Tuesday, August 28, 2012

Sockeye

Sockeye salmon (Oncorhynchus nerka) are one of the more desirable species of salmon in Alaska. Sockeye tend to have rich, fatty meat, and their muscle ranges from pink to deep red in color, making it the preferred fish of canneries. In this region, most people that eat fish think King is king-- King salmon have the best flavor of them all-- but Sockeye probably comes a close second.

Sockeye are, in my opinion, the prettiest of the bunch when they're breeding. Males and females both take on a deep red hue, with green heads and tails. They only develop this color scheme when they're spawning. When living in the ocean, and before they begin to spawn, Sockeye are silvery blue. Check out this video of Sockeye on their spawning grounds in Chilkoot Lake:


Remember that Sockeye (like all the salmon we study) are anadromous fishes. Anadromous comes from the Greek word anadromos, meaning "running upward." Anadromous fish spend most of their lives at sea before migrating to freshwater streams and running upriver to breed and die. Most Sockeye spawn between July and August, so we're just seeing the tail end of the Sockeye run around Haines.

Imagine seeing hundreds of fish swimming together in a narrow stream bed or shallow pond just off of a major river:


The setting seems idyllic. Tree boughs overhang the creek, providing shade. The rocky bottom, interspersed with sandy patches, is a great place for a female Sockeye to build a redd (nest), lay her eggs, and attract a male to fertilize her brood. In the spring, her eggs will hatch, and the fry (young fish) will spend up to three years living in this stream, growing, before migrating out to sea*.

But before too long, the strain of migrating anywhere from hundreds to thousands of kilometers, breeding, defending territories and redds, and chasing off competing fish, all without eating, begins to take its toll. During spawning, salmon put all of their energy into breeding. All the normal things that we do on a day-to-day basis to stay alive (eating, for example), and all the things our bodies do to keep us healthy (fight off infections, destroy damaged cells, etc.) salmon neglect in favor of procreation. In fact, by the time salmon reach their spawning grounds, they've already begun the descent to senescence. The salmon start rotting before they've even died.



Can you see this white patches on these salmon? Those are parts of their skin that have died and begun to decompose. Some salmon appear in relatively good condition before they die; others are heavily mottled with patches of decaying flesh. In a short period of time, the idyllic creek filled with spawning fish turns into a apocalyptic wasteland of decomposing salmon carcasses. Bears get to many of them:


Others are left in the stream to decay:


Just one week ago, Jenn and I set our trail cameras in this area and recorded the video of the peaceful stream above. When we returned, seven days later, to check the cameras, we walked into a wasteland of salmon carcasses. What a difference a single week makes! Very quickly the salmon in these areas are finishing their breeding cycle and dying off. It may seem unpleasant (and in fact they do smell terrible) but it is endlessly fascinating. The carcasses these decomposing salmon leave behind will provide valuable nutrients, like nitrogen and phosphorus, to both the stream bed and surrounding terrestrial vegetation. And, of course, they also provide plenty of food for the carnivores!


*Not all salmon species spend extended periods of time as frys in freshwater areas before migrating to sea. Some species spend more time (upwards of four years for some Sockeye), and others, less. Chum salmon, for example, are born in freshwater streams and migrate to sea immediately.

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