588 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



usually result in small pockets that are later aban- 

 doned, though they may be enlarged by other 

 lampreys at a later date. 



Sea lampreys utilize only certain portions of the 

 stream for spawning. The principal physical 

 characters that affect the suitability of an area as 

 a nesting site are the type of substrate and water 

 velocity. For successful spawning the lamprey 

 requires a substrate of stones small enough to be 

 moved and some fine sand to help sink and cover 

 the eggs. Also, a rather swift flow of water seems 

 to be required. The nests are commonly located 

 at the downstream end of a pool, where the rate of 

 flow is at least 2 feet per second. In Cayuga 

 Inlet, the center of the stream presents more at- 

 tractive nesting sites than do areas along the bank. 

 The lamprey nest is a shallow, irregular, bowl- 

 shaped pocket excavated in the streambed. For 

 nest construction the lamprey attaches its suctorial 

 mouth to a stone to be moved; if necessary the 

 stone is loosened from the bottom by a few violent 

 jerks. It is then carried to the edge of the nest 

 and dropped. Most stones are placed in a 

 crescent-shaped pile at the downstream edge, but 

 a few are carried to the upstream edge. Gravel 

 usually less than 1 inch in diameter remains to 

 make the nest floor. Most of the silt particles are 

 stirred up by the writhing bodies and carried out 

 of the nest by the current during the excavation. 

 Rocks comprising the streambed of Cayuga Inlet 

 are predominantly shales. In table 29 are listed 

 a number of nest measurements and the size of 

 stones lining the nest floor. The stone diameters 

 of the rubble represent only the larger flat surfaces. 

 The nests are usually oval with the long axis 

 parallel with the water current. Nest size varies 

 greatly but most are approximately 1 to 1 % feet in 

 diameter, and 3 to 5 inches deep. Nearly all nests 

 are located in water one-half to 2 feet deep. 



Customarily, males begin the nest construction 

 and are later joined by a female who assists with 

 the work. Males habitually start, several nests 

 which they abandon. Usually they proceed up- 

 stream as the nests are constructed and deserted. 

 Occasionally several males or several females are 

 together in one nest. These communal nests are 

 large, often 2 to 3 feet in diameter. Lack of 

 suitable nesting area does not appear to be the 

 cause of communal nesting. The fact that they 

 are more commonly found toward the latter part 



Table 29. — Measurements (inches) and materials in the floor 

 of sea lam-prey nests as observed in section E of Cayuga 

 Inlet on May SO, 1951 



1 Size of material in the floor of each nest was recorded in order of dominance 1 

 P pea gravel, Me to H inch in diameter; M marble gravel. \i to 1 incli in 

 diameter; E egg gravel, 1)4 to 2H inches in diameter; R rubble; S sand. 



of the nesting season suggests that the arrangement 

 may be a timesaving device of late spawners. 



Time of Construction and Location of Nests 



The first nesting activity of the 1951 season was 

 observed on the night of May 21 in section E of 

 Cayuga Inlet. Four male sea lampreys were seen 

 on nests in the earliest stage of construction. 

 Large-scale nest building started on May 25. By 

 May 30 a majority of the nests had been con- 

 structed, and spawning reached a peak May 30- 

 June 1. After June 1, nest building dropped off 

 rapidly and consisted mostly of enlarging pre- 

 viously existing nests. No spawning or nest 

 building was observed after June 10. 



During the 1951 spawning period, May 21 to 

 June 7, counts were made of the number of nests 

 in each of eleven 1-mile sections (fig. 10) of Cayuga 

 Inlet. All sections were examined at least twice, 

 and the most heavily populated areas as many as 

 six times. Some nest counts include an examina- 

 tion of the entire section; most counts however, 

 were based on samples of one-quarter to three- 

 quarters of a section. To provide a measure of 

 nest-building and spawning activity, nests were 

 classified as occupied or unoccupied (table 30). 

 Any nest in which one or more lampreys were 

 found was considered occupied. On May 21, all 

 nests were occupied. The percentage of occupied 

 nests decreased irregularly to about 50 percent on 

 May 24-25 and approximately 20 percent by the 



