Defense Date

3-21-2023

Document Type

Dissertation

Degree Type

Doctor of Philosophy

Degree Name

Oceanography/Marine Biology

First Advisor

Mahmood Shivji, Ph.D.

Second Advisor

Bradley Wetherbee, Ph.D.

Third Advisor

Christopher Lowe, Ph.D.

Fourth Advisor

Jeremy Vaudo, Ph.D.

Keywords

biologging, billfish, marlin, sailfish, recovery period, hunting behavior, oxygen minimum zone, habitat compression, pelagic predator, niche partitioning

Abstract

Pelagic apex predators exert strong influences on ecological communities, and often support valuable commercial or recreational fisheries worldwide. Yet, due to their rarity and pelagic lifestyle, many species, such as billfishes, have proven particularly difficult to study at resolutions necessary to define dynamics of recovery from fishery interaction, physical interaction with environmental features and prey exploitation, and competitive interactions among other billfish predators. This leads to a paucity of knowledge on billfish ecology and habitat use, and hinders management efforts. With the ever-improving and miniaturization of technology and oceanographic datasets, the ability to define and quantify these interactions of fish to each other and their environment has never been greater. In this dissertation, I developed a novel tag and deployment method to characterize the recovery dynamics of blue marlin (Makaira nigricans) and sailfish (Istiophorus platypterus) after catch and release in a typical recreational fishery. I also utilized these tags to document fine-scale movement and foraging behavior of these two species in the vertically compressed eastern tropical Pacific, where a large naturally occurring oxygen minimum zone exists. This oceanographic feature compresses the prey of these predators to a narrow range during the day, and I hypothesize that the billfishes are using this to their advantage to increase foraging opportunities. Indeed, animal-borne video and the associated high-resolution data documented a sailfish exploiting the hypoxic boundary, initiating a pursuit at depth, chasing it to the surface, and capturing the prey after a pursuit at the surface. Using physiological and bioenergetic modeling, I estimated the net energetic gain over the 24 hour period the event took place. In the final chapter, I used a multidisciplinary approach to investigate the competitive interactions and mechanisms of niche partitioning employed by blue marlin, sailfish, and black marlin (Istiompax indica) in the vertically compressed environment. This work demonstrated a seasonal response in vertical habitat use, alleviating competition and allowing these sympatric predators to coexist. Together, these works provide unparalleled insights into the fish-fishery interaction, biology, physiology, and ecology of these top pelagic predators, and provide necessary information for ecosystem function and management.

ORCID ID

0000-0002-4714-5632

Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.

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