Naslov
Condition index as an indicator of stock status: insights from composite modelling

Autori
Haberle, Ines ; Bavčević, Lav ; Klanjscek, Tin

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Skup
ISEM2023 – The International Society for Ecological Modelling Global Conference 2023

Mjesto i datum
Toronto, Kanada, 02.05.2023. - 06.05.2023

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
fisheries management ; Dynamic Energy Budget ; individual-based model ; carrying capacity

Sažetak
Condition index indicates individual performance from which, in principle, aspects of the population dynamics could be derived. Such information could be used in fisheries management to support stock assessment and the associated decision making. However, insufficient understanding of the relationship between individual-level processes and population-level metrics discourage managers to include condition index into the decision-making. Identifying the links between these two levels of biological organization would therefore foster the process of integrating condition index into standard management practice. We use process-based composite modelling to link individual condition of the small pelagic European pilchard, expressed through Fulton’s condition index, to its population-level status. We apply Dynamic Energy Budget (DEB) theory to model the individual ontogeny as a function of food and constant temperature, followed by integration into an individual-based modelling (IBM) framework to simultaneously track the individual- and population-level statistics. Ultimately, we explore the effects of fishing mortality on both statistics, for two constant and food-limited environmental carrying capacity scenarios. Expectedly, higher fishing mortality reduces stock size but, contrary to current wisdom, has positive effect on individual condition index, regardless of the environmental carrying capacity. We validate the observed patterns for a significantly different fish species, Gilthead seabream. This implies that very good fish condition could indicate reduced stock size and imminent threat of overfishing, opposing the traditional definition of a poor stock. Our study shows that, in food-limited populations, condition index can estimate stock size relative to carrying capacity, helping differentiate imminent stock collapse from under-fishing. We therefore promote condition index as inexpensive supplementary information alongside standard stock assessment. Lastly, we promote use of DEB-IBM composite modelling to investigate further feedback mechanisms between individual- and population-level traits, and to strengthen confidence in both condition index and any potential indicators that can simplify marine bioresources management.

Izvorni jezik
Engleski

Znanstvena područja
Matematika, Biologija, Interdisciplinarne prirodne znanosti

POVEZANOST RADA