Native Fish Resources 

Scientists specifically assess the age and growth rates of fish species by studying fish ear stones, called otoliths. Otoliths reveal the ages of individual fish, almost like counting the rings in a tree. Knowing the age distribution of a fish population helps to better monitor, assess, and manage stocks for long-term benefits. 

Scientists and fisheries managers can use these data to help understand how fish populations react to commercial and recreational fishing and environmental stressors, such as predation, pollution, and climate change.

Otoliths are is composed of alternating layers, which are referred to as being either opaque or translucent based on their optical properties. When a fish is feeding actively (often in summer), calcium from the fish's diet accretes a wide opaque layer on all surfaces of the otolith. When the fish is eating less, the otoliths grow more slowly and gain a narrower translucent layer. The two layers, the translucent and opaque, together represent one year of growth, called an annulus. Otolith growth and development may be affected by temperature or other external conditions for many species. 

On a crisp spring morning along the shores of Lake Erie, a team of biologists load equipment onto a research boat. These biologists are from the U.S. Fish and Wildlife Service's Lower Great Lakes Fish and Wildlife Conservation Office (FWCO) and New York State Department of Conservation (NYSDEC) Lake Erie Unit. But there’s no fishing gear on board–no nets, no rods, no reels–still, they’re fishing. Their mission? To find lake trout and cisco fitted with tiny transmitters, swimming unseen in the depths of one of North America’s most storied lakes.