Wednesday, November 4, 2009

The moon and the tide


Catching a glimpse of the full moon sparkling over the water last night got me to thinking about how connected the ocean and the heavens are. At this time of year a full moon is considered to be a Harvest Moon and as such has long had a special significance to farmers and folks who depend on the land. It also has a special significance for fishermen.

When I was a salmon troller, both the full and new moon phases were important times of the month because that's when I could count on salmon to bite the best. It was a convergence of consequences that worked in my favour and against the salmon. First of all, salmon always seem to bite best first thing in the morning. The rising sun and increasing light of the new day always gets them going. Dawn is the prime time of day when an angler wants to have his or her gear in the water. Also, when the tide changes four times a day the slackening and shifting currents have a powerful effect on all marine species, salmon included. Forage fish-known as feed or bait-seek refuge from the strong currents by hiding behind ridges and boulders on the bottom. I think they are saving energy that way. When the currents slacken you can see the bait rising up in clouds from their hiding places on a depth sounder. This will usually cause salmon to go into a feeding frenzy and increases the opportunities for a fisherman trolling through the balls of bait. Salmon also seem to bite better on a rising tide. And then, it seems to me at least, the harder the tide runs, the harder the fish bite. One thing for sure is all salmon seem to do something other than eat between about 2 in the afternoon and just before supper is served aboard. It doesn't matter if supper is at four in the afternoon or seven in the evening, as soon as you sit down to enjoy it you are guarranteed to get a fish on the line.

Early on in my fishing career I learned from the oldtimers, "When the moon comes up, the tide comes up and when the moon goes down, the tide goes down." This means you can always tell what the tide is doing if you can see the moon. As the moon rises in the east, it pulls the tide up with it. The tide is highest when the moon is highest. And as the moon starts on a downward trajectory and sets in the west, the tide goes out.

When the moon is full it is aligned opposite the sun and always sets early in the morning and rises in the evening. The new moon is aligned so it rises at the same time the sun does. Twice a month these two celestial orbs conspire during these two phases to create a strong gravitational pull on the ocean that leads to the "spring" or highest high and lowest low tides. The strongest tidal currents are generated during the "spring" tides. And all these factors favour the fisherman, not the fish.

So on a full or new moon, low water slack is first thing in the morning just as the sun is coming up. These "spring" tides flood or rise all morning creating the strongest currents during the time of day when salmon like to bite the best. After the tide turns to ebb and starts to go out, it's after lunch when most salmon do something other than eat anyway.

I think Sir Isaac Newton was the first physicist to correlate the cycles of tides to the phases of the moon based on his theory of universal gravitation, but I'm sure folks who spent their lives on the ocean had an idea about how these were connected long before Newton out it down on paper. I'm sure the fishermen had it pegged!

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