Establishing a sclerochronology lab at SPC – Bombs are never good, but their signature can be useful

Nouméa

Proper fisheries management across the Pacific region requires that we understand how our fishes live and grow to plan for ecosystem and resource sustainability. Closely coupled with this information is how long a species can live because its potential reproductive output throughout its lifespan is an important factor in understanding population dynamics. In general, the age at which a fish matures and how many years it can reproduce are important factors in estimating how many fish can be taken sustainably over time. A lack of understanding and use of incorrect ages and growth traits may lead to harvest levels that exceed the capacity of the population to replenish itself, potentially leading to declines in fishery productivity and risks to food security. For teleost fishes (bony fishes), the most used method of age estimation is counting growth rings in the ear stones, also known as otoliths, but the structure of the rings can be complicated, and as a result the age estimate from counting the rings needs to be tested. A method that can be used to validate fish age, as well as the age estimation procedures, is the use of a chemical signature that is stored in otoliths known as bomb-produced radiocarbon.

The use of bomb radiocarbon (14C) dating as a tool in the validation of fish age and lifespan has covered 30 years of progress in establishing a better understanding of fish ecology and stronger baselines for the sustainability of fisheries throughout the world. This approach uses a signal that was created in the 1950s and 1960s during cold-war efforts to increase the power of nuclear bombs. The sudden rise of bomb-produced 14C from these nuclear tests can function as a time-specific marker in conserved structures, like the rings of trees and in the growth rings of otoliths. While the rings in trees are easy enough to prove as annual growth (one set of layers or rings per year), it is not as easy to know if the rings being counted in otoliths are in fact annual. Hence, if the bomb 14C signal can be detected in the otoliths, then estimated age can be compared to the timing of this marker to determine if the age was correct.

The most common approach has been the use of the rise period as a reference to align 14C measurements from otoliths to references in time, but for fish collected in recent years the hatch dates would need to be in the 1950s and 1960s (Figure 2), making them more than 50–60 years old. While this scenario is appropriate today for some long-lived species, it is necessary to use the declining 14C signal that has occurred after peak levels were reached for recently collected fish that live no more than 20–30 years. A good example of success with this method is from recent findings for giant trevally (Caranx ignobilis) of Hawaii where ages up to 25 years were estimated from otoliths and then validated by a strong alignment of the otolith 14C values with the coral 14C chronology.

To read the full article; please click this link.

Download the SPC Fisheries newsletter:

0
Division
Pêche, Aquaculture et écosystèmes marins

Auteur(s)

Displaying 1 - 2 of 2
1433
Fisheries, Aquaculture & Marine Ecosystems
1433
Fisheries, Aquaculture & Marine Ecosystems
Fisheries Newsletter
Australian Department of Foreign Affairs and Trade (DFAT)
New Zealand Ministry of Foreign Affairs and Trade (MFAT)
European Union (EU)
Fisheries Newsletter
Australian Department of Foreign Affairs and Trade (DFAT)
New Zealand Ministry of Foreign Affairs and Trade (MFAT)
European Union (EU)