Rivers Inlet Ecosystem Study

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About Rivers Inlet

Where is Rivers Inlet?

Rivers Inlet is a fjord located on the central coast of British Columbia (BC), Canada. It is in the heart of one of the world's largest remaining tracts of temperate rainforest, and it is the traditional territory of the Wuikinuxv (Oweekeno) First Nations. Rivers Inlet epitomises a unique coastal environment, with rich and diverse marine resources that have sustained First Nations people for thousands of years, and that continues to sustain high value commercial and recreational fisheries, aquaculture, forestry, transportation and tourism into the 21st century (1,2).

The Rivers Inlet ecosystem

Rivers Inlet is approximately 40km long and 3km wide. Together with two major side branches (Moses and Drainey inlets), it represents a significant area of coastal marine habitat. Deeply scoured during glacial periods, the fjord is generally uniformly deep (200-300m) and has a relatively deep sill at its mouth, before opening into Queen Charlotte Sound. The head of the inlet is formed by an upper sill above which the U shaped glacial valley continues eastwards as Owikeno Lake, equal in size to the inlet itself.  Numerous rivers and streams flow into the lake, draining an extensive glacial fed watershed of ~4100 km2. The lake feeds into the inlet proper via the short Wannock River.   

river inlet map
Map of the Rivers Inlet system

Large quantities of glacial silt entering the lake, clearly evident in satellite photographs, and low nutrient levels, make Owikeno Lake quite unproductive (oligotrophic). Despite this low productivity the Owikeno watershed has provided excellent spawning (river) and rearing (lake) habitat for sockeye salmon [life cycle video / text] and historically Rivers Inlet had the third largest sockeye salmon fishery in British Columbia. The Rivers Inlet ecosystem also supports coho, chum, chinook and pink salmon.  

However, the annual return of sockeye salmon is now a shadow of what it used to be [see below], and this decline has had significant repercussions further up the food web. Although the annual salmon runs still draw many top marine predators to the inlet (e.g., orcas and seals), and support large populations of grizzly and black bears, evidence suggests that bear populations are in decline. Increased encounters between humans and bears in recent years, particularly in the fall, are a strong indication that bears are struggling to meet their pre-winter energy requirements. 

bear 2
Grizzly bear

The inlet itself is highly productive, with a significant spring and summer phytoplankton bloom supporting large quantities of zooplankton. Forage fish, such as sand lance and herring, feed on the plankton stocks and these species in turn attract higher order predators, including dolphins and humpback whales. Forage fish and benthic invertebrates support other commercially important fish such as halibut, lingcod and rockfish, although stocks of these species are currently depleted.  

Humpback whale

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The coast-wide decline of British Columbia sockeye

Rivers Inlet has experienced one of the most dramatic sockeye salmon fishery collapses witnessed on the coast of British Columbia, epitomises an alarming province wide trend for this species. Approximately 75% of northern and central BC coast sockeye salmon stocks are listed as depressed, declining, or of unknown status (2). This is of major concern as sockeye salmon is a keystone species in the ecology of many BC watersheds, a major component of the commercial fishery, and a focal point of the economy, sustenance, and culture of First Nation’s communities. Therefore, urgency is required in efforts to understand and manage the cause of these declines.

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The collapse of the Rivers Inlet sockeye salmon fishery

Historically, Rivers Inlet was one of the most productive sockeye salmon based ecosystems in British Columbia, vying with the Skeena River for position as the second largest commercial fishery for this species (1). Population highs of more than 3 million fish have been recorded and for most of the 20th century an annual average fishery catch of greater than 750 000 fish was maintained.  However, in the 1970's the Rivers Inlet sockeye population began to decline. Despite reduced harvest rates in the 1980’s, as part of an adaptive management strategy, stocks continued to decline and the commercial fishery was closed in 1996. In 1999 the stock reached a record low of ~ 3600 fish, just 0.1% of historic levels. Although the commercial fishery has remained closed since 1996, with only a small amount of fishing permitted by the Wuikinuxv First Nations for cultural purposes, the stock has not recovered to harvestable levels (a minimum of 200 000 spawners).

sockeye collapse figure

Figure caption: The decline in returns of Rivers Inlet sockeye salmon. Catch has been estimated from the onset of the commercial fishery in the late 1800’s. To this, escapement (the numbers of fish escaping the fishery and observed on the spawning grounds) estimates have been added from just before 1950 to the present (figure courtesy of Rick Routledge).

Causes of sockeye decline

Salmon have complex lifecycles, with both freshwater and marine phases, involving lengthy migrations [life cycle video / text]. The factors affecting their survival are therefore many and varied. Currently, one of the leading hypotheses for sockeye declines in British Columbia, including the Rivers Inlet population, is increased mortality in the early marine phase of their life cycle (1,2). Juvenile sockeye salmon feed on plankton and it is therefore expected that changes in the seasonal timing of plankton blooms, affecting the quality and quantity of plankton prey available to them, is critical to their growth and development in coastal waters before migration into the open ocean.

The Rivers Inlet Ecosystem Study

The Rivers Inlet Ecosystem Study (RIES), funded by the Tula foundation, was initiated in 2008 to build on the research platform laid by Rick Routledge’s team at Simon Fraser University (SFU) between 2002 and 2007. A collaboration between SFU and the University of British Columbia, the RIES developed around the objective to:

"Understand the dynamics of spring productivity and how it affects the growth of juvenile sockeye salmon."

Spring productivity is affected by many factors, including the weather (e.g., sunlight available for photosynthesis, wind induced mixing of the sea surface, freshwater runoff - rain and snow melt - and its seasonal timing) and ocean conditions. The juvenile sockeye do not use the spring production directly, but feed on the zooplankton grazers of phytoplankton. An understanding of the dynamics of spring production, and how it affects juvenile sockeye growth therefore, by necessity, requires a multidisciplinary approach that investigates as many components as possible of the pelagic ecosystem. In addition to present day ecology, paleoecogical investigations currently underway at SFU and Fraser Valley University are  being used to help us understand the historical ecology of this ecosystem. Working closely with the Wuikinuxv First Nations, the RIES objectives are  currently being tackled through multiple linked projects.

Future work

In 2004 the Canadian government formally recongnised the uniqueness and value of the BC central coast when it was designated one of five Large Ocean Management Areas for coordination of integrated management policy. The Pacific North Coast Integrated Management Area (PNCIMA) stretches from northern Vancouver Island to the British Columbia / Alaska border. However, this region is facing increasing pressure from many of the uses listed above, and growing interest in oil and gas exploration and development (1,3). Vulnerability to these direct human impacts is exacerbated, and management complicated, by the effects of climate change, including warming, changing productivity regimes, anoxic bottom waters, shifting oceanic currents, and more variable weather patterns (1,3,4).

The ecological changes and pressures faced at Rivers Inlet are symptomatic of those throughout coastal British Columbia, related to resource exploitation, climate and natural ecosystem change. Rivers Inlet is an ideal focal area for researching and understanding these ecological changes, their social and economic impacts, and developing effective integrated management strategies. As such the relevance of the RIES reaches far wider than Rivers Inlet itself. Future research aims to not only build on our understanding of the Rivers Inlet ecosystem in its present state, but also to reconstruct its historical ecology and produce modeling tools to predict future change and inform ecosytem based management, and to develop its scientific outputs for social and economic upliftment.

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1. McKinnell S.M. et al., 2001, North American Journal of Fisheries Management, 21(4): 774-791

2. Levy D., 2006, Sockeye salmon report, The Sierra Club of Canada – BC Chapter. [PDF].

3. Montenegro A. et al., 2009, Canadian Parks and Wilderness Society, pp. 62

4. State of the Oceans – Pacific Region, 2007, Canadian Science Advisory Secretariat Science Advisory Report 2008/028 [PDF]