Age and growth of pallid sturgeon in the free-flowing Mississippi River

Abstract

Trotlines were used to capture pallid sturgeon in the freeflowing Mississippi River, which extends from the Gulf of Mexico to the mouth of the Missouri River. Trotlines were baited with worms, and set overnight usually along the channel border. The pectoral fin rays of 165 pallid sturgeon caught in the Mississippi River were aged; 118 were from the lower Mississippi River (LMR) between the Gulf and mouth of the Ohio River, and 47 were from the middle Mississippi River (MMR) between the mouths of the Ohio and Missouri rivers. Initial agreement within ±1 year between two readers ranged from 53% for the LMR specimens, which were read first, to 84% for the MMR. Final age was agreed upon by both readers. For LMR pallid sturgeon, final age estimates ranged from 3 to 21 years with a mean (±SD) of 11.0 ± 4.7. For MMR pallid sturgeon, final age estimates ranged from 5 to 14 years with a mean of 9.5 ± 2.1. Seven pallid sturgeon marked with coded wire tags (CWT), indicating hatchery origin, were collected in the MMR. Age estimates for CWT fish were 7-8 years representing 1997 stocked fish, and 11-12 years representing 1992 progeny stocked in 1994. Von Bertalanffy growth equations for length indicated that pallid sturgeon in the MMR had higher growth rates for a given age than pallid sturgeon in the LMR. However, there were no significant differences (ANOVA ANOVA, P > 0.5) in the length-weight relationships between reaches. In the LMR, pallid sturgeon fully recruited to trotlines at age 11 and instantaneous total mortality (Z; slope of catch curve) was estimated at )0.12 (n ¼ 10 year classes, r 2 ¼ 0.55, P ¼ 0.01). Of the 118 sectioned rays from the LMR, 28 could not be reliably aged (only one section from the MMR could not be aged). Therefore, age was predicted from length using the von Bertalanffy equation. The catch curve was re-calculated using the predicted ages of the 28 pallid sturgeon in the LMR resulting in Z ¼ )0.07. In the MMR, pallid sturgeon fully recruited to trotlines at age 9 and Z was estimated at )0.36 (n ¼ 6 year classes, r 2 ¼ 0.67, P ¼ 0.04), which was significantly higher (ANOVA ANOVA, P ¼ 0.04) than the LMR estimate. Higher mortality in the MMR may be due to habitat limitations compared to a larger, more diverse channel in the LMR, and incidental take of larger, older individuals during commercial harvesting of shovelnose sturgeon. Commercial take of shovelnose does not occur in the LMR except in the northern portion of the reach. Considering the presence of pallid sturgeon with CWT, recruitment of older individuals in the MMR may have been influenced by stocking a decade earlier. Management strategies for this endangered species should consider the differences in mortality rates among reaches, the impacts of commercial fishing on recovery of pallid sturgeon in the MMR, and the long-term effects of hatchery fish now recruiting into the free-flowing Mississippi River.

Challenges in merging fisheries research and management: the Upper Mississippi River experience

“…Confirming concerns about incidental or intentional harvest, pallid sturgeon have appeared in the commercial creel (Bettoli et al, 2009), even with the efforts of resource agencies to educate fishers and attempts of conservation officers to enforce federal law in this large system. Mortality rates of pallid sturgeon are currently similar to those of shovelnose sturgeon in the harvested reach of the UMRS and greatly exceed those of sturgeon in unharvested reaches in the UMRS and the Missouri River (Colombo et al, 2007;Killgore et al, 2007). The USFWS is currently considering prohibiting fishing of shovelnose sturgeon based on the Similarity of Appearance Section of the Endangered Species Act (Federal Register, 2009), which will likely generate a diverse array of reactions among the stakeholders.…”

“…The unique physical characteristics of this area including turbulent water, scoured bed, and heterogeneous bedform appear to facilitate fisheries production. For example, catch rates of shovelnose and pallid sturgeon are high below the lowhead dam at this locale (Killgore et al, 2007). An alternate view is that this lowhead dam may be inhibiting upstream movement of these fishes and causing them to ''pile up.''…”

Considering a species-loss domino-effect before endangered species legislation and protected area implementation

“…Harvest of shovelnose sturgeon for roe (i.e., caviar) was allowed in eight states in the central US (Tennessee, Missouri, Kentucky, Arkansas, Indiana, Iowa, Illinois, and Wisconsin; Koch and Quist 2010). It has been estimated that pallid sturgeon mortality rates were about three times greater where shovelnose sturgeon were harvested (Colombo et al 2007;Killgore et al 2007b). Thus, the SOA provision was implemented to prevent suspected bycatch of the pallid sturgeon (Bettoli et al 2009).…”

Insight into Danube sturgeon life history: trace element assessment in pectoral fin rays

“…A final decision on the age and the border between growth zones was reached by consensus. If there was still a discordance and opinions about the counts differed by 1 year, the fish was assigned a higher age, as the age of older individuals is usually underestimated (Rien and Beamesderfer 1994;Paragamian and Beamesderfer 2003;Killgore et al 2007).…”

“…The innermost area represents the first annulus and corresponds to the first year of life, and the outermost annulus to the last year of life of the studied individual (Stevenson and Secor 2000). As suggested by a number of authors (e.g., Jackson et al 2007;Killgore et al 2007), age assessment was performed by four independent readers, in order to reduce errors in the process of age reading. A final decision on the age and the border between growth zones was reached by consensus.…”