Defense Date

8-12-2022

Document Type

Thesis

Degree Type

Master of Science

Degree Name

Marine Science

First Advisor

Tamara Frank

Second Advisor

Tracey Sutton

Third Advisor

Rosanna Milligan

Keywords

Sampling gear comparison, Deep sea, Gulf of Mexico, Micronekton, Euphausiacea, Decapoda, Lophogastrida, Deepwater Horizon Oil Spill

Abstract

Trawls are an effective and widely used method for collecting micronekton because they can sample large volumes of sparsely distributed organisms, as well as allow for direct species identification of collected samples. However, net sampling methods are known to be highly variable in terms of design and catchability, and comparisons of deep-sea trawl data from two different types of nets over the same spatial and temporal scale are relatively rare. The current study is unique because it provides such an analysis for micronektonic crustaceans in the Gulf of Mexico (GOM) by comparing the trawling efficacy of a smaller 10 m2 Multiple Opening and Closing Net and Environmental Sensing System (MOCNESS) and an Irish Herring Trawl (165.47 m2)) over the same time period and region. This was done by comparing parameters of the crustacean assemblage from samples collected by both nets from December 2010 – September 2011 in region surrounding the Deepwater Horizon oil spill in the GOM. This study demonstrated that net type significantly affects the characterization of the standardized abundances (n/m3), biomass (g/m3), and carapace/body lengths (mm) of crustacean species from the five dominant taxa analyzed in this study (i.e. Superfamily Oplophoroidea and families Sergestidae, Benthesicymidae, Euphausiidae, and Eucopiidae): the MOCNESS had higher abundances and biomass per trawl, and the IHT had larger specimen sizes and trawled volumes. Overall, this study demonstrates that net type significantly affects our description of the GOM pelagic shrimp and krill assemblage, indicating that generalizability of data from a single net type is limited.

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