Use of Stable Isotopes to Identify Redds of Putative Hatchery and Wild Atlantic Salmon and Evaluate Their Spawning Habitat and Egg Thiamine Status in a Lake Ontario Tributary

Abstract

Both wild and hatchery Atlantic Salmon Salmo salar can contribute to restoration but can exhibit differences in spawning habitat selection (e.g., water depth, current speed) and egg nutritional quality (e.g., thiamine), which affect reproductive success. Hence, there is a need to be able to differentiate the spawning contribution of the two groups in the wild. As diets of wild and hatchery-reared spawners are markedly dissimilar and diet is known to influence stable isotope signature, egg stable isotope signatures offer the potential to discriminate redds of each. Using stable isotope analysis of carbon and nitrogen (δ¹³C and δ ¹⁵N) of naturally spawned Atlantic Salmon eggs, we were able to discriminate the redds of putative wild (i.e., previously stocked life stage feeding in Lake Ontario; EWSR) from putative hatchery-reared Atlantic Salmon (EHSR). Eggs of EWSR were significantly more enriched in nitrogen (δ¹⁵N: 15.0 ± 0.5‰ [mean ± SE]) but more depleted in carbon (δ¹³C: −26.6 ± 0.3‰) than eggs of EHSR (δ¹⁵N = 9.8 ± 0.6‰; δ¹³C = −17.5 ± 0.0‰). Eggs of EHSR were indistinguishable from eggs of known hatchery Atlantic Salmon for both δ¹³C and δ ¹⁵N. Using stable isotopes to discriminate redd type, few differences were found between the spawning habitat of putative wild and hatchery spawners. Similarly using the same criteria, thiamine levels in eggs of EWSR (8,474 ± 840 pmol/g) were not significantly different from eggs of known wild Atlantic Salmon (3,691 ± 782 pmol/g) or of eggs of EHSR (14,865 ± 1,050 pmol/g), whose thiamine levels were indistinguishable from eggs of known hatchery Atlantic Salmon (14,200 ± 1,167 pmol/g). Egg thiamine levels for all groups were above established mortality thresholds. Our results indicate that both hatchery and wild Atlantic Salmon can make reproductive contributions, which can be differentiated and quantified using stable isotope signatures.

Received August 24, 2012; accepted May 15, 2013

ACKNOWLEDGMENTS

We thank the staff of the Ontario Ministry of Natural Resources for assistance during the study, and Marion Daniels, Bill Sloan, and the staff of the Ontario Ministry of Natural Resources Normandale Fish Culture station for making Atlantic Salmon available. Kimberlee Sparks facilitated the analysis of stable isotope analysis at the Cornell Stable Isotope Facility.