Oceanographic Studies

A detailed program to examine the oceanography of Cowichan Bay was developed during 2013. The key objective of this study has been to obtain spatial and temporal water property data from this area during the important fish migration period between April and August and augment these data with both shorter term (order of hours from small boats), medium term (order of several months from acoustic moorings) and order of year (from oceanographic moorings).

A repeat sampling grid covering Cowichan Bay and immediately connected waters was established, and then sampled using a small boat on weekly intervals between April and June  for temperature, salinity, chlorophyll fluorescence, nutrients and zooplankton. Oceanographic studies were carried out concurrently with fisheries assessments by researchers from the Pacific Biological station (PBS), Nanaimo. A longer section measuring the same variables was carried out at monthly intervals, with the purpose of connecting Cowichan Bay to the Strait of Georgia. Based on the scientific findings of that pilot study, a more comprehensive study was developed during 2014, to address some of the hypotheses behind the declining fish stocks and to support the biological sampling to be carried out by PBS researchers over the same period. This study began April 2014 and continued through July 2014, and is being continued in 2015. The Institute of Ocean Sciences effort addresses four components identified as possible causes of the high smolt mortality in the Cowichan Bay system:

  • Water Properties: They deployed an internally recording thermistor in the river near the estuary to measure river water temperatures throughout the study period. Weekly missions on their research boat Elvis took samples from 15 sampling stations within the Cowichan estuary and bay.  At each station CTD plus fluorescence and dissolved oxygen are taken, while collection of samples for nutrients and vertical net tows for zooplankton species and abundance estimation are done at a few select stations.
  • Substrate: Eelgrass habitat in the bay has been identified as important to marine survival. The group has attempted to map out substrate types, including eelgrass beds, using three different techniques:1) A 4-channel 100 kHz sidescan sonar system deployed from Elvis. 2) A GOPRO camera mounted to the boat when travelling in shallow water to determine whether bottom types and fish can be identified. 3) CHS Otter Bay multibeam sonar system as part of spring training and system testing.
  • Food: Chlorophyll sensors on the CTD and on 3 moorings within the Cowichan Bay provide estimates of phytoplankton blooms. The vertical net-tows at the stations also give weekly estimates of zooplankton composition and abundance.
  • Predation: To monitor the number and timing of predators, especially seals and birds in the estuary, a time-lapse camera has been set up to provide time series of predator type and abundance.
  • Moorings: One of the main scientific outcomes of the 2013 pilot study in Cowichan, was the significant variability in water properties, including chlorophyll and dissolved oxygen observations, from week to week, making it difficult to infer what was happening in the bay and its surrounding waters. To address this limitation IOS staff deployed three moorings during 2014; two in Cowichan Bay and one in Satellite Channel. These record temperature, conductivity, pressure and fluorescence. the moorings continue to record information during 2015.
  • They are using a bottom mounted upward pointing 4-frequency Acoustic Zooplankton and Fish Profiler (AZFP) during 2015 to monitor the water column outside the river mouth for both juvenile salmon, zooplankton, phytoplankton and larger predatory fish.
Figure 1. Oceanographic sampling stations in Cowichan Bay and Satellite Channel

The program will continue in the Cowichan region for the next 3-5 years.