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Trawl tracks |
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Trawl tracks |
You need to know about the bottom where you are fishing - and you know almost nothing directly about it. You may have some begin / end marks and lines on a plotter marking routes known to be free of obstacles; you may know that a particular contour line is safe to follow for a given segment; you may have thousands of depth marks on your plotter, each one showing the depth at that point, perhaps even colored by depth range - and you've got lots of effort expended by your brain to try and figure out how the bottom looks and where the net-eating obstacles and rich shoals of fish live.
Marimsys BRIDGE makes it possible for you to see the bottom. The system takes soundings data while you are fishing, you send that data to Marine Imaging over the internet, we make it into charts and send them back to you, pre-calibrated. These charts show the bottom with its obstacles and its places for fish to hide. You can determine in which sort of terrain the fish are found, and then looking at the charts - find more of the same habitat. Obstacles or "stubbies" which would tear the net are visible on the chart - you can avoid them without having to find them first with a net. You can look at a complicated and difficult bottom - the kind that fish live in, protected by the obstacles - and plot out trawl routes through the obstacles. You can estimate the effect of currents on bottom terrain, both to help you find fish, and to estimate where the trawl is. And if you have the Simrad ITI System, you can see the bottom from the perspective of the net - and scrape the fish off the sides of the ledges or duck around the stubbies.
A few miles west of the illustration area, the main flow of the cold and powerful Humboldt Current goes by, south to north. Where we are fishing is the inshore side of the current, on the edge of the continental shelf where it runs east-west for a bit. These sunken river valleys, created by faulting, were gouged-out back in the time of the glaciers. The underlying rock rises out of the Humboldt trench just to the west where it is created, and pushes this whole area up, creating a jungle of faults. Where the ship is, when you get a clear day you can see live volcanoes from the bridge. Its one hell of a piece of bottom to trawl - and most skippers don't.
As the current goes around these projections and valleys it eddies, moving the trawl in directions which are unpredictable from the surface - unless you happen to have this chart and can project how the current will jog. The high ridges, protruding into the current flow and surrounding the valleys push the current up into mini-upwellings which slows the water flow and causes sediments to fall out on the lee sides and into the valleys. To confuse the issue, current flows east and in with the tide up the valleys from the Humboldt Current. The outgoing tidal current slows down the current welling up the valleys - but generally doesn't stop it entirely. The force of this incoming current can bare the rocks at the narrow points, or where the valley makes abrupt turns. At the tops of the ridges jutting up into the currents, there will be almost bare (and jagged) rock.
In the area shown, you want to fish the zones where the sediments fall out at the bottoms and the sides of the valleys. This chart enables you to see the valley sides, steep places that won't hold enough sediment to cover the rock, knobs that stick out, and one way cul-de-sacs. You can also estimate the effects of a generally SW current. Beware, that current jogs around to the North when it enters the valley at the east of the image, with the rising tide.
If you noted that the fish were hugging the ledges, and needed to really fish the area tightly, you'd click up the Marimsys Chart with 1 or 2 meter contours. But, for this trawl, the chart shown displays the surrounding valley well, and you don't need it.
A bit of explanation about the screen: the upper left status bar gives cursor position, the bearing from the ship to the cursor, and vessel speed. The status bar along the bottom tells you that instrument data is entering, ship position, time, date, course, vessel speed, echosounder depth, temperature and the status of the Autolog. The ship position is represented by an arrow, and right below the tip of the arrow, you'll see the depth shown for the position on the Marimsys Chart - 435 meters - same as the echosounder.
With the image, you understand this area and its tortured ledges and valleys, and how the current flows. If you noted fish on the small step ledges, or on the lee side of the rock projecting into the current, or down in the bottom of the valley - you've learned where they are today. You file that away for future use, it is valuable information; and you click the next Marimsys Chart to the screen, spot the areas where the fish will be and go directly there. When you learn what the good spots look like in today's conditions, and if you've got the charts - you can find more of them and go directly there. That puts a lot of fish in the hold and saves fuel - or, you could call it increasing productivity.
With Marimsys BRIDGE and Marimsys Charts you have a view of the bottom. You can visualize your fishing in front of that view of the bottom. You will observe better fishing in some types of terrain, and not-so-good fishing in other types of bottom. You will observe bottom that will catch your gear - and be able to fish right beside it, not on it. You will spend more time fishing in the good areas, and less time in the others. It adds up to more highly productive fishing days.
BRIDGE is a full-fledged electronic plotter that uses many different types of charting. Notable among the types of charts it uses are Marimsys Charts, prepared by us from data gathered by your own vessel. These provide a view of your workplace - the seabed - that is unsurpassed. Scale can range down to about 1: 2500 for the difficult bottom where you need that level of detail to work. Our Marimsys BRIDGE System gathers the data to make Marimsys Charts of the bottom, and also displays many different types of charts such as: Satellite Bathymetry, and Satellite mGal Gravity charts for exploration of new areas; and of course, normal Sovereign Nautical Charts.
These Marimsys Chart images are very highly detailed views of the bottom and provide extensive habitat information, as well as make the obstacles to fishing visible. This means that you see the character of the ocean bottom where you are making (or not making) catches, and can visualize the movement of currents and eddies over and around the terrain. You can make connections over what combination of bottom type and feature (hill, valley, slope or flats) and current (ebb, set, various current layers, temperature, and season) are productive - and which combinations are not. BRIDGE is a fishing system and is designed to help you answer the question: Why am I catching (or not catching) right-here right-now?
If you have, or are thinking of purchasing the Simrad ITI system, take a look at that section too.
F/V Friosur VIII and Captain Jon Ivar Halvarsson collected the data for these Marimsys Charts. Grimur Eiricksson and Carlos Vial I. kindly gave us permission to use these images, the property of Friosur S.A. Our thanks to them and the Friosur team. Latitudes and Longitudes appearing in the screens have been changed to protect the actual locations.
