Research on Steelhead Salmon in the Russian River Estuary

Background

The Russian River Estuary is a roughly 1 by 0.25 mile stretch of water connecting the Russian River to the Pacific Ocean. Between September and March, the annual steelhead salmon run will enter this waterway on its way back to the original spawning grounds further inland. Heavily contributing to the freshwater supply in the Russian River Estuary is Jenner Gulch, a former waterway now covered by sediment. Fresh water still trickles out from beneath the sediment, but it wasn’t known how constant the supply was especially after a four-year absence of any data collected.

In order to influence the Sonoma County Water Agency on whether to excavate sandbars to increase flow (thereby increasing the outflow of fresh water) and determine how to manage the Russian River further inland, current CTD measurements of the waters off Jenner Gulch were needed.

But wait! Why does this even matter to us?

Salmon die shortly after spawning and their remains provide nutrients to scavengers as well as the trees and plants whose roots extend underwater. When these scavenger species are unable to feed on their annual expected food sources, they die off and allow untouched carcasses to rot and spread disease. Trees and plants that are unable to absorb this nutrient source will eventually perish, their roots no longer able to absorb and hold sediments. This cascades into eventual sediment erosion, which can destroy the habitats of countless animal and plant species downriver and block vital waterways. People living along river coastlines and watersheds will lose their homes as well as the soil beneath erodes and washes away.

Research Plan

With some understanding that water is more dense the colder and saltier it is combined with the high probability of there being some underwater outflow of cold fresh water from Jenner Gulch, my team of two researchers set out to map the waterway between the gulch and Penny Island in the hopes of generating three-dimensional data over the course of time to better aid decision-makers in visualizing the cold-water plume.

Site Selection

On the surface, our measurements were taken roughly 5 yards apart to keep a consistent grid across the waterway. We planned to gather CTD data at 5-foot depth intervals until we reached the bottom of the river. These measurements, taken three days apart and over the course of ten days, would be taken at 7:00AM to be consistent with tide levels.

Data Collection

Using a pair of kayaks, my research partner and I rowed out to the data collection points and used our YSI CTD probe to measure water conditions at 5-foot depth intervals (marked on our cable by tape). We took turns reading and recording the data in notebooks which would then be uploaded and graphed on Microsoft Excel.

Constraints

Due to a busy research schedule back at the Bodega Marine Laboratory, the best time to collect data at Jenner Gulch was early in the morning before lectures and lab work. Had this not been the case, it would have been useful to track the cold water plume and its changes in shape and size over the course of each day. Entering and exiting tides also would have made data collection tricky as the water pulled in and out of the estuary.

Findings

After the five-day period of data collection, my partner and I entered our data and generated graphs that allowed the Sonoma County Water Agency and Bodega Marine Laboratory scientists and researchers to visualize the cold-water plume and decide how to approach the incoming salmon run. Fortunately, my team detected the presence of a large and cold freshwater plume. These findings indicated that conditions were ripe for the salmon run to detect the river from whence they came and allow them to begin their arduous trek upriver and back to their spawning grounds.

Communicating Findings

Our findings were presented at an annual end-of-summer conference consisting of Bodega Marine Laboratory students, faculty, visiting scholars, and representatives from the Sonoma County Water Agency. We communicated our data and graphs before taking questions and addressing any confusion that might’ve occurred. Two years after the presentation, I decided to take a look and see what was done with our findings.

While the detected presence of the plume was good news in the short term, the water conditions of 2015 were still at only 67% of the freshwater discharge in 2000. This prompted the Sonoma County Water Agency to excavate parts of the sediment impeding continuous freshwater flow in order to create a larger volume of freshwater entering the estuary. The agency’s counts of the 2015 salmon run showed a healthy return of salmon given the levels of fresh water in the estuary.

Next Steps

With very little manpower, funding, and resources to focus on each river heading into the oceans, the scientific and conservation community would benefit from either students like myself of volunteer efforts to continue to monitor every coastal estuary. My team took detailed measurements of the water conditions in one estuary system for one year, but yearly collection of this type of data is vital to the future health of our riverine environments.

The Sonoma County Water Agency was able to benefit off the findings of this particular year, but a continuous monitoring of all estuary systems across the West Coast would prove most important to the health of all salmon species, the ecosystems in which they play a part, and the future of the planet as a whole.