upstream so that in some eases, the nest has a crater-like appear- 

 ance. Each pebble or stone is moved singly by picking it up vrith 

 the oral sucker. Great persistence is shorni on occasion ■vrfiere 

 an unvranted stone is firmly imbedded in the bottom. A sea lamprey 

 ■will return time after time to such a stone and tug at it until 

 e\'-entually it may be dislodged. Very large stones are occasion- 

 ally moved out of the center of the nest area by dragging them 

 along the bottcni with the aid of the current. The largest stone 

 I have seen moved measur-ed about ii by ^ by 5 l/2 inches and was 

 dragged about 2.5 feet from -bhe center of a nest area by a 17-inch, 

 male sea lamprey. 



The total amounts of material moved by a pair of sea lampreys 

 during nest-building and spawning seem extraordinary. All dis- 

 lodged materials from three nests in Zone 1 in which spaivning had 

 been completed were carefully collected and weighed. In the three 

 nests, 13.2 pounds, 18.0 pounds, and 23.5 pounds of small and 

 large gravel and stones had been moved respectively by each of 

 three pa.irs of spaT.vners. 



Nest construction is usually begun by the male. Early in 

 the season the male may work for U8 to 72 hours on a nest before 

 being joined by the female. In this time, a major portion of the 

 nest's construction has usually been completed, and further 

 elaboration by both sexes may only occur in the interval betiireen 

 £pa">vning acts. About the middle of the spawning season, the male 

 is frequently joined by the female shortly after the nest has 

 been started and both contribute to the building done prior to 

 spavmjjig. Toward the end of the spawning season, when females 

 frequently appear to be numerically dominant on some spaivning 

 beds, nest constru.ction may be initiated by them. 



Within acceptable spa"'.vning areas, some selectivity is ex- 

 ?aibited by male sea lampreys in establishing a nesting site. 

 Males frequently begin several nests in trial locations before 

 settling on a final locus. Abortive or trial nests vary from 

 mere clearings of a dozen or more pieces of large gravel to 

 structures about one-quarter completed. This selective behavior- 

 ism, is generally observable only during the earliest part of the 

 nesting period or in areas where spawning facilities are not 

 crowded. Later migrants readily occupy many of these trial netit- 

 ing sites and elaborate them into completed nests. 



Pr-ior to the beginning of the actual spawning process, sec- 

 ondary sexual characteristics develop among both sexes "iidiich s/.d 

 in the identification of the sexes upon the spawnin.g beds. Among 

 the males a very pronounced, median, rope-like ridge gradually 

 appears on the beck. This prominence, when complete, extends 

 from the branchial region to the anterior edge of the first 

 dorsal fin. Females lack such a dorsal elevation but develop 



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