Bluefin Tuna In Cape Town

By Author: Greenfish
Total Articles: 2
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Due to its geographic location, Cape Town lends itself perfectly to world class tuna fishing. The warm Mozambican current that runs down the east coast, overlapping with the cold Benguela current that moves down the west coast, brings with it an abundance of nutrients and baitfish. This upwelling, along with the hake long lining and trawling, congregated contours and depths are all contributing factors to why tuna congregate here.

The typical season tuna starts in October and is brought on after a good strong blow by the south-easterly wind which drives the warm currents closer to shore. The first half of the season peters out in January and then starts again at the end of March/beginning April. The tuna bonanza normally ends in about the first week of June when the cold fronts and big storms put an end to our season. However, in the last few years the weather patterns have changed, and we are fishing later into the year, almost right through to October again.

While chatting to a very experienced tuna pioneer and fisherman in Cape Town, Nick de Kock, he told me that in the 1950s and ’60s, as soon as the snow ...
... fell announcing winter, school size southern bluefin tuna (SBT) in the 30–40kg size range were caught, and that big fish were rare.
Back in 2007 I wrote a letter to SKI-BOAT magazine sharing news about the first southern bluefin tuna I had come across, as it was an unusual catch at the time. “Was it a lost fish?” I asked, “Or is it the beginning of these majestic fish returning to our waters? Only time will tell.”
After that we saw the odd SBT come out, and in 2010, at the Gordons Bay Tuna Classic a 135kg SBT was weighed in by the crew aboard Magoofter, taking top spot at the competition. In 2015, at the same competition, a 132kg SBT and 126kg big eye tuna took first and second place, respectively.

As a tuna buyer, processor and factory owner, I started noticing these fish more and more regularly from 2018 onwards, and numbers increased yearly until 2021. Numbers were so good that recreational anglers could go out and specifically target one of these incredible fish. With many fish hitting the 100kg mark, and most in the 80–120kg range, they gave many anglers their personal bests.
There are 15 types of tuna in the world’s oceans, of which three are bluefin, namely: Atlantic (giants), Pacific, southern. The tuna which are regularly caught off Cape Point are yellowfin, longfin (albacore), southern bluefin, big eye and other smaller tuna, skipjack and bonito etc.
Southern bluefin tuna are sometimes confused with big eye tuna and yellowfin, because to the untrained eye they can look similar. Here are a few tips for telling the difference:

Bluefin — the sickles are short and silver in colour; the underside of the tuna is more silver in colour; the tail is dark black.

Yellowfin — the sickles are very long and yellow in colour; the tail has a slight yellow-grey colouring; the bottom back half of the yellowfin has dots and a small irregular line pattern.

Big eye — the sickles are short and the fish look short and round/plump; the eye is bigger than in other tuna; black edges on finlets near tail.
SBT are slow-growing, large pelagic fish that swim at an average speed of 2–3km/h (maximum 75km/h) and can dive to at least 500m. They are found in the southern hemisphere, mainly on the line between New Zealand and South Africa. Fish start spawning when they’re 8–10 years old, and their only known breeding ground is off the south-east coast of Java (Indonesia).

They do not spawn every year, and can skip up to four years. These fish can live for up to 40 years, weigh up to 200kg and measure up to 2m in length. It’s these large individuals that produce the strongest offspring with the greatest chance of survival. Much like our big kob in SA — big fish produce more babies that survive. The current IGFA all tackle record for southern bluefin tuna is 167.5kg.

On 5 April 2021 there was an amazing recapture of a tagged SBT in Tasmania that had been at liberty for 19 years. At the time of its first capture it was 134cm long and weighed and approximately 40kg; after nearly 19 years at liberty it had grown around 60kg and tipped the scales at 98.5kg. This just shows us how old these fish are, and why we need to look after the stock.

It is largely accepted that 80% of the world’s bluefin tuna is consumed by the Japanese sashimi market and it is highly prized as a delicacy because of its high fat content. The value of these fish has put this fishery under tremendous pressure.

Australian stock assessments started in the 1940s, and it’s a matter of record that in the 1960s the SBT fishery was already under heavy fishing pressure. By 2000 the biomass was down to just 5.5%. In 2017 a Total Allowable Catch (TAC) for the species was issued of 17 647 tons. At the same time it was discovered that an additional 178 000 tons had been harvested illegally/not recorded over the previous 20 years by vessels from the East. With this information in hand, good management and tuna ranching, by 2020 there was a big improvement and the biomass of spawning stock had climbed back to 20%.

It is well known that we share the same stock and see a similar pattern to Australia and NZ, so it is due to their good management that we are now seeing these fish come back in Cape Town. Or a combination of that and the changes in weather and water temperature that we are experiencing. With little stats to go on regarding South African research, I can only surmise this from what I have noticed myself…

• Cape Town fishing operations are fishing later into the year. In the past during the traditional winter months the fleet was tied up and not going to sea, but that’s no longer the case.

• These SBT are being caught at the end of the season and right in the beginning.

• Fishermen are fishing harder and longer days. As SBT spend most of their day below 40ft, they seem to be getting caught at dawn and most commonly at dusk.

• Our water temperatures are changing and seem to be getting warmer offshore and colder inshore, with SBT liking the temperature breaks. This is also evident in the large number of marlin that we have seen in Cape Town over the last three years, and the absence of our inshore yellowtail due to colder waters — and possibly trek netting of spawning fish. This change of hot and cold is referred to as the water gradient; this gradient is more extreme than before, and in turn our currents appear stronger. It is now not uncommon for the water to be too hot for our yellowfin and hit up to 23⁰
So is this flurry of fish due to stock improvement, global warming or an alarm bell that the stock is in trouble and going to collapse due to overfishing?

Other examples of fisheries around the world show a collapse of a species comes when there is an absence of “schooling size” fish and anglers are catching the mature breeding stock. One view on this is because there is less competition for the same food and the few bigger fish get bigger and fewer as they get caught up or die off, resulting in less spawning until the collapse of the species.

I know our commercial sector records their catch and has a TAC and a tag system that they catch against. With the increase in recreational catches it would be amazing if catch information could be recorded so the information can be added to the commercial side to allow the stock to be managed in the best way possible. Then, if it is found that our stock is healthy, our TAC could be increased. After all, it is a shared resource, and everyone in the SBT community has a shared responsibility to be part of the solution so that we can all benefit in the future. Australia is seeing the results of good management and have a very positive story. Research and data definitely help manage the fishery.
What can anglers do to improve the situation? Start by reducing your wastage and looking after your catch.

As soon as you land your SBT, it should be bled and reamed, then placed into an ice slurry to get the core temperature down. The temperature of the fish increases during the fight and, once boated, will continue to increase and cook the meat if it’s not cooled down quickly in ice. Handle the fish gently both on the boat and once on shore, being careful not to drop your heavy prize. Correct handling and cooling will produce the best yield and make loining up your fish much easier.

Taking care of our catch is the first step in the right direction of changing our ethos towards these magnificent fish. A behaviour of releasing them can also be learned and should be encouraged by fishing clubs. Good release practices are easy to follow and a photo of your big tuna alongside your boat with all the colours lit up is more impressive than him hanging on the gantry in front of the club.

Co-operation between commercial and recreational anglers can help us protect and save the southern bluefin tuna fish for the next generation to appreciate.

Greenfish was founded by two brothers, Ryan and Andrew with the intention of providing the restaurant, hospitality and wholesale industry with high quality, seasonal and locally sourced fish and seafood products. We are committed to ensuring that all our seafood is sourced from suppliers using the lowest possible impact on the environment.