Although I claim to be a fly fisherman I probably spend more time trying to locate a trout rather than hooking it. From years of studying the life of a trout, what I’ve learned can be applied to any other species that is facing extinction.
To catch a trout takes many years of listening to and watching experts on the subject, reading lots of books and spending many hours, if not days, standing on a river bank. There are many factors that have to be pulled together before a cast can be made: how fast is the river flowing, its colour, height, width, the condition of the river bed, the time of year including the time of day, weather conditions such as temperature, wind direction, cloud cover, the list goes on. All of this information can be pulled into four criteria: oxygen levels ( yes they can drown! ), easy access to food, a place to hide from predators and conditions to breed. Using this information I try to locate likely areas where a trout might be, then I can wait for many of minutes to see if it moves, or in may cases, not. If it does then I am ready to cast a fly. The criteria that I use for trout fishing can be adapted for other species and in particular those many species that are in decline in the UK.
However, there is a deeper connection between the different criteria, which is that one species depends on other species for its survival. Take food for example. Trout primarily eat invertebrates that live in the river or lake, or drop on to the water from trees and plants on the banks. Some favourite trout food includes mayflies, caddis flies, stone flies, as well as worms, freshwater shrimp and if the trout is large then other fish. Low lying trees and roots in the river bank give cover for trout to hide from predators such as otter, mink, cormorants, ducks and other fish such as pike. However trout like many other fish are under threat from pollution in the river both from agriculture and sewage, damage to riverbanks from cattle and dogs accessing the river, and severe weather conditions driven by climate change which have been created by us. Pick any species and the criteria used for trout can be applied whether it is for a sustainable population of yellow hammers or hedgehogs.
The current approach to halting the decline, or the re-introduction of a species, is to concentrate on a key species and if their numbers appear to increase then it is assumed that the habitat is enough to sustain its population. But its introduction can have a detrimental impact on other species. For example, when Grayling were introduced on some of the chalk streams in southern England, so that that fishing could continue during the closed season for trout, they ate a lot of the trout’s food which resulted in a reduction in their population. When we put initiatives in place to halt the decline of a species there appears to be no assessment of its impact on other species.
Our level of understanding of the natural world is at the qualitative level: we understand which species relies on others e.g. the food chain for a red kite includes mice, voles, young hares, rabbits and carrion. But we have no quantitate level of understanding. For example, how many mice are required to form a healthy diet for a red kite, or if there is not enough mice available, then what would a balanced diet look like? We need a more accurate way of quantifying how one species relies on others. This would give a clearer picture that can be used for managing one species impact on others. It will require new measurement techniques to gather data about different species that will give us important insights into the inter-relationship and new statistical techniques to analyse the data. Maybe some government money could be diverted into developing a better science about the natural world? Let’s hope there will be a future when trout will return to our rivers in large numbers in such a way that their population will be sustainable for future generations.