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Pacific Herring: Underpinning the coastal foodweb

Program Coordinator Dr. 

 

A cornerstone in marine ecosystems

Other than salmon, few species in BC hold the ecological, cultural and economic importance of Pacific herring, Clupea pallasi. As one of the most abundant fishes in BC’s coastal waters, Pacific herring are a cornerstone of the marine foodweb and support a diversity of marine predators. In addition to wildlife, they have sustained coastal First Nation communities for many thousands of years and, in more recent decades, have been the focus of largest commercial fishery in BC, eclipsing all salmon species combined.

After the collapse of the Pacific sardine (above) commercial fishery in the late 1940s, Pacific herring became the largest fishery off Canada’s Pacific coast. Catches increased to over 200,000 ton/yr in the early 1960s but then dramatically declined over a few short years until the fishery was closed in 1967.

From their beginnings as tiny, translucent eggs scattered along the shore to dense schools consisting of hundreds of tonnes of energy-rich adults, Pacific herring are fed upon by a diversity of marine predators that include marine birds, mammals, fishes and invertebrates. For example, off the coast of Vancouver Island, adult herring comprise major proportions of predator diets (e.g. Chinook Salmon – 62%, Coho Salmon – 58%, Lingcod – 71% and Harbour Seals – 32%, source: DFO).

As one of the great fishes of the North Pacific Ocean, Pacific herring still underpin much of the coastal foodweb. Unfortunately, like many fishes throughout the world’s oceans, Pacific herring have been heavily exploited. BC’s herring populations collapsed in the 1960’s, mainly due to rampant overfishing. Following several decades of rebuilding, herring are again in trouble. Of the five major populations, three are closed to commercial fisheries due to low herring biomass. Included in these closures is the Central Coast population, which still spawn on the fragmented coast of the Great Bear Rainforest but over less coastline kilometers and at lower densities than in the past.

Our Work:  Understanding ecosystem linkages

Herring are a cornerstone species in marine ecosystems. These small, silvery fish fuel marine foodwebs and directly support predators such as salmon, pinnipeds, whales and a large diversity of marine birds. They also stage one of the natural world’s most spectacular events with their annual spawn. Each year, tens of thousands of tonnes of herring migrate from offshore waters to more sheltered nearshore bays and estuaries where they spawn en masse. Male herring release milt (containing sperm), which colors nearshore waters a chalky white, sometimes for many kilometers of coastline. In this opaque water, female herring lay eggs upon the intertidal and nearshore vegetation, which often includes eelgrass and kelp. These dense aggregations of spawning herring – and their deposited eggs – often attract tremendous numbers of predators and scavengers.

In some areas, millions of marine birds, hundreds of sea lions, seals and dozens of humpback and grey whales actively forage for several weeks. As part of our at-sea marine bird surveys, we had the opportunity to witness multiple herring spawn events at locations along the BC coast. The spawns we observed were several orders of magnitude smaller than in previous years, but which still attracted marine mammals and birds, including Bald Eagles, Black Brant, cormorants, loons, ducks and thousands of gulls.

Pacific herring eggs are negatively buoyant. By depositing many layers of eggs on fronds of kelp, the spawn of herring has been known to sink entire kelp forests. Upon hatching and the release of tiny, swimming herring larvae, the forests rise again.

From these initial observations, in addition to our memories of what truly large herring spawns looked like in the 1980’s, we asked a very broad question: does Pacific herring, perhaps somewhat analogous to salmon, provide a pulse of energy and nutrients to intertidal and terrestrial ecosystems? Having been immersed in the study of salmon and the influence of salmon to terrestrial ecosystems, including studies of coastal wolves and grizzlies, it was a natural progression to extend our research to encompass the ecological influences of Pacific herring. First, we sought out herring fishermen as well as DFO biologists, two groups who often spend significant amounts of time at herring spawns. We also drew heavily on what we’ve discovered in our collective decades of science and observation on coastal processes and salmon subsidies in British Columbia. From the start, our earliest conversations reaffirmed what we already suspected; the influences of Pacific herring reach up the intertidal zone and into the forests of this coast. Science, no big surprise, had just been slow to catch up. Already a diminished legacy due to significant herring population declines, we seek to trace the myriad of ecological relationships between Pacific herring and intertidal and terrestrial ecosystems. Similar to our research on the ‘salmon forest’, our work will broaden our understanding of herring and the coastal ecosystems they influence. This knowledge will also  support conservation measures that better integrate ecosystem values.

Initial Findings

the miky spawn of Pacific herring can cover kilometers of beaches and kelp beds

Science is a painstaking and methodical process. Added to this, Pacific herring spawns are relatively short-lived, lasting approximately three weeks each year at any given location. Complicating matters further, you never truly know when or where Pacific herring spawn until the water turns white with milt and the spawning begins. Each year, we have impatiently lain in waiting on the beaches of Quatsino Sound, located on the northern tip of Vancouver Island. Not quite the wilds of the Great Bear Rainforest, it’s true. But Quatsino Sound is the location of a moderate herring spawn, currently bigger than the spawns of the Great Bear, and it takes place against a terrestrial backdrop of mainly old-growth forests. Results, in the form of peer-reviewed publications, are forthcoming.

We’ve discovered, as suspected, that Pacific herring provide a subsidy to intertidal ecosystems. Not just carbon and nitrogen, we’ve traced the transfer of high quality lipids that originate in herring to animals that live in the high intertidal. Black bears, already major consumers in the cobble beaches where the herring spawn, also rely on herring eggs; in doing so, black bears transfer herring nutrients and energy back into the forests. Black bears are not the only terrestrial species to exploit herring; coastal wolves, songbirds and small mammals also directly rely on herring. From both scientific and conservation standpoints, our research opens up entirely novel areas of enquiry. To the best of our knowledge, no exploration of the relationships between Pacific herring and terrestrial ecosystems has ever been previously undertaken. Similarly, our knowledge of the ecological consequences of Pacific herring spawns to intertidal ecosystems are not currently understood in the context of a spatial subsidy. We’re still in the early stage of simply tracing out the ecological relationships – the next step is to understand the ecological consequences of herring spawns and conversely, what the loss of Pacific herring means to coastal ecosystems.

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