Estimating tissue-specific discrimination factors and turnover rates of nitrogen and carbon stable isotopes in the smallnose fanskate Sympterygia bonapartii (Rajidae)

DAVID E. GALVÁN; YAÑEZ J.; IRIGOYEN A. J.

JOURNAL OF FISH BIOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2016 vol. 89 p. 1258 - 1270

0022-1112

This study aimed to estimate TDFs and metabolic turnover rates of nitrogen and carbon stable isotopes in blood and muscle for the smallnose fanskate Sympterygia bonapartii (Rajidae) by feeding six adult individuals, maintained in captivity, with a constant diet during one year (365 days). TDFs were estimated as the difference between δ13C or δ15N values of the food and the skates? tissues after they had reached the equilibrium condition with diet. The duration of the experiment was enough to reach the equilibrium condition in blood for both elements (estimated time to reach 95% of turnover: C t95%blood = 150 days, N t95%blood = 290 days), whilst turnover rates could not be estimated for muscle because of the high variability between samples. Estimations of Δ13C and Δ15N values in blood and muscle using all individuals were Δ13Cblood = 1.7?, Δ13Cmuscle = 1.3?, Δ15Nblood = 2.5? and Δ15Nmuscle = 1.5?, but there was evidence supporting differences of ~0.4? in the Δ13C values between sexes. The present results of TDFs and turnover rates constitute the first evidence for dietary switching in marine skates based on long-term controlled feeding experiments. Overall the results showed that the smallnose fanskate have relatively low turnover rates and isotopic measurements would not adequately track seasonal movements. The estimated Δ13C values in skate?s blood and muscle were similar to previous estimations for elasmobranchs and to generally accepted values in bony fish (Δ13C = 1.5?). Regarding Δ15N, the results presented here were similar to published estimations for blood but smaller than published estimations for muscle and notably smaller than the typical values used to estimate trophic position (Δ15N ~-3.4?). Thus, trophic position estimations for elasmobranchs based on typical Δ15N values could lead to underestimates of actual trophic positions. Finally, the evidence of differences in TDFs between sexes supports the need for more experiments to elucidate the generality of this trend.