Whiting Merlangius Merlangus Research Articles

A gastric evacuation model for three predatory gadoids and implications of using pooled field data of stomach contents to estimate food rations

The general applicability of the square root model to describe gastric evacuation in predatory gadoids independently of meal size was verified through experiments on whiting Merlangius merlangus, saithe Pollachius virens and cod Gadus morhua fed different fish and crustacean prey. Gastric evacuation rate was related by a negative power function to energy density of fish prey over an extended range from 3·4 to 11·5 kJ g‐1 of the effector variable. Gastric evacuation of crustacean prey seemed to depend on the characteristics of their exoskeleton. Gastric evacuation of mixed meals composed of fish prey with different energy densities could be described as a function of the overall energy density. The evacuation rate of each of the prey could be described directly by their share of the stomach content. A full gastric evacuation model including predator size, temperature and prey energy density was established for whiting, saithe and cod. It was demonstrated that estimates of food rations might be severely biased by use of mean values for prey composition and total mass of stomach contents.

The regurgitation of stomach contents in trawl caught whiting, evidence of a predator size effect

The rate of regurgitation of food from the stomachs of trawl caught whiting Merlangius merlangus was negatively correlated with fish size. Increased musculature of the oesophageal sphincter in larger fish may enable them to resist the forced expulsion of their stomach contents to a greater extent.

The regurgitation of stomach contents in trawl caught whiting, evidence of a predator size effect

The rate of regurgitation of food from the stomachs of trawl caught whiting Merlangius merlangus was negatively correlated with fish size. Increased musculature of the oesophageal sphincter in larger fish may enable them to resist the forced expulsion of their stomach contents to a greater extent.

Seasonal variations in the energy density of fishes in the North Sea

The energy density (E D , kJ g -1 wet mass) of saithe Pollachius virens, haddock Melanogrammus aeglefinus, whiting Merlangius merlangus, Norway pout Trisopterus esmarki, herring Clupea harengus, sprat Sprattus sprattus, sandeel Ammodytes marinus and pearlsides Maurolicus Muelleri, from the North Sea, increased with total length, L T . However, there was not always a significant (P>0.05) linear relationship between L T and E D . Seasonal differences in E D were obvious in mature fish, while geographical differences were insignificant. For all species there was a highly significant correlation (P<0.0001) between the percent dry mass of the fish (D S ) and E D . A general relationship was established for gadoids and sandeel E D = - 3.1492+0.3459 D S and herring E D = 4.6395+0.4170 D S . Thus seasonal and size-specific data on E D needed for bioenergetics and gastric evacuation models can be determined simply from D S , which is considerably less costly and time consuming than calorimetry or proximate analysis.

Seasonal variations in the energy density of fishes in the North Sea

The energy density (ED, kJ g‐1 wet mass) of saithe Pollachius virens, haddock Melanogrammus aeglefinus, whiting Merlangius merlangus, Norway pout Trisopterus esmarki, herring Clupea harengus, sprat Sprattus sprattus, sandeel Ammodytes marinus and pearlsides Maurolicus Muelleri, from the North Sea, increased with total length, LT. However, there was not always a significant (P&gt;0·05) linear relationship between LT and ED. Seasonal differences in ED were obvious in mature fish, while geographical differences were insignificant. For all species there was a highly significant correlation (P&lt;0·0001) between the percent dry mass of the fish (DS) and ED. A general relationship was established for gadoids and sandeel ED=–3·1492+0·3459 DS and herring ED=–4·6395+0·4170 DS. Thus seasonal and size‐specific data on ED needed for bioenergetics and gastric evacuation models can be determined simply from DS, which is considerably less costly and time consuming than calorimetry or proximate analysis.

Ad hoc multispecies VPA tuning applied for the Baltic and North Sea fish stocks

Ad hoc multispecies tuning is a method for estimation of terminal fishing mortalities in multispecies virtual population analysis (VPA) using the existing single-species tuning packages. The method works by an iterative exchange of natural mortalities and terminal fishing mortalities between multispecies VPA and single species tuning modules, until equilibrium is obtained. Multispecies tuned assessment is compared with single species assessments using constant at-age natural mortality for the Baltic and the North Sea fish stocks. Correlation between estimated stock size and survey abundance indices is similar for tuned multi- or single species assessment. The tuned multispecies assessment gives, however, higher correlation coefficients for the North Sea whiting (Merlangius merlangus) and the Baltic Sea sprat (Sprattus sprattus), whilst the traditional single species assessment performed better for North Sea haddock (Melanogrammus aeglefinus) and herring (Clupea harengus). Tuned multispecies assessment performs best when there is a clear temporal trend in the estimated natural mortality whereas the correlation between estimated stock size and survey indices was not improved for species with highly variable natural mortalities. 2001 International Council for the Exploration of the Sea

Distribution of viral haemorrhagic septicaemia virus in wild fish species of the North Sea, north east Atlantic Ocean and Irish Sea.

A surveillance programme was initiated on the occurrence and distribution of viral haemorrhagic septicaemia virus (VHSV) in wild marine fish. Six research cruises were undertaken in an 18 mo period during 1997 and 1998, covering the North Sea, the Atlantic waters off the north and west coasts of Scotland and the Irish Sea. A total of 19,293 fish were sampled from 23 different species including cod, haddock, Norway pout, herring and sprat. Individual fish lengths were recorded and the fish were checked for lesions, haemorrhaging and other signs of disease. Pools of organ samples were taken for virus assay. The majority of fish sampled did not display clinical signs indicative of viral haemorrhagic septicaemia. A small number of cod were found with skin lesions and haddock with skin haemorrhaging. Of the 2081 organ and skin sample pools collected, 21 tested positive for VHSV by tissue culture and enzyme-linked immunosorbent assay. Seventeen of the isolates originated from Norway pout Trisopterus esmarkii, one from cod Gadus morhua (skin lesion), one from herring Clupea harengus, one from whiting Merlangius merlangus, and one from a previously unreported host species, poor cod Trisopterus minutus.

Changes in the demersal fish assemblages of British coastal waters during the 20th century

Catches of demersal fish from research vessel surveys in three areas around the British Isles from 1901 to 1907 were compared with survey catches in the same areas from 1989 to 1997. Mesh size and other characteristics of the trawls used suggested that some of these data were comparable, and could be used to describe changes in demersal fish assemblages over the last 80 years. In Start Bay (NW English Channel) and the Irish Sea, species diversity was the same in both periods, although the most abundant species in each period were not the same. In English coastal regions of the southern North Sea, fish populations became more diverse, as plaice Pleuronectes platessa and whiting Merlangius merlangus became less abundant, and the relative abundance of several non-target species such as dragonet Callionymus spp., bib Trisopterus luscus, and bull-rout Myoxocephalus scorpius increased. The proportion in the catch of small fish species (maximum body length 30 cm) in catches decreased in all regions during the time period, except in the Irish Sea where plaice replaced grey gurnard Eutrigla gurnardus as a dominant species. There was a decline in abundance of large sharks, skates and rays, including the common skate, Raja batis, white skate R. alba and the angel shark Squatina squatina. During historic surveys, 60% of the elasmobranch fauna consisted of thornback ray Raja clavata, whereas in contemporary surveys the lesser spotted dogfish Scyliorhinus canicula was the most abundant elasmobranch. Changes in length-frequency distribution of fish in both target and non-target categories, and other observed changes, were thought to be a response to commercial exploitation, and corresponded to similar observations recorded elsewhere. (C) 2000 British Crown Copyright.

Diet comparison between pelagic and demersal whiting in the North Sea

Pelagic North Sea whiting Merlangius merlangus preyed upon (pelagic) sprat and sandeel, while demersal whiting preyed upon (demersal) Norway pout and herring. Values of diet breadth were low for both feeding groups using Levin's index. Diet overlaps within layers were low (D &lt;0·25), while the between layer food overlap was moderate (D=0·25–0·74) to high (D &gt;0·74) using Schoener's index. Selection of prey was density dependent. However, prey size also played an important role. The diet of whiting shifted from amphipods and mysids to fish with increasing predator length, and the length of prey consumed increased significantly with length of whiting. The fact that the stomach contents differed between the feeding groups demonstrates the need for a sampling design that includes both pelagic and demersal habitats when trying to quantify the diet of whiting.

Isolation of viral haemorrhagic septicaemia virus (VHSV) from wild marine fish species in the Baltic Sea, Kattegat, Skagerrak and the North Sea

In order to analyse the occurrence of viral haemorrhagic septicaemia virus (VHSV) in the marine environment surrounding Denmark, fish tissue samples were collected on four cruises with the research vessel H/S Dana in 1996 and 1997. The sampling comprised 923 samples totalling 7344 fish representing 29 different species. VHSV was isolated from 24 fish samples from the Baltic Sea, four samples from Skagerrak and three samples from the North Sea. The virus-positive host species included herring Clupea harengus (11 isolates), sprat Sprattus sprattus (eight isolates), cod Gadus morhua (six isolates), rockling Rhinonemus cimbrius (one isolate), Norway pout Trisopterus esmarkii (one isolate), blue whiting Micromesistius poutassou (one isolate), whiting Merlangius merlangus (two isolates) and lesser argentine Argentina sphyraena (one isolate). VHSV has previously been reported from cod and herring, but not from the other five species. A virus belonging to serogroup II of the aquatic birnaviruses was isolated from three samples of flounder Platichthys flesus and three samples of dab Limanda limanda and a virus preliminary identified as iridovirus (lymphocystis virus) was isolated from seven samples of long rough dab Hippoglossoides platessoides.

Nematode infection in the whiting Merlangius merlangus euxinus off Turkish Coast of the Black Sea

The endoparasites of whiting, Merlangius merlangus euxinus from the Turkish Coast of the Black Sea were investigated during the years 1990–1993. Only the endoparasite, Hysterothylacium aduncum (Nematoda: Anisakidae) was recorded in all visceral organs examined. The prevalence and intensity of H. aduncum were significantly higher in the warm season (July–August) than in the colder period (January–February) ( P<0.01). Infection increased significantly with age and length of the fish ( P<0.01). The relationship between fecundity and length for infected and uninfected fish was calculated as log F=2.492 log L+1.531 and log F=2.611 log L+1.408, respectively. No significant difference between infected and uninfected fish was seen in either the fecundity-length data or the condition factor ( P>0.01).

The genera Ceratomyxa Thélohan, 1892, Leptotheca Thélohan, 1895 and Sphaeromyxa Thélohan, 1892 (Myxosporea: Bivalvulida) in gadid fish of the Northeast Atlantic

The gall-bladders of four species of gadid fish from the North Sea and Norwegian waters were examined for myxosporeans. The host species were cod Gadus morhua L. (350 examined), haddock Melanogrammus aeglefinus (L.) (592 examined), saithe Pollachius virens (L.) (205 examined) and whiting Merlangius merlangus (L.) (368 examined). Four species of myxosporeans are redescribed from these fish. Ceratomyxa arcuata Thélohan, 1892 was the most common species and was found in whiting (41.8%) and cod (0.6%). Leptotheca informis Auerbach, 1910 was found only in whiting (6.5%). L. longipes Auerbach, 1910 was found only in haddock (6.2%). Sphaeromyxa hellandi Auerbach, 1909 was found in haddock (9.1%) and whiting (0.3%). None of the saithe examined, and no cod or haddock from Norwegian waters, was infected with these myxosporeans. All four species appear to have distributions limited to the Northeast Atlantic, with S. hellandi having a more northern distribution than the other three. The validity of reports of C. arcuata, L. informis and L. longipes from outside this area is discussed.

Relating fish recruitment to stock biomass and physical environment in the Black Sea using generalized additive models

Relationships between recruitment, parental stock biomass and physical environment variables in four Black Sea species: sprat Sprattus sprattus, whiting Merlangius merlangus, anchovy Engraulis encrasicolus and horse mackerel Trachurus mediterraneus, were investigated using generalized additive models (GAMs). Sea surface temperature, wind speed, wind stress, wind mixing, sea level atmospheric pressure and river run-off data were used as indices of interannual variability of the Black Sea environment. The environmental variables were studied by means of the principal component analysis, which tended to account for the major patterns in the time series and approximate the main environmental forcing agents in the sea. Recruitment responses to the considered environmental predictors in the four cases were compared and possible interpretations were discussed. Significant correlations appear between fish recruitment, stock biomass and physical environment. Patterns of the recruitment response to wind variables and sea level atmospheric pressure were found similar in the four species. The relationships indicated similarities between anchovy and whiting, whose reproduction is related to the coastal habitat on the one hand, and between sprat and horse mackerel, which are open sea spawners on the other hand. Recruitment in the latter species appeared to be less dependant on the parental stock biomass and the river discharge and was negatively related with SST. GAM was found to be a suitable tool for fisheries and environmental data analysis, providing a flexible and powerful way to explore and model non-linear relationships.

Variability in frontal zone formation and distribution of gadoid fish larvae at the shelf break in the northeastern North Sea

Hydrography and larval fish distribution in the northeastern North Sea were studied during a research programme carried out during the period from 1991 to 1994. The aim was to examine the connection between frontal zone formation and nursery characteristics of gadoid larvae at the shelf break. Emphasis was placed on the year-to-year variation in frontal characteristics and distributional patterns of larvae. An area of about 67 000 km 2 covering the northeastern North Sea, the Skagerrak and the Kattegat was surveyed by grid or transect sampling. At each sampling station the hydrography was studied by CTD casts, and the abundance of fish larvae was measured by depth integrating tows of a 2 m ring net. Five species of gadoid larvae and small juveniles were found in the area: cod Gadus morhua, whiting Merlangius merlangus, haddock Melanogrammus aeglefinus, Norway pout Trisopterus esmarki and saithe Pollachius virens. Larval abundance differed markedly between species and years. The abundance of all species was the highest in 1992 and declined during the following 2 years. In 1994, cod and whiting were the only gadoid species observed. Peak abundance of all gadoids was found in the vicinity of the frontal zone; however, the relationship between larval distribution and hydrography differed among species. Correspondence between spatial and interannual variation in characteristics of frontal zones and larval distributions suggests that frontal zone variability is a central element in the early life of gadoid larvae from the area.

Food consumption of whiting, Merlangius merlangus, in the Eastern Irish Sea

In this paper, food intake of whiting Merlangius merlangus, in the Eastern Irish Sea is estimated using various models developed for food consumption. A new linear model for whiting is also developed and tested. The impact of whiting food consumption in the Irish Sea is considered. It was estimated that young whiting (age 0–3) eat between 1.29 and 6.57 g day −1 in February (temperature 7.8°C). By August when temperature has reached its annual maximum (18°C), these values increased by approximately 60–80%. The average recruited whiting stock in an area of approximately 150 km 2 in Red Wharf Bay, UK, was estimated to be 120 000 with a biomass of 22 t. Daily intake of sprat, sandeel and crab was 0.41, 0.14 and 0.14 g, respectively, for 0+ group. This was increased to 0.70, 0.80 and 0.94 g by the age of 4. On a daily basis the long term averages of the amount of sprat, sandeel and crab consumed were estimated to be 820, 370 and 520 g km −2 day −1. The total food intake per year by the recruited whiting stock was 44.8 t of sprat (approx. 11.5 millions of sprat), 20 t of sandeel and 28.5 t of crab. The daily food consumption by whiting in this part of the Irish Sea was compared with the data from the North Sea and the rest of the Irish Sea and it was concluded that whiting eat more in the Irish Sea than they do in the North Sea.

The effect of meal size on gastric evacuation in whiting

Gastric evacuation experiments were performed on whiting Merlangius merlangus fed discrete meals of different sizes. Herring Clupea harengus, sandeel Ammodytes tobianus, common goby Pomatoschistus microps, and brown shrimp Crangon crangon were tested as prey. A simple power model to describe gastric evacuation was evaluated and compared with a power model expanded as a function of meal size. The model parameters were estimated by means of nonlinear least squares. When all meal sizes were included the estimates of the power (curvature) parameter in the expanded model were within the range 0·36–0·77 for the different prey. The power estimates in the simple model were generally close to 0·5. The exception was crustacean prey, which gave a higher value. In the simple model the power estimate represents a compromise between the curvatures of the curves fitted to the observations for each meal size and the relationship between meal size and overall evacuation rate. Compared with an expanded model a simple model with a power value of 0·5 gave a suitable description of the gastric evacuation of fish prey independent of meal size. The variation of data was proportional to meal size, and this could be taken into account in the estimation procedure by expressing stomach contents relative to meal size.

Zooplankton diversity and the predatory impact by larval and small juvenile fish at the Fisher Banks in the North Sea

The biomass and diversity of the mesozooplankton and fish larvae community were inves- tigated across a frontal zone in the central North Sea in the early summer, to investigate whether larval fish predation is a regulator of mesozooplankton production. Pronounced changes in the meso- zooplankton community were observed across the front off the Jutlandic coast. The biomass and the diversity of copepods changed across the front as the population of Calanus finmarchicus became abundant in the deeper water. The crustaceans (Acartia spp. and Evadne spp.) and polychaete larvae dominated the mesozooplankton in the coastal water. The biomass of fish larvae was dominated by gadoid larvae. As in the copepods, a shift in fish diversity was observed in the frontal zone. On the coastal side of the front, whiting (Merlangius merlangus) dominated the biomass, while offshore from the front whiting were absent and cod (Cadus morhua) was the dominant larval fish species on the deeper stations. The present investigation demonstrates two different trophic pathways related to hydrography in the central North Sea. First, in the shallow coastal water, the abundant small neritic copepods are predominately predated by whiting, while in the offshore region the larger oceanic copepods are predated by cod larvae. However, the predation pressure by the fish larvae was in general low (<10%) relative to copepod production per day. Consequently, in the early summer, the copepod production potentially results in a build-up of copepod biomass on both sides of the front.

Stock trends in six North Sea stocks as revealed by an analysis of research vessel surveys

A model is developed for the analysis of age disaggregated indices of abundance from which stock trends can be estimated. The model is used to examine trends in North Sea cod (Gadus morhua), haddock (Melanogrammus aeglefinus), whiting (Merlangius merlangus), sole (Solea solea), plaice (Pleuronectes platessa) and herring (Clupea harengus). These are compared with the trends estimated from conventional ICES assessments which use commercial catch-at-age data. The catch data are known to be affected by misreporting which can affect the calculated stock trends. The surveys appear to be able to quantify the trends in recruitment and spawning stock with a high degree of consistency between independent surveys of the same stock and with the conventional assessment. Estimates of catch and fishing mortality rate are more uncertain. The well known problems of catch mis-reporting which affect the conventional ICES assessments do not appear large enough to alter the perception of stock trends.

Stock composition in North Atlantic populations of whiting using microsatellite markers

A size‐selected library constructed from DNA of the whiting Merlangius merlangus was screened. From about 3200 recombinant clones, 43 microsatellite loci were detected. Thirteen were sequenced in full. Primers were designed from the sequence of the flanking regions for six loci and used to test the allelic variability at these loci using the polymerase chain reaction (PCR). In addition, five primer pairs developed for the stickleback and another seven for cod were tested. Only six primer pairs revealed at least three alleles per locus. The three useful loci Gmo2, Mmer‐UEAW01 and Mmer‐UEAW02, had 14–23 alleles per locus in 370 samples. Estimates of genetic structure (φ) were not statistically significant. However, estimates of genetic differentiation (Fst) were significantly different from zero. Heterogeneity χ2‐analysis of allele frequencies among populations suggested relatively low levels of differentiation among samples. Significantly different allele frequency distributions were found for Borgensfjord and northern and southern North Sea samples for at least one locus, and between the latter samples for Mmer‐UEAW02 and Gmo2. There were significant excesses of homozygotes in all samples, over expectation for randomly mating populations in Hardy‐Weinberg equilibrium. The estimated frequencies of null alleles were 14.3%, for Mmer‐UEAW01, 10.2% for Mmer‐UEAW02 and 11.6% for Gmo2. This result calls for a careful interpretation of the significance of these microsatellite data.

Vertical distribution of fish eggs and larvae in the Irish Sea and southern North Sea

Fish eggs and larvae were analysed from 63 vertically stratified plankton hauls in the Irish Sea and southern North Sea. The dominant species were sprat (Sprattus sprattus), dragonet (Callionymus spp.), dab (Limanda limanda) and to a lesser extent rockling species, sandeel (Ammodytes spp.), whiting (Merlangius merlangus) and flounder (Platichthys flesus). There was little diVerence between species in the vertical distribution of either eggs or larvae. Most were concentrated in the upper 50 m of the water column, eggs in progressively increasing numbers towards the surface and larvae with a sub-surface peak at a depth of 10‐15 m. The vertical distribution of eggs extended deeper in the water column than larvae, possibly due to some combination of eggs being spawned deeper and their passive susceptibility to turbulent mixing. There were no significant diVerences between day and night distributions and under mixed or isothermal conditions. ? 1997 International Council for the Exploration of the Sea