Defense Date

12-3-2021

Document Type

Thesis

Degree Type

Master of Science

Degree Name

Marine Biology

First Advisor

Tracey Sutton Ph.D.

Second Advisor

Matthew Johnston Ph.D.

Third Advisor

Jon Moore Ph.D.

Abstract

The suborder Scorpaenoidei is among the most speciose fish taxa of the World Ocean, including the Gulf of Mexico (GoM). Most adult scorpionfishes are benthic and have a pelagic juvenile phase. Although the species descriptions and distributions of adult scorpionfishes within the GoM are well documented, their juvenile forms are largely undescribed. Due to the poorly resolved taxonomic status of juvenile scorpionfishes, their assemblage dynamics have not been accurately assessed. Specimens were collected from the GoM during seven research cruises (2010-2011), as part of the NOAA-supported Offshore Nekton Sampling and Analysis Program (ONSAP), and during six research cruises (2015-2018), as a part of the GOMRI-supported Deep Pelagic Nekton Dynamics of the Gulf of Mexico Consortium (DEEPEND). Members of the suborder Scorpaenoidei occurred within 47% of epipelagic trawls from the ONSAP and DEEPEND surveys. Juvenile scorpaenoids were as abundant within the upper 200 m of the GoM during the day from the DEEPEND survey as one of the most successful midwater fish groups, the Myctophidae. Nine unique morphotypes were defined, with putative identifications, based upon meristics, morphometrics, and internal and external features with an emphasis on head spines. Pontinus rathbuni accounted for the majority of specimens collected. Specimens of P. rathbuni that were of comparable size to juvenile myctophids (e.g., 15-19 mm standard-length) showed the same diet composition as myctophids but predated during the day as opposed to nocturnal feeding by the myctophids, suggesting a degree of niche partitioning between juvenile benthic and adult pelagic species in a low-latitude oceanic ecosystem.

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