Why Is It Important to Age Fish
Knowing the age of fishes allows fisheries managers to understand the dynamics of fish stocks and how fish populations react to environmental stresses like commercial/sport fishing, natural mortality, and predation. Basically, it is a way to monitor and better manage stocks for long-term benefits.
How Do You Age a Fish
The fishery biologist examines a structure of choice, which could be a scale, otolith, fin ray, dorsal spine, or vertebra. Generally the best structure to use is an otolith. An otolith is a bone located in a fish's skull and is analogous to the human earbone. Vertebrae are often used for sharks and skates which do not have otoliths. Scales are seldom used for ageing groundfish because they tend to underage.
Is Ageing an Otolith Like Counting Tree Rings
It is similar to counting tree rings, because the otolith also forms annual marks. However, the annual marks are not always clearly visible on the entire otolith. Environmental factors such as water temperature, food supply, salinity, water chemistry, and population density can cause stress on the fish, and marks other than those that are annual can form on the otolith. This can cause a complicated pattern that the biologist must interpret. Try your hand at ageing with the interactive Age Reading Demonstration (ARD).
Is There Special Equipment Used to "Read" Otoliths
Yes, the basic equipment needed is as follows:
- Dissecting Microscope ($1200-$8000)
- Low Speed Saw ($4000)
- Diamond Blade ($120)
- Alcohol Burner ($5)
- Lighter ($1)
- Tweezers ($12)
- Teasing needle ($7)
- Petri dish ($2)
- Clay ($1)
- Mineral oil ($1)
- Dish soap ($1)
- Paintbrush ($1)
What Are the Maximum Ages of Groundfish Aged by the Age and Growth Program
They can be over 100 years old!
How Many Otoliths Have Been Collected by the Alaska Fisheries Science Center
So far the Alaska Fisheries Science Center has collected over 1.1 million fish otoliths for ageing. The AFSC otolith collection database is a real-time inventory of survey and observer otolith collections.
What Species Are Aged by AFSC Age and Growth Program
The Age and Growth Program reads otoliths from groundfish species collected in the Bering Sea, Aleutian Islands, and Gulf of Alaska.
How Many Otoliths Are Read Per Year
Depending on the requests that are made and the availability of staff, our lab has aged anywhere from 25,000 to 36,000 specimens per year.
What is Done for Ageing Quality Control?
Typically 20% of our ages are blind read by a second age reader.