Day 5: Climate Change

Question of the Day:

What percent of Coho salmon survive from eggs to spawning adults?

ANSWER: aproximately 0.0008% (less than 1 in 1,000!) (Fisheries and Oceans Canada: source)

Character of the Day:

Spawning & Death: Upon reaching their birth streams, females build nests, or redds. These little depressions in the gravel are made by the female by turning on her side and using her tail to dislodge stones or pebbles. Males fight with other males for spawning rights with a female. The dominant male will court the female and upon spawning, they release eggs and milt simultaneously. The eggs will settle into the gravel, and the female will cover the eggs with loose gravel and move upstream in order to prepare another redd. Eventually, both the males and females die, supplying the river habitat with nutrients and the seeds of the next generation that will someday return to continue the cycle.

Key Concepts:

Impact of climate change on the Mattole River Salmon

Climate projections by scientists suggest that climate change presents a medium risk to salmon in the Mattole River basin. The effects of changing weather patterns are felt most strongly along the coastal areas of the basin, where summertime temperatures depend on the fog layer to remain cool. Usually, as inland temperatures climb, marine fog thickens and migrates inland (the fog “belt” changes). The consequent rise in coastal temperatures, if climate modelling is accurate, could particularly impact juvenile and adult salmon.

According to projections, average temperatures will increase over the next 50 years by up to one degree Celsius in the area, while annual precipitation is expected to decrease over this time. However, the critical factor for the Mattole River salmon is not just this fall in average precipitation, but also the way it is distributed across seasons. For instance, if rains stop sooner and begin later in fall, Coho salmon could be significantly impacted. In this scenario, cool rearing bonds would be subject to potential drying out, causing more mortality events. Alternatively, climate change might result in higher air temperatures, but also in more frequent summer storms that would bring in water from overland, reducing instances of no flow or low flow and expanding stream habitat for rearing juveniles. Nevertheless, increased flow in winter will likely scour nest, damaging salmon eggs and juveniles. Changes in stream flow are critical.

Next, changes in ocean composition and temperature have the potential to create significant problems as well. Altering the balance of saltwater to freshwater due to rising sea levels would affect near-shore ecology and thus available salmonid prey species. It is additionally possible that warming temperatures will push salmon to enter the ocean before critical planktonic "blooms", further causing a food scarcity. Meanwhile, warmer temperatures have been shown in some instances to reduce the populations of other smaller fish, thereby increasing predation of salmon. These problems pose a risk to Mottole River salmon survival.

Overall, the impact of climate change on the Mattole River salmon will most probably be negative, though the magnitude of its impact depends on the variability of temperature, precipitation, and near-ocean ecology. However, it is important to note that climate change is not the only risk to salmon. Dams, logging, high severity fire, and roads, among other issues, all pose a higher risk to salmon than climate change. It is the combination of all these factors that have made salmon in the Mattole River endangered and that continute to threaten their future.

Sources: Fish in hot water, Salmon and Global Warming, Mattole River Population

Youth Ambassador Activity:

Youth Ambassadors can find a stream, locate an area that would be considered a good place for salmon to lay eggs, explain why it would be a good location, and then discuss the impact of flow changes on this spot.

School Activity:

Have students make graphs comparing the survival rate of a Coho at different stages of life from egg to spawning adult. Adapt this worksheet to create and activity for the expedition: Then, remind students that survival rates decrease with added pressures, such as those causes by climate change or human disturbances.