Pacific herring, Clupea pallasii, a keystone species with significant ecological and commercial importance, is declining globally throughout much of its range. While traditional fishing equipment methods remain limited, new sensitive and rapid detection methods should be developed to monitor fisheries resources. To monitor the presence and quantity of C. pallasii from environmental DNA (eDNA) extracted from seawater samples, a pair of primers and a TaqMan® probe specific to this fish based on mitochondrial cytochrome b (COB) sequences were designed for the real-time PCR (qPCR) assay. The combination of our molecular markers showed high specificity in the qPCR assay, which affirmed the success of presenting a positive signal only in the C. pallasii specimens. The markers also showed a high sensitivity for detecting C. pallasii genomic DNA in the range of 1 pg~100 ng rxn-1 and its DNA plasmid containing COB amplicon in the range of 1~100,000 copies rxn-1, which produced linear standard calibration curves (r2=0.99). We performed a qPCR assay for environmental water samples obtained from 29 sampling stations in the southeastern coastal regions of South Korea using molecular markers. The assay successfully detected the C. pallasii eDNA from 14 stations (48.2%), with the highest mean concentration in Jinhae Bay with a value of 76.09±18.39 pg L-1 (246.20±58.58 copies L-1). Our preliminary application of molecular monitoring of C. pallasii will provide essential information for efficient ecological control and management of this valuable fisheries resource.

We measured the target strength according to the swimming tilt angle and size change for Pacific herring at the frequency of 70 kHz as the basic database in order to estimate its abundance as well as density in the survey area using the hydroacoustical method. The number of the sample used in this study was 14 individuals, and its size distribution by fork length ranged between 20.3 and 29.8 cm and wet weight was measured between 187.6 and 269.9 g. The variation of TS according to the swimming angle (-30~30°) was measured between 10.3 and 18.8 dB in frequency range, the highest value was measured at head-down of Pacific herring in the tilt angle range between 5 and 9 deg. of its swimbladder. The relationship between TS–FL of herring was the same as TS = 20log10 (FL) – 66.79 when its swimming tilt angle in the daytime (3.8 ± 6.0°) and nighttime (-3.2 ± 13.6°), respectively.

The feeding habits of larval (5.0~27.0 mm SL) Clupea pallasii were examined and 1,523 individuals were collected from November 2010 to March 2011 in the coastal water of Eastern Jinhae Bay, Korea. Larval C. pallasii were fed mainly on copepods that constituted 55.2% in IRI. Monogeneans were the second largest prey component, another prey items tintinnids, cladocerans and ostracoda. The results of analysis in ontogenetic changes exhibit high during the daytime, two small size classes (≤10 mm, 10~15 mm) mainly fed copepods. while the percentage of coperpods decreased, monogeneans ratio increased in 15~20 mm size class. Feeding rate in diel difference of larval C. pallasii were high during the daytime.

Pacific herring Clupea pallasii eggs were attached to the gill net in Korean coastal waters off Busan. To conservation and management the eggs attached to the gill net, we followed the natural hatching in coastal waters from five days after fertilization to the hatching finished, where the temperature was 9°C. The diameter of fertilized eggs was 1.24–1.55 mm (n= 50), and had a segmented pale yellow yolk, no oil globule. Natural hatching had started by 10 days after fertilization. Mass hatching occurred around 11–12 days after fertilization, most of eggs separated from the gill net. Therefore, when the Pacific herring eggs attached in gill net, should be natural hatching–induced in coastal waters during 12–14 days.

The mesh selectivity of the gillnet for Pacific herring (Clupea pallasii) was examined in field experiments with four different mesh sizes (63, 69, 75 and 81mm) from June to July, 2013 in the coastal areas of Imwon in Gangwon province. The fishing performance tests were conducted with a commercial Pacific herring gillnet and a biodegradable gillnet for Pacific herring together selectivity tests. The filed tests were carried out the total 11 times. The master curve of selectivity was estimated by the extended Kitahara's method. In the results, the catch number of Pacific herring was 9,409 (2,203kg) and occupied 84.2% in total catches weight. The optimal mesh size for 50% retention on first maturity size (female, 250mm) of Pacific herring was estimated as 64.5mm by master selectivity curves. The fishing performance of the biodegradable gillnet was showed to be equivalent with commercial gill for Pacific herring.

Physical characteristics of PA (Polyamide) gill net and biodegradable gill net made by PBS (Polybutylene succinate) (mesh size 63mm, mesh thickness number 2, 2.5, 3) were analyzed to investigate catching efficiency of the biodegradable gill net for Pacific herring. Total 11 numbers of catching efficiency tests were carried out using commercial fishing vessel at Imwon port in Kangwon province from May to June 2013. The amount of catches were 1,535.7kg (18 species) through the catching efficiency tests and it is expected that the practicalization of biodegradable gillnet is possible because there is no difference for catches between PA gillnet and PBS gillnet. Catches of herring according to the thickness of net twine was the highest at No.2 and the thicker net twine tends to decrease the catches.

The authors have investigated three species of Clupeidae such as herring, Korean anchovy and large-eyed herring, belonging to the order Clupeiformes. The fish is also indigenous to some parts of the southern regions of the West Sea. Fishes are the most popular marine products in Korea because of their taste and nutritional value, and Koreans consume them in large quantities. Especially, Korean anchovy and large-eyed herring are widely distributed in the entirety of brackish-water habitats and seawater areas of the West Sea in the Korean Peninsula, as well as in several areas in China. However, in spite of their economic and scientific consequences, a little information currently exist regarding the physiological and ecological levels only of crab species in Korea. During the last two decades, environmental contamination and various environmental disruptions by industries and city sewage, have threatened the coastal fisheries, and then reduction of individual number of this fish is an increasing trend in the 2000s. This study attempt is to elucidate the genetic distances within and between herring, Korean anchovy and large-eyed herring population from the West Sea. Three species of herring (C. pallasii), Korean anchovy (C. nasus) and large-eyed herring (H. zunashi) were obtained in close vicinity to the West Sea in Korea. Three species of fish muscle was collected in sterile tubes, placed on ice immediately, and stored under refrigeration until needed. Genomic DNA was extracted and purified under the conditions described previously (Yoon and Kim, 2004). The degree of variability was calculated by use of the Dice coefficient (F), which is given by the formula: F = 2nab / (na+nb), where nab is the number of bands shared between the samples a and b, na is the total number of bands for sample a and nb is the total number of bands for sample b (Jeffreys and Morton, 1987; Yoke-Kqueen and Radu, 2006). Euclidean genetic distances within-and between-species were also calculated by complete linkage method with the help of the hierarchical dendrogram program Systat version 10. The genomic DNA isolated from herring (C. pallasii), Korean anchovy (C. nasus) and large-eyed herring (H. zunashi) in the West Sea, were amplified several times by PCR reaction. The dendrogram obtained by the seven primers indicates three genetic clusters as shown in Fig. 1. The hierarchical dendrogram indicates three main branches: cluster 1 (PALLASII 01, 02, 03, 04, 06 and 07), cluster 2 (NASUS 08, 09, 10 and 11), and cluster 3 (NASUS 12, 13 and 14, ZUNASHI 15, 16, 17, 18, 19, 20 and 21, PALLASII 05). The genetic distance among the three fish species ranged from 0.018 to 0.318. In three fish population, the shortest genetic distance displaying significant molecular difference was between individual PALLASII no. 03 and PALLASII no. 02 (0.018). Ultimately, individual no. 05 of the PALLASII herring was most distantly related to PALLASII no. 06 (genetic distance = 0.318). From what has been said above, the potential of this PCR analysis to identify diagnostic markers for the identification of three fish populations has been demonstrated. Generally speaking, this PCR analysis method has been applied to identify specific markers particular to line, species and geographical population, as well as genetic diversity/polymorphism in diverse species of organisms (McCormack et al. 2000; Yoon and Kim 2003).