No abstract

on a southern Great Plains stock of paddlefish Polyodon spathula inhabiting the Neosho River, Spring River, and Grand Lake, Oklahoma, is characterized (1) in terms of the Acipenseriform life history framework outlined for the Yellowstone-Sakakawea stock of the Northern Plains and (2) in relation to the framework metabolic theory of ecology and associated latitudinal and environmental correlations with lifespan. In the Grand Lake stock, male fish typically mature at ages 6-7, and females mature at ages 8-9. The five stages of the lifespan (immature, maturing, growth and reproduction, prime reproduction, senescence to death) are compressed into a period of 15-20 years; the prime reproduction period occurs from ages 12 to 16 years for females. This lifespan compares to one of 40-50 years (and occasionally longer), and a prime reproduction period for females from ages 25 to 40 years, for the Yellowstone-Sakakawea stock. The more compressed lifespan of the Grand Lake stock and lower energy storage, as indicated by weights of gonadal fat bodies, are consistent with the framework metabolic theory of ecology. Over the course of a year, fish in Grand Lake are under a much higher metabolic demand than those in Lake Sakakawea. The distinct differences detailed between these two stocks from the southern and northern plains may exist between other paddlefish stocks, other Acipenseriform species, and other fish taxa separated by large latitudinal and climatic differences. The results have specific implications for harvest management and effects of climate change on Acipenseriform life histories and lifespan.

An approach is described to assess the accuracy and precision of age estimates for paddlefish Polyodon spathula of the Yellowstone-Sakakawea stock in Montana and North Dakota. Twenty-five of 30 fish tagged with coded wire tags as age-0 fish in 1995 and recaptured over the period 2002-2005 were independently aged correctly with dentaries (lower jaw bones); estimates for the other five fish deviated from actual ages by 1 year. For fish older than age 10, estimated ages based on dentaries collected from 1991 to 2004 were compared with the estimated minimum expected ages of recovered fish that were jaw-tagged during 1964-2004. Of 323 fish, 300 (93%) had estimated ages that were the minimum expected age or older. The ages for the remaining 23 fish were less than the minimum expected ages, mostly by three or fewer years; these fish spanned a range of ages but tended to be older. Precision estimates (mean coefficient of variation) for age determination ranged from 3.6% for female fish from Montana in 2003 to 7.1% for male fish from North Dakota in 2003. The results indicate that estimating ages from Yellowstone-Sakakawea paddlefish dentaries is generally a repeatable, straightforward process with sufficient accuracy and precision to be useful for stock assessment. Validation studies should be conducted on other paddlefish stocks because the ease of interpreting dentaries varies with locality.

No abstract

A long-term investigation (1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006) was conducted on the relation between Yellowstone and Missouri River discharges, water level (elevation) changes of Lake Sakakawea, a Missouri River mainstem reservoir in western North Dakota, and the ecology of the Yellowstone-Sakakawea stock of paddlefish Polyodon spathula, a zooplanktivorous Acipenseriform fish. After impoundment in December 1953, Lake Sakakawea filled gradually over a 13-year period (1953-1966). Water levels were lowered sharply and briefly in 1977 and 1981 and for much more prolonged periods of 1988-1993 and 2000-2006 associated with drought conditions in the central United States and water management decisions by the U.S. Army Corps of Engineers.The 1995 year class of paddlefish, by far the strongest in the 16-year study period, was associated with the sharp rise in water level from August 1993 through 1995, the longest continuous rise since the initial filling and the only period since initial filling when reservoir levels rose substantially in three consecutive years. High reservoir levels were associated with higher densities of zooplankton (all taxa combined and Leptodora kindtii, the primary food of age 0 paddlefish), stronger year classes (based on counts of age 0 fish along standard transects), greater mean weight and condition of age 0 fish in August, greater mean weights of recruits, higher growth rate of adult fish, and greater weight of gonadal fat bodies (GFBs), an indicator of energy storage, in absolute weight, as a percentage of gonad weight, and as a percentage of fish weight. Sixty-three percent of the variation in the ratio of GFB weight/gonad weight was explained by reservoir level. Fish tagged as adult migrants and recaptured in succeeding years after rearing in rising and high reservoir conditions gained an average of 0.04 kg/yr, whereas fish rearing in falling-and low-reservoir conditions lost an average of 0.19 kg/yr. Missouri River discharge during spring was significantly correlated with estimated age 0 year class strength, but a similar relationship did not hold for the Yellowstone River, which is the river used by most spawning paddlefish. Results of this study are consistent with studies from Lake Sakakawea and other reservoirs indicating that trophic upsurge in recently filled (and refilled) reservoirs favors the development of stronger year classes, faster growth, better condition, and larger size at maturity of fishes. Higher riverine discharges, thought to favor paddlefish reproductive success, were also typically associated with a rising or high reservoir. In contrast, low-reservoir levels over the period [2000][2001][2002][2003][2004][2005][2006] have negatively affected paddlefish year class strength, growth, and energy storage. If, in succeeding years, Lake Sakakawea once again is allowed to rise to full pool as it did over the period 1993-1995, inundation of the shorelines and the vegetation can be expected to result in another ups...