The Coos River Estuary is one of the most productive systems in the state for salmonids, particularly for Coho salmon (Oncorhynchus kisutch). Lessons we learn here, can lend insight to restoration efforts throughout the state.
Since 2004 the Coos Watershed Association (CoosWA) has conducted a life cycle monitoring (LCM) project to study coho salmon abundance, survival, life histories, and habitat use in tide gated lowland streams. Palouse and Larson Creeks were selected as initial study sites, but monitoring effort was switched from Larson Creek to Willanch Creek in 2015. For many years, the focus of stream restoration has been in the upper reaches of salmon bearing streams. However, recent data from this project, as well as other similar projects, have revealed that juvenile coho thrive in tidal rearing habitat and exhibit temporal /spatial migration throughout freshwater and estuarine habitat. Utilization of tidal habitat for foraging and winter shelter is a previously undervalued aspect of coho life histories that has been inhibited by human activity such as channelization, tides gates, and dike construction. Life cycle monitoring efforts help highlight the critical importance of diverse habitat and juvenile fish passage for recovering viable coho populations. CoosWA’s LCM project uses 5 main methods to monitor coho: spawning surveys, PIT tags, antenna arrays, rotary screw traps, and seining.
Spawning surveys are designed to track long-term trends in population abundance and involve surveyors hiking upstream to count live fish and corpses of spawned out salmon. A scale sample is also taken from every 10th salmon carcass and sent to the Oregon Department of Fish and Wildlife (ODFW) to be analyzed. Surveys are conducted every 10 days for the duration of the spawning season.
PIT tags, or passive integrated transponders, are small cylindrical chips, similar to the chips used in car key fobs, which emit a unique identifying code when activated by the electrical field of an antenna array. Tags are inserted into the body cavity of young parr as they pass downstream through the rotary screw trap on their way out to the ocean. PIT tagging allows fish movement up/ down stream to be recorded at antenna sites without having to physically recapture fish, even years after they were initially tagged.
Antenna arrays are used to track migration of PIT tagged salmon via radio frequency identification (RFID) telemetry network. Two rectangular antenna circuits spanning the width of the creek are set up approximately 3-4 yards apart from each other. As a PIT tagged salmon passes through the rectangular circuit, its ID, date, and time are logged. Using two logged points directionality and velocity of the salmon can be determined. There are currently antenna arrays in both Palouse and Willanch Creeks.
Rotary Screw Traps
Rotary screw traps (RST) consist of two large pontoons supporting a spinning screw drum that funnels fish into a collection reservoir. Staff members check this reservoir, or “live box” every day and PIT tag appropriately sized coho as they migrate downstream. Screw traps are installed seasonally, typically around early March, in both Palouse and Willanch Creeks to capture this downstream migration.
Seining nets provide a random, mobile, and cost effective trapping method off the shore of larger bodies of water or across streams using two lateral nets. One end of the net is dragged along the bottom of the stream while the top is supported by floats, creating vertical net surface in the water column that prevents fish from escaping. Seining is useful for sampling larger stream segments and may be used to assess size, abundance, and boost numbers of PIT tagged fish if RST capture was insufficient.
Beginning in 1997, coho salmon life cycle monitoring (LCM) efforts were implemented as part of the Oregon Plan for Salmon and Watersheds by the Oregon Department of Fish and Wildlife (ODFW) in 7 coastal subbasins on the Oregon coast to monitor fish abundance and survival (Suring et al. 2012). LCM efforts conducted by CoosWA in the Palouse and Willanch subbasins are intended to broaden the scope of the Oregon Plan projects by including tide gated lowland habitats that are not captured by other ODFW LCM sites primarily located in upland settings. This is particularly important given the extensive conversion of lowland habitat for agriculture or other human use in the Coos River estuary. The high degree of land development in lowland habitat critical to juvenile survival means that finding ways to connect local stakeholders, policy-makers, and scientists will be critical for the recovery of coho in the Coos Basin and coast wide.