Hewitt Daniel E, Johnson Daniel D, Suthers Iain M, Taylor Matthew D
Fisheries and Marine Environmental Research Lab, Centre for Marine Science and Innovation, School of Biological, Earth and Environmental Science, University of New South Wales, NSW, Sydney, 2052, Australia.
New South Wales Department of Primary Industries, Port Stephens Fisheries Institute, NSW, Locked Bag 1, Nelson Bay, 2315, Australia.
Mov Ecol. 2023 Apr 17;11(1):21. doi: 10.1186/s40462-023-00384-3.
Effective fisheries management of mobile species relies on robust knowledge of animal behaviour and habitat-use. Indices of behaviour can be useful for interpreting catch-per-unit-effort data which acts as a proxy for relative abundance. Information about habitat-use can inform stocking release strategies or the design of marine protected areas. The Giant Mud Crab (Scylla serrata; Family: Portunidae) is a swimming estuarine crab that supports significant fisheries harvest throughout the Indo-West Pacific, but little is known about the fine-scale movement and behaviour of this species.
We tagged 18 adult Giant Mud Crab with accelerometer-equipped acoustic tags to track their fine-scale movement using a hyperbolic positioning system, alongside high temporal resolution environmental data (e.g., water temperature), in a temperate south-east Australian estuary. A hidden Markov model was used to classify movement (i.e., step length, turning angle) and acceleration data into discrete behaviours, while also considering the possibility of individual variation in behavioural dynamics. We then investigated the influence of environmental covariates on these behaviours based on previously published observations.
We fitted a model with two well-distinguished behavioural states describing periods of inactivity and foraging, and found no evidence of individual variation in behavioural dynamics. Inactive periods were most common (79% of time), and foraging was most likely during low, incoming tides; while inactivity was more likely as the high tide receded. Model selection removed time (hour) of day and water temperature (°C) as covariates, suggesting that they do not influence Giant Mud Crab behavioural dynamics at the temporal scale investigated.
Our study is the first to quantitatively link fine-scale movement and behaviour of Giant Mud Crab to environmental variation. Our results suggest Giant Mud Crab are a predominantly sessile species, and support their status as an opportunistic scavenger. We demonstrate a relationship between the tidal cycle and foraging that is likely to minimize predation risk while maximizing energetic efficiency. These results may explain why tidal covariates influence catch rates in swimming crabs, and provide a foundation for standardisation and interpretation of catch-per-unit-effort data-a commonly used metric in fisheries science.
对洄游物种进行有效的渔业管理依赖于对动物行为和栖息地利用的深入了解。行为指标有助于解读单位努力捕捞量数据，该数据可作为相对丰度的替代指标。有关栖息地利用的信息可为放流策略或海洋保护区的设计提供参考。巨大泥蟹（锯缘青蟹；梭子蟹科）是一种生活在河口的洄游性蟹类，在印度 - 西太平洋地区支撑着重要的渔业捕捞，但对该物种的精细尺度移动和行为了解甚少。
我们在澳大利亚东南部一个温带河口，给18只成年巨大泥蟹佩戴了配备加速度计的声学标签，利用双曲线定位系统追踪它们的精细尺度移动，同时获取高时间分辨率的环境数据（如水温）。使用隐马尔可夫模型将移动（即步长、转弯角度）和加速度数据分类为离散行为，同时考虑行为动态中个体差异的可能性。然后，我们根据先前发表的观测结果，研究环境协变量对这些行为的影响。
我们拟合了一个具有两个明显行为状态的模型，分别描述不活动期和觅食期，未发现行为动态存在个体差异的证据。不活动期最为常见（占时间的79%），觅食最有可能发生在低潮涨潮时；而随着高潮退去，不活动的可能性更大。模型选择排除了一天中的时间（小时）和水温（摄氏度）作为协变量，表明在所研究的时间尺度上，它们不会影响巨大泥蟹的行为动态。
我们的研究首次定量地将巨大泥蟹的精细尺度移动和行为与环境变化联系起来。我们的结果表明，巨大泥蟹主要是固着性物种，并支持它们作为机会主义清道夫的地位。我们证明了潮汐周期与觅食之间的关系，这种关系可能会在将捕食风险降至最低的同时，将能量效率最大化。这些结果可能解释了为什么潮汐协变量会影响游泳蟹的捕捞率，并为单位努力捕捞量数据（渔业科学中常用的指标）的标准化和解读提供了基础。
