Novel approach to determining crustacean age

Editor/Mohmed Shihab

Traditional stock assessments for crustaceans rely on size to determine age, but Canadian scientists have tested the merits of a new approach that aims to more accurately conduct the process, improve the accuracy of sustainability assessments, and eventually increase harvest levels.

Otoliths-Lada Canada, a private laboratory based in Halifax, Nova Scotia, that specializes in fisheries and environmental sciences, has conducted a preliminary study to investigate the potential of using growth bands in the stomach gastric mill of crab species to more accurately gauge the age of crustacean species. 

The Sea Pact-funded study was part of an ongoing effort by Otoliths-Lada Canada CEO and Chief Scientist Raouf Kilada to find a more accurate method to age crustaceans, and the two species studied were blue crab – a species that hauled in around USD 220 million (EUR 205 million) in 2022 landings – and Jonah crab, which brought in USD 22 million (EUR 20.5 million) in landings in 2022.

“I have applied this approach in Alaska, Norway, Iceland, two fisheries in Australia, in the Mediterranean, and in Chile, in addition to a five-year project with the University of Maine and the government of the [U.S.] state of Maine to compare the age of American lobster in two areas with two different temperature regimes.” Kilada told SeafoodSource. “What we are learning is this method can improve the understanding of a species age distribution and this can have a positive impact on maximum sustainable yield (MSY) in many fisheries.”

The traditional use of size to determine age has a number of drawbacks, according to Otoliths-Lada Canada, including the fact that varying environmental conditions can significantly impact the size of crustaceans, and because crustaceans molt.

Further complicating using size as a reference, some crustaceans, like snow crab and blue crab, undergo a terminal molt, which means even though they may be aging, at a certain point, they do not grow larger.

“Eastern Canada’s snow crab is a very valuable fishery, [amassing] almost USD 1 billion [EUR 930 million] every year, and the management may be improved through more accurate stock assessments. Snow crabs reach their terminal molt at five to six years, but we were able to determine there were crabs as old as 12,” Kilada told SeafoodSource. “Similarly, the blue crab study that Sea Pact funded found that even though blue crabs reach their terminal molt in one year, I have individuals that are 3 years old.”

Kilada and the Otoliths-Lada team found that crustaceans’ gastric mill ossicles could be processed in a way that would expose growth rings, similar to the rings of a tree, and then verified the rings accurately corresponded with the correct age. Confirming the results with thousands of similar dissections provided encouraging, but still preliminary, results.

Now, Kilada is hopeful fishery managers can better react to environmental pressures that may be impacting a fishery and, simultaneously, better inform MSY.

“MSY is a mathematical model with a limited number of inputs. One of the major inputs is the age of sexual maturity and the natural mortality. Natural mortality relies entirely on age,” Kilada said. “If the natural mortality is smaller than the real value, you will decrease the output of this model, which is the MSY. So, if you assume a species stops aging when it stops growing, you will vastly underestimate MSY.”

Kilada has been working on innovative ways to age fish and bivalves for 20 years and has seen how these advances put to use in other fisheries can impact MSY.

“Where age-based stock assessments have replaced the size-based plans, the difference between the two plans is substantial. The former may increase MSY of a commercially exploited fish species by 15 to 20 percent compared with the size-based plan,” Kilada said. “Because this could have a significant impact on harvest levels, we want to continue the research on how to apply this approach to crustaceans’ fisheries management.”

As for Sea Pact’s role in this work, the collaboration represents an emerging trend of supply chain companies becoming more engaged in promoting effective management and, as a result, assuring supply.

“A seafood company's viability is linked to the fishery resources from which they source, so it is critical that the best available science is applied to support fisheries management, ensuring long-term sustainability,” Sea Pact Board Chair Andrea O’Donnell said. “Sea Pact's support of innovative studies like this crab-aging technique has the potential to improve fisheries management and is a great opportunity for industry members to contribute to the future of our fisheries.”

Traditional stock assessments for crustaceans rely on size to determine age, but Canadian scientists have tested the merits of a new approach that aims to more accurately conduct the process, improve the accuracy of sustainability assessments, and eventually increase harvest levels. Otoliths-Lada Canada, a private laboratory based in Halifax, Nova Scotia, that specializes in fisheries and environmental sciences, has conducted a preliminary study to investigate the potential of using growth