Spawning salmon increase fruit production of salmonberries

Researchers from Simon Fraser University Burnaby, BC studied the effects of spawning salmon species on fruiting of salmonberries, Rubus spectabilis. No surprise to anyone who has used fish guts, fish eggs and carcasses as fertilizer, the remnants of spawning salmon dragged or floated up on the banks of streams, adds a big fertilizer boost to salmonberries. These researchers studied 14 salmon streams and found that all that organic waste product promoted fruiting, and the density of chum salmon was correlated with increased fruit production. Pinks didn’t measure up. Seed count, fruit weight and sugar content were not correlated with salmon density. I’ll bet those traits are more related to bumble bee and other pollinator activity. Conclusion? Fish fertilizer makes great fertilizer!

 SIEMENS, L.D., A.M. DENNERT, D. S. OBRIST, J. D. REYNOLDS. Spawning salmon density influences fruit production ofsalmonberry (Rubus spectabilis). Ecosphere 11(11):e03282. 10.1002/ecs2.3282

 Abstract. Annual spawning migrations by Pacific salmon can provide substantial subsidies to nutrientlimited

Annual spawning migrations by Pacific salmon can provide substantial subsidies to nutrient-limited freshwater and riparian ecosystems, which can affect the abundance, diversity, and physical characteristics of plant and animal species in these habitats. Here, we provide the first investigation of how salmon subsidies affect reproductive output in plants, focusing on a common riparian shrub, salmonberry (Rubus spectabilis). We studied 14 streams with a range of spawning salmon densities on the central coast of British Columbia, Canada. We determined the effects of chum (Oncorhynchus keta), pink (O. gorbuscha), and total salmon spawning density on the number of fruits per shrub, number of seeds per fruit, fruit weight, and estimated sugar content (° Brix) of salmonberry fruits. We found that the number of fruits per salmonberry shrub increased with increasing salmon density. However, we found no effect of salmon density on the number of seeds per fruit, fruit weight, or sugar content. The effect of salmon density was species-dependent; the number of fruits per shrub increased with chum salmon density but was not affected by pink salmon density. This could be because chum salmon occur at higher densities and are transferred from water to land at higher rates than pink salmon in our study area. Higher salmonberry fruit production could lead to a larger input of salmonberry fruits to coastal food webs. These results demonstrate how salmon can cross ecological boundaries and influence reproductive output of terrestrial species.

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