Distribution, relative abundance and movements of pallid sturgeon in the free-flowing Mississippi River

Abstract

Summary A multiyear study of pallid sturgeon distribution and relative abundance was conducted in the lower and middle Mississippi river (LMR and MMR, respectively). The LMR and MMR comprise the free‐flowing Mississippi River extending 1857 river kilometers (rkm) from its mouth at the Gulf of Mexico upstream to the mouth of the Missouri River. A total of 219 pallid sturgeon and 6018 shovelnose sturgeon was collected during the periods 1996–1997 and 2000–2006. Trotlines baited with worms were the primary collecting gear. The smallest pallid sturgeon captured on trotlines was 405 mm FL and the largest was 995 mm FL. Mean size of pallid sturgeon was statistically smaller in the Mississippi River below the Atchafalaya River near Baton Rouge, LA (621 mm FL). Mean abundance (catch per trotline night) of pallid sturgeon was highest at water temperatures around 10°C. There was a latitudinal trend in mean abundance of pallid and shovelnose sturgeon, but the pattern differed between species. Pallid sturgeon abundance was statistically (P < 0.05) higher (0.3 fish per trotline night) in the lower reach between the Atchafalaya River and New Orleans (rkm 154–507), and at the Chain of Rocks (COR), a low water dam near the mouth of the Missouri River. Pallid sturgeon abundance between these two locations was statistically the same (0.12–0.23). Shovelnose sturgeon abundance increased going upstream, but was disproportionally higher at the COR (22 fish per line compared with <6 fish per line in other reaches). Overall, the ratio between pallid and shovelnose sturgeon varied from a high of 1 : 6 at the lower reach, and gradually decreased upstream to a low of 1 : 77 at the COR. Based on differences in sturgeon abundance, size and habitat characteristics, the free‐flowing Mississippi River can be divided into two reaches in the MMR (i.e. COR is a separate location), and four reaches (i.e., including the Atchafalaya River) in the LMR where management goals may differ.

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

“…Increasing shovelnose sturgeon numbers through reduced harvest may increase competition between the two species as juveniles within the protected area. Given that shovelnose sturgeon numbers are significantly greater than those of the pallid sturgeon (Killgore et al 2007a;Boley and Heist 2011), it is possible the shovelnose sturgeon may outcompete what young pallid sturgeon exist via much higher densities. Similarly, the pallid sturgeon is known to hybridize with the shovelnose sturgeon and the hybrids are reproductively viable (Campton et al 2000;Trana et al 2004).…”

Morphometric variation among river sturgeons (Scaphirhynchus spp.) of the Middle and Lower Mississippi River

“…Pallid specimens captured at this highly disturbed complex through the manipulation of flow regimes may not represent the general population of the unimpeded Lower Mississippi River. Pallid sturgeon have been collected historically as far south as Orleans Parish, LA (near New Orleans) (Bailey and Cross, 1954), and recently in St John the Baptist Parish, LA (rkm 233.3) (Killgore et al., 2007), making that the southernmost extreme of the pallid sturgeon's known range.…”

Evaluation of Potential Impacts of the Lake Maurepas Diversion Project to Gulf and Pallid Sturgeon

“…The established CPUE of pallid sturgeon in the Mississippi River at RM 154 to 507 was 0.31 per trotline, and the pallid to shovelnose ratio was 1:6. Based upon trotlines, the pallid sturgeon CPUE was 0.28 per trotline and not different from the value reported by Killgore et al (2007). The ratio of pallid to shovelnose sturgeon was 1:2.4.…”

“…The pallid sturgeon was listed as an endangered species in 1990 and occurs in the large rivers in the Mississippi River Basin (Lee et al 1980;Killgore et al 2007). The decline of this species is attributed to flood control and navigation projects, pollution, and overexploitation for caviar (Dryer and Sandoval 1993).…”