Our focus on a single family of freshwater fish, distributed across a relatively small yet significantly biodiverse part of the globe, brings into play any number of important issues. Mahseer fish, including Tor species, Neolissochilus and Naziritor species are small parts of the bewildering array of the faunal assemblage of the rivers where they live. They play vital roles in habitat function, from sediment transportation to seed dispersal, predating upon disease-carrying insects to themselves falling prey as food for other riverine predators. They are indicators of water quality and are often a highly prized food source for riverside communities.
The report issued by WWF - The World's Forgotten Fishes - is focused on the global status and value of freshwater fish and we are proud to have played a part in its publication. Some of the takeaway highlights about freshwater fish are here:
Dazzling diversity - 51% of all fish species & ¼ of all vertebrate species
Fisheries - food for 200 million + jobs for 60 million
Big business - fun fishing ($100 billion), world’s most popular pets ($30 billion)
Threats - 1/3rd are threatened with extinction + 80 species already extinct
Solutions - Emergency Recovery Plan for freshwater biodiversity under the New Deal
“Nowhere is the world’s nature crisis more acute than in our rivers, lakes and wetlands, and the clearest indicator of the damage we are doing is the rapid decline in freshwater fish populations. They are the aquatic version of the canary in the coalmine, and we must heed the warning,” said Stuart Orr, WWF global Freshwater Lead. “Despite their importance to local communities and indigenous people across the globe, freshwater fish are invariably forgotten and not factored into development decisions about hydropower dams or water use or building on floodplains. Freshwater fish matter to the health of people and the freshwater ecosystems that all people and all life on land depend on. It’s time we remembered that.”
Mahseer Trust included information about the critically endangered hump-backed mahseer, tor remadevii for this report. Quite rightly, this valuable and iconic fish gets and deserves a lot of attention, and, indeed, we have a team working on the life history and habitat threats for this fish as we speak. But it is not the only threatened mahseer species, and some may be under greater threat than we know.
An important part of the success of fish in all rivers is access to quality habitat. Our current focus is building a robust understanding of the critical habitat needs of individual species, to fulfil life history requirements (e.g. spawning, nursery etc). While this information is still lacking, our ability to protect priority habitats remains compromised.
Dams and industrial pollution are known to have major impacts on river health. Yet these issues present complex challenges in rapidly developing regions, and require a concerted and coordinated effort to minimise impacts on aquatic biodiversity. While individual behaviours (e.g. responsible water use) have the potential to contribute, awareness and buy-in from all sectors of the population (city-dwellers, industry and governments) will be essential to effect positive change.
Another recently published report looked at how human impacts upon rivers is leading to a decline in fish diversity. The report (here, abstract free-to-view, main body behind paywall) suggests that rivers in mahseer range countries are in a better shape than those of developed nations. It should be noted that large, monsoonal rivers are much more difficult places to collect data compared to the well-studied waterscapes of rivers like the Thames, in England. We may not, therefore be seeing the whole picture, and we certainly know that in the case of mahseer, there are huge gaps in our understanding.
This report also raises the question of whether all rivers may follow the same path and that the primary issues are: fragmentation of habitat and connectivity, and introductions of invasive, non-native species. In an article about this report in The Guardian newspaper, they named common carp and tilapia as culprits, both fish which are often released into mahseer rivers. As our colleague Vincent Jalabert, from Myanmar Fly Fishing Project has been showing in his outreach work, the common threats to rivers (pollution, destructive fishing, sand mining etc.) reduce the amount of habitat available to fish. Adding more fish does not relieve any pressure, in fact it adds new pressures.
Andy Gonzalez is Professor of Biology at McGill University, Montreal, and founding director of the Quebec Centre for Biodiversity Science. His comments suggest that: the study shows not only is biodiversity being lost but that fish species populations are becoming too similar.
We have used this theme in many presentations, with data from Nepal Peace Corps showing that in Himalayan rivers that used to hold three species of mahseer, now only Tor putitora remains. The impacts of losing fish diversity are still unknown, but local communities, who often rely upon certain species for catches, especially smaller fishes for tribals, are generally the losers.
Over the last year or so, we have received lots of messages asking if we will support a farmer or small business who are looking to develop breeding mahseer as a conservation measure. Our response has always been to look at breeding the easier, more commercial species in a controlled environment and to leave conservation to scientists under strict regulation.
This breakout (below) from World's Forgotten Fishes, looks at some of the reasons why releasing fish in an attempt to enhance populations may not be useful. With mahseer in mind, fish which have seen widespread breeding and releases into the wild over at least the last 40-years, we understand the calls for more fish to be released, especially in places where recreational angling is a major source of economic activity. However, there are other issues to consider, including overall habitat health as mentioned previously.
We know that mahseer are shoaling fish and are natal-homing migratory fish. Using predetermined triggers, they will move together to return to the same river where they were born. This has been demonstrated in Tor putitora and Neolissochilus hexagonolepis in Bhutan. Although not yet studied in mahseer, spawning movements in other species of fish that display similar characteristics become disrupted if artificially-bred stock are introduced to wild shoals. So although stocking is an understandable response to falling stocks, the very act could prove to be the end for natural spawning behaviours.
Seasonality and sustainability are two factors we should be discussing when considering consumption of freshwater fish. The use of closed seasons for either fishing, capturing (in the case of aquarium hobbyist trade) or selling fish is an established practise. In many developing countries around the region, rising levels of income are accompanied by increased understanding about sustainability and concern about protecting natural habitat and biodiversity, and this can be used to help raise awareness and share campaigns.
Setting seasons for use of freshwater resources should be established through quality science. Field studies to understand the ecology of wild fish is essential but can also be informed by local knowledge. Women cleaning fish for market will have intimate insight into which species are carrying eggs during which months of the year. Indigenous communities usually have ancient knowledge of when fish migrate for spawning.
Having these kinds of information as the starting point and then capitalising upon them will help to drive studies and demonstrate the importance of local knowledge.
Of the current 16 valid species of Tor mahseer, much attention gets focused on Tor remadevii and Tor putitora due to their known and understood threat statuses. What is more alarming is that 10 species are so poorly understood by scientists that it is not possible to give them an IUCN red listing. They are data deficient. That this list includes Tor tor, once the most widespread and populous mahseer within India, according to Indian scientists studying them from the early twentieth century up until the 1980s, and also the two most common fish of SE Asia, Tor tambra and tambroides, gives us much cause for concern.
If we can take heart from the two reports we have highlighted, it is that freshwater fish and their diversity are making the news. People are talking about fish, rivers and people, at least for a short while. This makes it all the more important that we add our voices to these publications, support all those working on freshwater species and habitat, and renew our efforts for the mighty mahseer.
Come and join us, share our article, help us find out more about these beautiful fish and in doing so, help the rivers of south and Southeast Asia hold on to their biodiverse nature.