Seasonal and interannual variation of ichthyoplankton off Mauritania

Changes of the quantitative and qualitative composition of ichthyoplankton off Mauritania (21–16° N) in different seasons of 1997–2008 are analyzed. In this area, pelagic eggs and larvae of over 120 fish species belonging to 71 families are recorded. In warm periods, the fish of the tropical fauna intensively spawn off Mauritania; round sardinella Sardinella aurita, West-African horse mackerel Trachurus trecae, and jack mackerel Caranx rhonchus are dominant. In cold periods, active spawning of fish belonging to the tropical fauna is recorded, the most abundant are European pilchard Sardina pilchardus, European horse mackerel Trachurus trachurus, and Atlantic mackerel Scomber japonicus. The spawning biomass of principal commercial fish species is calculated on the basis of the quantity of eggs laid by females. Environmental factors control fluctuations of abundance and distribution of ichthyoplankton in the considered region.     

Seasonal and interannual variation of ichthyoplankton off the coast of the Moroccan Sahara

Changes in the qualitative and quantitative composition of ichthyoplankton off the coast of the Moroccan Sahara (21–28° N) in different seasons of 1994–2007 are analyzed. In this region, the pelagic eggs and larvae of over 100 fish species belonging to 62 families have been recorded. In cold periods, off the coast of the Moroccan Sahara there is peak in the spawning of fish of the subtropical fauna. The majority of them are European pilchard Sardina pilchardus, common scad Trachurus trachurus, and Atlantic mackerel Scomber japonicus. In warm periods there is intensive spawning of fish of the tropical fauna. Among them, dominants are round sardinella Sardinella aurita, West-African scad Trachurus trecae, and Atlantic bonito Sarda sarda. The spawning biomass of principal commercial fish is calculated by the quantity of eggs laid by females. The environmental factors are indicated that influence the fluctuation of abundance and distribution of ichthyoplankton in the region under consideration.     

Summer-autumn ichthyoplankton of the Sea of Okhotsk and the Sea of Japan and special traits of feeding of fish larvae and fry in 2003–2004

In summer-autumn of 2003–2004, the ichthyoplankton of the Sea of Okhotsk comprised 35 species. In this period the most widely distributed and numerous were larvae of the lord Hemilepidotus gilberti, the Pacific stout sand lance Ammodytes hexapterus, and the Sakhalin dab Limanda sakhalinensis. The maximum catches of fish larvae were attributed to coastal waters off eastern Sakhalin and to the shelf of the northern part of the Sea of Okhotsk. In November of 2003, the ichthyoplankton of the Sea of Japan was represented by fish larvae belonging mainly to the boreal ichthyocomplex. The catches consisted predominantly of larvae of the arabesque greenling Pleurogrammus azonus, the ronquil Bathymaster derjugini, and the rockfish Sebastes owstoni. Fish larvae and fry in the northwestern part of the Sea of Japan were caught principally within 43°–45° N and 137°–139° E above the depth 1500–2000 m. The food spectrum of fish larvae in the Sea of Okhotsk and the Sea of Japan comprised over 20 plankters of various size belonging to seven taxa. Irrespective of fish species, the food items common of all fish were copepods Pseudocalanus minutus and Oithona similis. The daily rations were calculated for mass species (Hemilepidotus gilberti, Ammodytes hexapterus, Hexagrammos stelleri, Pleurogrammus azonus, Bathymaster derjugini, and Sebastes owstoni). The larvae of all considered species in the Sea of Japan and in the Sea of Okhotsk fed predominantly in the light period of the day.     

Ichthyoplankton of the Azores seamounts

Species composition and quantitative distribution of ichthyoplankton in the region of the oceanic seamounts of the Azores complex from 2000 to 2004 are considered. The spawning biomass of the main fishery item of this region—Atlantic jack Trachurus picturatus—is calculated. The ichthyoplankton of the Azores seamounts in the period under consideration included eggs and larvae of 60 fish species from 26 families. In the summer, 20 species of eggs and larvae from 11 families and, in winter, 57 species from 24 families were recorded. Larval Myctophidae and Gonastomatidae have the most mass in the plankton in both seasons. The eggs and larvae of commercial fish species (T. picturatus and Pacific mackerel Scomber japonicus) were recorded mainly in the cold period. The species and quantitative composition of ichthyoplankton of the South Azores seamounts is far more numerous than in the North Azores seamounts. The region of the seamounts of the South Azores complex, judging from the estimation of biomass of commercial fish with different methods, can be regarded as a reserve for the fishery of Russian vessels in the central eastern Atlantic.     

Life history and morphology of Eel Larvae in the Gulf of Guinea of western Africa: revisiting Jacques Blache’s research (1960–1977) 40 years later

Eel larvae (leptocephali) are rarely studied extensively both spatially and temporally, and detailed illustrations of most species are limited. This study uses the unique research reported in the monograph of Blache (Leptocéphales des poissons anguilliformes dans la zone sud du golfe de Guinée. ORSTOM Faune Tropicale 10:1–381, 1977, in French) to describe and evaluate the species composition, abundance, life history characteristics and morphology of 10,284 anguilliform leptocephali collected throughout the year during 15 ichthyoplankton surveys (1960–1971) in relation to regional oceanography. Leptocephali of 70 species of 7 families were described, with Ophichthidae (26 species), Muraenidae (13), and Congridae (13) being the most diverse, and local spawning indicated by ≥ 34 species. Larvae of biogeographically restricted Heterencheylidae eels (mud eels) were abundant along the continental shelf and 5 species comprised 35% of total catches. Their larval distributions may reflect adult depth-segregation from nearshore/estuaries to the outer shelf and slope and larval retention. Nettastomatid leptocephali of Hoplunnis punctata were the most abundant species, and Rhynchoconger sp., Uroconger syringinus, Chlopsis olokun, and Dalophis boulengeri were also abundant. Small leptocephali distributions indicated spawning occurred over or near the continental shelf, and length-frequency data indicated most spawning was during the November–May warm-water season. Detailed morphology illustrations showed the characteristics of all stages of larvae. The Gulf of Guinea eel fauna is not diverse compared to the Indo-Pacific possibly due to phylogeography and a lack of coral reef habitats and the unusual low-latitude seasonal influx of cold surface waters, but is unique in being the worldwide center of distribution of the burrowing eels of the Heterencheylidae.     

Summer Ichthyoplankon in Onega Bay of the White Sea: Species Composition and Spatial Distribution

Data on the species composition and distribution of ichthyoplankton in Onega Bay of the White Sea are presented for June–July 2007, 2010–2012, and 2015–2016. In the ichthyoplankton, the specimens of the early developmental stages of 21 fish species were registered; the larvae of the White Sea herring Clupea pallasi marisalbi, capelin Mallotus villosus, and Pacific sand lance Ammodytes hexapterus were the most abundant. It is shown that the northwestern and southeastern zones, distinguished in Onega Bay by hydrophysical parameters, also differ in species composition and in ichthyoplankton abundance.     

Fish assemblages in deep Italian subalpine lakes: history and present status with an emphasis on non-native species

We provide a comprehensive overview of the status of fish assemblages in eight Italian subalpine lakes using multiple data sources: historical records, standardised sampling and fishery catch statistics. Thirty-four fish species were recorded, twenty of which are native, seven introduced historically and another seven introduced recently. The number of fish species in individual lakes has increased by between 25 and 65% from 1855 to the present, with the increase being higher in the larger lakes. Non-native species contributed between 4.0 and 71.5% to standardised catches by numbers and between 4.8 and 65.1% by biomass. Roach Rutilus rutilus and pumpkinseed Lepomis gibbosus dominated electrofishing and benthic catches by number, while open-water catches were dominated by the coregonids European whitefish Coregonus lavaretus and gangfish Coregonus macrophthalmus. In terms of biomass, electrofishing catches were dominated by crucian carp Carassius carassius, largemouth bass Micropterus salmoides and wels catfish Silurus glanis, benthic catches were dominated by roach, European whitefish and crucian carp, and open-water catches by coregonids. Commercial fisheries are important ecosystem services provided by subalpine lakes, with their harvests now dominated by non-native species. To deliver effective biodiversity conservation and ecosystem services provision, the prioritisation of targets and interventions of management of non-native species is needed.     

Distribution of the larvae of capelin <Emphasis Type="Italic">Mallotus villosus</Emphasis> and lesser sandeel <Emphasis Type="Italic">Ammodytes marinus</Emphasis> in the White Sea

The early developmental stages of capelin Mallotus villosus and lesser sandeel Ammodytes marinus were the major representatives of the fish larvae in the ichthyoplankton of the open waters of the White Sea in June 2007 and 2010 and in July 2010 and 2011. The larvae of these two species were widely distributed in the White Sea and have been registered in the large bays and in the other parts of the sea. The larvae of capelin and lesser sandeel were the most abundant in Onega Bay and in Dvina Bay and in Gorlo Strait of the White Sea; the larvae of lesser sandeel have also been found in the coastal waters of Kandalaksha Bay. The schooling of the larvae of these two species were characterized by a relatively permanent localization that referred to the spawning grounds; the shape and the location of the schoolings usually depend on the presence and configuration of the areas of the pronounced gradients of the hydrophysical parameters in these areas.     

Biological features of the common fish species in Olyutorsky-Navarin region and the adjacent waters of the Bering Sea: 4. family sculpins (Cottidae)

Based on the materials of investigations conducted for 20 years (1995?2015), the features of biology of the common fish species of the family Cottidae from the northwestern Bering Sea are studied. These species are found during summer and fall in the waters of the Olyutorsky-Navarin region. The size–age parameters of the fishes collected with different fishing gears, as well as the features of their body length and body weight dynamics, spawning time, and spawning conditions, are described. The largest exemplars of shorthorn sculpin Myoxocephalus verrucosus and staghorn sculpins, armorhead sculpin Gymnocanthus galeatus and G. detrisus, are recorded in the catches of snurrevads, while the fishes caught in trawls are characterized by smaller size. Interannual variability of the size composition of the fish is related to the abundance of certain generations or to the fishery directed to different associations of sculpins. In the coastal waters, comparatively low average body size is usual for the majority of common sculpin species (with the exception of lords, yellow Irish lord H. jordani and Gilbert’s Irish lord H. gilberti) because of the dominance of juveniles.     

Biological features of common fish species in Olyutorsky-Navarin region and the adjacent areas of the Bering Sea: 3. Righteye flounders (Pleuronectidae)

Biological features of the seven abundant commercial species—the Pacific halibut Hippoglossus stenolepis, the Greenland halibut Reinhardtius hippoglossoides, the Alaska plaice Pleuronectes quadrituberculatus, the northern rock sole Lepidopsetta polyxystra, the yellowfin sole Limanda aspera, the flathead sole Hippoglossoides elassodon, and the Bering flounder H. robustus (Pleuronectidae)—have been studied for a 20-year period (1995?2015). These species are present in the northwestern Bering Sea in the summer–autumn season; they form the gatherings in Olyutorsky-Navarin region. The size-weight spectra of the fish caught by different fishing gear has been analyzed, the peculiarities of the linear growth and the weight gain, as well as the spawning period and scale and the spawning conditions, have been described. The largest halibut specimens have been registered in the bottom setlines and gill nets, while flounders were in snurrevad catches; the smallest specimens have been observed in trawl catches. The abundant year-class in most of the studied species is seen well on the long-term plots of the fish size spectra and is tracked by the decrease of their biological parameters. The species that demand vast growing grounds (Pacific halibut, Alaska plaice, northern rock sole, and yellowfin sole) are characterized by a smaller average body size of the fish sampled in the coastal waters due to the prevalence of the young specimens in this area.     

The ichthyofauna of coastal waters southwest of Crimea in 2003–2004

The ichthyofauna of the narrow coastal zone of southwest Crimea in 2003–2004 was represented by 79 fish species belonging to 36 families. The structure of the species composition of eggs, larvae, and adult fish in these years indicated to its restoration in comparison with the late 1980s to early 1990s. The abundance of commercial fish increased: Engraulis encrasicolus ponticus, Trachurus mediterraneus ponticus, and Mullus barbatus ponticus. The quantity of migratory fish increased: Pomatomus saltatrix and Sarda sarda. The presence in winter catches of Trachurus mediterraneus ponticus and Pomatomus saltatrix indicated favorable conditions for their wintering off South Crimea. Appearance in catches of the fish of elder age groups is evidence of the restoration of their age structure. The competitor for food Mnemiopsis leydyi still influences the food resources of the fish and, thus, their survival. If they appear in plankton simultaneously, the abundance of larvae drastically decreases. The obtained data indicate to the vulnerability of coastal biocenoses to anthropogenous impact and to the necessity of monitoring of fish resources and of their protection.     

Species composition and distribution of summer ichthyoplankton in Chupa Estuary (Kandalaksha Bay of the White Sea)

On the basis of ichthyoplankton surveys performed in July 2002 and June 2004–2005 in Chupa Estuary and adjacent waters of Kandalaksha Bay, species composition and distribution of eggs and larvae of fish were studied. Early stages of development of seven fish species were found in the composition of ichthyoplankton. The bulk of abundance of ichthyoplankton was formed of Clupea pallasii marisalbi larvae. It was shown that the sites of aggregation of larval C. pallasii marisalbi from June to July are constant and located in the central and preestuarine areas of Chupa Estuary. Possible routes of their passive migrations within Chupa Estuary and the adjacent water area of Kandalaksha Bay are considered. It is suggested that the drift of larvae beyond the estuary proceeds slowly, and after hatching they can long stay in the estuary concentrating in its central and preestuarine areas.     

Distribution of ichthyoplankton in the eastern Peter the Great Bay,Sea of Japan,in June and July of 2007

Comparison of the results of ichthyoplankton surveys conducted at 97 stations in the eastern part of the Peter the Great Bay of the Sea of Japan, in June–July 2007 with the similar research data of the 1950s shows that at present, as was the case 50 years ago, flatfish eggs belonging mainly to the yellowfin sole Limanda aspera and brown sole Pleuronectes herzensteini prevail in the local ichthyoplankton (up to 86%). The highest concentrations of these species’ eggs were recorded in the Vostok Bay and Strelok Bay. The spawning activity of flatfish in 2007 is found to be lower than in the mid 1900s, but the significance of the eastern part of the Peter the Great Bay for flatfish reproduction remains large. The importance of long-term monitoring in this area, which is being subjected to steadily growing anthropogenic impacts, is also proven.     

The search for proteins involved in the formation of crustacean cuticular structures

Summer ichthyoplankton surveys were conducted in the northern Gulf of Mexico from 2007 to 2010 to characterize the distribution and abundance of tuna larvae. Larval assemblages of tunas were comprised of four genera: Thunnus, Auxis, Euthynnus, and Katsuwonus. Thunnus were the most abundant and four species were detected; T. atlanticus [blackfin tuna], T. obesus [bigeye tuna], T. albacares [yellowfin tuna], and T. thynnus [bluefin tuna]. Intra- and inter-annual variability in the distribution and abundance of Thunnus species were observed with higher densities in 2008 and 2009, with a decline in abundance observed in 2010. Distribution and abundance of Thunnus larvae were influenced by physical and chemical conditions of the water mass, notably sea surface temperature and salinity. Distinct species-specific habitat preferences were observed and the location of mesoscale oceanographic features influenced larval abundance with higher densities of T. atlanticus, T. obesus, and T. albacares near anticyclonic (warm core) regions and the Loop Current, while T. thynnus was observed in higher densities near cyclonic (cold core) regions. This study demonstrates that spatial and temporal variability in the location of mesoscale oceanographic features may be important to partitioning nursery habitat among Thunnus species.     

Species composition and distribution of ichthyoplankton in the waters of northeast Sakhalin

Data on the species composition and abundance of the ichthyoplankton obtained in 2012, 2014, and 2015 in the waters of northeast Sakhalin are presented; these data were collected during the standard accounting surveys to estimate the egg concentration and breeders of Alaska pollock Theragra chalcogramma. The areas of the main concentrations of eggs and larvae of a number of commercial fish species have been determined, interannual variations in their abundance have been analyzed, and the distribution of ichthyoplankton with some parameters of the environment, such as depth, temperature, and main currents, has been linked. During the study period, 30 species representing 11 families were recorded in the ichthyoplankton. The average concentration of ichthyoplankton varies within the range of 113–201 ind./m². The pollock eggs absolutely dominated by 78–89%; followed by the eggs of the Bering flounder Hippoglossoides robustus (5–8%). It was found that the number of eggs and larvae of flounders and of a number of the other fish species in the northern part of the study area increases during the years characterized by a large volume of runoff of Amur River.     

On micronekton and ichthyoplankton of the frontal zone of the gulf stream and subpolar waters (Polygone “Titanic”)

Results of studies of the species composition of micronektonic fish and ichthyoplankton in the frontal zone of the Gulf Stream and subpolar waters at the stationary polygone “Titanic” performed in years with different hydrological situations (2000 and 2003) are provided. In July through August of 2000 during the penetration in the polygone of warm waters of the Gulf Stream, a considerable (almost by an order of magnitude) increase in the species composition of fish due to numerous tropical and subtropical species was recorded in comparison with the period of studies in 2003, close by dates, when the region was occupied by the cold waters of the Labrador Current. In the summer of 2000, of the 80 taxonomic forms found on the polygone, 48 were represented only by larval stages of development; 27, only by juvenile and adult specimens; and 5, by both larvae and juvenile and adult specimens. The last five species include Ceratoscopelus maderensis and Lampanyctus pusillus (Myctophidae), Arctozenus risso (Paralepididae), Stomias boa (Stomiidae), and Gonostoma elongatum (Gonostomatidae). In the summer of 2003, larval fish were absent in collections, and only juvenile and adult specimens of eight species from ten families were found. The bulk of the population of micronektonic fish in this period, as in the summer of 2000, was formed by the same arcto-boreal species of myctophids Benthosema glaciale.     

Pitfall trap construction affects the efficacy of ground beetle counts

Ground beetles were sampled in a broadleaved deciduous forest in Kaluga Province in April–October 1995 using 90 traps grouped in 18 experimental plots. Three types of pitfall traps were used: glass jars, white plastic cups, and cylindrical containers made of transparent plastic bottles. Two types of cover put above the traps were tested: transparent and black. Altogether, 72 carabid species were found, of which only 10 species were shared by all the experimental plots: Leistus terminatus, Carabus hortensis, C. glabratus, Cychrus caraboides, Pterostichus niger, P. oblongopunctatus, P. strenuus, P. melanarius, Calathus micropterus, and Badister lacertosus. The Jaccard binary similarity index between the experimental plots amounted to 37–68% while the Bray-Curtis similarity index was 66–89%. Both the trap type and the cover color significantly affected the similarity of the species structure and species composition of the samples. Plastic cups provided the highest catches of beetles, but this was due to the most abundant species, P. oblongopunctatus. Containers provided the highest catches of C. glabratus. The total abundance was higher for the traps with transparent covers than for those with black covers. Traps with transparent covers provided significantly higher catches of L. terminatus, P. oblongopunctatus, Asaphidion flavipes, and Harpalus rufipes. An adequate assessment of the species composition of a particular habitat requires at least 30 pitfall traps.     

Plant–insect interactions: gentians,seed predators and parasitoid wasps

While studying breeding systems and pollination ecology of nine Gentiana species (G. lutea, G. punctata, G. asclepiadea, G. pneumonanthe, G. cruciata, G. pyrenaica, G. verna, G. utriculosa, and G. nivalis) in the Bulgarian mountains, we recorded number of insects that feed on their maturing seeds. In addition, parasitoid wasps in connection to these seed predators were detected. Insects are identified and the impact on the seed set of afore mentioned Gentiana species is estimated. Fruit capsules of Gentiana spp. from different populations in the mountains in Bulgaria were investigated for the presence or absence of damage by larvae during the period of 16 years. The seed destruction varies among the nine investigated Gentiana species. The insects whose larvae damaged the seed/fruit set belonged mainly to Coleoptera and Diptera. The larvae of lycaenid butterflies, Maculinea spp. (Lepidoptera), were recorded only in seeds of G. asclepiadea, G. pneumonanthe and G. cruciata. Parasitoid wasps from the families Ichneumonidae, Braconidae, and Pteromalidae were identified, some of them new for the fauna of Bulgaria.     

Biological features of the common fish species in Olyutorsky-Navarin region and the adjacent waters of the Bering Sea: 2. Families Macrouridae,Clupeidae, and Osmeridae

Biological features of the four common fish species, giant grenadier Albatrossia pectoralis (Macrouridae), Pacific herring Clupea pallasii (Clupeidae), Pacific rainbow smelt Osmerus mordax dentex, and Pacific capelin Mallotus villosus catervarius (Osmeridae), were studied under the 20-year dataset (1995?2015). These species inhabit the northwestern Bering Sea in the summer–autumn period and form the schoolings in the Olyutorsky-Navarin region. The size–age parameters of the fish caught by different sampling gear, as well as the peculiarities of the body length and body weight dynamics, spawning periods, spawning range, and conditions, were analyzed. The largest specimens of giant grenadier, Pacific herring, and Pacific rainbow smelt were observed in the catches performed by the bottom setline and the gill nets; the smallest fish were found in the trawl catches. The body length and body weight of Pacific herring were larger in the pelagic trawls compared to the bottom trawls; an opposite pattern was observed for the Pacific capelin. The abundant year-class in the species with short life cycle (capelin and herring) is well tracked on the longterm plots of the fish body size; this is accompanied by the decrease of their biological parameters. Herring stock covers large growing grounds; smaller body size was observed for the herring grazing in the coastal waters; young specimens dominate here.