Publications

Here you will find publications from DTU Aqua:

Recent publications

2019
 

Modelling the spatio-temporal bycatch dynamics in an estuarine small-scale shrimp trawl fishery

Year: 2019

Modelling the spatio-temporal bycatch dynamics in an estuarine small-scale shrimp trawl fishery

Rezende, G. A., Rufener, M. C., Ortega, I., Ruas, V. M. & Dumont, L. F. C., 2019, In : Fisheries Research. 219, 105336.

Research output: Contribution to journalJournal article – Annual report year: 2019Researchpeer-review

The Patos Lagoon estuary in Southern Brazil is an important nursery ground for many commercially important fish and invertebrate species, with shrimp fisheries sustaining most of the surrounding small-scale fishermen. Although they are illegal, trawl gears are widely used by small-scale fishermen in order to catch shrimp. Shrimp trawl fisheries in tropical waters have high bycatch rates and cause a variety of problems, spanning from conflicts with other fisheries to changes in ecosystem trophic dynamics. A better understanding of the factors driving the bycatch process is therefore needed to establish reliable management measures. Here we used hierarchical Bayesian spatio-temporal models (HBSMs) to describe the bycatch of a small-scale shrimp trawl fishery in the Patos Lagoon estuary relative to a set of environmental and spatio-temporal predictors. Two different models were used to estimate bycatch trends: an effort-based method (BPUE) and a ratio-based method (BR, bycatch rate). A third model was used to evaluate the dynamics of shrimp catch per unit of effort (CPUE) as this measure is equally important to describe the underlying bycatch process. Overall, the bycatch consisted of 61 species of which 45 have market value. The mean bycatch rate was 86.2% for the entire period, which represents 6 kg of bycatch for every 1 kg of shrimp caught. Although the contribution of environmental variables differed among the models, the yearly spatial effect was identified as a common that explained bycatch dynamics. Moreover, the predictive maps revealed consistent hot and cold-spots from year-to-year, which varied in intensity for BR, BPUE and CPUE, and, therefore, represent a valuable benchmark for stakeholders and managers.

Original languageEnglish
Article number105336
JournalFisheries Research
Volume219
ISSN0165-7836
DOIs
Publication statusPublished - 2019

 

Proactive coping style in early emerging rainbow trout carries a metabolic cost with no apparent return

Year: 2019

The timing with which salmonid larvae emerge from their gravel nests is thought to be correlated with a particular suite of behavioural and physiological traits that correspond to the stress coping style of the individual. Among these traits, aggressiveness, dominance and resilience to stress, are potentially interesting to exploit in aquaculture production. In the present study a series of experiments were performed, with the purpose of characterising behavioural, metabolic and production related traits in rainbow trout juveniles from different emergence fractions. Newly hatched rainbow trout were sorted according to their emergence time from an artificial redd. The early, middle, and late fractions were retained and assessed for their physiological response to stress, growth performance, metabolism, fasting tolerance, and potential for compensatory growth. The early emerging fraction showed proactive behavioural traits; they were faster to reappear following startling, showed a reduced cortisol response following stress, and a reduced metabolic cost of recovery. Emergence time was not correlated with any differences in standard or maximum metabolic rates, but was however, correlated with higher routine metabolic rates, as demonstrated by significantly bigger weight losses during fasting in the early emerging group. Growth rates and feed conversion efficiencies were not significantly different when fish were co-habitated under a restrictive feeding regime, suggesting that early emerging fish are not able to monopolise food resources. The intermediate emerging group, which makes up the bulk of a population and is often ignored, appears to possess the best growth performance traits, possibly because they do not expend excessive energy on dominance behaviour such as the early emerging group, while they are also not overly timid or stress prone such as the late emerging group.
Original languageEnglish
JournalComparative Biochemistry and Physiology - Part A: Molecular & Integrative Physiology
Volume231
Pages (from-to)104-110
ISSN1095-6433
DOIs
Publication statusPublished - 2019

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Laks er i fremgang – men der er plads til forbedring

Year: 2019

Laks er i fremgang – men der er plads til forbedring

Ebert, K. M. & Sivebæk, F., 2019, In : Nationalpark magasin. 6, p. 30-35

Research output: Contribution to journalJournal article – Annual report year: 2019Communication

Siden 1990’erne er der investeret et trecifret millionbeløb i vandløbene, der munder ud i Vadehavet. Der er fjernet spærringer, udrettede strækninger er genslynget, og der er udlagt gydegrus og sten. Det har foreløbig givet gode resultater i form af flere vilde laks og skabt adgang til egnede gyde- og opvækstområder for flere andre fiskearter herunder snæbel, havørred og stalling. Der er stadig behov for forbedringer, hvis åerne skal have store fiskebestande.
Original languageDanish
JournalNationalpark magasin
Issue number6
Pages (from-to)30-35
Publication statusPublished - 2019

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Sea trout behaviour in the Limfjord - a fascinating display of the adaptability of the species?

Year: 2019

Sea trout behaviour in the Limfjord - a fascinating display of the adaptability of the species?

Kristensen, M. L., Birnie-Gauvin, K., Aarestrup, K. & Sivebæk, F., 2019, 2 p. Technical University of Denmark (DTU).

Research output: Other contributionNet publication - Internet publication – Annual report year: 2019Communication

Almost all surviving acoustically tagged sea trout smolts and kelts left a Danish fjord system using a similar 120 km long route. They also left with the highest recorded progression speed ever reported for sea trout in the literature. The repeatability of the behaviour and the geographical history of the Limfjord suggest that the sea trout are adapted to the specific conditions found in the area.
Original languageEnglish
Publication date2019
PublisherTechnical University of Denmark (DTU)
Number of pages2
Publication statusPublished - 2019
SeriesFiskepleje.dk

 

Adding perspectives to: “Global trends in carbon dioxide (CO2) emissions from fuel combustion in marine fisheries from 1950 - 2016"

Year: 2019

Adding perspectives to: “Global trends in carbon dioxide (CO2) emissions from fuel combustion in marine fisheries from 1950 - 2016"

Ziegler, F., Eigaard, O. R., Parker, R. W. R., Tyedmers, P. H., Hognes, E. S. & Jafarzadeh, S., 2019, In : Marine Policy. 107, 103488.

Research output: Contribution to journalJournal article – Annual report year: 2019Researchpeer-review

A contribution in this issue, Greer et al. (2019), models carbon dioxide emissions from fuel combustion in global fisheries. This is done based on a method using data on fishing effort, presenting results for two sectors: small-scale and industrial fisheries. The selection of these sectors is not motivated in relation to studying fuel use, and it is well-documented that other factors more accurately predict fuel use of fisheries and would constitute a more useful basis for defining sub-sectors, when the goal of the study is to investigate fuel use. Weakly grounded assumptions made in the translation of fishing effort into carbon dioxide emissions (e.g. the engine run time per fishing day for each sector) systematically bias results towards overestimating fuel use of “industrial” vessels, underestimating that of “small-scale”. A sensitivity analysis should have been a minimum requirement for publication. To illustrate how the approach used by Greer et al. (2019) systematically misrepresents the fuel use and emissions of the two sectors, the model is applied to Australian and New Zealand rock lobster trap fisheries and compared to observed fuel use. It is demonstrated how the approach underestimates emissions of small-scale fisheries, while overestimating emissions of industrial fisheries. As global fisheries are dominated by industrial fisheries, the aggregate emission estimate is likely considerably overestimated. Effort-based approaches can be valuable to model fuel use of fisheries in data-poor situations, but should be seen as complementary to estimates based on direct data, which they can also help to validate. Whenever used, they should be based on transparent, science-based data and assumptions.
Original languageEnglish
Article number103488
JournalMarine Policy
Volume107
ISSN0308-597X
DOIs
Publication statusPublished - 2019