Density‐ and size‐dependent mortality in fish early life stages

Leif Christian Stige,Lauren A Rogers,Joël M Durant,Geir Ottersen,Mary E Hunsicker,Øystein Langangen,Anna B Neuheimer,Lorenzo Ciannelli,Natalia A Yaragina

doi:10.1111/faf.12391

Abstract

AbstractThe importance of survival and growth variations early in life for population dynamics depends on the degrees of compensatory density dependence and size dependence in survival at later life stages. Quantifying density‐ and size‐dependent mortality at different juvenile stages is therefore important to understand and potentially predict the recruitment to the population. We applied a statistical state‐space modelling approach to analyse time series of abundance and mean body size of larval and juvenile fish. The focus was to identify the importance of abundance and body size for growth and survival through successive larval and juvenile age intervals, and to quantify how the dynamics propagate through the early life to influence recruitment. We thus identified both relevant ages and mechanisms (i.e. density dependence and size dependence in survival and growth) linking recruitment variability to early life dynamics. The analysis was conducted on six economically and ecologically important fish populations from cold temperate and sub‐arctic marine ecosystems. Our results underscore the importance of size for survival early in life. The comparative analysis suggests that size‐dependent mortality and density‐dependent growth frequently occur at a transition from pelagic to demersal habitats, which may be linked to competition for suitable habitat. The generality of this hypothesis warrants testing in future research.

Highlights

Understanding how processes early in life influence year‐class strength has been a central topic of fisheries research for more than a century
Consistent with the correlation analysis, we found no evidence for effects of length on subsequent abundance for Barents Sea (BS) capelin (Figure 4d, Table S9)
We found no evidence for size effects on abundance; this con‐ clusion did not change if the sparse age‐0 data were omitted from the model, and associations between larval abundance and length and age‐1 abundance were assessed directly

Summary

| INTRODUCTION

Understanding how processes early in life influence year‐class strength has been a central topic of fisheries research for more than a century. Quantifying associations be‐ tween changes in abundance and body size distribution through early life is an important step to explain, and potentially predict, fish recruitment. Such quantification may reveal intercon‐ nections between growth, survival and population regulation, and, thereby the relevance of growth and survival variations at different early life stages for recruitment. Quantifying at which life stage density dependence occurs is important, for example, to assess population conse‐ quences of environmental influences on abundances of fish eggs and larvae, as such environmental effects tend to be dampened if

| METHODS

| DISCUSSION

| CONCLUSIONS