Cycles, seasons and sediment of the Fraser Estuary

A chapter from Soul of the Fraser, which tells the story of the important intertidal habitat in the Fraser River Estuary.

The Soul of the Fraser by Ken Ashley, Director of the British Columbia Institute of Technology (BCIT), tells the story of the important intertidal habitat in the Fraser River Estuary, where the ocean’s saltwater meets the river’s fresh water, considered the most ecologically sensitive and threatened ecosystem in the entire Fraser River. 

The Soul of the Fraser includes essays by 12 different contributors who represent the past, present, and future of the Fraser Estuary, with perspectives from three generations of scientists and environmental engineers, including two BCIT graduate students.  

Below is a chapter of the book written by Misty MacDuffee, Raincoast’s Wild Salmon Program Director and one of the book’s contributing authors.

Cycles, seasons and sediment of the Fraser Estuary

The spring of 2016 was exceptionally dry and warm, the beginning of a severe six-month drought for southwestern British Columbia.  But in March of that year I readily welcomed the sun and blue skies.  They brought the start of my involvement in what has become a multiyear initiative to aid and understand the requirements of juvenile salmon in the Fraser River estuary.  

While I have been fortunate to spend my adult life working throughout coastal BC, my experience in Southern Georgia Strait was largely limited to ferry crossings.  And though there have been days since when I would have preferred the shelter of a ferry, I am eternally grateful for the opportunity to be immersed in the cycles, seasons…and interminable sediment…of the Fraser estuary.  

My introduction to navigating the interaction of weather, freshet and tides was from people whose history of this system extends 10,000 years.  I learned the winds coming across Georgia Strait or outflowing from the Fraser from the generosity and wisdom of Steve Stark, Tsawwassen First Nation council member and our seine captain.  His experience and teachings instilled our respect and caution for his nation’s remarkable traditional territory.  

At its core, the estuary is a summit of water bodies and geography where the outflow of the mighty river becomes part of an estuarine pump that carries fresh water out of Georgia Strait in the surface layers and draws nutrient rich, cold and salty water into Georgia Strait along the bottom.  It is this circulation that triggers plankton growth and the ensuing processes that feed terrestrial, ocean and avian life.  The volume of freshwater and strength of the tides make the Fraser one of the most productive and ecologically important estuaries on the Pacific coast and the foundation for a remarkable abundance of life. 

In my salmon centric world, the Fraser estuary is the rearing grounds for Canada’s largest runs of Pacific salmon.  Even at a fraction of their former abundance, the Fraser watershed remains one of Canada’s great wild salmon producers. All Chinook, sockeye, coho, pink, chum and steelhead coming from the upper and lower parts of the watershed must transit the estuary twice in their lifetimes: once as they migrate to the ocean as juveniles and again as adults when they return to spawn.  Many of these species also spend extended time rearing in the estuary preparing for their ocean migrations. 

Salmon smolt swimming in murky water in the estuary.
Photo by Fernando Lessa/ BCIT Rivers Institute.

Clearly, the reason we work in the Fraser is the salmon; but sometimes it’s hard to stay focussed on fish in nets and buckets when the estuaries seasonal events are unfolding around you.  Despite what some might refer to as “alarm calls” emitted by my co-workers, I’ve gotten lost to the wonder and sound of wings overhead when I should be looking down at the fish in our net.  It’s hard when you’re in the flight path of 10,000 lofting western sandpipers, or terns dive-bombing for fish, or the overhead calls of sandhill cranes…to keep your eyes averted.  

Despite the importance of estuary rearing for several salmon species, few studies have been conducted on habitat use since the formative work by scientists at UBC’s Westwater Research Centre and Fisheries and Oceans Canada ended in the 1980s.  When Raincoast started its field study a generation later in 2016, significant advances in genetic and other molecular techniques had ensued in the time lag.  In a similar way that Ancestory.com has revolutionized personal history searches, bio tech methods have given us insights into answers that could only be speculated on 30 years ago. 

Today, the five commercial species of Fraser salmon have been grouped into more than 50 unique populations called Conservation Units.  Intercepting these tiny migrating salmon with boats and nets at two dozen sites throughout the Fraser delta over the last five years has given Raincoast a window into their world.  We can track distinct salmon populations through the estuary, know the habitats they prefer at specific times and life stages, determine when they entered, how long they stayed, and how much they grew while feeding in the sheltered saltmarsh and eelgrass habitats.  

Whether it is the mixing of brackish waters across tidal mudflats that produces essential fatty acids for millions of migrating shorebirds on their way to the high arctic, or the saltmarsh that acts as a nursery for millions of tiny salmon preparing for a multi-year journey to the Gulf of Alaska or the Bering sea, the Fraser estuary is a vital linkage for species across space and time.  It ties freshwater to salt, coastal with pelagic, terrestrial with aquatic, the southern hemisphere with the north, one life stage to the next.  These linkages through the Fraser estuary connect a foodweb that extends tens of thousands of kilometres across the Pacific Ocean along the migratory pathways of birds, marine mammals and fish.

Landscape image with the estuary in the foreground, mountains in the background and a tanker centered over the water.
Photo by Fernando Lessa/ BCIT Rivers Institute.

Yet connectivity is one of the features lost over the last hundred years as the human footprint has stepped upon this ecosystem.  Physical barriers like dikes, jetties, and causeways lay as fingers that segregate, isolate and dissect the 30 km delta restricting fish from accessing their feeding and rearing habitats.  The processes within the estuary, such as the creation of biofilm on mudflats, are equally impacted by these structures that impede and change the natural flow of the river, the tides, the salinity and circulation.  The same is true on the arms of the river that once flowed unimpeded into backchannels and sloughs where young salmon would overwinter or take refuge from the main channel.  Emerging research indicates 80% of the natural floodplain and shoreline of the estuary has now been lost.

But for the first time, in some cases a century, this is changing. Raincoast’s work to better understand how juvenile salmon use the estuary is driven by a desire to give them the best possible chance of survival.  These chances increase when we restore their use of, and access, to historic habitats and act to protect what remains. In the estuary, our interests meet those of Indigenous Nations, governments, conservation groups, scientists and communities whose focus is aligning on the preservation and restoration of the estuary. 

This place has long been one of trade and transition for ecosystems, economies and culture.  This richness is reliant on the estuary’s natural resources. Economies and their industry can only be truly sustainable when they do not jeopardise that which gives the estuary its soul – the birds, the plants, the salmon, the people and the natural flow of a mighty river. 

If you ever are lucky enough to spend time here the experience will stay with you, as it has stayed with me.  My hope is that this place and its soul will survive for all generations to come.

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