Letting our oldest vertebrate back in

Glaciers and waterwheels have blocked the path of the salmon, our oldest native vertebrate. Can it, yet again, stage a comeback?

- CHARLES RANGELEY-WILSON

I read an interview many years ago with the palaeontologist Richard Fortey, in which he perfectly summarised the sibylline link between geology, natural history and human history. “Far from being the driest of sciences,” Fortey said, “geology informs almost everything on our planet and is rich with human entanglements. The rocks beneath us are like an unconscious mind beneath the face of the earth, determining its shifts in mood and physiognomy.”

The natural and unnatural history of our wonderful but beleaguered Atlantic salmon has been greatly determined by geology and the forces of the Earth’s evolution, suggesting one hopeful thought – that somehow the salmon will survive – and one terrible thought – that even so we may yet lose them from the British Isles.

Knowing exactly why the salmon is in such decline remains a Holy Grail of fisheries science, and the driving force behind much urgent research. But the shaping influence of that deeper geological history is not only fascinating, it may offer useful insights into how we hold on to what we’ve got.

William Smith drew the first and still the most beautiful geological map of Britain. In marbled swirls of pink and purple he mapped the bands of igneous and metamorphic rocks which stretch all across the south-west and up through Wales, north-west England and into Scotland, while in shades of blue, yellow and green he mapped the progressively younger and softer sedimentary rocks which cover southern and eastern England. There’s a discernible change from one spectrum to the next and this division, which marks the transition from Triassic to Jurassic also marks an approximate change in topography between a more generally upland and a lowland Britain.