Asymmetrical trophic release: Moray eels inconspicuously predominate heavily fished reefs
| dc.contributor.advisor | Donahue, Megan J. | |
| dc.contributor.author | Zill, Julie | |
| dc.contributor.department | Marine Biology | |
| dc.date.accessioned | 2024-10-09T23:46:14Z | |
| dc.date.available | 2024-10-09T23:46:14Z | |
| dc.date.issued | 2024 | |
| dc.description.degree | Ph.D. | |
| dc.identifier.uri | https://hdl.handle.net/10125/108705 | |
| dc.subject | Ecology | |
| dc.subject | Environmental science | |
| dc.subject | body size | |
| dc.subject | effects of fishing on non-target species | |
| dc.subject | fish surveying methods | |
| dc.subject | mesopredator release | |
| dc.subject | moray eels (Muraenidae) | |
| dc.subject | trait-mediated effects | |
| dc.title | Asymmetrical trophic release: Moray eels inconspicuously predominate heavily fished reefs | |
| dc.type | Thesis | |
| dcterms.abstract | Populations of marine apex predators have declined globally due to human activities. Without sufficient top-down control, mid-trophic level predator abundance can increase, termed ‘mesopredator release’. In the Hawaiian Archipelago, moray eels are consumed by large, transient predators that are scarce on densely populated coastlines of the Main Hawaiian Islands, indicating the potential for mesopredator release of moray eels. Additionally, human fishers have functionally replaced apex piscivores in heavily fished systems, but human prey selectivity differs from that of the natural predator assemblage, resulting in strong top-down control on targeted fishes of all trophic levels and, I hypothesize, the asymmetrical trophic release of non-targeted moray eels. Morays are generally excluded from fish biomass analyses because standard visual survey methods are unreliable for cryptic predators. Therefore, we conducted a novel, eel-specific baited camera survey on shallow reef habitats in the near-pristine Northwestern Hawaiian Islands (NWHI), where large carangids and reef-associated sharks are abundant, and in the populated Main Hawaiian Islands (MHI) where they are relatively rare. In the MHI, morays constituted the majority of piscivore biomass and, unlike most fish families, had a higher average biomass density in the fished MHI compared to the unfished NWHI, a result of both greater eel abundance and body size. Analysis of eel behavior in survey footage revealed that eels spent more time in risk-prone activities and degree of body exposure when large, transient predators were not present in video surveys. Due to their cryptic nature, changes in eel behavioral patterns and size frequency distribution may result in unique non-consumptive effects on the reef fish community. Morays specialize in hunting in the physical reef structures that would otherwise provide a size-dependent refuge to many benthic fishes. In a mesocosm experiment, eel presence decreased the shelter usage time and feeding patterns of a prey surgeonfish, and disrupted its refuge-seeking response during a simulated threat of a transient predator; these responses depended on both the relative size of predator and prey as well as shelter availability. Abundant, many-sized morays may reduce the ability of prey fish to achieve a spatial or body size refuge, and may shift community structure if they unevenly impact shelter-dependent fishes. The underdetection or exclusion of moray eels in spatial analyses of reef fish biomass patterns has led to the paradigm that native piscivorous fish are nearly absent from fished MHI reefs. Rather than a near extirpation of predatory fishes in areas of high human pressures, my data suggest a relative shift in biomass predominance from large roving predators to untargeted, cryptic mesopredators, which are emboldened in the absence of their natural predators—a phenomenon that may also occur outside of Hawaiʻi. | |
| dcterms.extent | 122 pages | |
| dcterms.language | en | |
| dcterms.publisher | University of Hawai'i at Manoa | |
| dcterms.rights | All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner. | |
| dcterms.type | Text | |
| local.identifier.alturi | http://dissertations.umi.com/hawii:12323 |
Files
Original bundle
1 - 1 of 1