Hydrometeorological Trends in the Miramichi River, Canada: Implications for Atlantic Salmon Growth

Abstract

Hydrometeorological conditions are important determinants of the distribution and productivity of Atlantic salmon Salmo salar in freshwater habitats. Environmental conditions, such as temperature, precipitation, and streamflow, affect an aquatic organism's growth rate, developmental rate, behavior, and ultimate survival. In the Miramichi River, New Brunswick, Canada, climatic and hydrological conditions have been monitored for over 30 years, providing a unique opportunity to examine long-term changes in temperature, precipitation, and streamflow and their effects on juvenile Atlantic salmon. Average air temperature in the Miramichi region increased over time, particularly in spring and summer months. Coincident changes in water temperature were not observed, with only summer water temperature increasing in the Southwest Miramichi River. Extreme summer water temperatures in the Southwest Miramichi River regularly exceeded the upper temperature threshold for growth of Atlantic salmon (22.5°C). Few changes in the amount of precipitation were observed in recent years. As a result, discharge in the Miramichi River was relatively unchanged in winter and autumn, when air temperatures were coldest. However, warmer air temperatures led to increased rates of evaporation, thereby contributing to low-flow conditions in the Miramichi River during spring and summer. Warmer air temperatures also may have contributed to the observed shifts in timing of hydrological cycles (earlier spring peak flows) in both the Northwest Miramichi and Southwest Miramichi rivers. Increased spring air temperatures and water temperatures were significantly associated with smaller sizes in Atlantic salmon parr (age 2). Changes in discharge and precipitation were also significantly associated with the size of juvenile Atlantic salmon. In the Miramichi River, further alterations in environmental conditions can be expected under future climate-change scenarios; as a result, productivity of Atlantic salmon populations in this region will likely be adversely affected.