Second, at least some current, passing consistently in one 

 direction over the nest, is essential to successful spamiing. 

 This is concluded from the mechanics of the spa-vming act, from 

 the spawning behavior of the sea lamprey, and from the distri- 

 bution of nesting sites in the river. Very siwift currents 

 hinder or preclude successful mating and •when it does occur 

 tinder these conditions, many eggs are swept beyond the nest 

 ■which are lost through exposure, abrasion, and predation. 



In the total absence of either gravel of the specified 

 sizes, or cxarrent, I have never observed spawning to take place 

 and where minijnal quantities of either or both exist, the 

 success of this activity, measured in terms of hatched-fry pro- 

 duction, is very low. 



These basic reproductive requirements of sea lampreys as 

 evidenced in the Ocqueoc River are substantiated by observations 

 made in other watersheds. Data relevant to the characteristics 

 of sea lamprey spawning grounds were recorded by field observers 

 for 29 other tributaries of Lalces Huron and Michigan (Appendix G, 

 Table 9). Any of the recorded physical or mechanical properties 

 such as -width, depth, amount of current, color, and turbidity 

 (with accompanying variations in the chemical quality of the 

 water) of a spawning stream or spaivning area varied mdely with 

 but one exception. Gravel, in combination with sand, or sand 

 rubble, was always present. All records thus obtained of stream 

 width, depth, and degree of current at spaiivning areas fell well 

 within the range of these properties as observed in the Ocqueoc 

 River. 



Water temperatures suitable for spawning are tentatively 

 identified as those extant in the Ocqueoc watershed during the 

 period April-July when the runs are entering the river. There 

 is some evidence that certain cold, spring-fed tributaries, 

 otherwise suitable for sea lamprey spaivning, are abandoned by 

 spawning migrants (sometime after entry) when the water fails 

 to warm rapidly during the months of May and June. This condi- 

 tion has been encountered in Pendill's Greek, Chippewa County 

 (Lake Superior basin). However, since my temperature records 

 in this stream are limited to intermittent pocket-thermometer 

 readings, no critical comparisons can be made. 



The question has been raised: do sea lampreys spawn on the 

 gravelly shoals of the Great Lalces proper when blocked from their 

 spavn:iing areas in streams by dams or other obstructions. There 

 is no direct evidence that they do or do not. If it does occur, 

 the success of this spawning must indeed be very low. Nest con- 

 struction, the spawning act itself, and the normal, and presuma- 

 bly successful, deposition of the eggs in the nest are predicated 

 on an unidirectional current passing over the nest; the entire 

 spaivning behavior of the sea lamprey reflects a positive orienta- 

 tion to this consistent, uni-directional current. Shoal areas 



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