Spatial and Temporal Variation in Caspian SeaTrout Densities in the Lar National Park Streams

Document Type : Original Article

Authors

Department of Biodiversity, Environmental Sciences Research Institute, Shahid Beheshti University, Tehran, Iran

Abstract

Introduction: Quantitative assessment of fish abundance is the basis of scientific research and
management of their population. Demographic studies of stream-dwelling salmonids have
shown that variation in their abundance on a spatio-temporal scale is common, and trout
populations are no exception. Understanding this variation is crucial for several reasons,
including designing and interpreting environmental impact assessment studies and monitoring
fishery management strategies. The present study aimed to estimate the spatial and temporal
variations in the density of Caspian Sea trout in some of the Lar National Park streams and
investigate the relationship between the density of fish in these streams and the density of
benthic invertebrates as their primary food sources.
Material and Methods: Fish densities were calculated using the Le Cren depletion method to
achieve reliable population estimates. After two removal steps, the total number of fish caught
was standardized and expressed as density per 100 m2 of the river channel. To investigate the
temporal changes of fish abundance, the study results in 2009 were qualitatively compared with
the results of another study in 2017.
Results and Discussion: According to the 2009 results, the highest Caspian Sea trout density
was recorded in the Delichay (44 per 100 m2), Lar (43.2 per 100 m2), and Siah Palas sites (33.4
per 100 m2), respectively, and the lowest densities were recorded in the Lar (Kharsang, 10.5
per 100 m2) and Lar (Sorkhak, 11.5 per 100 m2). In 2017, the highest density of trout was
documented in Siah Palas (175 per 100 m2), Delichay (Vararo, 118 per 100 m2), and Elam (112
per 100 m2) streams, and the lowest density was recorded in the Delichay (downstream, 48 per
100 m2) and Absefid (49 per 100 m2) streams.
The distribution and abundance of stream-dwelling salmons are primarily regulated by food and
space. The abundance of Caspian Sea trout on a local scale indicates variety in quality and habitat
access for Caspian Sea trout in the Lar National Park. We speculated that habitat diversity has
influenced the density of Caspian Sea trout in various streams in the region by affecting the
abundance of aquatic invertebrates, which are the main prey source. However, the results of
regression (R2= 0.02, p value = 0.72) and correlation (Spearman, r = 0.24) analyses showed no
significant relationship between the density of fish and benthic invertebrates in the Lar National Park
streams. Despite the enough abundance of prey in Lar streams, the fish were low in density. The
cause 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 higher
than the trout density in 2009.
Conclusion: Considering that in 2014, the Department of Environment stopped issuing fishing
licenses in this area, one of the reasons for the increase in fish density is probably a positive
effect of the fishing prohibition on this species. Since Caspian Sea trout abundances in the Lar
National Park streams are spatio-temporally variable, it is necessary to provide reasonable
management strategies and continuous monitoring to prevent them from global warming and
conserve them in the streams of the Lar National Park. Furthermore, due to climate change and
being at risk of other populations of Caspian Sea trout in different habitats in Iran, this
population should be protected as a support population.

Keywords


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