Age axid size of larvae at time of departure from the 



nest , and production from the redds 



At an average water temperature of about 71 degrees F., larval 

 sea lampreys burrow out of j and leave, the nest 18 to 21 days after 

 the completion of sparming by the parent fish. The greatest number 

 leave iiie nest on the 20th day. All of them, upon leaving the nest, 

 have completed their early developmental stages and are perfectly 

 formed but diminutive ammocoetes. Preliminary experiments indi- 

 cated that the production of larvae from these nests varied from 

 O.li percent to 1,1 percent of the reproductive potential of the 

 female spaivning in a given nest. 



These studies were made on the Ocqueoc River in June and July, 

 I9I1.7. A site was selected in the lower river -vvhere a natural 

 spav/ning area was present, A wood-walled raceway was installed in 

 the stream across several small gravel bars and parallel to the 

 current (Figure Ii.9)o The enclosure was 12 feet long, 2.$ feet 

 high, and 3 feet wide. The upstream end of this pen was blocked 

 with copper screening having 20 meshes to the inch. A funnel of 

 the same screen material was installed at, and as an extension of, 

 the downstream end of the raceway. The mouth of a plankton tow net 

 was fitted to the spout of the screen funnel; the net was anchored 

 in an extended position. All seams, cracks, and joints were filled 

 ivith marine pitch and the walls of the raceway were carefully sealed 

 to the bottom. To the best of my knowledge, any larvae produced in 

 this racevray had no point of egress from the device except into the 

 trap of the plankton tow net (Figure I|.9). 



In I9U7, I succeeded in inducing two pairs of sea lampreys to 

 build nests and spa'vvn on the natural stream bed inside of the ex- 

 perimental raceway. Except for a slight diminution of current due 

 to the head screen and the relative confining space of the raceway, 

 conditions were believed identical to those existing naturally 

 elsewhere in that area of the river. A third pair of lampreys, 

 spavming on a site of their orm selection near the raceway, were 

 surrounded by a hardware cloth screen until they had completed their 

 acti^dties and died. This coarse screen was then removed and one 

 of the screen material used in the raceway substituted for it. The 

 downstream end of this second enclosure was a funnel and trap iden- 

 tical with that described for the larger, first one. 



Tlie time of completion of spa-vmingwas recorded in each case. 

 The females, which died verj' shortly after spaiming, were recovered, 

 measured, and examined for residiral eggs. Twice daily thereafter, 

 the traps of the plankton tow nets were examined and v/hen larvae 

 were present they were removed and preserved. Routine inspections 

 of the traps were continued for 20 days after the last lanm was 

 captured. Vfeter temperatures were recorded with a maximum-mixiimum 

 thermometer. During the period when development, hatching, and 



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