Date of Award

12-2018

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Forestry and Environmental Conservation

Committee Member

Dr. Brandon Peoples, Committee Chair

Committee Member

Mr. S. Chad Holbrook

Committee Member

Dr. Christopher Post

Abstract

Quantitative understanding of reproductive ecology is vital to the conservation and recovery of imperiled fishes. Atlantic Sturgeon (Acipenser oxyrinchus) and Shortnose Sturgeon (Acipenser brevirostrum) are endangered diadromous fish that range across the Atlantic Coast of North America. Historically, populations of both species were exploited for the black caviar trade range-wide. Although moratoria ended commercial harvest, populations are currently threatened by habitat degradation and alteration. This research represents an initiative to increase our understanding of reproductive behavior for both Atlantic and Shortnose Sturgeon by estimating adult population levels as well as the effects of environmental covariates on the initiation of spawning migrations in the Savannah River. We used generalized and linear mixed models to investigate the relationship between sturgeon migration behavior and water temperature and discharge within the lower Savannah River from January 2013 – May 2018. Throughout the duration of the study period, we detected six Atlantic Sturgeon attempt nine fall migrations (n = 918 records), four Atlantic Sturgeon attempt eight spring migrations (n = 257 records), and 15 Shortnose Sturgeon attempt 29 spring migrations (n = 3,542 records). Cues for initiation of migration, as well as spatial position within the river during spawning migrations, were species-specific. Depending on the species and index of spawning, we observed significance in both water temperature and the water temperature-discharge interaction. Traditionally, capture mark-recapture techniques are used to estimate sturgeon abundance. As a non-invasive alternative, we sampled Atlantic Sturgeon putative spawning habitat within the Savannah River over 50 occasions (days) from August – November 2017 using the Hummingbird Helix 12 CHIRP-Mega-SI-GPS-G2N side scan sonar unit. We used N-mixture modeling within a Bayesian framework to estimate Atlantic Sturgeon abundance, as well as covariate significance in detection and abundance, using spatially and temporally replicated count data obtained from sonar recordings. We detected at least one Atlantic Sturgeon on each sampling occasion and estimated a maximum abundance between 35 – 55 individuals within the putative spawning area during the 2017 fall spawning season. Site average max depth was significant in predicting Atlantic Sturgeon abundance, and discharge had a significant negative effect on our ability to detect Atlantic Sturgeon using side scan sonar as a sampling gear. Routine standardized sampling using our methods will efficiently produce spawning stock estimates and provide insight regarding the effects of environmental covariates on spawner abundance seasonally.

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