FISHERY BULLETIN: VOL. 86, NO. 2 



0600. Catches in this study were also low in mid- 

 day. Either this is a reflection of 2 peaks of activ- 

 ity, dawn and dusk, as is common in salmonids in 

 freshwater, or this is possibly due to salmon 

 avoiding the nets in high light levels. Thus 

 postsmolts and 1- and 2-sea-year salmon appear 

 to have a similar behavior at sea. They move in 

 small schools close to the surface and are possibly 

 more active at dusk and dawn. 



Food items in the stomachs of postsmolts 

 changed markedly in summer and indicated a low 

 diversity of prey. This is in contrast to findings 

 reported for salmon in the Northwest Atlantic. 

 Grande Trinite River postsmolts had fed mostly 

 on chironomids and gammarids in late-July. 

 Baltic salmon postsmolts fed mainly on aerial in- 

 sects though small fish and crustaceans also oc- 

 curred in the stomachs of postsmolts in the south- 

 ern Baltic (reviewed by Christensen and Larsson 

 1979). Jutila and Toivonen (1985) also found 

 aerial insects to be the dominant food items in the 

 stomachs of small postsmolts ( <20 cm) in the Gulf 

 of Bothnia (Baltic). They observed that post- 

 smolts were not selective and must have fed near 

 the surface (20 cm surface layer). Postsmolts col- 

 lected later in the present study relied mainly on 

 small sand lance. Insects and gammarids had 

 been replaced by vertically migrating crus- 

 taceans such as Meganyctiphanes noruegica 

 (Kulka et al. 1982). Thurow (1968) estimated 25 

 cm to be the length threshold for piscivorous feed- 

 ing by Baltic salmon. In the present study, this 

 size was likely reached in the first half of August 

 1982. This coincides with a major change in stom- 

 ach contents and a high percentage of stomachs 

 containing no food. The data on postsmolts in 

 July are too limited to suggest that sand lance 

 abundance could limit the early success of 

 postsmolts at sea, but potential relationships in 

 late summer should be tested as was done for 

 capelin by Reddin and Carscadden (1981). Data 

 on 1- and 2-sea-year salmon indicate they will 

 readily feed on a diversity of prey items, main 

 items including Arctic squid, Gonatus fabricii; 

 paralepids, Paralepis coregonoides ; and lantern 

 fishes (Lampenyctus sp., Notoscopelus sp.) (Tem- 

 pleman 1967, 1968; Lear 1980). Sand lance and 

 capelin are dominant items in West Greenland 

 and on the coast of Newfoundland (Lear 1972, 

 1980), and on the Grand Bank (Reddin 1985). 

 Reddin ( 1985) observed major changes in stomach 

 contents between salmon on the Grand Bank 

 (sand lance and capelin) and east of the Grand 

 Bank (Bathylagidae, Paralepis sp., and crus- 



taceans), emphasizing that salmon are not selec- 

 tive predators. 



The rate of increase in mean length averaged 

 1.65 mm/day in the Gulf of St. Lawrence over the 

 summer period in 1982 and 1983. This value is 

 based on the hypothesis that smolts migrated to 

 estuaries in mid-June. Smolt migration took 

 place in the first half of June in Restigouche River 

 in the southern Gulf of St. Lawrence (Peppar 

 1982) and in the second half of June in Grande 

 Trinite River in the northern Gulf of St. 

 Lawrence (Caron 1984). Downstream migration 

 of smolts peaked at various dates in June in West- 

 ern Arm Brook in western Newfoundland (Chad- 

 wick 1981). The calculated rate of increase is also 

 based on a mean back-calculated smolt length of 

 135 mm. Length at smoltification averaged 125- 

 130 mm in Grande Trinite River (mean and SD: 

 127.5 ± 12.3, n = 88, in 1981; 125.8 ± 10.9, 

 n = 92, in 1982; see also Caron 1984). Matamek 

 River and Moisie River smolts measured 125-150 

 mm (Schiefer 1972). They measured 150 mm in 

 Little Codroy River (Murray 1968) and 174 mm in 

 Western Arm Brook (Chadwick 1981). There are 

 no data in the literature concerning the rate of 

 increase in size of smolts and postsmolts in the 

 marine environment. Postsmolts in the Bay of 

 Fundy reached a mean length of 296 mm in mid- 

 August 1952 (Allen et al. 1972), some 3 cm more 

 than postsmolts in this study: 265 mm and 

 306 mm on 1 September and 30 September. How- 

 ever the high value of the power exponent of the 

 length-weight relationship as compared with 

 salmon in Newfoundland and Labrador (Lear 

 1973) indicates postsmolts were not in poor condi- 

 tion. There was possibly a decline in the rate of 

 increase in length in mid-summer as suggested 

 by the large proportion of scales showing a sum- 

 mer check (false-annulus) in 1983. This occurred 

 10 circuli from the smolt check in mid-summer in 

 postsmolts 20-22 cm in length, i.e., prior to this 

 study period, and may have been produced as a 

 response to a shortage of prey or to deteriorating 

 environmental conditions. Elson (1953) also no- 

 ticed the frequent occurrence of a slowing of 

 growth 6-10 circuli out from the last parr an- 

 nulus. The percentage of occurrence of the check 

 varied between locations (1982) and between 

 years (1982 < 1983 < 1984). Therefore it is not 

 likely to be a response to a change in postsmolt 

 biology such as a scheduled shift in prey selection. 

 However, the summer check can be thought of as 

 a potential tool for stock discrimination. Some 

 26-32 circuli are formed before the first sea an- 



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