Abstract: No field studies have been performed on the selectivity of herring and sprat in the southern Baltic Sea in relation to their entire range of prey. Accordingly, we tested in the field the following hypotheses: (i) sprat and herring are selective feeders and (ii) sprat and herring selectivity is size- and season- dependent. The results show that (i) smaller herring and all size classes of sprat are strictly zooplanktivorous, selecting principally Temora longicornis and Bosmina maritima during the autumn and Pseudocalanus elongatus in winter; (ii) larger herring are essentially nektobenthos feeders, predating on Mysis mixta during the autumn and amphipods and polychaetes during the winter; and (iii) herring and sprat seem to avoid Acartia spp. in both autumn and winter. During the autumn, herring are zooplanktivorous up to 18e20 cm, whereas in winter herring feed on nektobenthos starting from 14e15 cm. Selectivity was not an absolute process but it was related to prey relative abundance in the sea and, possibly, to prey profitability (e.g. size, conspicuousness, and reaction time).

Abstract: The stock of Norwegian spring-spawning herring Clupea harengus collapsed to a state of commercial extinction in the 1960s, probably due to both overexploitation and unfavourable climatic conditions. Since the 1980s, the stock has fully recovered. Following the collapse, the fish matured at much earlier ages and somewhat larger sizes than previously. Currently, age and size at 50% maturity have only to some extent returned to pre-collapse levels. Two non-exclusive hypotheses that may account for the maturity changes are (1) the 'compensatory response' hypothesis, predicting that reduced stock size resulting from exploitation leads to faster growth and hence earlier maturity as a phenotypically plastic response to environmental change; and (2) the 'evolutionary response' hypothesis, predicting that intensive exploitation causes selection for early maturation, since few late-maturing phenotypes survive until first spawning. Trends in length-at-age suggest a strong compensatory response, but leave the possibility of evolutionary change unaddressed. In order to disentangle phenotypic and possible genetic changes in maturation, we examined the reaction norm for age and size at maturation to see if any changes had occurred. This reaction norm describes the probabilities of maturing at each relevant age and size. We found small but statistically significant changes in maturation reaction norms; these changes were restricted to 2 out of 6 of the maturation ages. This confirms that growth-related phenotypic plasticity has largely been responsible for the documented changes in maturity, and suggests at most a weak evolutionary response. This is in line with theoretical expectations from the dominating fishing pattern, where pure schools of only mature or only early immature fish were targeted, rather than a fishery on both immature and mature fish simultaneously, as has been the case in stocks of cod Gadus morhua and plaice Pleuronectes platessa, where significant evolutionary responses have been found.

Abstract: Functional, nutritional, and thermal properties of freeze-dried protein powders (FPP) from whole herring (WHP), herring body (HBP), herring head (HHP), herring gonad (HGP), and arrowtooth flounder fillets (AFP) were evaluated. The FPP samples have desirable nutritional and functional properties and contained 63-81.4% protein. All FPP samples had desirable essential amino acid profiles and mineral contents. The emulsifying and fat adsorption capacities of all FPP samples were higher than those of soy protein concentrate. The emulsifying stability of WHP was lower than that of egg albumin but greater than that of soy protein concentrate. Thermal stability of the FPP samples is in the following order: HGP > HBP > WHP > HHP > AFP.

Abstract: The commercial importance of Pacific and Atlantic herring (Clupea pallasii and Clupea harengus) has ensured that much of their biology has received attention. However, their sound production remains poorly studied. We describe the sounds made by captive wild-caught herring. Pacific herring produce distinctive bursts of pulses, termed Fast Repetitive Tick (FRT) sounds. These trains of broadband pulses (1.7-22 kHz) lasted between 0.6 s and 7.6 s. Most were produced at night; feeding regime did not affect their frequency, and fish produced FRT sounds without direct access to the air. Digestive gas or gulped air transfer to the swim bladder, therefore, do not appear to be responsible for FRT sound generation. Atlantic herring also produce FRT sounds, and video analysis showed an association with bubble expulsion from the anal duct region (i.e. from the gut or swim bladder). To the best of the authors' knowledge, sound production by such means has not previously been described. The function(s) of these sounds are unknown, but as the per capita rates of sound production by fish at higher densities were greater, social mediation appears likely. These sounds may have consequences for our understanding of herring behaviour and the effects of noise pollution.

Abstract: Sightings of minke whales Balaenoptera acutorostrata were recorded in waters off the Isle of Mull between March and November each year from 1992 to 1999. Survey effort amounted to 42 342.5 km, and 850 minke whale encounters were recorded. Data were analysed in relation to undersea topography and seabed sediment type using multiple logistic regression. The effect of potential minke whale prey distribution was inferred from maps predicting suitable habitats for the lesser sandeel Ammodytes marinus and herring Clupea harengus constructed using a Geographical Information System (GIS). Whale distribution changed with season, and this may be a response to a shift in prey preferences. In spring, sediment type was a significant predictor of whale presence and sightings predominated over mixtures of gravel/sand seabed sediments. This distribution closely matched that of the sandeel, which is dependent on suitable winter settlement grounds. Throughout summer, the distribution of the minke whale underwent considerable change. In June, minke whales were predominately distributed over the sandeel habitat, but in July they dispersed to the predicted pre-spawning herring habitat, clustering in that area by August. In the waters around Mull, shifts in prey distribution and abundance occur between March and November and are the most likely factor governing the distribution and abundance of the minke whale.

Abstract: We used the longest available weight-at-age (WAA) time series (from 1950 to 1999) for Baltic herring (Clupea harengus membras L.) in the Gulf of Finland to investigate which environmental factors a...

Abstract: The survival of Atlantic salmon Salmo salar in the Baltic Sea was examined in relation to smolt traits (length and origin) and annual environmental factors [sea surface temperature (SST) and seasonal North Atlantic Oscillation (NAO) index], and prey fish abundance (herring Clupea harengus and sprat Sprattus sprattus) in the main basin and the southern Gulf of Bothnia. The study was based on recapture data for Carlin-tagged hatchery-reared and wild smolts from the Simojoki, a river flowing into the northern Gulf of Bothnia. The survival of the wild and reared groups was analysed using an ANOVA model and a stepwise regression model, with the arcsin-transformed proportion of recaptured fish as the response variable. The results demonstrated a combined influence of smolt traits and environmental factors on survival. For the reared Atlantic salmon released in 1986–1998 (28 groups), the increasing annual mean SST in July in the southern Gulf of Bothnia and increasing mean smolt size improved survival. If the SST in July was excluded from the model, the NAO index in May to July also had a positive effect on survival (P < 0·10). The log10-transformed abundance of 0+ year herring in the southern Gulf of Bothnia entered the model (P < 0·15) if the SST and NAO index were excluded. For the wild Atlantic salmon released in 1972–1993 (21 groups), only the increasing SST in July showed a significant association with improved survival (P = 0·004). Prey fish abundance in the main basin of the Baltic Sea had no influence on the survival of reared or wild smolt groups. The interaction between smolt size and the SST in July was not significant. The origin was a better, but not a significant, predictor of marine survival compared to the smolt size or the SST in July. The mean recapture rate of the wild groups was twice that of the reared groups in the whole data. The results suggest that cold summers in the Gulf of Bothnia reduce the survival of young Atlantic salmon in both wild and reared groups. The larger smolt size of the reared groups compared with the wild groups to some extent compensated for their lower ability to live in the wild.

Abstract: Stomach content analyses were conducted on Atlantic salmon Salmo salar post-smolt (average size, 119-154 mm fork length, L F ) caught in eight large Norwegian fjord systems along a north-south geographical axis during 1998-2001. In general, post-smolts from southern Norway showed low feeding intensity in the fjords, whereas extensive feeding was observed in fjords in the northern and middle parts of Norway. The marine diet mainly included different crustaceans and in particular marine pelagic fish larvae (sand-eels Ammodytes spp., herring Clupea harengus and gadoids), but with a substantial spatial and annual variation in prey diversity and feeding intensity. Insects were most frequently taken in the estuary, although fishes often made a large contribution in mass. In contrast, fishes, and to some extent various crustaceans (particularly Hyperiidae, Gammaridae, Euphausiacea and Copepoda) dominated the diet in the middle and outer parts of the fjords, where post-smolts also fed more extensively than in the inner part. The results indicate that extensive feeding immediately after sea entrance may be more common for post-smolts in the northern and middle parts of Norway, than in the southern fjords. The observed differences in post-smolt feeding may be due to spatial and temporal differences in prey availability within and between the different types of fjord systems, and this might influence post-smolt growth and survival.

Abstract: Norwegian spring-spawning herring larvae ( Clupea harengus L.) were reared at different temperature combinations in the laboratory, and marked twice with a fluorescent dye, alizarin complexone, to estimate otolith growth and increment deposition rate. A daily increment deposition rate was confirmed in the sagittae of larvae reared at 12 °C from day 16 (first marking age), while the apparent rate of increment formation of larvae reared at 4 °C was clearly less than one per day. A reduction in rearing temperature from 12 to 8 °C between days 16 and 30 (second marking age), significantly affected sagitta growth during the inter-mark period compared with those reared at 12 °C throughout. Similar somatic growth rates were observed in both groups temporarily reared at 8 °C between markings (about 6% day −1 ), but the otolith growth rate was more than four times higher in the group originating from 12 °C compared with the one originating from 4 °C. The body size versus otolith size relationship was temperature d...

Abstract: Abundance of the exotic predatory cladoceran Cercopagis pengoi (Ostroumov, 1891) in the Gulf of Riga has increased during the first ten years of invasion (1992–2001) and peaked with an annual mean of 420 ± 109 (s.e.) ind. m−3 in 2001. As a long-term mean, Cercopagis population reached its highest abundance in the first week of August (mean 269 ind. m−3) and the seasonal population development followed the course of water temperature. Presence of Cercopagis in the plankton community tended to last longer over the years by shifting its population development to earlier in the year. The latter correlated significantly (r 2=0.88, p<0.01) with a similar pattern of Eurytemora. After the invasion of Cercopagis, the annual mean abundance of Bosmina was significantly lower than during the pre-invasion time (t-test, p<0.01). Although populations of the other mesozooplankton taxa did not follow this pattern at the annual scale, seasonal population development of copepod nauplii and Acartia has changed, which can be caused by the invasion. The mean share of Cercopagisin the diet of most abundant planktivorous fish remained low (<7%) but the cladoceran constituted a substantial portion in the fish diet during warm months. Consumption of Cercopagis by herring, Clupea harengus membras, and smelt, Osmerus eperlanus, increased with increasing fish size. This was not evident in the case of sticklebacks, Gasterosteus aculeatus and Pungitius pungitius. The study points out that the invasion of Cercopagis has caused changes in zooplankton dynamics. Therefore, dietary overlap with fish larvae and planktivorous fish may occur in the Gulf of Riga.

Abstract: Peltonen, H., Vinni, M., Lappalainen, A., and Ponni, J. 2004. Spatial feeding patterns of herring (Clupea harengus L.), sprat (Sprattus sprattus L.), and the three-spined stickleback (Gasterosteus aculeatus L.) in the Gulf of Finland, Baltic Sea. e ICES Journal of Marine Science, 61: 966e971. The pelagic-fish fauna in the Gulf of Finland, Baltic Sea was sampled by trawling and hydroacoustics in September 2002. Spatial and size/age-dependent patterns in the diets of herring (Clupea harengus), sprat (Sprattus sprattus), and the three-spined stickleback (Gasterosteus aculeatus) were explored. At night the fish concentrated at thermocline depth but at dawn they scattered over a larger depth range. All three fish species fed on mesozooplankton but nektobenthos, for example, was scarce. In the eastern Gulf of Finland, where there is a strong freshwater inflow, the cladoceran Bosmina longispina was the dominant prey item, but it was also abundant in the diets of young-of-the-year (total length !10 cm) clupeids in the western Gulf of Finland. In these more saline western areas, calanoid copepods, especially Eurytemora affinis, were the most important prey for large (R 10 cm) clupeids. The large clupeids in particular, also fed on Temora longicornis. The diet of three-spined stickleback overlapped with that of the clupeids. However, Cercopagis pengoi, a recent arrival to the area, was much more abundant in the diet of stickleback than in the diet of clupeids.

Abstract: Acoustic measurements at 1.5-5 kHz on fish in the Gulf of Maine showed a swimbladder-resonance peak near 2.5 kHz at 160-190-m depth. Midwater trawls confirmed that the fish were likely to be Atlantic herring (Clupea harengus) of 19-29 cm length. Calculation using a model of swimbladder resonance gives swimbladder volumes of 1.2% of fish weight at 160-190 m. Extrapolation of this volume of gas using Boyle's Law suggests that at the sea surface, these herring would need to inflate their swimbladders by up to five to six times the volume required for neutral buoyancy. If these fish were to maintain this volume of gas with surface “gulping”, they would need to submerge from the sea surface with a 30% excess buoyancy. In general, swimbladders of the Clupeidae may have greater volumes of gas than if the fish were neutrally buoyant at the sea surface and the interpretation of HF-echosounder surveys may be additionally complex when the volume of gas and swimbladder volume are difficult to predict. Mechanisms of how herring obtain additional swimbladder gas are discussed.

Abstract: The Baltic Sea is heavily polluted yet supports major commercial fisheries for cod (Gadus morhua), herring (Clupea harengus), and sprat (Sprattus sprattus). Emissions of persistent organic pollutants, such as polychlorinated biphenyls (PCBs) and DDT, were high during the 1960s and 1970s, and concentrations in fish and other fauna are still significant. Several models of the fluxes of these pollutants among the water, sediment, and atmosphere have been developed, but these generally omit the roles of fish and fisheries. We show that the standing stock of the most abundant fish species in the Baltic Sea was a sink for 260 kg of PCBs in the late 1980s to early 1990s and that the fishery removed as much or more PCB (31 kg yr-1) than other budget components (e.g., degradation in the water column). Accounting for fish and fisheries could increase our understanding of the fluxes of pollutants, and banning the discard of highly contaminated organs such as cod liver could be part of the pollution management.

Abstract: Predator-dependent functional responses decouple predation mortality from fluctuations in predator abundance and therefore can prevent strong "top-down" interaction strengths in food webs. We evaluated whether contrasts in the functional response of Baltic Sea cod (Gadus morhua) were consistent with the contrasting population dynamics of two prey species, herring (Clupea harengus) and sprat (Sprattus sprattus): sprat abundance increased nearly threefold following a sharp decline in the cod population (a strong interaction), whereas herring abundance failed to increase (a weak interaction). We found striking differences in the functional response of cod on alternative prey, and these were consistent with the observed patterns in interaction strengths. Cod predation was the dominant source of mortality for age-1 and age-2 sprat but was only important for age-1 herring. Moreover, the magnitude of predation mortality on age-1 and age-2 sprat was highly sensitive to cod biomass, whereas predation mortality on ...

Abstract: Fish and krill were studied at a 120 m deep site in the Oslofjord, Norway. Herring (Clupea harengus), whiting (Merlangius merlangus), and Norway pout (Trisopterus esmarkii) were foraging on krill (Euphausiacea, Meganyctiphanes norvegica) during both day and night. During daytime, herring and whiting were foraging in the upper and middle part of the krill assemblage, while the deep-living, and often benthopelagic Norway pout was approaching the krill from below. Krill and fish ascended and fish schools dispersed at dusk. At night, herring and whiting were feeding near the surface, with the shallowest distribution suggested for herring. Norway pout foraged in midwater. Krill antipredator behaviour comprised diel vertical migration and instantaneous escape reactions, and the krill also appeared to actively seek out strata with low acoustic recordings of fish. Fish accumulated beneath the research vessel when the ship was anchored at a fixed location during acoustic studies, apparently resulting in artificially high local fish abundances. Since we suggest that krill respond to the presence of fish, such high fish abundance may bias studies of interactions between the fish predators and their krill prey.

Abstract: During 1992^2002 approximately 110 strandings of minke whales Balaenoptera acutorostrata were recorded in Scotland (UK). Most strandings were recorded between April and November, with a peak of strandings of males in July and August. There were two length modes at 4^ 6ma nd 7^10 m. Stomach contents samples were obtained from ten animals. The diet comprised mainly sandeels (Ammodytidae, around two-thirds of the diet by number or weight) and clupeids (herring Clupea harengus and sprat Sprattus sprattus). Results on diet are consistent with results from whaling catches in the North Sea. The possibility that minke whales compete with ¢sheries is discussed.

Abstract: A biological model belonging to the Beverton-Holt age-structured family for the Norwegian spring spawning herring (Clupea harengus) (NSSH) is simulated, the outcome of which compares well with actual data on the fishery. This model is then combined with an economic model to help investigate how optimal a management policy of constant fishing mortality will be for a fishery such as the NSSH, which has a highly fluctuating stock biomass. For the range of constant values of fishing mortality explored, and a simulation time horizon of 20 years, a constant fishing mortality of 0.15 turns out to be economically optimal. It should be noted that this result is sensitive to variations in the assumptions underlying key variables of the fishery. For example, when a constant rather than variable recruitment was assumed, a different optimal fishing mortality rate was obtained.

Abstract: Differences in the acoustic characteristics of forage fish species in the Gulf of Alaska and the Bering Sea were examined using Kirchhoff ray-mode (KRM) backscatter models. Our goal was to identify species-specific characteristics and metrics that facilitate the discrimination of species using acoustic techniques. Five fish species were analyzed: capelin (Mallotus villosus), Pacific herring (Clupea pallasii), walleye pollock (Theragra chalcogramma), Atka mackerel (Pleurogrammus monopterygius), and eulachon (Thaleichthys pacificus). Backscatter amplitude differences exist among these species, especially between swimbladdered and non-swimbladdered fish. Echo intensities were variable within and among species. The effect of morphological variability was indexed using the ratio of the Reducedscattering length (RSL) standard deviation over its mean. Morphological variability was low only at fish length to acoustic wavelength ratios less than eight. Target strength differences between pairs of carrier frequencies (ranging from 12 kHz to 200 kHz) differed among species, and were dependent on fish size and body orientation. Frequency differencing successfully discriminated between fish species but the choice of frequency to maximize target strength differences was not consistent among species pairs. Frequencydependent, backscatter model predictions facilitate comparison of target strength differences prior to acoustic data collection.

Abstract: Consumption of different age groups of juvenile, Norwegian, spring-spawning herring (Clupea harengus) by northeast Arctic cod (Gadus morhua) in the Barents Sea in 1992–1997 is estimated using cod s...

Abstract: The Black-legged Kittiwake Rissa tridactyla is a small gull that is widely distributed in the North Atlantic and Pacific. During the breeding season it feeds mainly on fish and, in the North Sea, the Lesser Sandeel Ammodytes marinus typically forms the main species in the diet. We compared the diet and breeding performance of Kittiwakes at four colonies in east Britain with potentially overlapping foraging ranges where both Lesser Sandeels and alternative prey (clupeids: Sprat Sprattus sprattus and Herring Clupea harengus) were potentially available. During the four years of the study Kittiwakes at all four colonies showed similar within-season shifts in the age class of sandeel taken with older (1 + group) fish being replaced by young of the year (0 group). However, in every year the predominant prey differed between the two marine colonies, where birds fed mainly on sandeels, and the two estuarine colonies, where clupeids were the most important prey. We suggest that these dietary differences reflect differences in foraging areas such that Kittiwakes from marine colonies feed offshore in areas with a sandy seabed, habitat favoured by sandeels, and birds from estuarine colonies feed closer inshore in areas with a more rocky seabed, habitat favoured by clupeids. Breeding success of Kittiwakes at the four colonies followed a similar trend over the first three years but the marked increase recorded at the marine colonies in 2000 was not apparent at the estuarine colonies.

Abstract: Genetic studies on Atlantic herring, Clupea harengus, have generally revealed a low level of genetic variation over large geographic areas. Genetically distinct herring populations in some of the Norwegian fjords are exceptions, and juvenile herring from the large oceanic herring, Norwegian Spring Spawners (NSS), are often found in mixture with local fjord populations as well as widely distributed in the Barents Sea. Research surveys in the eastern Barents Sea (Goose Bank) in 1993, 1994 and 2001 included collection of herring samples for allozyme analyses. As expected the results identified juveniles from NSS stock, but an additional unique group of herring (low vertebrae number), being almost fixed for alternative alleles at several allozyme loci, was detected. In some cases, the two groups of herring were taken in the same trawl catches as documented by highly significant departure from Hardy-Weinberg expectation with large excess of homozygotes providing evidence for population mixing. Large genetic differences (Nei’s genetic distance = 1.53; FST = 0.754) were detected in pairwise comparisons based on five allozyme loci. The two herring groups were also compared with reference samples of Pacific herring, Clupea pallasi, including one sample from Japan Sea and three Alaskan samples. UPGMA dendrogram based on five allozyme loci revealedaclose genetic relationship between the low vertebrae herring in the Barents Sea and the group of samples of Pacific herring. Although significant different in allele frequencies, one of the herring samples clustered together with the reference sample from Bering Sea with genetic distance of 0.008 and FST value of 0.032. The close genetic relationship found in this paper, suggest a re-evaluation of the taxonomic status of the Barents Sea herring populations investigated.

Abstract: The infectious salmon anemia (ISA) virus causes lethargy, anemia, hemorrhage of the internal organs, and death in farmed Atlantic salmon Salmo salar. It has been a cause of disease in Norwegian farmed Atlantic salmon since 1984 and has since been identified in Canada, Scotland, the United States, and the Faroe Islands. Wild fish have been proposed as a viral reservoir because they are capable of close contact with farmed salmon. Laboratory studies have shown that brown trout and sea trout Salmo trutta, rainbow trout Oncorhynchus mykiss, and herring Clupea harengus tested pos- itive for the virus weeks after intra-peritoneal injection of the ISA virus. Pollock Pollachius virens are commonly found in and around salmon cages, and their close association with the salmon makes them an important potential viral reservoir to consider. The objective of this study was to determine the presence or prevalence of ISA virus in pollock cohabitating with ISA-infected farmed Atlantic salmon. Kidney tissue from 93 pollock that were living with ISA-infected salmon in sea cages were tested with reverse transcription-polymerase chain reaction (RT-PCR) test. Results yielded the expected 193 bp product for positive controls, while no product was observed in any of the pollock samples, resulting in an ISA viral prevalence of 0%. This study strengthens the evidence that pollock are unlikely to be an ISA virus reservoir for farmed Atlantic salmon.

Abstract: The sensory properties of marinated herring produced immediately post mortem of raw material from different fishing ground and seasons were described and related to biological, biochemical and functional properties. Subtle variation was encountered in the appearance of whole marinated herring fillets. Fishing ground did not influence the odor, flavor or texture, but there was an apparent effect of season on the sensory profile. The sensory properties were influenced by body weight, but not by age, sex and gonad maturity. The influence of varying lipid content, water content and liquid holding capacity resulted in similar effects showing the high correlation between these properties. The results indicated that variation in sensory quality observed by the industry is not primarily due to the parameters fishing ground and season.

Abstract: To quantify and characterize the spatial distribution of clupeid fish schools, sonar data were collected during surveys off the coast of Namibia in 1994 (pilchard (Sardinops sagax), anchovy (Engraulis capensis), and round herring (Etrumeus whiteheadi)), off Angola in 1995 (sardinella (Sardinella sp.)) and in the Norwegian Sea in 1997 and 1998 (Norwegian spring-spawning herring (Clupea harengus L.)). The two-dimensional distances between clupeid schools were calculated in the order that the different schools were observed along the survey vessels transect lines. In all four surveys, two different modes (frequency distribution maximums) were observed. The first mode, representing the most usual interschool distance, was about 60 m. The second mode, around 1600 m, probably represented the distances between different clusters. The distances between clupeid schools and between different clusters were found to be about the same for separate pelagic clupeid species, locations, and years of observation. The mean diameters of the school clusters were estimated to vary between 450 and 1450 m.