Table 3. — Total mercury (ppm) in food species taken from stomachs of swordfish. 



Specimens 



Number Total mercury content Dietary importance 

 sampled (ppm) 



Stromateidae (Butteifishes) 



Centrolophus niger (Black Ruff) 

 Stomiatidae (Scaled dragonfishes) 



Stomias boa (Boa dragonfish) 

 Myctophidae (Lanternfishes) 

 Paralepididae (Barracudinas) 

 Alepisauridae (Lancetfishes) 



Alepisaurus ferox (Longnose lancetfish) 

 Nemichthyidae (Snipe eels) 



Nemichthys scolopaceus (Slender snipe eels) 

 Gadidae (Cods) 



Merluccius bilinearis (Silver hake) 

 Carangidae (Jacks) 

 Scombridae (Mackerels) 



Scomber scombrus (Atlantic mackerel) 

 Scorpaenidae (Scorpionfishes) 



Sebastes marinus (Redfish) 

 Monacanthidiae (Filefishes) 

 Cephalopoda (Squids) 



Ilex illecebrosus (Shortfinned squids) 



2 



0.14 



Occasional 



1 



0.17 



Occasional 



15 



0.24 



Important 



36 



0.20 



Important 



2 



0.41 



Occasional 



4 



0.24 



Occasional 



9 



0.17 



Locally important 



2 



0.13 



Occasional 



73 



0.17 



Bait 



14 



0.34 



Locally important 



14 



0.21 



Occasional 



63 



0.31 



Important 



Variation Between Sexes 



Female swordfish predominated in all catches 

 from the northern parts of the range in the northwest 

 Atlantic: only 21 of the 193 fish caught in areas B, C, 

 D. and E were males. Mercury levels offish of the 

 same size from the same area may differ between the 

 sexes. The data for areas A, D, and E, which were 

 the areas where most of the males were caught, are 

 given in Table 5. The results are conflicting: In area 



Canada // -^C r^_ 



1wj x 



Browns St _ 



U.S.A. O^c^S"^ 



s^f ' C *•* 



B 



Includes Caribbean 



Figure 1. — Map of Northwest Atlantic Ocean showing 

 areas of capture of swordfish used for mercury analysis. 



A, males, on the average, contained higher levels 

 than females of the same size; in area D, similar 

 levels were found in both sexes for fish of the same 

 average size : and in area E, similar levels were found 

 but the males, on average, were smaller. Should the 

 tendency for higher levels in males be confirmed, 

 this may be due to a slower growth rate, and hence 

 greater age at a given size. 



Owing to the small sample sizes and the low rela- 

 tive numbers of males except in area A, the sexes 

 were combined for subsequent discussion. 



Variation with Time and Area 



The localities sampled are listed chronologically 

 in Table 4, with area C (Georges Bank) repeated 

 since it was fished twice (July and October). Gener- 

 ally, the average total mercury content of the dorsal 

 muscle decreased with time. The only exception was 

 the average for fish from area E (Grand Banks), 

 which was higher ( 1 .42 ppm) than the average in any 

 other northern area (B, C, or D) either earlier or 

 later. The average size offish from area E, at 167 cm 

 fork length, was, however, considerably larger than 

 that of fish from these other areas (Table 4). Evi- 

 dence that the decrease in average mercury content 

 was a result of time rather than locality (decreasing 

 to the westward) is suggested by the reduction of the 



156 



