7824 - Laserfiche WebLink

Home Browse Search

that spawning squawfish in the Clearwater River mixed with, similar numbers of spawning chiselmouth chubs (Acrocheilus alutaceus), some hybridization apparently results, as fish were collected with appearances and meristic characteristics intermediate between the two species. Large aggregations of spawning squawfish have been reported by a number of authors. In Cooper's Lake, Montana, Hill (1962) observed a school of several hundred adult northern squawfish, believed to be a spawning group, concentrated within a few yards of shore. Most activity consisted of slow mass movements back and forth along the shore, but no activity interpreted as actual spawning was noted. Jeppson and Platts (1959) observed vigorous splashing and vibrations among fish spawning in congregations in Hayden and Cocolalla lakes in north Idaho. In tribu- taries to Cascade Reservoir, Idaho, Casey (1962) observed schools con- sisting of several hundred squawfish and noted each female was attended by several males. In the St. Joe River, Idaho, large schools of squaw- fish accompanied by solitary females were, thought by Reid (1971) to represent spawning populations. The spawning behavior observed 'in the St. Joe River is virtually identical to that observed by divers in Merwin Reservoir, Washington (Patten and Rodman 1969). As many as 5 to 8 thousand fish were observed congregating on one spawning site and the male to female ratio was estimated at between 50-200:1. Behavior was classed as swarming or chasing. Swarming was restricted to males and consisted of a dense aggregation of slowly swimming fish, milling within 30 cm of the sub- strate. Chasing consisted of pursuit of females passing near the swarm. From 1 to 6 males chased each female. Females did,not swarm and approached the site only for spawning. Females move faster than males and it was thought this movement elicited the chase response in males. Any fish including male squawfish and largescale suckers (Catostomus macrocheilus) were chased when they attained a threshold speed of about 60 cm per second. Spawning acts occurred within 3 cm of the substrate and were often observed by the swarm. As in the St. Joe River, Merwin squawfish on the spawning grounds had a dark lateral band from their snout to the base of their caudal fin. Seas9nal timing , No squawfish were observed on June 23, 1981, on any of the sites where fish were seen spawning in 1980. Two days later, a total of over 700 fish were counted and by June 27 at least 2,000 fish were present. June 27 was the first day when spawning acts were observed and when the majority of fish on spawning sites had lateral bands. Spawning activity remained high for approximately 1 week, but was interrupted abruptly between July 5 and 7 when counts declined from highs of 3,000 fish to less than 200. This decline in numbers coincided with cessation of spawning activity and an absence of lateral bands, on most fish remaining at spawning sites. By July 14, large numbers of fish returned and spawning activity and lateral banding were again common, although numbers never reached those recorded prior to the interruption. Spawning was completed by July 28, following a gradual decline through the preceding • 2 weeks. 52