Gillnet - Groundfish

Click the small image at any time to go right to the full sized gillnet images. 

Gillnet set - Groundfish	Gillnet haul - Groundfish

You want to know about the bottom in the area you are going to fish, to make good decisions as to where to set the net.  You often set to take advantage of fish following tidal or current flows.   These fish will be moving along the bottom at a particular time, whether it is with sunset, at the change of the tide, or with the tidal flow.  Maximum netting efficiency is obtained when the net is placed in an area where fish movements are naturally focused by the contours of the bottom.  Groundfish will tend to go around obstacles and hold to the same distance from the bottom at the same time of day.  If you can locate key valleys and passages for fish movements, know the time and state of the tide at which the fish move, and use the currents to place your net exactly where you want it - you'll catch more.

Marimsys Charts can be of great advantage in locating these highly productive fish movement locations, and pinpointing the area where the net can be placed without encountering obstacles which can damage it.  Hit and miss setting between marks on a conventional plotter, or looking for fish on the sounder isn't going to make the most effective set. 

With Marimsys Charts, made using soundings gathered in Marimsys BRIDGE, we can change the way you fish. When you have a visual understanding of what the bottom is like, you can see the contours and make perfect sets.  Just looking at the terrain on the chart gives you a good idea of the natural paths groundfish use as they go about their business.  The key narrow point in the valley, (click on the small image at the top of the page to see) looks good, but will your net span it?   With BRIDGE you would know the distances with a point and a click. 

There are other secrets to be revealed by these charts, but first a bit of background on the general area.  A few miles west of the fishing area, the main flow of the cold and powerful Humboldt Current goes by, South to North.  Where we are fishing is in the zone of the inshore eddies.  These sunken river valleys, part of the Chilean Continental Shelf were gouged-out back in the time of the glaciers, and are now hundreds of meters below the ocean surface.  The high ridges surrounding the valleys push the current up into mini-upwellings which slows the water flow and causes sediments to fall out 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. 

Currents will change close to the bottom based upon how the hills and valleys are laid out.  You can use your set and haul points for the net to judge currents, the net should have set on the bottom close to midway between the set and haul points.  You get a good idea of the current by doing a point and click distance measurement between set and haul points - or you can just look halfway between the set and haul point.  The current is going to change in different places, and over the lunar cycle. When you have a good idea of what the current is going to be like today - you make sets that pay. You build up a "knowledge base" of how current affects your sets and note the information down on the chart - the information will be right there on the chart to view when you need it.

Here in the valley 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, to estimate the effects of a generally SW current and work out where to set.   If you were going into some of the more complex areas with bare rock, you'd want the Marimsys Chart with 1 or 2 meter contours.  For this "neck" of the valley, the chart shown displays the surrounding valley well, and you don't need the detail.  The set is across the valley, at the bottleneck where the width is less than a mile. The red down arrows are the set points, the net buoys.  To follow this description of the screens from the Marimsys BRIDGE set, click on the Gillnet - set to see it (this is the same image as appears above).

For the haul you'll want to retrace just the track segment you saved while shooting, saved as the red heavy line.  Knowing where and in what conditions you caught fish will help plan your next set.  You will click in a catch entry for every 10 fish coming in over the side and see how the catch compares to the terrain.  These icons on the image    show a catch entry, which in the actual BRIDGE program you could click to see the catch at that point.  We filled in a catch entry for every 10 fish coming over the side, so we would know where the catches were spaced along the line.  Click the catch icon     to see a sample report for 10 fish.

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 - 488 meters - same as the echosounder. 

After the haul you'll want to know where on the net you fished best, and where you didn't do so well, and to figure out why.  The haul image displays the haul points (green up arrows) connected as a route (with a red heavy line).  You also see the shoot points (red heavy down pointing arrows).   With them side by side, you look at the icons, assume that the line rested on the bottom close to the midpoint, and you can estimate current drift while setting.  Or if you prefer, you can measure the distance between the marks and hence the drift, with a right button click.  

Now let's look at the actual haul, click on  . 

The net sank quite a bit East of the set point, going right up the valley with the current.  It looks like the net hit bottom just where you wanted it, right at the bottleneck - good current estimation!  You may be cleaning a bit of bottom crud off both wings of the net where it laid up against the ledge - but that's a small price to pay for sealing that valley up tight. 

You understand this valley and the current.  But, the current changes with the lunar cycle.  It would be best to "tack" a message right on the side of this valley saying, "8 days before the full moon - #29 set positions worked perfectly".  That way when you next set here and want to put the net right in the bottleneck -  you can look at the state of the tide and estimate moving the set point a bit East or West so that you drop right in the same place.   We're tying information to the portion of the bottom to which it applies and making it readable with a Click - and the result is that you have more information available to help you make good "where to set" decisions.

This image could just as easily have been of a beach, or a rocky part of the shore.  It would have shown the clear areas where a gillnet could be set without fouling.  Or, the clear areas where the net could be set that are right next to the rocky cover where fish spend much of their time.

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: Bathymetric, and 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? 

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.