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

许多海洋鱼类在其一生中会改变性别，其中许多是商业和休闲捕鱼的目标。这些动物性别变化的时间通常与体型有关，因此种群通常由许多初始性别的小鱼（通常是雌性）和少数其他性别的大鱼（通常是雄性）组成。在自然界中，较小的鱼由于被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，使足够多的体型较大的个体消失，从而阻碍繁殖。然而，尺寸选择性死亡对变性鱼类的影响程度尚不清楚。本研究将利用一套综合的野外实验和数学模型来探讨大小选择性死亡率对性别变化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。研究结果将提高我们对变性生物对不同类型的尺寸选择性死亡的敏感性和恢复力的认识，并将揭示变性物种在尺寸选择停止后如何恢复，比如在突然禁止捕鱼的海洋保护区内的种群。这些发现将为渔业管理政策提供信息，目前在制定渔业法规时没有考虑到一个物种改变性别的能力。该项目将为来自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发布以及通过公开的建模练习与渔业管理人员进行交流。该项目将包括一项为期三年的研究，研究大小不同的死亡率对变性鱼类的影响。实地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，可以在实地操作和直接测量生殖产量。该物种包括一个原生雌雄同体（在收获的物种中常见的一种从雌性到雄性的性别变化模式）和两个同时发生的雌雄同体，它们在雄性和雌性之间转换的能力不同。在加州圣卡塔利娜岛的复制斑状珊瑚礁上建立的种群将进行两种类型的实验：(1)操纵性别比例，以确定雄性的稀缺何时限制了种群水平的生殖产出；(2)将死亡率强度与大小选择的形式（即，大个体或小个体的死亡率更高）交叉分解的实验将检验大小选择死亡率的人口统计学后果。结合实地实验，将开发规模和性别结构的种群模型（积分投影模型），用于以下三方面：(1)评估不同类型的选择性死亡率如何影响种群动态；(2)预测野外试验结果，测试/验证模型，并允许直接预测短期选择的生态意义；(3)与现有的第四种鱼类的调查数据相吻合，这是一种在海洋保护区内外被广泛捕捞的变性鱼。第(3)部分将评估该物种的交配系统和繁殖产出（在野外无法直接测量）是否以及以多快的速度在保护区内恢复。这套综合的野外实验和模型将对大小选择性死亡率对性别变化海洋物种种群动态的影响产生新的见解。

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.