Pikeminnow are historically the dominant piscivore in the Lumsden reach of the Tuolumne. They are large, opportunistic predators, consuming everything large enough to fit in their mouths. Pikeminnow are elegant fish with respectable sporting qualities. They grow to immense sizes in rivers as large as the Tuolumne, though seeing many of them at once is rare, as they disperse throughout the river. Seeing high densities of pikeminnow would be likely only around spawning time. However, our research suggested we would possibly observe pikeminnow spawning in the Clavey River.
It was with much anticipation that we began diving the Clavey. Would we see the massive and majestic pikeminnow, migrating up from the mainstem in search of suitable spawning habitat? Or would the unusually cool spring weather keep them from the river? Our first dive went off without seeing one adult pikeminnow. All we found in the clear, fast flowing water were small suckers and a few scrawny rainbow trout. Disappointment was beginning to mount as we trudged up to the next pool.
The next pool was, fortunately and amazingly, the antithesis of the first barren stretch. Where you had to work to find a fish in the first pool, you could not miss them in the second. Schools of large pikeminnow swarmed around us as we dove the sparkling waters, conjuring up Discovery Channel footage of salmon runs in Alaska. Though most of the fish were less than 18 inches, some true bruisers also lurked in the depths.
As we counted the pikeminnow schools and moved up stream, one could not help but admire the strength and grace of these dominant predators, rulers of their own aquatic world.
Later when we passed by the pool on the way back to camp, we observed the pikeminnow in spawning behavior, shuddering and flashing among the gravels. Several of the beauties were brought to hand later and proved to loaded with milt and roe.
The pikeminnow we observed were not spawning in the pool, but rather be moving into the riffles above and below it to spawn. The eggs then washed down stream into the edge waters and pools where they remain for about seven days before hatching (Moyle 2002). Upon hatching the larval pikeminnow cluster in the shallows where their parents cannot eat them and where temperatures are warmer and growth is faster.
Though the adults likely migrated in from the mainstem, they may remain in the Clavey all summer long, and no data is available on this. Regardless, the opportunity to observe these beautiful fish in full spawning mode is one that I will not likely forget in the near future.