Using stable isotopes to compare seasonal and spatial variation … · 2019-04-18 · among the most abundant predatory fishes in permanent and seasonal floodplains of Louisiana,

Figure 2. Water quality will be tested at each site (left). Spotted Gars will be processed immediately upon returning to the lab (right).

Figure 3. We hypothesize that trophic position will be variable between the two basins., with Spotted Gars from UBE at a higher position than Spotted Gars from ARB based on diet (Bonvillain et al. 2008 ) and stable isotope analysis (δ15N, δ13C) . Photo credit: ODNR Division of Wildlife, Brian Zimmerman

δ1

5N

ARB UBE

• Understanding how species respond to seasonality and resource availability is crucial for anticipating consequences of anthropogenic alterations to the environment.

• Consumer trophic positions can respond variably to seasonally fluctuating environments and resources. Stable isotope analysis is an effective method for tracking energy flow through trophic levels within ecosystems.

Figure 1. Spotted Gar (Lepisosteus oculatus) is among the most abundant predatory fishes in permanent and seasonal floodplains of Louisiana, however, no previous studies have used stable isotopes to explore spatial and seasonal variation in trophic position of this key predator.

Introduction

Our two study sites are the Atchafalaya River Basin (ARB) which receives an annual flood pulse from the Mississippi River, and the Upper Barataria Estuary (UBE), which is disconnected from the Mississippi River and no longer receives a flood pulse. • Spotted Gars will be collected seasonally from the

UBE (spring, summer, winter, fall ) and collected twice from the ARB (summer and fall)

• Gut contents and life history characteristics (age, growth, sex) will be compared to stable isotope analysis (δ15N, δ13C) of fin and muscle tissues .

• Snails will be used as a baseline organism to compare the relative nitrogen)enrichment for each basin

• Fin and muscle tissue stable isotope results will be compared to develop a model based on non-lethal sampling

Methods Hypothesis

Objectives

1. Compare spatial and seasonal variation in life history characteristics and trophic ecology of Spotted Gar populations from two hydrologically distinct basins in Louisiana.

2. Develop a stable isotope model using fin clips as a non lethal alternative to white muscle tissue for future trophic ecology studies on Spotted Gars.

References Bonvillain C. P., A. M. Ferrara, and Q. C. Fontenot. 2008. Relative abundance and biomass estimate of a spotted gar population in a seasonally connected large river floodplain lake. Proceedings of the

Annual Conference of the Southeastern Association of Fish and Wildlife Agencies 62:177-182. Jardine, T. D., et al. 2011. A non-lethal sampling method for stable carbon and nitrogen isotope studies of tropical fishes. Marine and Freshwater Research 62(1):83. Post, D. M. 2002. Using stable isotopes to estimate trophic position: models, methods, and assumptions. Ecology 83:703– 718.

Significance

• This study will provide a comprehensive description of seasonal and spatial trophic level variation of Spotted Gars in the Atchafalaya River Basin and the Upper Barataria Estuary.

• The creation of a fin-based isotope model will allow for non-lethal sampling of Spotted Gars from threatened or endangered populations (e.g. Pennsylvania and Canada).

Anthea Fredrickson1, Solomon R. David1, Quenton Fontenot1, Guillaume Rieucau2 1Nicholls State University, 2Louisiana Universities Marine Consortium

Using stable isotopes to compare seasonal and spatial variation in trophic position of the Spotted Gar Lepisosteus oculatus in Louisiana floodplains