FISH INNER EAR This is not a bone-dry account about the bone inside the ear of a fish, nor a mere science story. A small bony structure takes center stage, yes, because it holds mystifying secrets about the future, your future on this planet. NOT JUST A TALL TALE Thousands of visitors come to Namibia annually with the sole purpose of relaxing at the seaside with a fishing rod. Maybe one of these fishers told you a tall tale recently: for example, that they caught a fish that can speak, just like the golden fish of the famous Pushkin poem. Well, that was a blatant lie. But it is a scientific fact that fish can hear. And that the ear bone in the fish’s inner ear holds the key to exactly where the selfsame fisher will fish most successfully in future. THE BLACK BOX OF FISHERY SCIENCE One of Namibia’s experienced marine biologists, Dr Margit Wilhelm, lectures at the University of Namibia’s Department of Fisheries and Aquatic Sciences. She explains: “Fish do not have ears, but they can hear and feel pressure with an inner ear bone; a hard stony structure located directly behind the brain of bony fishes. And it has rings on it much like a tree. Scientists refer to the otoliths as “the black box” of fishery science because it records information and it keeps it forever.” As the saying goes, some facts are mind-blowing and sometimes stranger than fiction. A small fish in the southern waters of the Atlantic Ocean, home of the cold Benguela current, has something very specific in common with Namibia’s oldest tree in the heat of Outapi in Owamboland. The science of dendrochronology – which dates events through the study of tree rings – is well known and enables scientists to date trees like our massive Baobabs, believed to be a staggering 800 years old. The science of sclerochronology applies the same principles to fish.
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Dr Wilhelm explains: “The width of the increment for a tree especially – everyone can picture that – provides telltale signs. If it was formed in the rainy season of a good year, the tree will grow lots and form a wide ring or increment, for example, and when examined later that will point to a very good rainy season. And in bad years the ring will be really narrow. This enables you to literally go back in time and assign a particular calendar year or season to each ring. With this you can look back very far in time, especially considering that trees can get hundreds of years old.” According to Dr Wilhelm, the same principle can be applied to fish. Counting the annual growth rings on the otoliths is a common technique in estimating the age of fish. She gained valuable experience when she worked in Texas after completing her doctoral degree studies. There she learned from Dr Bryan Black, one of the world’s foremost experts in the field. ADAPTING TO A WARMER OCEAN IN THE TIME OF CLIMATE CHANGE In the long term, scientists can use the data gained through this “tree-ring-technique” to determine how fish will respond to temperature in the future. This is extremely important in the context of rising ocean temperatures due to climate change. Dr Wilhelm explains: “The ocean is a very big heat sink – so, as the land temperatures are heating up the ocean is also heating. Consequently, climate also affects the fish stocks.”
