Effects of five years of intensive trawling on a previously unexploited smelt stock

In the years 1989–1993, over 1000 metric tons of fish (392 kg ha⁻¹) was removed by trawls from the Enonselkä basin in Lake Vesijärvi in order to enhance the water quality. Roach (52%) and smelt (28%) were the most abundant species in the catches. In this study, the effects of the mass removal on the previously unexploited smelt stock was assessed. The total smelt catch was c . 282 metric tons. Due to the mass removal, the density of the stock collapsed from c . 46 000 fish ha⁻¹ in 1989 to c . 14 000 fish ha⁻¹ in 1993 ( M =1.0). The biomass of the stock decreased from 75 kg ha⁻¹ in 1989 to 12 kg ha⁻¹ in 1993. The age group composition of the stock changed clearly towards the dominance of younger age groups. The male/female relationship in the samples changed from clear dominance of females to the dominance of males and the infection rate by the sporozoan parasite Glugea hertwigi declined. The growth rate of the smelt did not change considerably during the years of mass removal. The results suggest that in biomanipulated lakes several mechanisms may prevent the exploited stock from responding to the increased mortality.     

Genetic structure and relationships among anadromous and landlocked populations of rainbow smelt, Osmerus mordax, Mitchill, as revealed by mtDNA restriction analysis

Larvae of anadromous rainbow smelt originating in various spawning tributaries are retained in the St Lawrence estuary. We proposed that these smelt represent one population genetically differentiated from adjacent populations characterized by geographically distinct larval retention areas. We also analysed four landlocked populations to evaluate the phylogenetic basis of dwarf and normal-sized phenotypes and their relation to an adromous smelt. A phylogenetic distinction was revealed between anadromous and landlocked smelt, with only one of the two mtDNA phylogenetic groups of anadromous fish observed among landlocked smelt. Significant geographical heterogeneity in the distribution of mtDNA genotypes was observed among landlocked smelt, suggesting that dwarfism in smelt may be polyphyletic in origin. St Lawrence smelt were genetically identical but distinct from adjacent populations, supporting the proposition that population genetic structure reflects the number of larval retention zones rather than spawning sites.     

Age, growth, mortality and sex ratio of sand smelt, Atherina boyeri Risso, 1810 (Pisces: Atherinidae) in the estuary of the Mala Neretva River (middle-eastern Adriatic, Croatia)

The present study investigated the age, growth, mortality and morphometry of the sand smelt, Atherina boyeri, in the Mala Neretva River estuary (mid‐eastern Adriatic Sea). The study of scale annuli showed that the population is up to 4 years of age. However, most sand smelt are in their first and second year; the numbers of older individuals are very low because they migrate upstream and are heavily fished. The von Bertalanffy parameters for the total sample of sand smelt were found to be L_∞ = 13.5 cm, K = 0.37 year^?1 and t₀ = ?0.97. Overall total mortality was estimated at 1.81 year^?1, natural mortality was 0.90 year^?1 and fishing mortality was 0.91 year^?1.     

Abundance and distribution of Neomysis mercedis and a major predator, longfin smelt (Spirinchus thaleichthys) in Lake Washington

Seasonal variations in the horizontal and depth distributions of Neomysis mercedis and longfin smelt (Spirinchus thaleichthys) were examined using night-time mid-water trawl and Bongo net samples collected in Lake Washington from July 1989 to February 1992. Mysid density varied spatially, seasonally and yearly. For example, during summer, and fall (odd years), mysid abundance was highest in the northern, and lowest in the southern sections of the lake, except in December 1991 when they were uniformly distributed. In fall (November 1990), mysid density was highest in the central basin of the lake. Furthermore, in winter of even years, highest mysid density occurred in the southern region of the lake, but in the central region in winter (February) of odd year. Longfin smelt horizontal distribution also varied seasonally. For example, density of the 1988 YC smelt (1+) was highest in the northern area of Lake Washington in summer but highest in the southern area in fall. During winter, distribution seemed random. The abundance of the 1990 YC smelt (YoY) was also highest in the northern section of the lake in summer, but highest in the southern section in fall; density remained high in the southern section in winter. But, by late spring when they were more than one year old, the distribution had changed such that highest abundance occurred in the northern and mid-section of the lake. By winter when they were about two years old and about to begin spawning, density had become highest again in the southern section. These suggest extensive movement of mysids and smelt from one area to another, perhaps driven by wind-induced water currents in the lake. Depth distribution patterns of mysids and smelt are discussed. Smelt were captured mainly in the shallow strata (8 m) of the lake during all seasons except during winter when they predominated at 50 m. Mysids were also mainly caught in the shallow strata of the lake during all seasons, although a significant proportion occurred at greater depths (> 30 m). The abundance of both species was positively correlated in spring and summer but negatively correlated in fall. A poor correlation was observed in winter. Negative correlation in fall was primarily due to the occurrence of mysids and smelt in different areas of the lake whereas poor correlation in winter was particularly due to their occurrence at different depths. Because of considerable overlap in the distribution of both species in the lake, mysids face a high risk of predation by smelt. This piece of information is consistent with the hypothesis that smelt control mysid abundance in Lake Washington. This revised version was published online in July 2006 with corrections to the Cover Date.     

Temperature effects on egg and larval development rate in European smelt,Osmerus eperlanus,experiments and a 50 year hindcast

This study investigates the effect of water temperature on the development rate of eggs and larvae, the duration of the endogenous feeding period and its consequences for recruitment of smelt (Osmerus eperlanus) in Dutch lakes IJsselmeer and Markermeer. This study measured temperature-dependent egg and larval development rates as well as mortality rates from fertilization till the moment of absorption of the yolk-sac and from yolk-sac depletion onwards in temperature-controlled indoor experiments. Using multinomial modelling the authors found significant differences in development time of egg development stages under different temperature regimes. Based on historic water temperatures, the model predicted that the larval endogenous feeding period has advanced at a rate of about 2.9 days per decade in a more than 50 year period since 1961, yet there was no change in the duration of the endogenous feeding period. As zooplankton is more responsive to daylight than water temperature cues, a mismatch between the peak of the onset of exogenous feeding of smelt and the peak of zooplankton blooms could lead to high mortality and therefore low recruitment of smelt. Such a mismatch might contribute to a decline in the smelt population in Lake IJsselmeer and Lake Markermeer.     

Large-bodied Crustacea and rainbow smelt in Lake George, New York: trophic interactions and phytoplankton community composition

The phytoplankton community of south Lake George, New York,has recently undergone a dramatic shift in composition; froma community dominated by Chrysophytes, Cryptomonads, and Chlorophyta(1975–1976) to one currently dominated by blue-green algae,i.e.Anacystis incerta and Aphanothece nidulans. No increasesin nutrient concentrations or inputs have been documented beforeor during this period. This shift in dominance can be relatedto changes in higher trophic levels, i.e. grazers and planktivores.Standing crop and abundance of the small-bodied filter feeders,Bosmina longirostris, Daphnia galeata, D. dubia, Holopediumgibberum, Diaptomus minutus and D. sicilis are significantlygreater in the south basin. Standing crop and abundance of thelarge-bodied Crustacea, Daphnia pulicaria, Epishura lacustrisand Mysis relicta, are significantly greater in the north basin.The clutch sizes of all herbivorous species except D. minutuswere significantly greater in the south basin populations. Thesedifferences are consistent with greater productivity and sizeslective planktivory in the south basin. Stomach analysis ofthe recently introduced rainbow smelt, Osmerus mordax indicatesa marked selection for the large-bodied Crustacea. The establishmentof large populations of rainbow smelt in the south basin ofLake George is responsible for significant basin differencesin the abundance of large-bodied Crustacea and appears to havecontributed to the changes in phytoplankton community composition.The shift to small-bodied Crustacea in the south basin has resultedin significantly lower grazing rates but generally higher Prelease rates in the south basin. These factors contribute togreater springtime phytoplankton production and silica depletionin the south basin. Coccoid blue-green algae are able to dominatewaters with low phosphorus and silica concentrations, i.e. LakeGeorge. Thus, the establishment of rainbow smelt in Lake Georgecoincides with, and appears to be responsible for, changes inphytoplankton community composition.     

Resident spawning of Japanese smelt,Hypomesus nipponensis,along gravel shorelines in Lake Nojiri,Central Japan

In Lake Nojiri, the Japanese smelt, Hypomesus nipponensis McAllister, 1963, population has been thought to be maintained by artificial spawning, and stocking efforts as natural spawning in in-flowing streams is unlikely due to the lack of inflowing stream habitat. In this study, novel resident Japanese smelt spawning was observed along the lakeshore in shallow areas with clean gravel and flow. Spawning occurred at night during early March to mid-April and eggs, confirmed on gravel substrate, progressed to the eyed state in 5–6 weeks. Although natural spawning was observed, the ratio of eggs that progressed to the eyed stage was minimal, possibly due to thick algae cover in areas with low flow velocity. Therefore, resident Japanese smelt spawning along the lake shoreline is physically possible and potentially contributes to the overall population in Lake Nojiri, but in-lake spawning alone presumably is not a biologically viable method for population sustainability due to low survival rates and egg density at present. Environmental improvements such as construction of fish ladders to suitable in-flowing spawning habitat, introduction of clean gravel to shorelines, and water level management adjusted to the smelt spawning run would contribute to higher recruitment by natural smelt reproduction, and consequently enhance the smelt production in Lake Nojiri.

     

Occurrence of the parasite Glugea hertwigi in young‐of‐the‐year smelt in Lake Tuusulanjärvi

Young‐of‐the‐year smelt Osmerus eperlanus in Lake Tuusulanjärvi were examined for Glugea hertwigi cysts. Cysts were visible on smelt in the beginning of August and showed a peak at the end of August. Glugea hertwigi may cause mortality among the most heavily infected young‐of‐the‐year smelts.     

Consequences of temperature and temperature variability on swimming activity,group structure,and predation of endangered delta smelt

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Seasonal variation of phosphatidylcholine hydroperoxides in blood of sweet smelt Plecoglossus altivelis

Sweet smelt was reared at two fishery experimental stations for 5 months from June to October. Every 2 weeks blood was collected from the caudal vessels and, subsequently, the phosphatidylcholine hydroperoxide contents and the fatty acid compositions in the blood were determined by high-performance liquid chromatography and gas chromatography, respectively. The seasonal variation of the contents of accumulated hydroperoxides and fatty acids in the sweet smelt blood were observed in both experimental stations. Sweet smelt started performance of cucumber-like or watermelon-like aroma in the middle of July and the aroma was enhanced in August. The content of phosphatidylcholine hydroperoxides and the amount of total fatty acid in the fish blood, in terms of possible precursors of volatile compounds, were also extremely high in the same period. According to lipid peroxidation mechanisms, the strong characteristic aroma of sweet smelt during July to August might be due to the high contents of accumulated lipid hydroperoxides and polyunsaturated fatty acids in their tissues.     

Host and geographic range extensions of the North American strain of viral hemorrhagic septicemia virus

Viral hemorrhagic septicemia virus (VHSV) was isolated from populations of Pacific sardine Sardinops sagax from the coastal waters of Vancouver Island, British Columbia, Canada, and central and southern California, USA. The virus was also isolated from Pacific mackerel Scomber japonicus in southern California, from eulachon or smelt Thaleichthys pacificus, and surf smelt Hypomesus pretiosus pretiosus from Oregon, USA. Mortality and skin lesions typical of viral hemorrhagic septicemia in other marine fish species were observed among sardine in Canada and in a few surf smelt from Oregon, but the remaining isolates of VHSV were obtained from healthy appearing fish. The prevalence of VHSV among groups of apparently healthy sardine, mackerel and smelt ranged from 4 to 8%, in California and Oregon. A greater prevalence of infection (58%) occurred in groups of sardine sampled in Canada that sustained a naturally occurring epidemic during 1998-99. A captive group of surf smelt in Oregon exhibited an 81% prevalence of infection with clinical signs in only a few fish. The new isolates were confirmed as North American VHSV and were closely related based on comparisons of the partial nucleotide sequence of the glycoprotein (G) gene. The VHSV isolates from sardine in Canada and California were the most closely related, differing from isolates obtained from other marine fish species and salmonids in British Columbia, Canada, Alaska and Washington, USA. These new virus isolations extend both the known hosts (sardine, mackerel and 2 species of smelt) and geographic range (Oregon and California, USA) of VHSV.     

Ecology and exploitation pattern of a landlocked population of sand smelt, Atherina boyeri (Risso 1810), in Trichonis Lake (western Greece)

Age, growth, mortality and exploitation pattern of sand smelt, Atherina boyeri (Risso 1810), in Trichonis Lake (western Greece) were studied from samples taken from catches of local fishermen. Individuals ranged between 44 and 109.53 mm in total length (TL). Age determinations based on scale readings show that the population has a 4-year life cycle. Sand smelt grows allometrically (b=3.18) and relatively rapidly, achieving 52.3% of the growth during the first year; thereafter the annual growth rate drops quickly. The von Bertalanffy growth parameters for all individuals are: L_∞=112.40 mm, k= 0.42 years⁻¹και t_o=−0.40 years. The total mortality rate was Z=1.65 years⁻¹ and the natural mortality rate M=1.07 years⁻¹. The exploitation rate indicates that the population is rather underexploited (E=0.35).     

Hydroacoustic monitoring of the distribution,density and the mass-removal of pelagic fish in a eutrophic lake

A large scale biomanipulation of pelagic fish by trawling was started in the eutrophic Enonselkä basin (26 km²) of Lake Vesijärvi to improve the water quality which had remained poor in spite of the termination of nutrient loading. The distribution and density of the fish were studied by hydroacoustics before and during the removal. The initial annual fish density varied between 13 000–21 000 fish ha^–1 in the study area in August 1984–89. The mass-removal of the fish by pelagic trawling took place in 1989–1992. The catch varied annually between 64 and 92 kg ha^–1. Roach (Rutilus rutilus (L.)) and smelt (Osmerus eperlanus (L.)) accounted for c. 85% of the weight of the catch. The mass-removal decreased the pelagic fish density in the Enonselkä basin during the trawling. An increase in the density was observed after the trawling ceased in these years, and the initial density level was reached within one month. The density level after mass-removal remained high compared with oligotrophic lakes. The pelagic fish had a diurnal ascending trend with the decreasing light intensity in August, and the fish were significantly (p < 0.01) higher in the water mass in temperature non-stratified water in autumn than in stratified water in summer. The fish were somewhat deeper in the years of mass-removal than before it. Mass-removal did not affect the individual length of the echosurveyed fish. Fish smaller than c. 15 cm (TS < –44 dB; mainly smelt) were numerically dominant throughout the whole study period.     

Pond smelt <Emphasis Type="Italic">Hypomesus olidus</Emphasis>, a new species of the ichthyofauna of the Commander Islands

The population of pond smelt Hypomesus olidus has been registered for the first time in the water bodies of Bering Island (Commander Islands). The spawning of this species has been observed in the Sarannoe Lake system, and the maturing breeders have been caught in the freshwater-brackish Gavanskoe Lake system. The spawning grounds, the spawning period, the environment, and the morphology of the breeders have been described. The ratio of Ca and Sr isotopes in the otoliths of the pond smelt inhabiting the Sarannoe Lake system evidenced that this species here was presented by the resident ecotype. The problem of the smelt phylogeny and resettlement in the northern Pacific Ocean is discussed.     

Predation by longfin smelt ( Spirinchus thaleichthys ) on the mysid Neomysis mercedis in Lake Washington

1. Longfin smelt and mysid samples collected in Lake Washington from 1988 to 1992 were examined, and historic data on smelt and mysid abundance were reviewed to assess the impacts of smelt predation on Neomysis mercedis. The feeding habits of smelt were also examined for differences between odd and even years, and seasonal and ontogenetic variations in smelt diet were described. 2. A reciprocal relationship in the abundance of 1+ smelt and Neomysis suggested that smelt regulate mysid abundance in the lake. 3. The proportion of smelt diet contributed by mysids was higher for less abundant year classes of smelt. 4. These results indicate that intraspecific competition for scarce mysids occurs in the even-year classes of smelt.     

Characterization of 24 microsatellite loci in delta smelt, Hypomesus transpacificus, and their cross-species amplification in two other smelt species of the Osmeridae family

We characterized 24 polymorphic tetranucleotide microsatellite loci for delta smelt (Hypomesus transpacificus) endemic to the San Francisco Bay Estuary, CA, USA. Screening of samples (n = 30) yielded two to 26 alleles per locus with observed levels of heterozygosity ranging from 0.17 to 1.0. Only one locus deviated from Hardy–Weinberg equilibrium, suggesting these individuals originate from a single panmictic population. Linkage disequilibrium was found in two pairs of loci after excluding the locus out of Hardy–Weinberg equilibrium. Twenty‐two primer pairs cross‐amplified in wakasagi smelt (Hypomesus nipponensis), and 15 primer pairs cross‐amplified in longfin smelt (Spirinchus thaleichthys).     

Chemical chaperoning action of glycerol on the antifreeze protein of rainbow smelt

Rainbow smelt (Osmerus mordax) accumulate high levels of glycerol and moderate levels of trimethylamine oxide (TMAO) that lower the colligative freezing point of the serum and thereby contribute to seasonal freeze resistance. In the current study, the possibility that one or both of these compounds might also have a chaperoning role at low temperatures in smelt was investigated by studying their effects on the smelt antifreeze protein (AFP). Activity of the AFP in the presence of physiological levels of TMAO and glycerol was observed by means of ice crystal morphology and measured as thermal hysteresis. Ice crystals in AFP solutions were not visibly modified by either compound and TMAO at 25 and 50 mM had no appreciable effect on hysteresis; however, glycerol at 250 and 500 mM increased hysteresis. An equiosmolar level of NaCl was not as effective as glycerol in enhancing hysteresis, suggesting that osmolarity had little or no role. Although cross-linking experiments showed dimerization of AFP to be unchanged in the presence of glycerol, circular dichroism and intrinsic fluorescence analyses revealed enhanced protein folding. As glycerol enhances the folding and consequent activity of smelt AFP, protein chaperoning appears to be an endogenous role of glycerol in this vertebrate species.     

Distinguishing trophic and habitat partitioning among sympatric populations of the estuarine fish Osmerus mordax Mitchill

Sympatric populations of rainbow smelt Osmerus mordax of the St Lawrence middle estuary exhibited distinct morphologies suitable for exploiting either pelagic or benthic habitats in the absence of consistent morphological features related to specific diets. The magnitude of morphological differentiation was elevated and constant over 3 years even though statistically significant differences were observed among samples within populations. Both populations were spatially segregated in the estuary but some population mixing occurred at low densities of rainbow smelt. Diet analysis revealed that both populations opportunistically feed on large macrozooplankton. An amended version of Schoener's D was developed and used to compare the magnitude of niche overlap. It revealed that the diet of the middle estuary rainbow smelt differed according to the area where samples were collected but no differences existed between populations. The exploitation of ecologically distinct habitats appeared to be effective in maintaining morphologically distinct sympatric populations within an estuarine setting in the absence of diet differentiation.