Collaborative Research: RUI: Impacts of size-selective mortality on sex-changing fishes

许多海洋鱼类物种在一生中改变性别，其中许多是商业和休闲捕鱼的目标。这些动物变性的时机通常与身体大小有关，因此种群通常由许多初始性别的小鱼(通常是雌性)和很少的其他性别的大型鱼(通常是雄性)组成。在自然界中，较小的鱼因捕食而死亡的风险更大，但渔民倾向于寻找较大的鱼。因此，以体型较大的个体为目标的捕捞可能会扭曲性别比例，移除足够多的体型较大的性别以阻碍生殖。然而，大小选择性死亡对变性鱼的影响程度却知之甚少。这项研究将利用一套完整的野外实验和数学模型来探索大小选择性死亡对变性物种种群动态的影响。它将首次对不同的性别变化模式和生殖策略对选择性死亡的敏感性进行实验探索。这一结果将增进我们对不同类型的大小选择死亡的易感性和弹性的了解，并将揭示性别变化物种在大小选择停止后如何恢复，例如在突然禁止捕鱼的海洋保护区内的种群中。这些发现将为渔业管理政策提供参考，这些政策目前在制定渔业法规时没有考虑物种改变性别的能力。该项目将为加州州立大学北岭分校、莫斯·兰丁海洋实验室和北卡罗来纳大学威尔明顿分校的三名研究生和多名本科生提供专业培训和研究支持。研究结果将通过国家和国际科学会议、在机构网站和社交媒体上张贴以及通过公开可用的建模活动与渔业管理者交流。该项目将包括一项为期三年的关于特定大小死亡率对变性鱼的影响的研究。野外实验将使用三种关系密切的岩礁鱼，它们的性别变化模式不同，可以进行野外操作和直接测量繁殖产量。这些物种包括一个雌雄同体的雌雄同体(在收获的物种中常见的雌雄同体的性别转换模式)和两个同时存在的雌雄同体，它们在转换雄性和雌性的能力上存在差异。将在加利福尼亚州圣卡塔利纳岛的复制斑块珊瑚礁上建立的种群上进行两种类型的实验：(1)性别比率将被操纵，以确定何时雄性稀缺限制了种群水平的生殖产出；(2)将死亡强度与大小选择形式(即大小个体的更高死亡率)进行交叉因子分析的实验将测试大小选择死亡的人口统计学后果。与实地试验相结合，将开发按大小和性别结构的种群模型(综合预测模型)，用于三个方面：(1)评估不同类型的选择性死亡应如何影响种群动态；(2)预测实地试验的结果，对模型进行检验/验证，并能够直接预测短期选择的生态意义；(3)与海洋保护区内外的第四种鱼类--一种广泛捕捞的变性鱼类--的现有调查数据相适应。第(3)部分将评估该物种的交配系统和繁殖产量(无法在野外直接测量)是否在保护区内恢复以及恢复的速度有多快。这套综合的野外实验和模型将为大小选择性死亡对性别变化海洋物种种群动态的影响提供新的见解。

Many marine fish species change sex during their lifetimes, and many of them are targets of commercial and recreational fishing. The timing of sex change in these animals is often related to body size, so populations typically consist of many small fish of the initial sex (usually female) and few large fish of the other sex (usually male). In nature, smaller fish are at a greater risk of mortality due to predation, but fishermen tend to seek larger fish. Thus fishing that targets larger individuals may skew sex ratios, removing enough of the larger sex to hinder reproduction. However, the extent to which size-selective mortality affects sex-changing fishes is poorly understood. This research will explore the effects of size-selective mortality on the population dynamics of sex-changing species using an integrated set of field experiments and mathematical models. It will provide the first experimental exploration of the sensitivity of different sex-change patterns and reproductive strategies to selective mortality. The results will advance our knowledge of the susceptibility and resilience of sex-changing organisms to different types of size-selective mortality and will reveal how sex-changing species can recover after size-selection ceases, as in populations within marine reserves where fishing is suddenly prohibited. The findings will inform fisheries management policies, which do not currently consider the ability of a species to change sex in setting fisheries regulations. The project will provide professional training and research support for three graduate students and multiple undergraduates from California State University Northridge, Moss Landing Marine Laboratories, and University of North Carolina Wilmington. The research findings will be communicated with fisheries managers, via national and international scientific meetings, posted on institutional websites and social media, and through publicly available modeling exercises.This project will consist of a three-year study of the effects of size-specific mortality on sex-changing fishes. Field experiments will use three closely related rocky-reef fishes that differ in sex-change pattern and are amenable to field manipulation and direct measurement of reproductive output. The species include a protogynous hermaphrodite (a female-to-male sex-change pattern common among harvested species) and two simultaneous hermaphrodites that differ in their ability to switch between male and female. Two types of experiments will be conducted on populations established on replicate patch reefs at Santa Catalina Island, California: (1) sex ratios will be manipulated to determine when the scarcity of males limits population-level reproductive output; and (2) experiments cross-factoring the intensity of mortality with the form of size-selection (i.e., higher mortality of large or small individuals) will test the demographic consequences of size-selective mortality. In concert with the field experiments, size- and sex-structured population models (integral projection models) will be developed for use in three ways: (1) to evaluate how different types of selective mortality should affect population dynamics; (2) to predict outcomes of the field experiments, testing/validating the model and allowing direct prediction of the ecological significance of short-term selection; and (3) to fit to existing survey data for a fourth species, a widely fished, sex-changing fish, inside and outside of marine reserves. Part (3) will evaluate whether and how quickly the mating system and reproductive output of that species (not directly measurable in the field) is recovering inside reserves. This integrated set of field experiments and models will yield novel insight into the effects of size-selective mortality on the population dynamics of sex-changing marine species.