Author
Topic: Thermocline! The "invisible" Marlin Magnet!  (Read 7136 times)

0 Members and 1 Guest are viewing this topic.

Offline Reel Magic Charters

  • Senior Member
  • **
  • Join Date: Jan 2012
  • Posts: 589
  • Cred: 39
  • Gender: Male
  • Are u up for it!
  • Location: Richards Bay
Thermocline! The "invisible" Marlin Magnet!
« on: February 17, 2013, 08:01:21 am »
REEL MAGIC SUCCESS :  THERMOCLINE: - THE “INVISIBLE” MARLIN MAGNET
by Trevor Hansen     



After an awesome 2011/2012 season on the water off Richards Bay running  Reel Magic Charters, where we caught 26 marlin and released 22. In the process  catching the biggest fish to be caught off Richards Bay, an 800lb beauty and 4  more fish over 500lbs, I wanted to share some info that may be of help to some  struggling skippers out there. It has been interesting being out their  regularly and observing the way many of the skippers “work” the waters on the  drop-off with limited success. Although I wrote this article some time ago, it  has not been published, as the info provided is a huge advantage to any skipper  in our waters. I have also added some recent info here and there, which may be  of further interest.
   
I am assuming that everyone knows what a thermocline is, and if you  don’t, then learning about it now will give you a much greater understanding of  its effects on the fishing in your area. Any fisherman worth his salt should be  well aware of the phenomenon and its value when fishing for all species of  fish, not only game fish. The effect on various species may differ, but each  will have a definite reaction to the presence of a thermocline, whether it is  in shallow or deep water. Being aware of its presence can hugely benefit a  fisherman in forecasting where the different species will hold and whether they  will feed on a given day or not.
 
It was however learning and understanding the effect of thermocline on  Yellowfin in the Eastern Cape waters that has proved very beneficial in  predicting the feeding pattern of the Marlin in the warmer waters of the  Richards Bay area.
Thermoclines are very well defined especially in our temperate water  areas where there are great differences in temperature in the water column.  Having grown up on the PE coast, where the cold-water thermocline is a regular  occurrence after strong NE or NW winds, we have become accustomed to the  effects of the cold-water upwelling, on our fishing.
There are huge benefits to be gained from observing its position and  depth in the water column, especially when well defined 30 to 40 miles  offshore. A strong thermocline concentrates plankton and baitfish and therefore  gamefish, on a defined line offshore, and is a great tool for predicting where  the gamefish will feed. For those who have the equipment to see it and the  knowledge to interpret it, it is a goldmine.
 
What really surprised me on my first visit to Richards Bay in 2007, was  not its presence in the warm water off the coast but how well defined it was in  some areas, and how effective it was as a tool in catching Blue Marlin.
 
 
 

Richards Bay Thermocline  showing from 50 – 200 meters


 
My first trip off Richards  Bay on Reel Magic, was shortly prior to the last Black Watch marlin  competition. We did a recce off the Dawson’s / Druk-gang area before the comp  and I was amazed to see the presence of several well-defined thermoclines off  the coastline, something that I was only accustomed to seeing off our coast. Having  the best equipment on board also played a huge part in being able to put the  puzzle together. The thermocline only shows properly on low frequency with  certain set-ups on at least a 1 kw transducer.
I had had the luxury of  having two 2 kw echo sounders, one set on high frequency and the other on low  frequency or I may have missed its presence completely. When we saw the  thermocline for the first time, I was amazed at its presence and how strong it  was.  I was sure that it was going to  have equal significance for the marlin as it has for tuna down south. I knew it  would concentrate the food and therefore the bait and the marlin. We set up a  pattern and started to work the thermocline. The first strike came immediately  but it didn’t stick. It didn’t matter as I was totally focused on seeing what  else we could produce on the thermocline. With only two of us on the 45 ft  vessel, it was going to be tough, and so it proved, as we hooked four marlin,  losing 3 on jump offs, and one after a good fight when the hooks pulled. We  were sorry to have lost the fish but I was so impressed with the success we  were having, knowing that the information gained was going to prove invaluable.
 
 
 
 
 
 
It was some days later that  I took to photographing the set-up on the Raymarine equipment for exactly this  article.
 
Take note of the position of  the blue flag, which marks the start of the thermocline at 50m below the  surface. The boat track shows us working the thermocline edge from 50 – 200m.  On this day, one strike occurred at the 75 /100m thermocline depth and the  other at 150m thermocline depth. This corresponded with the position of the  bait in the thermocline, which was marked with the small fish. The other marlin  strikes are not from this days fishing.
 
There are 3 main  thermoclines visible in this area on most days, one in the 150-250m depth area,  one around the 500m area and a very weak thermocline on the 700-900m area. One  must remember that these thermoclines are not stationary and move all the time  depending on the conditions. The trick is to find the thermocline carrying the  bait and hence the marlin. Once one has locked onto the correct thermocline the  game becomes much simpler and the results will follow. Setting up ones  equipment to maximise the view is very important and many of the smaller  systems do not have the ability to see this structure due to lack of low  frequency or enough power to bring the info on board. 
 
 
Below I have taken photos to  show the difference in picture with high frequency and low frequency settings  for the exact same position. Note the way the low frequency transducer shows  the bait clearly as well as the thermocline while it is almost  indistinguishable on high frequency.   


 

Baitfish in the thermocline  as seen on low frequency
 



Same baitfish and  thermocline on high frequency


 
 

 Baitfish in the thermocline  at 114 meters.


 

 
 

 
Marlin above the bait fish!
 
 

 
It is essential to mark the  position of the baitfish on the plotter and to work the area thoroughly. These  bait positions will vary through the day as the tide moves in and out, and  concentrating on these areas is essential. The bait will usually rise to the  surface at the top of the tide and become visible, as will the bird life. It is  unbelievable to see how birds are always in the proximity of these bait balls  even though they are at 100 meters plus below the surface. They will fly in the  area or sit on the water waiting for the bait to rise. It is also amazing that  this bait seems to hold its position fairly constantly even though the current  is strong. Essentially they are holding on or below the thermocline, and thus  are out of the worst of the current and will wait for the current to slack at  the top and bottom of the tide before rising up in the water column. When it does  the birds will be ready, and it is at this time that we should be ready too. It  is exactly then that most strikes will occur!
Marlin will wait for these  moments and become more active during this golden hour. Being on the  thermocline in the right place at this time is crucial if one wants to increase  ones chances. Blindly trolling an area in hope of a strike is like looking for  a needle in a haystack! Yes from time to time one will get lucky by being in  that zone at the right time but then it’s a stroke of blind luck. Knowing where  the zone is and staying in it 100% of the time is how one will guarantee  success and out do your mates! Good skippers know their equipment and can see  these structures in the water column, and use this information to guarantee success.
 
There have been times that  working the thermocline has not produced exceptional results. As was the case  for us in February at the 2012 SADSAA Classic where we had water temperatures  of 27/28 C from the harbour wall to the 1000 m depth line. There was therefore  no real break in temperature or defined current line, but these things happen  when overly warm currents push over the shelf close inshore and spread the fish  over a vast area. The result was fish feeding anywhere from 50-1500m, but this  is not the norm and once there is cooler water on the inside the pattern will  re-establish itself. We did drop a very nice fish exactly on the line, but we  also released a fish on the 200m contour. In fact most the fish came out in the  shallows for the comp. A few weeks later the south-westerly wind forced a  cooler wedge of water inshore and the pattern was back to normal.   
 
What is also interesting and  something I have found over the past 5 years is a predominance of strikes on  the line where the thermocline is at a depth of 100m. With all the adverse  weather this year there was much time to read and research some of the data  that is available on marlin catch stats from long line research. It was amazing  to read their info and find that it corroborated with what I have found off  Richards Bay. The most strikes on long line baits takes place when the baits  are set in the “marine mixing layer” (thermocline) when it lies at a depth of  100m. Another interesting stat was the fact that there were very few strikes on  baits after 3pm, something we have also found when trolling, and is strange as  their data indicates the marlin rising up in the water column at this time and  staying there for the night. This may be due to a digestive process, but this  is not confirmed.
 
One thing is for sure and  that is that to be successful on the water, one needs to use all the  information at ones disposal, and LUCK has very little to do with it. Labouring  Under Correct Knowledge (LUCK) does!!
 
So next time you venture  out, take a new look at the expensive echo sounder on the dash and tune it in  on the “ invisible “ structures in the water column. I guarantee you the  results will amaze you.   
 
   
 
The fruits of “LUCK” 800lb  Blue Marlin Richards Bay 2012
Angler Gavin Van der Merwe
Reel Magic Charters

Offline craigb

  • Ultimate member
  • ***
  • Join Date: Jan 2011
  • Posts: 323
  • Cred: 13
  • i just wanna fish
  • Location: durban
Re: Thermocline! The "invisible" Marlin Magnet!
« Reply #1 on: February 17, 2013, 08:04:04 am »
 :tkx: very interesting reading
I'm not addicted to fishing,i can quit anytime my wife makes me.

Offline Kumz

  • Retired
  • *
  • Join Date: Jun 2010
  • Posts: 0
  • Cred: 0
  • Gender: Male
Re: Thermocline! The "invisible" Marlin Magnet!
« Reply #2 on: February 17, 2013, 08:33:11 am »
Very nice read ... Thanks

Offline Reel Magic Charters

  • Senior Member
  • **
  • Join Date: Jan 2012
  • Posts: 589
  • Cred: 39
  • Gender: Male
  • Are u up for it!
  • Location: Richards Bay
Re: Thermocline! The "invisible" Marlin Magnet!
« Reply #3 on: February 17, 2013, 08:49:08 am »
Pics will be inserted shortly!

Offline REEFMAN

  • Ultimate Champ
  • ****
  • Join Date: Jun 2010
  • Posts: 15888
  • Cred: 744
  • Gender: Male
  • Location: Jozi
Re: Thermocline! The "invisible" Marlin Magnet!
« Reply #4 on: February 17, 2013, 01:02:35 pm »
Ok Pics sorted...

Flippin' AMAZING article Trevor! Grand of you to share such valuable information!!  :+ cred:

Now is not a good time to go fishing... said nobody... EVER!!

Offline L Hooker

  • Ultimate Champ
  • ****
  • Join Date: Nov 2010
  • Posts: 1602
  • Cred: 55
  • Gender: Male
  • Location: Pretoria
Re: Thermocline! The "invisible" Marlin Magnet!
« Reply #5 on: February 18, 2013, 07:56:16 am »
Thanks for sharing excellent info  :tkx:

Offline skip

  • Senior Member
  • **
  • Join Date: Jul 2011
  • Posts: 89
  • Cred: 0
  • Gender: Male
  • Location: Durban
Re: Thermocline! The "invisible" Marlin Magnet!
« Reply #6 on: February 18, 2013, 01:27:50 pm »
Now thats what Im talking about! Thank you very much for such an informative article.  :+ cred:
 

Offline lebaka

  • Ultimate member
  • ***
  • Join Date: Apr 2012
  • Posts: 1093
  • Cred: 66
  • Gender: Male
  • i break bills
  • Location: boksburg
Re: Thermocline! The "invisible" Marlin Magnet!
« Reply #7 on: February 18, 2013, 02:19:52 pm »
this should if it has not yet be nominated for post of the month tx trevor i am a new skipper and appreciate this article immensely :+ cred:   
The gods do not deduct from man's allotted span the hours spent in fishing.  ~Babylonian Proverb

Offline Prego

  • Ultimate Hero
  • *****
  • Join Date: Sep 2010
  • Posts: 3820
  • Cred: 166
  • Gender: Male
  • Because I said so
  • Location: Glenvista, Johannesburg
Re: Thermocline! The "invisible" Marlin Magnet!
« Reply #8 on: February 18, 2013, 02:57:59 pm »
Fantastic piece  :tkx:
Quick question when finding a showing on the thermocline at 100-150m  do you work the area with lures to raise the fish or drop a live bait to the depths?

Offline Shaun17

  • Ultimate Champ
  • ****
  • Join Date: Jan 2012
  • Posts: 2894
  • Cred: 262
  • Gender: Male
  • Location: Durbs
Re: Thermocline! The "invisible" Marlin Magnet!
« Reply #9 on: February 18, 2013, 03:40:48 pm »
Fantastic piece  :tkx:
Quick question when finding a showing on the thermocline at 100-150m  do you work the area with lures to raise the fish or drop a live bait to the depths?


Trevor, thanks a million for the post - awesome info!!! Looks like I have some testing to do with my new Raymarine setup...  :+ cred:


I've got the same question as Prego if you don't mind...

Offline skip

  • Senior Member
  • **
  • Join Date: Jul 2011
  • Posts: 89
  • Cred: 0
  • Gender: Male
  • Location: Durban
Re: Thermocline! The "invisible" Marlin Magnet!
« Reply #10 on: February 18, 2013, 04:17:16 pm »
Quick question when finding a showing on the thermocline at 100-150m  do you work the area with lures to raise the fish or drop a live bait to the depths?
Same??^^^^^^

Offline Reel Magic Charters

  • Senior Member
  • **
  • Join Date: Jan 2012
  • Posts: 589
  • Cred: 39
  • Gender: Male
  • Are u up for it!
  • Location: Richards Bay
Re: Thermocline! The "invisible" Marlin Magnet!
« Reply #11 on: February 18, 2013, 06:05:53 pm »
Lures!

Offline John F

  • Moderator
  • *****
  • Join Date: Jul 2010
  • Posts: 11041
  • Cred: 514
  • Gender: Male
  • Location: Maputo - Mozambique
Re: Thermocline! The "invisible" Marlin Magnet!
« Reply #12 on: February 18, 2013, 06:36:12 pm »
What sort of equipment one needs to have as a minimum to be able to spot these thermoclines? I assume transducer wattage is key?

UA/Columbia Angler of the Month: Oct 2012
UA Post of the Month: Oct 2011; Apr 2012; Sep 2013

Offline Reel Magic Charters

  • Senior Member
  • **
  • Join Date: Jan 2012
  • Posts: 589
  • Cred: 39
  • Gender: Male
  • Are u up for it!
  • Location: Richards Bay
Re: Thermocline! The "invisible" Marlin Magnet!
« Reply #13 on: February 18, 2013, 07:02:18 pm »
Installation of the equipment is key u can see it on 600W systems if installed well. Through hull in solution with wiring taken to the data box seperate from the main engine and power looms is key to eliminating disturbance. One needs a clear screen on maximum gain to look for water column structure. There is so much to tell its hard to explain here I have just fished with Sean van Veijeren who has major experience and is amazed at what I look at. Have spent my life at sea needing to be better than others to earn a living and learning the skills take  Time and observation. One needs to see it in practice and have a lot more info to make it work. Hope this helps!

Offline John F

  • Moderator
  • *****
  • Join Date: Jul 2010
  • Posts: 11041
  • Cred: 514
  • Gender: Male
  • Location: Maputo - Mozambique
Re: Thermocline! The "invisible" Marlin Magnet!
« Reply #14 on: February 18, 2013, 07:13:49 pm »
Thanks

UA/Columbia Angler of the Month: Oct 2012
UA Post of the Month: Oct 2011; Apr 2012; Sep 2013

Offline Reel Magic Charters

  • Senior Member
  • **
  • Join Date: Jan 2012
  • Posts: 589
  • Cred: 39
  • Gender: Male
  • Are u up for it!
  • Location: Richards Bay
Re: Thermocline! The "invisible" Marlin Magnet!
« Reply #15 on: February 18, 2013, 09:29:45 pm »
Have not had a good weekend but will be up and running soon. No more comps for me so fire away any question -would love to answer...glad to be of service w;k   

Offline Capt. Hook

  • Simple Fisherman
  • Ultimate Champ
  • ****
  • Join Date: Jul 2010
  • Posts: 3055
  • Cred: 327
  • Gender: Male
  • www.bluewatercharters.co.za
  • Location: Durban, KZN
Re: Thermocline! The "invisible" Marlin Magnet!
« Reply #16 on: February 18, 2013, 10:37:09 pm »
 :+ cred:  Thank you Trevor.
 
Nominated for Article of the month
BLUE WATER CHARTERS DURBAN - Marlin, Tuna and Big Game Fishing - www.bluewatercharters.co.za

ADVENTURE FISHING SAFARIS - Tiger Fish, Bass and Estuary Fishing - www.adventurefishing.co.za

Offline skip

  • Senior Member
  • **
  • Join Date: Jul 2011
  • Posts: 89
  • Cred: 0
  • Gender: Male
  • Location: Durban
Re: Thermocline! The "invisible" Marlin Magnet!
« Reply #17 on: February 18, 2013, 11:07:48 pm »
Sorry to hear about your blowout at RHB. Man that sucks!!


So basically you would work the area with plastic until the Marlin/bait comes up? At what point would you move on? Work the area until say an hour after high tide?


I'm with Mike, how do I nominate for article of the month?

Offline John F

  • Moderator
  • *****
  • Join Date: Jul 2010
  • Posts: 11041
  • Cred: 514
  • Gender: Male
  • Location: Maputo - Mozambique
Re: Thermocline! The "invisible" Marlin Magnet!
« Reply #18 on: February 18, 2013, 11:15:42 pm »
Nominations for post of the month must be done in the corresponding thread (referring to the month the article was posted) in the Competitions section. Further instructions and rules are also posted there.
In this case http://www.ultimateangling.co.za/index.php?topic=12967.0

UA/Columbia Angler of the Month: Oct 2012
UA Post of the Month: Oct 2011; Apr 2012; Sep 2013

Offline in the lip

  • Member
  • *
  • Join Date: Nov 2010
  • Posts: 23
  • Cred: 1
  • Gender: Male
  • Location: Westville, Durban, Kwa-Zulu Natal
Re: Thermocline! The "invisible" Marlin Magnet!
« Reply #19 on: February 19, 2013, 06:39:15 am »
Superb article, please post pic of lure. White/red/blue ???