Briones-Hernández, S.A., U., Jakes-Cota, J.M., Logan, J., O'Sullivan, J.C., Mengel & S., Ortega-García (2023). Evidence of potential differences in habitat use andmovements between juvenile and adult dolphinfish off Cabo San Lucas, Mexicothrough multiple tissue stable isotope analysis. 73rd Annual Tuna Conference. LAKE ARROWHEAD, CALIFORNIA, Estados Unidos de América, mayo 22 - 25, 2023, 25.
Sergio Alejandro Briones-Hernández 1, Ulianov Jakes-Cota 1, John M. Logan 2, John O'Sullivan 3, Jeffrey C. Mengel 4 y Sofía Ortega-García 1
The application of stable isotopes to study trophic ecology or movements of marine organisms strongly relies in knowledge of different aspects of the ecology, biology, and physiology of the studied organisms. Tissue turnover rate is one of the key components, as it determines the period in which each tissue is storing stable isotope data from diet and trophic habitat, metabolically active tissues, such as liver, tend to have faster turnover rates than others like muscle, lastly stomach content analysis provides taxonomic resolution of recent diet (i.e., hours) consumed by the organism. Therefore, by coupling techniques and tissues we can reconstruct past (i.e., muscle), more recent (i.e., liver), and immediate (i.e., stomach) diet of the captured organisms to observe any variation. We analyzed 365 stomach samples of juvenile and adult dolphinfish captured by the sport fishing fleet off Cabo San Lucas during July to December of 2018 to 2021. We selected 90 organisms of which we analyzed both liver and muscle tissue for and values. We used a tissue steady state analysis to identify recent shifts in diet of habitat through variations in values. As trophic discrimination factors are usually lower in liver than in muscle, an organism without any recent shift in diet or habitat is assumed to have liver < muscle values. Therefore, we used = – , in which values >0 would show organisms without any recent shifts in diet/habitat (i.e., resident) whereas values <0 would inform of recent shifts or movements (i.e., migrant). A variation was recorded for in both muscle and liver tissues from July to December where values where higher during September ( = 17.5 ‰) and lower in November ( = 13.7 ‰) during the four years of study, which could be explained as baseline variation, however, further analysis is required to identify this variation. Stomach content analysis showed dolphinfish feed mainly of fish (PSIRI = 74%) and statistical differences were observed in diet between months, being September the month that differed with the other months according to ANOSIM, however, no statistical difference was observed between months when trophic position was estimated through stomach contents. The tissue steady state analysis showed statistical differences between juvenile and adult organisms, where 90 % of adult dolphinfish had <0 classifying this group as migrant or recent diet shift, as were usually lower than meaning they recently arrived from a region with lower baseline (i.e., southern Mexican Pacific) or increased trophic position recently. Regarding juveniles 60 % of the organisms showed >0 classifying this group as resident or without diet shift. This result show that Cabo San Lucas is potentially a converging feeding ground where resident juveniles and migrant adults from different regions mix into a single area throughout the years.
Palabras clave: Dolphinfish; stable isotopes; isoescapes
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