Mathematical individual-based model for habitat suitability simulations

Individualistic mathematical models based on bioenergy theory are the latest research in modeling river habitats. This study explains the principles and method of individualistic population modeling based on bioenergy theory. Moreover, it presents the application of the model in the evaluation of red-trout habitats of the Red River in the National Park. Investigating the capabilities of the individualistic inSTREAM model as well as the results of bioenergy modeling presented in the present study showed that modeling presented in this study can make changes in different types of growth and habitat quality, as well as areas for biomonths with respect to both Biological and non-biological factors were used to distribute energy in the management and engineering of river ecosystems and to estimate ecological flows. This model is also applicable in the field of fisheries and aquaculture in order to provide more fish production and sustainable use of these resources assessment.

Mechanistic, individual-based simulation models (IBMs) have been developed to overcome well-known limitations of “habitat suitability” models such as PHABSIM (Bovee et al., 1998). InSTREAM is an individual-based stream salmonid population model designed to support river management decisions; it predicts how stream trout populations respond to habitat alteration, including altered flow, temperature, turbidity regimes, and changes in channel morphology. The model represents individual trout, with population responses emerging from how individuals are affected by their habitat and each other (especially via competition for food). Since its initial release in 2001 (Railsback and Harvey, 2001), its capabilities have been steadily developing. InSTREAM has been shown to reproduce a variety of observed patterns in salmonid behavior (e.g., Harvey and Railsback, 2014; Penaluna et al. 2015, Bjørnås et al. 2020, Hajiesmaeili, 2019). This study represents pioneering work that applies inSTREAM as an IBM in Iran for river habitat assessment of trout populations.

The process overview and the schedule executed in inSTREAM are represented by introducing the four main action groups, including habitat, fish, redd (the nests laid by spawning trout), and observer. We use an example application of the model for brown trout populations in Elarm River, Lar National Park of Iran to illustrate how inSTREAM can provide a more comprehensive understanding of river habitat assessment and management actions. To investigate the temporal variations of fish growth and how different parameters such as flow, velocity, and water temperature affect the growth variations, the monthly time series of the average specific growth rate is evaluated in terms of both length and weight. In addition, the quality of the Elarm River habitats is also assessed by examining the temporal variations in the net rate of energy intake (NREI) against mean monthly discharge per unit width that indicates the combined effects of both depth and velocity for both juvenile and adult life stages of the target species. We also develop the flow-bioenergetics (Q-NREI) curve for Elarm River to assess the range of optimal energy flow and energy variation in the actual existing condition of the river.

Our results indicated that in spring, especially during the two months of May and June, the growth rate of the fish decreased due to an increase in the flow rate and consequently the flow velocity and the increase in temperature during this time period also in the summer. Increasing discharge, flow velocity, and temperature will increase energy consumption of fish metabolism, which will lead to a decrease in growth. The growth of the juvenile life stage was more than adult. It is likely because the fish are growing at younger ages, and they need more energy to meet their physical energy demands, so they feed more. The decline in fish growth at older ages is presumably because they need less food which reduces their energy requirement to the extent that it is only required for vital functions and reproduction. During the two months of May and June NREI also decreased, and this value is negative for the adult life stage. In other words, energy consumed for metabolism used for fish respiration and swimming was more than the energy intake from food. Because this parameter depends on the length and weight of the fish and with increasing fish weight at older ages, the energy consumed will increase, thus making NREI negative. Moreover, our results showed that the flow range of 0.22-0.31 m3/s can be considered the optimal energy flow for Elarm River to maintain the sustainability of the river ecosystem.

Considering the key habitat variables affecting individuals and the mechanisms through which those variables affect individual fitness (growth, survival and reproduction), an IBM like inSTREAM can predict population responses by aggregating the fates of simulated individuals over time. A key feature of IBMs is representing adaptive behavior: how individuals trade off the conflicting demands of growth, survival, and reproduction through behaviors such as selecting where to feed and when to hide instead of feeding. IBMs using this approach can predict population responses to realistically varying habitat conditions, making results directly applicable to management decisions and testable against field observations.