ABSTRACT
Trichiurus japonicus is an economically valuable species in the East China Sea, whose allowable capture size varies with fishing effort in different years. To clarify the optimum capture size for T. japonicus in the East China Sea, we collected samples and data from T. japonicus targeting fishing gears such as trawls, canvas spreader stow nets and longlines from 2016 to 2020. We estimated growth and mortality parameters using the FiSAT II software, and calculated the size limit standards for capture. The results showed that the inflection point of anal length, the critical anal length and the anal length of one-year-old T. japonicus was 382.84, 397.12, and 216.05 mm, respectively. The anal length of maturity was 230.38 mm, and the minimum capture size (anal length) was 219.23 mm. Based on the yield per recruitment analysis using Beverton-Holt model, the current fishery reference points were under overfishing condition (tc=0.38 a, F=2.11), and the suggested optimum capture size was 364.64 mm. There would be a sharp decline of T. japonicus catches in the East China Sea if the suggested minimum capture size was substantially higher, which might be non-practical for local fishermen. Therefore, we suggested 220 mm as the capture size limit, which was close to the anal length of one-year-old fish and the anal length of maturity.
Subject(s)
Conservation of Natural Resources , Perciformes , Animals , Fisheries , ChinaABSTRACT
We study the relationship between the structures of the nonlinear localized waves and the distribution characteristics of the modulation stability regime in a nonlinear fiber with both third-order and fourth-order effects. On the background frequency and background amplitude plane, the modulation stability region consists of two symmetric curves on the left and right and a point on the symmetry axis. We find that the higher-order excitation characteristics are obviously different at different positions in the modulation stability region. Their excitation characteristics are closely related to the modulation instability distribution characteristics of the system. It is shown that asymmetric high-order rational solitons are excited at the left and right stable curves, and the symmetric one is excited at the stable points. Interestingly, the asymmetric higher-order rational solitons on the left and right sides are mirror-symmetrical to each other, which coincides with the symmetry of the modulation instability distribution. These results can deepen our understanding of the relationship between nonlinear excitation and modulation instability and enrich our knowledge about higher-order nonlinear excitations.
ABSTRACT
Engraulis japonicus, an important fishery resource, is a key species in ecosystem trophodynamics studies. In this study, we examined stomach content of E. japonicusby stable isotope analyses, with samples collected from the East China Sea in 2008-2009 and 2020. The aim of this study was to demonstrate their diet composition, diel and ontogenetic changes in feeding habits and trophic level. Results of the stomach content analysis showed that E. japonicus mainly fed on planktonic crustaceans and small fish. The main prey species were Euphausia pacifica [index of relative importance (IRI)=87.6%; frequency(F)=57.6%], Paracalanus parvus (IRI=3.2%, F=15.3%), and Themisto gracilipes (IRI=2.1%, F=13.1%). Results of the stable isotope analysis showed that Copepoda were the main food source of E. japonicus, followed by Euphausiacea, and the contribution rate of Amphipoda was the least, which was less than 1%. There was significant diel change in diet composition. Feeding intensity was higher in the daytime than at night, with the highest in the dusk and the lowest at midnight. Ontogenetic change in feeding habit occurred when fork length reached 90 mm, over which the fish fed both zooplankton and small fishes. The δ13C of E. japonicus was between -21.66 and -18.14, with an average of (-19.92±0.86). The δ15N of E. japonicus ranged from 4.07 to 10.78, with an average of (8.14±2.48). Both δ13C and δ15N values were positively correlated with fork length. Trophic level of the fish was 3.4 with stomach content analysis and 2.7 with stable isotope analysis. The results would provide important reference for understanding nutritional status of pelagic small fish, and offer some basic data to establish ecopath model.
Subject(s)
Ecosystem , Gastrointestinal Contents , Animals , Carbon Isotopes/analysis , China , Feeding Behavior , Fishes , Food Chain , Gastrointestinal Contents/chemistry , Nitrogen Isotopes/analysisABSTRACT
To understand the characteristics and living conditions of shrimp population in the Zhongjieshan Islands Marine Protected Area (MPA), according to the trawl survey data of the area in January, April, July and October 2018, we analyzed the spatio-temporal niche of dominant shrimp species based on the indices of relative importance, Shannon index, Pianka formula and Pearson correlation coefficient. The results showed that 16 shrimp species from 10 families and 13 genera were collected and identified. Palaemon gravier, Solenocera crassicorni, Alpheus distinguendus, Parapenaeopsis hardwickii and Alpheus japonicus were dominant species, belonging to four fami-lies and four genera. The temporal niche breadth of the dominant species varied greatly, while their spatial niche breadth was stable. The temporal niche breadth was significantly correlated with temperature suitability. The spatio-temporal niche breadth value of A. japonicus, the small shrimps, was highest. The temporal niche overlap value between P. hardwickii and S. crassicornis was the largest, indicating that the time synchronization was high and the seasonal competition was severe. There was a significant spatial niche overlap in all dominant species, indicating that the dominant species of shrimp had the same spatial homology, with strong regional competition. The spatio-temporal niche overlap value between P. hardwickii and P. gravieri was the largest, indicating that they had high similarities in physical and biological environment selecting, spawning and migratory habits, and fierce inter-specific competition. Our results could provide reference for the application of spatio-temporal niche of marine organisms.
