Search Results (9)

Small-scale inshore fisheries significantly contribute to the total landing volumes and have an important role in Vietnamese socioeconomic development, food security, livelihoods, and social well-being. The setnet fishery has been used throughout coastal communities of Vietnam for many decades. Being a passive fishing gear, the catch efficiency of setnet depends on various conditions such as fish density, season, oceanography, environment, and others. However, very little information exists about the relationship between catch rates and national conditions. Recognizing this research gap, this study examined the effect of temporal and environmental conditions on the catch rates of the narrow-barred Spanish mackerel (Scomberomorus commerson) setnet fishery using long-term data from 2005 to 2016. Overall, the catch of narrow-barred Spanish mackerel decreased over the course of the study. The generalized additive model (GAM) showed that catch rates were significantly affected by sea surface temperature (SST), which peaked at 27 °C. After this temperature point, the catch rates significantly decreased. Temporal variables also contributed to the catch variation. The setnet caught the highest yield in April and May, and more fish were caught during periods of low nightlight intensity than during high illuminated periods. Our study contributes to the understanding of critical factors affecting the catch rates of valuable species, which helps to determine the optimal fishing process of the setnet fishery within the shifting of marine heatwaves. Full article

Scomberomorus guttatus and Scomberomorus commerson are both important marine economic fish species worldwide, with high scientific and ecological value. In this study, the complete mitochondrial genome sequences of these two species of mackerel were obtained by using next-generation sequencing technology, with total lengths of 16,562 bp and 16,594 bp, respectively. Like most teleosts, both species possess 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes, and 1 non-coding region D-loop. The base composition showed significant AT bias (55.1%, 53.4%) and anti-G bias (16.0%, 16.2%). In their control area, the terminal-associated sequence (TAS) was identified, and a total of three core sequences with repeated “---TACAT---ATGTA---” were found. There are typical CSB-E structures and CSB-D-like structures in the central conserved domain (CD), but no CSB-F structures have been found. Meanwhile, the CSB-2 and CSB-3 structures were identified in the conserved sequence block (CSB), but the CSB-1 structure was missing. To further investigate the phylogenetic relationships within the Scombridae family, this study conducted a comparative analysis of mitochondrial genomes from 30 Scombridae species. Phylogenetic trees encompassing 60% of the documented Scombridae species were constructed using the Neighbor-Joining (NJ) and Maximum Likelihood (ML) methods. The results revealed a close evolutionary relationship between the genus Scomber and Rastrelliger, while the genus Scomberomorus exhibited closer affinities to Thunnus, Euthynnus, and Katsuwonus. At the species level, Scomberomorus guttatus diverged earlier from Scomberomorus commerson. These findings refine and update the phylogenetic relationships among Scombridae species, providing critical molecular evidence and insights for deeper exploration of their evolutionary history and genetic affinities. Full article

Being a biologically diversed hotspot in the global marine ecosystem, the Beibu Gulf is inhabited by a high diversity of fish and serves as a vital fishing ground in China. Due to continuous overfishing, the fishery resource has drastically declined in the Beibu Gulf. However, information about the ichthyoplankton assemblages in this area is still lacking. In this present study, ichthyoplankton diversity, spatial and temporal distribution patterns, and assemblage structures were examined using the specimens collected in the late summer–autumn and winter of 2022 in the Beibu Gulf, and the relationship between ichthyoplankton assemblage and environmental variables was studied. A total of 117 ichthyoplankton taxa, belonging to 13 orders and 42 families, were recorded. The most abundant families were Gerreidae, Leiognathidae, and Sillaginidae in late summer–autumn, accounting for 38.74%, 27.95%, and 9.94%, respectively. Sparidae, Platycephalidae, and Sillaginidae were the most abundant families in winter, accounting for 34.03%, 17.15%, and 8.20%, respectively. Cluster analysis identified five assemblages in late summer-autumn and four assemblages in winter. The most characteristic species in each cluster were Terapon jarbua, Sillago sihama, Leiognathus brevirostris, Mene maculate, and Scomberoides tol in late summer-autumn and Scomberomorus commerson, Acanthopagrus latus, Sillago sp., and Evynnis cardinalis in winter. The results of the canonical correspondence analysis indicated that pH, chlorophyll-a (Chl-a), depth, dissolved oxygen (DO), sea surface salinity (SSS), total nitrogen (TN), and total phosphorus (TP) were the major environmental variables affecting the ichthyoplankton assemblage structure in the Beibu Gulf. The finding of this study will provide valuable information in conserving fish spawning grounds and developing fishery management practices to protect fishery resources in the Beibu Gulf. Full article

A new gillnet made from multiple mesh sizes ranging from 125 to 180 mm of stretched mesh (experimental gillnet) was tested under commercial fishing conditions to compare the fishing performance with that of conventional gillnets with a 125 mm mesh opening (control gillnet). Catch efficiency and size selectivity between the two gillnet types were evaluated throughout one year of fishing in three different locations in the waters of Vietnam. Experimental gillnets caught narrow-barred Spanish mackerel (Scomberomorus commerson), spotted mackerel (Scomberomorus guttatus), and wahoo (Acanthocybium solandri) in comparable amounts to the control gillnets, with the moon phase, month, and depth explaining some of the variation in the catch per unit effort (CPUE). An analysis of the size-dependent catch comparison rates and selectivity parameters showed that the experimental gillnets captured a wider range of narrow-barred Spanish mackerel sizes, but with a substantial proportion of individuals larger than those caught by the control gillnets. This is of higher weight per unit effort, and fishing enterprises therefore could improve their economic benefits by using modified gillnets with multiple mesh sizes. Our findings also support the biological and environmental benefits of the modified gillnet size selection, which might also extend to other species. Full article

We developed and applied a method to quantify spearfisher effort and catch, shark interactions and shark depredation in a boat-based recreational spearfishing competition in the Great Barrier Reef Marine Park in Queensland. Survey questions were designed to collect targeted quantitative data whilst minimising the survey burden of spearfishers. We provide the first known scientific study of shark depredation during a recreational spearfishing competition and the first scientific study of shark depredation in the Great Barrier Reef region. During the two-day spearfishing competition, nine vessels with a total of 33 spearfishers reported a catch of 144 fish for 115 h of effort (1.25 fish per hour). A subset of the catch comprised nine eligible species under competition rules, of which 47 pelagic fish were weighed. The largest fish captured was a 34.4 kg Sailfish (Istiophorus platypterus). The most common species captured and weighed was Spanish Mackerel (Scomberomorus commerson). The total weight of eligible fish was 332 kg and the average weight of each fish was 7.1 kg. During the two-day event, spearfishers functioned as citizen scientists and counted 358 sharks (115 h effort), averaging 3.11 sharks per hour. Grey Reef Sharks (Carcharhinus amblyrhynchos) comprised 64% of sightings. Nine speared fish were fully depredated by sharks as spearfishers attempted to retrieve their catch, which equates to a depredation rate of 5.9%. The depredated fish included four pelagic fish and five reef fish. The shark species responsible were Grey Reef Shark (C. amblyrhynchos) (66%), Bull Shark (Carcharhinus leucas) (11%), Whitetip Reef Shark (Triaenodon obesus) (11%) and Great Hammerhead (Sphyrna mokarran) (11%). There were spatial differences in fish catch, shark sightings and rates of depredation. We developed a report card that compared average catch of fish, sightings of sharks per hour and depredation rate by survey area, which assists recreational fishers and marine park managers to assess spatio-temporal changes. The participating spearfishers can be regarded as experienced (average 18 days a year for average 13.4 years). Sixty percent of interviewees perceived that shark numbers have increased in the past 10 years, 33% indicated no change and 7% indicated shark numbers had decreased. Total fuel use of all vessels was 2819 L and was equivalent to 6.48 tons of greenhouse gas emissions for the competition. Full article

To begin to understand the impact of food chain dynamics on ciguatera risk, we used published data to model the transfer of ciguatoxins across four trophic levels of a marine food chain in Platypus Bay, Australia. The data to support this first attempt to conceptualize the scale of each trophic transfer step was limited, resulting in broad estimates. The hypothetical scenario we explored generated a low-toxicity 10 kg Spanish mackerel (Scomberomorus commerson) with a flesh concentration of 0.1 µg/kg of Pacific-ciguatoxin-1 (P-CTX-1, also known as CTX1B) from 19.5–78.1 µg of P-CTX-1 equivalents (eq.) that enter the marine food chain from a population of 12–49 million benthic dinoflagellates (Gambierdiscus sp.) producing 1.6 × 10⁻¹² g/cell of the P-CTX-1 precursor, P-CTX-4B. This number of Gambierdiscus could be epiphytic on 22–88 kg of the benthic macroalgae (Cladophora) that carpets the bottom of much of Platypus Bay, with the toxin transferred to an estimated 40,000–160,000 alpheid shrimps in the second trophic level. This large number of shrimps appears unrealistic, but toxic shrimps would likely be consumed by a school of small, blotched javelin fish (Pomadasys maculatus) at the third trophic level, reducing the number of shrimps consumed by each fish. The Spanish mackerel would accumulate a flesh concentration of 0.1 µg/kg P-CTX-1 eq. by preying upon the school of blotched javelin and consuming 3.6–14.4 µg of P-CTX-1 eq. However, published data indicate this burden of toxin could be accumulated by a 10 kg Spanish mackerel from as few as one to three blotched javelin fish, suggesting that much greater amounts of toxin than modelled here must at certain times be produced and transferred through Platypus Bay food chains. This modelling highlights the need for better quantitative estimates of ciguatoxin production, biotransformation, and depuration through marine food chains to improve our understanding and management of ciguatera risk. Full article

The narrow-barred Spanish mackerel Scomberomorus commerson is an economically essential species; however, few studies have investigated its demographic structure in the northwestern Pacific, which includes Taiwan’s waters. This study examined the growth parameters, age composition, mortality, and sex ratio of S. commerson catches by examining sagittal otoliths and other biological data collected in a 3-year project from June 2018 to June 2021. The transverse sections of sagittal otoliths exhibited alternating translucent and opaque zones, in annual cycles, and this observation was validated by otolith edge analysis. Opaque zones began to form in October; the growth peaked in December and lasted until March. Growth parameters were estimated for female (L_∞ = 144.1 cm fork length [FL], k = 0.39 y⁻¹, t_o = −0.85 y) and male (L_∞ = 136.0 cm FL, k = 0.32 y⁻¹, t_o = −1.49 y) specimens. The maximum recorded FL, body weight, and age were 159.0 cm, 27 kg, and 9.2 y for female and 135.0 cm, 17.8 kg, and 7.2 y for male specimens. Rapid growth was observed for both sexes, with FL reaching 66.8 ± 14.2 cm in female specimens and 70.1 ± 11.0 cm in male specimens during the first year of life. An age–length key based on the direct otolith aging and FL dataset (N = 646) was used to estimate the age composition of 3-year catches measured at landing (N = 16,133). The results verified that the S. commerson currently caught in the central Taiwan Strait are mainly young fish aged 1⁺ to 2⁺ y. The estimated fishing mortality (0.27 y⁻¹) and exploitation rate (0.30) suggested that overfishing was not occurring in this stock. The findings of this study have helped clarify the population dynamics of the S. commerson in the Taiwan Strait, and the biological parameters reported herein can aid the management and conservation to ensure the sustainability of this species in this region. Full article

We review and develop conceptual models for the bio-transfer of ciguatoxins in food chains for Platypus Bay and the Great Barrier Reef on the east coast of Australia. Platypus Bay is unique in repeatedly producing ciguateric fishes in Australia, with ciguatoxins produced by benthic dinoflagellates (Gambierdiscus spp.) growing epiphytically on free-living, benthic macroalgae. The Gambierdiscus are consumed by invertebrates living within the macroalgae, which are preyed upon by small carnivorous fishes, which are then preyed upon by Spanish mackerel (Scomberomorus commerson). We hypothesise that Gambierdiscus and/or Fukuyoa species growing on turf algae are the main source of ciguatoxins entering marine food chains to cause ciguatera on the Great Barrier Reef. The abundance of surgeonfish that feed on turf algae may act as a feedback mechanism controlling the flow of ciguatoxins through this marine food chain. If this hypothesis is broadly applicable, then a reduction in herbivory from overharvesting of herbivores could lead to increases in ciguatera by concentrating ciguatoxins through the remaining, smaller population of herbivores. Modelling the dilution of ciguatoxins by somatic growth in Spanish mackerel and coral trout (Plectropomus leopardus) revealed that growth could not significantly reduce the toxicity of fish flesh, except in young fast-growing fishes or legal-sized fishes contaminated with low levels of ciguatoxins. If Spanish mackerel along the east coast of Australia can depurate ciguatoxins, it is most likely with a half-life of ≤1-year. Our review and conceptual models can aid management and research of ciguatera in Australia, and globally. Full article

Between 2014 and 2016, five cases of ciguatera fish poisoning (CFP), involving twenty four individuals, were linked to Spanish Mackerel (Scomberomorus commerson) caught in the coastal waters of the state of New South Wales (NSW) on the east coast of Australia. Previously, documented cases of CFP in NSW were few, and primarily linked to fish imported from other regions. Since 2015, thirteen individuals were affected across four additional CFP cases in NSW, linked to fish imported from tropical locations. The apparent increase in CFP in NSW from locally sourced catch, combined with the risk of CFP from imported fish, has highlighted several considerations that should be incorporated into risk management strategies to minimize CFP exposure for seafood consumers. Full article