Recent advances in statistical methodology applied to the Hjort liver index time series (1859-2012) and associated influential factors

2026-05-13

AI Summary

This study addresses the accurate modeling of the Hjort liver index time series for Northeast Arctic cod from 1859 to 2012 and investigates its dynamic relationships with environmental and biological covariates, including Kola Peninsula winter temperature, length distribution, mortality, and food availability. To this end, the research innovatively integrates advanced statistical methodologies—such as focused model selection, dynamic goodness-of-fit testing, change-point detection, quantification of predictive uncertainty, and confidence-distribution-based synthesis of multi-source information. The findings elucidate long-term shifts in energy allocation strategies of cod, demonstrate the applicability of novel statistical tools in marine biology, and provide a robust scientific foundation for the sustainable management of fishery resources.

Abstract

Certain recent advances in statistical methodology have promising potential for fruitful use in general biology and the fisheries sciences. This paper reviews and discusses some of the relevant themes, including accurate modelling via focused model selection techniques, dynamic goodness-of-fit testing of processes evolving over time, finding break points for phenomena experiencing changes, prediction uncertainty, and optimal combination of information across diverse sources via confidence distributions. The methods are illustrated for the Hjort liver quality index time series. Its roots lie in the classic Hjort (`Fluctuations in the Great Fisheries of Northern Europe, Viewed in the Light of Biological Research', 1914), where liver quality of the Atlantic cod {\it (Gadus morhua)} for 1880--1912 is reported on and studied, along with related factors, making it one of the first teleost time series ever published. Diligent work by Kjesbu et al. (`Making use of Johan Hjort's `unknown' legacy: reconstruction of a 150-year coastal time-series on northeast Arctic cod (Gadus morhua) liver data reveals long-term trends in energy allocation patterns', 2014), involving both archival and calibration efforts, have extended the series both backwards and forwards in time, to 1859--2012, yielding one of the longest time series of marine science. Our study offers a detailed examination of this series and how it relates to and interacts with associated factors, including Kola winter temperatures, length distribution parameters, cod mortality, and a certain index related to availability of food.

Problem

• time series
• liver quality index
• Atlantic cod
• environmental factors
• long-term trends

Innovation

• focused model selection
• dynamic goodness-of-fit testing
• change-point detection
• prediction uncertainty
• confidence distributions