Disentangling density‐dependent effects on egg production and survival from egg to recruitment in fish

Abstract

Understanding of density‐dependent effects is key to achieving sustainable management of self‐regulating biological resources such as fish stocks. Traditionally, density‐dependent effects on population abundance in fish have been considered to occur from hatching to recruitment, based on the paradigm of proportionality between spawning stock biomass and total egg production. Here, we demonstrate how the existence of intraspecific and interspecific density dependence in egg production changes the current understanding of density‐dependent processes in the life history of fish, by disentangling density‐dependent effects on egg production and survival from egg to recruitment, using sardine (Sardinops melanostictus, Clupeidae) and anchovy (Engraulis japonicus, Engraulidae) as model species. For sardine, strong intraspecific density‐dependent effects occurred in egg production, but no density‐dependent effects occurred or if any they were weak enough to be masked by environmental factors from hatching to recruitment. In contrast, for anchovy, interspecific density‐dependent effects occurred in egg production. In the survival after hatching, anchovy experienced stronger intraspecific density‐dependent effects than currently recognized. This analysis could overturn the current understanding of density‐dependent effects in the life history, highlighting contrasts between the effects on individual quality and population abundance and between the model species. We propose to reconsider the basis of fisheries management and recruitment studies based on the revised understanding of density‐dependent effects in the life history of the respective species.

A fine-scale multi-step approach to understand fish recruitment variability

“…This supports the role of fish population demographics as a buffer to recruitment, as already demonstrated for several fish stocks 56 . Further work, however, will be needed to better understand and quantify the effect of age structure versus density-dependant processes on spawning behaviour 57 . Note that the absence of an effect of female body condition on egg numbers was unexpected and might be a statistical artefact or result in part from the consideration of total egg production per unit of biomass.…”

“…Total egg production Spawning stock effects Maternal effects on fecundity Maternal body condition ( K n ) 10 , 38 Step 2. Recruitment Spawning aspects Spawning mean location, area and duration influence the probability to encounter larvae favorable conditions and recruitment Spawning mean location (lat/long), area and duration 8 Total egg production determines recruitment strength Total egg production 57 Environmental effects SST increases the probability of larval survival SST 61 Predators affect larval survival Spring herring biomass 36 Early life stage prey quantity affects larval survival Copepods egg daily production (CEDP, C. finmarchicus, Pseudocalanus spp. and Temora spp.)…”

Regulation of fish stocks without stock–recruitment relationships: The case of small pelagic fish

“…For instance, body growth can be density‐dependent beyond recruitment, and therefore not detected in the SRR (Lorenzen, 2008). Also, spawning biomass may not be a good reflection of egg production, if the latter depends on maternal feeding conditions (Takasuka, Yoneda, & Oozeki, 2019b). In addition, random variation in the environment may hide SRRs, while leaving “soft” floors and ceilings on abundance that regulate populations (Turchin, 1995)—the absence of an SRR does not imply an absence of density‐dependent regulation.…”

Transcriptome characterization of BPG axis and expression profiles of ovarian steroidogenesis-related genes in the Japanese sardine

“…The Japanese sardine has been a key species for studies of population dynamics because of its high level of population fluctuation [21]. Although some evidence of the mechanisms of population dynamics has been presented from an ecological perspective [21][22][23][24][25], the available information on aspects of the endocrine regulation of ovarian development is still limited. RNA-seq was performed using sardine brain, pituitary, and gonad from both sexes to generate a high-quality transcriptome assembly.…”

“…The objective of the present study was to provide transcript data and genes related to the BPG axis with the goal of establishing a molecular basis for the endocrine regulation of ovarian development using the Japanese sardine ( Sardinops melanostictus , Clupeidae). The Japanese sardine has been a key species for studies of population dynamics because of its high level of population fluctuation [ 21 ]. Although some evidence of the mechanisms of population dynamics has been presented from an ecological perspective [ 21 – 25 ], the available information on aspects of the endocrine regulation of ovarian development is still limited.…”