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，其中许多是商业和娱乐捕鱼的目标。这些动物的性别变化的时间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，较小的鱼类由于捕食而面临更大的死亡风险，但渔民倾向于寻找较大的鱼类。因此，以较大个体为目标的捕捞可能会扭曲性别比例，消除足够的较大性别以阻碍繁殖。然而，在多大程度上大小选择性死亡率影响性别变化的鱼类知之甚少。本研究将探讨大小选择性死亡率对性别转换物种种群动态的影响，使用一套完整的现场实验和数学模型。它将提供第一个实验探索不同的性别变化模式和生殖策略的选择性死亡率的敏感性。这些结果将推进我们对性别改变生物对不同类型的大小选择性死亡率的敏感性和弹性的认识，并将揭示性别改变物种在大小选择停止后如何恢复，就像海洋保护区内突然禁止捕鱼的种群一样。这些发现将为渔业管理政策提供信息，目前渔业管理政策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州威尔明顿大学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、机构网站和社交媒体以及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，研究特定大小死亡率对变性鱼类的影响。野外实验将使用三个密切相关的岩石礁鱼类，不同的性别变化模式，适合现场操作和直接测量的生殖输出。这些物种包括一个先雌后雄的雌雄同体（一种在收获物种中常见的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。在加州的圣卡塔利纳岛，将对建立在复制的斑块珊瑚礁上的种群进行两种类型的实验：（1）操纵性别比例，以确定何时雄性的稀缺限制种群水平的生殖输出;和（2）实验交叉因子的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）将检验大小选择性死亡率的人口后果。 与田间试验相一致，大小和性别结构的种群模型（积分投影模型）将被开发用于三个方面：（1）评估不同类型的选择性死亡率如何影响种群动态;（2）预测田间试验的结果，测试/验证模型，并允许直接预测短期选择的生态意义;及（3）与第四种鱼类的现有调查数据相符，第四种鱼类是在海洋保护区内外广泛捕捞的变性鱼类。第（3）部分将评估该物种的交配系统和繁殖输出（在野外无法直接测量）是否以及如何快速恢复。这套综合的现场实验和模型将产生新的见解大小选择性死亡率的影响，性别变化的海洋物种的种群动态。

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.