blue water trolling and sonar useage - The Hull Truth

Lil John · 03-13-2005, 07:30 AM

I left this out of the electronics section as I didn't want to start a debate/discussion on various brands of fish finders and who thought which was the better brand. This is a rather basic question not from a newcomer to trolling but from a relative newbie at using sonar when trolling blue water. I mainly troll various skirted jet heads and feathers for Mahi, Yellow Fin, Wahoo, and Black Marlin in the Asia/South Pacific region in water depths of 2,000-8,000ft. To get the most out of a quality sonar unit in these conditions, how exactly does one employ it? Currently, I use my dual frequency 50/200kHz unit in manual mode and set the range at 200-300 ft - gain and sensitivity are adjusted accordingly. My reasoning for this - and perhaps I am looking at it wrong - is why look any deeper with these species since I am surface trolling.

In the past four outings, I have caught Mahi, Yellow Fin, and Wahoo yet none of them ever came up on sonar prior to the strike and this is confusing as all heck to me. Am I using my sonar incorrectly or are these speedy fish simply "zooming in under the radar" so to speak? I get varied recommendations from other local anglers that are all over the map on this topic. Some say use 50kHz due to its wider cone and deeper penetration while others say since I am only sounding down to 200-300ft, use 200kHz for its better detail. Others say the reason I am not picking up these fast gamefish up is they are coming in from the side out of sonar cone and striking before my transducer picks them up. Still others say to set my range much deeper and that will pick them up. I am literate on the strengths and weaknesses of each frequency and when to use them (I think) but neither frequency seems to pick up these fast gamefish prior to the strike.

How are you guys setting up your fish finders when trolling out in the deep blue and what am I doing incorrectly? My transducer is installed perfectly and works just fine at locating fish closer to the bottom in depths to 500ft. Any ideas?

Thanks.....

tprice · 03-13-2005, 07:50 AM

I am by far no expert on trolling but my understanding is that any changes in bottom structure can create habitat for fish to live/feed. Now I am not sure about those kind of depths but most folks will fish along a ledge, drop off or a sudden rise in bottom depth(humps).

I am sure someone else can help you a little more on this.

buxtales · 03-13-2005, 11:20 AM

I'm no expert but I'll offer my oppinion. The 50khz gives a wider cone better for shallower water. The 200khz is deeper more narrow. I actually use both when trolling. Sometimes you go over the fish and can see them on the screen but many times they came from the side. When trolling offshore it's not uncommon to see a fish screaming towards the spread from the side...most times this woudn't be picked up from your sonar...especially on the 200khz setting. I just purchased a new FF so now I need to spend some time getting comfortable with it. To me, it's all about the confidence that a good ff can provide. Good luck!

Bullshipper · 03-13-2005, 12:43 PM

Tuna will stay away from the boat and will sound when you get near. Mahi and wahoo are usually around surface rips or debri, so it is not advisable to try to get directly over them, or you will kill the bite.

What you might see is a bait ball deep or a thermocline, but these thermoclines will usually block out the fish underneath them

When real deep, I turn up my gain to 4 out of 5, then adjust the filter to see if I can see them, the bait or the thermocline.

My water is deep here too, so I use batho charts to find structure that always holds fish, then use the zoom depth range scales so the finder is not looking at shallow or real deep depths. Turn the fish alarm beeper on to get your attention.

Nomans · 03-13-2005, 01:36 PM

Can't speak to what happens out there in the Pacific, but my experience trolling off the northeast US offshore is that the only game fish I routinely see on the sounder are tuna in schools. Hard to miss those big red blobs on the screen. I do the same thing you do, which is set my sounder to a "slice" of the water. In my case, that would usually be the depth range between 20 feet and 300 feet. What I am really hoping to see is a school of bait fish trapped by a temperature break so I can concentrate my efforts trolling in the vicinity. I use the 200 hz for this purpose.

I think that even with the wider beam angle on the 50hz setting, the chance that the fish will swim into the cone before showing up in the spread behind the boat is pretty slim. When I have seen the fish heading in (visually), they are usually coming up from behind or from way out to the side.

Fish Magician · 03-13-2005, 04:36 PM

Your sounder is set up okay. It's just that we don't always run directly over the fish we catch. Many of the come from outisde the area of the cone of the sounder. Directly under the boat the beams are pretty narrow. I use mine, set just like yours, to look for the bait fish that the bigger guys have to feed on. When I locate the bait, them I'll see the predators. Try locating some bait, run over it so you can get familar with how that stuff looks on the screen. Best of Luck.

Capt. Mike Fisher

Lil John · 03-14-2005, 07:20 AM

Thanks guys for sharing your insight. After spending nearly 2 grand on high-end combo ff/plotter (NAVMAN 6600), I thought it had problems when I wasn't picking up the fast-moving gamefish prior to the strike. In auto mode, the unit is just fine to run right out of the box for depths to around 300ft. Then I read in the manual that for best deep water performance, you need to take it out of auto mode and manually adjust it for top performance. I was confident after about 5 outings that I had the various adjustments down pat and I learn more each and every time I adjust. I will look for the thermoclines, bait balls, and dropoffs and work them regardless of what the sonar picks up. Again, thanks for your help.
Lil John