R_Code_Submission.Rmd from Field assessments of heart rate dynamics during spawning migration of wild and hatchery-reared Chinook salmon

During spawning, adult Pacific salmonids (Oncorhynchus spp.) complete challenging upriver migrations during which energy and oxygen delivery must be partitioned into activities such as locomotion, maturation and spawning behaviours under the constraints of an individual's cardiac capacity. To advance our understanding of cardiac function in free-swimming fishes, we implanted migrating adult Chinook salmon (Oncorhynchus tshawytscha) collected near the mouth of the Sydenham River, Ontario, with heart rate (fH) biologgers that recorded fH every 3 min until these semelparous fish expired on spawning grounds several days later. Fundamental aspects of cardiac function were quantified, including resting, routine and maximum fH, as well as scope for fH (maximum−resting fH). Predictors of fH were explored using generalized least-squares regression, including water temperature, discharge, fish size and fish origin (wild versus hatchery). Heart rate was positively correlated with water temperature, which aligned closely with daily and seasonal shifts. Wild fish had slower resting heart rates than hatchery fish, which led to significantly higher scope for fH. Our findings suggest that wild salmon may have better cardiac capacity during migration than hatchery fish, potentially promoting migration success in wild fish.This article is part of the theme issue ‘Measuring physiology in free living animals (Part I)’.在产卵期间，成年太平洋鲑属鱼类（Oncorhynchus spp.）需要完成极具挑战的溯河洄游旅程。在此过程中，在个体心脏功能容量的约束下，机体必须将能量与氧气分配至运动、性腺成熟以及产卵行为等各项生命活动中。为深化我们对自由游动鱼类心脏功能的认知，本研究对在加拿大安大略省赛登汉河河口附近捕获的洄游成年奇努克鲑（Oncorhynchus tshawytscha）植入了心率（fH）生物记录仪，该设备每3分钟记录一次心率数据，直至这些终生一胎型鱼类在数日后的产卵场死亡。本研究对心脏功能的多项核心指标进行了量化分析，包括静息心率、日常心率与最大心率，以及心率储备（最大心率−静息心率）。研究采用广义最小二乘回归分析，探究了影响心率的各项预测因子，包括水温、径流量、鱼类体型以及鱼类来源（野生与人工养殖）。心率与水温呈显著正相关，这一结果与每日及季节性的水温变化趋势高度吻合。野生鲑鱼的静息心率低于人工养殖个体，这使得野生个体拥有更高的心率储备。本研究结果表明，洄游过程中野生鲑鱼的心脏功能容量优于人工养殖个体，这或有助于提升野生鲑鱼的洄游成功率。本文隶属于“自由生活动物的生理测量（第一部分）”专题专栏。