PETERSON, KLAWE, and SHARP: MERCURY IN TUNAS 



that this variation was inconsistent among 

 the species examined, e.g., mercury concentra- 

 tion in some species was highest in the northern 

 area while for other species from the same 

 area it was lowest. 



A proper understanding of the cause(s) of 

 geographic variations in mercury levels of 

 fishes is confounded by the possibility that a 

 complex of factors may be involved. For 

 example, Beckett and Freeman (in press) in 

 a study of 210 swordfish from six areas extend- 

 ing from the Caribbean Sea to the Grand Banks 

 found that the average mercury level of this 

 species varied significantly from area to area. 

 They suggested that this variation may be 

 related to (1) the passage of time, i.e., the 

 mercury content appeared to decrease with 

 time in the northern part of the area of 

 investigation; (2) a higher rate of mercury 

 uptake and/or excretion in the southern areas; 

 (3) differences in size composition of swordfish 

 among areas; and (4) the occurrence of forage 

 fishes of high mercury content near the Grand 

 Banks. 



Furthermore, Forrester et al. (1972), in a 

 study of about 200 spiny dogfish from four 

 areas in the Strait of Georgia, British Columbia, 

 found differences in mercury content of this 

 species among areas. Mercury level was highest 

 in the Point Grey — U.S. Border area. The 

 authors suggest that contamination by effluents 

 from industrial plants along the Fraser River 

 and its estuary may be a contributing factor. 

 They go on to point out that "The differences 

 in mercury content among areas suggest that 

 dogfish in Georgia Strait are not a homogeneous 

 stock or, if they are, that mercury uptake is 

 very rapid." The authors also state that "If 

 uptake is rapid the extreme variation in mercury 

 content for dogfish of a given length may indi- 

 cate time spent by various fish in the region of 

 apparent high mercury contamination. On the 

 other hand, there may be large differences in 

 growth rates among individuals, reflecting dif- 

 ferences in accumulation with time." 



Finally, it is interesting to note that mercury 

 levels in Aldrovandia macrochir, a benthopelagic 

 fish captured off the U.S. Atlantic coast, were 

 about an order of magnitude lower than those 

 of several other benthopelagic fishes — macrou- 



rids and morids {Aiitimora rostmta, Bathy- 

 saurus agassizi, Chalimira brevibarbis, and 

 C. carapiiia) — from the same area-time stratum 

 and of about the same average length, even 

 though their feeding habits and ecological re- 

 quirements appear to be very similar (Barber 

 et al., 1972). The authors suggest the existence 

 of fundamental metabolic differences to account 

 for the great differences in mercury concentra- 

 tion. 



We were unable to find any published data 

 on geographical variations in the mercury levels 

 of tunas, but it is reasonable to suppose that 

 they do occur in view of (1) the geographic 

 variation of mercury concentrations in seawater 

 (Weiss et al., 1972); (2) the geographic exposure 

 of tunas — they are known to occur in all of 

 the major temperate and tropical oceans of the 

 world, and some species migrate many thou- 

 sands of miles; and (3) the fact that tunas are 

 known to be quite nonselective in their feeding 

 habits (Alverson, 1963). 



MERCURY CONTAMINATION 

 AND TOXICOLOGY 



As stated earlier, although mercury has been 

 present in our environment since the begin- 

 ning of time, there are indications that man 

 has been adding significant amounts of this 

 metal to the atmosphere, land, and waters. An 

 analysis of mercury in ice in Greenland has 

 revealed a substantial increase in deposition 

 since 1940 (Weiss, Koide, and Goldberg, 1971). 

 In Sweden, concentrations of mercury in bird 

 feathers were measured, and it was found that 

 mercury levels were low in museum specimens 

 of fish-eating birds collected from 1840 to 

 1880-90. In the years following, the level has 

 been continuously on the rise. An analysis of 

 seed-eating birds and birds which prey upon 

 them did not show a corresponding rise in 

 levels of mercury until 1946 (Berg et al., 1966). 

 The increase in mercury in the fish-eating 

 birds has been associated with the period when 

 Sweden started to industrialize whereas the 

 marked increase in the seed-eating birds and 

 terrestrial birds of prey has been related to the 

 introduction of organomercurial dressing for 



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