Trachurus Research Articles

Development of species‐specific multiplex real‐time PCR assays for tracing the small pelagic fishes of North Pacific with environmental DNA

AbstractEnvironmental DNA (eDNA) has become a popular non‐invasive method to study the presence of organisms in the environment. To study the ecological behavior and migration routes of small pelagic fishes that are difficult to trace with traditional capturing methods, we developed multiplex real‐time PCR assays to measure the eDNA of chub mackerel, blue mackerel, Japanese jack mackerel, Japanese anchovy, Japanese sardine, and Pacific saury. To test the validity, eDNA samples collected from the water near fisherman set nets in Northeast Japan between 2018 and 2019 were analyzed. Warm‐climate species including blue mackerel, jack mackerel, and anchovy were prominent in autumn, while cold‐climate species such as chub mackerel and sardine were richly present in winter. Pacific saury is an off‐coast species and was not detected in the coastal set net area. The eDNA data were partially correlated to the fishery catch records, suggesting that the eDNA quantities are relevant to the biomass of the fish schools, and our PCR assays can quantify the biological traces left by the small pelagic fish schools. Different patterns of eDNA occurrence were observed between the chub and blue mackerels, indicating that the specificity of the multiplex assay is applicable to field samples to measure the presence of the two closely related species separately. The methods are useful to evaluate the eDNA samples collected from the open water in the North Pacific to elucidate the life cycles and monitor the sustainability of the small pelagic fishes, which not only are important food sources, but also carry a role in the Japanese food culture.

Spatio-temporal diet variability of the California sea lion Zalophus californianus in the southern California Current Ecosystem

Characterizing predator diets is essential to understanding food web dynamics. We investigated the dietary breadth and variation of the California sea lion (CSL) Zalophus californianus at 3 of the California Channel Islands from 1981-2015. Prey species were identified from hard parts and soft-tissue remains of pyrosomes recovered from fecal samples, revealing a diverse diet of fish and cephalopods. Percent frequency of occurrence and percent split-sample frequency of occurrence were used to describe long-term trends, correlations between prey taxa, diet diversity, and diet similarity. The most common of 142 prey taxa identified to species were market squid Doryteuthis opalescens, northern anchovy Engraulis mordax, shortbelly rockfish Sebastes jordani, jack mackerel Trachurus symmetricus, Pacific sardine Sardinops sagax, Pacific hake Merluccius productus, and Pacific mackerel Scomber japonicus. Dietary differences were observed between male and female sea lions, and between animals from different islands and seasons. Intra-island diets at 2 locations were more similar than inter-island diets. Important inter-annual and decadal changes in diet were identified. CSL diet shifted from an anchovy-based diet in the 1980s to a market squid based-diet in the 1990s and 2000s, with other prey taxa being consumed more frequently when consumption of those 2 main prey declined. Prey-switching likely provides flexibility needed in the dynamic California Current Ecosystem, and may allow CSLs to adapt to changes in food supply and availability driven by climate change.

Reproduction of the Blue Jack Mackerel, Trachurus picturatus, in Western Portugal: Microscopic Gonad Analysis Reveals Indeterminate Fecundity and Skipped Spawning Patterns.

Blue jack mackerel, Trachurus picturatus, is the fifth most landed fish species in mainland Portugal, but information on its reproductive biology is scarce. From September 2018 to August 2019, 626 specimens were collected from commercial vessels to clarify the reproductive strategy of the T. picturatus population off the west coast of Portugal. The proportion and length range of males and females were similar. Only three of the specimens collected were categorized as immature, indicating that the fish caught in the fishery are primarily mature. The spawning season lasted from late January until the end of March, with gonadosomatic indices being similar for males and females. Fecundity was indeterminate, and estimated batch fecundity ranged between 6,798 (at 25.4 cm TL) and 302,358 oocytes (at 33.8 cm TL). The low number of females showing direct evidence of imminent or recent spawning suggests a low number of spawning events. In addition, 12.7% of females were considered non-reproductive due to ovary abnormalities including parasitic infection by Kudoa species, atretic structures and skipped spawning events. This study highlights the importance of accounting for skipped spawning events and ovary abnormalities in the management of species fisheries.

Regional variations in growth of Jack mackerel Trachurus japonicus in the waters off the Pacific coast of Japan

Regional variations in growth of Jack mackerel <i>Trachurus japonicus</i> in the waters off the Pacific coast of Japan

Temperature strongly correlates with regional patterns of body size variation in Mediterranean small pelagic fish species

In this study, we consider the applicability of Bergmann’s rule to the populations of small pelagic fish species in the Mediterranean Sea. Under Bergmann’s rule, body size increases with decreasing temperature and increasing latitude. Although this macroecological pattern in body sizes is well established for many taxa of endotherms and ectotherms, it remains not universal and the proposed mechanisms underlying it are multiple and still lack consensus. We explored here the occurrence of geographical body size clines using measurements of average body sizes of 10 species collected in pelagic trawl hauls carried out during acoustic surveys in the Mediterranean Sea. Bergmann’s rule was evaluated by correlating body sizes with latitude and temperature for each species while accounting for potential confounding variables and sampling bias. For 5 species, namely anchovy, sardine, Atlantic chub mackerel, bogue, and blue jack mackerel, we demonstrate that they follow a Bergmann’s rule, with a decline in average body size by about 3.01, 3.43, 3.67, 3.82, and 3.76 % per 1°C of warming respectively, although this did not translate with an increase in size with latitude. The adherence of these 5 pelagic fish to Bergmann’s rules strongly suggests that temperature is a major determinant of their body sizes and enables them to act as sentinel species for identifying the drivers and consequences of warming in the Mediterranean ecosystems.

Concurrent habitat fluctuations of two economically important marine species in the Southeast Pacific Ocean off Chile in relation to ENSO perturbations

AbstractENSO‐driven concurrent habitat fluctuations of two economically important marine species jumbo squid Dosidicus gigas and jack mackerel Trachurus murphyi in the Southeast Pacific Ocean off Chile during 1950–2017 were examined using a habitat suitability index (HSI) modeling approach. The optimal HSI models sourced from 10 weighing‐based scenarios were developed, selected and validated using the crucial factors water temperature at 400 m depth (Temp_400m), sea surface height anomaly (SSHA) and sea surface salinity (SSS) for D. gigas and sea surface temperature (SST), Temp_400m, and mixed layer depth (MLD) for T. murphyi. Results suggested that the optimal HSI model could accurately predict the habitat hotspots for D. gigas and T. murphyi. The ENSO event (indicated by Niño 3.4 index, NI) was significantly related to environmental conditions off Chile. Cross‐correlation revealed positive relationships between NI and SST, SSHA, SSS, and Temp_400m and negative correlation between NI and MLD. Synchronous opposite habitat fluctuations were shown between D. gigas and T. murphyi under different ENSO events. The NI was significantly negatively related to the HSI of D. gigas and positively correlated with the HSI of T. murphyi. Comparing with the El Niño years, suitable habitats of D. gigas and T. murphyi dramatically enlarged and contracted, respectively, during the La Niña years. Both suitable habitats moved southwestward under this climate conditions. Our finding suggested that ENSO‐driven environmental changes played important roles in the concurrent habitat fluctuations of D. gigas and T. murphyi. Such studies are conducive to the effective utilization and management of multiple related species.

Relationships between environmental variables and spatial and temporal distribution of jack mackerel (Trachurus japonicus) in the Beibu Gulf, South China Sea.

The jack mackerel (Trachurus japonicus) is both a dominant pelagic fish species and an important fishing target in the Beibu Gulf, South China Sea. However, the resource status of this species fluctuates dramatically, and it has recently been added to a “red list” of threatened species of the International Union for Conservation of Nature (IUCN). Despite its economic importance and decreasing population status, limited research on its spatiotemporal distribution has been undertaken over the last decades. In order to evaluate the most crucial factors that influence the spatiotemporal variability of T. japonicus and to determine GAM performance and predictability, we analyze catch per unit effort (CPUE) of T. japonicus from Beibu Gulf over four seasons (months) from 2013 to 2014. A generalized additive model (GAMs) is populated with water depth and remotely sensed sea surface temperature (SST), sea surface salinity (SSS), sea surface chlorophyll-a concentration (Chl-a) and sea level anomaly (SLA). The CPUE of T. japonicus varies seasonally, with higher CPUE in summer and autumn than in spring and winter, and the highest CPUE in summer. GAM results explain 57% of the deviation explained in CPUE, with the most important variables being SLA, Month, Depth, SSS, and SST , each explaining 21.2%, 18.7%, 10.7%, 5.1%, and 1.3% of the variation in CPUE, respectively. This species occurs mainly between 50 and 75 m depth, SSS values 32.3–33.5 PSU and SST 25–30.5 °C. High CPUE sites occur near SLA ≤ 0 m, on the edge of cold eddies, and there is a certain catch near the sea surface with SLA ≥ 0 m. The spatial and temporal distribution of T. japonicus is affected by the season and the marine hydrological environment. This study might contribute to a better understanding of the distributional patterns of T. japonicus as well as provide a basis for sustainable management in the Beibu Gulf.

Thinking of Fish Population Discrimination: Population Average Phenotype vs. Population Phenotypes

The genetic polymorphism and phenotypic variation are key in ecology and evolution. The morphological variability of the contour of fish otoliths has been extensively used for the delimitation of stocks. These studies are conventionally based on average phenotype using elliptic Fourier analysis and lineal discriminant analysis as classifier. Considering new analytical options, such as the wavelet transform and non-parametric algorithms, we here analyzed the otolith shape ofTrachurus picturatus(blue jack mackerel) from mainland Portugal, Madeira, and the Canaries. We explore the phenotypic variation throughout a latitudinal gradient, establish a hypothesis to explain this variability based on the reaction norms, and determine how the use of average phenotype and/or morphotypes influences in the delimitation of stocks. Four morphotypes were identified in all regions, with an increase of phenotypes in warmer waters. The findings demonstrated that stocks were clearly separated with classification rates over 90%. The use of morphotypes, revealed seasonal variations in their frequencies and per region. The presence of shared phenotypes in different proportions among fishing grounds may open new management approaches in migratory species. These results show the importance of the phenotypic diversity in fisheries management.

Universal performance of benzalkonium chloride for the preservation of environmental DNA in seawater samples

AbstractEnvironmental DNA (eDNA) analysis allows noninvasive and cost‐effective monitoring of macroorganisms' distribution and composition in aquatic ecosystems. Benzalkonium chloride (BAC) is an inexpensive and simple preservative for eDNA in water samples and has been used in many eDNA studies for preventing its degradation during transportation. However, its preservation performance has limitedly been evaluated by species‐specific assays, targeting short fragments of mitochondrial DNA in freshwater and brackish ecosystems. Here, we examined the performance of BAC in preserving eDNA in seawater samples, targeting different fragment lengths of mitochondrial and nuclear eDNA, and community information inferred by eDNA metabarcoding. We quantified the time series changes of Japanese jack mackerel (Trachurus japonicus) eDNA concentrations in experimental tanks and inshore seawater to compare the yields and decay rates of eDNA between BAC treatments. For both tank and field samples, BAC treatment substantially suppressed the degradation of all types of target eDNA and increased the eDNA yields at the start of the experiment. In addition, we performed eDNA metabarcoding targeting fish community to compare the species richness and composition in seawater samples between BAC treatments, showing that the number of fish species in field samples hardly varied throughout a day by BAC treatment. Our findings indicate high versatility of BAC in preserving both the quantitative (copy number) and the qualitative (species richness) information on various types of aqueous eDNA in various environmental conditions. BAC should therefore be used to minimize the false‐negative detection of eDNA, regardless of target genetic regions, fragment sizes, environmental conditions, and detection strategies.

Linking environmental drivers, juvenile growth, and recruitment for Japanese jack mackerel Trachurus japonicus in the Sea of Japan

AbstractGrowth traits of juvenile Japanese jack mackerel (Trachurus japonicus) were estimated based on otolith daily increments in spring during 2011–2016 in the southwestern part of the Sea of Japan (SWSJ). Spatial variability in growth traits was examined between the western and eastern areas of the study area. Back‐calculated body length at 50 days post hatch varied among areas and years between 26 and 40 mm. Body lengths at age in the eastern area were significantly smaller than those in the western area. Slower growth rate in the eastern area was associated with the lower ambient temperature in the eastern area than in the western area. In the eastern area, interannual variations in the instantaneous growth rate positively correlated with ambient temperature. Furthermore, interannual variations in back‐calculated body length during the late larval and early juvenile stages positively correlated with the juvenile abundance. These results suggest that the thermal conditions in the eastern area are indicative of the growth rate and abundance of juvenile T. japonicus in SWSJ. We further examined relationships between juvenile abundance and thermal conditions during 2003–2019 using archived data of this survey and found that the ambient temperature in the eastern area positively correlated with the juvenile abundance and also the strength of the Tsushima Warm Current. Thus, higher temperatures derived from the Tsushima Warm Current result in a faster growth rate during the late larval and early juvenile stages and subsequently higher abundance of T. japonicus juveniles in SWSJ.

Fish allergy tolerance 16 months after diagnosis.

Fish allergy is generally thought to be persistent, and approximately 80% of patients with fish allergies do not develop tolerance even 10 years after diagnosis. There have been no reports of rapid tolerance development in patients with severe fish allergies. We report the development of tolerance 16 months after the diagnosis of fish allergies. A 13-month-old boy was diagnosed with rosefish allergy (Sebastes matsubarae) and Japanese jack mackerel allergy (Trachurus japonicus). To find out which species of fish he could consume safely, he underwent several oral food challenge (OFC) tests. It was determined that he could consume tuna, salmon, cod, sardine, chub mackerel (Scomber japonicus), and Japanese amberjack (Seriola quinqueradiata) without eliciting signs of allergy. He continued to eat the fish that did not produce allergic reactions three to four times a week. The titer of serum allergen-specific immunoglobulin E (IgE) to fish had decreased in a subsequent ImmunoCAP®-specific IgE blood test performed 16 months after the diagnosis of the rosefish allergy. Following this test result, he underwent OFCs with rosefish and Japanese jack mackerel, both of which turned out to be negative, and it was determined that he had developed tolerance to fish. In this case, the repeated OFCs were useful in identifying fish species that were safe for consumption. In addition, the decrease in allergen-specific IgE was useful in predicting the development of tolerance. We hypothesize that proactive consumption of available fish species may lead to this rapid induction of tolerance to fish allergens.

Dietary inclusion effect of various levels of jack mackerel meal on the growth performance, feed efficiency and whole body composition of rockfish (Sebastes schlegeli)

Inclusion effect of various levels of jack mackerel meal (JMM) acting as feed attractants and/or stimulants in diets on the growth, feed consumption, feed utilization and whole body composition of rockfish was investigated. Three hundred juvenile rockfish were randomly allocated into 15 flow-through tanks. Five experimental diets supplemented with JMM at 0%, 1%, 3%, 5%, and 10% at the expense of anchovy meal were prepared and referred to as the JMM0, JMM1, JMM3, JMM5, and JMM10 diets, respectively. Weight gain, specific growth rate (SGR) and feed consumption of fish tended to improve with dietary levels of JMM. The greatest weight gain, SGR and feed consumption were observed in fish fed the JMM10 diet, followed by the JMM5, JMM3, JMM1, and JMM0 diets, in that order. Condition factor (CF) of fish tended to improve with dietary inclusion levels of JMM. Growth performance, feed consumption and CF of fish tended to improve with dietary inclusion levels of JMM ranging from 0% to 10%.

Environmental DNA preserved in marine sediment for detecting jellyfish blooms after a tsunami

Environmental DNA (eDNA) can be a powerful tool for detecting the distribution and abundance of target species. This study aimed to test the longevity of eDNA in marine sediment through a tank experiment and to use this information to reconstruct past faunal occurrence. In the tank experiment, juvenile jack mackerel (Trachurus japonicus) were kept in flow-through tanks with marine sediment for two weeks. Water and sediment samples from the tanks were collected after the removal of fish. In the field trial, sediment cores were collected in Moune Bay, northeast Japan, where unusual blooms of jellyfish (Aurelia sp.) occurred after a tsunami. The samples were analyzed by layers to detect the eDNA of jellyfish. The tank experiment revealed that after fish were removed, eDNA was not present in the water the next day, or subsequently, whereas eDNA was detectable in the sediment for 12 months. In the sediment core samples, jellyfish eDNA was detected at high concentrations above the layer with the highest content of polycyclic aromatic hydrocarbons, reflecting tsunami-induced oil spills. Thus, marine sediment eDNA preserves a record of target species for at least one year and can be used to reconstruct past faunal occurrence.

Using otolith chronologies to identify extrinsic drivers of growth of 2 commercially targeted small pelagic fish species

Climate variability is a major cause of changes in marine ecosystems, including changes in both the environment and in many fish species. Understanding the factors influencing key biological characteristics, such as growth, is important for commercially targeted species because these characteristics are used in stock assessments that inform fisheries management. In this study, otoliths were used to examine the growth rates and growth chronologies of 2 commercially targeted small pelagic fish species, the common jack mackerel (Trachurus declivis) and redbait (Emmelichthys nitidus), from 2 regions of southeastern Australia. Both species grew larger off Kangaroo Island (common jack mackerel: asymptotic length [L∞]=299.40; redbait: L∞=259.79) than off southern New South Wales (common jack mackerel: L∞=249.52; redbait: L∞=238.89). Temporal growth synchrony in both species and regions (0.17–3.50%) was low compared with that of more-site-attached benthic species. Interannual variations in growth rates of common jack mackerel off Kangaroo Island were positively correlated with sea-surface temperature (SST), with growth rates 18% higher at 18.0°C than at 16.4°C. However, growth was not correlated with SST or chlorophyll-a concentration for the other species and locations. Developing a more complete understanding of the environmental drivers of growth in these small pelagic fish species may require chronologies to be extended and extrinsic variables in the models to be increased.

Interannual variations in diet of Japanese jack mackerel (Trachurus japonicus) juveniles in the southwestern Sea of Japan in relation to recent growth rate

AbstractWe examined interannual variations in the diet of Trachurus japonicus juveniles in relation to prey density and recent 5‐day instantaneous growth rate (IGR) in the southwestern part of the Sea of Japan (SJ) in late spring during 2011–2013. Habitat temperature of juveniles in 2011 was lower than the other 2 years. In all 3 years, more than 97% of juveniles had food in the stomach. Small juveniles &lt;35‐mm standard length (SL) fed mainly on adult female Paracalanus parvus s.l., the most dominant calanoid copepod in the water column, without a significant interannual difference. In 2011 and 2012, large juveniles ≥35‐mm SL predated heavily upon adult female Calanus sinicus which form a high‐energy food for the juveniles. In contrast, in 2013, the large juveniles preyed on a large number of a variety of small‐sized prey items, such as P. parvus s.l., euchaetid copepods, and ostracods. In 2011 when the feeding condition was considered to be favorable, but the habitat temperature was lowest, the IGR of large juveniles was markedly lower than in the other 2 years. Meanwhile, there was no significant difference in the IGR between 2012 and 2013 when the diet composition was markedly different, but habitat temperature was comparable. The present observations indicate that the between‐year difference in juvenile IGR was not explained well by variations in the diet composition. Instead, habitat temperature was concluded to be the more dominant factor causing the observed between‐year differences in the IGR in the southwestern SJ.

Improved Raman spectroscopy-based approach to assess microplastics in seafood

Microplastics represent an emerging environmental issue and have been found almost everywhere including seafood, raising a great concern about the ecological and human health risks they pose. This study addressed the common technical challenges in the assessment of microplastics in seafood by developing an improved protocol based on Raman spectroscopy and using the green-lipped mussel Perna viridis and the Japanese jack mackerel Trachurus japonicus as the test models. Our findings identified a type of stainless-steel filter membranes with minimal Raman interference, and a combination of chemicals that achieved 99–100% digestion efficiency for both organic and inorganic biomass. This combined chemical treatment reached 90–100% recovery rates for seven types of microplastics, on which the surface modification was considered negligible and did not affect the accuracy of polymer identification based on Raman spectra, which showed 94–99% similarity to corresponding untreated microplastics. The developed extraction method for microplastics was further combined with an automated Raman mapping approach, from which our results confirmed the presence of microplastics in P. viridis and T. japonicus collected from Hong Kong waters. Identified microplastics included polypropylene, polyethylene, polystyrene and poly(ethylene terephthalate), mainly in the form of fragments and fibres. Our protocol is applicable to other biological samples, and provides an improved alternative to streamline the workflow of microplastic analysis for routine monitoring purposes.

Individual growth in Jack mackerel (Trachurus murphyi) of the Southeastern Pacific Ocean using sagitta otolith weight, daily rings, and annual rings

We estimated the growth of Jack mackerel (Trachurus murphyi) using increments of daily growth, otolith weight and annual ring reading in sagittal otoliths. The daily micro-increments were used to fit ring density to the otolith radius (n = 4481) and then to estimate the age of the individual in days. The parameters of the von Bertalannfy growth equation were: maximum theoretical fork length, FL∞ = 75 cm; individual growth coefficient, K = 0.16 year-1; theoretical age at which fish length is zero, t0= –0.19 years. The growth parameters of T. murphyi estimated using annual rings reading were: K = 0.10 year-1, FL∞ = 74.7 cm, t0 = –0.50 years. The growth parameters estimated using otolith weight were: K = 0.15 year-1, FL∞ = 75.0 cm, t0 = –0.48 years. The parameter K estimated with the daily micro-increments was similar to the K estimated using sagittal otolith weights. We constructed a size-age key for T. murphyi using otolith weight, OW (milligrams) as a variable was: OW= 0.0323*t-15.197 (r2= 0.68). We recommend using otolith weight to estimate age in T. murphyi due to this technique is statistically reliable, but also cheap and fast.

Diet and trophic position of two mackerel species in the archipelago of Madeira, Portugal

The Atlantic chub mackerel Scomber colias and the blue jack mackerel Trachurus picturatus are two abundant species in the Macaronesia region which includes the archipelago of Madeira, Portugal. Both are key species in the trophic web, being important prey for several local top predators, such as seabirds and marine mammals. Nonetheless, little is known about their feeding ecology in oceanic environments. In this study, the authors describe the seasonal variation in the diet of S. colias and T. picturatus in the oceanic region of Madeira throughout a year. Visual inspection of stomach contents revealed that S. colias fed on a broader range of prey groups than T. picturatus, but for both species, zooplankton (particularly calanoid copepods) and fish were the most important food items. The diet of S. colias included a higher proportion of fish, namely Atlantic saury Scomberesox saurus and S. colias, than that of T. picturatus, that included mostly the longspine snipefish Macroramphosus scolopax. T. picturatus consumed a higher proportion of decapods and other copepods. Seasonal variation was found in the diet of both species, with zooplanktonic species being more important in colder months (February to April) for S. colias and during warm months (May to October) for T. picturatus. Their diet in other seasons was dominated by fish. Although they consume similar prey, carbon and nitrogen stable isotope analysis of muscle of S. colias and T. picturatus showed little overlap in their diets, and T. picturatus showed higher δ15 N and a narrower isotopic niche.

First target strength measurement of Trachurus mediterraneus and Scomber colias in the Mediterranean Sea

Knowing the species-specific target strength (TS) allows converting volume backscattering strength to numerical abundance. Since the acoustic surveys conducted for biomass assessment in the Mediterranean Sea currently focus on the echoes of two or three target pelagic species, the TS of non-target species has seldom been investigated in this basin. This is the first study of the TS of two pelagic species – Mediterranean horse mackerel (Trachurus mediterraneus) and Atlantic chub mackerel (Scomber colias) – in the Mediterranean Sea. A pilot approach using tethered live fish but not involving hooks and anesthetic was tested in experiments using a split-beam scientific echosounder operating at 38, 120, and 200 kHz. The mean TS was estimated for 29 live fish. The relationship between TS and fish length was determined with a standard linear regression model; the b20 conversion parameter was obtained with the slope forced to 20. b20 was computed at all frequencies for both species. The key values at 38 kHz were −71.4 dB for T. mediterraneus and −71.6 dB for S. colias. Although these results differ from those obtained with in situ and ex situ experiments using Pacific chub mackerel and other species of the genus Trachurus, they have the potential to provide new reference values for T. mediterraneus and S. colias biomass assessment in the Mediterranean Sea. The proposed method removes some potential biases due to the unnatural behavior of anesthetized fish. Moreover, it provides an alternative to hooks, although the use of a piece of rope instead of the hook seems to increase the acoustic reflectivity of the tethering apparatus.

Feeding Habits of the Jack Mackerel Trachurus japonicus in the Southern Sea of the Republic of Korea

Feeding Habits of the Jack Mackerel Trachurus japonicus in the Southern Sea of the Republic of Korea