Below Captain Dave on the front cover of the September/ October 2009 Inwater Magazine.

Article page 10. The Seasons Tips for Cape YELLOWFIN by David Christie

Cape Town is blessed with what can only be described as one of the best yellowfin tuna fisheries in the world. Yellowfin tuna are seasonal in our waters arriving in March and departing early June and then again arriving end September, early October and departing early January. There are no fixed dates when they come and go, rather their movements are governed by the seasonal wind variations ultimately driving the ocean currents and governing their passage.

Why are yellowfin tuna only around for about 6 months of the year? Where do they go to for the rest of the year? What we do know from world tagging efforts is that the tuna migrate to the equator to spawn and then move to areas of high food concentration to feed and condition where after they move back to the equator to spawn again repeating the cycle. Because of a heat exchange system between their core muscle and the rest of their body, yellowfin are capable of maintaining their core body temperature much higher than the ambient water temperature. This means that can feed in cold water and maintain fast speeds which gives them an edge on their prey. This is also one of the reasons that they are such powerful fighters on the end of a line.

No conclusive tagging studies have been conducted on the local yellowfin schools that have shown if they move up the east or west coast of South Africa when they move back to the equator to spawn. We do know that yellowfin are caught off the east coast but are these the same fish caught in the cape? Mostly the yellowfin are smaller off the east coast which points to them not being of the same stock. However this is another topic on its own and I won’t go further into it in this article.

Why are the seas around Cape Town so sought after by the tuna? The answer lies with the summer south easterly winds which are the engine behind the Benguella current ultimately driving upwelling. Upwelling is key as nutrient rich water from depth gets driven to the surface resulting in rapid growth and incredible productivity throughout the food chain. This gives rise to large numbers of bait fish and other prey species which in turn attract the tuna. The west coast of South Africa is governed by fewer species than the east coast, however it makes up for this by its sheer multitudes which rely on the upwelling to sustain them.

Yellowfin prefer warmer water and if you are targeting them is is the first thing to look for. By warmer I mean temperatures above 16 degrees centigrade. I have caught yellowfin in dirty green water of 14 degrees, but this is definitely not the norm and have found that although they still do feed in the warmer temperatures that we get of up to about 24 degrees they tend to be a bit more sluggish. The most common temperatures I catch them in are between 18 and 20 degrees.

Particularly if the south easter has been blowing for a few days the water up against the coast can be very cold between 12 and 14 degrees and dirty green in colour. This is as a result of upwelling. Upwelled water is cold, (12 to 14 degrees) the colour is as a result of the plankton (small plant organisms) in the water. When upwelling occurs it wedges itself between the warm clear ocean water and the coastline, pushing the warmer clean water further out to sea. Depending on how long the south easter blows from the warm water can be anywhere from a few miles offshore to over 30 miles offshore. When traveling offshore one often comes across current lines with marked colour and temperature changes. After passing through these current lines one often hits the warmer water. You can expect to catch yellowfin anywhere from these current lines further out to sea.

Depending on the time in the season and the movements of the tuna you can expect to find them over a very large distance indeed. Sometimes we find the tuna west of Hout Bay, other times they move off into the north and of course they are also often in the south off Cape Point or anywhere in between. It is difficult to predict exactly where the tuna will be and nothing is better than obtaining first hand knowledge from other fishermen. Although most will be reluctant to divulge exactly where they found tuna hopefully some will steer you at least in the right direction.

The commercial tuna pole boats tend to concentrate their efforts along the 500m contour. Most of the bank is about 200 to 250m deep. As you near the edge of the bank the sea bed bed drops off to 500m and then 1000m and further offshore even deeper. The drop off starts around 25 to 35 nautical miles off the coast. This area produces good catches as does the area in the south known as the “canyon”. In this area there is a circular shaped drop off giving the canyon it’s name. You know you are in the correct area near the drop off when you see the larger trawlers pulling demersal nets for hake and kingklip as well as the longliners working. Both these commercial fishers like to fish in up to 600m water depth. The trawlers drag their nets along the muddy seabed trapping hake and the longliners set many different drops each beginning with a bright orange marker buoy indicating the start of the line, they also mainly target hake.

More important than where you are fishing is that you are fishing in suitable tuna water and this is what brings about high success in catches. Conditions are always changing and it is seldom that you find the fish in the same place two days in a row. One needs to look for water with the correct colour and temperature. After that you need to make sure you are pulling suitable lures. Now this opens a can of worms as I think one can safely say that there are just about as many favourite lure patterns as there are anglers. One often only sticks to a few patterns that you know work and they continue to work as they are the only patterns you pull…if you catch my drift…

Tuna predominantly feed on baitfish and squid so any lures resembling these food sources are likely to achieve success. Cutting open the tuna’s stomach to see what it has been feeding on is often a good idea. I have come across garfish, pilchards, squid, some interesting looking fish obviously from very deep down as we don’t know what they are and then of course hake. What is important is to make sure you have decent quality hooks attached to the lures as most of the shop bought lures are supplied with cheap hooks to cut costs. These hooks will often be bent straight by the first yellowfin strike. So be warned, change the hooks. Also make sure you have a piece of thick mono as a bite trace to prevent your catch from sawing through your mainline. Tuna have small teeth but they are sharp and quickly abrade though line that is too thin, Particularly if the tuna is of a decent size.

As a matter of personal preference I usually fish plastic squids as they swim true and I have yet to find a tuna that won’t have a go at one of them. Although many fishermen do use them I find that swimming lures with a lip often do not swim straight especially after catching a fish and having the lip bent a little. What usually happens is that you carefully put out your spread and the very last lure you put in decides to track right across all the other lines tangling in a huge mess, resulting in a waste of time and a lot of cutting and retying. This is the reason I usually swim plastic squids. We also often pull what we term a “bird” which is a wooden teaser with two arms that throws a lot of water when it is trolled and creates quite a commotion. This is particularly effective in enticing the larger yellowfin.

I use the plastic squids to locate tuna or often not at all if I feel the water looks right for tuna and I can see them marking on my echosounder. I then switch to fishing baits and working jigs and spinners. Jigging is a new technique for catching tuna that has become popular throughout the world but has only recently been tried here in the Cape. The technique is effective and we have already caught both yellowfin and longfin on jigs. I must admit having a yellowfin hit your jig when being in direct contact fishing a braid line does give quite a rush!