Semester of Graduation

Summer 2020

Degree

Master of Science (MS)

Department

Renewable Natural Resources

Document Type

Thesis

Abstract

Estuaries along the northern Gulf of Mexico represent some of the most productive ecosystems in the world, providing vital habitat for many recreationally and commercially valuable species, including the blue crab, Callinectes sapidus. The mixing of fresh river and saline ocean water in coastal estuaries contribute to this productivity. Dominated by large river influences and consisting of multiple estuaries, Louisiana contributes the largest commercial fishery in the Gulf of Mexico, and remains, on average, the largest supplier of blue crabs in the nation. However, across southeast Louisiana, freshwater flow is largely dependent on Mississippi River discharge, which is highly variable and changing rapidly due to multiple factors including river leveeing and changing precipitation patterns. As Louisiana is experiencing high rates of coastal land loss, large restoration projects diverting river sediment and water into adjacent estuaries further impact freshwater flow, yet the impacts on dependent nekton species, including the economically important blue crab, remain largely unknown. Managers lack basic data on population dynamics, habitat use and environmental factors influencing blue crabs in the region. For this study, we quantified nekton species assemblages and blue crab populations seasonally using throw traps (N=96) and bag seines (N=96) within an active delta characterized by high freshwater flow (Mississippi River Delta) and an inactive delta characterized by low freshwater flow (Terrebonne Basin). Nekton species composition differed between both deltas, though differences for crustacean and fish densities, nekton species richness, and blue crab densities were largely seasonally driven and reflected individual species life history. Both deltas supported similar densities of recently settled, juvenile blue crabs during fall when abundances were highest within both deltas. Panaeid shrimp were largely absent from active delta sites, though densities where consistently high in the inactive delta during summer and fall. The most pronounced differences between the active and inactive deltas largely occurred in the spring during an extended period of flooding for the Mississippi River, which in 2019 exceeded previous river flows in both volume and length of time providing a stark contrast between the deltas. This unusually high riverine flow provides some indication of the impact that extended, high river flow may have on nekton assemblages and habitat availability within an estuary. As changes in freshwater flow are associated with numerous water quality and habitat availability effects, determining direct linkages to nekton and economically important species remains critical, and may be location and estuarine dependent.

Date

3-4-2020

Committee Chair

La Peyre, Megan

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