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January 14, 2013

Use Side-Scan Sonar to Catch More Fish

Innovative side-scan sonar broadens your view of the underwater realm.

The In-Between Grounds

Side-scanning is a big benefit when fishing reefs and wrecks to 150 feet. Carl Grassi and I had my MARC VI in the Abacos, getting set to drop anchor in shallow water on a large wreck that holds grouper and snapper. By ­initially making a few passes over it with my Lowrance HDS 10 Gen2 unit and its StructureScan, we saw its ­entire layout, areas of activity, and the precise zones we wanted to fish. 

When Holliday fishes 50- to ­60-foot wrecks for permit — and ­especially in off-color water — he’ll use his ­Humminbird to mark the wreck with GPS, and then activate side imaging to see exactly where in the water ­column the permit are staging. “I will hold over the top of the wreck and then tell my clients to cast off to the right 100 feet, if that’s where I’m marking the permit. I can also tell them just how far down to drop the bait, based on whether the permit are 10 feet down or holding near bottom.” 

Says Holliday: “It also helps detect fish moving in on our live chumming, like bonito, blackfin tuna, and even kings and wahoo. I’ll know what outfit and bait to use for that fish, and where to place it. It’s invaluable for wreck ­fishing.”

Fine-Tuning Details

Stuart Wood — a Hallandale, Florida-based senior manager for Navico, and an ardent offshore angler — discovered by accident how to fine-tune his company’s StructureScan feature to scour offshore weed lines for bait and fish. “I do a lot of dolphin fishing with friends, and one day we were trolling along this weed line, and I wondered why we couldn’t see anything,” says Wood. “I played with the settings, and once I manually overrode the ranges and got the unit out of its default setting, I was amazed at the views we got underneath those weeds. I’m talking about submerged weeds, debris, bait and even dolphin out to 300 feet.”

To side-scan weed lines and fish high in the water column, Wood ­recommends three adjustments. First, increase the side range of ­StructureScan to 200 to 300 feet. Next, choose a color palette that offers the clearest picture: He suggests orange. Last, turn up the gain until you wipe out the screen. Then slowly bring down the gain until it begins to clear up. When it first clears is the perfect gain for such situations. “Use the 455 kHz frequency, ” says Wood. “Even though the 800 kHz is designated more for clarity, with advancements in our transducers, you won’t have to go beyond the 455 kHz.”

The same side-scanning ­technology can be used to view beneath your boat. DownScan (Navico) and ­Down Imaging (Humminbird), utilize the same high frequencies to provide the same ultrasharp views.

Traditional sonar reveals the ­bottom, bait and fish, but it’s just shy of the lifelike imagery provided by ­side-scanning technology. Traditional sonar is invaluable, especially in waters beyond 300 feet, where the high frequencies of Downscan and ­Down-Imaging run out of steam. 

I’ll often have three screens up on my Lowrance HDS 10 Gen 2 unit: a left and right view, a DownScan view and a traditional sonar view.