Biology subjects

Yukami, R.

Publications and source records attributed to Yukami, R..

4 recordsLinked to original sources

bioRxiv2021

Intra- and inter-specific density dependence of body condition, growth, and habitat temperature in chub mackerel (Scomber japonicus)

The density dependence of growth and body condition have important impacts on fish population dynamics and fisheries management. Although population density is known to affect the temperature of the habitat selected, how this affects the density dependence of growth and body condition remains unclear. Here, we investigated annual changes in body condition, habitat temperature, and cohort-specific growth of chub mackerel (Scomber japonicus) in the western North Pacific and examined quarterly changes in the density dependence of body condition. We hypothesized that chub mackerel body condition is affected both directly (e.g., through competition for food) and indirectly (through changes in habitat temperature) by the abundance of both conspecifics (i.e., chub mackerel) and heterospecifics (the Japanese sardine Sardinops melanostictus). Indeed, chub mackerel body condition, habitat temperature, and growth all decreased with increasing conspecific and heterospecific abundance. Mean annual growth rates in chub mackerel were positively corelated with body condition. The best model showed that conspecific and/or heterospecific abundance had strong negative effects on chub mackerel body condition in all seasons, and influenced habitat temperature in some seasons. By contrast, temperature effects on body condition were weak. Therefore, direct effects likely have more impact than indirect effects on density-dependent body condition and growth.

ecology↗

bioRxiv2020

Length-length and length-weight relationships for four small pelagic fishes in the Kuroshio-Oyashio current system

Length-length relationships and length-weight relationships were estimated for four small pelagic fishes (Japanese sardine Sardinops melanostictus, Japanese anchovy Engraulis japonicus, chub mackerel Scomber japonicus, and spotted mackerel Scomber australasicus) in the Kuroshio-Oyashio current system. Fish samples were collected from surface-midwater trawl surveys and commercial purse-seine fisheries between September and October of 2020 in the western North Pacific. Total length (TL), fork length (FL), and standard length (SL) were measured to 0.01 cm, and whole body weight (W) was measured to the nearest 0.01 g for each individual. All length-length relationships (TL-FL, TL-SL, and FL-SL) were highly significant (p < 0.0001), with r2 > 0.98 in all species. Length-weight relationships (W-TL, W-FL, and W-SL) were also highly significant (p < 0.0001), with r2> 0.98 in all species. This study provides a useful reference for biological studies and stock assessments of these small pelagic fishes.

ecology↗

bioRxiv2020

Spatio-temporal spawning patterns and early growth of Japanese sardine in the western North Pacific during the recent stock increase

Spatio-temporal patterns in spawning influence growth and survival by affecting the environment experienced by offspring during their early life stages. Therefore, identifying changes in spawning patterns can help researchers understand population dynamics and recruitment fluctuations. The Japanese sardine Sardinops melanostictus is a small pelagic fish that undergoes large stock fluctuations. Although spawning patterns are known to change spatially and temporally with stock abundance, little information is available on the processes underlying stock increases. This study aimed to describe changes in spawning pattern and early growth of Japanese sardine during the recent period of stock increase, and to clarify the effects of different spawning periods on offspring growth. We examined trends in egg abundance in the western North Pacific in 2004-2018 and analyzed hatch dates and growth trajectories by otolith microstructure analysis of juveniles from the Kuroshio-Oyashio transitional region (the species main nursery area). During the study period, the main spawning area shifted from the western to the eastern part of this region off Japan, and spawning in the eastern part roughly coincided with juvenile hatch dates. Hatch dates also shifted from mid-March at the earliest to February and early March from 2013 onwards. Although early-hatched cohorts (which originate offshore of eastern Japan) experienced slower initial growth, they likely played an important role in the recent stock increase. Successful recruitment of these cohorts may have been facilitated by factors such as early hatching and transport to the nursery, which reduces the frequency of predator encounters.

ecology↗

bioRxiv2020

Spatio-temporal model reduces species misidentification bias of spawning eggs in stock assessment of spotted mackerel in the western North Pacific

Species identification based on morphological characteristics includes species misidentification, leading to estimation bias of population size. The eggs of spotted mackerel Scomber australicus and chub mackerel S. japonicus in the western North Pacific has been identified based on egg diameter. Recent density of spotted mackerel was considerably high despite its low stock biomass. A possibility of this phenomenon is due to overestimation because the difference in egg diameter has become ambiguous between two species. However, we cannot test this possibility using DNA analysis because the eggs are fixed with formalin. Here, we estimated the index of egg density of spotted mackerel using a spatio-temporal model that incorporates the effect of egg density of chub mackerel on the catchability of spotted mackerel, using 15 years data of spawning eggs. We then examined how retrospective biases in estimated stock abundance were reduced when using the index from the model. The index estimated from the model decreased temporal fluctuation and showed smooth patterns. Especially, the recent index was considerably revised down rather than the nominal index. Additionally, the retrospective bias decreased ca. half compared with the nominal index. Therefore, incorporating species misidentification bias should be an essential process for improving stock assessment.

ecology↗