Herring Spawning in Active Pass

Active Pass up until the late 1970’s was a high density spawning area for Pacific Herring. Herring are a very important food fish for many species of fish (significantly salmon) and marine birds. Recently herring spawn occurrences have again appeared in the waters around Mayne Island with the most recent in Horton Bay last winter – the aquamarine stain in the water is a sure sign of a spawning event. With this in mind, the Conservancy along with support from the Mayne Island Residents and Ratepayers Association are undertaking a pilot program this December to try to re-establish a spawning population of Herring in Miners Bay.


Divers at work

The Project

The procedure to be applied is one that has been successfully tested in False Creek, Squamish Harbour and Pender Harbour. In these areas it was found that creosoted pilings supporting docks were being used by herring as spawning substrate (herring have adhesive eggs and attach them to bare surfaces). The result was total killing of the eggs from the toxic compounds leaching from the creosote. To overcome this, it was found that if the subtidal portions of the pilings were wrapped with a heavy geotextile cloth (commercial landscaping type or other), this would act as a barrier between the eggs and the treated pilings. In all the cases, within the first year Pacific Herring laid eggs on this new substrate and observations confirmed that the vast majority of the eggs lived to the hatching of the herring young. With this in mind, the Miners Bay Community Dock has been selected as an ideal site to pilot a program for Mayne Island.

Using the high tide slack and the low range between high and low tides, the Herring Project team installed the artificial herring spawn substrate December 3 and 4, 2014. The process was to wrap the pilings under the centre part of the Miners Bay Dock deck with a durable and non-toxic vinyl deck covering. The object is to create a clean substrate upon which herring can attach their eggs and provide a barrier to the toxic effects of the creosote leaching from the pilings. Experience with this procedure in Pender Harbour, Squamish Harbour and False Creek has indicated that herring will readily spawn on this substrate and that the egg survival is increased. These other programs have been successful enough to re-establish spawning populations to these marine areas.

The project team included two seasoned divers who were also marine biologists, supported by volunteers from the two sponsoring groups – the Mayne Island Conservancy and the Mayne Island Residents and Ratepayers Association. As the work was done at high tides the vinyl wraps needed to be installed loosely at the surface then slid down to the subtidal level where they were secured using marine grade stainless steel bands. The individual panels were approximately 2 m by .3 m and two could be installed per piling to cover the subtidal spawning range of herring. In total, eight pilings now have been wrapped and over the next few months before the late winter spawning season, they will be inspected by divers to ensure they are still secure. The wraps and attachments have been designed so that they may be removed at the end of egg emergence and cleaned. They will be reinstalled again the following early winter.

With a re-established herring population to Miners Bay, the number and diversity of species (bird, fish and mammals) that are dependent on this forage fish for part of their food requirements would be expected to also increase. The team was reminded of this potential outcome, when a pair of adult Humpback Whales spent an hour cruising around Miners Bay to within 20 meters of the dock. Needless to say, this made what we were doing all the more significant.


Thanks to our team – Sarah Verstegen, Project Biologist, Seachange Marine; Mark Thompson, volunteer commercial diver; Ian Dow, MIRRA; Bill Jamieson, Diver support and tanks and Michael Dunn, MICS. Funding gratefully acknowledged from the Public Conservation Assistance Fund, the Green Angels Woodchoppers and the CRD.


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