Where the River Meets the Tides: Salmon and Estuaries

CONVERGENCE

A few miles out from the town of Sitka, literally at the end of the road, is an exquisitely beautiful estuary — a verdant jewel cradled by dense rainforests and high mountains. A magical place where fresh water from the river mixes with the sea, remade twice each day by the tides.

For townies and tourists alike, the Starrigavan Creek estuary is a favorite place for a stroll on the rough-cut boardwalk to watch an elegant great blue heron standing perfectly still, as if lost in a dream, intent on spotting her next meal of small fish; to hear the abundant songbirds trill their morning declarations of territory and joy (click to hear “Starrigavan Estuary Songbirds audio by Richard Nelson); to see a brown bear and her cubs grazing lush spring grasses — and later in the summer — catching salmon.

Mid-summer in Starrigavan Bay, pink salmon jump and splash, sometimes stacking up row upon row in the river’s clear, swirling outflow. Later, chum salmon leap across the water, grazing the surface like skipping-stones. A small batch of cohos will return here too.

It’s a premium place for sport and commercial fishing, as well as for marine and avian predators. Pinks, cohos, and chums lucky enough to escape the nets and hooks of fishermen and the pursuit of non-human hunters, will make their last journey, up the river to spawn, via the estuary.

Starrigavan is one of over 10,000 estuaries in southeast Alaska. Only about 15 acres at mean high tide, it’s small compared to the major systems in the state, but it’s incredibly important habitat for salmon, both at the beginning and at the end of their lives.

And this little estuary helps to support a highly productive seine fishery for pink salmon in Sitka Sound.

In a good year, a million salmon are harvested at the confluence of Starrigavan Bay and Katlian Bay, and as many as 150,000 of those are likely bound for Starrigavan Creek. Amazingly, as much as several hundred thousand dollars of economic activity can be generated just from the harvest of salmon that were reared in the small Starrigavan estuary.

It’s a great example of why estuaries — thousands of them, ranging from the biggest to the smallest — are so important for salmon and for Alaska’s economy.

THE RAVENOUS MILLIONS

We all know that salmon spend part of their lives at sea. But what drives a fish to leave the fresh water environment where they were born and head off into the ocean?

In a word: Food. There’s a lot more for salmon to eat in the ocean than in the streams and lakes.

And while each salmon species has evolved its own survival and reproduction strategies, all salmon eventually migrate out to sea. But before that can happen, they need to prepare themselves by spending time in the mixing zone of fresh and saltwater.

Consider just how incredible this is. Every salmon is a fresh water fish. It’s born in the gravels of a stream or lake, and then it undergoes a physiological change — called smoltification. This makes it possible for the fish to survive in a completely foreign saltwater environment. And then, at the end of its life, this same animal changes back, from a sea-going creature to one that can live in freshwater.

For young salmon, one of the most important functions of an estuary is as a transition zone — a place to acclimatize to the saltwater environment.

Cohos, kings, and sockeye salmon take their time getting to an estuary. They’ll spend a minimum of a year, two years, sometimes three years in freshwater before making this transition. Chums and pinks on the other hand, practically bolt downstream and will be schooling in saltwater within a couple of days of emerging from the gravel.

This early move to the estuary is a successful strategy because in a river like Starrigavan — where an average of 50,000 adult pink salmon can produce a huge number of eggs — several million ravenous fry will all emerge around the same time. Getting to the relative food abundance of the estuary as quickly as possible makes sense.

This is another important role of the estuary in the lives of salmon — it’s a place to gorge and grow.

ALL-YOU-CAN-EAT BUFFET

Estuaries offer a rich environment for all sorts of plants and animals: Fresh water and terrestrial nutrients and silt running in from rivers and rivulets; ocean nutrients pouring in with the tides; sunlight and warmth in the shallow water; the mixing action of winds and tides — all contribute to this fertile brew and create some of the most productive places in the world.

If things go well, all those Starrigavan pink salmon fry will arrive at the estuary in time for the nearly all-you-can eat buffet of the zooplankton bloom — those tiny animals that juvenile fish love to munch. And in the words of one fisheries biologist, hungry salmon fry will eat “practically anything that’s digestible that they can get their mouths around.”

Of course, it’s not all a party for the young salmon — lots of predators take advantage of the influx of fry into the estuary. For birds such as gulls, mergansers, and great blue herons, and for fish like dolly varden, salmon in the estuary equal a smorgasbord of little nutritious morsels.

The highest mortality for salmon is in the first few months of life, so lots of fry entering the estuary won’t survive because of hungry predators, disease or starvation.

But some lucky pinks and chums will find enough food to reach about finger length, at which time they’re ready to migrate into the nearshore areas along the coast. Here they continue to feed and grow until they’re ready to move into deeper water.

Cohos, chinook, and sockeye salmon stay in the lakes and rivers longer, so they’re actually juvenile salmon when they move into the estuary and go through the smoltification process. And when they emigrate, it’s not en mass as with chums and pinks. Cohos, for example, first meander down the faster rivers and streams, then spend several years in smaller, warmer tributaries that open into the estuaries and are flooded by higher tides. Eventually, all of these salmon will head out to the nearshore coastal areas and then off to the deeper ocean waters.

THE SCENT OF HOME

On their way out, the particular smell of their homeport river and estuary imprints on salmon — and this helps guide them back after their time at sea.

All species of salmon spend part of their lives far offshore, in the great, slowly spiraling gyre of the North Pacific Ocean — feeding, rapidly growing, and hopefully avoiding predators. Pinks stay out the shortest time — about 18 months — while chinooks stay out the longest — five to seven years. During their lives, some salmon may travel thousands of miles.

Then, eventually, each fish receives physiological cues that it’s time to head back home.
 
No one is sure exactly how salmon navigate back to their natal stream from far out at sea; it’s thought that the earth’s magnetic field plays a role and that salmon may even imprint the unique magnetic signature of their home area.

But when they get closer to home, it’s their marvelous ability to smell the particular water chemistry of their natal stream that reminds a fish where to turn in.

THE GREAT TRANSITION

When they reach the outflow of an estuary like Starrigavan, salmon congregate, often in schools that look like dark clouds eddying beneath the clear water. Sometimes these schools are revealed by swirling bursts in the water, or by great shimmering jumps — as if the fish were celebrating their return.

When the time is right, the salmon will head upstream to spawn. But first their bodies have to change again, so they can survive in freshwater. Just as with smoltification, this process isn’t like a switch that instantly turns a saltwater organism into a freshwater one…it takes a little time.

For many salmon at the end of their journey this change to a freshwater-tolerant state happens in the estuary.

Pink salmon begin to arrive at Starrigavan in mid-July, schooling up in the thousands, moving in and out with the tide, while their eggs and milt ripen. A few hundred chums show up around the same time and often mix in with the pinks.

Finally, they are ready for the single most important event in their lives. Both pinks and chums run up the river to their spawning beds and begin laying their eggs within 48 hours. In years with huge returns, some of the salmon even spawn in the estuary itself.

Cohos arriving at Starrigavan move at a slower pace. They hang out in deep pools upriver for two to three weeks before they spawn.

Sockeye salmon use waterways that virtually always include lakes, and they spawn either in the lake or its tributaries. King salmon spawn in large, deep rivers and often make very long freshwater migrations.

No matter the style of delivering themselves to their spawning grounds, for many salmon the estuary is an important gateway back to freshwater.

GIVING BACK

Of course, on the return trip to their natal waters, large numbers of salmon are intercepted — by fishermen, sea lions, seals, sharks, killer whales; and by bears, otter, mink, marten, eagles, gulls and an impressively long list of other predators and scavengers.

The decaying bodies of spawned salmon fertilize the rivers, lakes, and forests. Some of these nutrients flow back into the estuaries where they enrich the plants and insects and fish, providing nutrients that spread through the entire ecosystem.

Which in turn, keeps the estuary pumping with life…the perfect place for the next generation of young salmon to grow and thrive and begin their new lives in the northern sea.

THE ESTUARY STATE

Alaska has nearly 21 million acres of estuaries — more than all the estuaries in the rest of the United States combined.

In addition to the many thousands of small estuaries like Starrigavan, there are great, sprawling estuary systems in Alaska that produce massive numbers of salmon. Among the best known are the Stikine and Chilkat Rivers; the Alsek River and the Yakutat Forelands; the Copper and Susitna Rivers; the Naknek and Nushagak Rivers in Bristol Bay; the Yukon and Kuskokwim Rivers.

Alaska’s estuaries comprise a vast and infinitely complex treasury of prime, pristine habitat — the greatest, most valuable natural system on earth for producing wild salmon and feeding people throughout the world.

The ten-year average commercial harvest of salmon in Alaska (2004–2013) totaled 174 million fish per year. And these fish brought an average of $381 million dollars every year into the Alaskan economy.

Of course, it’s not just the estuary that’s important for the salmon — it’s the rivers and the lakes, the tiny tributaries, the watersheds, the tide-washed coasts and the ocean. Each plays an integral and irreplaceable role in the lives of wild salmon and in Alaska’s salmon economy.

And the humble, yet highly productive Starrigavan Creek is a good reminder that even a small estuary, hidden at the end of the road, is bursting with life — life that gives back to all of us.

By Liz McKenzie for SalmonWorld