Seasonal Comparison of Abundance and Catch Per Unit Effort of Sturgeon Broodstock in the Southern Caspian Sea (Case Study: Golestan Province)

Abstract

This article examines the seasonal abundance and Catch Per Unit Effort (CPUE) of sturgeon broodstock in the southern Caspian Sea, with a focus on Golestan province. Research findings from studies conducted during 2003–2022 indicate significant seasonal variation in sturgeon abundance and catch rates. Across the southern Caspian, fish abundance is highest in October and November, particularly in Mazandaran and Golestan coastal waters . Persian sturgeon (Acipenser persicus) consistently comprises the largest proportion of the catch across all seasons, constituting 62.2% of winter catches up to 70.3% of autumn catches . CPUE values for Persian sturgeon in Golestan province waters ranged from 0.21 to 0.69 during 2003–2005, with notable inter-annual fluctuations . The spring season accounts for more than eighty percent of Iran’s annual sturgeon catch and caviar production . However, a significant long-term declining trend in relative abundance has been observed across all species, with abundance forecast to decline further by 2025 . The findings provide critical baseline data for fisheries management and conservation planning in the region.

1. Introduction

Sturgeon populations in the Caspian Sea have experienced dramatic declines over recent decades, with all commercially valuable species now classified as Critically Endangered on the IUCN Red List. The southern Caspian, particularly the coastal waters of Iran’s Golestan, Mazandaran, and Guilan provinces, represents a critical habitat for sturgeon spawning and juvenile development. Understanding the seasonal patterns of abundance and catch rates is essential for effective fisheries management and conservation planning.
This article synthesizes findings from multiple research studies conducted in the southern Caspian Sea to compare seasonal abundance and CPUE of sturgeon broodstock, with a specific focus on Golestan province. The analysis draws on data from trawl surveys, commercial landing statistics, and gillnet sampling conducted between 2003 and 2022.

3. Seasonal Abundance Patterns

3-1. Overall Seasonal Variation
Across the southern Caspian Sea, sturgeon abundance shows distinct seasonal patterns. Research covering 2006–2022 found that fish abundance was highest in October and November, particularly in Mazandaran and Golestan coastal waters . This peak in autumn abundance is consistent with the timing of sturgeon feeding aggregations and pre-spawning migrations.
3-2. Catch Per Trawl by Season
A study conducted in 2001–2003 documented seasonal variation in the relative catch of sturgeon in Iranian waters :

The dramatically higher catch rate in summer (13.5 specimens per trawl) compared to other seasons is notable, though this may reflect trawl survey timing and location rather than overall population abundance.
3-3. Seasonal Species Composition
Species composition varies significantly across seasons :
Season Persian Sturgeon (% of catch) Stellate Sturgeon (% of catch)
Spring 45.2% 42%
Summer 62% 45%
Autumn 70.3% 26%
Winter 62.2% 36%
Persian sturgeon consistently comprises the largest proportion of catch across all seasons, with autumn showing the highest representation (70.3%). Stellate sturgeon shows its highest seasonal representation in summer (45%) and its lowest in autumn (26%).
3-4. Golestan Province Specific Findings
Research focused on Golestan province coastal waters during 2003–2005 documented the following CPUE values for Persian sturgeon :
Period CPUE Value
2003–2005 (overall) 0.21 to 0.69
2003–2004 Higher
2004–2005 Lower
The CPUE for Persian sturgeon was 0.69 during 2003-2004, declining to 0.58 during 2004-2005 . Other species showed much lower CPUE values: stellate sturgeon (0.28), ship sturgeon (0.21), Russian sturgeon (0.03), and beluga (0.03) .

Species Composition and Size Structure

. Species Composition in Golestan Waters
Based on catch data from Golestan province during 2003–2005, Persian sturgeon is the most abundant species, followed by :
1. Persian Sturgeon (Acipenser persicus) – Most frequent at Tazeabad, Mian Ghalea, Khajanafac, and Turkman fishery stations
2. Stellate Sturgeon (A. stellatus)
3. Ship Sturgeon (A. nudiventris)
4. Russian Sturgeon (A. gueldenstaedtii)
5. Beluga (Huso huso) – Rarest
Length Structure
The length structure of Persian sturgeon in Golestan waters during 2003–2005 ranged from 10 to 140 cm . Significant differences in mean length were found between the 2003–2004 and 2004–2005 periods (Tukey test, p<0.05), indicating changes in population age structure over time .

Implications for Fisheries Management

Seasonal Management Considerations
The spring season accounts for more than eighty percent of Iran’s annual sturgeon catch and caviar production . This concentration of fishing effort in spring has significant implications for broodstock conservation:
⦁ Spring spawners: Migrate to rivers in spring (February–June)
⦁ Autumn spawners: Migrate in autumn (August–September)
⦁ By-catch: Autumn catches often represent by-catch from beach seine operations for whitefish and perch
Determination of Optimal Catch Periods

Research has identified optimal catch periods for different species and regions :
Persian Sturgeon:
Province Spring Season Autumn Season Winter Season
Guilan & Mazandaran Late March – May 10 September 23 – December 1 March 1–21
Golestan March 21 – May 31 October 12 – December 21 February 9 – March 20
Stellate Sturgeon:
⦁ Guilan & Mazandaran: Best catches from April 21 – June 20
⦁ Golestan: Best catches from April 9 – May 31
⦁ Winter catch possible from February 20 – March 20
Conservation Implications

The research clearly documents a continuing decline in sturgeon stocks. A study conducted in 2001–2003 concluded that: “Due to decrease of natural and artificial breeding during the decade of 1990 and increased exploitation of the sturgeon stocks (legal and poaching), the decrease of sturgeon stock is continued” .
Based on the present situation, researchers have proposed banning any fishing on sturgeons, allowing only collection of limited broodstock for artificial propagation and research .

Conclusion

Seasonal comparison of sturgeon abundance and CPUE in the southern Caspian Sea reveals several key findings:
1. Peak abundance occurs in October and November, particularly in Mazandaran and Golestan coastal waters .
2. Persian sturgeon is the most abundant species across all seasons, comprising 45.2% to 70.3% of total catches .
3. CPUE values for Persian sturgeon in Golestan province ranged from 0.21 to 0.69 during 2003–2005, with significant inter-annual variation .
4. Spring season accounts for over 80% of Iran’s sturgeon catch and caviar production .
5. Long-term decline in abundance is evident across all species, with relative abundance forecast to decline further by 2025 due to environmental changes and continued fishing pressure .
The findings provide critical baseline data for managing sturgeon fisheries in the southern Caspian. The seasonal patterns of abundance and catch rates suggest that targeted management interventions—including seasonal closures and selective fishing restrictions—could help protect spawning stocks while maintaining sustainable use of the resource. However, given the severity of stock declines, researchers have recommended an outright ban on sturgeon fishing, with only limited harvest allowed for broodstock collection .

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