This week’s work
took me to the Columbia River for a two day trip to gather a population sample
of sub-yearling salmon. These Salmon will be used to continue research on
growth, development, genetics, health and a myriad of other things. The
collection method on this day was a fishing technique known as purse seining. Purse seining is a good method
to take samples in an area because the net is the same size every time you
deploy it and it is stationary so unlike a towed trawling net the purse seine
net captures organisms in the same size area each time. This is advantageous
because it can tell someone what is in that area at that given time.
The operation requires
two boats; the main boat and a skiff. The main boat is designed for this purpose
and is outfitted with a winch, a boom and a water pump. The deck is large and
open on one side to allow for the net to be hauled on board.
The skiff is
smaller an looks much like a fishing boat that you might see on a lake with the
exception of an anchor point that the net is attached to while it is being
deployed. The smaller boat shadows the larger boat for the majority of the day
and I was constantly amazed at the degree of skill that the operators of both
vessels showed throughout the day.
Day one started
out with smooth waters and cloudy skies. After a safety and equipment check we
headed out into the mighty Columbia. The drive across the flat water took about
25 minutes. Once we reached the correct location we quickly got to work and
began to deploy the net. After some preparations were made a rope which is
fastened to one end of the net is thrown to the skiff driver who hooks it to
his boat and pulls away.
As the skiff
driver pulls the rope the net begins to slither off of the boat and into the
water. The bottom of the net is weighted and sinks. The top is lined with
floats which float behind the skiff. The 500 foot long net is stretched in a
large circle and the skiff driver brings his end back to the boat where it is
reunited with its opposite side.
When the circle is
complete a large weight is dropped into the water to close the bottom of the
net and the net is pulled in by hand, the whole crew helps with this task and it is carefully piled back on the deck for the next deployment. Fish are collected, identified, weighed,
and the samples which we set out to collect are quickly frozen and stored for
later analysis. Other fish are simply recorded and let go without harm.
The net is
deployed many times throughout the tide as a way to identify when the fish are
where in the water, in relation to tidal changes. The location also changes to
see where the majority of the population is at a given time. Many types of fish
were collected from herring to anchovies, salmon and smelt. During the final
haul of the first day I was shocked to see the water in the net boiling as it
was pulled onto the boat. I found it difficult to focus my eyes on what it was
that was causing this phenomenon but as it got closer to the surface I realized
that we had caught an estimated 16,000 anchovies! Luckily we only had to count
a small portion of them and all were released back into the ocean.
A quick thank you
to Brian the skipper of the Pelican who’s expertise got us out and back both
days without the slightest difficulty. I do enjoy watching someone who is a
master of their craft, perform a skillful task as if it is the most natural
thing in the world. What a great opportunity!
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