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Fish species with high mortality during early life may maximize fitness using adaptive strategies to time hatching to match favorable environmental conditions (match/mismatch) or extending spawning/hatching to disperse risk (bet-hedging). We examined support for these strategies in a collapsed forage fish, capelin (Mallotus villosus), in coastal Newfoundland (2018–2021). Capelin shift from spawning at warm, intertidal to cool, subtidal (15–40 m) habitats in warmer years, with unknown recruitment consequences. We hypothesized that match/mismatch (specifically, Coastal Water Mass Replacement Hypothesis) would be supported if densities of recently hatched larvae showed pulses that overlapped with high prey and low predator densities. Generalized additive models revealed that larval densities increased with zooplankton prey biomass, but were not influenced by predator biomass or temperature, contrasting with pre-collapse studies and providing equivocal support for match/mismatch. Protracted larval emergence and previously documented high variability in larval traits supported a bet-hedging strategy. Larval condition (i.e. length, yolk-sac diameter) did not differ between habitats but varied among years, where the highest proportion of larvae in poor condition was from the intertidal site in the warmest year (2018). Findings suggest that spawning habitat shifts may have limited impact on stock recovery relative to year-specific environmental conditions that influence larval condition. [ABSTRACT FROM AUTHOR]

The 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. [ABSTRACT FROM AUTHOR]

Recruitment dynamics are challenging to assess or predict because of the many underlying drivers that vary in their relevance over time and space. Stock size, demographic and trait composition, condition and distribution of spawning fish and the spatio‐temporal dynamics of trophic and environmental interactions all influence recruitment processes. Exploring common patterns among stocks and linking them to potential drivers may therefore provide insights into key mechanisms of recruitment dynamics. Here, we analysed stock‐recruitment data of 64 stocks from the north‐east Atlantic Ocean for common trends in variation and synchrony among stocks using correlation, cluster and dynamic factor analyses. We tested common trends in recruitment success for relationships with large‐scale environmental processes as well as stock state indicators, and we explored links between recruitment success and demographic, environmental and ecological variables for a subset of individual stocks. The results revealed few statistically significant correlations between stocks but showed that underlying common trends in recruitment success are linked to environmental indices and management indicators. Statistical analyses confirmed previously suggested relationships of environmental–ecological factors such as the subpolar gyre and Norwegian coastal current with specific stocks, and indicated a large relevance of spawning stock biomass and demographics, as well as predation, whereas other suggested relationships were not supported by the data. Our study shows that despite persistent challenges in determining drivers of recruitment due to poor data quality and unclear mechanisms, combining different data analysis techniques can improve our understanding of recruitment dynamics in fish stocks. [ABSTRACT FROM AUTHOR]

Abstract: Gulf (Brevoortia patronus, Clupeidae) and Atlantic menhaden (Brevoortia tyrannus, Clupeidae) support large fisheries that have shown substantial variability over several decades, in part, due to dependence on annual recruitment. Nevertheless, traditional stock–recruitment relationships lack predictive power for these stocks. Current management of Atlantic menhaden explicitly treats recruitment as a random process. However, traditional methods for understanding recruitment variability carry the very specific hypothesis that the effect of adult biomass on subsequent recruitment occurs independently of other ecosystem factors such as food availability and predation. Here, we evaluate the predictability of menhaden recruitment using a model‐free approach that is not restricted by these strong assumptions. We find that menhaden recruitment is predictable, but only when allowing for interdependence of stock with other ecological factors. Moreover, while the analysis confirms the presence of environmental effects, the environment alone does not readily account for the complexity of menhaden recruitment dynamics. The findings set the stage for revisiting recruitment prediction in management and serve as an instructive example in the ongoing debate about how to best treat and understand recruitment variability across species and fisheries. [ABSTRACT FROM AUTHOR]

In fishes, the growth-mortality hypothesis has received broad acceptance as a driver of recruitment variability. Recruitment is likely to be lower in years when the risk of starvation and predation in the larval stage is greater, leading to higher mortality. Juvenile snapper, Pagrus auratus (Sparidae), experience high recruitment variation in Port Phillip Bay, Australia. Using a 5-year (2005, 2007, 2008, 2010, 2011) data set of larval and juvenile snapper abundances and their daily growth histories, based on otolith microstructure, we found selective mortality acted on larval size at 5 days post-hatch in 4 low and average recruitment years. The highest recruitment year (2005) was characterised by no size-selective mortality. Larval growth of the initial larval population was related to recruitment, but larval growth of the juveniles was not. Selective mortality may have obscured the relationship between larval traits of the juveniles and recruitment as fast-growing and large larvae preferentially survived in lower recruitment years and fast growth was ubiquitous in high recruitment years. An index of daily mortality within and among 3 years (2007, 2008, 2010), where zooplankton were concurrently sampled with ichthyoplankton, was related to per capita availability of preferred larval prey, providing support for the match-mismatch hypothesis. In 2010, periods of low daily mortality resulted in no selective mortality. Thus both intra- and inter-annual variability in the magnitude and occurrence of selective mortality in species with complex life cycles can obscure relationships between larval traits and population replenishment, leading to underestimation of their importance in recruitment studies. [ABSTRACT FROM AUTHOR]