Christoffer Moesgaard Albertsen

MSc Statistics, PhD,
Researcher at DTU Aqua

Publications

I am currently a contributing author on 18 published peer reviewed publications, where I am the first author on seven. Further, I am a contributing author on two papers that have been accepted for publication

Below is a list of my peer reviewed publications that are either published or accepted for publication. The list is in reverse chronological order.

Where do you come from, where do you go: Early life stage drift and migrations of cod inferred from otolith microchemistry and genetic population assignment

Accepted for publication in Canadian Journal of Fisheries and Aquatic Sciences
Hüssy, K.; Albertsen, C. M.; Hemmer-Hansen, J.; Eero, M.; Vinther, M.; Serre, S. H. and Thomsen, T. B..

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Abstract:
This study investigates stock mixing of genetically distinct Atlantic cod (Gadus morhua) stocks in the Kattegat, an area geographically located between the North Sea and the Baltic Sea, by combining genetic population identification with habitat assignments from hatch to capture from otolith microchemistry. Cod captured in Kattegat were genetically assigned to either the North Sea or the endemic Kattegat population. Otolith chemical fingerprints differed significantly between populations during the larval and pelagic juvenile stage with higher strontium and lower barium and manganese concentrations in the North Sea population than the Kattegat population, indicating that North Sea cod are spawned in the North Sea or Skagerrak and drift into the Kattegat during the early life stages. Individual cod of both populations undertook frequent, but predominantly short term, migrations to other areas than the Kattegat, with < 25 % of individuals remaining resident within the Kattegat throughout their life. Across seasons and age classes, the two populations were both most frequently distributed in the Kattegat (67 %), with approximately 25 % of both population distributed in the western Baltic Sea and less than 10 % in the Skagerrak/North Sea. This study demonstrates the usefulness of this approach to infer population-specific connectivity and migration trajectories for individual fish and its potential applications in basic and applied fields of fish ecology and fisheries sciences.

APA:
Hüssy, K., Albertsen, C. M., Hemmer-Hansen, J., Eero, M., Vinther, M., Serre, S. H. and Thomsen, T. B. (In Press) Where do you come from, where do you go: Early life stage drift and migrations of cod inferred from otolith microchemistry and genetic population assignment. Canadian Journal of Fisheries and Aquatic Sciences. doi: 10.1139/cjfas-2020-0409

MLA:
Hüssy, K., Albertsen, C. M., Hemmer-Hansen, J., Eero, M., Vinther, M., Serre, S. H. and Thomsen, T. B. “Where do you come from, where do you go: Early life stage drift and migrations of cod inferred from otolith microchemistry and genetic population assignment” Canadian Journal of Fisheries and Aquatic Sciences. In Press. doi: 10.1139/cjfas-2020-0409

CBE:
Hüssy, K., Albertsen, C. M., Hemmer-Hansen, J., Eero, M., Vinther, M., Serre, S. H. and Thomsen, T. B. In Press. Where do you come from, where do you go: Early life stage drift and migrations of cod inferred from otolith microchemistry and genetic population assignment. Canadian Journal of Fisheries and Aquatic Sciences. doi: 10.1139/cjfas-2020-0409

BibTeX:
@article{hussy2021a,
title = "Where do you come from, where do you go: Early life stage drift and migrations of cod inferred from otolith microchemistry and genetic population assignment",
author = "Hüssy, {K.} and Albertsen, {C. M.} and Hemmer-Hansen, {J.} and Eero, {M.} and Vinther, {M.} and Serre, {S. H.} and Thomsen, {T. B.}",
year = "In Press",
volume = "",
number = "",
journal = "Canadian Journal of Fisheries and Aquatic Sciences",
pages = "",
issn = "",
doi = "10.1139/cjfas-2020-0409",
}

Estimating migration patterns of fish from otolith chemical composition time-series

Accepted for publication in Canadian Journal of Fisheries and Aquatic Sciences
Albertsen, C. M.; Hüssy, K.; Serre, S. H.; Hemmer-Hansen, J. and Thomsen, T. B..

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Abstract:
Understanding migration patterns and habitat use is of great importance for management and conservation of marine living resources. The chemical composition of otoliths is influenced by the surrounding environment; therefore, they are indispensable data archives. To extract migration patterns and historical habitat use of individual fish, we analyse otolith chemical compositions obtained by laser ablation inductively coupled plasma mass spectrometry by a regime-switching state-space model. The state-space model filters the measurement noise from the environmental signal. In turn, the filtered signal is converted to geographical positions through a calibration of strontium to salinity. The method is validated by a simulation study and applied to 404 Atlantic cod otoliths.

APA:
Albertsen, C. M., Hüssy, K., Serre, S. H., Hemmer-Hansen, J. and Thomsen, T. B. (In Press) Estimating migration patterns of fish from otolith chemical composition time-series. Canadian Journal of Fisheries and Aquatic Sciences. doi: 10.1139/cjfas-2020-0356

MLA:
Albertsen, C. M., Hüssy, K., Serre, S. H., Hemmer-Hansen, J. and Thomsen, T. B. “Estimating migration patterns of fish from otolith chemical composition time-series” Canadian Journal of Fisheries and Aquatic Sciences. In Press. doi: 10.1139/cjfas-2020-0356

CBE:
Albertsen, C. M., Hüssy, K., Serre, S. H., Hemmer-Hansen, J. and Thomsen, T. B. In Press. Estimating migration patterns of fish from otolith chemical composition time-series. Canadian Journal of Fisheries and Aquatic Sciences. doi: 10.1139/cjfas-2020-0356

BibTeX:
@article{albertsen2021a,
title = "Estimating migration patterns of fish from otolith chemical composition time-series",
author = "Albertsen, {C. M.} and Hüssy, {K.} and Serre, {S. H.} and Hemmer-Hansen, {J.} and Thomsen, {T. B.}",
year = "In Press",
volume = "",
number = "",
journal = "Canadian Journal of Fisheries and Aquatic Sciences",
pages = "",
issn = "0706-652X",
doi = "10.1139/cjfas-2020-0356",
}

2020

The impact of rising sea temperatures on an Arctic top predator, the narwhal

Published in Scientific Reports
Chambault, P.; Tervo, O. M.; Garde, E.; Hansen, R. G.; Blackwell, S. B.; Williams, T. M.; Dietz, R.; Albertsen, C. M.; Laidre, K. L.; Nielsen, N. H.; Richard, P.; Sinding, M. H. S.; Schmidt, H. C. and Heide-Jørgesen, M. P..

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Abstract:
Arctic top predators are expected to be impacted by increasing temperatures associated with climate change, but the relationship between increasing sea temperatures and population dynamics of Arctic cetaceans remains largely unexplored. Narwhals (Monodon monoceros) are considered to be among the most sensitive of Arctic endemic marine mammals to climate change due to their limited prey selection, strict migratory patterns and high site fidelity. In the context of climate change, we assume that the population dynamics of narwhals are partly influenced by changes in environmental conditions, with warm areas of increasing sea temperatures having lower abundance of narwhals. Using a unique large dataset of 144 satellite tracked narwhals, sea surface temperature (SST) data spanning 25 years (1993-2018) and narwhal abundance estimates from 17 localities, we (1) assessed the thermal exposure of this species, (2) investigated the SST trends at the summer foraging grounds, and (3) assessed the relationship between SST and abundance of narwhals. We showed a sharp SST increase in Northwest, Mideast and Southeast Greenland, whereas no change could be detected in the Canadian Arctic Archipelago (CAA) and in the Greenland Sea. The rising sea temperatures were correlated with the smallest narwhal abundance observed in the Mideast and Southeast Greenland (<2,000 individuals), where the mean summer sea temperatures were the highest (6.3°C) compared to the cold waters of the CAA (0.7°C) that were associated with the largest narwhal populations (>40,000 individuals). These results support the hypothesis that warming ocean waters will restrict the habitat range of the narwhal, further suggesting that narwhals from Mideast and Southeast Greenland may be under pressure to abandon their traditional Arctic habitats due to ocean warming.

APA:
Chambault, P., Tervo, O. M., Garde, E., Hansen, R. G., Blackwell, S. B., Williams, T. M., Dietz, R., Albertsen, C. M., Laidre, K. L., Nielsen, N. H., Richard, P., Sinding, M. H. S., Schmidt, H. C. and Heide-Jørgesen, M. P. (2020) The impact of rising sea temperatures on an Arctic top predator, the narwhal. Scientific Reports, 10, 18678. doi: 10.1038/s41598-020-75658-6

MLA:
Chambault, P., Tervo, O. M., Garde, E., Hansen, R. G., Blackwell, S. B., Williams, T. M., Dietz, R., Albertsen, C. M., Laidre, K. L., Nielsen, N. H., Richard, P., Sinding, M. H. S., Schmidt, H. C. and Heide-Jørgesen, M. P. “The impact of rising sea temperatures on an Arctic top predator, the narwhal” Scientific Reports. 2020, 10, 18678. doi: 10.1038/s41598-020-75658-6

CBE:
Chambault, P., Tervo, O. M., Garde, E., Hansen, R. G., Blackwell, S. B., Williams, T. M., Dietz, R., Albertsen, C. M., Laidre, K. L., Nielsen, N. H., Richard, P., Sinding, M. H. S., Schmidt, H. C. and Heide-Jørgesen, M. P. 2020. The impact of rising sea temperatures on an Arctic top predator, the narwhal. Scientific Reports 10: 18678. doi: 10.1038/s41598-020-75658-6

BibTeX:
@article{chambault2020a,
title = "The impact of rising sea temperatures on an Arctic top predator, the narwhal",
author = "Chambault, {P.} and Tervo, {O. M.} and Garde, {E.} and Hansen, {R. G.} and Blackwell, {S. B.} and Williams, {T. M.} and Dietz, {R.} and Albertsen, {C. M.} and Laidre, {K. L.} and Nielsen, {N. H.} and Richard, {P.} and Sinding, {M. H. S.} and Schmidt, {H. C.} and Heide-Jørgesen, {M. P.}",
year = "2020",
volume = "10",
number = "",
journal = "Scientific Reports",
pages = "18678",
issn = "2045-2322",
doi = "10.1038/s41598-020-75658-6",
}

2020

Synthetic harbour porpoise (Phocoena phocoena) communication signals emitted by acoustic alerting device (PAL, 'Porpoise ALert') significantly reduce their bycatch in Western Baltic set net fisheries

Published in Fisheries Research
Chladek, J. C.; Culik, B. M.; Kindt-Larsen, L.; Albertsen, C. M. and von Dorrien, C..

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Abstract:
Gillnet fisheries are one of the main anthropogenic causes of harbour porpoise (Phocoena phocoena, L. 1758) mortality in the Baltic Sea. A new kind of acoustic alerting device (Porpoise ALert, PAL) was tested in commercial gillnet fisheries of the Western Baltic. PAL emits 133 kHz synthetic harbour porpoise communication signals, unlike conventional acoustic deterrent devices (‘pingers‘) which emit artificial noise. Trials were conducted by three commercial gillnet vessels conducting 778 trips during standard fishing operations from 2014 to 2016. 1,120 PAL-equipped net strings were tested against 1,529 simultaneously set control strings with no devices. We tested two versions of the PAL (v1 and v2). These were spaced < 210 metres apart from each other on the gillnet floatlines, all devices pointing in the same direction to ensure complete acoustic coverage of the strings. Two vessels fished in Kiel Bight and around Fehmarn Island in German waters, and the third vessel fished in the Öresund, in inner Danish waters. Overall, 18 harbour porpoises were bycaught in control strings (mean 0.01 ± 0. 1 per haul), while five harbour porpoises were bycaught in strings equipped with PALs (0.004 ± 0.07 per haul). Number of net string bycatches were analysed using a generalized linear mixed model (GLMM). The model applied to all observations revealed that the expected bycatch was significantly influenced by PAL deployment (p < 0.05), decreasing the expected bycatch by 64.9% (95% confidence interval (CI): 8.7 - 88.7%). PAL effectiveness was also increased by reducing device spacing to <210 m (16 bycatches in control, 3 in PAL strings; mean bycatch reduction 79.7%). Additional model cases were applied to the data and are discussed. We conclude that with this specific communication signal, PAL can significantly reduce harbour porpoise bycatch in gillnets deployed in the Western Baltic Sea, thus reconciling anthropogenic activities with protection of the marine environment.

APA:
Chladek, J. C., Culik, B. M., Kindt-Larsen, L., Albertsen, C. M. and von Dorrien, C. (2020) Synthetic harbour porpoise (Phocoena phocoena) communication signals emitted by acoustic alerting device (PAL, 'Porpoise ALert') significantly reduce their bycatch in Western Baltic set net fisheries . Fisheries Research, 232, 105732. doi: 10.1016/j.fishres.2020.105732

MLA:
Chladek, J. C., Culik, B. M., Kindt-Larsen, L., Albertsen, C. M. and von Dorrien, C. “Synthetic harbour porpoise (Phocoena phocoena) communication signals emitted by acoustic alerting device (PAL, 'Porpoise ALert') significantly reduce their bycatch in Western Baltic set net fisheries ” Fisheries Research. 2020, 232, 105732. doi: 10.1016/j.fishres.2020.105732

CBE:
Chladek, J. C., Culik, B. M., Kindt-Larsen, L., Albertsen, C. M. and von Dorrien, C. 2020. Synthetic harbour porpoise (Phocoena phocoena) communication signals emitted by acoustic alerting device (PAL, 'Porpoise ALert') significantly reduce their bycatch in Western Baltic set net fisheries . Fisheries Research 232: 105732. doi: 10.1016/j.fishres.2020.105732

BibTeX:
@article{chladek2020a,
title = "Synthetic harbour porpoise (Phocoena phocoena) communication signals emitted by acoustic alerting device (PAL, 'Porpoise ALert') significantly reduce their bycatch in Western Baltic set net fisheries ",
author = "Chladek, {J. C.} and Culik, {B. M.} and Kindt-Larsen, {L.} and Albertsen, {C. M.} and von Dorrien, {C.}",
year = "2020",
volume = "232",
number = "",
journal = "Fisheries Research",
pages = "105732",
issn = "0165-7836",
doi = "10.1016/j.fishres.2020.105732",
}

2020

Model-based estimates of reference points in an age-based state-space stock assessment model

Published in Fisheries Research
Albertsen, C. M. and Trijoulet, V..

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Abstract:
Reference points are central in the current management of marine living resources. However, reference points are estimated from data and model estimates. Therefore, they are inherently uncertain. We present two objective methods for estimating reference points and quantifying their uncertainty. The first method uses per-recruit calculations, while the second method relies on a long-term forecast of the managed system. Confidence intervals are calculated through a combination of the implicit function theorem and the delta method. Both methods are illustrated for 12 recruitment models using data from the Northeast Arctic cod assessment. Finally, the methods are validated in a simulation study.

APA:
Albertsen, C. M. and Trijoulet, V. (2020) Model-based estimates of reference points in an age-based state-space stock assessment model. Fisheries Research, 230, 105618. doi: 10.1016/j.fishres.2020.105618

MLA:
Albertsen, C. M. and Trijoulet, V. “Model-based estimates of reference points in an age-based state-space stock assessment model” Fisheries Research. 2020, 230, 105618. doi: 10.1016/j.fishres.2020.105618

CBE:
Albertsen, C. M. and Trijoulet, V. 2020. Model-based estimates of reference points in an age-based state-space stock assessment model. Fisheries Research 230: 105618. doi: 10.1016/j.fishres.2020.105618

BibTeX:
@article{albertsen2020a,
title = "Model-based estimates of reference points in an age-based state-space stock assessment model",
author = "Albertsen, {C. M.} and Trijoulet, {V.}",
year = "2020",
volume = "230",
number = "",
journal = "Fisheries Research",
pages = "105618",
issn = "0165-7836",
doi = "10.1016/j.fishres.2020.105618",
}

2020

The need for spatio-temporal modeling to determine catch-per-unit effort based indices of abundance and associated composition data for inclusion in stock assessment models

Published in Fisheries Research
Maunder, M. N.; Thorson, J. T.; Xu, H.; Oliveros-Ramos, R.; Hoyle, S. D.; Tremblay-Boyer, L.; Lee, H. H.; Kai, M.; Chang, S.; Kitakado, T.; Albertsen, C. M.; Minte-Vera, C. V.; Lennert-Cody, C. E.; Aires-da-Silva, A. and Piner, K. R..

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Abstract:
We describe and illustrate a spatio-temporal modelling approach for analyzing age- or size-specific catch-per-unit-of-effort (CPUE) data to develop indices of relative abundance and associated composition data. The approach is based on three concepts: 1) composition data that are used to determine the component of the population represented by the index should be weighted by CPUE (abundance) while the composition data used to represent the fish removed from the stock should be weighted by catch; 2) due to spatial non-randomness in fishing effort and fish distribution, the index, index composition, and catch composition, should be calculated at a fine spatial scale (e.g., 1°x1°) and summed using area weighting; and 3) fine-scale spatial stratification will likely result in under-sampled and unsampled cells and some form of smoothing method needs to be applied to inform these cells. We illustrate the concepts by applying them to yellowfin tuna (Thunnus albacares) in the eastern Pacific Ocean.

APA:
Maunder, M. N., Thorson, J. T., Xu, H., Oliveros-Ramos, R., Hoyle, S. D., Tremblay-Boyer, L., Lee, H. H., Kai, M., Chang, S., Kitakado, T., Albertsen, C. M., Minte-Vera, C. V., Lennert-Cody, C. E., Aires-da-Silva, A. and Piner, K. R. (2020) The need for spatio-temporal modeling to determine catch-per-unit effort based indices of abundance and associated composition data for inclusion in stock assessment models. Fisheries Research, 229, 105594. doi: 10.1016/j.fishres.2020.105594

MLA:
Maunder, M. N., Thorson, J. T., Xu, H., Oliveros-Ramos, R., Hoyle, S. D., Tremblay-Boyer, L., Lee, H. H., Kai, M., Chang, S., Kitakado, T., Albertsen, C. M., Minte-Vera, C. V., Lennert-Cody, C. E., Aires-da-Silva, A. and Piner, K. R. “The need for spatio-temporal modeling to determine catch-per-unit effort based indices of abundance and associated composition data for inclusion in stock assessment models” Fisheries Research. 2020, 229, 105594. doi: 10.1016/j.fishres.2020.105594

CBE:
Maunder, M. N., Thorson, J. T., Xu, H., Oliveros-Ramos, R., Hoyle, S. D., Tremblay-Boyer, L., Lee, H. H., Kai, M., Chang, S., Kitakado, T., Albertsen, C. M., Minte-Vera, C. V., Lennert-Cody, C. E., Aires-da-Silva, A. and Piner, K. R. 2020. The need for spatio-temporal modeling to determine catch-per-unit effort based indices of abundance and associated composition data for inclusion in stock assessment models. Fisheries Research 229: 105594. doi: 10.1016/j.fishres.2020.105594

BibTeX:
@article{maunder2020a,
title = "The need for spatio-temporal modeling to determine catch-per-unit effort based indices of abundance and associated composition data for inclusion in stock assessment models",
author = "Maunder, {M. N.} and Thorson, {J. T.} and Xu, {H.} and Oliveros-Ramos, {R.} and Hoyle, {S. D.} and Tremblay-Boyer, {L.} and Lee, {H. H.} and Kai, {M.} and Chang, {S.} and Kitakado, {T.} and Albertsen, {C. M.} and Minte-Vera, {C. V.} and Lennert-Cody, {C. E.} and Aires-da-Silva, {A.} and Piner, {K. R.}",
year = "2020",
volume = "229",
number = "",
journal = "Fisheries Research",
pages = "105594",
issn = "",
doi = "10.1016/j.fishres.2020.105594",
}

2019

Generalizing the first-difference correlated random walk for animal movement data

Published in Scientific Reports
Albertsen, C. M..

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Abstract:
Animal telemetry data are often analysed with discrete time movement models. These models are defined with regular time steps. However, telemetry data from marine animals are observed irregularly. To account for irregular data, a time-irregularised first-difference correlated random walk model with drift is introduced. The model generalizes the commonly used first-difference correlated random walk with regular time steps by allowing irregular time steps, including a drift term, and by allowing different autocorrelation in the two coordinates. The model is applied to data from a ringed seal collected through the Argos satellite system, and is compared to related movement models through simulations. Accounting for irregular data in the movement model results in accurate parameter estimates and reconstruction of movement paths. Further, the introduced model can provide more accurate movement paths than the regular time counterpart. Extracting accurate movement paths from uncertain telemetry data is important for evaluating space use patterns for marine animals, which in turn is crucial for management. Further, handling irregular data directly in the movement model allows efficient simultaneous analyses of several animals.

APA:
Albertsen, C. M. (2019) Generalizing the first-difference correlated random walk for animal movement data. Scientific Reports, 9, 4017. doi: 10.1038/s41598-019-40405-z

MLA:
Albertsen, C. M. “Generalizing the first-difference correlated random walk for animal movement data” Scientific Reports. 2019, 9, 4017. doi: 10.1038/s41598-019-40405-z

CBE:
Albertsen, C. M. 2019. Generalizing the first-difference correlated random walk for animal movement data. Scientific Reports 9: 4017. doi: 10.1038/s41598-019-40405-z

BibTeX:
@article{albertsen2019a,
title = "Generalizing the first-difference correlated random walk for animal movement data",
author = "Albertsen, {C. M.}",
year = "2019",
volume = "9",
number = "",
journal = "Scientific Reports",
pages = "4017",
issn = "2045-2322",
doi = "10.1038/s41598-019-40405-z",
}

2018

Sea surface temperature predicts the movements of an Arctic cetacean: the bowhead whale

Published in Scientific Reports
Chambault, P.; Albertsen, C. M.; Patterson, T. A.; Hansen, R. G.; Tervo, O.; Laidre, K. L. and Heide-Jørgensen, M. P..

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Abstract:
The effects of climate change constitute a major concern in Arctic waters due to the rapid decline of sea ice, which may strongly alter the movements and habitat availability of Arctic marine mammals. We tracked 98 bowhead whales by satellite over an 11-year period (2001-2011) in Baffin Bay - West Greenland to investigate the environmental drivers (specifically sea surface temperature and sea ice) involved in bowhead whale’s movements. Movement patterns differed according to season, with aggregations of whales found at higher latitudes during spring and summer likely in response to sea-ice retreat and increasing sea temperature (SST) facilitated by the warm West Greenland Current. In contrast, the whales moved further south in response to sea temperature decrease during autumn and winter. Statistical models indicated that the whales targeted a narrow range of SSTs from -1.5 to 2°C. Sea surface temperatures are predicted to undergo a marked increase in the Arctic, which could expose bowhead whales to both thermal stress and altered stratification and vertical transport of water masses. With such profound changes, bowhead whales may face extensive habitat loss. Our results highlight the need for closer investigation and monitoring in order to predict the extent of future distribution changes.

APA:
Chambault, P., Albertsen, C. M., Patterson, T. A., Hansen, R. G., Tervo, O., Laidre, K. L. and Heide-Jørgensen, M. P. (2018) Sea surface temperature predicts the movements of an Arctic cetacean: the bowhead whale. Scientific Reports, 8, 9658. doi: 10.1038/s41598-018-27966-1

MLA:
Chambault, P., Albertsen, C. M., Patterson, T. A., Hansen, R. G., Tervo, O., Laidre, K. L. and Heide-Jørgensen, M. P. “Sea surface temperature predicts the movements of an Arctic cetacean: the bowhead whale” Scientific Reports. 2018, 8, 9658. doi: 10.1038/s41598-018-27966-1

CBE:
Chambault, P., Albertsen, C. M., Patterson, T. A., Hansen, R. G., Tervo, O., Laidre, K. L. and Heide-Jørgensen, M. P. 2018. Sea surface temperature predicts the movements of an Arctic cetacean: the bowhead whale. Scientific Reports 8: 9658. doi: 10.1038/s41598-018-27966-1

BibTeX:
@article{chambault2018a,
title = "Sea surface temperature predicts the movements of an Arctic cetacean: the bowhead whale",
author = "Chambault, {P.} and Albertsen, {C. M.} and Patterson, {T. A.} and Hansen, {R. G.} and Tervo, {O.} and Laidre, {K. L.} and Heide-Jørgensen, {M. P.}",
year = "2018",
volume = "8",
number = "",
journal = "Scientific Reports",
pages = "9658",
issn = "2045-2322",
doi = "10.1038/s41598-018-27966-1",
}

2018

Connecting single-stock assessment models through correlated survival

Published in ICES Journal of Marine Science
Albertsen, C. M.; Nielsen, A. and Thygesen, U. H..

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Abstract:
Fisheries management is mainly conducted via single-stock assessment models assuming that fish stocks do not interact, except through assumed natural mortalities. Currently, the main alternative is complex ecosystem models which require extensive data, are difficult to calibrate, and have long run times. We propose a simple alternative. In three case studies each with two stocks, we improve the single-stock models, as measured by AIC, by adding correlation in the cohort survival. To limit the number of parameters, the correlations are parameterized through the corresponding partial correlations. We consider six models where the partial correlation matrix between stocks follows a band structure ranging from independent assessments to complex correlation structures. Further, a simulation study illustrates the importance of handling correlated data sufficiently by investigating the coverage of confidence intervals for estimated fishing mortality. The results presented will allow managers to evaluate stock statuses based on a more accurate evaluation of model output uncertainty. The methods are directly implementable for stocks with an analytical assessment and does not require any new data sources.

APA:
Albertsen, C. M., Nielsen, A. and Thygesen, U. H. (2018) Connecting single-stock assessment models through correlated survival. ICES Journal of Marine Science, 75(1), 235-244. doi: 10.1093/icesjms/fsx114

MLA:
Albertsen, C. M., Nielsen, A. and Thygesen, U. H. “Connecting single-stock assessment models through correlated survival” ICES Journal of Marine Science. 2018, 75(1), 235-244. doi: 10.1093/icesjms/fsx114

CBE:
Albertsen, C. M., Nielsen, A. and Thygesen, U. H. 2018. Connecting single-stock assessment models through correlated survival. ICES Journal of Marine Science 75(1): 235-244. doi: 10.1093/icesjms/fsx114

BibTeX:
@article{albertsen2018a,
title = "Connecting single-stock assessment models through correlated survival",
author = "Albertsen, {C. M.} and Nielsen, {A.} and Thygesen, {U. H.}",
year = "2018",
volume = "75",
number = "1",
journal = "ICES Journal of Marine Science",
pages = "235-244",
issn = "1054-3139",
doi = "10.1093/icesjms/fsx114",
}

2017

Validation of ecological state space models using the Laplace approximation

Published in Environmental and Ecological Statistics
Thygesen, U. H.; Albertsen, C. M.; Berg, C. W.; Kristensen, K. and Nielsen, A..

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Abstract:
Many statistical models in ecology follow the state space paradigm. For such models, the important step of model validation rarely receives as much attention as estimation or hypothesis testing, perhaps due to lack of available algorithms and software. Model validation is often based on a naive adaptation of Pearson residuals, i.e. the difference between observations and posterior means, even if this approach is flawed. Here, we consider validation of state space models through one-step prediction errors, and discuss principles and practicalities arising when the model has been fitted with a tool for estimation in general mixed effects models. Implementing one-step predictions in the R package Template Model Builder, we demonstrate that it is possible to perform model validation with little effort, even if the ecological model is multivariate, has non-linear dynamics, and whether observations are continuous or discrete. With both simulated data, and a real data set related to geolocation of seals, we demonstrate both the potential and the limitations of the techniques. Our results fill a need for convenient methods for validating a state space model, or alternatively, rejecting it while indicating useful directions in which the model could be improved.

APA:
Thygesen, U. H., Albertsen, C. M., Berg, C. W., Kristensen, K. and Nielsen, A. (2017) Validation of ecological state space models using the Laplace approximation. Environmental and Ecological Statistics, 24(2), 317-339. doi: 10.1007/s10651-017-0372-4

MLA:
Thygesen, U. H., Albertsen, C. M., Berg, C. W., Kristensen, K. and Nielsen, A. “Validation of ecological state space models using the Laplace approximation” Environmental and Ecological Statistics. 2017, 24(2), 317-339. doi: 10.1007/s10651-017-0372-4

CBE:
Thygesen, U. H., Albertsen, C. M., Berg, C. W., Kristensen, K. and Nielsen, A. 2017. Validation of ecological state space models using the Laplace approximation. Environmental and Ecological Statistics 24(2): 317-339. doi: 10.1007/s10651-017-0372-4

BibTeX:
@article{thygesen2017a,
title = "Validation of ecological state space models using the Laplace approximation",
author = "Thygesen, {U. H.} and Albertsen, {C. M.} and Berg, {C. W.} and Kristensen, {K.} and Nielsen, {A.}",
year = "2017",
volume = "24",
number = "2",
journal = "Environmental and Ecological Statistics",
pages = "317-339",
issn = "1573-3009",
doi = "10.1007/s10651-017-0372-4",
}

2017

A Hidden Markov Movement Model for rapidly identifying behavioral states from animal tracks

Published in Ecology and Evolution
Whoriskey, K.; Auger-Méthé, M.; Albertsen, C. M.; Whoriskey, F. G.; Binder, T. R.; Krueger, C. C. and Flemming, J. M..

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Abstract:
Electronic telemetry is frequently used to document animal movement through time. Methods that can identify underlying behaviors driving specific movement patterns can help us understand how and why animals use available space, thereby aiding conservation and management efforts. For aquatic animal tracking data with significant measurement error, a Bayesian state-space model called the first-Difference Correlated Random Walk with Switching (DCRWS) has often been used for this purpose. However, for aquatic animals, highly accurate tracking data are now becoming more common. We developed a new hidden Markov model (HMM) for identifying behavioral states from animal tracks with negligible error, called the hidden Markov movement model (HMMM). We implemented as the basis for the HMMM the process equation of the DCRWS, but we used the method of maximum likelihood and the R package TMB for rapid model fitting. The HMMM was compared to a modified version of the DCRWS for highly accurate tracks, the DCRWSNOME formula, and to a common HMM for animal tracks fitted with the R package moveHMM. We show that the HMMM is both accurate and suitable for multiple species by fitting it to real tracks from a grey seal, lake trout, and blue shark, as well as to simulated data. The HMMM is a fast and reliable tool for making meaningful inference from animal movement data that is ideally suited for ecologists who want to use the popular DCRWS implementation and have highly accurate tracking data. It additionally provides a groundwork for development of more complex modeling of animal movement with TMB. To facilitate its uptake, we make it available through the R package swim.

APA:
Whoriskey, K., Auger-Méthé, M., Albertsen, C. M., Whoriskey, F. G., Binder, T. R., Krueger, C. C. and Flemming, J. M. (2017) A Hidden Markov Movement Model for rapidly identifying behavioral states from animal tracks. Ecology and Evolution, 7(7), 2112-2121. doi: 10.1002/ece3.2795

MLA:
Whoriskey, K., Auger-Méthé, M., Albertsen, C. M., Whoriskey, F. G., Binder, T. R., Krueger, C. C. and Flemming, J. M. “A Hidden Markov Movement Model for rapidly identifying behavioral states from animal tracks” Ecology and Evolution. 2017, 7(7), 2112-2121. doi: 10.1002/ece3.2795

CBE:
Whoriskey, K., Auger-Méthé, M., Albertsen, C. M., Whoriskey, F. G., Binder, T. R., Krueger, C. C. and Flemming, J. M. 2017. A Hidden Markov Movement Model for rapidly identifying behavioral states from animal tracks. Ecology and Evolution 7(7): 2112-2121. doi: 10.1002/ece3.2795

BibTeX:
@article{whoriskey2017a,
title = "A Hidden Markov Movement Model for rapidly identifying behavioral states from animal tracks",
author = "Whoriskey, {K.} and Auger-Méthé, {M.} and Albertsen, {C. M.} and Whoriskey, {F. G.} and Binder, {T. R.} and Krueger, {C. C.} and Flemming, {J. M.}",
year = "2017",
volume = "7",
number = "7",
journal = "Ecology and Evolution",
pages = "2112-2121",
issn = "2045-7758",
doi = "10.1002/ece3.2795",
}

Figure 3 from Albertsen et al. (2017)
2017

Choosing the observational likelihood in state-space stock assessment models

Published in Canadian Journal of Fisheries and Aquatic Sciences
Albertsen, C. M.; Nielsen, A. and Thygesen, U. H..

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Abstract:
Stock assessment models rely on aggregated and uncertain data, which makes it difficult to choose a family of distributions for modelling errors on observations a priori. By implementing several observational likelihoods, modelling both numbers- and proportions-at-age, in an age based state-space stock assessment model, we compare the model fit for each choice of likelihood along with the implications for spawning stock biomass and average fishing mortality. We show that the model fit is improved by modelling the correlation of observations within years. Through a simulation study, we demonstrate that whether likelihoods based on numbers-at-age or proportions-at-age provide the best model fit depends on where the data uncertainty lies. If the measurement uncertainty in the total catch is high compared to the measurement uncertainty in age classification, numbers-at-age is preferred, whereas in the opposite situation proportions-at-age provide the best model fit. However, the best choice of observational likelihood differs for different stocks, and the choice is important for the conclusions drawn from the assessment model.

APA:
Albertsen, C. M., Nielsen, A. and Thygesen, U. H. (2017) Choosing the observational likelihood in state-space stock assessment models. Canadian Journal of Fisheries and Aquatic Sciences, 74(5), 779-789. doi: 10.1139/cjfas-2015-0532

MLA:
Albertsen, C. M., Nielsen, A. and Thygesen, U. H. “Choosing the observational likelihood in state-space stock assessment models” Canadian Journal of Fisheries and Aquatic Sciences. 2017, 74(5), 779-789. doi: 10.1139/cjfas-2015-0532

CBE:
Albertsen, C. M., Nielsen, A. and Thygesen, U. H. 2017. Choosing the observational likelihood in state-space stock assessment models. Canadian Journal of Fisheries and Aquatic Sciences 74(5): 779-789. doi: 10.1139/cjfas-2015-0532

BibTeX:
@article{albertsen2017a,
title = "Choosing the observational likelihood in state-space stock assessment models",
author = "Albertsen, {C. M.} and Nielsen, {A.} and Thygesen, {U. H.}",
year = "2017",
volume = "74",
number = "5",
journal = "Canadian Journal of Fisheries and Aquatic Sciences",
pages = "779-789",
issn = "0706-652X",
doi = "10.1139/cjfas-2015-0532",
}

2017

Spatiotemporal modelling of marine movement data using Template Model Builder

Published in Marine Ecology Progress Series
Auger-Méthé, M.; Albertsen, C. M.; Jonsen, I. D.; Derocher, A. E.; Lidgard, D. C.; Studholme, K. R.; Bowen, W. D.; Crossin, G. T. and Flemming, J. M..

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Abstract:
Tracking of marine animals has increased exponentially in the past decade, and the resulting data could lead to an in-depth understanding of the causes and consequences of movement in the ocean. However, most common marine tracking systems are associated with large measurement errors. Accounting for these errors requires the use of hierarchical models, which are often difficult to fit to data. Using three case studies, we demonstrate that Template Model Builder (TMB), a new R package, is an accurate, efficient, and flexible framework for modelling movement data. First, to demonstrate that TMB is as accurate but 30 times faster than bsam, a popular R package used to apply state-space models to Argos data, we model polar bear (Ursus maritimus) Argos data and compare the locations estimated by the models to GPS locations of these same bears. Second, to demonstrate how TMB's gain in efficiency and frequentist framework facilitate model comparison, we develop models with different error structures and compare them to find the most effective model for light-based geolocations of rhinoceros auklets (Cerorhinca monocerata). Finally, to maximize efficiency through TMB's use of the Laplace approximation of the marginal likelihood, we model behavioural changes with continuous rather than discrete states. This new model directly accounts for the irregular sampling intervals characteristic of Fastloc-GPS data of grey seals (Halichoerus grypus). Using real and simulated data, TMB is shown to be a fast and powerful tool for modelling marine movement data. We discuss how TMB's potential reaches beyond marine movement studies.

APA:
Auger-Méthé, M., Albertsen, C. M., Jonsen, I. D., Derocher, A. E., Lidgard, D. C., Studholme, K. R., Bowen, W. D., Crossin, G. T. and Flemming, J. M. (2017) Spatiotemporal modelling of marine movement data using Template Model Builder. Marine Ecology Progress Series, 565, 237-249. doi: 10.3354/meps12019

MLA:
Auger-Méthé, M., Albertsen, C. M., Jonsen, I. D., Derocher, A. E., Lidgard, D. C., Studholme, K. R., Bowen, W. D., Crossin, G. T. and Flemming, J. M. “Spatiotemporal modelling of marine movement data using Template Model Builder” Marine Ecology Progress Series. 2017, 565, 237-249. doi: 10.3354/meps12019

CBE:
Auger-Méthé, M., Albertsen, C. M., Jonsen, I. D., Derocher, A. E., Lidgard, D. C., Studholme, K. R., Bowen, W. D., Crossin, G. T. and Flemming, J. M. 2017. Spatiotemporal modelling of marine movement data using Template Model Builder. Marine Ecology Progress Series 565: 237-249. doi: 10.3354/meps12019

BibTeX:
@article{augermethe2017a,
title = "Spatiotemporal modelling of marine movement data using Template Model Builder",
author = "Auger-Méthé, {M.} and Albertsen, {C. M.} and Jonsen, {I. D.} and Derocher, {A. E.} and Lidgard, {D. C.} and Studholme, {K. R.} and Bowen, {W. D.} and Crossin, {G. T.} and Flemming, {J. M.}",
year = "2017",
volume = "565",
number = "",
journal = "Marine Ecology Progress Series",
pages = "237-249",
issn = "0171-8630",
doi = "10.3354/meps12019",
}

2016

State-space models’ dirty little secrets: even simple linear Gaussian models can have parameter and state estimation problems

Published in Scientific Reports
Auger-Méthé, M.; Field, C.; Albertsen, C. M.; Derocher, A.; Lewis, M. A.; Jonsen, I. D. and Flemming, J. M..

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Abstract:
State-space models (SSMs) are increasingly used in ecology to model time-series such as animal movement paths and population dynamics. This type of hierarchical model is often structured to account for two levels of variability: biological stochasticity and measurement error. SSMs are flexible. They can model linear and nonlinear processes using a variety of statistical distributions. Recent ecological SSMs are often complex, with a large number of parameters to estimate. Through a simulation study, we show that even simple linear Gaussian SSMs can suffer from parameter- and state-estimation problems. We demonstrate that these problems occur primarily when measurement error is larger than biological stochasticity, the condition that often drives ecologists to use SSMs. Using an animal movement example, we show how these estimation problems can affect ecological inference. Biased parameter estimates of a SSM describing the movement of polar bears (Ursus maritimus) result in overestimating their energy expenditure. We suggest potential solutions, but show that it often remains difficult to estimate parameters. While SSMs are powerful tools, they can give misleading results and we urge ecologists to assess whether the parameters can be estimated accurately before drawing ecological conclusions from their results.

APA:
Auger-Méthé, M., Field, C., Albertsen, C. M., Derocher, A., Lewis, M. A., Jonsen, I. D. and Flemming, J. M. (2016) State-space models’ dirty little secrets: even simple linear Gaussian models can have parameter and state estimation problems. Scientific Reports, 6, 26677. doi: 10.1038/srep26677

MLA:
Auger-Méthé, M., Field, C., Albertsen, C. M., Derocher, A., Lewis, M. A., Jonsen, I. D. and Flemming, J. M. “State-space models’ dirty little secrets: even simple linear Gaussian models can have parameter and state estimation problems” Scientific Reports. 2016, 6, 26677. doi: 10.1038/srep26677

CBE:
Auger-Méthé, M., Field, C., Albertsen, C. M., Derocher, A., Lewis, M. A., Jonsen, I. D. and Flemming, J. M. 2016. State-space models’ dirty little secrets: even simple linear Gaussian models can have parameter and state estimation problems. Scientific Reports 6: 26677. doi: 10.1038/srep26677

BibTeX:
@article{augermethe2016a,
title = "State-space models’ dirty little secrets: even simple linear Gaussian models can have parameter and state estimation problems",
author = "Auger-Méthé, {M.} and Field, {C.} and Albertsen, {C. M.} and Derocher, {A.} and Lewis, {M. A.} and Jonsen, {I. D.} and Flemming, {J. M.}",
year = "2016",
volume = "6",
number = "",
journal = "Scientific Reports",
pages = "26677",
issn = "2045-2322",
doi = "10.1038/srep26677",
}

Figure 1 from Hüssy et al 2015
2016

Evaluation of otolith shape as a tool for stock discrimination in marine fishes using Baltic Sea cod as a case study

Published in Fisheries Research
Hüssy, K.; Mosegaard, H.; Albertsen, C. M.; Hemmer-Hansen, J.; Nielsen, E. E. and Eero, M..

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Abstract:
In the Baltic Sea two genetically distinct cod stocks are found, the “Eastern Baltic cod” and “Western Baltic cod”. In this study we evaluated the applicability of otolith shape analysis for classification of individuals caught in mixed stock fishery, using SNP (Single nucleotide polymorphism) based genetic validation of the otolith based classifications. The otoliths of eastern Baltic cod were generally wider in the dorso-ventral direction in relation to the anterior-posterior length than those of western Baltic cod. These differences were captured by otolith area and 7 – 10 Elliptic Fourier Descriptors of primarily low number harmonics. Traditional standardisation of Descriptors in relation to size could not remove the size effect entirely, highlighting the need for a balanced size-stratified baseline sample. Genetic validation of otolith shape based classification of samples from the mixed-stock area revealed that in both approaches eastern Baltic otoliths had a higher risk of being classified as western Baltic cod than the opposite, but classification success was considerably lower when using a baseline of spawning individuals than when a baseline consisting of genotyped individuals from all areas was used. Furthermore, the latter to a large extent removed a strong size related trend in classification success with low success in small eastern and large western Baltic cod. These results demonstrate the interplay of environmental and genetic influences on otolith shape, which complicates the application of otolith shape for stock discrimination in mixed-stock scenarios. Rigours genetic validation and further studies on the temporal dynamics of shape formation are necessary.

APA:
Hüssy, K., Mosegaard, H., Albertsen, C. M., Hemmer-Hansen, J., Nielsen, E. E. and Eero, M. (2016) Evaluation of otolith shape as a tool for stock discrimination in marine fishes using Baltic Sea cod as a case study. Fisheries Research, 174, 210-218. doi: 10.1016/j.fishres.2015.10.010

MLA:
Hüssy, K., Mosegaard, H., Albertsen, C. M., Hemmer-Hansen, J., Nielsen, E. E. and Eero, M. “Evaluation of otolith shape as a tool for stock discrimination in marine fishes using Baltic Sea cod as a case study” Fisheries Research. 2016, 174, 210-218. doi: 10.1016/j.fishres.2015.10.010

CBE:
Hüssy, K., Mosegaard, H., Albertsen, C. M., Hemmer-Hansen, J., Nielsen, E. E. and Eero, M. 2016. Evaluation of otolith shape as a tool for stock discrimination in marine fishes using Baltic Sea cod as a case study. Fisheries Research 174: 210-218. doi: 10.1016/j.fishres.2015.10.010

BibTeX:
@article{hussy2016a,
title = "Evaluation of otolith shape as a tool for stock discrimination in marine fishes using Baltic Sea cod as a case study",
author = "Hüssy, {K.} and Mosegaard, {H.} and Albertsen, {C. M.} and Hemmer-Hansen, {J.} and Nielsen, {E. E.} and Eero, {M.}",
year = "2016",
volume = "174",
number = "",
journal = "Fisheries Research",
pages = "210-218",
issn = "0165-7836",
doi = "10.1016/j.fishres.2015.10.010",
}

Figure 1 from Karlsen et al 2015
2015

From Fishing to Fish Processing: Separation of Fish from Crustaceans in the Norway Lobster-Directed Multispecies Trawl Fishery Improves Seafood Quality

Published in PLoS ONE
Karlsen, J. D.; Krag, L. A.; Albertsen, C. M. and Frandsen, R. P..

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Abstract:
Fishing gears have negative impacts on seafood quality, especially on fish in the mixed trawl fishery targeting Norway lobster (Nephrops norvegicus). In this fishery, which is worth about € 80 millions in Denmark alone, the quality of fish can be significantly improved by simple gear changes. A trawl codend divided into an upper and lower codend was designed to separate fish from Norway lobster during the fishing process by encourage fish to swim into the upper codend by using a frame at the entrance of the lower codend. Separate codends for fish and Norway lobster in the same gear provide the opportunity to selectively reduce small low-value fish, which will reduce catch weight and sorting time onboard the vessel. For this horizontally divided test codend and a standard codend, in which the catch was mixed, quality assessments were performed on the same batches of fish during three steps of the value chain: i) aboard the fishing vessel; ii) at the Fishermen's Collection Central, and iii) in the production plant. Four species of fish and fillets from fish caught in the upper codend of the test codend were of significantly better quality for several of the assessed parameters compared with those caught in the standard codend: i) newly caught fish showed significantly less scale loss and discolourations and had significantly better texture; ii) landed fish had significantly better skin appearance and texture and significantly fewer discolourations; and iii) fillets showed significantly fewer blood spots and had significantly better texture. There were no differences in injuries for newly caught fish or gaping and bruises for fillets between the test and standard codends. The decrease in catch-related damages in the test codend is explained by little contact between fish and animals with hard or spiny surfaces due to successful separation of fish and Norway lobster into the upper and lower codends, respectively, and by lower catch weight in the upper codend of the test codend compared with the standard codend. The decrease in damages may also improve quality indirectly by inflicting less stress to the fish and subsequently give better texture, which offers advantages such as pre-rigor filleting and fresher products for the market. Significant improvements in fish quality can potentially increase the catch value in nationally important fisheries.

APA:
Karlsen, J. D., Krag, L. A., Albertsen, C. M. and Frandsen, R. P. (2015) From Fishing to Fish Processing: Separation of Fish from Crustaceans in the Norway Lobster-Directed Multispecies Trawl Fishery Improves Seafood Quality. PLoS ONE, 10(11), e0140864. doi: 10.1371/journal.pone.0140864

MLA:
Karlsen, J. D., Krag, L. A., Albertsen, C. M. and Frandsen, R. P. “From Fishing to Fish Processing: Separation of Fish from Crustaceans in the Norway Lobster-Directed Multispecies Trawl Fishery Improves Seafood Quality” PLoS ONE. 2015, 10(11), e0140864. doi: 10.1371/journal.pone.0140864

CBE:
Karlsen, J. D., Krag, L. A., Albertsen, C. M. and Frandsen, R. P. 2015. From Fishing to Fish Processing: Separation of Fish from Crustaceans in the Norway Lobster-Directed Multispecies Trawl Fishery Improves Seafood Quality. PLoS ONE 10(11): e0140864. doi: 10.1371/journal.pone.0140864

BibTeX:
@article{karlsen2015a,
title = "From Fishing to Fish Processing: Separation of Fish from Crustaceans in the Norway Lobster-Directed Multispecies Trawl Fishery Improves Seafood Quality",
author = "Karlsen, {J. D.} and Krag, {L. A.} and Albertsen, {C. M.} and Frandsen, {R. P.}",
year = "2015",
volume = "10",
number = "11",
journal = "PLoS ONE",
pages = "e0140864",
issn = "1932-6203",
doi = "10.1371/journal.pone.0140864",
}

Figure 1 from Albertsen et al 2015
2015

Fast fitting of non-Gaussian state-space models to animal movement data via Template Model Builder

Published in Ecology
Albertsen, C. M.; Whoriskey, K.; Yurkowski, D.; Nielsen, A. and Flemming, J. M..

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Abstract:
State-space models (SSM) are often used for analyzing complex ecological processes that are not observed directly, such as marine animal movement. When outliers are present in the measurements, special care is needed in the analysis to obtain reliable location and process estimates. Here we recommend using the Laplace approximation combined with automatic differentiation (as implemented in the novel R-package: Template Model Builder (TMB)) for the fast fitting of continuous time multivariate non-Gaussian SSMs. Through Argos satellite tracking data, we demonstrate that the use of continuous time t-distributed measurement errors for error-prone data is more robust to outliers and improves the location estimation compared to using discretized time t-distributed errors (implemented with a Gibbs sampler) or using continuous time Gaussian errors (as with the Kalman filter). Using TMB, we are able to estimate additional parameters compared to previous methods, all without requiring a substantial increase in computational time. The model implementation is made available through the R-package argosTrack.

APA:
Albertsen, C. M., Whoriskey, K., Yurkowski, D., Nielsen, A. and Flemming, J. M. (2015) Fast fitting of non-Gaussian state-space models to animal movement data via Template Model Builder. Ecology, 96(10), 2598-2604. doi: 10.1890/14-2101.1

MLA:
Albertsen, C. M., Whoriskey, K., Yurkowski, D., Nielsen, A. and Flemming, J. M. “Fast fitting of non-Gaussian state-space models to animal movement data via Template Model Builder” Ecology. 2015, 96(10), 2598-2604. doi: 10.1890/14-2101.1

CBE:
Albertsen, C. M., Whoriskey, K., Yurkowski, D., Nielsen, A. and Flemming, J. M. 2015. Fast fitting of non-Gaussian state-space models to animal movement data via Template Model Builder. Ecology 96(10): 2598-2604. doi: 10.1890/14-2101.1

BibTeX:
@article{albertsen2015a,
title = "Fast fitting of non-Gaussian state-space models to animal movement data via Template Model Builder",
author = "Albertsen, {C. M.} and Whoriskey, {K.} and Yurkowski, {D.} and Nielsen, {A.} and Flemming, {J. M.}",
year = "2015",
volume = "96",
number = "10",
journal = "Ecology",
pages = "2598-2604",
issn = "0012-9658",
doi = "10.1890/14-2101.1",
}

Figure 1 from Christensen et al 2015
2015

Aggregation and attachment responses of blue mussels, Mytilus edulis - impact of substrate composition, time scale and source of mussel seed

Published in Aquaculture
Christensen, H. T.; Dolmer, P.; Hansen, B. W.; Holmer, M.; Kristensen, L. D.; Poulsen, L. K.; Stenberg, C.; Albertsen, C. M. and Støttrup, J. G..

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Abstract:
Survival after transplantation of mussel seeds is crucial for the production output of blue mussels (Mytilus edulis L.) in bottom cultures. Hence, an understanding of the interactions between bed formation, habitat structure and performance of mussel seed of different origins can contribute to an optimization of the production. The effect of substrate composition and timing of formation of a mussel bed in relation to aggregation and attachment of mussels were investigated with mussel seeds obtained from two different sources: mussel seed dredged from a natural mussel bed and mussel seed collected from a suspended long line culture. The mussels were applied to experimental units of complex and smooth substrate on the sea bed. Data on aggregation (day 0, day 1 and day 2), attachment strength (day 2 and 30), loss (day 2 and 30) and growth (day 0–30) of mussels were collected during the experiment. The results showed that complex substrate indeed had a stabilizing effect on the mussel structure resulting in less aggregation and increased attachment strength. The 3D matrix forming a mussel bed was achieved faster on complex substrate, and led to reduced mortality of transplanted mussels. Despite significantly lower specific growth rates on the complex substrate, the total biomass of mussels was significantly higher on complex substrate compared to on smooth substrate due to the higher survival of mussels. Furthermore, suspended mussels aggregated more and faster and had a stronger and more rapid attachment as compared to bottom mussels. Consequently, it was concluded that when transplanting mussels, seeding with substrate increases surface complexity on the seabed and increases survival of the mussels.

APA:
Christensen, H. T., Dolmer, P., Hansen, B. W., Holmer, M., Kristensen, L. D., Poulsen, L. K., Stenberg, C., Albertsen, C. M. and Støttrup, J. G. (2015) Aggregation and attachment responses of blue mussels, Mytilus edulis - impact of substrate composition, time scale and source of mussel seed. Aquaculture, 435(0), 245-251. doi: 10.1016/j.aquaculture.2014.09.043

MLA:
Christensen, H. T., Dolmer, P., Hansen, B. W., Holmer, M., Kristensen, L. D., Poulsen, L. K., Stenberg, C., Albertsen, C. M. and Støttrup, J. G. “Aggregation and attachment responses of blue mussels, Mytilus edulis - impact of substrate composition, time scale and source of mussel seed” Aquaculture. 2015, 435(0), 245-251. doi: 10.1016/j.aquaculture.2014.09.043

CBE:
Christensen, H. T., Dolmer, P., Hansen, B. W., Holmer, M., Kristensen, L. D., Poulsen, L. K., Stenberg, C., Albertsen, C. M. and Støttrup, J. G. 2015. Aggregation and attachment responses of blue mussels, Mytilus edulis - impact of substrate composition, time scale and source of mussel seed. Aquaculture 435(0): 245-251. doi: 10.1016/j.aquaculture.2014.09.043

BibTeX:
@article{christensen2015a,
title = "Aggregation and attachment responses of blue mussels, Mytilus edulis - impact of substrate composition, time scale and source of mussel seed",
author = "Christensen, {H. T.} and Dolmer, {P.} and Hansen, {B. W.} and Holmer, {M.} and Kristensen, {L. D.} and Poulsen, {L. K.} and Stenberg, {C.} and Albertsen, {C. M.} and Støttrup, {J. G.}",
year = "2015",
volume = "435",
number = "0",
journal = "Aquaculture",
pages = "245-251",
issn = "0044-8486",
doi = "10.1016/j.aquaculture.2014.09.043",
}

Figure 1 from Albertsen et al 2014
2014

Depth preference in released juvenile turbot Psetta maxima

Published in Journal of Experimental Marine Biology and Ecology
Albertsen, C. M.; Støttrup, J. G.; Nielsen, A. and Christoffersen, M. O..

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Abstract:
Hatchery-reared juvenile turbot Psetta maxima were tagged with Passive Integrated Transponder (PIT) tags and released at three different depths in a sandy bay in Denmark. About 2–7% of the released fish were registered daily to monitor their distribution using a tag antenna mounted on a modified beam trawl, thus avoiding actually sampling the fish. The change in distribution of the three groups was adequately represented by a two-dimensional movement model. Movement along the shore was described by a Brownian motion with group specific drift. Movement perpendicular to the shore line was described by a Cox–Ingersoll–Ross process with a group specific attraction point. All three groups exhibited similar depth preferences of 1.7 m. Immediately after the release, fish were concentrated around the release points but after one day, fish had moved to the preferred depth and subsequently maintained their position at this depth. Farmed turbot exhibited strong site fidelity and an innate behaviour for selecting a preferred depth.

APA:
Albertsen, C. M., Støttrup, J. G., Nielsen, A. and Christoffersen, M. O. (2014) Depth preference in released juvenile turbot Psetta maxima. Journal of Experimental Marine Biology and Ecology, 461, 179-184. doi: 10.1016/j.jembe.2014.07.013

MLA:
Albertsen, C. M., Støttrup, J. G., Nielsen, A. and Christoffersen, M. O. “Depth preference in released juvenile turbot Psetta maximaJournal of Experimental Marine Biology and Ecology. 2014, 461, 179-184. doi: 10.1016/j.jembe.2014.07.013

CBE:
Albertsen, C. M., Støttrup, J. G., Nielsen, A. and Christoffersen, M. O. 2014. Depth preference in released juvenile turbot Psetta maxima. Journal of Experimental Marine Biology and Ecology 461: 179-184. doi: 10.1016/j.jembe.2014.07.013

BibTeX:
@article{albertsen2014b,
title = "Depth preference in released juvenile turbot Psetta maxima",
author = "Albertsen, {C. M.} and Støttrup, {J. G.} and Nielsen, {A.} and Christoffersen, {M. O.}",
year = "2014",
volume = "461",
number = "",
journal = "Journal of Experimental Marine Biology and Ecology",
pages = "179-184",
issn = "0022-0981",
doi = "10.1016/j.jembe.2014.07.013",
}

Figure from Albertsen and Daetz 2014
2014

Are the house prices moving up or down?

Published (in Danish) in Finans/Invest
Albertsen, C. and Daetz, B..

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Abstract:
This article considers the development in house prices. Whether prices are moving up or down, they generate debate in the media. Further, the price development is attributed great economic importance, wich makes it problematic when the prices are reported as rising one day, while it is reported that they are falling the following day. This article gives a thorough introduction to how the development in house prices is measured; including why measuring residential property prices development is so complicated and subject to great uncertainty. Thus, both the calculation and the data basis have a decisive bearing on the conclusion drawn.

APA:
Albertsen, C. and Daetz, B. (2014) Are the house prices moving up or down?. Finans/Invest, 324(4), 24-31.

MLA:
Albertsen, C. and Daetz, B. “Are the house prices moving up or down?” Finans/Invest. 2014, 324(4), 24-31.

CBE:
Albertsen, C. and Daetz, B. 2014. Are the house prices moving up or down?. Finans/Invest 324(4): 24-31.

BibTeX:
@article{albertsen2014a,
title = "Are the house prices moving up or down?",
author = "Albertsen, {C.} and Daetz, {B.}",
year = "2014",
volume = "324",
number = "4",
journal = "Finans/Invest",
pages = "24-31",
issn = "0106-1798",
doi = "",
}