Sture Hansson - Profile on Academia.edu (original) (raw)

Papers by Sture Hansson

Fisheries Research, 1999

We compared results from analysis of split-beam and single-beam acoustic surveys using two data s... more We compared results from analysis of split-beam and single-beam acoustic surveys using two data sets, one from the Baltic Sea (both systems at 70 kHz) and one from Lake Erie (70 kHz single beam, 70 and 120 kHz split beam). First, we show that there is a bias towards smaller targets associated with implementation of a commonly used algorithm for deconvolving target strength distributions from single beam data (modi®ed Craig±Forbes). This bias is 0.8 dB for a circular transducer. Differences in water column ®sh density estimates were not large although the single beam analysis consistently resulted in lower ®sh densities (85±95% of split beam densities). Target strength distributions obtained by split and single beam methods were very similar for the Baltic Sea data resulting in almost identical overall average TS. This was also true for epilimnetic targets strength distributions in Lake Erie. However, hypolimnetic target strength distributions still yielded smaller target strengths with single than with the two split beam units.

Ekologiska undersökningar i Luleå skärgård 1976 = Ecological investigations in the archipelago of Luleå in 1976

ABSTRACT Pages: 320 p.

Functional response by young-of-the-year Baltic Sea herring (Clupea harengus)

C.M. / International Council for the Exploration of the Sea ; 1994/J:16, Ref. H Pages: 9 p. The d... more C.M. / International Council for the Exploration of the Sea ; 1994/J:16, Ref. H Pages: 9 p. The daily food consumption of the young-of-the-year (YOY) decreased from 17% of body weight for small fish in the summer to 1% for larger juveniles in late autumn. Stomach content varied in a daily cycle. The observed daily food consumption was on average 38% (range 9-95%) of an estimated maximum consumption. We describe the relation between food consumption and food availability as functional response type 2 (Holling 1959).

Resultatredovisning för projektet Minskad övergödning och förbättrat fiske

Zooplankton is an important part of Baltic ecosystem and ecosystem-based management requires prod... more Zooplankton is an important part of Baltic ecosystem and ecosystem-based management requires productivity assessment of the region what involves zooplankton identification and abundance estimation. Acoustics is recognized as a reliable monitoring method. Thus, the ability of understanding of backscattering by zooplankton becomes a priority. It was the main motivation of the paper. The main approach is based on (i) the numerical modeling of acoustic backscattering by the typical representative of Baltic zooplankton, mysids and (ii) comparison of the theoretical results with the measured acoustic data. The Modal Based Deformed Wave Born Approximation (MB-DWBA) model was employed. The readily available biologic data for mysids were used. The sensitivity of the backscattering to acoustic frequency, individual size, width of orientation distribution and acoustic properties of biologic tissue was analyzed. The results of modeling were verified using the measured acoustic and biologic data...

Stuck between a rock and a hard place: zooplankton vertical distribution and hypoxia in the Gulf of Finland, Baltic Sea

Marine Biology, 2015

ABSTRACT Zooplankton often migrate vertically to deeper dark water during the day to avoid visual... more ABSTRACT Zooplankton often migrate vertically to deeper dark water during the day to avoid visual predators such as fish, a process which can strengthen benthic-pelagic coupling. In the Gulf of Finland, Baltic Sea, a pronounced hypoxic layer develops when there is an inflow of anoxic bottom water from the Central Baltic Sea, which could be a barrier for vertical migrants. Here, we report an acoustic study of the distributions of crustacean zooplankton (mysid shrimp and the copepod Limnocalanus macrurus), gelatinous zooplankton (Aurelia aurita) and fish. Zooplankton trawl nets were used to ground-truth acoustic data. Vertical profiles of oxygen concentration were taken, and the physiological impact of hypoxia on mysids was investigated using biochemical assays. We hypothesised that the vertical distribution of zooplankton and fish would be significantly affected by vertical heterogeneity of oxygen concentrations because anoxia and hypoxia are known to affect physiology and swimming behaviour. In addition, we hypothesised that mysids present in areas with hypoxia would exhibit a preparatory antioxidant response, protecting them from oxidative damage during migrations. The acoustic data showed peaks of crustacean zooplankton biomass in hypoxic (75 m), whereas fish shoals and A. aurita medusae were found in normoxic (5-6 mL L−1) upper water layers (

Environmental science & technology, Jan 20, 2015

The potential for using stable isotope analysis in risk assessment of environmental contaminants ... more The potential for using stable isotope analysis in risk assessment of environmental contaminants is crucially dependent on the predictability of the trophic transfer of isotopes in food webs. The relationship between contaminant levels and trophic position of consumers is widely used to assess biomagnification properties of various pollutants by establishing trophic magnification factors (TMF). However, contaminant-induced variability of the isotopic composition in biota is poorly understood. Here, we investigated effects of toxic exposure on δ(15)N and δ(13)C values in a consumer, with a main hypothesis that these effects would be largely mediated via growth rate and metabolic turnover of the test animals. Using the cladoceran Daphnia magna, two experiments were conducted to manipulate growth and body condition (assayed as C:N ratio) by food availability and temperature (Experiment 1) and by toxic exposure to the pesticide lindane (Experiment 2). We found a significant negative eff...

Acoustic fish abundance in a Baltic archipelago: comparison between results from echo integration and from analysis of echo peaks

ABSTRACT C.M. / International Council for the Exploration of the Sea ; 1989/B:27 Pages: 23 p. We ... more ABSTRACT C.M. / International Council for the Exploration of the Sea ; 1989/B:27 Pages: 23 p. We compared fish abundance, biomass and size distribution estimated from sonar data collected with two single-beam echo sounders (70 and 38 kHz) in a coastal area of the Baltic proper. The acoustic signals were analyzed using analysis of a single fish echoes (70 kHz) and using echo integration interpreted with catches in pelagic trawls (38 kHz). Fish were also collected with vertical gill nets. The two sonar systems gave similar echo integration values along an inter-calibration transect. +

Hydrobiologia, 1997

Predation by the Baltic Sea mysid Mysis mixta onnewly hatched Artemia sp. and culturedDaphnia mag... more Predation by the Baltic Sea mysid Mysis mixta onnewly hatched Artemia sp. and culturedDaphnia magna was examined in the laboratory. Wedesigned experiments to study the effects onconsumption rate of different experimental conditions:light, container size, diel variation, duration ofadaptation period, starvation and the duration of afeeding experiment.Consumption differed significantly between mysids keptin bright light vs mysids in complete darkness, withabout twice

Oecologia, 2005

Cercopagis pengoi, a recent invader to the Baltic Sea and the Laurentian Great Lakes, is a potent... more Cercopagis pengoi, a recent invader to the Baltic Sea and the Laurentian Great Lakes, is a potential competitor with fish for zooplankton prey. We used stable C and N isotope ratios to elucidate trophic relationships between C. pengoi, zooplankton (microzooplankton, 90-200 lm, mostly copepod nauplii and rotifers; mesozooplankton, >200 lm, mostly copepods), and zooplanktivorous fish (herring, size range 5-15 cm and sprat, 9-11 cm) in a coastal area of the northern Baltic Sea. The isotope ratios in C. pengoi and fish were much higher than those of zooplankton, showing general trends of enrichment with trophic level. Young-of-theyear (YOY) herring had a significantly higher 15 N/ 14 N ratio than C. pengoi, suggesting of a trophic linkage between the two species. To evaluate the possible relative importance of different food sources for C. pengoi and YOY herring, two-source isotope-mixing models for N were used, with micro-and mesozooplankton as prey for C. pengoi and mesozooplankton and C. pengoi as prey for YOY herring. These models indicate that mesozooplankton was the major food source of both species. However, microzooplankton may be important prey for young stages of C. pengoi. Comparative analyses of the herring trophic position before and after the invasion by C. pengoi showed a trophic level shift from 2.6 to 3.4, indicating substantial alterations in the food web structure. Our findings contribute to a growing body of evidence, showing that C. pengoi can modify food webs and trophic interactions in invaded ecosystems.

Marine Ecology Progress Series, 1994

Diurnal variation in stomach fullness of young-of-the-year (YOY) Baltic Sea herring Clupea hareng... more Diurnal variation in stomach fullness of young-of-the-year (YOY) Baltic Sea herring Clupea harengus was used to estimate gut evacuation rates and food consumption rates. The specific food consumption of these fish increased w t h decreasing body length (25 to 84 mm) and increased with increasing temperature, ranging from 17 % of body weight d -' in summer to 2 % d-' at the end of October. The YOY food consumption rates do not differ significantly from consumption rates estimated from growth and a bioenergetics model (Rudstam 1988; Kieler Meeresforsch., Sonderh. 6: 312-322) based on physiological data (respiration rates, egestion and excretion) from adult fish. This result, and our earlier find~ngs, imply that the weakest points in estimat~ng the food consumption of the Baltic Sea herring population are not bioenergetic assumptions, but assumptions related to YOY abundances, mortality rates and growth rates.

Marine Ecology Progress Series, 1999

We have determined the in situ food consumption rate of young-of-the-year (YOY, length 25 to 94 m... more We have determined the in situ food consumption rate of young-of-the-year (YOY, length 25 to 94 mm) Baltic Sea herring. This consumption Increased with increasing food availablhty, which suggests that the growth rate of young Baltic herring is food lirmted. This has been described previously for larval stages, but not for metamorphosed fish. The daily food consumption rate of YOY herring decreased from about 8 to 15% of body weight for small fish in the summer to 0.6 to 2% for larger juveniles in late autumn.

Marine Ecology Progress Series, 1992

We studied the seasonal dynamics of zooplanktivory by the major zooplanktivores (sprat Sprattus s... more We studied the seasonal dynamics of zooplanktivory by the major zooplanktivores (sprat Sprattus sprattus, herring Clupea harengus and the mysid shrimp Mysis mrxta) in 3 coastal areas of the northern Baltic Sea proper from the beginning of July through the end of October, 1985. The 3 areas are within 30 km of each other and dffer in nutrient loading and primary productivity. Consumption rates were obtained by combining abundance estimates of the planktivores (from Bongo nets, gill nets and acoustics) with diet analysis and bioenergetics models. Both the dominating planktivore groups and total planktivory rates changed over the study period. Sprat and yearling herring were the major zooplanktivores in July and August whereas young-of-year herring and M. mixta were more important in September and October. Planktivory rates increased from low levels at the beginning of July to a peak in August coinciding with a late summer decline in crustacean zooplankton biomass. Planktivory rates were lower than estimated zooplankton production rates in July and early August when zooplankton biomass was increasing and similar to or higher than production in the autumn when zooplankton biomass declined. Both clupeids and mysids consistently selected prey in the order cladocerans (Bosmina longispina maritima and Pleopis polyphemoides) > Eurytemora affinis hirundoides copepods > Acartia copepods. The selected species represented a smaller proportion of total zooplankton biomass and decreased earlier in the season in the least productive area, indicating a larger and earlier effect of planktivory in that area compared to the most productive area.

Marine Ecology Progress Series, 1993

The total food consumption of herring Clupea harengus L. and sprat Sprattus sprattus (L.), the do... more The total food consumption of herring Clupea harengus L. and sprat Sprattus sprattus (L.), the dominant zooplanktivorous fish in the Baltic Sea, was estimated from published data on abundances, growth, mortality rates and diets uslng a bioenergetics model. The annual food consumption was 5.0 X 107 tonnes for herring and 2.4 X 107 tonnes for sprat. For herring ca 90 % of the food consumed was zooplankton and the rest n~ysids and benthos. Larvae and young-of-the-year (YOY) of sprat and herring accounted for 50 and 45% of the total consumption respectively. Peak consumption rates occurred in August-September. Our estimate for annual consumption of zooplankton by clupeids in the Baltic sea is 4 times higher than previous estimates. One major explanation for this is that we included the consumption by YOY and 1 yr old fish. Our simulations also show that a diet shift, from a mix of zooplankton, mysids and amphipods to only zooplankton, could have a significant effect on fish growth rate. At a fixed biomass consumption, the lower energy density of zooplankton would mean that thls shift would decrease growth by about 25 % for older age groups. This decrease is similar to that observed in the Baltlc Sea in the late 1980s.