Nova Southeastern University NSUWorks All HCAS Student Capstones, Theses, and Dissertations HCAS Student Theses and Dissertations 4-21-2021 Journey into Midnight: Population Dynamics, Vertical Distribution, and Trophic Ecology of Whalefishes (Cetomimidae) in the Bathypelagic Gulf of Mexico Rachel Eckley Nova Southeastern University Follow this and additional works at: https://nsuworks.nova.edu/hcas_etd_all Part of the Marine Biology Commons Share Feedback About This Item NSUWorks Citation Rachel Eckley. 2021. Journey into Midnight: Population Dynamics, Vertical Distribution, and Trophic Ecology of Whalefishes (Cetomimidae) in the Bathypelagic Gulf of Mexico. Master's thesis. Nova Southeastern University. Retrieved from NSUWorks, . (40) https://nsuworks.nova.edu/hcas_etd_all/40. This Thesis is brought to you by the HCAS Student Theses and Dissertations at NSUWorks. 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Thesis of Rachel Eckley Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science Marine Science Nova Southeastern University Halmos College of Arts and Sciences April 2021 Approved: Thesis Committee Committee Chair: Tracey Sutton, Ph.D. Committee Member: Tamara Frank, Ph.D. Committee Member: Jon Moore, Ph.D. This thesis is available at NSUWorks: https://nsuworks.nova.edu/hcas_etd_all/40 HALMOS COLLEGE OF ARTS AND SCIENCES Journey into Midnight: Population Dynamics, Vertical Distribution, and Trophic Ecology of Whalefishes (Cetomimidae) in the Bathypelagic Gulf of Mexico By Rachel Marie Eckley Thesis Submitted to the Faculty of Halmos College of Arts and Sciences in Partial Fulfillment of the Requirements for the Degree of Master of Science with a Specialty in: Marine Biology Nova Southeastern University April 2021 Acknowledgements I would like to thank Dr. Tracey Sutton, my major advisor, without whose support this project would not have been possible. I was very fortunate to be a member of his Oceanic Ecology Lab. My time spent under his guidance has made me a better ecologist and I am forever grateful. I would like to thank my committee members, Dr. Tammy Frank and Dr. Jon Moore, for their gracious assistance in the details of this thesis. They helped bounce ideas and gave very thoughtful edits. Without their help, this project would not have come to realization. I owe an enormous thank you to Dr. John Paxton, an incredible mentor and leading researcher of whalefishes. Being in Australia, our communication was sometimes at odd hours, but he was always more than willing to give insight and advice on my project. I am grateful to have had the opportunity to meet and work with such an inspiring scientist. I would like to thank my lab mates, who were always there when I needed them. I greatly appreciate their donated time in helping me whiteboard an issue. Most importantly, I thank them for keeping me sane during long hours of data collection. They will forever be the reasons I look back on graduate school with a big smile on my face. To my friends and family, I will never be able to thank you enough for your continued encouragement as I chase my dream. Mom, dad, thank you for telling me I could accomplish anything I put my mind to. To my fiancé Mal, you have been my rock during these years and my biggest advocate. Thank you for your unwavering support and for always being my hype-man. Finally, I would like to thank the funders of this thesis. This project was supported by the Gulf of Mexico Research Initiative through a grant to the DEEPEND Consortium. I Abstract Despite comprising the largest biome on Earth, the bathypelagic zone inhabitants represent a “black hole” in the understanding of deep-oceanic functioning due to physical and monetary limitations. The characteristics of the global bathypelagic realm create a limiting environment only inhabitable by specially adapted fauna. These include whalefishes (Stephanoberycoidei: Cetomimidae), which are a taxonomically and systematically challenging group of primarily bathypelagic fishes. Cetomimids were collected in the Gulf of Mexico using high-speed rope trawls and a multiple-opening-and-closing net system. Population dynamics were described using morphometric analysis. Vertical distributions, including diel variation, were described using a modified boxplot of abundance standardized by volume of filtered water. Finally, trophic ecology of male and larval Cetomimus/Gyrinomimus was described through gut-content analysis. In total, 493 Cetomimidae were collected, including six new records for the region (Cetomimus compunctus, C. picklei, Danacetichthys galathenus, Gyrinomimus bruuni, G. grahami, and male Cetomimus/Gyrinomimus TBD) and one new record for the Atlantic Ocean (C. compunctus). The assemblage is dominated by Cetostoma regani and Ditropichthys storeri and is highly skewed to favor adult females. Cetomimids were collected most often in the upper bathypelagic zone, including the smaller males and larvae. Asynchronous diel vertical migration is likely in C. regani and D. storeri and possible in species of Gyrinomimus. Specimen SL and depth of capture were not correlated. Male Cetomimus/Gyrinomimus primarily consume copepods although opportunistic feeding of larger crustacea including euphausiids and/or mysids is likely. Larvae gorge on copepods (in quantities reaching 1709) and may display a selective feeding strategy targeting swarming copepods. Keywords: Cetomimidae, deep-sea, faunal composition, species abundance, vertical range, diel variation, diet. II Table of Contents Acknowledgements ........................................................................................................................ I Abstract ......................................................................................................................................... II Table of Contents ........................................................................................................................ III List of Figures ............................................................................................................................... V List of Tables ............................................................................................................................ VIII 1. Introduction ............................................................................................................................... 1 1.1. Bathypelagic zone ............................................................................................................... 1 Limiting environment ........................................................................................................................... 2 Knowledge gap ..................................................................................................................................... 2 Gulf of Mexico ...................................................................................................................................... 3 1.2. Cetomimidae ....................................................................................................................... 4 Systematics and taxonomy .................................................................................................................... 4 Global horizontal and vertical distribution ........................................................................................... 5 Trophic ecology .................................................................................................................................... 7 1.3. Statement of problem and significance of work .............................................................. 8 2. Methods ...................................................................................................................................... 9 2.1. Sampling and processing ................................................................................................... 9 2.2. Faunal composition and population dynamics .............................................................. 12 2.3 Abundance and vertical distribution ............................................................................... 16 2.4. Dissection and trophic ecology ........................................................................................ 17 3. Results ...................................................................................................................................... 20 3.1. Faunal composition and population dynamics .............................................................. 20 Cetomimidae ....................................................................................................................................... 22 Cetostoma regani ................................................................................................................................ 30 Ditropichthys storeri ........................................................................................................................... 31 Cetomimus........................................................................................................................................... 33 Gyrinomimus ....................................................................................................................................... 34 Male Cetomimus/Gyrinomimus (“Ataxolepis”)..................................................................................