Search Results (10)

The use of multiple sampling instruments during ichthyoplankton surveys could require a significant amount of time for sample collection procedures; moreover, their use is highly dependent on weather conditions. During surveys aimed at the application of the Daily Egg Production Method (DEPM), two different kinds of sampler are employed: PairoVET and Bongo 40. The possibility of using only one of these samplers may allow for a reduction in the sampling time on board and the subsequent analyses; thus, a study was carried out to test the use of the Bongo 40 sampler alone (i.e., without PairoVET sampling) in DEPM application. Samples collected during five ichthyoplankton surveys (from 2007 to 2010 and in 2014) were analyzed to compare the efficiency in anchovy egg collection. Although the compared ichthyoplankton samplers provided differences in the collected number of eggs, as well as in the filtered volume, non-significant differences between them were recorded in the egg density. An ANCOVA revealed a significant relationship (F_1,5 = 606.80; p < 0.001) between the density estimates from the two nets, but no differences were recorded among years (F_1,5 = 0.99; p < 1). The slopes of the linear regressions for the two datasets were close to 1, suggesting a substantial equivalence of the two samplers in estimating the egg density. Finally, since only a few sampling stations showed densities higher than 20 ind. m⁻², conversion equations were provided to estimate the PairoVET density from the Bongo 40 data at different density levels (i.e., 20 ind. m⁻² or higher). Full article

The abundance, spatial distribution of and dynamic changes in ichthyoplankton species affect the recruitment and fish population dynamics, which are fundamental for stock assessment and fisheries management. An evaluation of alternative sampling designs needs to be carried out to determine the optimal scheme that is cost-effective in collecting high-quality ichthyoplankton data. A simulation study was conducted to evaluate the performances and consistency of six potential sampling designs for an ichthyoplankton survey in the coastal waters of the central and southern Yellow Sea. Relative estimation error (REE) and relative bias (RB) were used to measure the performances in estimating the population abundances of five target ichthyoplankton species in different sampling designs. In general, the two systematic sampling (SYS) designs had high precision and accuracy estimation and remained stable over years for estimating the population abundance of ichthyoplankton species compared with the other four sampling designs. SYS did not result in the overestimation or underestimation of the mean population abundance. Most sampling designs showed relatively high accuracy in abundance estimation when sample sizes were higher than medium levels. This study could improve the performances of sampling designs of ichthyoplankton surveys and provide a reference for the further optimization of sampling designs. Full article

The National Yancheng Rare Birds Nature Reserve is a vitally important staging habitat for the wild population of red-crowned cranes (Grus japonensis) in China. The population relies on local high-protein food sources, such as fish juveniles, to fuel their migratory journeys. However, little is known about the ecology of the fish larvae and juveniles that migrate to the inshore area via tidal rhythm in Subei Shoal, which is adjacent to the reserve. Therefore, we used a fixed study station (32°55′1.2″ N, 121°19′58.8″ E) to conduct a continuous 15-day ichthyoplankton survey at 2 h intervals beginning at 05:00 on 25 April and ending at 03:00 on 10 May 2019. We identified the tidal variations in the number of fish larvae and juveniles and the number at various developmental stages and assessed how they were related to environmental variables such as sea surface temperature, salinity, turbidity, and tidal height in the Dafeng Sea area of Subei Shoal. We found that the number of species and larval individuals were highest and lowest, respectively, at the highest and lowest tidal height, and they obviously increased and decreased with the rising and ebb tide, respectively. Our findings indicate that the variation in numbers of the larvae and juveniles depends on species and developmental stage. The species Acanthogobius ommaturus, Pholis fangi, Cynoglossus joyneri, Liza haematocheila, and Lateolabrax japonicus and the total number of larvae were most influenced by tidal height. These results provide a better understanding of the habitat of prey species of the red-crowned crane wild population as well as scientific data that can be applied to manage the wild population in the reserve sustainably. Full article

The daggertooth pike conger, Muraenesox cinereus, is an important demersal fish species in East Asia but the catch amount has declined in recent years. Spawning areas of M. cinereus have not yet been determined; identifying these have serious implications for resource management. Ichthyoplankton surveys are an effective method of distinguishing fish spawning areas and periods. Fish eggs were sampled from the waters adjacent to South Korea in August 2020 and 2022 using a Multiple Opening/Closing Net and Environmental Sensing System or a bongo net. In 2021, M. cinereus eggs were not collected. Three unidentified eggs (2.0–2.2 mm in diameter) were collected from the southeastern sea of Jeju Island at a seawater depth of 20–30 m and temperature of 20–22 °C. Muraenesox cinereus preleptocephali were gathered at 10–20 m depths from Jeju Island’s southernmost and eastern sea areas. The eggs and preleptocephali were identified as M. cinereus by their mitochondrial DNA 16S rRNA sequences. This is a new finding of eggs and leptocephalus of Muraenesox cinereus off Jeju Island, South Korea, which increases our understanding of the recruitment process of M. cinereus to facilitate resource management and species conservation. Full article

Abundance indices are essential data for the application of stock assessment models to obtain fish abundance estimates. Abundance indices have usually been derived from fishery-dependent data, yet the increase in fisheries-independent surveys is now offering new opportunities for these calculations. In this study, we explored the usefulness of ichthyoplankton indices derived from scientific surveys in estimating spawning biomass. In addition, we also investigated whether the strength of the year–class of the commercial cohort of Atlantic hake, as a determinant, could be defined at an early life stage. We used samples collected during the triennial mackerel and horse mackerel egg surveys (MEGS), which cover the hake spawning area in the Bay of Biscay. The biomass indices were determined as the abundance of eggs in the early development stage (stage 1) when transformed into egg production (EP) from 1995 to 2019 in the months of March and April—which is considered a period of high spawning activity for hake in this area. Additionally, we built a metric for larval abundance and converted larval length into age. This was in addition to constructing a pre-recruit year-class index (YCI) while using the EVHOE bottom trawl abundance database for hake for the period of 1997 to 2016. The results of regression analysis of egg production and spawning stock biomass indicate that both parameters are significantly correlated (r = 0.76). By connecting the abundance of eggs and larvae in the adjoining stages, we are able to identify two periods of high mortality associated with the transition from “yolk-sac-first” to “feeding larvae” and “late larvae-YCI10”, but we were unable to discover when the strength of the recruitment year–class is determined. As such, it appears that for the northern stock of hake, recruitment is established in the late juvenile stages. Full article

High-throughput DNA metabarcoding of mitochondrial 12S rRNA and Cyt b gene sequences was coupled with a morphology-based identification tool to assess ichthyoplankton community structure in Oujiang River Estuary, China. The performances of 12S and Cyt b barcoding markers were compared in terms of taxonomic resolution, detection and coverage, and their suitability was established for use as a quick and powerful ichthyoplankton assessment tool. A total of 30,138 ichthyoplankton (2462 eggs and 27,676 larvae) samples were collected from April to August 2015 and identified to 145 taxa belonging to 57 families and 105 genera. June and July were the main spawning months. Ichthyoplankton were more abundant around Lingkun and Qidu Islands and the upper parts of Oujiang River Estuary. The 12S gene marker presented higher species coverage and detection rate than Cyt b. DNA metabarcoding exhibited more representative species identification power than morphology. The findings reported in this study provided a key attempt towards the development of time-efficient and cost-effective ichthyoplankton identification and assessment tool. Full article

The larval distributions of the small-sized fishes Omobranchus elegans, Erisphex pottii, Benthosema pterotum, Acropoma japonicum, Upeneus bensasi, and Apogonichthys lineatus in the East China Sea ecosystem are important due to their ecological and economic benefits. To date, however, there have been few studies describing their population distributions and dynamics. In the current study, ichthyoplankton surveys were carried out from April to July 2018 to analyze variations in the larval abundance, distribution, and development stages of these species. In addition, the spatiotemporal larval distribution was investigated in terms of measured environmental variables. It was found that larvae were mainly distributed at depths of 5.00–66.00 m, in areas with sea surface temperature of 4.40–29.60 °C, sea surface salinity of 16.54–34.60 psu, pH of 7.00–9.00, and dissolved oxygen concentration of 2.54–8.70 mg/L. Benthosema pterotum and A. lineatus migrated from 30.00–31.00° N 123.17–123.50° E in June to 30.00–32.50° N 122.22–123.50° E in July. The results of this study can help to preserve spawning and nursery grounds and contribute to sustainable coastal fisheries management. Full article

Sardine (Sardina pilchardus) and horse mackerel (Trachurus trachurus) are two key species in marine food webs and have a high commercial value in the Iberian Peninsula. The populations of these species are known to have exhibited marked fluctuations in abundance over the years, however the causes for such variability are still not totally understood. One of the identified sources of mortality in the early life phase, is the parasitism by Ichthyodinium chabelardi, an endoparasite of pelagic fish eggs, which leads to the host death. A total of 4000 ichthyoplankton samples, and over 30,000 eggs, from 10 surveys conducted by IPMA, in the Iberian Atlantic area, were analyzed to assess the percentage of eggs infected by the parasite (prevalence). The results showed interannual variability in the infection prevalence, with values between 0.80% and 4.32% for sardine eggs and between 0.82% and 10.97% for horse mackerel eggs. The number of samples with infected eggs varied between 2.53% and 15.32% in the case of sardine eggs and between 2.00% and 12.59% for horse mackerel eggs. GLM analyses highlighted location variables, as the main responsible for the spatial distribution patterns observed. Comparisons of infection prevalence and total egg mortality values obtained by the daily egg production method estimations clarify the relevance of I. chabelardi infection for sardine egg mortality. Full article

The ecology of the mesopelagic fish genus Trachipterus, which is rarely found in oceans, remains unclear. In this study, we found 22 eggs of T. trachypterus and T. jacksonensis around the Ulleung Basin of the East/Japan Sea during ichthyoplankton surveys from 2019 to 2021. The eggs were identified through genetic relationships with the genus Trachipterus based on partial sequences (COI and 16S) or concatenated sequences of 13 protein-coding genes and 2 rRNA genes of mitochondrial DNA. T. trachypterus eggs were discovered in all seasons, but more frequently during the winter. One T. jacksonensis egg that appeared during the autumn was the first in the northwestern Pacific Ocean. Identifying Trachipterus pelagic eggs would provide insight into their spawning ecology and biogeography. Full article

The summer ichthyoplankton characteristics in the Laibin section of the Xijiang River were analyzed based on a survey during summer 2017. The ontogenetic structure and temporal patterns of ichthyoplankton and the correlation between environmental parameters and the temporal patterns were investigated. A total of 10,665 eggs and 447 larval belonging to four orders, ten families, and 28 species were collected. According to the flood regime, summer is divided into three periods (pre-flood, flood period, and post-flood). Ichthyoplankton proved to be heterogeneous between periods in summer with differences in the composition and abundance. The assemblages were distinguished by multiple analytical tools, and presented a chronological pattern of marked variability in composition of the species between the periods, and under the strong influence of flood. The assemblages were mainly represented by eggs of S. wui Fang and S. robusta in the pre-flood period, S. argentatus and S. macrops in the flood period, and H. leucisculus and S. curriculus in the post-flood period, while, the larval occurred mainly in the flood period. Understanding these temporal patterns of the upper course of the Xijiang River is useful for the recruitment of fish resources and conservation of fish community diversity. Full article