Briones Hernández, S.A., U., Jakes-Cota, J.M., Logan, J.O., Sullivan & S., Ortega-García (2024). Using multi-taxa marine isoscapes to assess potential provenance ofdolphinfish captured off Cabo San Lucas, México . 74th Annual Tuna Conference. Lake Arrowhead, California, Estados Unidos de América, mayo 20 - 23, 2024, 37.
Sergio Alejandro Briones Hernández 1, Ulianov Jakes-Cota 1, John M. Logan 2, John O. Sullivan 3 y Sofía Ortega-García 1
The use of stable isotope analysis for feeding habit studies is a well stablished practice in modern ecology. However, the potential use of stable isotope (SI) data to assess movement of marine organisms through the description of their isotopic niches (isoscapes) is a growing field and it is known to have important limitations due to the availability of data, especially in oceanic environments. Recent availability of stable isotope data has allowed the description of robust isoscapes of marine consumers in different “trophic bins” in the North Pacific Ocean. To represent their isoscapes along the different Longhurst provinces (CCAL, PNEC, CAMR, NPTG, PEQD), available literature on carbon and nitrogen SI data of marine consumers categorized as trophic bin 4 was used. Each of the Longhurst provinces isoscapes were compared to measured muscle SI values of adult and juvenile dolphinfish captured off Cabo San Lucas (CSL) from July to December 2018-2021. This was done to infer the provenance probability (Pp) through the Bayesian overlap probability of the ellipses in the SIBER package in R. Further, to estimate expected carbon and nitrogen SI values of a consumer such as dolphinfish, that feeds in CSL area (ResidenceSI) SI available data of prey species of the dolphinfish in the Longhurst provinces off CSL were used. The ResidenceSI value was calculated using the weighted average of the SI values of carbon and nitrogen on the prey species consumed by the dolphinfish inferred through stomach content analysis plus a trophic discrimination factor. The average of the prey species was weighed according to the proportion of importance of the Prey-specific index of relative importance (%PSIRI). ResidenceSI values for dolphinfish for our study area were d13C = -16.7‰ and d15N = 16.5‰ while measured stable isotope values (mean±SD) for juvenile dolphinfish were -16.4 ± 0.6 and 16.0 ± 1.5‰ for d13C and d15N, respectively. For adults, measured isotope values were -16.8 ± 0.4 and 13.5 ± 1.2‰ for d13C and d15N, respectively. Isotopic niches of each of the analyzed Longhurst provinces were successfully separated in d-space and differences were observed in the distribution of juvenile and adult dolphinfish samples in d-space. Juveniles had similar provenance probability values (Pp = 0.4) for CAMR, CCAL, and PNEC, while this probability was lower for PEQD and NPTG. The isotopic niche for adults showed similar Pp values for every province, with the highest value for PEQD (Pp = 0.3). This approach to study the provenance of dolphinfish supports previous hypotheses regarding the differences in habitat use between juvenile and adult dolphinfish where juveniles tend to show SI values in steady state with local isoscapes in the region where they were captured while adults tend to show more variation in their SI values. Adult dolphinfish showed isotopic niches in between the distribution of the Longhurst isoscapes in d-space which might be an insight into the movement capabilities of the species, as it appears to show an average of those provinces as if those animals were constantly feeding across isoscapes without reaching a stable isotope steady state with local isoscapes in their muscle tissue. This is an experimental approach on trying to infer the provenance of oceanic species using available isoscapes in the Northern Pacific Ocean and potential biases due oversimplification of processes that might influence our observations. However, we considered this as a potential tool to further improve our application of isotopic methods in movement ecology of marine predators.
Palabras clave: stable isotopes; isoscapes; Dolphinfish
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