Table 4. — Comparison of total mercury content (ppm) of dorsal muscle tissue with size of swordfish caught in different 



areas. 



Size 



Total mercury content 



*Significant at 0.90 level. 

 ♦♦Significant at 0.95 level. 



7" for 



average mercury level in area C between the July 

 and October samples for fish of essentially the same 

 size. Swordfish from area B (Cape Hatteras to Hy- 

 drographer Canyon) were considerably smaller (av- 

 erage 129 cm) than fish taken in other areas. This 

 size difference may also account, at least in part, for 

 the lowest average mercury level (0.57 ppm) being 

 encountered in area B. 



Variation of Mercury Content 

 Between Tissues 



The total mercury content of the various tissues 

 sampled from swordfish is shown in Table 6. Gener- 

 ally red muscle, liver, kidney, and heart contained 

 higher levels of total mercury than dorsal muscle 

 while other tissues contained less. 



The mercury content of the various tissues was 

 examined by area and time of capture in the same 

 manner as for the dorsal muscle samples. When 

 these data were expressed (Table 7) as proportion 

 (percentages) of the dorsal muscle values, most tis- 

 sues showed relatively little variation, with the ex- 

 ception of the liver and kidney values. The mercury 

 content of the latter two tissues ranged from about 

 the same as that of the dorsal muscle (areas C and D) 

 to approximately twice that level (areas A, B, and 

 E). The elevated average levels in kidney and liver 

 from area E were due to one large fish which had a 

 mercury content in these tissues of over three times 



that of the dorsal muscle. The elevated levels for 

 areas A and B are shown by all specimens, however, 

 and appear to be characteristic. These elevated 

 levels suggest that mercury was either being more 

 rapidly eliminated from the body in areas A and B, or 

 likely was being taken up in greater quantities from 

 the environment. The average mercury level (Table 

 4) in dorsal muscle from area A was considerably 

 higher (2.02 ppm) than from any other area, but that 

 from area B was the lowest (0.857 ppm). However, it 

 has already been noted that area B fish were much 

 smaller than fish from other areas and Table 4 also 

 indicates that the relation between size and mercury 

 content (slope of regression line 0.009671) in area B 

 was steeper than elsewhere, so that larger fish would 

 presumably have shown high levels similar to those 

 from area A. 



Mercury Levels in Food Items 



Food organisms collected from swordfish 

 stomachs and analyzed for the total mercury content 

 (Table 3) all show fairly high values (average 0. 14-0.3 

 ppm for each species); although the possible con- 

 tribution of mercury from the digestive juices of the 

 predator cannot be ignored . The relatively high mer- 

 cury content of redfish (0.34 ppm) may be of signifi- 

 cance in considering the high values in the liver and 

 kidney obtained from one large swordfish (212 cm) 

 caught in area E (Grand Banks). Redfish form a 



157 



