Development and Application of a Size Structure Index for Blue Sucker

Abstract

Blue Sucker Cycleptus elongatus is a species of concern across much of its native range due to population fragmentation and habitat loss. A primary component of managing this species is monitoring various population characteristics, including size structure. A common way to quickly index population size structure is to calculate the proportional size distribution (PSD). However, no standard length categories have been established for Blue Suckers, precluding the use of this index. We used databases, literature searches, field guides, and sampling records to find the largest recorded Blue Sucker. The maximum size Blue Sucker on record was 93 cm, so we propose the following standardized length categories: stock = 23 cm, quality = 38 cm, preferred = 51 cm, memorable = 59 cm, and trophy = 74 cm. We estimated mean values for PSDs using a Bayesian generalized linear mixed model, with a multinomial likelihood for populations of Blue Suckers from six rivers: the James, Big Sioux, Colorado, Red, Wabash, and Missouri. Most of these populations exhibited large size structures except for the James River. The length categories that we derived from the values for PSD should provide an additional tool for evaluating spatial and temporal changes in the size structure of Blue Sucker populations when monitoring the status of this species of concern.

Mismatch between temperature and discharge disrupts spawning cues in a fluvial specialist, blue sucker Cycleptus elongatus

“…During this study, there was no evidence of successful spawning (young‐of‐year [YOY] or juveniles), despite efforts directed at capturing YOY and juveniles. Additionally, the age and size structure of the blue sucker population in the lower Colorado River suggests highly variable recruitment among years with multiple repeated year classes missing from the population (Acre, 2019; Carlson et al, 2022).…”

“…During this study, there was no evidence of successful spawning (young-of-year [YOY] or juveniles), despite efforts directed at capturing YOY and juveniles. Additionally, the age and size structure of the blue sucker population in the lower Colorado River suggests highly variable recruitment among years with multiple repeated year classes missing from the population(Acre, 2019;Carlson et al, 2022).Understanding how a long-lived species such as blue sucker responds to various discharge conditions will require further researchcapturing a wider range of discharges as well as a thorough investigation of tributary use in the Colorado River and more broadly throughout their distribution. The LCRA 2010 water management plan (WMP) contained a discharge rubric to maintain habitat availability in the mainstem based on the inundation of rocky outcrops for blue sucker.…”