Atlantic Herring Clupea Harengus Research Articles

Completing the picture: using vertebrae as well as otoliths in diet analysis reveals new preferred prey of great skuas

Knowledge of the diet of marine predators such as seabirds is fundamental to understanding the ecological cascades they may influence and the impact that environmental changes may have on them. Diet analysis of seabirds frequently relies on the identification of fish otoliths in pellets. However, it is recognised that the true dietary importance of fish with small and fragile otoliths is likely underestimated, requiring an additional method. In this study, we compared the identification of otoliths with that of vertebrae in pellets to gain a more complete picture of seabird diet. We identified fish otoliths and vertebrae from 2584 great skua Stercorarius skua pellets collected between 2014 and 2017 from five colonies in Scotland. Diet varied markedly between colonies, comprising mostly fish in Shetland and mostly birds in St Kilda. 10% of pellets contained otoliths compared to 70% with fish vertebrae. Atlantic herring Clupea harengus and Atlantic mackerel Scomber scombrus were the most common fish species at all colonies when using vertebrae in contrast to being virtually absent when using otoliths. Conversely, the occurrence of Norway pout Trisopterus esmarkii and pollock Pollachius pollachius otoliths was six and eight times, respectively, higher than for vertebrae. Therefore, combining data from both otoliths and vertebrae provides a more complete profile of the fish component of seabird diet. This is fundamental to improving our understanding of the impacts of marine management policies on seabirds, as well as how changes in the population size of such seabird species might affect their prey species.

Location and elimination of Anisakis simplex third stage larvae in Atlantic herring Clupea harengus L

We here describe the location of anisakid third stage larvae in Atlantic herring Clupea harengus L. caught in the North Sea in August 2023. We further demonstrate how industrial processing (mechanical gutting, removal of entrails, head, tail, hypaxial anterior musculature and vertebral column) reduces the overall infection and worm load in the musculature. The isolated anisakid larvae were identified as Anisakis simplex sensu stricto by a combination of morphometrics and molecular methods (PCR of rDNA and mtDNA, sequencing, BLAST analysis). As a baseline we examined a total of 75 specimens of freshly caught and ungutted herring and showed a positive correlation between host size (fish length and weight) and infection level. The overall prevalence of infection was 84 %, the mean intensity 11.3 (range 1–38 parasites per fish) and the abundance 9.52. The main part of the overall worm population was associated with stomach and pyloric caeca in the body cavity (77 %) and only 5 % was found in the musculature. Larvae occurred in the hypaxial part of the musculature (21), the epaxial part (7 worms) and the caudal part (5 worms). The prevalence of muscle infection was 28 % and the mean intensity 1.6 (range 1–5) parasites per fish and abundance 0.44 parasites per fish. In order to assess the effect of industrial processing on worm occurrence in the fish we examined a total of 67 specimens of herring, from exactly the same batch, but following processing. This included removal of organs in the body cavity, cutting the lower part of the hypaxial segment but leaving the right and left musculature connected by dorsal connective tissue. Five out of these fish carried one larva (prevalence 7.5%, mean intensity 1, abundance 0.07 larvae per fish), and these worms were located in the ventral part of the anterior musculature (2), in the central part of the anterior musculature (2) and one larva in the central part of the caudal musculature. The industrial processing reduced the overall occurrence (abundance) of worms in the fish from 9.52 to 0.07 (136 times reduction) and the occurrence in the musculature from 0.44 to 0.07 (6.28 times reduction). The overall prevalence was reduced from 84 % to 7.5 % (11.2 times reduction). Muscle infection prevalence fell from 28 % to 7.5 % (3.7 times reduction). We then followed another batch of herring following a marinating process (11% NaCl for 24 h and subsequent incubation in acetic acid and vinegar) by artificially digesting the flaps during week 1–8. Although a total of 31 larvae were recovered from 144 fish examined no live nematode larvae were isolated. The importance of fish handling, processing and marination for consumer safety is discussed.

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.

Chick diet in UK Little Terns Sternula albifrons

ABSTRACT Capsule We studied the diet of Little Tern chicks in the UK using new data collected as part of the EU LIFE-funded Little Tern Recovery Project (2014–2018) (the LIFE Project), which shows that, despite a wide variety of prey items being recorded, diet at UK colonies is dominated by two types of lipid-rich marine fish: sandeel Ammodytes spp. and clupeid species (Atlantic Herring Clupea harengus and European Sprat Sprattus sprattus). Aims To analyse data on the diet of Little Tern chicks from the LIFE Project and assess what additional insight these provide in comparison to the findings in previous literature. Methods Timed chick-feeding observations were made at 12 English and Welsh Little Tern colonies between 2014 and 2018 and compared to descriptions of chick diet from other UK studies (published and unpublished). Results Chick diet data from the LIFE Project were dominated by lipid-rich marine fish, principally sandeels and clupeid species (82% of all recorded prey items). Adult Little Terns feeding chicks with crustaceans or other invertebrates were recorded at 75% of colonies, but there was no evidence that these routinely made up a substantial proportion of chick diet. We found no significant inter-annual differences in diet composition between individual colonies. However, analysis of records of chick diet over a longer time series (Long Nanny colony in Northumberland, with data available for 17 of the years between 1998 and 2018) showed some significant differences in diet composition between years. Conclusion Although Little Terns are generalist feeders, 82% of the prey diet consisted of two prey types: sandeels and clupeids. This may leave existing UK Little Tern colonies vulnerable to any future climate change impacts affecting either the distribution or nutritional quality of their main prey species.

The Role of Fishery‐Independent Bottom Trawl Surveys in Providing Regional and Temporal Context to Offshore Wind Farm Monitoring Studies

AbstractBottom trawl surveys are commonly used to examine potential effects on fishes and invertebrates from offshore wind (OSW) farms in Europe and in the northeastern United States. Because OSW surveys typically occur over a limited spatial footprint, comparison of OSW monitoring results to long‐term fishery‐independent surveys may provide a regional and temporal context for OSW data sets. We compared results of the Block Island Wind Farm (BIWF) bottom trawl survey (2013–2019) to three fishery‐independent bottom trawl surveys (Northeast Area Monitoring and Assessment Program, Northeast Fisheries Science Center, and Rhode Island Department of Environmental Management [RIDEM]) using catch rates of 12 federally managed species. We evaluated temporal trends in annual residual catches for each species calculated within each survey as the difference between the mean annual biomass per trawl and the long‐term mean. Regional consistency in relative catches was apparent for species exhibiting synchronous interannual variability among surveys (Black Sea Bass Centropristis striata, Scup Stenotomus chrysops, Summer Flounder Paralichthys dentatus, and Winter Flounder Pseudopleuronectes americanus) or a decreasing trend in residual catch rates across the 7‐year study period (Little Skate Leucoraja erinacea, longfin inshore squid Doryteuthis pealeii, and Winter Skate L. ocellata). For other species, catches among surveys were asynchronous (Atlantic Herring Clupea harengus, Butterfish Peprilus triacanthus, and Windowpane Scophthalmus aquosus) or anomalous catches in a single year affected the results (Red Hake Urophycis chuss and Silver Hake Merluccius bilinearis). Monitoring of BIWF occurred during a period with lower‐than‐average historical catches in a 32‐year RIDEM data set for Atlantic Herring, Butterfish, Little Skate, longfin inshore squid, Red Hake, Silver Hake, and Winter Flounder and higher‐than‐average catches for Black Sea Bass, Scup, and Summer Flounder. There was no evidence that variation in catches near BIWF differed from regional trends in a way consistent with a detrimental impact of OSW farm operation. The regional context provided from multiple bottom trawl surveys varies by species and thus may be limited for interpreting OSW monitoring results.

Postcranial skeletal development of the Atlantic herring (Clupeomorpha: Clupeidae: Clupeaharengus)

The Atlantic herring Clupea harengus is a small pelagic schooling fish belonging to the Clupeiformes. It constitutes a key species for fisheries and marine ecosystems of the Northern hemisphere. Due to its key importance for fishery several studies refer to the larval development of C. harengus and aim to further understand its reproductive biology. However, not much is known about the skeletal development of herring larvae. This study describes the axial skeleton development of Western Baltic herring. Cartilage and bone formation were traced by clearing and double staining herring larvae with a size spectrum of 6–35 mm. During the yolk-sac phase, the caudal fin starts to differentiate. Then, in the next phase the dorsal fin develops, followed by notochord flexion and anal fin formation. After a phase of pelvic fin development, the transition to the juvenile fish starts. The development of herring is compared to other clupeiforms, especially Alosa sapidissima, Engraulis japonicus and Sardinops melanostictus, for which information was available, and to previous research on herring larvae.

Ocean Acidification Alters the Predator – Prey Relationship Between Hydrozoa and Fish Larvae

Anthropogenic CO2 emissions cause a drop in seawater pH and shift the inorganic carbon speciation. Collectively, the term ocean acidification (OA) summarizes these changes. Few studies have examined OA effects on predatory plankton, e.g. Hydrozoa and fish larvae as well as their interaction in complex natural communities. Because Hydrozoa can seriously compete with and prey on other higher-level predators such as fish, changes in their abundances may have significant consequences for marine food webs and ecosystem services. To investigate the interaction between Hydrozoa and fish larvae influenced by OA, we enclosed a natural plankton community in Raunefjord, Norway, for 53 days in eight ≈ 58 m³ pelagic mesocosms. CO2 levels in four mesocosms were increased to ≈ 2000 µatm pCO2, whereas the other four served as untreated controls. We studied OA-induced changes at the top of the food web by following ≈2000 larvae of Atlantic herring (Clupea harengus) hatched inside each mesocosm during the first week of the experiment, and a Hydrozoa population that had already established inside the mesocosms. Under OA, we detected 20% higher abundance of hydromedusae staged jellyfish, but 25% lower biomass. At the same time, survival rates of Atlantic herring larvae were higher under OA (control pCO2: 0.1%, high pCO2: 1.7%) in the final phase of the study. These results indicate that a decrease in predation pressure shortly after hatch likely shaped higher herring larvae survival, when hydromedusae abundance was lower in the OA treatment compared to control conditions. We conclude that indirect food-web mediated OA effects drove the observed changes in the Hydrozoa – fish relationship, based on significant changes in the phyto-, micro-, and mesoplankton community under high pCO2. Ultimately, the observed immediate consequences of these changes for fish larvae survival and the balance of the Hydrozoa – fish larvae predator – prey relationship has important implications for the functioning of oceanic food webs.

Atlantic herring (Clupea harengus) population structure in the Northeast Atlantic Ocean

The Atlantic herring Clupea harengus L has a vast geographical distribution and a complex population structure with a few very large migratory units and many small local populations. Each population has its own spawning ground and/or time, thereby maintaining their genetic integrity. Several herring populations migrate between common feeding grounds and over-wintering areas resulting in frequent mixing of populations. Thus, many herring fisheries are based on mixed populations of different demographic status. In order to avoid overexploitation of weak populations and to conserve biodiversity, understanding the population structure and population mixing is important for maintaining biologically sustainable herring fisheries. The aim of this study was to investigate the genetic population structure of herring in the Faroese and surrounding waters, and to develop genetic markers for distinguishing between four herring management units (often called stocks), namely the Norwegian spring-spawning herring (NSSH), Icelandic summer-spawning herring (ISSH), North Sea autumn-spawning herring (NSAH), and Faroese autumn-spawning herring (FASH). Herring from the four stocks were sequenced at low coverage, and single nucleotide polymorphisms (SNPs) were called and used for population structure analysis and individual assignment. An ancestry-informative SNP panel with 118 SNPs was developed and tested on 240 individuals. The results showed that all four stocks appeared to be genetically differentiated populations, but at lower levels of differentiation between FASH and ISSH than the other two populations. Overall assignment rate with the SNP panel was 80.7%, and agreement between the genetic and traditional visual assignment was 75.5%. The NSAH and NSSH samples had the highest assignment rate (100% and 98.3%, respectively) and highest agreement between traditional and genetic assignment methods (96.6% and 94.9%, respectively). The FASH and ISSH samples had substantially lower assignment rates (72.9% and 51.7%, respectively) and agreement between traditional and genetic methods (39.5% and 48.4%, respectively)

Combined Use of Otolith Morphometry and Microchemistry to Study the Origin of Spring‐Spawning Atlantic Herring in the St. Lawrence Estuary and the Gulf of St. Lawrence

AbstractAn important goal for the conservation of marine fish metapopulations is to maintain the diversity of components spawning in areas subjected to different environmental pressures. The usefulness of otolith morphometry combined with microchemistry to generate new information on the diversity of spawning components was assessed in declining spring‐spawning Atlantic Herring Clupea harengus in the St. Lawrence Estuary (SLE), Restigouche Estuary and adjacent areas (RE), and southern and northern Gulf of St. Lawrence (SGSL and NGSL). Mature Atlantic Herring (6–10 years old) were captured during the spring spawning season from 2013 to 2015 at nine sites with different salinity and temperature conditions along estuarine–marine and southern–northern gradients. Otoliths were measured by image analysis, and various shape indices were calculated. Elemental concentrations (Sr, Ba, and Mg) in the otolith cores were measured using laser ablation inductively coupled plasma mass spectrometry. Natal groups were inferred by hierarchical clustering analysis conducted on shape and microchemical variables separately or combined. Both types of analysis indicated the presence of two main natal groups: one predominant in the SLE and the other predominant in the RE. Proportions of fish having the characteristics of each natal source decreased with increasing distances from the head of the SLE and RE, respectively. Shape analysis provided higher discrimination in the SLE/NGSL, revealing temporal stability of a specific “pygmy” morphotype in the SLE that was previously described in the 1980s and 1990s. Microchemical analysis was more discriminating in the RE/SGSL, revealing a group of fish within the RE that had low Sr in the otolith core. Thus, otolith morphometry and microchemistry provided concordant and complementary information on natal groups, and both markers indicated the potential importance of estuaries as nursery grounds for the recovery of spring‐spawning Atlantic Herring stocks in the SGSL and NGSL.

Existence in the actin world of a specialized slow skeletal muscle isoform.

1) Teleosts such as Atlantic salmon Salmo salar and Atlantic herring Clupea harengus , in contrast to other vertebrates such as mammals, synthesize two contextually very different skeletal muscle actins. Each isoform has been studied at the protein level. One isoform accounts for the total actin in the lighter ‘fast’ trunk muscle. Based on closest pairings - two amino acid substitutions (salmon vs. herring) and four substitutions (salmon or herring vs. mammal or bird) - it is classified as ‘fast’ skeletal actin. The other isoform accounts for the total actin in the darker ‘slow’ muscle in the lateral line and represents a specialized slow skeletal muscle actin which is an unrecognized isotype. 2) Atlantic salmon and Atlantic herring also synthesize a cardiac actin that is distinct to the skeletal actins in 1). Intraspecies pairings of fast skeletal actin and cardiac actin have two amino acid substitutions. Conversely, those involving slow skeletal actin have 12 or 13, which is a contextual record. 3) The Salmonidae skeletal actins in 2) differ at residues 2, 3, 103, 155, 165, 278, 281, 310, 329, 358, 360 and 363 (numbering system for mature protein of 375 amino acids). The changes are restricted to subdomains 1 and 3 and have affected the net charge at pH 7, polarity and glycine content. Six can be considered non-conservative: Val103Thr (Val in ‘slow’, Thr in ‘fast’); Ala155Ser; Thr278Ala; Gly281Ser; Gly310Ala and Asp360Gln. The change at residue-360 provides a convenient means of detection via electrophoresis. Biochemical characterization of protein points to an advantageous function by which ‘slow’ actin contributes to the distinct physiology of the dark cruise muscle in the trunk. 4) Slow skeletal muscle actin (no more than two substitutions per pairing) is encoded in the genomes of the following families of Teleostei: Salmonidae, Clupeidae, Anguillidae; Cyprinidae; Esocidae; Ictaluridae; Osteoglossoidei and Serrasalmidae. However, many NCBI entry descriptions are confusing. The ‘slow’ actin group is expected to grow as more genomes are sequenced. 5) Slow skeletal actin genes display variable exon structure in the region encoding amino acids 44–151 (numbering system for 377 amino acids). The other exon-intron boundaries are conserved. In most cases to date, but not all, the ‘slow’ actin gene contains a greater number of exons than the ‘fast’ actin gene from the same species. 6) Slow skeletal actin falls into one of the new actin groups, namely epsilon which has representation in fish, reptile, bird and mammal. To date, only the protein products from Salmonidae and herring have been studied biochemically. • Atlantic salmonidae and herring synthesize slow skeletal, fast skeletal and cardiac muscle isoactins. • The distribution is specific; one isoform per muscle type. • The biochemical properties of slow skeletal actin confer an advantageous function on the dark cruise muscle in the trunk. • Slow skeletal actin is encoded in the genomes of more than a dozen other Teleosts. • Slow skeletal actin falls in the new actin group given the description ACT epsilon 1.

An evaluation of temporal changes in the trophic structure of Gulf of Maine ecosystem

The Gulf of Maine (GOM) ecosystem has experienced significant changes in the last few decades with a great increase in the American lobster Homarus americanus population and substantial reduction in some groundfish populations like Atlantic cod Gadus morhua. This study evaluated and compared the energy flows and trophic structures of the GOM ecosystem in the mid-2000s and mid-2010s. Following an early study, two mass-balance ecosystem models, each of which include 25 functional groups, were updated for the mid-2000s and mid-2010s using Ecopath. Fishing efforts were used as forcing drivers to simulate the variation of the GOM ecosystem in the mid-2000s to mid-2010s. Similar to the GOM ecosystem from the 1980s to 1990s found in a previous study, dominant species in both the mid-2000s and mid-2010s ecosystems were transferred from top predators to crustacean species in the last decade. However, food web structure of the GOM ecosystem became more complex, stable, and flexible to perturbations, indicating that the GOM ecosystem is moving toward a more mature stage. Simulation results indicated that fishing activities were considered to be the main driver to the variations dynamics of most species in the GOM ecosystem, while some species like Atlantic herring Clupea harengus might also suffer from changes in environmental conditions. This study provides a comprehensive overview on the changes in the GOM ecosystem in the last two decades.

ОБОСНОВАНИЕ СПОСОБА ПОСОЛА СЕЛЬДИ АТЛАНТИЧЕСКОЙ В УСЛОВИЯХ МАЛЫХ ПРОИЗВОДСТВ

In this paper, we offer technological solution to produce low-salted Atlantic herring (Clupea harengus) for small-business production. The method of salting in buckets consisted of two stages, including salting herring in saturated brine at a ratio of 70 (fish) : 30 (salting solution) and subsequent storage in isotonic solution. This allows speeding up the technological salting process by 2 times in comparison with the finished unsaturated method in an aqueous solution with 15% salt concentration. The possibility of secondary use of brine is shown. The shelf life of 14 days at (4 ± 2)oC was recorded for the low-salted products from Atlantic herring (C. harengus) with a mass fraction of salt (5 ± 0.5)% produced by an interrupted saturated salting method using secondary brine. The organoleptic parameters of salted Atlantic herring during the entire storage time corresponded to GOST 815 “salted herring”. Indicators that characterize the degree of maturation of salted herring, such as buffering and form-titrated nitrogen, were optimal. A technological scheme to produce low-salted herring using secondary brine and isotonic solution was developed. The proposed production technology allows to produce a high-quality low-salted product and is economically less expensive in comparison with the traditional salting method.

Introgressive Hybridization in the Secondary Contact Area of the Atlantic Herring Clupea harengus and the Pacific Herring C. pallasii (Clupeidae): Ecological Basis, Geographical Structure, and Temporal Variability of the Hybridization Zone

The geographical structure and dynamics of introgressive hybridization with Atlantic herring Clupea harengus were studied for the Pacific herring Clupea pallasii based on long-term monitoring of genetic variation of C. pallasii from the White, Barents, and Kara seas using multivariate statistical analysis procedures in the Structure and NewHybrids programs. An unequal level of introgression of the Atlantic herring’s genes have been reported for the population of the White Sea summer-spawning and spring-spawning herring as well as for the Chesha-Pechora herring. The factors involved in supporting the hybridization of herring species in the zone of their secondary contact were considered. The predominant role of hybridization and introgression of genes in the formation of intraspecific genetic diversity of the Pacific herring was revealed.

Using long and linked reads to improve an Atlantic herring (Clupea harengus) genome assembly

Atlantic herring (Clupea harengus) is one of the most abundant fish species in the world. It is an important economical and nutritional resource, as well as a crucial part of the North Atlantic ecosystem. In 2016, a draft herring genome assembly was published. Being a species of such importance, we sought to independently verify and potentially improve the herring genome assembly. We sequenced the herring genome generating paired-end, mate-pair, linked and long reads. Three assembly versions of the herring genome were generated based on a de novo assembly (A1), which was scaffolded using linked and long reads (A2) and then merged with the previously published assembly (A3). The resulting assemblies were compared using parameters describing the size, fragmentation, correctness, and completeness of the assemblies. Results showed that the A2 assembly was less fragmented, more complete and more correct than A1. A3 showed improvement in fragmentation and correctness compared with A2 and the published assembly but was slightly less complete than the published assembly. Thus, we here confirmed the previously published herring assembly, and made improvements by further scaffolding the assembly and removing low-quality sequences using linked and long reads and merging of assemblies.

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.

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

AbstractFor the period 1999–2003, diet composition, diet similarity, and major predator–prey interactions between the 15 most abundant demersal and pelagic fishes (N = 12,163 stomachs) were described for Northumberland Strait - a semienclosed, 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 zoea, and Atlantic Mackerel Scomber scombrus and Alewife A. 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 Raven Hemitripterus americanus consumed small benthic fishes (especially flounders); Winter Skate Leucoraja ocellatus consumed sand lance (Ammodytes sp.) and Rainbow Smelt; and White Hake Urophycis tenuis consumed Atlantic Herring and Atlantic Mackerel. Cluster analysis revealed seven feeding guilds of which fo...

Can collective memories shape fish distributions? A test, linking space‐time occurrence models and population demographics

Social learning can be fundamental to cohesive group living, and schooling fishes have proven ideal test subjects for recent work in this field. For many species, both demographic factors, and inter‐ (and intra‐) generational information exchange are considered vital ingredients in how movement decisions are reached. Yet key information is often missing on the spatial outcomes of such decisions, and questions concerning how migratory traditions are influenced by collective memory, density‐dependent and density‐independent processes remain open. To explore these issues, we focused on Atlantic herring Clupea harengus, a long‐lived, dense‐schooling species of high commercial importance, noted for its unpredictable shifts in winter distribution, and developed a series of Bayesian space‐time occurrence models to investigate wintering dynamics over 23 yr, using point‐referenced fishery and survey records from Icelandic waters. We included covariates reflecting local‐scale environmental factors, temporally‐lagged prey biomass and recent fishing activity, and through an index capturing distributional persistence over time, derived two proxies for spatial memory of past wintering sites. The previous winter's occurrence pattern was a strong predictor of the present pattern, its influence increasing with adult population size. Although the mechanistic underpinnings of this result remain uncertain, we suggest that a ‘wisdom of the crowd’ dynamic may be at play, by which navigational accuracy towards traditional wintering sites improves in larger and/or denser, better synchronized schools. Wintering herring also preferred warmer, fresher, moderately stratified waters of lower velocity, close to hotspots of summer zooplankton biomass, our results indicative of heightened environmental sensitivity in younger cohorts. Incorporating spatiotemporal correlation structure and time‐varying regression coefficients improved model performance, and validation tests on independent observations one‐year ahead illustrate the potential of uniting demographic information and non‐stationary models to quantify both the strength of collective memory in animal groups and its relevance for the spatial management of populations.

Microplastics in livers of European anchovies (Engraulis encrasicolus, L.)

Microplastics (MPs) are thought to be ingested by a wide range of marine organisms before being excreted. However, several studies in marine organisms from different taxa have shown that MPs and nanoplastics could be translocated in other organs. In this study, we investigated the presence of MPs in the livers of commercial zooplanktivorous fishes collected in the field. The study focuses mainly on the European anchovy Engraulis encrasicolus but concerns also the European pilchard Sardina pilchardus and the Atlantic herring Clupea harengus. Two complementary methodologies were used to attest the occurrence of MPs in the hepatic tissue and to exclude contamination. 1) MPs were isolated by degradation of the hepatic tissue. 2) Cryosections were made on the livers and observed in polarized light microscopy. Both methods separately revealed that MPs, mainly polyethylene (PE), were translocated into the livers of the three clupeid species. In anchovy, 80 per cent of livers contained relatively large MPs that ranged from 124 μm to 438 μm, showing a high level of contamination. Two translocation pathways are hypothesized: (i) large particles found in the liver resulted from the agglomeration of smaller pieces, and/or (ii) they simply pass through the intestinal barrier. Further studies are however required to understand the exact process.

Trends and Potential Drivers of Distribution Overlap of River Herring and Commercially Exploited Pelagic Marine Fishes on the Northeast U.S. Continental Shelf

AbstractConcern has been increasing over the impacts of incidental catches of river herring (Alewife Alosa pseudoharengus and Blueback Herring A. aestivalis) in commercial fisheries for Atlantic Herring Clupea harengus and Atlantic Mackerel Scomber scombrus, but historical information on mixed-species catches and their driving factors is lacking. We examined data from spring and fall bottom trawl surveys (National Oceanic and Atmospheric Administration, Northeast Fisheries Science Center) for temporal trends in overlap and potential ecosystem drivers of overlap trends. Species overlap changed substantially over time, with changes varying by season and region of the northeastern U.S. continental shelf. In the fall, changes in overlap were positively related to abundance in Georges Bank and southern New England. In the spring, most changes in species overlap were positively related to increasing species abundances. Positive relationships between overlap and abundance suggested that as species distributions ...