Ever wonder why lead fishing tackle has been banned in some states? Because wildlife that ingests even one piece of lead can develop lead toxicity, which manifests as severe neurologic signs that almost always leads to death. Loons are especially well-known as victims of lead poisoning—because as diving birds, they eat a lot of fish—and in states with endangered populations (like Vermont) or threatened populations (like Michigan and New Hampshire), reducing loon mortality caused by lead fishing tackle should be a fairly easy fix: simply ban the use of lead fishing sinkers.
As part of an ongoing loon mortality study at Tufts, I took part in a weekend loon necropsy wet lab, put on by the Pathology Club. After being trained by the DVM researcher, we students paired up to perform full necropsies on 9 loons, under the careful supervision of experienced graduate researchers. Only after performing a full physical exam on our loon—noting body condition, palpating for bone fractures, pulling feather samples—did we proceed to inspecting organs for possible cause of death. Our loon, a female from Vermont, had a penny-sized healing puncture wound in the bone of her sternum. The tissue surrounding the heart revealed a quarter-sized fibrous scar, but the overlying muscle and skin were unmarked— further evidence that the puncture wound was old, and probably not the cause of death. The supervising DVM explained that intraspecies aggression over territory was common, and that fighting with their beaks causes wounds similar to this. After carefully photodocumenting and measuring the sternum wound and the fibrous scar, we continued with our necropsy.
We took several liver samples to send to 3 different researchers across the country, and took careful note of the stomach contents (several pebbles, lots of hard scales, and a 4-cm fish). Blood lead levels were normal. Overall, this bird was healthy: no fractures, good feather condition, plump, no parasites, no suspicious lumps, bumps, or discoloration of internal organs…In the end, we never did find cause of death for our bird, which was frustrating. However, fishing tackle was discovered in the stomach of 2 other loons, and another loon had ingested 3 sinkers, fishing line, and a fish hook. The metal of the hook and sinkers was clearly seen on x-ray, and after brushing a color-changing reagent on the sinker, it turned pink in the presence of lead. The suspected lead toxicity was confirmed by checking the lead level in the blood, which was 2.5 times higher than normal.