Table 4.

Diet-to-tissue trophic discrimination factors (TDF) of carbon and nitrogen stable isotope ratios (Δ¹³C and Δ¹⁵N, ‰) from this and other studies on captive- held (captive or rehabilitated) marine carnivores. All values are separated by species and tissue, and Δ¹³C values are further separated into estimates obtained from bulk or lipid-corrected/extracted prey (LC). Predator samples were lipid extracted prior to the calculation of the TDF are marked with an asterisk (*). All values are given as mean ± SD (as available). Sample sizes (n) are provided for reference.

Species			Whisker			RBC			Plasma			Serum
		n	Δ13C NLC	Δ13C LE	Δ15N	Δ13C NLC	Δ13C LC	Δ15N	Δ13C NLC	Δ13C LC	Δ15N	Δ13C NLC	Δ13C LC	Δ15N
This study:
Monk seal		1	+3.9	+2.7	+2.6	+2.9	+1.4	+2.2	+2.8	+1.1	+3.1	---	---	---
Elephant seal		1	+4.1	+3.5	+2.8	+1.7 ± 0.2j	+1.1±0.2j	+3.1 ± 0.7j	+2.3	+1.7	+3.8	+2.1	+1.5	+4.0
Bearded seal		1	+4.4	+2.6	+3.0	---	---	---	---	---	---	+2.2	+0.8	+4.3
Ringed seal#1		1	+4.6	+3.9	+3.0	+2.3	+1.6	+2.7	+1.8	+1.2	+4.1	---	---	---
Ringed seal #2		1	+4.4	+3.8	+3.2	---	---	---	---	---	---	---	---	---
Spotted seal#1		1	+4.3	+3.7	+4.0	+2.2	+1.5	+2.8	+1.7	+1.1	+4.0	---	---	---
Spotted seal#2		1	+4.3	+3.7	+3.9	+2.2	+1.6	+3.3	+2.0	+1.4	+4.1	---	---	---
Harbor seal		1	+4.4	+3.4	+3.4	+2.1	+1.6	+2.6	+1.8	+1.2	+3.9	---	---	---
California sea lion		1	---	---	---	+3.2	+1.9	+3.2	+2.8	+1.5	+4.2	+2.6k	+1.1k	+4.3k
Other studies:
Harbor seala		4	---	---	---	---	---	---	---	---	---	---	−0.6 to +1.7	+3.9 to +4.6
Harbor sealb		11	---	---	---	---	---	---	---	---	---	+1.5±0.9*	---	+3.8±0.5*l
Harbor sealb		102	---	---	---	+1.8*	---	+3.2*l	---	---	---	---	---	---
Harbor sealc		3	---	---	---	---	+1.6	+2.0i	---	---	---	---	+0.8	+3.5i
Harbor sealc		3	---	---	---	---	+1.2	+1.5i	---	---	---	---	+0.6	+2.7i
Harbor sealc		4	---	---	---	---	+1.1	+2.0i	---	---	---	---	+0.7	+2.7i
Harbor, harp, ringed seald		7	---	+3.2±0.2	+2.8±0.1i	---	---	---	---	---	---	---	---	---
Harbor, harp, ringed seald		14	---	---	---	---	+1.7±0.1	1.7±0.1i	---	---	---	---	---	---
Harp sealc		8	---	---	---	---	+1.7	+1.7i	---	---	---	---	+0.8	+3.3i
Gray sealc		5	---	---	---	---	+1.7	+1.7i	---	---	---	---	+1.0	+3.4i
Gray sealc		2	---	---	---	---	+1.2	+1.6i	---	---	---	---	+0.5	+2.9i
Northern fur seale		6	---	---	---	---	+1.4	+4.1i	---	+1.0	+5.2i	---	+0.6	+5.2i
South American sea lionf		2	---	---	---	---	+0.2±0.1*	+2.0±0.1	---	+1.0±0.1*	+2.4±0.2	---	+1.0±0.1*	+2.6±0.3
Steller sea liong		4	+6.5±0.3	+3.3±0.3	+3.7±0.3	---	---	---	---	---	---	---	---	---
Southern sea otterh		5	+2.4±0.2	+2.8±0.2	+5.5±0.2	---	---	---	---	---	---	---	---	---

^aZhao et al.^[17];

^bGermain et al.^[29];

^cLesage et al.^[15];

^dHobson et al.^[6];

^eKurle^[16];

^fDrago et al.^[18];

^gStricker et al.^[19];

^hTyrrell et al.^[36]

ⁱLipid extracted prey samples were used for calculation of Δ¹⁵N values

^jThe TDF was estimated using the average offset between the δ¹³C and δ¹⁵N values in whiskers and RBCs in free ranging northern elephant seals collected upon return to the colony from a foraging trip (the present study)

^kSerum samples were collected twice, approximately one year apart and used to calculate an average TDF

^lSamples were collected from rehabilitated animals