Information on the age of fish in a
population, in relation to size and maturity, underpins the comprehensive
management of commercially exploited species.
Similarly, the age structure of an exploited populations allows the
creation of detailed productivity models, which, in turn, can be used to simulate
population responses to various management strategies. This feedback is key to
ensuring that regulations permit the sustainable harvest of fisheries stocks,
or, importantly, the recovery of those species that have been historically overfished.
Estimating fish age is
a time-consuming, and therefore expensive, task. In bony fishes, otoliths
are often used to estimate age by counting regions of diffuse growth bands
(similar to the rings in a tree) that are laid down sequentially and outwardly
as the fish ages. The process of otolith
preparation and interpretation requires a major investment in time, resources, and expertise and is, unfortunately, subject to human error. Production
ageing, as this process is called when applied to large-scale studies of
managed species, is carried out on behalf of management organizations
worldwide, and comprises thousands of age estimates generated annually per
species.
In the latest Editor's Choice paper, Passerotti and co-authors evaluated the feasibility of using an alternative method for determining fish age that uses Fourier-Transform Near Infrared Spectroscopy (FT-NIRS) to generate ages for red snapper (Lutjanus campechanus), a species that is heavily managed and undergoes production ageing in the United States. FT-NIRS uses a non-destructive laser to determine the type and relative proportion of organic chemical bonds within a substance of interest; prior studies have shown that it can successfully predict the ages of fish from rapid scans of whole otoliths. FT-NIRS has the potential to revolutionize the means by which production ageing is carried out by reducing effort, expense, and human error.
By generating and comparing FT-NIRS ages to traditional ages (those derived from counting growth bands) for over 1300 red snapper otoliths across three management regions, the authors determined that FT-NIRS ages were equivalent to traditional ages for fish up to ca. 30 years old. They also found, experimentally, that NIR light did not fully penetrate the thickest otolith from the oldest fish in the study, which could contribute to the underestimation of ages for fish with the largest and thickest otoliths.
Passerotti states, "Our study is the first to address the role that the physical structure of otoliths might play in FT-NIRS mediated production ageing, a critical step for the applicability of FT-NIRS to age fish".
With a processing time of approximately one minute per individual otolith via FT-NIRS and several hours per otolith for traditional ages, the potential time and cost savings of FT-NIRS ageing is compelling, and our study provides a platform for fisheries managers to assess its suitability for use in future production ageing of red snapper in particular as well as other exploited finfish.
Read the full paper in ICES Journal of Marine Science.
