Time-variant productivity in biomass dynamic models on seasonal and long-term scales

Tobias Mildenberger*, Casper Willestofte Berg, Martin Wæver Pedersen, Alexandros Kokkalis, J. Rasmus Nielsen

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

The productivity of fish populations varies naturally over time, dependent on integrated effects of abundance, ecological factors, and environmental conditions. These changes can be expressed as gradual or abrupt shifts in productivity as well as fluctuations on any time scale from seasonal oscillations to long-term changes. This study considers three extensions to biomass dynamic models that accommodate time-variant productivity in fish populations. Simulation results reveal that neglecting seasonal changes in productivity can bias derived stock sustainability reference levels and, thus, fisheries management advice. Results highlight the importance of biannual biomass indices and their timing relative to the peaks of the seasonal processes (i.e. recruitment, growth, mortality) for the estimation of seasonally time-variant productivity. The application to real-world data of the eastern Baltic cod (Gadus morhua) stock shows that the model is able to disentangle differences in seasonal fishing mortality as well as seasonal and long-term changes in productivity. The combined model with long-term and seasonally varying productivity performs significantly better than models that neglect time-variant productivity. The model extensions proposed here allow to account for time-variant productivity of fish populations leading to increased reliability of derived reference levels.
Original languageEnglish
JournalI C E S Journal of Marine Science
Volume77
Issue number1
Pages (from-to)174-187
ISSN1054-3139
DOIs
Publication statusPublished - 2020

Keywords

  • Eastern Baltic cod (Gadus morhua)
  • Fisheries management
  • Fish stock assessment
  • Maximum sustainable yield
  • Population dynamics
  • Seasonality
  • SPiCT
  • Surplus production model

Cite this

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title = "Time-variant productivity in biomass dynamic models on seasonal and long-term scales",
abstract = "The productivity of fish populations varies naturally over time, dependent on integrated effects of abundance, ecological factors, and environmental conditions. These changes can be expressed as gradual or abrupt shifts in productivity as well as fluctuations on any time scale from seasonal oscillations to long-term changes. This study considers three extensions to biomass dynamic models that accommodate time-variant productivity in fish populations. Simulation results reveal that neglecting seasonal changes in productivity can bias derived stock sustainability reference levels and, thus, fisheries management advice. Results highlight the importance of biannual biomass indices and their timing relative to the peaks of the seasonal processes (i.e. recruitment, growth, mortality) for the estimation of seasonally time-variant productivity. The application to real-world data of the eastern Baltic cod (Gadus morhua) stock shows that the model is able to disentangle differences in seasonal fishing mortality as well as seasonal and long-term changes in productivity. The combined model with long-term and seasonally varying productivity performs significantly better than models that neglect time-variant productivity. The model extensions proposed here allow to account for time-variant productivity of fish populations leading to increased reliability of derived reference levels.",
keywords = "Eastern Baltic cod (Gadus morhua), Fisheries management, Fish stock assessment, Maximum sustainable yield, Population dynamics, Seasonality, SPiCT, Surplus production model",
author = "Tobias Mildenberger and Berg, {Casper Willestofte} and Pedersen, {Martin W{\ae}ver} and Alexandros Kokkalis and Nielsen, {J. Rasmus}",
year = "2020",
doi = "10.1093/icesjms/fsz154",
language = "English",
volume = "77",
pages = "174--187",
journal = "I C E S Journal of Marine Science",
issn = "1054-3139",
publisher = "Oxford University Press",
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}

Time-variant productivity in biomass dynamic models on seasonal and long-term scales. / Mildenberger, Tobias; Berg, Casper Willestofte; Pedersen, Martin Wæver; Kokkalis, Alexandros; Nielsen, J. Rasmus.

In: I C E S Journal of Marine Science, Vol. 77, No. 1, 2020, p. 174-187.

Research output: Contribution to journalJournal articleResearchpeer-review

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AU - Berg, Casper Willestofte

AU - Pedersen, Martin Wæver

AU - Kokkalis, Alexandros

AU - Nielsen, J. Rasmus

PY - 2020

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AB - The productivity of fish populations varies naturally over time, dependent on integrated effects of abundance, ecological factors, and environmental conditions. These changes can be expressed as gradual or abrupt shifts in productivity as well as fluctuations on any time scale from seasonal oscillations to long-term changes. This study considers three extensions to biomass dynamic models that accommodate time-variant productivity in fish populations. Simulation results reveal that neglecting seasonal changes in productivity can bias derived stock sustainability reference levels and, thus, fisheries management advice. Results highlight the importance of biannual biomass indices and their timing relative to the peaks of the seasonal processes (i.e. recruitment, growth, mortality) for the estimation of seasonally time-variant productivity. The application to real-world data of the eastern Baltic cod (Gadus morhua) stock shows that the model is able to disentangle differences in seasonal fishing mortality as well as seasonal and long-term changes in productivity. The combined model with long-term and seasonally varying productivity performs significantly better than models that neglect time-variant productivity. The model extensions proposed here allow to account for time-variant productivity of fish populations leading to increased reliability of derived reference levels.

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