9488 - Laserfiche WebLink

Home Browse Search

,.". Spawning occurred along the river levee shoreline at the same locations where eggs were found last year. Eggs were not visible; however, they were found in the interspaces of small riprap where beaver had been active. The majority of spawning occurred on the central portion of the levee, at the terminus of a large beaver trail and in relatively shallow water (<50 em). The three suspected spawning sites were relatively small in area (<3 m2) and limited to disturbed areas. Selection of previously cleaned substrate is not uncommon for other desert cyprinids (Mueller 1984). Bonytail appear to be very interactive and social. Smaller fish (10-15 em) were constantly over the spawning area, especially during the night. These fish would form loose schools as they would dart from place to place. Social interactions. generally included darting about, chasing and nudging one another with their snout, and foraging for food. Bonytai1 densities (video estimates) over known spawning sites averaged 17.44 fish/m2 (3.6 to 55.4, n=222); considering the relatively small spawning area (<9 m2), this suggests that only a small portion (5%) of the community spawned at any given time (2002 estimate: 6,000 bonytai1 > 15 em). Unlike razorback suckers, individual spawning may be shorter in duration (hours versus days) and number of events. It is also quite I possible that we have not discovered all the areas used by spawners. I It was difficult to determine what was actual spawning because of all the activity. By all indications, spawning was infrequent and rapid. The video recorded two definite spawning acts. The act would often only take 1-2 sec and involved several fish (3-7) and would be followed by the telltale feeding frenzy by several dozen egg scavengers. One event involved a larger, presumed female that was tightly flanked by two smaller males. The three fish dipped in unison to the substrate, with their backs arched. Immediately, two dozen other bonytails aggressively drove into the gravels to feed. The second observation was of a larger group of fish. Again, 4 to 5 smaller males flanked a larger female. They rested their heads in a depression and pressed their bodies together and tails slightly elevated. Unlike the first sighting, these fish finned vigorously for nearly 2 see, which again triggered a feeding frenzy involving about 4 dozen fish. Other "Factors & Organisms". The videos revealed that razorback sucker were spawning over substrate composed of a mixture of small filles to cobble, while bonytail were spawning over more coarse material, composed of small to large angular rip-rap. This difference in material size may influence survival. Horns and Magnuson (1981) reported that substrate composition was an important factor determining lake trout egg survival. They found that crayfish consumed large numbers of trout eggs. Savino and Miller (1991) showed a correlation between substrate size and survivability of lake trout fry. We also observed high densities of bullfrog tadpoles and to a lesser extent crayfish feeding among spawning fish. This prompted us to examine their possible role in this pond's ecology. 10