علوم محیطی (Jun 2024)
Spatial and Temporal Variation in Caspian SeaTrout Densities in the Lar National Park Streams
Abstract
Introduction: Quantitative assessment of fish abundance is the basis of scientific research andmanagement of their population. Demographic studies of stream-dwelling salmonids haveshown that variation in their abundance on a spatio-temporal scale is common, and troutpopulations are no exception. Understanding this variation is crucial for several reasons,including designing and interpreting environmental impact assessment studies and monitoringfishery management strategies. The present study aimed to estimate the spatial and temporalvariations in the density of Caspian Sea trout in some of the Lar National Park streams andinvestigate the relationship between the density of fish in these streams and the density ofbenthic invertebrates as their primary food sources.Material and Methods: Fish densities were calculated using the Le Cren depletion method toachieve reliable population estimates. After two removal steps, the total number of fish caughtwas standardized and expressed as density per 100 m2 of the river channel. To investigate thetemporal changes of fish abundance, the study results in 2009 were qualitatively compared withthe results of another study in 2017.Results and Discussion: According to the 2009 results, the highest Caspian Sea trout densitywas recorded in the Delichay (44 per 100 m2), Lar (43.2 per 100 m2), and Siah Palas sites (33.4per 100 m2), respectively, and the lowest densities were recorded in the Lar (Kharsang, 10.5per 100 m2) and Lar (Sorkhak, 11.5 per 100 m2). In 2017, the highest density of trout wasdocumented in Siah Palas (175 per 100 m2), Delichay (Vararo, 118 per 100 m2), and Elam (112per 100 m2) streams, and the lowest density was recorded in the Delichay (downstream, 48 per100 m2) and Absefid (49 per 100 m2) streams.The distribution and abundance of stream-dwelling salmons are primarily regulated by food andspace. The abundance of Caspian Sea trout on a local scale indicates variety in quality and habitataccess for Caspian Sea trout in the Lar National Park. We speculated that habitat diversity hasinfluenced the density of Caspian Sea trout in various streams in the region by affecting theabundance of aquatic invertebrates, which are the main prey source. However, the results ofregression (R2= 0.02, p value = 0.72) and correlation (Spearman, r = 0.24) analyses showed nosignificant relationship between the density of fish and benthic invertebrates in the Lar National Parkstreams. Despite the enough abundance of prey in Lar streams, the fish were low in density. Thecause of this incongruence is probably related to the salmon fishing in Lar National Park in the past.Comparing fish densities in 2009 and 2017 showed that the trout density in 2017 was higherthan the trout density in 2009.Conclusion: Considering that in 2014, the Department of Environment stopped issuing fishinglicenses in this area, one of the reasons for the increase in fish density is probably a positiveeffect of the fishing prohibition on this species. Since Caspian Sea trout abundances in the LarNational Park streams are spatio-temporally variable, it is necessary to provide reasonablemanagement strategies and continuous monitoring to prevent them from global warming andconserve them in the streams of the Lar National Park. Furthermore, due to climate change andbeing at risk of other populations of Caspian Sea trout in different habitats in Iran, thispopulation should be protected as a support population.
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