Science Behind Sustainable Seafood

1. Science Behind Sustainable Seafood • Age Matters! • Alaska Fisheries Science Center

2. Why is age information important to understand the health of a fish population?

3. How to age a fish? Find their otolith… • Otoliths are hard, calcareous bodies, located in the cranial bones near the brain of teleost fishes. • Otoliths, sometimes referred to as ear bones, are of unique value for age determination of teleost fishes because across taxa they are the only hard structures that continue growing even after somatic growth has ceased.

4. How to age a shark or skate… • In cartilaginous fishes such as sharks and skates, otoliths are not well-calcified, so researchers must rely on other hard structures such as vertebrae or spines for age estimation.   http://www.whoi.edu/oceanus/viewImage.do?id=198453&aid=125909

5. Count the rings… • Age determination science relies on growth marks deposited on a daily or annual basis within the hard structures of marine organisms. • Although annual marks in otoliths and vertebrae are similar to tree rings, their appearance is generally much fainter and more irregular. • Another major problem in counting annual marks is that the timing of the deposition of new growth zones varies considerably by species, age, and exogenous factors such as geographic location and climate.

6. Importance of age composition of a population • Age data can provide considerable insight into fish population dynamics. • Age determination is particularly important for marine fishes because they are often difficult to census at every life cycle stage.

7. Typical age composition of Pollock in Bering Sea

8. Knowing age of fish helps understand life history!

9. How do scientists use age data? • Fisheries scientists develop age-structured stock assessment models, using age composition data, to determine how many adult fish are available for harvest. • These models evaluate the overall health of fish populations and guide fishery managers in setting catch limits.

10. What age can fish first reproduce? • Fishery scientists have learned that knowing a fish population’s age structure means knowing how old the fish can get, how many individuals in the population are at each age and how old a fish is when it first spawns (age at reproductive maturity). • Scientists have learned that some fish grow fast and live less than 10 years, and other fish grow slow and live to be over 100 years old.

11. Age distribution of Pollock Pollock age at maturity

12. Why is age structure analysis important to sustainable seafood? • Age is important to know because a sustainably harvested population means not harvesting fish when they are too young or too old. • Both would decrease the size of future populations. http://www.capecentralhigh.com/not-exactly-cape/seattles-pike-place-market/attachment/pike-place-fish-market-08-02-2011_2481/

13. Population distribution of catch… Which one is best? Boat 1 Boat 2 Boat 3 Note: These are not pollock data. What would be the best case scenario of catch in the previous chart with pollock data?

14. Pollock Data Write down the following questions in your notes: • What years had strong cohorts? • At what age do pollock recruit to the fishery? • What range of ages is caught in the fishery? • Does the survey sample those ages? • Are there any ages the survey does not sample? Why? • What type of gear may be able to sample these ages better?