PETERSON ET AL.: EARLY LIFE STAGES OF ATLANTIC TOMCOD 



Joouor y 



Febiuory 



Match 



Figure 5.— Similar to Figure 4 but for 1977-78. Upper panel 

 includes water levels (vertical bars). Asterisk indicates occur- 

 rence of a winter freshet, at which time drift samplers were 

 washed out. 



20 



10 - 



5 - 



C- 



lected ranged from a few hundred to a few 

 thousand per 24 h during these first 15-20 d. In 

 mid-February, stream flow rates decreased as the 

 precipitation accumulated in snow and ice. Typi- 

 cal numbers of eggs sampled/24 h during this 

 period were 10-100. Hatching occurred in March 

 and April (Figures 4, 5). Larvae began to be cap- 

 tured somewhat earlier in 1976-77 and were taken 

 in greater numbers than in 1977-78. This latter 

 phenomenon is thought to be because the sampler 

 was totally submerged in 1977-78, whereas part of 

 it was emergent in 1976-77. Larvae probably 

 emigrate into saltwater near the surface im- 

 mediately after hatching, as will be discussed in a 

 later section and may have passed over the sub- 

 merged sampler in 1977-78. Some of the earliest 

 larvae may have hatched in the samplers as a 

 result of warming on the return to the laboratory. 

 These larvae appeared normal and viable. The 

 hatching period in nature corresponded to rising 

 stream water levels in late March in 1977-78. Sea 

 surface temperatures had also risen to 3.0°-4.0° C 

 during fry emigration. Catches of larvae termi- 

 nated in early to mid- April of both years. 



The earliest stages of development obtained in 

 the drift samplers were stage 3 and 4 eggs (Figure 

 6), owing to lag from spawning to sampling. By the 

 third week of January the embryonic axis was 

 discernible in most eggs sampled. By mid- 

 February, eyes and body axis had become pig- 

 mented, nasal placodes and fin fold were appear- 

 ing, and the tail had curled past the posterior 



Notching 



1976-77 



1977 -78 



16) 



(10) 



(2) 



(I) 



(6) (I2)(4) (25) 



(4) 



(12) 



(III 



(2) 



(4) 



T (20)(3I 



(3) 

 I 



(9) (7) 



(2) 

 I 



(3) 



(3) 



(2) 

 I 



(3) 



T 



(5) 



(21 

 I 



(5) 

 I 



(3) 

 I 



20 



30 



January 



10 20 



February 



10 20 



March 



30 



Figure 6. — Stages of embryonic development for eggs sampled from Frost Fish Creek with drift 

 samples in 1976-77 and 1977-78. Vertical bars indicate ranges of development observed. Numbers 

 of eggs inspected are in parentheses. Small arrows indicate samples where all eggs were at the 

 same stage. 



151 



