Dear Colleagues, On behalf of my co-authors, I am pleased to announce the publication of the following article in Ecology and Evolution: Schleimer A, Ramp C, Delarue J, Carpentier A, Bérubé M, Palsbøll PJ, Sears R, Hammond PS (2019) Decline in abundance and apparent survival rates of fin whales (Balaenoptera physalus) in the northern Gulf of St. Lawrence. Ecol Evol:ece3.5055 This mark-recapture study includes a critical assessment of the assumption of capture homogeneity in relation to divergent site fidelity patterns and the effects of terminal bias on long time-series of survival estimates. Abstract: 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 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 noncalf apparent survival rates with a sharp decline in the last 5 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 analysis was employed to categorize 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. The open-access paper is available online at: https://onlinelibrary.wiley.com/doi/10.1002/ece3.5055 Alternatively, you can contact me (achs@st-andrews.ac.uk) for PDF requests or comments. best wishes, Anna Schleimer PhD student University of St Andrews | University of Groningen