Distribution of myctophid resources in the Indian Ocean

Mesopelagics are one of the largest under-exploited marine resources with wide distribution in the world oceans. Lanternfishes are the key members of mesopelagic communities and the total resource in the world oceans is estimated at 600 million tons. Lanternfishes belong to the family Myctophidae which comprises of about 250 species in 35 genera. Myctophids account for about 75% of total global catch of small mesopelagic fishes. They are known to exhibit diel vertical migration, concentrating during the day time between 400 and 1,000 m, and between 5 and 100 m, during the night. In this paper, an attempt is made to review the existing information on the occurrence and distribution of myctophid resources in the Indian Ocean. 137 myctophid species have been reported from the entire Indian Ocean. Studies in the Arabian Sea have indicated that the area is rich in the midwater fish stocks dominated by myctophids with an estimated potential of 100 million tons.     

Distribution,quantitative composition,and feeding of jellyfish in the Western Bering Sea in summer and fall

Materials from six complex trawl surveys conducted by the TINRO-Center in the upper epipelagic zone of the Western Bering Sea during the summer-fall seasons from 2002 through 2006 were used as the basis of this paper. The overall biomass (and abundance) of jellyfish increased from 0.6–0.8 million t (1.1–1.8 billion individuals) in the summer up to 0.9–1.7 million t (4.4–4.8 billion individuals) in fall. Scyphomedusa Chrysaora melanaster and the Hydromedusa Aequorea forskalea made up the major part of the jellyfish biomass (67–97%). Their distribution varied significantly. A. forskalea aggregated mainly in the deepwater part of the Bering Sea. Ch. melanaster was widely dispersed across the entire area of the investigations and formed the most considerable aggregations in the Anadyr-Navarin area. In the fall of 2006 the diet of jellyfish generally consisted of plankton organisms (copepods, euphausiids, amphipods, pteropods, chaetognaths, ostracods, and larval decapods). However, Ch. melanaster had a greater portion of fish and larval squid in its diet.     

Feeding patterns of post-larval and juvenile notothenioids in the southern Weddell Sea (Antarctica)

Summary The food of 163 juvenile specimens of 13 species of notothenioid fishes collected in the southern Weddell Sea (Antarctica) was analyzed. Investigated fish size range was 3–13 cm SL. Principal food items were calanoid copepods Metridia gerlachei, Calanoides acutus, and Calanus propinquus; all developmental stages of Euphausia crystallorophias, and post-larval nototheniid fish Pleuragramma antarcticum. Diet of juvenile channichthyids is limited to few species of euphausiids and fish in the size > 10 mm, but does not include significant numbers of copepods. Pelagic stages of nototheniids feed on copepods and/or larval euphausiids smaller than 10 mm. At similar size, nototheniids and bathydraconids take smaller prey items than channichthyids.     

Prey selection by age-0 walleye pollock, Theragra chalcogramma, in nearshore waters of the Gulf of Alaska

Juvenile walleye pollock, Theragra chalcogramma, is the dominant forage fish on the continental shelf of the Gulf of Alaska, yet little is known about the feeding habits of this important interval of pollock life history. The taxonomic composition and size of prey found in the stomachs of age-0 juveniles collected at three nearshore locations in the Gulf of Alaska in September 1990 were compared to the composition and size of zooplankton collected in concurrent plankton tows. The maximum length of prey consumed increased dramatically over the length range of pollock examined (58–110 mm) from approximately 7 mm to 30 mm, due mainly to the consumption of large euphausiids and chaetognaths by the bigger individuals. The maximum width of prey changed little over this size range although there was a general increase in prey width with increasing predator size. The minimum prey length and width did not change with increasing fish size. Juvenile pollock generally selected the larger prey sizes relative to what was available. Juvenile pollock showed a marked preference for adult euphausiids and decapod larvae and an avoidance of copepods and chaetognaths relative to the numbers collected in net tows. These results are discussed relative to the feeding ecology of these juvenile fishes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Prey selection by larvae of Prochilodus lineatus (Pisces: Curimatidae): indigenous zooplankton versus veligers of the introduced bivalve Limnoperna fortunei (Bivalvia: Mitilidae)

We studied experimentally the feeding selectivity of larvae of Prochilodus lineatus (Pisces), with particular emphasis on the role of veligers of the exotic bivalve Limnoperna fortunei. Three concentrations of veligers were offered to three developmental stages of P. lineatus. Veliger concentrations were: (1) higher than in the field (“enriched”, 0.09 ind. ml⁻¹), (2) unmodified from field conditions (“normal”, 0.06 ind. ml⁻¹), and (3) lower than in the field (“low”, 0.02 ind. ml⁻¹). Fish developmental stages were protolarvae (approx. 10 days old), mesolarvae (17 days), and metalarvae (25 days). Proportions (in terms of numbers and biomass) and selectivity values were calculated for each prey item evaluated: veligers, small cladocerans + nauplii, medium-sized cladocerans, copepodits, and large cladocerans + copepods. Protolarvae and mesolarvae consumed veligers almost exclusively (88–90%, both in numbers and in biomass) when offered prey enriched in veligers, whereas for metalarvae veligers represented only 16.0% of the food consumed. At lower veliger concentrations, only protolarvae preferred Limnoperna veligers, whereas older fishes switched gradually to crustacean plankton. We conclude that veligers are preferred by the early fish developmental stages, and we speculate that this may be because their slower swimming makes them easier to capture than planktonic crustaceans. However, as fish larvae grow larger, veligers become too small a prey for their energetic needs, and they switch to larger items like cladocerans and copepods. We anticipate that this new and abundant food resource has an important impact on the survival and growth of P. lineatus.     

Parasite communities of the Schlei Fjord (Baltic coast of northern Germany)

The parasite faunas of snails, mussels, crustaceans and small-sized fishes were investigated over a period of six months in the Schlei fjord, on the Baltic coast of Schleswig-Holstein. Two sites differing in salinities were compared: Missunde with 5–9 ‰ and Olpenitz with 12–20 ‰. Prevalences, number of host-parasite combinations, numbers of core and secondary species were generally higher in Olpenitz than in Missunde. In the latter site, only prevalences of cestodans in planktic copepods and the number of rare species were apparent. Specificity of parasites was relatively high in snails, mussels and fishes, but lower in benthic crustaceans. Parasites may survive in an extreme environment like brackish water by means of special strategies which differ from those acquired in the marine milieu: suspension of specificity, adaptation to hosts which are genuine brackish water species, extension of host spectra, and shortening of life-cycles. Although the parasite communities of the Schlei fjord were primarily influenced by the prevailing salinities, the influence of other factors, e.g. environmental stress, was also confirmed. Whereas generally low prevalences in Missunde may contradict Thienemann’s biocoenotic rule, planktic parasites infested their hosts often at higher rates than in Olpenitz. This phenomenon is explained by the poorer environmental condition of the benthal zone in Missunde compared to that of the pelagial or the benthal zones of Olpenitz.     

Simulated annual plankton production in the northeastern Pacific Coastal Upwelling Domain

A microcomputer simulation model is presented that describesthe generalized plankton production dynamics, in the surfacemixed layer, of the Juan de Fuca Eddy located on the southwesternBritish Columbia continental shelf. The Juan de Fuca Eddy simulationmodel evaluates how the annual biomass production of diatoms,copepods and euphausiids is forced by plankton feeding interactions,seasonal variability in upwelling, water temperature and solarradiation, and generalized fish predation. The model estimatesannual primary production of 345 g C m^–2 year^–1and secondary production of 19.4 g C m^–2 year^–1for copepods and 6 g C m^–2 year^–1 for euphausiids,during 1985–89; -90% of the annual plankton productionwas generated during the April-October upwelling season. Perturbationsof 22 abiotic and biotic parameters, one at a time by ±10%of nominal values, indicated that oceanic variability (e.g.upwelling rate) most strongly affected primary production. Conversely,zooplankton production was most sensitive to variability inbiological parameters describing zooplankton grazing potentialand growth (e.g. gross growth efficiency). Simulated seasonalbiomass patterns of diatoms, copepods and euphausiids were foundto closely match empirical data. However, euphausiid biomassproduction in the Juan de Fuca Eddy alone was unable to meetthe demands of estimated pelagic fish consumption. Local Eddyeuphausiid populations had to be supplemented, from regionaleuphausiids. by a mechanism that is proposed to be linked tothe seasonal pattern and intensity of positive Ekman transport(upwelling).     

The influence of flood cycle and fish predation on invertebrate production on a restored California floodplain

Although floodplains are known to be tightly controlled by the flood cycle, we know comparatively little about how flooding influences predators and their consumption of secondary production, particularly in highly seasonal floodplains typical of Mediterranean climates. In this study, we investigate how the seasonal dynamics of a central California floodplain influence the timing and magnitude of fish predation and the abundance and composition of invertebrates. For 3 years (2000–2002), we compared changes in abundances and size distributions of invertebrates through the flood season (January–June) with seasonal changes in the abundance of larval and juvenile fishes. Using diet analysis of fishes and manipulative feeding experiments with fishes in field enclosures, we link specific changes in invertebrate populations directly to feeding preferences of seasonally abundant fish. Early in the flood season prior to March, we found little influence of fish predation, consistent with the near absence of larval and juvenile fishes during this period. Coinciding with the midseason increase in the abundance of larval and juvenile fishes in April, we found significant declines in zooplankton abundance as well as declines in the size of zooplankton consistent with fish feeding preferences. Our results were consistent with results from feeding enclosure experiments that showed that fish rapidly depressed populations of larger cladocerans with much less effect on smaller cladocerans and calanoid copepods. At the end of the flood season, zooplankton abundances rapidly increased, consistent with a switch in the feeding of juvenile fish to aquatic insects and subsequent fish mortality. We also found that zooplankton biomass on the floodplain reached a maximum 2–3 weeks after disconnection with the river. We suggest that floodplain restoration in this region should consider management strategies that would ensure repeated flooding every 2–3 weeks during periods that would best match the peaks in abundance of native fishes. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

Larval fishes and zooplankton in a cyclonic eddy in Hawaiian waters

A cold-core eddy occurred off the Kona coast of the island ofHawaii in July 1982. It remained in that area for {small tilde}70days, sufficient time for many reef fish species to completetheir planktonic larval phase. The deployment of eight currentdrogues in the eddy showed how entrainment of plankton fromthe reef and adjacent offshore waters can occur and that passivedrift can return drifters from the deep sea to shore. Larvalfishes may be swept past the island every 7–8 days ina weak eddy and 3.5–5 days in a strong eddy. Planktoncollections were made at night near the surface and at the samedepth as the current drogues. Zooplankton were most concentratedat the eddy center. Taxonomic analysis of the plankton showedthat the dominant animals were calanoid copepods, malacostracans,hyperud amphipods, gastropod and bivalve larvae and chaetognaths.The densities of zooplankton and larval fishes in the eddy werehigher than in the same area before the arrival of an eddy.Larval fishes were most abundant in the periphery and amongthese, midwater fish larvae (gonostomatids and myctophids) werethe most numerous. Other numerous fish larvae in the eddy includedscombrids, particularly Thunnus albacares. carangids and thereef fish, Abudefduf abdominalis is (Pomacentridae).     

Diel variation in feeding rate and prey composition of herring and mackerel in the southern Gulf of St Lawrence

Diel feeding patterns of herring Clupea harengus and mackerel Scomber scombrus in the southern Gulf of St Lawrence were examined based on samples obtained by midwater trawling between 19 and 26 June 2001. Within 3 h time periods, stomach contents tended to be more similar between fish from the same tow than between fish from different tows. Thus, in contrast to previous diet studies, which have used individual fish stomachs as independent observations, tow was used as the experimental unit in statistical analyses in this study. Diel patterns in stomach fullness were identified using generalized additive models. Two peaks in stomach fullness occurred for herring, one in the morning and the other in the evening. Mackerel showed an increase in feeding intensity throughout the day with a peak in mid‐afternoon. The diel changes in stomach contents suggested rapid gastric evacuation rates for both species, especially for herring. The estimate of the instantaneous evacuation rate for herring was twice that for mackerel. Calanus copepods (mainly C. hyperboreus ), fishes (mainly capelin Mallotus villosus ) and euphausiids were the main prey found in the stomachs of both species. Calanus copepods dominated the diet of herring regardless of time period. They also dominated the diet of mackerel during the late afternoon, evening and night while fishes and euphausiids were dominant during the morning and early afternoon. These diel patterns emphasize the need for sampling throughout the day and night in order to estimate ration and diet composition for bioenergetic and ecosystem models.     

Distribution of euphausiids in the Kuroshio front and warm water tongue with special reference to the surface aggregation of Euphausia pacifica

The distribution of euphausiids and other macrozooplankton wasinvestigated in and around the Kuroshio front formed in theKa.shima-nada Sea. Japan. during the summer of 1993. Zooplanktonwere dominated by copepods, chaetognaths and euphausiids. andtheir biomass was significantly higher at the frontal stations.Eighteen species belonging to six genera of euphausiids werecollected. The species composition and community structure ofeuphausiids changed drastically with the ‘areas’corresponding to the hydrological conditions. In the area underthe influence of the Kuroshio. most euphausiids were warm-waterspecies. In contrast. euphausiids found in the frontal areawere those usually predominating in subarctic or cold Oyashiowaters. In the area of the warm water tongue. where warm Kuroshiowater lay above cold Oyashio water, the species compositionof euphausiids represented a mixture of both warm- and cold-waterspecies. Surface aggregations of Euphausia pacifica were observedin the frontal area during the night. The biomass and densityof the aggregations ranged between 90 and 136 mg C m^–3and 164 and 238 md. m^–3 respectively. These aggregationswere mostly made up of immature individuals of < 12 mm. Passivetransportation by convergent flow at the front seems to explainthe observed surface aggregations of E.pacifica.     

Proximate composition and energy density of nototheniid and myctophid fish in McMurdo Sound and the Ross Sea,Antarctica

Nototheniid and myctophid fish are primary prey for marine piscivores, yet little is known about their nutritional value. In this study, we characterized the proximate composition [PC: water, fat (neutral lipids), crude protein (CP) and ash] and energy density (ED; kJ g⁻¹) of fifteen fish species from McMurdo Sound and the Ross Sea, Antarctica. We assayed the entire fish for all species except for the large Antarctic toothfish, Dissostichus mawsoni (muscle tissue only). On a wet mass basis (WM), fish were variable in composition: moisture content ranged from 64.9 to 87.3% WM, fat from 0.5 to 17.4% WM, CP from 7.7 to 16.7% WM, ash from 11.2 to 21.0% FFDM (fat-free dry mass), and ED from 2.9 to 10.3 kJ g⁻¹. Myctophids and pelagic nototheniids such as Pleuragramma antarcticum and D. mawsoni were high in fat content (7–17% WM), while a bathylagid and benthic nototheniids including most Trematomus spp. and Lepidonotothen squamifrons were low in fat (0.5–4% WM). The epibenthic Trematomus species (T. eulepidotus and T. lepidorhinus) were intermediate. Energy density tracked fat content, with highest values in myctophids and pelagic nototheniids. The variation in nutrient and energy density confirms that prey composition must be taken into account when modelling energy and nutrient fluxes within the Antarctic ecosystem. Further analyses of prey collected over a number of different locations and seasons are needed in order to determine how the nutritional value of certain species might affect annual or decadal variation in reproductive success or population size of top predators.     

Diet of five species of the family Myctophidae caught off the Mariana Islands

Myctophids are important components of marine food webs, but little is known about the diets of many species in large stretches of the ocean. To fill this knowledge gap, Myctophum lychnobium, Symbolophorus evermanni, Centrobranchus andreae, Myctophum aurolaternatum, and Myctophum nitidulum were collected off the previously unsampled Mariana Islands in 2007. Myctophum lychnobium predominately consumed pelagic molluscs (28 % by number), amphipods (26 %), and copepods (24 %). Symbolophorus evermanni consumed copepods (53 %) and larval fishes (22 %). Centrobranchus andreae consumed molluscs (90 %). Little dietary overlap occurred among these fishes, and the reliance on molluscs was unusual compared to results from previous studies.     

Ecological effects of longline fishing and climate change on the pelagic ecosystem off eastern Australia

Pelagic longline fisheries target (or catch incidently) large apex predators in the open ocean (e.g. tunas, billfish and sharks) and have the potential to disrupt the ecosystem functionality if these predators exert strong top–down control. In contrast, warming of oceans from climate change may increase bottom–up effects from increases in primary productivity. An ecosystem model of a large pelagic ecosystem off eastern Australia was constructed to explore the potential ecological effects of climate change and longlining by Australia’s Eastern Tuna and Billfish Fishery. The model reproduced historic biomass and fishery catch trends from 1952 to 2006 for seven functional groups. Simulated changes in fishing effort and fishing mortality rate on individual target species from 2008 to 2018 resulted in only modest (<20%) changes in the biomass of target species and their direct predators or competitors. A simulated increase in phytoplankton biomass due to climate change resulted in only small increases (<11%) in the biomass of all groups. However, climate-related changes to the biomass of micronekton fish (−20%) and cephalopods (+50%) resulted in trophic cascades. Our results suggest there may be ecological redundancy among high trophic level predators since they share a diverse suite of prey and collectively only represent <1% of the total system biomass. In contrast, micronekton fishes and cephalopods have high biomasses and high production and consumption rates and are important as both prey and predators. They appear to exert ‘wasp–waist’ control of the ecosystem rather than top–down or bottom–up processes reported to drive other pelagic systems.     

Zooplankton Community During the Transition from Spring Bloom to Oligotrophy in the Open NW Mediterranean and Effects of Wind Events. 2. Vertical Distributions and Migrations

Vertical distribution of zooplankton was investigated over a3-week period at a fixed station in the open NW Mediterraneanduring the DYNAPROC cruise (May 1995). The observational periodcoincided with the transition from spring bloom to oligotrophyin this area. Vertical distribution and migration in the 0–1000m water column are described in detail for the main speciesof copepods (>500 µm). Ontogenetic migration is reportedfor Neocalanus gracilis, Euchaeta acuta and Pleuromamma abdominalis.This study also documented the downwards seasonal migrationof Calanus helgolandicus. Short-term changes in the verticaldistribution of the small-sized organisms (>50 µm)in the upper 100 m are discussed in relation to the two majorwind events that occurred during the cruise. The naupliar stagesof copepods and euphausiids appeared unable to counter the upwardsvertical advection and the wind-induced mixing, while no markedchanges were observed for Oithona spp. and Microsetella spp.     

Ross seal (<Emphasis Type="Italic">Ommatophoca rossii</Emphasis>) annual distribution,diving behaviour,breeding and moulting,off Queen Maud Land,Antarctica

Six out of ten adult Ross seals that were tagged with Argos satellite-linked dive recorders off Queen Maud Land, just after the moult in February, provided data on location and diving activity throughout a year. Shortly after tagging, the animals headed 2,000 km north and stayed pelagic in the area south of the Antarctic Polar Front, until October when they went south into the pack-ice. Throughout the year they made about 100 dives a day, most to a depth of 100–300 m, the deepest dive on record being 792 m, while some dives were very shallow during their stay in the pack-ice. Most dives, outside the breeding and moulting period, lasted for 5–15 min throughout the year. This diving behaviour is consistent with feeding on mid-water fish, like Pleurogramma antarcticum, squid, and to some extent krill (Euphausia superba), when in the pack-ice, and myctophid fish and several species of squid, when in the open ocean. The nursing period was 13 days in mid-November, and moulting occurs in late January–early February, which is the period when sightings surveys for this species should be done.     

Marine macroalgae as foods for fishes: an evaluation of potential food quality

Synopsis A revitalized view of feeding by herbivorous marine fishes is sought through two questions. First, What characteristics of major taxa of algae identify them as predictably high or low quality foods? Second, are marine algae valuable foods for fishes which do not mechanically disrupt cell walls and do not harbor specialized enzymes or microbes capable of lysing cell walls? Energy, ash and nutrient content of 16 species of marine algae were employed to assess food quality of fleshy red, green, brown and calcareous red algae. On the basis of ash, calories, total protein and total lipid content, fleshy algae should be superior to calcareous algae as foods for fishes; in addition, green algae should be superior to brown algae and brown algae superior to red algae. When the probable digestibility of storage and extracellular carbohydrates is considered, green and red algae are predicted superior to brown algae as food. Two species of damselfishes (Pomacentridae) from the Gulf of California,Eupomacentrus rectifraenum andMicrospathodon dorsalis, eat red and green algae and ignore brown and calcareous algae. They feed, therefore, in a fashion consistent with predictions based only on algal chemistry. These fishes absorb at least 20–24% of the biomass, 57–67% of the protein, 46–56% of the lipid and 37–44% of the carbohydrate contained in algae eaten in the wild. Since these damselfishes do not masticate their food, it appears that herbivorous fishes can digest major fractions of algal nutrients without mechanical destruction of algal cells.     

The importance of protozooplankton as prey for copepods in the coastal areas of the central Irish Sea

This study evaluates food supply for copepods, highlighting the trophic relationship between copepods and protozooplankton. To test the hypotheses that protozooplankton prey are capable of sustaining the copepod standing stock in the western Irish Sea, the taxonomic and size composition of these two groups and the size-specific predation of copepods on protozooplankton were investigated. Protozooplankton and copepod samples were collected off the southwest coast of the Isle of Man using 1.7 l Niskin water bottles and two nets (64 and 280 μm meshes), respectively. Copepod predation on protozooplankton was calculated using weight-specific clearance rates from the literature, considering the availability of prey that was accessible to a given size of copepod. Low protozooplankton biomass was dominated by small cells (<60 μm), and high copepod biomass was dominated by small species, which were more efficiently collected by a 64-μm mesh net. However, large copepods were only collected by a 280-μm mesh net, suggesting that the combination of the two nets provided a better estimate of copepod biomass. Predation by the copepod assemblage in the Irish Sea removed 1–47% and 0.5–22% of ciliates and dinoflagellates standing stock, respectively, resulting in 1–40% of the copepod feeding requirement per day. Contrary to our hypothesis, copepods could not meet their feeding requirements by grazing only on the microzooplankton prey (15–200 μm), and other food sources (i.e. nanoplankton) must be important additional dietary components to copepods in the Irish Sea. Handling editor: S. M. Thomaz     

Aspects of the ecology and life history of Alligatorfish <Emphasis Type="Italic">Aspidophoroides monopterygius</Emphasis>

The Alligatorfish (Aspidophoroides monopterygius) is one of numerous non-commercial marine fishes for which basic elements of life history and biology are poorly known. More than 200 individuals were collected from the southern Gulf of St. Lawrence, Canada, in September 2000 and 2001, during fisheries-independent surveys. The standard length of Alligatorfish averaged 10.9 cm in 2000 and 9.2 cm in 2001, and putative age ranged between 2 and 7 years. Males possessed significantly longer pelvic fins, relative to body size, than females. We hypothesize that Alligatorfish undergo internal gametic association and that spawning takes place in mid- to late-autumn. Diet was comprised primarily of amphipods and isopods; other diet items included euphausiids, mysids, copepods, pteropods and calcareous algae. Based on analysis of individuals collected in 2000, 6.8% were affected by parasites (nematodes). Our research on the life history and ecology of Alligatorfish contributes to our knowledge of the biodiversity of Canada’s sub-Arctic marine fish fauna.