Population Structure of Alligator Gar in a Gulf Coast River: Insights from Otolith Microchemistry and Genetic Analyses

Abstract

Growing interest in the Alligator Gar Atractosteus spatula among anglers and fishery managers has inspired efforts to better manage populations. Successful management requires identifying population structure and understanding the distribution of stocks and associated differences in life history. This is particularly important in river systems along the coast of the Gulf of Mexico, where transitions from freshwater rivers to saltwater bays provide the potential for life history diversification. We used otolith microchemistry and genetics to assess population structure of Alligator Gars in the Guadalupe River–San Antonio Bay system, Texas. Lifetime Sr:Ca revealed three, distinct life histories that differed in prevalence across the system. River‐resident fish (i.e., fish exclusive to freshwater) were present throughout the river but were most common in the uppermost river reach (74% of upper river fish). Transient fish that used both river and bay habitats were also found throughout the river but were most prevalent in the lowermost river reach (66% of lower river fish) and bay (91% of bay fish). Bay residents (i.e., fish exclusive to salt water) were detected but comprised only 9% of bay fish. Haplotype diversity based on mitochondrial DNA was lowest in the upper river, indicating limited gene flow compared with the lower river and bay. Similarly, nuclear DNA analyses indicated nonrandom mating between fish from the upper river, lower river, and bay. The differences in Alligator Gar movement and genetics along the river–bay continuum suggest the presence of a river resident stock that predominates the upper river, and a transient stock that predominates the lower river and bay. Therefore, a local‐scale management approach, consistent with the spatial partitioning between stocks, would conserve life history and genetic diversity within the system and provide opportunities to meet the needs of a diverse angling constituency. Understanding how population dynamics differ between stocks is needed to develop appropriate fishery management objectives and corresponding regulations for Alligator Gar. Received May 20, 2016; accepted December 2, 2016 Published online February 27, 2017

Modeling the Responses of Alligator Gar Populations to Harvest under Various Length‐Based Regulations: Implications for Conservation and Management

“…; Daugherty et al. ). Our goal in this study was to integrate this new data into a simulation model to examine the effects of harvest on Alligator Gar populations.…”

Sex‐Specific Dynamic Rates in the Alligator Gar: Implications for Stock Assessment and Management

“…Daugherty et al. () found that 90% of Alligator Gar collected with monofilament gill nets (46‐mm to 152‐mm bar mesh) were between 500 and 1,200 mm TL despite a much broader TL range of fish in the sample (113–2,040 mm). The authors attributed the resulting size distribution to gear selectivity due to the limited strength of monofilament to retain large fish (Froeschke et al.…”

“…Juvenile and adult Alligator Gar ( n = 30) were collected from San Antonio Bay using monofilament gill nets as described by Daugherty et al. (). In the Guadalupe and Trinity rivers, we collected adult Alligator Gar ( n = 296) using weighted‐effort multifilament gill nets designed to minimize size bias among adult age‐classes (Schlechte et al.…”

Alligator Gars in Texas Coastal Bays: Long‐Term Trends and Environmental Influences

“…; Daugherty et al. ). Collectively, these studies suggest that Alligator Gars of various life history stages occupy a wide range of estuarine and marine habitats.…”