The Vernal Equinox and the Steelhead

Astronomically speaking, the vernal equinox is the day in the Northern Hemisphere (March 20 or 21) on which the length of night and day are more or less equal and the Sun is at the Earth's equator.  From this day forward, the Sun begins to shine on the higher latitudes in the Northern Hemisphere until the Summer Solstice on June 20 or 21.  The inclination of the Earth on it's axis relative to the Sun is the reason for the changing seasons.  Essentially, the Vernal Equinox marks the point in the year in the Northern Hemisphere when the Earth is inclined on it's axis toward the Sun.  The greater the angle of the Earth toward the Sun, the warmer the temperatures.  This is obviously reversed for the Autumnal Equinox and Winter Solstice, but that can be discussed at a later time.

Now that we've covered the basic science here, what does this mean in terms of.....(you guessed it!).....aquatic organism behavor (specifically those belonging to the Oncorhynchus genus of the Salmonidea family)?  Let's keep it simple and focus on steelhead (Oncorhynchus mykiss) for this particular post.  The anadromous steelhead (native to Pacific Ocean tributaries of North America and Asia) was introduced into Lake Ontario.  The steelhead from Lake Ontario begin their migration into tributaries in waves starting in the mid to late fall.  They enter the tribs to follow the spawning salmon and gorge on eggs floating downstream.  Steelhead will continue to enter the tributaries throughout the winter months, depending on water flow.

The winter fish have a much slower metabolism due to extremely low water temperatures.  Colder water has a higher capacity to carry dissolved oxygen.  So, the fish don't have to brave the faster, highly oxygenated  riffles and runs as they do in warm weather.  The fish can sit tight in deep, slow water and current seams and not worry as much about feeding during the winter.  Winter steelheading can be more difficult for this reason in addition to the weather conditions.

So what does this seasonal transition from winter to spring mean us anglers and, more importantly, the steelhead?  First is the obvious warming temperatures.  This alone can make for more enjoyable days on the river.  The melting snow, birds chirping and trees budding can be food for the soul.  It is a wonderful thing to be able to head out in the morning and not worry about frozen toes and iced up guides.  But, better bring a backpack because those necessary layers in the morning might quickly become too much in the warm afternoon sun!

The fish also respond to the increase in temperatures.  The warming air temperatures have the necessary side effect of melting the snow pack from the winter.  This, of course, can cause rapidly increasing water flows and actually keep the river water pretty darn cold until the snow is gone.  Once the water begins to warm up above 40 degrees F, the fish become much more active.

The females begin to set up to dig their spawning beds, called redds.  This can be very entertaining to watch.  You will see the female flailing around, beating the river bed with her tail to break up the gravel bottom and make it more suitable for her eggs.  The males will also vie for position with the female in order to be the one to fertilize the eggs once she drops them.  The males can be very aggressive, attacking each other to exert their dominance.  The spring steelhead can look like a fall salmon, with wounds and white battle scars.  This male has gotten into a couple scuffles with other males during the spawn.
 

The females are tougher to target during the spawn.  And, honestly, I think a spawning female should be left alone if possible during the spawn.  She has a very important job ahead of her in depositing her eggs in the river bed.  The offspring from her eggs can help to sustain the fishery in the years to come.  The males can be caught very readily during the spawn, though.  They will often be found behind a female excavating on the redd.  Throwing an egg pattern or bead to these aggressive males is very effective.

Spring is a wonderful time of year, a new beginning of sorts.  The only negative aspect of this is that soon these beautiful steelhead will have spawned and made their way back to Lake Ontario for the summer.  But, all this means is that it is time to focus on some other fish species.  And, let's be honest, the steelhead is quite an attention hog from November until May!  We are just turning the corner from winter into spring in Central New York.  Let's hope this is another great spring season for fishing!  Here are a few more photos from a great April day in 2010 on the Salmon River.