorders seem to be lung infections, like pneumonia. These are common but 

 usually occur as a secondary infection in the wake of some other disability, 

 mechanical injury, or parasitism, which lowers the animal's resistance (Katona 

 et al. 1977). 



Marine mammals are also afflicted by a variety of degenerative and deficiency 

 diseases, including eye failure, cardiovascular disease, ulcers, hepatic and 

 renal dysfunction, vitamin deficiencies, stress, metabolic disorders, and a 

 broad range of developmental abnormalities. 



Internal and external parasites are common in marine mammals. Cetaceans, in 

 particular, are known to host certain parasitic barnacles, lice, and lampreys. 

 Internal parasites are dominated by nematodes, which invade the respiratory, 

 cardiovascular, gastrointestinal, and cranial systems. Examples include 

 lungworm, tapeworm, heartworm (specific to harbor seals), and flukes. 

 Parasitism is not usually a clinical problem. Most strong, healthy animals 

 tolerate the parasites. Young, old, or otherwise debilitated animals may be 

 sensitive to excessive infestations and may die from them. 



A seal parasite of particular concern is the nematode Porrocaecum decipiens 

 (codworm). The adult codworm is found in the gastrointestinal tract of harbor 

 seals, gray seals, and harp seals. Its life cycle is not known completely. 

 Its eggs may hatch in the sea and the larvae invade an intermediate 

 (invertebrate) host, which may be eaten by a fish. The larval codworm burrow 

 into the flesh of many groundf ishes , including cod. Large infestations do not 

 necessarily affect the health or nutrition of fish but may render it 

 undesirable and unmarketable. Improperly frozen or cooked fish can be a 

 health hazard to people; the codworm can invade the human gastrointestinal 

 system. Areas of codworm infestation in groundfish have been correlated with 

 high abundance of gray seals in European waters (Piatt 1975 and Young 1972) 

 and with the distribution of harbor seals and gray seals in eastern Canada 

 (Scott and Martin 1957). Mansfield (1968) estimated that harbor, gray, and 

 harp seals accounted for 2%, 45%, and 53°/ respectively of the codworm 

 infestation in the Gulf of St. Lawrence. Presently, codworm is not a problem 

 in most New England fisheries but appears to be more common in eastern Maine. 

 It is unknown what effect on fisheries would result from increased numbers of 

 gray and harbor seals in coastal Maine. 



Predation 



In addition to people, sharks and killer whales are natural predators on 

 marine mammals in the wild. Predation on orphaned harbor seal pups (which are 

 unlikely to survive anyway) by black-backed gulls and ospreys has been 

 observed (Richardson 1978) . Data on the magnitude of predation exclusive of 

 hunting and its effect on the natural populations of marine mammals are 

 lacking. Hunting is discussed below under "Importance to Humanity." 



Pollutants 



Since aquatic media are the eventual sinks for most types of pollutants, 

 contaminants in the oceans and estuaries have posed serious problems to many 

 forms of aquatic life. Marine mammals have been exposed to these pollutants 



13-15 



10-80 



