Atlantic Mackerel Scomber Scombrus Research Articles

Variation in energy density of northwest Atlantic forage species: Ontogenetic, seasonal, annual, and spatial patterns

AbstractObjectiveEnergy density (ED) estimates for marine forage species have been limited, impeding our understanding of this important trophic level. We studied the EDs of eight key forage species: Alewife Alosa pseudoharengus, Atlantic Herring Clupea harengus, Silver Hake Merluccius bilinearis, Northern Sand Lance Ammodytes dubius, Atlantic Mackerel Scomber scombrus, Butterfish Peprilus triacanthus, northern shortfin squid Illex illecebrosus, and longfin inshore squid Doryteuthis pealeii (also known as Loligo pealeii).MethodsSamples were obtained during spring and fall bottom trawl surveys across five regions (Gulf of Maine, Georges Bank, southern New England, northern Middle Atlantic Bight, and southern Middle Atlantic Bight) from 2017 to 2019. In the laboratory, we developed predictive relations between the percent dry weight (%DW) and ED (kJ/g wet weight) determined by proximate composition analysis (n = 606; r2 = 0.76–0.98) to estimate the ED of additional samples (n = 4583). For each species, we modeled ED as a function of size, depth, season, and year (as factors) as well as location (latitude, longitude) using generalized additive models (GAMs).ResultAlewife, Atlantic Herring, Northern Sand Lance, Atlantic Mackerel, and Butterfish were classified as high‐quality prey (ED > 6 kJ/g), although Atlantic Herring ED was nearly half the values reported in earlier studies. Silver Hake, northern shortfin squid, and longfin inshore squid were classified as moderate‐quality prey (4 kJ/g < ED < 6 kJ/g). Most species had higher EDs in the fall following summer feeding than in the spring after spawning and/or reduced winter feeding. The best‐fitting GAMs included weight, depth (by season), season, and year effects for most species. Location (by season) explained significant amounts of variation.ConclusionObserved variation in ED across regions, species, seasons, and years provides the empirical data necessary to consider hypotheses related to “upstream” regulation of ED (via environmental drivers and productivity) and “downstream” effects on recruitment for these forage species as well the species that prey on them.

Detection of different Betanodavirus genotypes in wild fish from Spanish Atlantic coastal waters (Galicia, northwestern Spain).

The nervous necrosis virus (NNV; genus Betanodavirus) is an aquatic pathogen that is responsible for a neurological disease affecting marine fish. Despite its almost worldwide distribution, global warming could favor the spread of NNV to new areas, highlighting the importance of conducting epidemiological surveys on both wild and farmed marine fish species. In this study, we assessed NNV prevalence in wild fish caught along the Galician Atlantic coast. In total, 1277 fish were analyzed by reverse transcription real-time polymerase chain reaction. Twenty two (1.72%) of those fish tested positive for NNV, including two species in which the pathogen had not yet been reported. The reassortant RGNNV/SJNNV (red-spotted grouper NNV/striped jack NNV) was detected in 55% of NNV-positive individuals, while the remaining 45% harbored the SJNNV-type genome. Moreover, from European Pilchard Sardina pilchardus and Atlantic Mackerel Scomber scombrus, we isolated four reassortant strains that carried amino acid mutations at key sites related to NNV-host interaction.

Forage Fish Species Prefer Habitat within Designated Offshore Wind Energy Areas in the U.S. Northeast Shelf Ecosystem

AbstractAs the world develops sources of renewable energy, there is an intensifying interest in offshore wind energy production. The Northeast U.S. Continental Shelf (NES) ecosystem has favorable wind dynamics, with active development of wind energy. In this study, we present species distribution models that consider both occupancy and biomass responses for a broad spectrum of fish and macroinvertebrate taxa (n = 177). Building upon prior analyses, habitat was differentiated into overall and core habitats based on statistical distributions of habitat scores. Overall habitat was used to show each species' regional distribution based on fishery‐independent survey captures between 1976 and 2019, whereas core habitat represented where the focus of the species' abundance was located as a subset of overall habitat. Wind energy developments may modify the water column in ways that impact lower‐trophic‐level productivity; therefore, added attention was given to the response of forage species. Over 20% of species showed preferential use of putative and potential wind development areas, including a disproportionate number of forage taxa. Principal usage varied by season, with forage species like Atlantic Menhaden Brevoortia tyrannus and Atlantic Mackerel Scomber scombrus preferentially using the lease areas in spring and Round Herring Etrumeus teres and longfin inshore squid Doryteuthis pealeii using lease areas in autumn. For species with relatively low usage of the lease areas, there was a tendency for the usage related to overall habitat to be lower than usage for core habitat; in contrast, for species with high usage of the lease areas, that usage was higher for overall habitat than for core habitat. The area of habitat tended to have positive trends across species, with these positive trends being disproportionately higher among forage taxa. These results frame the importance of wind lease areas for species in the NES, particularly forage taxa that fulfill many important ecological functions.

Trophic ecology of northern gannets Morus bassanus highlights the extent of isotopic niche overlap with other apex predators within the Bay of Biscay

Understanding the linkages within complex and evolving marine food webs is essential to comprehend marine ecosystem structure and dynamics. Carbon (δ13C) and nitrogen (δ15N) stable isotope signatures are recognized to be powerful descriptors of the trophic ecology and trophic relationships within marine communities. Apex predators such as seabirds can influence the structure of communities by predating in lower trophic levels. They also convey information both over a range of spatial and temporal scales due to their high mobility and longevity, respectively. For this reason, here, we studied the trophic ecology of northern gannets and the extent of niche overlap with other apex predators within the Bay of Biscay (North-East Atlantic), a key feeding area for numerous predatory species. Mixing models indicated that northern gannets fed primarily on European anchovy Engraulis encrasicolus and on a mixed group composed of European sardine Sardina pilchardus, European sprat Sprattus sprattus, juvenile hake Merluccius merluccius, Atlantic mackerel Scomber scombrus and Atlantic horse mackerel Trachurus trachurus. Within the apex predator community, the northern gannets trophic niche overlapped the most with common guillemots Uria aalge (15.58%, based on Stable Isotope Bayesian Ellipses (SIBER)) and overlapped to a lesser extent with cetacean species occupying shelf habitats (i.e., the harbour porpoise Phocoena phocoena (9.99%) and the short-beaked common dolphin Delphinus delphis (10.37%)). Overall, the overlap found was moderate indicating trophic similarities and dissimilarities between these species. Information on trophic interactions between co-existing species is necessary for holistic environmental management, particularly in areas where several megafauna species share their foraging grounds with fisheries activity.

Distribution of Kudoa thyrsites (Cnidaria, Myxozoa) myoliquefactive stages in Northeast Atlantic mackerel (Scomber scombrus) inferred from qPCR and histology

Kudoa thyrsites is a myxosporean parasite (Cnidaria, Myxozoa) that infects the skeletal and cardiac muscle of Northeast Atlantic (NEA) mackerel (Scomber scombrus). Heavy infections are associated with post-mortem myoliquefaction of the host skeletal muscle which reduces the quality of the fish product. The biological infection characteristics of the parasite in NEA mackerel are poorly known. This study examined the distribution of K. thyrsites in various organs of NEA mackerel from the northern North Sea, and elucidates the relationship between density of infection, developmental stage and parasite distribution in the musculature, and the extent of visible flesh myoliquefaction. Quantitative polymerase chain reaction (qPCR) data showed that K. thyrsites is unevenly distributed in the somatic musculature of the fish host, with highest density in the anterior ventral muscle sections—the belly flaps. A weak positive correlation was observed between the level of myoliquefaction and the parasite density in the fish host muscle. This relationship was also reflected by the amount and distribution of parasite developmental stages seen during histological examinations. Histological findings indicate an association between the dispersion of free myxospores and the level of myoliquefaction of the fish host muscle. Visceral organs were also found infected using qPCR, although at lower densities compared to the musculature.

Prevalence of Kudoa thyrsites (Myxozoa, Multivalvulida) in Atlantic Mackerel, Scomber scombrus L., in the Vicinity of the Faroe Islands

Atlantic mackerel Scomber scombrus is an important migratory fish in Faroese waters and the Northeast Atlantic at large. Similar to other fish species from marine environments, mackerel can be infected by the myxozoan parasite Kudoa thyrsites, leading to myoliquefaction that renders the fish commercially unviable. Despite the ecological and economic significance of K. thyrsites as a parasite, little is known regarding its prevalence in the Faroese mackerel fishery. Prior to analysing field samples, we examined 104 samples of Atlantic mackerel selected from a Faroese processing plant on the basis of visible soft-tissue. Using microscope smears we observed K. thyrsites in 98% of the soft-tissue mackerel specimens and a direct comparison with qPCR demonstrated strong agreement between the two techniques (Φ = 0.429, p<0.01; Fisher’s exact test). We used qPCR to analyze a total of 594 Atlantic mackerel specimens, collected from Faroese fishing grounds during 2017 and 2018. Overall prevalence was 4.1% (95% confidence interval; 2.5-5.7%) and ranged from 0-14% at different locations. Infection by K. thyrsites was documented in fish as young as 2 years (195g) and up to 14 years (615g) of age. A logistic regression model indicated the odds of infection were statistically associated with sampling location and month, but not gender, age, weight or length, although a Chi-squared test on age categories showed the oldest fish (>10 years) had highest prevalence (10.8%, CI: 4.2-17.5%). In order to investigate potential infection pathways we performed qPCR analysis on eDNA in water samples collected from the Faroese Plateau. However, we found no molecular evidence for K. thyrsites spores in Faroese plankton assemblages. Our data support the prevailing hypothesis that both the alternating invertebrate host and infection of Atlantic mackerel by K. thyrsites occurs in more southern waters.

First thorough assessment of de novo oocyte recruitment in a teleost serial spawner, the Northeast Atlantic mackerel (Scomber scombrus) case

The understanding of teleost fecundity type (determinate or indeterminate) is essential when deciding which egg production method should be applied to ultimately estimate spawning stock biomass. The fecundity type is, however, unknown or controversial for several commercial stocks, including the Northeast Atlantic mackerel (Scomber scombrus). Aiming at solving this problem, we applied state-of-the-art laboratory methods to document the mackerel fecundity type, including any de novo oocyte recruitment during spawning. Initially, active mackerel spawning females were precisely classified according to their spawning status. The number and size of all phasei-specific oocytes (12 phases), with a special attention to previtellogenic oocytes phases (PVO [PVO2 to PVO4a–c]), were also thoroughly investigated. Examinations of relative fecundity (RFi) clarified that the latest phase of PVOs (PVO4c) are de novo recruited to the cortical alveoli–vitellogenic pool during the spawning period, resulting in a dome-shaped seasonal pattern in RFi. Hence, we unequivocally classify mackerel as a true indeterminate spawner. As PVO4c oocytes were currently identified around 230 µm, mackerel fecundity counts should rather use this diameter as the lower threshold instead of historically 185 µm. Any use of a too low threshold value in this context will inevitably lead to an overestimation of RFi and thereby underestimated spawning stock biomass.

Multi-decadal trends in contingent mixing of Atlantic mackerel (Scomber scombrus) in the Northwest Atlantic from otolith stable isotopes

The Atlantic mackerel (Scomber scombrus) in the Northwest Atlantic is comprised of northern and southern components that have distinct spawning sites off Canada (northern contingent) and the US (southern contingent), and seasonally overlap in US fished regions. Thus, assessment and management of this population can be sensitive to levels of mixing between contingents, which remain unknown. Multi-decadal trends in contingent mixing levels within the US fisheries region were assessed, and the contingent composition across seasons, locations, ages, and size classes were characterized using archived otoliths and developing a classification baseline based on juvenile otolith carbon and oxygen stable isotopes (δ13C/δ18O values). Classification of age ≥ 2 adults demonstrated that northern contingent mixing was prevalent within the US continental shelf waters during the past 2 decades (2000–2019), providing an important seasonal subsidy to the US winter fishery despite substantial depletion in spawning stock biomass of the dominant northern contingent. While the majority of older fish were of the northern contingent during the early 2000s, the southern contingent contribution increased with age/size class during the recent period (2013–2019). Spatial mixing was most prevalent during February and March when the northern contingent occurred as far south as the Delmarva Peninsula, but were mostly absent from US waters in May. A positive relationship (albeit not significant; r = 0.60, p = 0.07) occurred between northern contingent mixing and US fisheries landings, which could imply that higher contingent mixing levels might be associated with greater landings for the US winter mackerel fishery. The yield of the Northwest Atlantic mackerel depends upon the status of the northern contingent, with the southern contingent possibly more prone to depletion. Spatially explicit stock assessment models are recommended to conserve both productivity and stability in this two-component population.

Effect of Rosemary on Stabilization of Proteins during Frozen Storage of Mackerel (Scomber scombrus)

ABSTRACT The effect of rosemary extract (Rosmarinus officinalis L) as an antioxidant on the quality of Atlantic mackerel (Scomber scombrus) fillets stored at −30°C for nine months was studied. Results showed that immersion in rosemary extract prior to frozen storage decreased the oxidative reactions in lipids and peroxide value (PV) and thiobarbituric acid (TBARS) as well as in proteins. For proteins, the most distinct changes were observed in the myofibrillar proteins, and carbonyls were found to be the most affected parameter. Formation of carbonyls increased significantly in fillets without rosemary extract, while carbonyl content in fillets immersed in rosemary extract remained stable.

Evidence of post-larval growth-selective mortality in Atlantic mackerel revealed by the collection of young-of-the-year juveniles ingested by the northern gannet

The growth-survival paradigm predicts that year-class strength is determined by growth-dependent mortality during the larval stage. In Atlantic mackerel Scomber scombrus, the possibility that strong growth-dependent mortality extends into the early juvenile stage has not previously been tested because of the difficulty in sampling young-of-the-year (YOY) juveniles. The present study determined the timing of the ‘endpoint’ during the early ontogeny, when growth-selective mortality decreases and recruitment is set. We relied on regurgitations from one of the main predators of mackerel, the northern gannet Morus bassanus, as a source of YOY juveniles. Early growth trajectories of YOY mackerel were reconstructed from the otolith microstructure and were compared to those of 1-yr-old (OYO) juveniles from the same cohort for the year classes of 2015 and 2017. In both cohorts, the early growth trajectory of OYO fish was faster than that of YOY juveniles, indicating that growth-selective mortality extended beyond the larval stage. For the 2017 cohort, the comparison of larval growth trajectories between 2-mo-old YOY, 3mo-old YOY and OYO juveniles indicated that strong selection for fast growth persisted until the pre-wintering period, but that winter mortality likely did not play an important role in shaping year-class strength. These findings suggest that in Atlantic mackerel, the endpoint when the relative strength of cohorts is fixed occurs at the age of 3 mo. These results highlight the importance of considering growth-dependent mortality processes occurring beyond the larval stage to obtain a better understanding of causes of recruitment variability.

Mercury intake via consumption of imported Atlantic mackerel (Scomber scombrus) in Istanbul

The aims of this study were to determine the concentrations of mercury (Hg) in frozen imported Atlantic mackerel consumed in Istanbul and to predict their potential health consequences. In this study, the concentration of Hg was determined following US EPA Method 7473 (2007) using a direct mercury analyzer (DMA-1). Mercury level of the Atlantic mackerel ranged between 0.045 to 0.065 mg/kg. The mercury levels were well below the limit value of 1.00 mg/kg wet weight (EC, 2006; Turkish Food Codex, 2011) for fish such as mackerel. The potential human health risks of Atlantic mackerel sold in Istanbul were also assessed in terms of Hg levels. The estimated weekly intakes (EWI) of the mercury were lower than established provisional tolerable weekly intakes (PTWI). Target hazard quotient (THQ) values were below 1, indicating that Atlantic mackerel consumption is not a potential health risk in adults and children. According to the amount of Hg, this fish can be consumed safely 3 times a week. Furthermore, it is determined that consumption of fish from the IV. Region 4 times a week will not be a problem because of the low amount of Hg. Our results provide a good tool to determine the Hg exposure of Turkish consumers (adult and children) via Atlantic mackerel consumption in terms of food monitoring and food safety.

The Potential to Improve the Sustainability of Pelagic Fisheries in the Northeast Atlantic by Incorporating Individual Fish Behavior Into Acoustic Sampling

With increased uncertainty due to climate change and fishing pressure, accurate estimates of fish populations are essential for global ecological and economic health. Acoustic surveys are an efficient way to determine population size for pelagic species in the Northeast Atlantic (NEA), but still contain uncertainty and are difficult for some species. For example, Atlantic mackerel (Scomber scombrus), one of the most valuable fisheries in the NEA, is not monitored acoustically, as mackerel lack the swim bladder that provides the strongest acoustic echo (target strength) at common assessment frequencies. For all pelagic species behavior is a source of variation in acoustic measurements and therefore in population estimates. Behavior is mediated by both extrinsic and intrinsic factors, such as the environment and the life history of the fish. In turn, behavior affects the density of the shoal and the tilt angle of the fish relative to the survey vessel, affecting their target strength, which affects the biomass estimate. Some fish may also undergo an anti-predator response to survey vessels, changing their behavior in response to the survey. Understanding these behaviors and incorporating them into acoustic stock assessment methods can improve the accuracy of population estimates. Individual-based models (IBM) of fish shoals provide a pathway for incorporating behavior into acoustic methods. IBMs have been used extensively to build theoretical models of fish shoals, but few have been successfully tested in lab or field conditions. As computational power and monitoring technology improve, modelling the collective behavior of pelagic fishes will be possible. Novel, interdisciplinary approaches to data collection and analysis will help translate theoretical IBMs to the fisheries science domain. Beyond acoustic stock assessments, this approach can be used to investigate knowledge gaps in the effects of fisheries-induced evolution and the potential for range shifts under climate change. Further work to synthesize existing models and incorporate field data will help determine how environmental, ecological, physiological, and anthropogenic factors, often affecting both behavior and acoustic surveying, are interconnected. Moving from theoretical models to practical applications will be a valuable tool in tackling the uncertainty that accompanies further fisheries exploitation and warming oceans.

Reproductive biology of the Atlantic mackerel Scomber scombrus Linnaeus, 1758 in Mediterranean coast of Sinai, Egypt.

This work aims to investigate reproductive biology of the Atlantic mackerel (Scomber scombrus L. 1758) to provide biological base for management of its fisheries in the Mediterranean coast of Sinai, Egypt. Monthly samples of S. scombrus were collected from the commercial catch in different landing sites of the Mediterranean coast of Sinai during 2019. The length-weight relation was found as W= 0.0116 L2.9556, W= 0.0077 L3.091 and W= 0.0094 L3.022715 for males, females and combined sexes respectively. Overall sex ratio (males: females) was 1: 1.4 during the period of study.  Gonado- Somatic Index (GSI) of females showed that S. scombrus spawn during March, April and May, since GSI peaked in these months (6.5, 7.2 and 5.2 % respectively). The lowest value of GSI of females was recorded in October (0.05%). Lengths at first sexual maturity (Lm) were determined as 23.2 and 23.4 cm for males and females respectively. The absolute fecundity (F) was increasing with the fish length and described by a power equation: F = 0.0014 L5.6414. The relative fecundity gradually increased from 2481.8 to 7599.3 eggs per cm (average 4748.9 eggs / cm). To protect and maintain the stock of Atlantic mackerel in the Mediterranean coast of Sinai, it is recommended to ban using fishing nets of illegal mesh sizes and other destructive fishing methods which catch small fish sizes. Length at first capture should be larger than length at first sexual maturity (> 23.4 cm) and ban fishing nets targeting S. scombrus during its spawning season (from March to May).

Performance of Two Survey Gears Targeting Elasmobranchs in a Shallow, Subtropical Estuary

AbstractFishery‐independent surveys have become increasingly prevalent in recent decades for monitoring the population trends of highly mobile species like elasmobranchs (sharks and rays). Despite the utility of gear evaluations for streamlining costs and increasing the efficiency of fishery‐independent surveys, these assessments are sparse for elasmobranch‐specific surveys. Catch data were examined from a fishery‐independent longline and gill‐net survey that targeted elasmobranchs in Florida's southern Indian River Lagoon from July 2016 to September 2018. The goal of the study was to assess the effects of the type of longline bait that is used (Striped Mullet Mugil cephalus versus Atlantic Mackerel Scomber scombrus) and the size of gill‐net mesh (15.2‐ versus 20.3‐cm stretch mesh) on the species composition, catch per unit effort (CPUE), and size distribution of captured elasmobranchs. Elasmobranchs were caught more often in the gill net than on the longline. Striped Mullet yielded a significantly higher CPUE of elasmobranchs than Atlantic Mackerel did. Although Striped Mullet caught more sharks than Atlantic Mackerel did, the mean length of the sharks did not differ between groups that were captured with the two bait types. Species composition differed with respect to bait type; significantly more Bull Sharks Carcharhinus leucas and Atlantic Sharpnose Sharks Rhizoprionodon terraenovae were caught with Striped Mullet. Elasmobranch abundances were similar between the two sizes of gill‐net mesh. However, species composition differed, with a greater abundance of both Atlantic Stingrays Hypanus sabinus and Bull Sharks caught in the 15.2‐cm mesh. Elasmobranchs that were caught in the 20.3‐cm mesh were significantly larger than those caught in the 15.2‐cm mesh. The length distributions for the common species (Bull Sharks, Atlantic Stingrays, and Bluntnose Stingrays H. say) differed significantly with respect to the two mesh sizes. This study is the first assessment of a standardized elasmobranch‐specific survey in this nationally significant estuary and increases our understanding of the performance of complementary gear types for targeting sharks and rays in a shallow lagoonal system.

APPLICATION OF SMOKED PREPARATIONS IN MODERN TECHNOLOGY OF SMOKED FISH PRODUCTION

The article is devoted to the actual problem of creating of new types of smoked fish products. The article discusses the modern technologies of production of smoked fish products, shows that the development of smoked sausages from ocean fish is a promising trend in the fishing industry. The analysis of sausage casings used for sausage production is carried out. Polyamide shells have been shown to have several advantages over both natural (from intestinal raw materials of slaughtered animals) and artificial (from collagen skins of slaughtered animals or cellulose). These advantages are high barrier, elasticity, mechanical strength, biological inertia, gas- and moisture-proof, heat resistance. As a result, the shelf life of the finished product is significantly extended (for some products more than 60 days). Skimmed fillet of Atlantic mackerel Scomber scombrus was selected as the main raw material for the production of sausages. The choice of this type of fish based on good organoleptic properties, high biological value, large industrial reserves, relatively low price and a long tradition of using in smoked products. Information on the chemical composition and basic properties of a wide range of smoke preparations available on the market has been collected. It is shown that, notwithstanding the availability of a wide range of preparations on the market, which are manufactured in different countries of the world, none of them has the properties inherent to the traditional smoke. Smoke EZ PN 9, manufactured by Red Arrow, USA, is very close to them. For this reason, it was used in our work. The dose of the preparation was 2 g per 1 kg of minced fish.The technology of production of smoked sausages was developed, which includes the following operations: obtaining of frozen blocks of skimmed mackerel fillet, inspection of blocks, defrosting of blocks, grinding of fillet, salting the minced fish, aging in salting, stirring with smoking preparation, forming of sausages, thermal processing of sausages in water, cooling of sausages in water, subsequent cooling with air, storage of sausages.The obtained products are characterized by high organoleptic characteristics, microbiological indicators are within the normal limits for 14 days of storage, which allows us to recommend the developed technology.

О регистрации атлантической скумбрии Scomber scombrus Linnaeus, 1758 (Scombridae) в прибрежной зоне Севастополя и о перспективах возрождения её промысла

Приведены сведения о поимке атлантической скумбрии Scomber scombrus Linnaeus, 1758 — вида, ставшего очень редким в последние 50 лет для Чёрного моря. Несколько экземпляров обнаружены в период с 7 по 15 июня 2018 г. в уловах промысловых ставных неводов в нижней части Балаклавской бухты и в прибрежной зоне недалеко от бухты. Одна особь была передана авторам для изучения; результаты морфометрических и биологических исследований этой особи приведены в работе. Кратко рассмотрены особенности ареала атлантической скумбрии, а также распространения и биологии четырёх основных популяций вида, обитающих в европейских водах, при этом основное внимание уделено черноморской. Приведены сведения об уровне современного промысла вида в мире в целом и отдельно в Турецкой Республике. Сделан ретроспективный анализ вылова скумбрии в Чёрном море, в частности возле побережья Крыма. Рассмотрены причины полного исчезновения её черноморской популяции в конце 1960-х гг. в Чёрном и Мраморном морях. Хотя единичные случаи поимки скумбрии у берегов Крыма, Северного Кавказа и Турции участились, сделан вывод, что черноморская популяция либо полностью исчезла, либо находится в очень угнетённом состоянии; возрождение её промыслового потенциала малоперспективно. На основе анализа приведённого материала сделано предварительное заключение, что выловленный в районе Севастополя экземпляр может относиться к средиземноморской популяции атлантической скумбрии.

Investigation Some Biological Properties of Atlantic Mackerel Scomber scombrus Linnaeus, 1758 in the Sea of Marmara

In this study, length-frequency, length-weight and length-length relationships and condition factors of Atlantic mackerel Scomber scombrus Linnaeus, 1758 were investigated. In 2016, a total of 163 individuals were examined by random sampling from commercial fishermen in the Sea of Marmara. It was determined that the total length distribution of the samples varied between 12.0-27.0 cm. The length-weight relationships were calculated as W=0.0040L3.2975 (r2=0.978) for females, W=0.0045L3.2537 (r2=0.973) for males and W=0.0042L3.2782 (r2=0.976) for all specimens. The t-test showed that the growth pattern was positive for all sex groups and for all samples (b˃3, P<0.05). The relationship between length-length for all sex groups was also found to be quite strong (mean value: r2=0.94; P<0.05). Fulton’s condition factor (K) was calculated as 0.938±0.11 for females, 0.909±0.10 for males and 0.947±0.09 for all samples. The sex ratio (F:M) of the population was found to be 1:0.94

Morphological and molecular identification of a new Kudoa thyrsites isolate in Mediterranean silver scabbardfish Lepidopus caudatus.

Myxozoans of the genus Kudoa (Myxosporea, Multivalvulida) infect marine and estuarine fish species worldwide. Some Kudoa species are of concern to the seafood industry since they may generate macroscopic cysts in the fish host's musculature, or cause post mortem myoliquefaction, commonly known as 'soft flesh'. One of the economically most important species is K. thyrsites, a myoliquefactive myxosporean parasite that occurs in many wild and cultured marine fish species worldwide. Here we identified a K. thyrsites isolate as the causative agent of myoliquefaction in silver scabbardfish Lepidopus caudatus from the Alboran Sea (western Mediterranean Sea). For comparative and validation purposes, the morphological and molecular characteristics of the isolate were compared with fresh spores of a K. thyrsites isolate infecting Atlantic mackerel Scomber scombrus from the Norwegian Sea. Myxospores of both isolates shared a stellate appearance and contained 4 unequal pyriform polar capsules (1 large, 1 small and 2 intermediate). These morphological traits were consistent with all other previously described K. thyrsites isolates. Moreover, the small subunit rDNA sequences of the Mediterranean and Norwegian Sea isolates revealed 100% similarity, and matched 100% with K. thyrsites isolates previously recorded in myoliquefactive Atlantic mackerel from the North Sea and off southern England. The findings suggest that K. thyrsites is the primary cause of myoliquefaction in silver scabbardfish from the Alboran Sea. This report represents the first morphological and molecular characterization of K. thyrsites in the Mediterranean Sea. A set of new allometric characters is proposed as additional descriptors for more accurate and specific description of kudoid myxospores.

Feeding dynamics of Northwest Atlantic small pelagic fishes

Small pelagic fishes represent a critical link between zooplankton and large predators. Yet, the taxonomic resolution of the diets of these important fishes is often limited, especially in the Northwest Atlantic. We examined the diets, along with stable isotope signatures, of five dominant small pelagic species of the northeast US continental shelf ecosystem (Atlantic mackerel Scomber scombrus, Atlantic herring Clupea harengus, alewife Alosa pseudoharengus, blueback herring Alosa aestivalis, and Atlantic butterfish Peprilus triacanthus). Diet analyses revealed strong seasonal differences in most species. Small pelagic fishes predominantly consumed Calanus copepods, small copepod genera (Pseudocalanus/Paracalanus/Clausocalanus), and Centropages copepods in the spring, with appendicularians also important by number for most species. Krill, primarily Meganyctiphanes norvegica, and hyperiid amphipods of the genera Hyperia and Parathemisto were common in the stomach contents of four of the five species in the fall, with hyperiids common in the stomach contents of butterfish in both seasons and krill common in the stomach contents of alewife in both seasons. Depth and region were also found to be sources of variability in the diets of Atlantic mackerel, Atlantic herring, and alewife (region but not depth) with krill being more often in the diet of alewife in more northerly locations, primarily the Gulf of Maine. Stable isotope data corroborate the seasonal differences in diet but overlap of isotopic niche space contrasts that of dietary overlap, highlighting the differences in the two methods. Overall, the seasonal variability and consumer-specific diets of small pelagic fishes are important for understanding how changes in the zooplankton community could influence higher trophic levels.

Feeding Interactions between Fishes in a Coastal Ecosystem in the Southern Gulf of St. Lawrence, Atlantic Canada

AbstractDiet composition, diet similarity, and major predator–prey interactions between the 15 most abundant demersal and pelagic fishes (N = 12,163 stomachs) during the period 1999–2003 were described for Northumberland Strait, a semi‐enclosed, marine coastal ecosystem. Of the five pelagic species, Rainbow Smelt Osmerus mordax ate benthic prey (shrimps and polychaetes); Atlantic Herring Clupea harengus and American Shad Alosa sapidissima consumed small copepods and crab zoeae; and Atlantic Mackerel Scomber scombrus and Alewives Alosa pseudoharengus ate small copepods and moderate amounts of benthic prey and small fishes. Three demersal species were strongly piscivorous but with minimal diet overlap: Sea Ravens Hemitripterus americanus consumed small benthic fishes (especially flounders); Winter Skate Leucoraja ocellata consumed sand lances Ammodytes sp. and Rainbow Smelt; and White Hake Urophycis tenuis consumed Atlantic Herring and Atlantic Mackerel. Cluster analysis revealed seven feeding guilds, of which four contained a single species; consequently, the potential for compensation of predatory function was nonexistent for these guilds. The three multispecies guilds comprised consumers of (1) small copepods and crab zoeae; (2) small benthic invertebrates and polychaetes; and (3) shrimps and crabs. Based on diets, the principal route of energy transfer seemed to be the benthic–detrital pathway; however, confirmation requires representative abundance estimates for the various fishes. Moreover, abundances of many fish species have changed (i.e., most have decreased) since this study was completed, with unknown consequences for food web structure and functioning.