Biology subjects

Semmens, B. X.

Publications and source records attributed to Semmens, B. X..

4 recordsLinked to original sources

bioRxiv2024

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

Feeding success and maternal effects on larval size have long been hypothesized as important contributors to interannual recruitment variability in marine fishes. This study examined the feeding ecology and influences of diet and size-at-birth on length and growth of larval rockfishes (Sebastes spp.). Prey carbon biomass and selection were calculated from gut contents, size-at-birth was estimated using otolith core size, and recent growth was derived from outer otolith increment widths. Biomass contributions of preferred prey and otolith data were integrated into Bayesian hierarchical models predicting length and growth. Larvae primarily fed on and selected for copepod nauplii and Calanoid copepodites, modulating feeding with ontogeny and in response to prey availability. Based on carbon weight, the relative contribution of Calanoid copepodites to the diet was more strongly and positively correlated with length and growth than that of nauplii. Younger larvae experienced faster growth in association with Calanoid copepodite consumption than older larvae. Positive effects of core radius suggest that initial larval size, believed to be mediated by maternal provisioning, increases the likelihood of survival, larger size and faster growth. These findings ultimately provide evidence that selective feeding and size-at-birth mediate rockfish survival in early life stages.

ecology↗

bioRxiv2023

Trophic Efficiency Facilitates Larval Shortbelly Rockfish (Sebastes jordani) Development

Identifying the factors influencing fish recruitment is critical for fishery management, and failure to do so can have major ecological and economic consequences. Many hypotheses over the past century have been proposed, and the recently postulated Trophic Efficiency in Early Life (TEEL) hypothesis argues that a shorter food chain length can result in more efficient energy transfer from primary producers to young fishes, thereby increasing growth rate and larval condition, reducing early-life mortality and ultimately leading to a stronger recruitment cohort. To test this hypothesis, we analyzed the trophic position (TP) through compound-specific isotopic analysis of amino acids, as well as otolith microstructure and stomach content of larval shortbelly rockfish (Sebastes jordani). Results show larval rockfish that ate lower TP prey were both heavier and faster growing. This suggests the trophic characteristics of early life diet are critical to larval survival, and provide evidence in support of the TEEL hypothesis.

ecology↗

bioRxiv2023

Recruitment limitation increases susceptibility to fishing-induced collapse in a spawning aggregation fishery

Aggregation-based fisheries are notorious for booms and busts driven by aggregation discovery and subsequent fishing-induced collapse. However, environment-driven sporadic recruitment in some since-protected populations has delayed recovery, suggesting recruitment-limitation may be a key driver of their population dynamics and fishery recovery potential. To glean insight into this dynamic, we focused on an overexploited temperate aggregate spawner (Barred Sand Bass; Paralabrax nebulifer) and leveraged a long-term mark-recapture data set spanning different oceanographic and harvest histories in a custom Bayesian capture-mark-reencounter modeling framework. We coupled this demographic analysis with long-term trends in sea surface temperature, harvest, adult and juvenile densities, and historical accounts in the literature. Our results point to a history of multidecadal windows of fishing opportunity and fishing-induced collapse that were largely driven by sporadic, warm water recruitment events, which may be externally sourced. Nevertheless, we found that environment-driven sporadic recruitment was not a factor impeding recovery following the last collapse, as recruitment remained elevated due to novel, anomalously warm conditions. Despite signs of incipient population recovery, spawning aggregations remain absent, indicating other potential factors (e.g., continued fishing during spawning season, residual Allee effects) have delayed fishery recovery to date. Aggregate spawner populations that are dependent on sporadic recruitment, especially those at their geographic margins, are thus highly susceptible to sudden and potentially extended periods of collapse, making them ill-suited to high CPUE fishing that occurs on spawning grounds. If the goal is to balance the protection of spawning aggregations with long-term fishery sustainability, then limiting aggregation-based fishing during spawning season may be the best insurance policy against collapse and recovery failure.

ecology↗

bioRxiv2023

Environment-driven trends in fish larval abundance predict fishery recruitment in two temperature reef congeners: mechanisms and implications for management

Environmental and biological processes acting on fish larvae can drive fishery cohort strength, but predictive ability oftentimes falls short, and larval abundance is generally considered more useful as a proxy for spawning biomass. Under a changing ocean, studies that relate environmental covariates, larval abundance, and fishery recruitment are worthy of continued research, especially in data-limited contexts. We focus on a popular, recreational-only, multispecies saltwater bass fishery (genus Paralabrax) whose population status and recovery potential are uncertain. We used 54 years of ichthyoplankton data (1963-2016) and a species distribution model to 1) deconstruct species-specific standardized indices of larval abundance, 2) test these indices as indicators of adult stock status or predictors of future fishery recruitment, and 3) evaluate spatiotemporal trends in their population dynamics relative to environmental variables. Contrary to expectation, species-specific larval abundance predicted future catch, with recent elevated larval abundance suggesting imminent fishery recovery. Additionally, we identified strong relationships with environmental variables, thereby providing additional tools for predicting fishery recruitment and anticipating population change. Our findings paint a path forward for improving estimates of current and future fishery status under changing natural and anthropogenic influences and the incorporation of ecosystem considerations into fishery management.

ecology↗