T03_08

Lifespan of fishes and LA-AMS – Investigations of maximum age for grouper and alligator gar

Andrews A¹, Welte C^2,3, Wertnik M^2,3, Sanchez P⁴, Rooker J⁴, Daugherty D⁵, Smith N⁵

¹Age and Longevity Research Lab, Honolulu, United States, ²Laboratory of Ion Beam Physics, ETH Zürich, Zürich, Switzerland, ³Geological Institute, ETH Zürich, Zürich, Switzerland, ⁴Texas A&M University at Galveston, Department of Marine Biology, Galveston, USA, ⁵Texas Parks and Wildlife Department, Heart of the Hills Fisheries Science Center, Mountain Home, USA

The longevity of fishes is an important consideration for a proper understanding of population dynamics, survivorship strategies, and consequently management policy. Bomb radiocarbon dating of otoliths (ear stones) has validated lifespans that exceed 50-60 years for long-lived alligator gar and deep-water grouper in North America and the Gulf of Mexico (GoM). However, low variability in radiocarbon concentrations prior to the bomb-produced rise sets a limit for this technique to carbonates deposited after the mid-1950s.

Laser ablation accelerator mass spectrometry (LA-AMS) provides a novel approach through a high-resolution analysis that can locate the rise of bomb-produced radiocarbon within the growth zone structure, away from the otolith core or nucleus (birth year material) typically sampled with a micromilling machine. In this study, we expand on previous results from red snapper in the GoM (Andrews et al. 2019) by applying the technique to three large-bodied grouper species of the GoM and to three specimens of large and likely very old alligator gar from tributaries to the GoM.

Eight otolith thin sections were analyzed with scanning velocities between 5 and 10 µm/s. Each laser scan was approximately 10 minutes and was unique with regard to the radiocarbon signal. The rise of the bomb peak was identified for each specimen and linked to a location on the sample allowing assignment of a calendar year to that growth zone layer. Overall, ages for each species were validated as being older than a single core extraction could resolve, thus extending longevity estimates for each species.