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.

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Long-term changes in trophic patterns of Iceland cod and linkages to main prey stock sizes

ICES Journal of Marine Science ◽

10.1093/icesjms/fsr057 ◽

2011 ◽

Vol 68 (7) ◽

pp. 1488-1499 ◽

Cited By ~ 21

Author(s):

Ólafur K. Pálsson ◽

Höskuldur Björnsson

Keyword(s):

Gadus Morhua ◽

Atlantic Water ◽

Type I ◽

Feeding Response ◽

Total Consumption ◽

Stock Size ◽

Main Prey ◽

Northern Shrimp ◽

Long Term Changes

Abstract Pálsson, Ó. K., and Björnsson, H. 2011. Long-term changes in trophic patterns of Iceland cod and linkages to main prey stock sizes. – ICES Journal of Marine Science, 68: 1488–1499. Data on the diet composition of Iceland cod (Gadus morhua) were collected in March of the years 1981–2010 and in autumn of the years 1988–2010. Capelin, northern shrimp, and euphausiids dominate the diet in all years and may be classified as the stable food of Iceland cod. Overall, total consumption by the smallest cod (20–29 cm) remained stable over the three decades, whereas that of larger fish has declined since the mid-1990s. This decline may explain the reduced growth rate of cod in recent years. Long-term, prey-specific patterns were identified in consumption, and significant trophic links were found between cod consumption and stock sizes of capelin and northern shrimp. In March, the correlation between cod consumption on capelin and capelin stock size was highly significant, a type I functional feeding response, but not significant in autumn. The correlation deteriorated in the early to mid-1990s and in the early 2000s. Increased inflow of Atlantic water into north Icelandic waters, and associated changes in capelin distribution, may have contributed to this trend. The interaction between cod consumption on northern shrimp and shrimp stock size showed a highly significant type I functional feeding response in both seasons.

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Ecology of the collapse of Rapa Nui society

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2020.0662 ◽

2020 ◽

Vol 287 (1929) ◽

pp. 20200662 ◽

Cited By ~ 1

Author(s):

M. Lima ◽

E. M. Gayo ◽

C. Latorre ◽

C. M. Santoro ◽

S. A. Estay ◽

...

Keyword(s):

Recurrent Events ◽

Dynamic Models ◽

Ecological Factors ◽

Long Term Effects ◽

Rapa Nui ◽

Radiocarbon Dates ◽

Underlying Causes ◽

Capita Food ◽

Past Population

Collapses of food producer societies are recurrent events in prehistory and have triggered a growing concern for identifying the underlying causes of convergences/divergences across cultures around the world. One of the most studied and used as a paradigmatic case is the population collapse of the Rapa Nui society. Here, we test different hypotheses about it by developing explicit population dynamic models that integrate feedbacks between climatic, demographic and ecological factors that underpinned the socio-cultural trajectory of these people. We evaluate our model outputs against a reconstruction of past population size based on archaeological radiocarbon dates from the island. The resulting estimated demographic declines of the Rapa Nui people are linked to the long-term effects of climate change on the island's carrying capacity and, in turn, on the ‘per-capita food supply’.

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