The re-Tise of nests or nesting sites by late migrants was 

 only obser-ved after all suitable nest-building locations had 

 been utilized. In the latter halJ" of the season in Zone 1, 

 ijmi-ediately beloiT Ocqueoc Falls, unfavorable \vater levels at 

 the falls and reduced "/itality aavong t^\e sea lai:ipreys ultl^uatel;'- 

 forced many cf them to spawn in. locations that had already been 

 completely utilized. On many transverse gravel bar^-j, this con- 

 dition resulted in a complete obliteration of the outlines of 

 the original nests. The result was Tjhat appeared to be a con- 

 tinuous, straight nest across the entire face of the bar (Figure 

 33). Even under such circumstances, several pairs ^pavming on 

 these ill-defined, continuous structures tended to remain dis- 

 crete as pairs and spavmed across a consistent and limited 

 breadth of tlie reworked composite structure. 



(Zone 2) 



In Zone 2 (see Figure 28), the general type of nest ivas one 

 built of gravel, rubble, and small rocks in an area which was 

 more or less iiniformly composed of varjT-ng amounts of these three 

 bottom tjpes (Figure 37f, g). Little choice was offered the sea 

 lamprey in selecting sites for nest construction in this area of 

 the watershed. Riffle areas of gravel and rubble vrere more or 

 less level in bottom contour containing few if any bars or ridges 

 as found in Zone 1. Nests ivere found across the length and 

 breadth of these riffles in a well-distributed pattern — they were 

 seldom built in groups or close to each other. 15any of these 

 rubble-streTm riffles had relatively sTdft cui^rents, and T/riiere 

 thi.s occurred, nests tended to be concentrated in the less s'^Lft 

 vraters nearer the banks. 



Individua.l nesting sites were generally selected ivhere gravels 

 were relatively abundant among the rubble and slab rock (Appendix G, 

 Table 8). These nests were usually symmetrical in form i^ere the 

 rubble was of such a size that it could be moved and/or utilized 

 in nest construction (Figure 37g). In rocky or large rubble areas, 

 many asymmetrical types were built (Figure }7t). Limited amo-onts 

 of gravel and swift currents restricted most construction In such 

 c)j.-ea3 to a downstream rim in xvhich the eggs were to be depi-ir:=;ited. 

 In pD^edominan.tly r^abble and slab rock areas, so little gravel 

 was occasionally available that a very meager nest structure was 

 completed and the ultimate success of sparming on such sites was 

 limited. Below these nests, eggs could be found lodged (aiid 

 exposed) among the rubble for many feet. 



Among a sample of 2^ nests on one of the more favorable nest- 

 ing riffles in this zone (Station 26), the depths of the nests 

 averaged 10.9 inches (range: 3.0 to 13,$ inches). These nests 

 averaged 18,8 inches in diameter, varying from 13 to 26 inches 

 (Appendix G, Ta.ble 8 ) , 



109 - 



