Momma's larvae: Maternal oceanographic experience and larval size influence early survival of rockfishes

Abstract

Identifying factors that affect larval mortality is critical for understanding the drivers of fish population dynamics. Although larval fish mortality is high, small changes in mortality rates can lead to large changes in recruitment. Recent studies suggest maternal provisioning can dramatically affect the susceptibility of larvae to starvation and predation, the major sources of early‐life mortality. We measured otolith core width‐at‐extrusion and validated that this is a proxy for larval size‐at‐extrusion for eight species of rockfishes (genus Sebastes) to examine the influence of initial larval size on larval growth and survival and to understand how oceanographic conditions experienced by gestating females affect larval size (i.e., quality). Otolith core width‐at‐extrusion was significantly positively related to larval rockfish recent growth rate (5/7 species with sufficient sample size) and survival (all eight species). This suggests that individuals that are larger at extrusion generally grow faster and are more likely to survive early life stages. Otolith core width‐at‐extrusion was positively related to higher presence of Pacific Subarctic Upper Water and was negatively related to warmer, saline waters at the depths gestating mothers inhabited during the months prior to larval collection. In addition, otolith core width was larger further from fishing ports, possibly because these locations were historically less fished, contained more older, larger females, and/or had inherently better habitat quality (higher Pacific Subarctic Upper Water) than sites closer to shore. These results indicate that the environmental conditions female rockfish experience during gestation drive the size of the larvae they produce and impact larval growth and survival.

Diet and Size-at-Birth Affect Larval Rockfish Condition and Survival

“…Thus, improving knowledge of how larval feeding influences growth in wild fishes at multiple life stages is essential for gaining a more mechanistic understanding of the ecological drivers of the "critical period" hypothesized over a century ago (Hjort 1914). In similar fashion, while maternal investment has emerged as a common driver of variation in size-at-birth and size-at-age in larval fishes as diverse as sardine, anchovy and rockfish (Garrido et al 2015, Fennie et al 2023, Robidas et al 2022, studies investigating the joint effects of in situ size-at-birth and feeding ecology on larval ontogeny and condition are, to the best of our knowledge, non-existent. In this study, larval rockfishes shifted diet and selection towards specific prey taxa with ontogeny and exhibited active selection in response to prey availability in the surrounding environment.…”

“…The positive correlations between otolith core size (a proxy for larval size-at-hatch/birth; Garrido et al 2015, Fennie et al 2023, and age, length and recent growth suggest that size-atbirth increases survivorship, as individuals born larger are more likely to survive to older ages, reach larger sizes, and grow faster. These results are consistent with trends observed in recent studies, in which core size was positively correlated with age, size, and condition in fishes with very different adult life history traits (European Sardine - Garrido et al 2015, rockfishes -Fennie et al 2023, Northern Anchovy -Robidas et al 2022.…”

“…Maternal provisioning is another factor believed to affect recruitment success, with observed positive effects on larval size-at-birth, endogenous energy stores, body condition and survival (Hislop 1988, Chambers & Leggett 1996, Berkeley et al 2004, Fennie et al 2023.…”

“…Otolith core size (aka nuclear width, hatch check diameter) has been correlated with size-at-birth and early life survival in multiple species (Meekan & Fortier, 1996, Garrido et al 2015, Fennie et al 2023, and this metric has been recently proposed to be a robust indicator of maternal provisioning. Through this, we can use otolith core size to assess the effects of size-at-birth on larval condition and performance.…”

“…First, Schroeder et al (2019) found that recruitment for multiple rockfish species correlated with the exposure of adults to cold, high oxygen, high nutrient, low salinity Pacific subarctic water (California Current water) in the months prior to recruitment. Second, Fennie et al (2023) demonstrated that females spawn larger larvae when bathed in Pacific subarctic water during gestation and that larvae born larger were more likely to survive the first few weeks of life. We build on these findings to evaluate the combined role of size-at-birth and larval prey on growth and condition.…”