Award: OCE-1436545

The goals of the project were to investigate the effects of size-selective harvesting practices on the demography of sex-changing fishes, through a combination of: (1) large-scale field experiments manipulating the densities, size structure, and sex ratios of fishes to simulate the effects of different types (i.e., removal of large or small body sizes) and intensities of fishing mortality and (2) ecological modeling studies designed to compare and contrast the effects of fishing on single sex (i.e., gonochoristic) and sex-changing (i.e., protogyny or female to male sexual transition) reproductive strategies and the transient population dynamics that occur following the adoption of management strategies, like marine reserves, which prohibit fishing. Over three years, we conducted field experiments at Santa Catalina Island, CA, using two species of gobies (blackeye gobies, Rhinogobiops nicholsii, and bluebanded gobies, Lythrypnus dalli) as model organisms. We constructed an array of 69 patch reefs (2 x 2 m in size) out of natural rocks and cinderblocks in a large sandy bay, with reefs separated by 10 m, and covered each reef with predator exclusion cages. We then stocked the reefs with fish (tagged to indicate their size and sex) in a series of experiments separately testing how the type and instensity of size-selective harvesting or skewed sex ratios (holding density constant) will impact reproduction, growth, and sex change. Experiments testing the effects of size-selective harvesting on population demography found that size-selective removal of large individuals, as is common in many fisheries, caused a much larger reduction in reproductive output for our two sex-changing fish than different intensities of removal (i.e., reductions in population abundance). However, populations were able to compensate somewhat for the removal of large individuals as the remaining fishes grew significantly faster and changed sex from female to male at high rates when subjected to selective removal of large bodied individuals. These results will have important implications for fisheries management of sex-changing fishes. Surprisingly, sex change is a common reproductive strategy in many commercially important species (e.g., groupers, snappers, parrotfish, wrasses, etc.), but most models and stock assessment do not take it into account. In the experiments testing the effects of skewed sex ratios, we found that for both species total egg production, female per capita production, and the number of nests per reef were not affected by sex ratio. By contrast, male per capita production and the percentage of males guarding nets significantly increased as sex ratios became more female-biased. For blackeye gobies, growth rates were highest for individuals that completed sex change during the experimental period and the frequency of sex change was highest on reefs that were strongly female-biased. Both species defend demersal nests and are highly resilient to sex ratio skew, potentially because intrasexual competition between males (i.e., territory and mate monopolization) or females (i.e. competition for nest space) limit reproductive potential. To set expectations for the adaptive management of Marine Protected Areas (MPAs) we need models that predict shorter-term, transient population dynamics. We designed the first population dynamic models to address this question for a protogynous (female-first) sex-changing fish. In these populations, fishing prior to MPA implementation both reduces abundance and skews sex ratios, because fishing removes more males than females. The post-MPA trajectory then depends on how much fishing there had been, and how quickly the sex ratio returns to its unfished state. We used a two-sex age-structured model parameterized for a generic protogynous species to simulate a range of possible scenarios. We found that in general, protogynous species should recover faster than non-sex-changing (gonochore) species. However, late-maturing protogynous species that required higher male:female sex ratios for fertilization exhibited longer, more oscillatory recovery trajectories. Importantly, we found that changes in sex ratio inside MPAs were not indicative of population recovery. The project trained 9 graduate students from MLML who participated in the field experiments. Stephen Pang was the lead graduate student on the project and completed his Master's degree from MLML in May 2019, studying the effects of skewed sex ratios on reproduction in sex-changing fish. He also gave poster and oral presentations at the Western Society of Naturalists meeting in 2016 and 2017. 6 undergraduate students from CSU Monterey Bay served as research assistants for 3 months during each of the 3 summer field seasons. 5 of these students were part of the Undergraduate Research Opportunity Center (UROC) program and each student developed and conducted an independent research project, related to the broad goals of the experiments. Those projects resulted in 2 poster presentations at the Western Soecity of Naturalists meeting in 2016 and 2017. In addition, we had 3 NSF REU students participate through the University of Southern California REU program. Three of the participating undergradautes were subsequently accepted to Master's programs following their involvement in this project. We held outreach events for the public at Catalina Island. Last Modified: 05/31/2019 Submitted by: Scott Hamilton