تحلیل زمانی و مکانی تراکم ماهی قزل آلای خال قرمز (Salmo trutta )در رودخانه های پارک ملی لار

نوع مقاله : مقاله پژوهشی

نویسندگان

گروه تنوع زیستی، پژوهشکده علوم محیطی، دانشگاه شهید بهشتی، تهران، ایران

چکیده

سابقه و هدف: ارزیابی کمی فراوانی ماهیان اساس تحقیقات علمی و مدیریت جمعیت­ های آن­هاست. مطالعات جمعیتی درباره آزادماهیان رودخانه ­ای نشان داده است که به طور طبیعی تنوع در فراوانی عددی این ماهیان در مقیاس های فضایی - زمانی یک قاعده است و جمعیت ­های قزل­ آلای خال قرمز از این قاعده مستثنی نیستند. درک این تنوع و تغییرات به دلایل متعدد از جمله برای طراحی و تفسیر مطالعات ارزیابی اثرات محیط زیستی و برای نظارت بر استراتژی­ های مدیریت ماهیگیری بسیار حائز اهمیت است. هدف از مطالعه حاضر برآورد و بررسی تغییرات مکانی و زمانی تراکم قزل­ آلای خال قرمز در رودخانه ­های پارک ملی لار و همچنین بررسی رابطه بین تراکم ماهیان قزل­ آلا در این رودخانه­ ها با تراکم بی­ مهرگان کف­زی بعنوان غذای اصلی آن­ها بود.
مواد و روش­ ها: تراکم ماهیان با استفاده از روش حذفی لو کرن محاسبه شد. تعداد کل ماهیان صید شده بعد از دو مرحله حذف، با منطقه مورد نظر استاندارد و به صورت تراکم در هر 100 متر مربع از سطح رودخانه بیان شد. برای بررسی تغییرات زمانی فراوانی ماهیان، نتایج مطالعه تراکم سال 1388 با نتایج مطالعه تراکم این گونه در سال 1396به صورت کیفی مقایسه گردید.
نتایج و بحث: با توجه به محاسبات در سال 1388 بیشترین فراوانی به ترتیب مربوط به تراکم قزل آلا در ایستگاه دلیچای (آرو)، لار ( گزل دره) و سیاه­پلاس ( به ترتیب 44، 2/43 و 4/33 در 100 متر مربع) و کمترین فراوانی مربوط به لار ( خرسنگ) و لار ( سرخک) ( به ترتیب 5/10 و 5/11 در 100 متر مربع ) بود. در سال 1396 بیشترین تراکم به ترتیب در رودخانه­ های سیاه ­پلاس، دلیچای (ورآرو) و الرم ( به ترتیب 175، 118 و 112 در 100 متر مربع ) و کمترین تراکم در رودخانه ­های دلیچای ( پایین دست) و آب­ سفید ( به ترتیب 48 و 49 در 100 متر مربع ) مشاهده شده است.
توزیع و فراوانی آزادماهیان در درجه اول توسط غذا و فضا تنظیم می­ شود. تنوع مشاهده شده در فراوانی عددی ماهیان قزل­ آلای خال قرمز در مقیاس منطقه ­ای نشان­ دهنده تنوع در کیفیت و دسترسی به زیستگاه این گونه در پارک ملی لار است. پیش ­بینی می­ شد که تنوع زیستگاهی همچنین با تاثیر بر فراوانی بی­ مهرگان آبزی که بعنوان منبع اصلی طعمه برای آزادماهیان رودخانه ­ای محسوب می ­شوند، تراکم ماهیان قزل ­آلای خال قرمز را در رودخانه ­های مختلف این منطقه تحت تاثیر قرار ­داده باشد. برخلاف پیش­ بینی­ ها در سال 1388 نتایج آنالیز رگرسیون (R2 = 0.02, p value = 0.72) و همبستگی اسپیرمن (r = 0.24) رابطه معنی داری را بین تراکم ماهیان و بی­ مهرگان کف­زی در رودخانه­ های پارک ملی لار نشان نداد. یکی از دلایل این عدم همبستگی احتمالا مرتبط با صید ماهیان در پارک ملی لار در گذشته می ­باشد که با وجود وفور طعمه در برخی رودخانه­ ها ماهیان از تراکم کمی برخوردار بوده ­اند. نتایج مقایسه تراکم ماهیان در سال­ های 1388 و 1396 نشان داد که تراکم قزل ­آلا در رودخانه ­های لار در سال 1396در وضعیت مناسب­ تری نسبت به سال 1388 می ­باشند.
نتیجه ­گیری: با توجه به اینکه در سال 1393 سازمان حفاظت محیط زیست صدور مجوزهای صید در این منطقه را متوقف نموده است یکی از علل افزایش تراکم ماهیان در سال 1396 احتمالا اثر مثبت ممنوعیت صید است. نظر به اینکه فراوانی ماهیان قزل ­آلا در رودخانه ­های پارک ملی لار به لحاظ فضایی – زمانی متغیر می ­باشد، نظارت پیوسته و ارائه برنامه ­های مدیریتی مناسب با افزایش گرمایش جهانی و آسیب ­پذیری این گونه ارزشمند به تغییرات دمایی برای حفظ این ماهیان در رودخانه ­های پارک ملی لار ضروری است. ضمن آنکه با توجه به تغییر اقلیم و در خطر انقراض بودن سایر جمعیت ­های قزل ­آلای خال قرمز در دیگر زیستگاه ­هایش باید از این جمعیت بعنوان یک جمعیت پشتیبان حفاظت نمود.

کلیدواژه‌ها

عنوان مقاله [English]

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

نویسندگان [English]

  • Fahimeh Rashidabadi
  • Asghar Abdoli
Department of Biodiversity, Environmental Sciences Research Institute, Shahid Beheshti University, Tehran, Iran
چکیده [English]

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.

کلیدواژه‌ها [English]

  • Brown trout
  • Population size
  • Le Cren method
  • Conservation

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فصلنامه علوم محیطی
دوره 22، شماره 2
1403
صفحه 183-196

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