Data from: Decline in abundance and apparent survival rates of fin whales (Balaenoptera physalus) in the northern Gulf of St. Lawrence

Estimates of abundance and survivorship provide quantifiable measures to monitor populations and to define and understand their conservation status. This study investigated changes in abundance and survival rates of fin whales (Balaenoptera physalus) in the northern Gulf of St. Lawrence (GSL) in the context of anthropogenic pressures and changing environmental conditions. A long-term data set, consisting of 35 years of photo-identification surveys and comprising more than 5,000 identifications of 507 individuals, formed the basis of this mark-recapture study. Based on model selection using corrected Akaike Information Criterion, the most parsimonious Cormack-Jolly-Seber model included a linear temporal trend in non-calf apparent survival rates with a sharp decline in the last five years of the study and a median survival rate of 0.946 (95% confidence interval (CI) 0.910-0.967). To account for capture heterogeneity due to divergent patterns of site fidelity, agglomerative hierarchical cluster (AHC) analysis was employed to categorise individuals based on their annual and survey site fidelity indices. However, the negative trend in survivorship remained and was corroborated by a significant decline in the estimated super-population size from 335 (95% CI 321-348) individuals in 2004-2010 to 291 (95% CI 270-312) individuals in 2010-2016. Concurrently, a negative trend was estimated in recruitment to the population, supported by a sharp decrease in the number of observed calves. Ship strikes and changes in prey availability are potential drivers of the observed decline in fin whale abundance. The combination of clustering methods with mark-recapture represents a flexible way to investigate the effects of site fidelity on demographic variables and is broadly applicable to other individual-based studies.种群丰度与存活率的估算可为种群监测、明确并理解其保护现状提供可量化的评估指标。本研究在人为压力与环境条件变化的背景下，对圣劳伦斯湾北部（Gulf of St. Lawrence, GSL）长须鲸（Balaenoptera physalus）的丰度与存活率变化展开了调查。本项标记重捕研究的基础数据集源自一项为期35年的照片识别调查，该调查共完成了507头个体的5000余次识别记录。基于校正赤池信息准则（corrected Akaike Information Criterion）的模型选择结果显示，最优简约Cormack-Jolly-Seber模型纳入了非幼鲸表观存活率的线性时间趋势：研究周期的最后五年间该存活率出现显著下降，其存活率中位数为0.946（95%置信区间（CI）为0.910~0.967）。为修正由栖息地保真度模式差异导致的捕获异质性，本研究采用聚集层次聚类（agglomerative hierarchical cluster, AHC）分析，基于个体的年度与调查栖息地保真度指数对其进行分类。但存活率的负向趋势依然存在，且通过超种群规模的显著下降得到了佐证：估算得到的超种群规模从2004~2010年的335头（95%置信区间（CI）为321~348）降至2010~2016年的291头（95%置信区间（CI）为270~312）。与此同时，种群补充量呈现负向趋势，该结果得到了观测到的幼鲸数量骤降的支持。船舶撞击事件与猎物可获得性变化，是观测到的长须鲸丰度下降的潜在驱动因素。聚类方法与标记重捕法的结合，为探究栖息地保真度对种群动态变量的影响提供了灵活的研究路径，且可广泛推广应用于其他基于个体的研究中。