The Great Salmon Run

Sockeye Salmon, or Oncorhynchus nerka, have a very peculiar way of reproducing. Millions of Sockeye Salmon migrate from their adult lives in the ocean to the stream in which they were born. The Sockeye Salmon spawn in the rivers of British Columbia, Canada and other nearby rivers systems and provide valuable nutrients to the plants and animals in this area. People have coined this amazing migration The Salmon Run. This event occurs annually in the fall for Sockeye Salmon, as it does for most other species of Salmon.

Life cycle

salmon-lifecycle-diagram
The stages of the salmon life cycle from egg to maturity. Source.

This fish’s life cycle is very similar to that of other species of salmon. They are born in freshwater streams and develop from a simple egg to eventually become a fry. This fry stage marks the time in which they begin to migrate downstream and to the ocean. As they approach the ocean, their body begins a physiological change to prepare the salmon for life in saltwater. This stage is called the smolt stage. Combined, these stages make up approximately 3 years of the Sockeye Salmon’s life, after which they are ready to make the migration out into the open ocean where they will gain most of their mass. This Oceanic phase will last a few years until they are ready to begin to reproduce. Little is known about when salmon finally decide they are ready to reproduce but some believe it has to do with hormone accumulation as they reach maturity. Once they are sexually mature, they travel to their native stream with the goal of reproducing and then the salmon perishes. Then, this process starts over again for the next generation of salmon.

Migration

When salmon are born, they stay in their natal stream for up to 3 years until they are ready to move onto their adult life in the Ocean. Once out in the open waters, they spend up to 4 years growing and maturing. Their growth proceeds quickly due to their diet of krill and other zooplankton. This diet also gives the Sockeye Salmon meat it’s red-orange hue (as seen on the right).

img_3236-jpg
Salmon have a distinct meat color due to their diet. These salmon were on display at whole foods.

After their Oceanic phase, the Sockeye Salmon is usually 2-2.5 feet in length and can weigh between 5 and 15 pounds. An adult Sockeye Salmon has a silvery hue to their scales, like most marine fish, to help camouflage themselves from predators. Some of these features change as the start their extreme migration. Once they are ready to return, they start a mass migration towards their natal streams and gather in the estuary that lead to this stream. Sockeye Salmon are anadromous meaning that they return to freshwater to spawn after living their adult lives in the saltwater of the ocean. They begin the long climb up to their spawning grounds. During this time, Sockeye Salmon stop eating food and rely on their energy stored in their fat, muscles, and organs. Slowly, the salmon start to die on this journey to reproduce. Some don’t even make it to the spawning grounds and die en route. The long swim up to their natal streams can be strenuous and there are often barriers that block them from moving upstream. Some small waterfalls are overcome by the salmon’s ability to “leap” out of the water. Some can jump heights of 12 feet. It is estimated that millions of salmon enter the streams every year. Although many of the Salmon don’t make it to their natal stream, they have strength in numbers. Pre-spawn death, disease, and predatory animals mark some of their biggest obstacles. But they never give up on their goal of making it home to reproduce.

 

Spawning

Sockeye Salmon make the perilous journey up fast running rivers and waterfalls all for one purpose, to reproduce. While on their journey upstream, changes start to occur in their bodies, getting themselves ready for reproduction. In males, the silvery scales turn a bright in addition to a few other changes that are used when fighting other males for the chance to reproduce with a female. The large hump forms on their back and their jaw begins to develop a kype, or a hooked snout, to show that they are dominant.

sockeye_salmon_spawning
The differences in males and females during reproduction.  Notice the small kype that has developed on the top jaw of the male. Source.

In females, the same red hue forms on their scales and eggs are finally ready to be laid and, once in her natal stream; she begins to prepare a nest. She does this by finding a nice spot with soft gravel and flaps her tail repeatedly forming a small divot in the ground called a reed. Here the female deposits thousands of eggs and then the male release his milt, which contains sperm cells. The pair then moves upstream and repeats this process. The female continues making her reeds and the gravel that she moves is pushed downstream and covers the newly fertilized eggs for protection. Once reproduction is complete and the Sockeye Salmon are drained of all energy, they die. This semelparous characteristic is distinct in Sockeye Salmon with an almost 100% mortality rate. Sockeye Salmon truly give everything they have for the next generation to have a chance to make it to the ocean.

Keystone Species

A keystone species is a plant or animal that has a unique characteristic that helps to support the ecosystem around it. Without this species, the ecosystem would change significantly or perish in the process. Sockeye Salmon are a keystone species of British Columbia supporting many different wildlife with the nutrients that they bring in their bodies from the open ocean. Bears are just one of the organisms that rely on salmon for vital nutrients to survive. Most bears haven’t had a sufficient meal since before hibernating, which can be up to 10 months ago. They gather in the small streams and waterfalls and wait patiently for their meal. As the salmon leap up small waterfalls, bears are waiting for the best time to strike. This video shows how accurate bears can be when catching salmon. The bears have a feeding frenzy and put on pounds and pounds of fat to prepare themselves for the winter and hibernation. Even after the Salmon have died after they reproduced, young bears will pick up the carcasses and eat those as well. Bears are not the only predators that benefit from the salmon. Wolves are active predators that will hunt for Sockeye Salmon in shallow streams to feed their young. While the salmon still wait in the estuary, before entering the streams, bald eagles fish for them and pluck them out of the streams with amazing accuracy.  Their sharp talons only need to grab a little bit of flesh to perform a successful catch. Although the Salmon Run brings many nutrients to the animals of the temperate forests of British Columbia, the forest itself benefits the most. Bears and wolves will carry salmon with them before dropping them on the forest floor. As the salmon decay, they release many nutrients such as Carbon, Nitrogen, and Phosphorus into the ground. These elements are crucial in supporting the growth of trees and other plants in the forest.

Conclusion

After years of living in the ocean, feeding on of zooplankton, Sockeye Salmon decide that they must continue the life cycle that their parents endured before them. They make the perilous journey upstream, fighting vicious predators and risky obstacles, all with one goal in mind, to reproduce. The Salmon Run is one of the most interesting migrations in the animal kingdom. The Sockeye Salmon is truly one of the most important fish to the plants and animals of British Columbia.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s