• Where is Rivers Inlet?
• The Rivers Inlet ecosystem
• The coast-wide decline of British Columbia sockeye
• The collapse of the Rivers Inlet sockeye salmon fishery
• Causes of sockeye decline
• The Rivers Inlet Ecosystem Study
• Future work
• References

Where is Rivers Inlet?

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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.   

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. 

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).

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

The Rivers Inlet Ecosystem Study

Future work

References