Virtual Population Analysis, Episodic Recruitment, and Harvest Management of Paddlefish with Applications to Other Acipenseriform Fishes

Abstract

Virtual population analysis (i.e., cohort analysis) was conducted on the Yellowstone–Sakakawea paddlefish Polyodon spathula stock to evaluate recruitment patterns using a combined Montana–North Dakota dataset from the recreational snag fishery over the period 1993–2012. Distinct differences were found in the pattern of reconstructed virtual population sizes of the sexes. There existed a sharp increase in virtual male population size related to first recruitment only for the 1995 year-class. A much smaller increase was found in the female virtual population sizes because the female fish had just begun to recruit as of 2012. Episodic paddlefish recruitment seen in this study and elsewhere (e.g., Oklahoma) is probably common in other Acipenseriform stocks and may have an adaptive basis. However, adequate sex-specific age structure information is not available in many stocks for recruitment variations to be confirmed. Evidence suggests that episodic recruitment in the Yellowstone–Sakakawea paddlefish and other stocks is related to high spring discharge and resulting increasing reservoir water levels and subsequent trophic upsurge. Episodic recruitment poses some substantial challenges for harvest management, including the need to sustainably allot annual harvest until the occasional strong year-classes recruit. Knowledge of recruitment variations and its causes is critical for maintaining harvested stocks of paddlefish and other Acipenseriform species. Sustainable harvest for meat or caviar production in Acipenseriform species with episodic recruitment will require age- and sex-specific data allowing variations in annual recruitment success to be identified and harvest allotted accordingly.