A way to increase coho returns? Matching release time with food availability


by Paula Galloway
StreamTalk 2010-01 (page 7)

The BC Centre for Aquatic Health Sciences, in partnership with DFO’s Quinsam River Hatchery and the A-tlegay Fisheries Society, is studying the food needs of juvenile coho salmon and the availability of these food sources as the young fish enter the marine environment. This research will help determine optimal release times for juvenile coho that will improve early survival and ultimately increase returns to the hatchery.

Availability of food following hatchery release is crucial to the early survival of salmon. Without better knowledge about food sources or the ability to monitor and correlate early food availability with stock return data, good early survival of juvenile salmon as they enter the marine environment is hard to achieve. The goal of the Discovery Passage Plankton Monitoring Project is to develop a simple tool to help monitor marine productivity and use this information to adjust enhanced coho releases from Fisheries and Oceans Canada hatcheries. The monitoring program is being used to assess the following:

  1. Is poor survival due to a mismatch of smolt release timing and food availability in the near-shore marine environment?
  2. Is good survival correlated to improved food quality and availability at the time of smolt release?
  3. Can chlorophyll a (a pigment in phytoplankton) be used as an indicator of increasing phytoplankton levels followed by increasing zooplankton levels in Discovery Passage?

To address these questions, chlorophyll a levels are compared to phytoplankton levels and zooplankton composition (type/species) and abundance. This information is compared to the stomach contents of juvenile coho salmon to correlate what the fish are eating compared to what is available in the near-shore marine environment.

This pilot project is in its fourth of five years and to date the data collected has confirmed that there is no predictability to the productivity cycles and food availability and, therefore, monitoring is the best way to ensure that juvenile coho get maximum benefit from well-timed release dates. Other interesting and important findings include:

  •  Juvenile coho stomach content analysis indicates that wild and hatchery reared salmon may prefer different zooplankton upon immediate arrival in the marine environment.
  • Fish released into plankton blooms in 2007 and 2008 had higher survivals and returns than those released outside of bloom times. Staggered release dates may help ensure that some populations are released when food sources are good.
  • Chlorophyll a values are an effective way to monitor phytoplankton levels; however, these values are not a predictor of ensuing zooplankton levels and composition.

While the project has focused on coho out-migrating from two neighbouring rivers, this study’s findings can be applied to the specific needs of other Pacific salmon species and to rivers throughout BC.

Initially funded by the BC Ministry of Environment, the ongoing project relies on community funding. In 2010, the following organizations contributed funding to this project:  Campbell River Salmon Foundation, Aboriginal Fisheries Society, Positive Aquaculture Awareness, Marine Harvest Canada, City of Campbell River, and Campbell River and District Fishing Guides Association.

Their generous support is much appreciated.

To learn more about the Discovery Passage Plankton Monitoring Project and to view 2007-2009 project reports, go to www.cahs-bc.ca.



871A Island Hwy
Campbell River, BC
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