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Trout ‘voracious predators’ of indigenous Redfins
Author: Brian van Wilgen, Centre for Invasion Biology
Published: 13/04/2021

Prof Brian van Wilgen, emeritus professor in invasion biology, recently replied to an article published on 3 April in Daily Maverick's 168 weekly newspaper by Ed Stoddard, entitled “Trout wars: In a developing country with so many challenges, the fuss looks fishy" (Online at

His reply, titled “Contrary to Ed Stoddard's contention, trout are voracious predators and legislation has been proposed to regulate the fish, not to declare it illegal" was published in DM168 on 6 April 2021. Read the reply below:

By Brian van Wilgen, emeritus professor, DSI/NRF Centre for Invasion Biology, Stellenbosch University

The article by Ed Stoddard (“Spawning debate: the fuss over trout looks fishy"; Daily Maverick, 3 April 2021) is unfortunately flawed, and arguably heavily partisan because of his own admitted status as a “passionate fly-fisher". The issue of regulating trout has recently become particularly contentious. Debates like these prevail where alien species are introduced to provide some form of benefit, but then go on to become invasive, causing harm to the environment. It is important in these cases to present a balanced view, so I will address some of the points made in Mr Stoddard's article.

In general, Mr Stoddard's article acknowledges that invasive species can cause harm, notably on islands, but also contends that in many cases this damage is negligible. It is true that islands are more vulnerable to invasive alien species, but these impacts are now increasingly being felt on the mainland, and they certainly are not negligible. The impacts of invading alien plants in South Africa have recently been conservatively estimated at over R13 billion per year, for water resources, rangeland productivity and biodiversity only – and they are growing alarmingly.

Mr Stoddard has uncritically repeated arguments by a group within the trout industry as to why trout should not be regulated, namely that trout do minimal harm to the environment; that they have been naturalized in the country for so long (over 100 years) that they should be regarded as indigenous (rather than as alien species); and, that regulation would cause the lucrative trout industry to go “belly-up" (to use Mr Stoddard's terminology).

The contention that trout have a “fairly minimal" impact, only posing a threat to the rare redfin minnow in the Krom River in the Western Cape, is incorrect. Trout are voracious predators, and their impact is far greater than posing a mere threat to one indigenous fish species. There is now a mounting body of evidence that trout have caused the local extinction of many indigenous freshwater fish species, as well as amphibians and large invertebrates, with knock-on effects for plant life in streams. More importantly, many of the threatened fish species are found nowhere else on Earth, and South Africa is obliged to protect such species both in terms of its own laws, and in terms of the international Convention on Biodiversity.

The notion that introduced (alien) species should be granted indigenous status if they have been here for a long time is also unsound. This notion is argued in Duncan Brown's book (Are trout South African?), cited in Mr Stoddard's article. Any informed South African alive today would have known trout as occupants of our streams all of their lives. However, our lives are short. Indigenous fish, frogs and dragonflies have evolved over hundreds of thousands of years in environments without voracious predators. They have no instinctive means to avoid predation, and will be driven to extinction long before they are able to learn how to respond to this relatively new and deadly threat.   No “new balance" has been reached, as is often contended. 

It is also dangerous to start regarding invasive alien species as indigenous. Consider, for example, the case of mice on Marion Island, where they have been for over 200 years. They have decimated the invertebrates found (mostly) only on the island, have impacted on the indigenous plants, and now are attacking the nesting sea-birds.  Projections are that they will cause the local extinction of 18 species of birds, if left alone.

The nub of the argument though is that regulating trout will impose an unreasonable burden on the industry, requiring a permit for “every step in the trout value chain". Such a requirement would make unpermitted hatcheries, trout-fishing farms, and restaurants serving trout illegal. Further, it is contended that the government does not have the capacity to administer this, and so the industry will simply have to go out of business. However, if one reads the proposed regulations, it immediately becomes clear that many trout “value chain" activities have been exempted from requiring permits, making it perfectly legal, for example, to process, transport, consume, sell or serve trout as long as they are not alive.

The government's approach to regulating trout is carefully nuanced. The intention is to grant long-term permits that will allow for the continuation of all existing operations in demarcated areas, allowing the industry to continue to operate and to generate benefit. They have even conceded that this can continue in proclaimed protected areas. The main issue here is to prevent the spread of trout to new areas where they do not yet occur. It is well known that freshwater anglers regularly introduce new fish species into catchment areas where they do not yet occur, for the purposes of recreational fishing, and for angling competitions. To prevent the consequent harm to these ecosystems, and to the unique indigenous species that occur there, regulation is necessary. This approach should be seen as a win-win compromise, rather than a cause for prolonged and expensive litigation, which is simply unnecessary and wasteful. As Mr Stoddard points out, there are bigger fish to fry.

 On the photo: Redfin minnows are one of the indigenous fish species that form the prey of trout. Streams with trout in them are simply devoid of these charming fishes. Photo supplied by Brian van Wilgen​