Fish condition as an indicator of stock status: Insights from condition index in a food‐limiting environment

Abstract

Individual performance defines population dynamics. Condition index -a ratio of weight and some function of length -has been louded as an indicator of individual performance and recommended as a tool in fisheries management and conservation.However, insufficient understanding of the correlation between individual-level processes and population-level responses hinders its adoption. To this end, we use composite modelling to link individual's condition, expressed through the condition index, to population-level status. We start by modelling ontogeny of European pilchard (Sardina pilchardus, Clupeidae) as a function of food and constant temperature using Dynamic Energy Budget theory. We then provide a framework to simultaneously track the individual-and population-level statistics by incorporating the dynamic energy budget model into an individual-based model. Lastly, we explore the effects of fishing pressure on the statistics in two constant and food-limited environmental carrying capacity scenarios. Results show that, regardless of the species' environmental carrying capacity, individual condition index will increase with fishing mortality, that is, with reduction of stock size. Same patterns are observed for gilthead seabream (Sparus aurata, Sparidae), a significantly different species. Condition index can, therefore, in food-limited populations, be used to (i) estimate population size relative to carrying capacity and (ii) distinguish overfished from underfished populations. Our findings promote a practical way to operationally incorporate the condition index into fisheries management and marine conservation, thus providing additional use for the commonly collected biometric data. Some real-world applications, however, may require additional research to account for other variables such as fluctuating environmental conditions and individual variability.

Length-Weight Relationships and Growth Patterns of Eight Indigenous Fish Species from Lancang River, Southwest China

“…Besides, fshing pressure could also afect their condition factor because S. lissolabiatus, T. sinensis, and M. lepturus were important components of local fsheries [18,19]. According to Haberle et al [29], the body length, body weight, and average condition factor increased with an increase in fshing pressure but decreased with an increase in population abundance. Diferences of condition factor of H. macrolepis, S. porthos, and G. lampris across sampling seasons were not discussed because these fshes were captured only in one season.…”

Unravelling mechanisms behind population dynamics, biological traits and latitudinal distribution in two benthic ecosystem engineers: A modelling approach

“…They constitute promising tools for predicting species responses to climate change and understanding the mechanisms behind those responses. Among these approaches, Dynamic Energy Budget (DEB) models have been associated to Individual Based Models (IBM) to predict population dynamics and address an variety of ecological questions ranging from ecotoxicology (David et al, 2019;Beaudouin et al, 2012), fish ecology and fisheries management (Haberle et al, 2023), aquaculture (Bacher and Gangnery, 2006), and the study of potential impacts of climate change (Thomas and Bacher, 2018;Thomas et al, 2020). Dynamic Energy Budget (DEB) models simulate the effect of changing environmental conditions on the individuals' bioenergetics by quantifying the energy allocation to reserve, growth, maturation, reproduction and maintenance of a species at the individual level throughout its life cycle, thus providing predictions of growth, reproduction and life-history traits of individuals according to environmental conditions such as temperature and food availability (Kooijman, 2010).…”

Life-history Characteristics of Recreational Lake Trout (Salvelinus namaycush) Fisheries in Manitoba

“…From this metric alone, Manitoba's lake trout appear to be in better condition than 50% of individuals across its geographical range. Haberle et al (2023) used an energetics model to better understand the relationship between individual fitness and stock status and found a negative correlation between individual fitness and stock status. Furthermore, as fishing mortality increases and reduces the population size, that would lead to an increase in individual body condition due to lower competition for limited food resources (Haberle et al, 2023).…”