Are billfish disappearing?

Are billfish disappearing?

As a start to our ‘deep dive’ into the saga of Bill Fishing Competitions, first we need a better understanding of the relevant fish and the need for their conservation. Worldwide, several species of marlin have been named, and four are now generally accepted as valid: the blue (Makaira nigricans), black (Istiompax indica), striped (Kajikia audax), and white marlin (Kajikia albida). The blue, black and striped marlin are found in our waters. White marlin are not nearly as common in South African waters, and are only found off our west coast in the cooler waters of the Atlantic. Other species we will investigate during these articles are shortbill spearfish (Tetrapturus angustirostris) and sailfish (Istiophorus platypterus).

Stamps depicting black marlin.

The billfish in our waters do not belong to us. Why do I say this? Because most billfish are highly migratory. Information has been obtained by various tag-and-release programmes, and the migration distances are startling! Blue marlin = 14 893 km; black marlin = 14 556 km; striped marlin = 6713 km; white marlin = 6517 km; and sailfish = 3861 km. The blue and black marlin are effectively travelling the ocean distance between South Africa and Australia. These species migrate thousands of miles across international boundaries and are fished by many nations. Effective conservation and management of this resource thus requires international cooperation as well as strong domestic management to succeed. One only has to look at all of these stamps to see the wide range of these beautiful creatures.

Stamps depicting blue marlin.

Founded in 1948, the International Union for Conservation of Nature (IUCN) has become the global authority on the status of the natural world and the measures required for conservation. So, what has the IUCN got to say about the species we’re looking at? Whilst the striped marlin is listed as Least Concern, the blue marlin and the sailfish are listed as Vulnerable (which means that it is at a high risk of extinction in the wild). The black marlin and the shortbill spearfish are listed as Data Deficient (not enough data to assess its risk of extinction). Counting these fish in the ocean (much as you would do a ‘game count’) is obviously not feasible, so scientists rely on catches and how much effort these catches took over the years. This is called a catch per unit effort (or CPUE) index. You would still need to account for changes in effort or, for example, if fish had perhaps moved due to changes in their environment. These are accounted for by various complicated methods of standardization. 

Stamps depicting sailfish.

A “grander” is a specific designation given to a marlin that weighs at least 1,000 pounds. It has been suggested that the frequency of trophy catches may be a good indicator of stock health and can be used as an early warning of overfishing or even a clear end point denoting stock recovery. I was unable to find a comprehensive list of the increase/decrease of granders caught over the years, but I would hazard a guess that they’re on the decline.

Stamps depicting striped marlin.

These creatures face several challenges including overfishing. Habitat loss and degradation are also influencing them. For example, the blue marlin depends on healthy coral reefs and seagrass beds for feeding and breeding, and these habitats are under threat from pollution, coastal development, and climate change. As ocean temperatures rise due to climate change, their water can hold less oxygen. These fish are forced to migrate to cooler waters, which can make it harder for them to find food and reproduce. And so the list continues…

Total catch of blue marlin and white marlin. (Please see reference below for source and to read the research).

As with most apex predators, the only significant threats to these fish are humans and human activities. They’re caught as a bycatch in commercial long-liners, trolling, harpooning, set nets, gill nets, and surface tuna long liners. More conservation efforts are being implemented, such as angling size limitations, the encouragement of catch-and-release fishing, and the use of circle hooks instead of the standard J-hooks when fishing as this improves the post-release survival of the fish. We’ll discuss some of these issues in futures columns. What is interesting to note looking at the graph above, is that recreational fishermen (the red line) do the least damage to the populations (many graphs of different species and areas had similar results). They are also uniquely positioned to assist with the direct conservation of these animals which provide them with such an incredible sport, in a way which is both feasible and viable.

Next week we continue exploring this subject…

Jacqui Ikin & The Cross Country Team


Find all the info pertaining to the graph here: 
Fisheries and Resources Monitoring System

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