and studies show that both cetaceans and pinnipeds may absorb them in their 

 tissues in significant amounts. Organochlorines , heavy metals, and petroleum 

 will be discussed in light of their known impacts on the ecology of marine 

 mammals. Some of these pollutants have been discovered in marine mammals at 

 higher levels than those found in any other animal. The major avenue for 

 intake of these types of pollutants is through consumption of contaminated 

 prey. There appear to be two related mechanisms for the observed accumulation 

 and concentration of organochlorine and heavy metal pollutants. Lower trophic 

 level organisms (fish and invertebrates) filter these pollutants from the 

 water or sediments and thereby concentrate them. Marine mammals feeding on 

 these fish and invertebrates incorporate the accumulated pollutants, store 

 them, and may concentrate them further. It is expected that those marine 

 mammals (toothed whales, porpoises, and seals) that feed on contaminated 

 organisms of a higher trophic level would exhibit the highest concentrations 

 of pollutants. Marine mammals, being long-lived, also would accumulate large 

 amounts of pollutants over time. 



Organochlorines. These include the pesticide compounds DDT and dieldrin 

 and other halogenated hydrocarbons, such as PCBs (polychlorinated biphenyls). 

 These manufactured compounds degrade very slowly and are extremely persistent 

 in the environment. Residues of these compounds have been found in certain 

 seals and cetaceans, probably because of their relatively high-level position 

 in the aquatic food chain and long life span. The vulnerable site of 

 organochlorine deposition and retention in marine mammals is the fatty tissue 

 of the blubber layers. Death or injury can occur when the animal's food 

 supply is cut short or it ceases feeding (e.g., during breeding and calving or 

 pupping) and the body's fat reserves are used for energy. The stored 

 toxicants are then released into the bloodstream in usually harmful 

 quantities. Equally disasterous is the conversion of the contaminated fat 

 reserves in reproduction. Katona and coworkers (1977) present a summary of 

 numerous studies reporting analyses of organochlorine residues in marine 

 mammals known to inhabit the Gulf of Maine (table 13-7). Because of the 

 migratory behavior of most of the cetaceans it is difficult to determine where 

 these animals picked up the contaminants. It is safe to assume that among the 

 harbor seals and harbor porpoises the sources are quite local. Several 

 species listed by Katona and coworkers, particularly the harbor porpoise, 

 pilot whale, harbor seal, and striped dolphin, showed very high levels of DDT 

 and PCB which may adversely affect those populations. Helle and coworkers 

 (1976) have attributed uterine occlusions in female gray seals to high PCB 

 levels. In a review of current research, Katona and coworkers (1977) 

 attributed low reproductive rates in Baltic Sea seals to heavy organochlorine 

 pollution. 



The organochlorine residue levels found in marine mammals may vary 

 considerably with local conditions, even within relatively short distances. 

 Residue amounts appear to be influenced by the level of contaminant usage in 

 the area of the hydrologic regime of the area, the diet of the animal, the 

 reproductive state, age and, in some cases, sex of the individual. Gaskin and 

 coworkers (1976) noted that harbor porpoises from the Bay of Fundy region had 

 significantly higher DDT levels than those sampled from St. Mary's Bay (Nova 

 Scotia, Canada) and Rhode Island. Possible reasons for this include: (1) DDT 

 is concentrated in the Bay of Fundy because of runoff from New Brunswick 

 streams, which drain areas of heavy DDT use; (2) the mixing and upwelling in 

 the mouth of the Bay of Fundy stimulates remixing and resuspension of sediment 



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