Results & Discussion
Warming Annual Temperatures
MAT Over Time
Figure 14. Mean annual temperature trend in Alaska measured over time from 1992 to 2019. Trendline has been added to show the average from all communities where weather station datasets were gathered. (Standard deviation of 1.26˚C.)
The trend in mean annual temperatures across all communities in Alaska shows a consistent increase of more than 2 degrees Celsius (2˚C) (Figure 14). This upward shift is indicative of a warming climate. The data's standard deviation, at 1.26 degrees Celsius (1.26˚C), suggests that while the overall trend is towards warming, there is some variability in temperature changes across different communities in Alaska.
These environmental shifts can have far-reaching consequences for the communities that rely on salmon subsistence harvests, leading to economic and cultural challenges, food security concerns, and necessitating a comprehensive understanding of the multifaceted relationship between climate change and salmon populations.
Decreasing Salmon Harvests Across Most Species
Mean number of salmon harvested each year over all species has a negative correlation to increasing temperatures. When looking at species harvest data with mean annual temperatures, there is a negative correlation between mean number harvested and higher temperatures for Chinook, Coho, Fall Chum, and Summer Chum, and a slightly positive correlation for Pink Salmon (Figure 15). In other words, higher temperatures appear correlated with reduced harvests for the majority of species included in this study; however, there are multiple factors that may contribute to this correlation and further research would be required to rule these factors out. For example, the restrictions on subsistence fishing may be a factor for why we observe declines in total harvest for most species except Pink Salmon which have not been restricted. The number of fishing households per year may also be influenced by other social factors which we have not taken into consideration, such as shifts to other food sources.
Mean Harvest per Year as a Function of Mean Annual Temperature
Figure 15. Portrays Mean Fish Harvest per Year for each species (Chinook, Coho, Fall Chum, Pink, and Summer Chum) as a Function of Mean Annual Temperature (MAT) (In degrees Celsius).
Correlation and Trends
Table 3. Displays results of Mann-Kendall test for trends
Table 3 depicts the results of the Mann Kendall Test executed in R. The data is grouped by species and tested for trends in mean harvest. The Mann-Kendall test is a non-parametric statistical test used to detect trends in time-ordered datasets. Specifically, it assesses whether there is a monotonic trend (either increasing or decreasing) over time.
Chinook and Coho salmon harvests exhibit strong and significant decreasing trends. Fall Chum salmon harvest shows a significant decreasing trend, but the effect is not as strong as in Chinook and Coho. Pink salmon harvest shows a weak and non-significant increasing trend. Summer Chum salmon harvest has a significant decreasing trend similar to Chinook and Coho.
These results provide valuable insights into the temporal patterns of salmon harvest for each species, which can have implications for fisheries management and conservation efforts. It's important to consider these trends in the context of ecological, environmental, and climatic factors that may influence salmon populations over time.
As shown in Table 4, Coho and Summer Chum salmon harvests show significant negative correlations with Mean Annual Temperature. Chinook and Fall Chum salmon harvests exhibit negative correlations, but they are not statistically significant at the 0.05 level. Pink salmon harvest shows a non-significant positive correlation with Mean Annual Temperature.
These results provide insights into the potential relationships between salmon harvest and temperature, contributing to our understanding of the ecological dynamics of salmon populations. It's essential to interpret these correlations cautiously and consider other environmental factors that may influence salmon abundance.
Overall, the data suggests that there are decreasing subsistence harvest levels for most Salmon species along the Yukon River in Alaska. There appears to be a correlation between decreasing harvests and increasing mean annual temperatures, but there are other factors which may be influencing these results. Whether due to climate change or other factors, subsistence harvest numbers are decreasing while number of households with fishing permits is generally increasing. This is a concern, especially for local Indigenous communities who not only rely on Salmon as a food staple, but also have deep cultural ties to Salmon (ANWA, n.d.; NOAA Fisheries, 2019; Rosen, 2023).
Table 4. Pearson Correlation and p-value for mean harvest and MAT
Conclusions
The correlation analysis presented in Table 4 reveals notable patterns in salmon harvests along the Yukon River in Alaska, particularly concerning Mean Annual Temperature (MAT). Coho and Summer Chum salmon exhibit significant negative correlations with MAT, suggesting that warmer temperatures may adversely impact their harvest levels. Although Chinook and Fall Chum salmon also show negative correlations, these are not statistically significant at the 0.05 level. Intriguingly, Pink salmon demonstrates a non-significant positive correlation with MAT, indicating a potential resilience to temperature changes.
These findings contribute to our understanding of the intricate dynamics between salmon populations and climate. However, caution is warranted in interpreting these correlations, as other environmental factors may influence salmon abundance. The decreasing subsistence harvest levels for most salmon species, despite an increasing number of households with fishing permits, suggest complex interactions at play. Whether driven by climate change or other factors, the declining harvests pose concerns for local Indigenous communities deeply connected to salmon both as a dietary staple and a cultural symbol.
Results of the Mann-Kendall Test show that Chinook, Coho, and Summer Chum salmon display strong and significant decreasing harvest trends, though number of fishing permits had been increasing from 1992 to 2020. Fall Chum salmon also shows a decreasing trend, though less pronounced. In contrast, Pink salmon exhibits a weak and non-significant increasing trend.
These results underscore the importance of considering ecological, climatic, political, and legal factors in fisheries management and conservation efforts. The observed trends provide a foundation for further research into the complex interactions that influence subsistence harvests of salmon in the Yukon River.