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Early life survival is critical to successful replenishment of fish populations, and hypotheses developed under the Growth-Survival Paradigm (GSP) have guided investigations of controlling processes. The GSP postulates that recruitment depends on growth and mortality rates during early life stages, as well as their duration, after which the mortality declines substantially. The GSP predicts a shift in the frequency distribution of growth histories with age towards faster growth rates relative to the initial population because slow-growing individuals are subject to high mortality (via starvation and predation). However, mortality data compiled from 387 cases published in 153 studies (1971–2022) showed that the GSP was only supported in 56% of cases. Selection against slow growth occurred in two-thirds of field studies, leaving a non-negligible fraction of cases showing either an absence of or inverse growth-selective survival, suggesting the growth-survival relationship is more complex than currently considered within the GSP framework. Stochastic simulations allowed us to assess the influence of key intrinsic and extrinsic factors on the characteristics of surviving larvae and identify knowledge gaps on the drivers of variability in growth-selective survival. We suggest caution when interpreting patterns of growth selection because changes in variance and autocorrelation of individual growth rates among cohorts can invalidate fundamental GSP assumptions. We argue that breakthroughs in recruitment research require a comprehensive, population-specific characterization of the role of predation and intrinsic factors in driving variability in the distribution and autocorrelation of larval growth rates, and of the life stage corresponding to the endpoint of pre-recruited life.

Early life survival is critical to successful replenishment of fish populations, and hypotheses developed under the Growth-Survival Paradigm (GSP) have guided investigations of controlling processes. The GSP postulates that recruitment depends on growth and mortality rates during early life stages, as well as their duration, after which the mortality declines substantially. The GSP predicts a shift in the frequency distribution of growth histories with age towards faster growth rates relative to the initial population because slow-growing individuals are subject to high mortality (via starvation and predation). However, mortality data compiled from 387 cases published in 153 studies (1971–2022) showed that the GSP was only supported in 56% of cases. Selection against slow growth occurred in two-thirds of field studies, leaving a non-negligible fraction of cases showing either an absence of or inverse growth-selective survival, suggesting the growth-survival relationship is more complex than currently considered within the GSP framework. Stochastic simulations allowed us to assess the influence of key intrinsic and extrinsic factors on the characteristics of surviving larvae and identify knowledge gaps on the drivers of variability in growth-selective survival. We suggest caution when interpreting patterns of growth selection because changes in variance and autocorrelation of individual growth rates among cohorts can invalidate fundamental GSP assumptions. We argue that breakthroughs in recruitment research require a comprehensive, population-specific characterization of the role of predation and intrinsic factors in driving variability in the distribution and autocorrelation of larval growth rates, and of the life stage corresponding to the endpoint of pre-recruited life. -- Keywords : critical period ; growth-mortality ; individual characteristics ; larval physiology ; predation ; recruitment endpoint.

During the spring in the coastal waters of Hakodate Bay the shrimp Crangon uritai is the predominant predator on larval and juvenile marbled sole, Pleuronectes yokohamae. To investigate the prey preferences of C. uritai, P. yokohamae and two other prey species, a mysid Nipponomysis sp. and a gammarid Haustorioides japonicus, were used for predation experiments. Among the three prey organisms studied, Nipponomysis sp. was preyed on first, followed by P. yokohamae, and finally H. japonicus. Prey profitability did not differ between P. yokohamae and Nipponomysis sp., though H. japonicus was less profitable. Nipponomysis sp. was larger, more perceptible, and slower to escape than P. yokohamae. A relatively high abundance of mysid Nipponomysis sp. could restrict and reduce predation on P. yokohamae by C. uritai. Gammarid H japonicus was able to escape relatively more easily, because its harder and slippery skin required more handling time than the other prey, possibly making it an undesirable food source for C. uritai. High perceptibility and low escape ability may be the most important factors affecting prey choice of C. uritai.

To examine predation on larval and juvenile Pleuronectes yokohamae by Crangon uritai, the spatial distribution and feeding habits of C. uritai were studied. Crangon uritai fed on various prey, including P. yokohamae. Density-dependent predation on juvenile Crangon spp., larval and juvenile gobiid fish Chaenogobius heptacanthus, mysids, and gammarids was observed. The abundance of alternative prey might, therefore, play an important role in reducing the pressure of predation on P. yokohamae. In each year, C. uritai migrated from depths of 10 m in March to depths of 3 m in May. There was a significant negative correlation between the weighted mean depth (WMD) of C. uritai and the weighted mean bottom water temperature (WMBWT). The migration was, therefore, delayed in the cold spring, during which C. uritai occupied depths of approximately 10 m. In contrast, no significant correlation was found between the WMD of P. yokohamae and WMBWT. Settlement of P. yokohamae began at depths of 15 m, mainly during early April. The spatial distributions of these two organisms show greater overlap during the cold spring, resulting in increased opportunities for predation.