2019
 

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

År: 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

År: 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

År: 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?

År: 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"

År: 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

 

Behaviour of adult sea trout Salmo trutta that survive or die at sea

År: 2019

Behaviour of adult sea trout Salmo trutta that survive or die at sea

Kristensen, M. L., Righton, D., Villar-Guerra, D. D., Baktoft, H. & Aarestrup, K., 2019, In : Estuarine, Coastal and Shelf Science. 227, 106310.

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

We tagged 125 sea trout kelts (460–925 mm) in seven Danish rivers with positively buoyant DSTs. Fifty-three (42%) tags were recovered, enabling a comparison of behaviour in kelts that survived the marine period and kelts that did not. Data revealed an estimated mean survival time at sea of 14.3 days (range 1–65 days) for fish that died at sea. Fish that did not survive had lower weight/length ratios when tagged than survivors (P = 0.005) but exhibited a similar diel diving pattern while at sea. Both surviving and non-surviving fish gradually increased diving activity and the daily visited maximum depths after sea entry, but some performed fewer dives and resided in shallower depths than others. This difference was pronounced when comparing surviving fish (most active divers) with fish caught by anglers (least active divers). The results show that the first weeks at sea are critical for kelt survival and that physical status of kelts may affect behaviour and probability of survival. The preference for shallower waters and less diving activity in some individuals indicate that coastally based fisheries and recreational angling may select against specific behavioural phenotypes which should be investigated more intensively.
Original languageEnglish
Article number106310
JournalEstuarine, Coastal and Shelf Science
Volume227
ISSN0272-7714
DOIs
Publication statusPublished - 2019

 

Maritim arealplanlægning i Øresund: Scenarier for udvikling af erhvervs-, samfunds- og miljømæssige forhold

År: 2019

Maritim arealplanlægning i Øresund: Scenarier for udvikling af erhvervs-, samfunds- og miljømæssige forhold

Riemann, B., Al-Hamdani, Z., Olafsson, A. S., Hasler, B., Kaae, B. C., Murray, C., Göke, C., Kallenbach, E., Olesen, H. J., Nabe-Nielsen, J., Tougaard, J., Andersen, J. H., Egekvist, J., Overgaard Leth, J., Dahl, K., Christoffersen, M., Zandersen, M., Termansen, M., Sveegaard, S. & Harvey, T., 2019, 174 p. (MiljøBiblioteket; No. 6).

Research output: Book/ReportBook – Annual report year: 2019Research

Øresund er et af de mest befærdede farvande og kystområder i verden. Store container- og krydstogtskibe passerer igennem på langs, mens færgetrafikken og Øresundsbroen går på tværs mellem Danmark og Sverige. Samtidig skal der være plads til både havmølleparker, byudvikling, fiskeri, lystbådesejlads og friluftsliv, ligesom områdets rige natur og dyreliv skal tilgodeses. Det stiller store krav til planlægningen af arealudnyttelsen.
Maritim arealplanlægning i Øresund giver indblik i, hvordan vi kan bevare havmiljøet i regionen og samtidig skabe en bæredygtig erhvervs- og samfundsudvikling. Én mulighed er at lave Øresund om til et stort naturreservat og på den måde understøtte en positiv udvikling af havmiljøet, tiltrække turister og styrke friluftslivet. Men det vil formentlig også betyde
et stop for indvinding af råstoffer til byggebranchen og restriktioner for fiskeriet. Som i ethvert andet økosystem er det afgørende at finde frem til den rette balance mellem forskellige aktiviteter og interesser. Her kan det travle stræde mellem Sjælland og Skåne tjene som eksempel på, hvordan man kan analysere konflikter og muligheder for sameksistens, og erfaringerne kan med fordel overføres til andre danske havområder.
Original languageDanish
Number of pages174
ISBN (Print)978-87-7184-887-8
Publication statusPublished - 2019
SeriesMiljøBiblioteket
Number6

 

Hypoxia but not shy-bold phenotype mediates thermal preferences in a threatened freshwater fish, Notropis percobromus

År: 2019

Hypoxia but not shy-bold phenotype mediates thermal preferences in a threatened freshwater fish, Notropis percobromus

Enders, E. C., Wall, A. J. & Svendsen, J. C., 2019, In : Journal of Thermal Biology. 84, p. 479-487

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

For ectothermic animals, ambient temperature strongly influences developmental growth rate and individual fitness. While many ectotherms live in environments that are spatially hetero-thermal, the coupling between behavioural phenotypes (e.g., shy or bold behaviour) and thermal preferences remains uncertain. Relative to shy counterparts, bolder phenotypes may exert higher preference for ambient temperatures that are closer to their thermal optimum, thereby accelerating development. In addition, ectotherms should select colder temperatures in low oxygen conditions (hypoxia) according to the oxygen- and capacity-limited thermal tolerance (OCLTT) hypothesis. Using wild caught carmine shiner (Notropis percobromus), this study examined thermoregulatory behaviour in individuals exhibiting consistent behavioural phenotypes along the shy-bold continuum and between ecologically relevant normal oxygen concentration (normoxic) and hypoxic treatments. Furthermore, the behaviour observed in the laboratory was compared to environmental data from the natal stream. Results demonstrated that individual shy-bold behavioural phenotype was consistent before and after a simulated aerial predator attack, indicating consistency of behaviour across situations. Individual preferred and avoidance temperatures varied substantially, but were unrelated to shy-bold behavioural phenotypes. In contrast, individual preferred and maximum avoidance temperatures were significantly reduced in hypoxia, consistent with the OCLTT hypothesis. These findings might indicate suppressed development rates in hypoxia, not only by the limited oxygen for aerobic metabolism, but also by the preference for colder water in hypoxia. Furthermore, the tolerated thermal ranges were reduced in hypoxia. Using test conditions confirmed by field data, our study demonstrates the strong influence of oxygen availability on thermoregulatory behaviours and preferences in aquatic environments.
Original languageEnglish
JournalJournal of Thermal Biology
Volume84
Pages (from-to)479-487
ISSN0306-4565
DOIs
Publication statusPublished - 2019

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Optimal Salmon Lice Treatment Threshold and Tragedy of the Commons in Salmon Farm Networks

År: 2019

Optimal Salmon Lice Treatment Threshold and Tragedy of the Commons in Salmon Farm Networks

Kragesteen, T. J., Simonsen, K., Visser, A. & Andersen, K. H., 2019, In : Aquaculture. 512, 734329.

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

The ectoparasite Lepeophtheirus salmonis has for decades plagued salmon aquaculture by decreasing profits and impacting wild salmon stocks. To protect migrating wild salmon stocks and avoid excessive cross-farm infections, authoritiesrequiretreatmentswhensealicelevelreachagiventhreshold. The treatment threshold is set to protect wild salmonid stocks but also to avoid costly lice infections on neighbouring farms. Here we make a bio-economic estimation of optimal treatment thresholds. We are particularly interested in identifying conflicts between the optimal threshold of for the entire system of farms and for the individual farmer. We show that isolated individual farms can maximize profit by operating with a high threshold, while the maximum profit for an entire network of farms occurs with a threshold about 0.1 gravid female lice/salmon. These findings substantiate the Norwegian policy of lowering the lice treatment threshold below 0.5 gravid lice/salmon. The results also demonstrate that too low a treatment threshold results in high treatment rates. The difference between the optimal treatment strategy of individual farmers and that for the total system demonstrates that management of salmon lice infections operates in a tragedy-of-the-commons environment, where individual farmers may have an incentive to disregard legislation at the expense of the others in the network. This means that strong enforcement is needed to achieve optimal management of salmon lice infections.
Original languageEnglish
Article number734329
JournalAquaculture
Volume512
ISSN0044-8486
DOIs
Publication statusPublished - 2019

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Challenges in quantifying, interpreting and predicting distributional shifts of marine species

År: 2019

Challenges in quantifying, interpreting and predicting distributional shifts of marine species

Marshall, C. T., Audzijonyte, A., Baudron, A., Champion, C., Fallon, N., Haynie, A. C., Haltuch, M., Townhill, B., van Denderen, P. D., Pecl, G., Pinnegar, J. K., Pinsky, M. L., Spencer, P., Stawitz, C. & Thorsen, J., 2019. 1 p.

Research output: Contribution to conferenceConference abstract for conference – Annual report year: 2019Research

Oceans are absorbing approximately 80% of the extra heat and 50% of additional CO2 trapped in the atmosphere and, as a result, have undergone rapid changes in temperature and acidity. The evidence for climate-driven global re-distribution of marine species is growing but often based on the distribution of fish species, many of which are mobile and able to rapidly shift their ranges in response to changing environmental conditions. Standardised surveys are commonly used for inferring spatial distribution, however, there are many examples of species moving beyond the bounds of a survey which then limits our understanding. Additionally, there are often non-climate factors that confound the interpretation of range shifts, e.g. fishing or habitat changes. Quantifying the magnitude and rates of distributional shifts is further complicated by the variety of metrics that are used to describe historical species distributions and then contemporary changes in these distributions. Accurately specifying both the suite of drivers underpinning range shifts and the magnitude of range shifts is essential due to the societal importance of marine species for food, local economies and future projections of commercial fish species. Here, based on a cross-comparison of methodological approaches from a range of globally important marine ecosystems, we make recommendations for appropriate approaches to the collection, analysis and interpretation of data describing the abundance and location of marine species.
Original languageEnglish
Publication date2019
Number of pages1
Publication statusPublished - 2019
EventSpecies on the Move - Kruger National Park, South Africa
Duration: 22 Jul 201926 Jul 2019
http://www.speciesonthemove.com/

Conference

ConferenceSpecies on the Move
LocationKruger National Park
CountrySouth Africa
Period22/07/201926/07/2019
Internet address


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