Evaluation of Classification Algorithms to Predict Largemouth Bass (Micropterus salmoides) Occurrence

This study aimed to evaluate classification algorithms to predict largemouth bass (Micropterus salmoides) occurrence in South Korea. Fish monitoring and environmental data (temperature, precipitation, flow rate, water quality, elevation, and slope) were collected from 581 locations throughout four major river basins for 5 years (2011–2015). Initially, 13 classification models built in the caret package were evaluated for predicting largemouth bass occurrence. Based on the accuracy (>0.8) and kappa (>0.5) criteria, the top three classification algorithms (i.e., random forest (rf), C5.0, and conditional inference random forest) were selected to develop ensemble models. However, combining the best individual models did not work better than the best individual model (rf) at predicting the frequency of largemouth bass occurrence. Additionally, annual mean temperature (12.1 °C) and fall mean temperature (13.6 °C) were the most important environmental variables to discriminate the presence and absence of largemouth bass. The evaluation process proposed in this study will be useful to select a prediction model for the prediction of freshwater fish occurrence but will require further study to ensure ecological reliability

National-Scale Assessment of Climate Change Impacts on Two Native Freshwater Fish Using a Habitat Suitability Model

Climate change, which has the potential to alter water flow and temperature in aquatic environments, can influence the freshwater fish habitat. This study used an ecological habitat suitability model (EHSM), which integrates hydraulic (water depth and velocity) and physiologic (water temperature) suitability, to investigate the impact of climate change on two native freshwater fish species (Zacco platypus and Nipponocypris koreanus) in South Korea. The model predicted that in 2080 (2076–2085), the decrease in average ecological habitat suitability (EHS) will be higher for N. koreanus (19.2%) than for Z. platypus (9.87%) under the representative concentration pathway (RCP) 8.5 scenario. Under the same condition, EHS for Z. platypus and N. koreanus at 36.5% and 44.4% of 115 sites, respectively, were expected to degrade significantly (p < 0.05). However, the habitat degradation for Z. platypus and N. koreanus was much lower (7.8% and 10.4%, respectively) under the RCP 4.5 scenario, suggesting a preventive measure for carbon dioxide emission. Partial correlation analysis indicated that the number of hot days (i.e., days on which the temperature exceeds the heat stress threshold) is the variable most significantly (p < 0.05) related to EHS changes for both species. This study suggests that the EHSM incorporating the effect of water temperature on the growth and heat stress of fish can be a promising model for the assessment of climate change impacts on habitat suitability for freshwater fish

National-Scale Assessment of Climate Change Impacts on Two Native Freshwater Fish Using a Habitat Suitability Model

Climate change, which has the potential to alter water flow and temperature in aquatic environments, can influence the freshwater fish habitat. This study used an ecological habitat suitability model (EHSM), which integrates hydraulic (water depth and velocity) and physiologic (water temperature) suitability, to investigate the impact of climate change on two native freshwater fish species (Zacco platypus and Nipponocypris koreanus) in South Korea. The model predicted that in 2080 (2076–2085), the decrease in average ecological habitat suitability (EHS) will be higher for N. koreanus (19.2%) than for Z. platypus (9.87%) under the representative concentration pathway (RCP) 8.5 scenario. Under the same condition, EHS for Z. platypus and N. koreanus at 36.5% and 44.4% of 115 sites, respectively, were expected to degrade significantly (p Z. platypus and N. koreanus was much lower (7.8% and 10.4%, respectively) under the RCP 4.5 scenario, suggesting a preventive measure for carbon dioxide emission. Partial correlation analysis indicated that the number of hot days (i.e., days on which the temperature exceeds the heat stress threshold) is the variable most significantly (p < 0.05) related to EHS changes for both species. This study suggests that the EHSM incorporating the effect of water temperature on the growth and heat stress of fish can be a promising model for the assessment of climate change impacts on habitat suitability for freshwater fish

Life-history habitat suitability modelling of a potential invasive alien species, smallmouth bass (Micropterus dolomieu), in South Korea

The aim of this study was to predict the distribution of a potential invasive alien species, smallmouth bass (Micropterus dolomieu), in South Korea using a life-history-based habitat suitability model. Environmental data (air temperature, water temperature, and fish occurrence) at present (2011–2020) were collected from 160 representative sites across the five river basins (Han, Nakdong, Guem, Seomjin, and Yeongsan). Future predictions were conducted under the representative concentration pathway 8.5 scenario in the 2050s (2046–2055) and the 2080s (2076–2085). Two spawning scenarios were implemented in the future, where smallmouth bass will not change the spawning season in the non-adaptive scenario and change the season in the adaptive scenario. The life-history habitat suitability (LHS) of smallmouth bass was evaluated using the geometric mean of the annual habitat suitability indices (HSIs) for each life stage (adult, juvenile, fry, and spawner). The LHS model was validated using the occurrence data of largemouth bass (Micropterus salmoides), which shares most of its habitats with smallmouth bass. The average LHS of smallmouth bass in South Korea was predicted to be 0.519 at present and expected to be 0.491 and 0.541 in the 2080s under non-adaptive and adaptive scenarios, respectively. Considering that the period for spawner fish may change in the future under climate change, the adaptive scenario seems to be more reasonable. The potential presence rate of smallmouth bass in South Korea was 100% at present, except for the Han River Basin (66%) which was expected to increase to 86% in the 2080s under the adaptive scenarios. The LHS model predicted that smallmouth bass could inhabit South Korea, and its distribution may expand under global warming, requiring urgent preventive measures