Continental-scale nutrient and contaminant delivery by Pacific salmon

Area of Science:

• Ecology
• Environmental Science
• Fisheries Science

Background:

• Migratory animals transport nutrients, benefiting ecosystems but also spreading contaminants.
• Pacific salmon migrations are key examples, moving marine resources inland, boosting productivity, and increasing contaminant exposure.
• Changes in Pacific salmon populations over the last century have altered the balance of nutrient and contaminant delivery.

Purpose of the Study:

• To quantify the impact of community structure changes on marine-to-freshwater nutrient and contaminant inputs from Pacific salmon.
• To analyze 40 years of Pacific salmon returns alongside nutrient and contaminant data.

Main Methods:

• Analysis of nutrient and contaminant concentrations in salmon.
• Utilizing 40 years of annual Pacific salmon return data (1976-2015).
• Quantifying salmon-derived nutrient and contaminant loads to freshwater ecosystems.

Main Results:

• Pacific salmon annually transported substantial amounts of nutrients and contaminants inland.
• Increased salmon returns from 1976-2015 led to a 30% rise in nutrient inputs and a 20% rise in contaminant inputs.
• Pink salmon, with high nutrient-to-contaminant ratios, dominated these inputs, causing nutrient delivery to increase faster than contaminant delivery.

Conclusions:

• Salmon-derived nutrient inputs became more ecologically beneficial over time due to a faster increase in nutrients than contaminants.
• Despite the improved ratio, contaminant levels may still pose risks to certain salmon predators.
• The Pacific salmon system serves as a model for understanding how environmental changes affect nutrient and contaminant transport by migratory species.