Research Document - 2012/019

Sex determination of belugas and narwhals: understanding implications of harvest sex ratio

By S.D. Petersen, D. Tenkula, S.H. Ferguson, T. Kelley, and D.J. Yurkowski

Abstract

Monodontids, narwhal (Monodon monoceros) and beluga (Delphinapterus leucas), are harvested in the Arctic as part of a subsistence fishery. Maintaining sustainable harvest requires monitoring hunter statistics such as the sex ratio of the harvest. Hunter selection is important harvest information allowing managers to optimize hunter effort (pressure) away from vulnerable groups (i.e., mature females). The sex ratio of harvested animals was determined in the field by inspection of carcasses by hunters and by researchers in the laboratory using genetic techniques. We calculated the technical error rate for narwhal (1.5%) and beluga (7.0%) by comparing reproductive organs to molecular sex determination results. We then determined the field error rate, as the proportional difference between the reported sex and the molecular sex for narwhal (6.3%) and beluga (17.2%). The higher field error rate for beluga is likely due to the lack of distinguishing secondary sexual characteristics. The occurrence of tusked female narwhal in the harvest was also estimated at 6%. To use the precautionary approach of managing stocks or populations increased effort is required to obtain reliable sex ratio determinations for the natural and harvested population. Molecular sex determination can reliably fill this role using available and future hunter collections.

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