Northern Pikeminnow Life History
Figure 3. Juvenile northern pikeminnow (top) and an adult pikeminnow (bottom). Not to scale.
- The northern pikeminnow (Ptychocheilus oregonensisare) is large cyprinid native to the Columbia River basin (Gadomski et al. 2001). These predatory fish can reach a fork length of up to 600 mm (Friesen and Ward 1999) and prey upon a wide variety of aquatic organisms including insects, crayfish and fishes (Thompson 1959).
- Understanding the various life history stages of the northern pikeminnow is important for the NPSRP to succeed (as the program targets adult pikeminnow that prey upon salmonid). Knowledge of the approximate time it takes for an egg to become an adult can be useful in predicting how many predatory fish are actually present. Additionally, this information could be potentially useful if it is determined that the removal of more pikemminow is necessary for the program’s success. In that case, the eradication effort could be increased by expanding it to the predator’s earlier life stages.
- Adult northern pikeminnow form into large spawning aggregations during the summer months. Broadcast spawning has been determined to occur in both the main Columbia River as well as its smaller tributaries. Ideal conditions for the spawning fish include optimal water temperature of around 14°C (Gadomski et al. 2001).
- Female pikeminnow will typically produce about 25,000 eggs (Parker et al. 1995). These adhesive eggs will gradually sink down to the substrate and after 8 - 10 days (depending on the temperature) they will hatch (Gadomski et al. 2001).
Northern Pikeminnow Life Cycle
Figure 4. Northern pikeminnow life cycle from (Gadomski et al. 2001).
- Once the eggs hatch, small larvae remain in the substrate. After about 11 days the larvae emerge from the sediment, and then drift in the river for 2 - 3 days before settling near the shoreline to rear (Gadomski et al. 2001).
- Rearing pikeminnow typically occur in the shallow bank waters of the main river channel (such as the Columbia) where the current is slower. Other pikeminnow may also develop in the shallows of backwater channels. The larvae tend to do best over fine grain sediments and in areas that have relatively high densities of aquatic vegetation (likely used for cover). These near-shore waters also have higher temperatures than the deeper parts of rivers, which enhances growth (Gadomski et al. 2001).
- Northern pikeminnow mature after reaching a length of between 200 - 350 mm (Beamesderfer 1992; Parker et al. 1995). The fish typically reach maturity between ages 3 - 8, with females taking slightly longer to mature (Turner et al. 2006). At any given time, the majority of the adult population is composed of individuals between the ages of 3 - 10 years (Rieman and Beamesderfer 1990). Upon reaching a mature size, the fish’s diet becomes more orientated towards fish (Vigg et al. 1991).
- Most adults will migrate up the main river to spawn while others will spawn in tributaries, lakes and reservoirs. Spawning groups can range in size from a few hundred fish to several thousand. Broadcast spawning can occur in a wide range of water depths, usually over gravel or rubble substrate (Gadomski et al. 2001). Spawning in pikeminnow is believed to occur in June and early into July.
General Salmonid Life History
Figure 5. A Chinook (left) and steelhead salmon (right).
- Salmonid species in the Columbia River basin include the spring, fall, and summer-run Chinook (Oncorhynchus tshawytscha), summer and winter-run steelhead (Oncorhynchus mykiss), coho (Oncorhynchus kisutch), and sockeye (Oncorhynchus nerka) (Poe et al. 1991).
- Summer-run steelhead fry in the Columbia River hatch in late spring to early summer and remain in fresh water from 1 to 3 years before migrating to the ocean (Quinn 2005). Downstream migration times occur between April and June (Quinn 2005). These steelhead return to the Columbia River during the summer to spawn after 1 to 4 years in the ocean (Carter et al. 2009).
- Spring-run Chinook usually spend 1 year in freshwater after hatching before out migration. Migration occurs in the spring from April to June (Healy 1991).
- Fall-run Chinook migrate to the ocean within the first year of hatching(Healy 1991). These sub-yearling Chinook migrate during the summer months of July through August.
- Both spring and fall-run Chinook average 3 to 4 years in the ocean before returning to their natal rivers to spawn. Spring-run Chinook return in the spring, while fall-run Chinook return during the fall (Carter et al. 2009).
- Spring and fall-run Chinook salmon and the summer-run steelhead are the species shown to have the most benefit from the NPSRP (Beamersderfer et al. 1996). Predation by northern pikeminnow peaks with the out migration of juvenile salmonids in April and May, leading to significant losses of juvenile salmonids during these months (Poe et al. 1991).