Nutrient flow between land and sea: bears and salmon

1. Nutrient flow between land and sea: bears and salmon

2. Background • Salmon runs have been declining for decades • Many runs are endangered or completely extirpated • Can have economic/cultural/ecological repercussions

3. Background • Salmon runs can yield as much as 5.4 x107 kg of biomass kg of biomass • A significant pulse of P,N,Ca and other macroelements • Distribute nutrients as far as 1000km away with a 2000m gain in elevation (Columbia River to Redfish Lake, Idaho)

4. How do we know? • Radioisotope data shows the nutrient movement • One of few examples of documented nutrient flow between marine, freshwater, and terrestrial ecosystems.

5. Salmon Female salmon prepare a redd in the streambed and lay eggs Males fertilize the eggs and they hatch in 8-12 weeks The small fry live in their natal stream for 1-3 years, eating aquatic insects

6. Salmon • They grow from fry to parr • At about 3 years they go to the open ocean • They live in the open ocean for 1-7 years as adults, eating fish and growing larger. • Then they return to the exact same place they were born to spawn.

7. Returning to their natal grounds is challenging! • Dams and fish ladders • Waterfalls and rugged rivers • Miles upstream against the current • Predators await them • Not eating during the entire journey

8. Bear feeding Bears are in hyperphagy- they need weight for winter torpor period They will need to put on hundreds of pounds to support hibernation through the winter.

9. Bear feeding Bears are under pressure to consume as many calories as possible in a short time Therefore, they eat the most fat and protein rich portion of the fish; the brains and roe Then throw the fish onto the shore, distributing marine nutrients to a terrestrial system.

10. Bear feeding • K of bears increases with salmon availability • 80x denser in coastal areas than interior • Bears distribute 83-84% of salmon onto shores • 96% of nitrogen excreted in urine, 3% by feces (spatial effect)

11. Different endings Some cannot complete journey and die in transit Some make it, spawn, and die in the water column, adding nutrients that support algae and stream insect populations

12. Insects • The fish become a source of protein for the developing insects • Flies oviposit in the carcasses (50% infection rate) • 50,000 maggots per carcass, can consume an entire fish in 5 days

13. Insects • Blowflies dominate salmon carrion and consume about 90% of the 4000 kg of carcasses abandoned by bears • With a single carcass, insect abundance increases several levels of magnitude • Macroinvertebrates derive up to 75% of their nitrogen from salmon

14. Insects • Young salmon who ate aquatic insects that were higher in density were larger due to salmon nutrients • Young salmon had a higher proportion of lipids allocated to energy reserves • This may lead to higher survival rates and fecundity

15. Other carnivores in the system • Eagles and otter eat the salmon along river banks. • Greater food availability allows for higher fecundity and more offspring in following seasons

16. Other animal species Bird community densities increase with the pulse of invertebrates due to salmon presence Muscles of small mammals show marine nitrogen signatures through indirect assimilation via terrestrial vegetation

17. Humans in the system Anglers Tribal fisheries Commerical fisheries Hatcheries

18. Vegetation Plants on the shore get a sudden influx of nitrogen, a limiting nutrient. This allows for growth of willow, sedges, and trees along the river bank. These act to shade the river and provide shady pools for fry to grow away from predators Tree growth is measured in rings that reflect accelerated growth that coincide with years of particularly high nutrient availability (large salmon runs).

19. Vegetation Salmon affect the quality of in-stream habitat through: • Shading • Sediment filtration • Nutrient contribution • Production of woody debris • Improved spawning and rearing habitat for subsequent salmon generations

20. Plant response • The salmon nitrogen is incorporated into streamside plant life • 500 m from streams vegetation showed marine nitrogen radioisotopic signatures • Trees and shrubs near spawning streams derive 22-24% of their foliar nitrogen from spawning salmon • growth rates were significantly higher near spawning streams- more habitat

21. Plant response • Salmon derived wood samples from old-growth riparian areas show marine nitrogen • Show that this nutrient transfer has been happening for centuries

22. Back to the start The fish that make it through all those challenges, and back to their natal grounds Create a redd and lay their eggs, and males fertilize the eggs The males and females then die near the redd, and their nutrients supply the local aquatic invertebrates and algae with nitrogen for growth

23. Integrated approach to management • Climate cycles • Salmon ecology • Riparian vegetation • Flooding and hydrologic cycles • Predator ecology and nutrition • Marine nutrient flowpaths • Feedback loops • Economic drivers