مدل‌سازی اثرات تغییرات اقلیم بر پراکنش سس ماهی بزرگ (زرده‌‌پر) (luciobarbus capito) در رودخانه‌‌های حوضه جنوبی دریای خزر

کشور ایران یکی از نواحی مهم تنوع زیستی در جهان است. اما در حال حاضر اکثر گونه‌های ماهی‌‌های اکوسیستم آب شیرین در این کشور به دلیل فعالیت‌‌های انسانی با تهدید جدی روبه‌رو هستند. علاوه بر این تهدیدات، تغییرات اقلیمی نیز تهدید مضاعفی بوده که ممکن است سبب تسریع انقراض یا کاهش جمعیت گونه‌‌ها شود. سس ماهی بزرگ (luciobarbus capito) یکی از گونه‌‌های بومی و باارزش شیلاتی حوضه جنوبی دریایی خزر است که در آخرین فهرست ارائه شده از اتحادیه بین‌المللی حفاظت از طبیعت (iucn)[1]، در طبقه آسیب‌پذیر (vu)[2] قرار دارد. بدین منظور از 9 متغیر به عنوان متغیرهای اولیه در نظر گرفته شدند، پس از انجام آزمون همبستگی اسپیرمن اگر دو متغیر همبستگی بالای 75% داشتند، یکی از آنها با توجه به نظر کارشناسی و مطابق با نیاز اکولوژیک گونه انتخاب گردید. همچنین در این مطالعه پراکنش گونه مذکور در دو رویکرد خوش‌بینانه (rcp2.6)[3] و بدبینانه (rcp8.5) سال‌‌های 2050 و 2080 با استفاده از مدل حداکثر آنتروپی (maxent) پیش‌بینی‌شده است. نتایج نشان داد که عملکرد مدل در پیش‌‌بینی پراکنش گونه بر اساس معیار ارزیابی auc[4] ، عالی (0.934) بوده است. بر اساس پیش‌‌بینی‌‌های مدل شده، مشخص کرد که این گونه احتمالاً در آینده در تمامی رویکردهای خو‌‌ش‌‌بینانه و بدبینانه‌‌ 2050 و 2080 با کاهش مطلوبیت زیستگاه روبرو خواهد بود. بنابراین، پیشنهاد می‌‌شود، مدیران و تصمیم گیرندگان حفاظت از این‌گونه اقتصادی را در اولویت خود قرار دهند و با برنامه‌ریزی‌‌های فوری و تصمیمات قابل اجرا و اقدامات موثر مانع از کاهش جمعیت آنها در آینده شوند. در ضمن، چنین مطالعه‌‌ای برای سایر گونه‌‌های حوضه‌‌های ایران می‌‌تواند به حفاظت از تنوع زیستی ارزشمند کشوردر برابر تهدیدات مختلف به‌خصوص تغییر اقلیم کمک موثری نماید.

predicting impacts of climate change on bulatmai barbel (luciobarbus capito) distribution in the rivers of the southern part of the caspian sea basin

introductiontoday, the phenomenon of climate change has become one of the biggest challenges and serious threats to the biodiversity of aquatic ecosystems (mostafavi et al., 2017). based on studies, climate change has already affected the distribution of aquatic life (lam et al., 2020; alegria et al., 2023). due to the role of human factors, this phenomenon is occurring with a greater speed and intensity, therefore species and ecosystems may not have enough time to adapt and harmonize with environmental changes (lovejoy and hannah, 2006) and finally, it is possible with changes in species communities (zurell et al., 2020), spatial and temporal changes in the level of species interactions (kelly et al., 2012; forrester, 2014), displacement of ecological niches and distribution basins (bellard et al., 2012) as well as extinction or adaptation of species (román-palacios et al., 2020). the results of studies show that during the next few decades, climate change can be one of the biggest threats to biodiversity in the world (mostfavi et al., 2014, 2015; makki et al., 2023). in addition, changes in the distribution of species, population and structure of communities will bring many threats in the future (moss et al., 2009). during the last century, the most vulnerable habitats to climate change were freshwater ecosystems (bouska et al., 2015). the decrease in river flow, the decrease in rainfall, and the increase in temperature in these ecosystems have all had negative consequences on freshwater fish (harrod, 2015).methodologythe studied area is the rivers of the southern basin of the caspian sea, which has native species with economic and fishery value. in this study, attendance method was used for modeling. environmental and climatic data used for modeling including habitat and climatic data were extracted from reliable foreign sites such as www.worldclim.org and internal (from domestic organizations such as natural resources and environment). in this connection, 9 variables include the maximum width of the river, elevation, slope, flow accumulation, temperature range, average the average temperature, the average minimum temperature, the average maximum temperature and (ave-precipitation) were considered as primary variables, which after performing the spearman correlation test if two variables have a correlation above 75%, one of them is selected according to the expert opinion and according to the ecological needs of the species (mostafavi et al., 2014; makki et al., 2023) (fig. 1).then species distribution modeling using maxent model (phillips et al., 2017) in r v3.2.3 software environment (r core team, 2020) and dismo v1.1-4 software package (hijmans et al., 2017) was done. in order to evaluate the accuracy of the model performance and modeling results, the area under the curve (auc) (table 1) of the system performance characteristic (roc) was calculated (lobo et al., 2008). according to the range of auc between 0 and 1, values less than 0.5 indicate random prediction performance and 1 values with perfect prediction. in fact, values less than 0.5 indicate inappropriate models (elith et al., 2009). also, using the jackknife test, the variable that had the greatest effect in determining the distribution of the studied species was determined. finally, the distribution map of big fish sauce in the caspian watershed was produced under climate scenarios in 2050 and 2080 (tables 1 and 2).resultsmodel performance: according to the results of the performance evaluation of the maxent model using the auc index, the model performance for the species l. capito was at an excellent level (auc = 0.922), so the results of this model show that it has excellent ability in predicting the distribution of large-bodied fish (large-bodied fish, steelhead fish, fish, yellowtail) in the southern basin of the caspian sea (fig. 2).importance of variables: based on the results, the annual precipitation variable (bio12) is more important than other variables in determining the distribution of this species (fig. 3). species distribution prediction according to table (3), the potential distribution of l. capito species is affected by rcp2.6 and rcp8.5 climate scenarios in the years 2050 and 2080, and these changes are increasing.discussion and conclusionin response to the phenomenon of climate change, species usually choose one of four scenarios: a decrease in habitat desirability, an increase in habitat desirability, both a decrease and an increase in habitat desirability, or no change in habitat (carosi et al., 2019; yousefi et al., 2020). also, the results showed that annual rainfall, average annual temperature and cumulative flow are the main factors affecting the distribution of this species, and these factors will reduce the favorable habitat of fish sauce in the scenarios of 2050 and 2080 in both optimistic and pessimistic scenarios. according to the present results, the percentage of unfavorable habitats is more than favorable and the species will be forced to migrate to new places. of course, this success in changing location or migration depends on various factors such as the suitability of the physical and biological conditions of the habitat and the continuity of the river (mostafavi et al., 2015, 2019). this is despite the fact that the natural condition of the rivers of the southern caspian basin, according to the studies of researchers in the last few decades, has been affected by factors such as climate change, population increase, excessive use of running and underground water for the expansion of agriculture. , construction of dams in the migration path of freshwater fish, overfishing of some species of fish, overtaking of sand from the riverbed (destruction of the habitat), increase in environmental pollution, lack of a plan environmental management as well as the introduction of non-native species have caused double pressure on aquatic ecosystems, and all these issues have caused a lot of habitat changes and limited the habitat and biodiversity of many fish in the rivers of the southern caspian basin. (mostafavi et al., 2015 and 2019; mousavi-sabet et al., 2023; abbasi et al., 2023). as a result, the fish will have less chance to reach the right part of the river. therefore, it is necessary to reduce all the obstacles and problems in the way of this type with local value and proper management, and also with proper protection strategies in each region to facilitate the migration and movement of freshwater fish in the rivers. (mostafavi et al., 2022). if the species does not adapt and migrate to the changes in ecosystems, the species will be doomed to extinction (bednarek and mołoniewicz, 2023; makki et al., 2023). it is important that the managers do the necessary planning to solve these problems although today the main cause of species extinction is habitat destruction, it seems that the first factor in the next few decades will be climate change (leadley, 2010). the results of most studies show that each of the fish species show a specific reaction to the environmental changes resulting from climate change, according to the initial conditions of their ecosystems, which in each species can be different (buisson et al., 2008; carosi et al., 2019). these changes in potential distribution can be different for each species due to specific ecological characteristics, their needs, as well as diversity in climatic scenarios (moëzzi et al., 2022). as can be seen, usually different species show different reactions apart from being under threat, exclusive nativeness, non-nativeness, which is probably related to their inherent and genetic characteristics. mustafavi et al., 2017). in addition, another very important point that should be noted is that uncertainty in modeling must be considered for all studies and species, which will include: - sampling with precision and standard methods (such as mostafavi et al., 2015, 2019) - using more points in modeling - use of more accurate and new variables - using different modeling methods and comparing the results the present study has shown the effect of climate change on the distribution of large fish sauce in the caspian sea. considering that the studied species is in the uv category in the iucn list and is one of the valuable species of the caspian sea basin, the policy makers and managers of the country's fisheries institute can make use of the information of such studies. identify the distribution of native, sensitive, endangered and economic species and prevent their extinction by restoring their habitat and adopt and implement a suitable strategy to preserve the reserves of these species.