Maturation 



Individuals captured May through August in 

 saltwater show little development of the gonads, 

 except for specimens >250 mm taken 31 August 

 1979 (OS 6858). These specimens have gonads 

 visibly larger than those of smaller individuals. 

 In addition, at least one of the allometric changes 

 associated with sexual maturity is evident. The 

 eyes of this 250-304 mm group constitute <25% 

 of the preorbital length, whereas in 181-245 mm 

 specimens from OS 6858 the eye constitutes be- 

 tween 25 and 33% of preorbital length. One 

 specimen (OS 17) of 205 mm TL captured 14 

 November 1949 in Yaquina Bay had developing 

 gonads. The season of spawning in the Columbia 

 and Yaquina systems is deduced to be April and 

 May, based on four specimens as follows: OS 112, 

 267 mm, March 1940, mature migrant, Bonne- 

 ville Dam, Columbia R.; OS 343, 263 mm, 30 

 April 1958, mature migrant. Tongue Point, 

 Columbia R.; OS 537, 181 mm, 15 April 1959, 

 spawner, Yaquina R.; OS 471, 203 mm, 9 May 

 1959, spawner, Simpson Cr. (trib. Yaquina R.). 

 Vladykov and Follett (1958) suggested that 

 spawning of the species took place in April and 

 May. Beamish (1980) reported spawning in hold- 

 ing tanks during May. 



October if these animals grow at the rate 

 observed by Beamish (1980) in British Columbia. 

 In that study, an increase of 100 mm from mid- 

 June to mid-August was noted. In the present 

 study, a rough estimate of growth in the 

 Columbia can be made by comparing early June 

 samples (n = 110), which had a mean length of 

 186 mm, with combined samples from 31 August 

 and 2 September {n — 31), which averaged 242 

 mm. 



In a system such as the Columbia, assessment 

 of size and growth is complicated by factors 

 other than sampling problems. Some individuals 

 may spend more years as larvae than others, 

 some may transform and migrate to saltwater 

 earlier in the year than others, some may feed in 

 freshwater before entering saltwater (Beamish 

 1980), and those destined to migrate back to 

 distant tributaries might have the genetic 

 capacity for rapid growth and early departure 

 from the feeding grounds. Kan (1975) noted that 

 Pacific lampreys showed a rough correlation 

 between size and distance of migration in the 

 Columbia, but in that species large size can be 

 reached not only by fast growth but by spending 

 up to 3 or 4 yr in marine waters, rather than the 

 few to several months spent by the river 

 lamprey. 



Growth and Upstream Migration 



Although occasional adult specimens of the 

 river lamprey have been taken from Yaquina 

 Bay during October and November, no river 

 lampreys have been captured in the Columbia 

 River estuary from early September to May. The 

 Pacific lamprey, Lampetra tridentata, has 

 appeared December to June in catches from the 

 Columbia estuary, intimating that the gear used 

 during the winter is capable of capturing 

 lampreys and that the absence of the river 

 lamprey from the catch indicates their absence 

 from the estuary. We suggest the absence means 

 that river lampreys move into freshwater in 

 early autumn. 



Judging from the specimens caught from mid- 

 August on, adult river lampreys must move into 

 freshwaters of the Columbia system at lengths of 

 of about 200 mm to >300 mm. Those that feed in 

 Yaquina Bay probably leave saltwater at similar 

 sizes, although the largest specimen captured 

 there was 260 mm. Specimens up to 255 mm have 

 been taken in Yaquina Bay in June, thus lengths 

 of 300 mm could be reached by September or 



Ecological Observations 



All but two of the eight ocean-caught river 

 lampreys were taken in tows or hauls made 

 within 34 m of the surface. The remaining two 

 were taken close to the surface by anglers. Speci- 

 mens from Yaquina Bay were taken by seine (3 

 m deep), but usually by lampara net (21 m deep) 

 from subtidal channels. Specimens from the 

 Columbia estuary were taken from shallow 

 water by purse seine and beach seine. "Pelagic" 

 coloration of blue to black on the back and silver 

 on sides and belly appears to be typical of 

 actively feeding L. ayresi, as reported by Kan 

 (1975) and Beamish (1980). This contrasts 

 sharply with the grey coloration of the deep- 

 dwelling Pacific lamprey. 



Water temperature in Yaquina Bay at times of 

 capture of river lampreys ranged from 13° to 

 21°C. Salinity ranged from 12 to 29%« (Myers 

 1980). Associated fishes in Yaquina Bay were 

 usually American shad, Alosa sapidissima; 

 Pacific herring, Clupea harengus pallasi; 

 juvenile coho salmon, Oncorhynchus kisutch; 

 juvenile chinook salmon, O. tshawytscha; surf 



166 



