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Blackfin Tuna Thunnus Atlanticus and Little Tunny Euthynnus Alletteratus

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Blackfin Tuna Thunnus Atlanticus and Little Tunny Euthynnus Alletteratus Nova Southeastern University NSUWorks HCNSO Student Theses and Dissertations HCNSO Student Work 12-12-2014 Reproductive parameters of two coastal pelagic fishes off southeast Florida: Blackfin unT a Thunnus atlanticus and Little unnT y Euthynnus alletteratus Sonia Ahrabi-Nejad Nova Southeastern University, [email protected] Follow this and additional works at: https://nsuworks.nova.edu/occ_stuetd Part of the Marine Biology Commons, and the Oceanography and Atmospheric Sciences and Meteorology Commons Share Feedback About This Item NSUWorks Citation Sonia Ahrabi-Nejad. 2014. Reproductive parameters of two coastal pelagic fishes off southeast Florida: Blackfin Tuna Thunnus atlanticus and Little Tunny Euthynnus alletteratus. Master's thesis. Nova Southeastern University. Retrieved from NSUWorks, Oceanographic Center. (25) https://nsuworks.nova.edu/occ_stuetd/25. This Thesis is brought to you by the HCNSO Student Work at NSUWorks. It has been accepted for inclusion in HCNSO Student Theses and Dissertations by an authorized administrator of NSUWorks. For more information, please contact [email protected]. NOVA SOUTHEASTERN UNIVERSITY OCEANOGRAPHIC CENTER Reproductive parameters of two coastal pelagic fishes off southeast Florida: Blackfin Tuna Thunnus atlanticus and Little Tunny Euthynnus alletteratus. By Sonia Ahrabi-Nejad Submitted to the Faculty of Nova Southeastern University Oceanographic Center in partial fulfillment of the requirements for the degree of Master of Science with a specialty in: Marine Biology Nova Southeastern University December 12, 2014 ! Table of Contents Abstract .............................................................................................................................. ii! Keywords ........................................................................................................................... ii! Acknowledgements .......................................................................................................... iii! Introduction ....................................................................................................................... 1! Reproduction and Histology ........................................................................................... 2! Coastal Pelagic Fish ........................................................................................................ 5! Blackfin Tuna .................................................................................................................. 9! Little Tunny .................................................................................................................. 12! Objectives ..................................................................................................................... 14! Materials and Methods ................................................................................................... 14! Sample Collection ......................................................................................................... 14! Laboratory Processing .................................................................................................. 17! Histological Analysis .................................................................................................... 17! Statistical Analysis ........................................................................................................ 18! Results .............................................................................................................................. 19! Sample Collection ......................................................................................................... 19! Histological Gamete Description .................................................................................. 20! Gonadosomatic Index (GSI) ......................................................................................... 33! Spawning Seasonality ................................................................................................... 35! Female Spawning Frequency ........................................................................................ 40! Discussion ........................................................................................................................ 44! Conclusion ....................................................................................................................... 54 Appendix A: Histological Procedure ............................................................................. 56! References ........................................................................................................................ 58! ! ! i! Abstract The ability to manage a fish stock relies on an understanding of life history characteristics and basic biology of the species. Numerous age-growth studies are facilitated by the relative ease of ageing fishes through hard-part analyses. Determining reproductive parameters for fish populations is equally important for stock assessments and management, and histological examination of gonads provides the most accurate determination of fecundity and spawning periods. Coastal pelagic fishes are often targeted commercially and recreationally due to their easy access by private vessels. However, there are few studies researching the biology and reproduction of recreational fishes in the waters of Southeastern Florida that would lead to a better understanding for management practices. The objective of this study was to provide baseline reproductive data for two fishes particularly important to Florida fisheries: the coastal pelagic scombrids Blackfin Tuna Thunnus atlanticus and Little Tunny Euthynnus alletteratus. Archived gonad samples from 2010-2014 for these two species were evaluated, and GSI values and histological examination indicated one spawning season for both species. Little Tunny spawn April through August, and Blackfin Tuna spawn May through June. Additionally both species have asynchronous oocyte development, and are batch spawners. Postovulatory follicles were used to estimate spawning frequency; for Blackfin Tuna, mean spawning occurs once every 1.49 days, and for Little Tunny, mean spawning occurs once every 1.47 days. Comparison of otolith age data to these results indicates that Little Tunny mature at a smaller size and younger age than Blackfin Tuna. Size at 50% maturity for male Blackfin Tuna was 435.2 mm TL, for female Blackfin Tuna was 392.3 mm TL, and for male Little Tunny was 347.77 mm TL. Age at 50% majority for male Blackfin Tuna was 0.66 years, and for male Little Tunny was 0.50 years. In addition to providing important baseline data for fisheries management, this study collaborated with previous research to improve accuracy of reproductive age assessments. Finally, reproductive parameter studies of fishes in Florida and the Greater Caribbean area commercial and recreational fisheries provide information important for future ecosystem based management. Keywords: coastal pelagic, gonadal histology, Blackfin Tuna, Little Tunny ! ii! Acknowledgements ! Thank you to my family, friends, and loved ones for supporting me throughout this journey. Thanks to all my committee members for knowledge and laboratory assistance; especially my major professor, Dr. David Kerstetter, for his expertise with fisheries and fish biology; Abby Renegar for helping with the histology techniques; and Nancy Brown-Peterson with helping me learn to read the slides and reproduction guidance. Thanks to the fisheries lab for help with collection and processing of samples, and volunteering at fishing tournaments. Special thanks go to Travis Moore for his initial collections and information on the coastal pelagic fish complex and Jessy Adams for sharing her age-growth data. Thanks to everyone who helped provide samples, including the fishing captains and tournament coordinators. This project was funded by the Nova Southeastern University President Faculty Research and Development Grant. Additional support was provided by a scholarship from the Yamaha Contender Miami Billfish Tournament and the Gulf and Caribbean Fisheries Institute Ronald L. Schmied Scholarship. !iii! Introduction A majority of the human population lives in close proximity to the ocean (Worm et al. 2006), and an even greater percent relies on services provided by the ocean. Humans have been consuming fish caught from the ocean for thousands of years, but the onset of industrialized fishing methods has allowed access to new fishing areas and reduced ocean biomass (Myers and Worm 2003, Pauly and Palomares 2005, Worm et al. 2006). Obtaining an estimate of fish biomass reduction as a result of fishing is complicated, as catch per unit effort does not account for naturally occurring changes in fish populations (Walters 2003). Human-impacted marine ecosystems are experiencing a decline of species richness and average fish size (Worm et al. 2006). With the exploitation of large fish, fishing pressure often moves to the next desirable species lower on the food web. However, animals occupying lower trophic levels are smaller leading to an increase in numbers caught to equal total weight of catches for larger fishes (Pauly et al. 1998). To sustain a fish population, management needs to maintain a balance of spawning stock to continue population growth. An accurate method to estimate the spawning stock biomass and female egg production of commercially important fish will improve our collective knowledge of factors influencing population dynamics
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