Identification of Factors Affecting the Reduction of Sturgeon Stocks in the Southern Caspian Sea Based on Fishermen’s Survey Using Smart PLS Structural Equation Modeling
Abstract
Sturgeon populations in the Caspian Sea have experienced a dramatic decline over recent decades, with all commercially valuable species now classified as Critically Endangered (CR) on the IUCN Red List. This article presents findings from a comprehensive study that identified and prioritized factors contributing to sturgeon stock reduction based on surveys of 270 fishermen across Golestan, Mazandaran, and Guilan provinces using Smart PLS structural equation modeling . The research revealed that illegal fishing has the most significant impact on stock decline, followed by overfishing, low release rates for stock restoration, inadequate fishing management, and non-standard fishing gear. While water pollution and contaminant inflow were perceived as having a positive effect on the declining trend, this relationship was not statistically significant . The findings provide a validated framework for fisheries managers to prioritize interventions for sturgeon conservation in the Caspian region.
Introduction
1-1. The Status of Caspian Sturgeon
Caspian sturgeon (Acipenseridae) are among the most economically valuable fish species globally, historically supplying over 90% of the world’s caviar. Five native sturgeon species inhabit the Caspian Sea: beluga (Huso huso), Russian sturgeon (Acipenser gueldenstadtii), Persian sturgeon (A. persicus), stellate sturgeon (A. stellatus), and ship sturgeon (A. nudiventris) .
Unfortunately, natural sturgeon stocks have experienced a sharp decline over recent decades, with all commercially important species now listed as Critically Endangered (CR) on the IUCN Red List . The average annual loss of spawning stock between 2000-2020 was 2% for beluga, 7% for Russian sturgeon, and 10% for stellate sturgeon . This decline represents a biodiversity crisis with significant economic implications for the Caspian littoral states, particularly Iran, which maintains a substantial sturgeon aquaculture and caviar export industry.
1-2. Rationale for the Study
Given the ecological and economic importance of sturgeon, identifying the factors that contribute to stock reduction is essential for effective conservation planning . While multiple studies have examined specific drivers of sturgeon decline individually, there has been limited research that systematically prioritizes these factors based on the on-the-ground perspectives of those most directly affected—fishermen. This study addresses that gap by applying a rigorous quantitative methodology to capture and prioritize factors affecting sturgeon stock reduction on the southern Caspian coast.
Research Methodology
2-1. Study Design and Approach
The study was applied in terms of purpose type and employed a descriptive-analytical and survey method . Data collection was conducted through structured questionnaires based on a Likert scale, administered through in-person interviews with fishermen across three northern provinces: Golestan, Mazandaran, and Guilan .
2-2. Sampling
The sample size was calculated using the Cochran formula, yielding 270 respondents . Participants were selected through available and voluntary sampling methods. This sample size ensures adequate statistical power for structural equation modeling using Smart PLS.
2-3. Analytical Framework
Questionnaire data were analyzed using structural equation modeling (SEM) with Smart PLS software . This approach was selected because PLS-SEM is particularly suitable for:
⦁ Exploratory research where theoretical frameworks are being developed
⦁ Complex models with multiple constructs and indicators
⦁ Studies with relatively small sample sizes
⦁ Research that prioritizes prediction and explanation
2-4. Validity and Reliability
While the specific Cronbach’s alpha coefficients for this particular study are not detailed in the available sources, similar research on sturgeon stock assessment using questionnaire-based methodologies has demonstrated high reliability. For instance, SWOT-based studies of sturgeon stock restoration achieved an overall Cronbach’s alpha of 0.94, with individual component scores of 0.89 for strengths, 0.83 for weaknesses, 0.92 for opportunities, and 0.88 for threats .
Identified Factors and Their Impacts
Non-Significant Factor: Water Pollution and Contaminants
Interestingly, while the influx of pollutants and water contamination had a positive effect on the downward trend of sturgeon stocks, this relationship was not statistically significant in the fishermen’s perspectives . This finding is somewhat counterintuitive given the documented environmental degradation in the Caspian Sea.
Possible interpretations:
1. Focus of attention: Fishermen may be more directly aware of fishing-related pressures than of pollution impacts, which are less visible in daily operations
2. Time lag: Pollution effects may operate over longer timeframes than fishermen’s direct experience
3. Conflation with other drivers: The effects of pollution may be attributed to other factors by respondents
It should be noted, however, that scientific literature strongly documents pollution as a significant threat to sturgeon. Studies confirm that habitat destruction and pollution from “industrial, urban, and agricultural activities” are key reasons for sturgeon decline . Similarly, the decline of Russian sturgeon is attributed in part to “pollution of habitats with industrial wastes” .
4. Broader Context and Cumulative Impacts
4-1. Multiple Stressors
The Caspian Sea sturgeon decline cannot be attributed to any single factor. Research using qualitative loop analysis has confirmed that the decline of sturgeon populations is “compatible with a net effect of the concomitant perturbations” that occurred during 1990-2010 . These multiple stressors include:
⦁ Overfishing (legal and illegal)
⦁ Habitat destruction (dam construction, spawning ground loss)
⦁ Pollution (industrial, agricultural, urban)
⦁ Climate change (water level decline, temperature changes)
⦁ Invasive species (particularly the ctenophore Mnemiopsis leidyi)
4-2. Ecosystem-Level Interactions
The interplay between concurrent drivers produces complex trade-offs. For example, while M. leidyi had a particularly strong negative impact on kilka species (reducing anchovy kilka spawning stocks by a factor of 4 and big-eyed kilka by a factor of 46), its impact on sturgeon has been primarily indirect through food web interactions .
For sturgeon specifically, the continuous decline in spawning stocks is primarily attributed to:
⦁ Deterioration in diet quality
⦁ Loss of spawning grounds
⦁ Reduction in natural reproduction
⦁ Low efficiency of artificial breeding
⦁ Illegal fishing
5. Comparison with Other Research Perspectives
The Smart PLS findings align closely with results from other methodological approaches:
5-1. SWOT Analysis Findings
A complementary study using SWOT analysis to assess sturgeon stock restoration trends in Iranian waters identified key weaknesses and threats that mirror the Smart PLS findings :
Highest-ranked weaknesses:
1. Environmental destruction and pollution entering spawning habitats (score: 12.5/15)
2. Illegal fishing driven by socio-economic problems in coastal areas (score: 12.2/15)
3. Absence of long-term sustainable exploitation strategy (score: 12.0/15)
Key threats:
⦁ Overfishing and illegal fishing
⦁ Habitat destruction from dams and pollution
⦁ Lack of effective management and sustainable exploitation
5-2. IUCN and International Perspectives
The International Union for Conservation of Nature (IUCN) has identified similar priority issues for sturgeon conservation in the Caspian Sea :
⦁ Bycatch and poaching as the most pressing survival threats
⦁ The need for harmonized conservation measures among Caspian range states
⦁ The importance of combining ex situ (hatchery) and in situ conservation measures
⦁ The challenge of restoring self-sustaining populations
Conclusion
The application of Smart PLS structural equation modeling to survey data from 270 fishermen along Iran’s southern Caspian coast has identified a clear hierarchy of factors contributing to sturgeon stock decline. Illegal fishing emerges as the most significant driver, followed by overfishing, low release rates for stock restoration, inadequate fishing management, and non-standard fishing gear .
While water pollution was not statistically significant in this particular analysis, it remains a documented threat in the broader scientific literature and should not be overlooked . The discrepancy between fishermen’s perceptions and scientific evidence highlights the value of integrating multiple research methodologies for comprehensive conservation planning.
The findings provide a validated, empirically grounded framework for prioritizing conservation interventions. By focusing resources on combating illegal fishing, improving fisheries management, and strengthening stock restoration programs, Iran can make meaningful progress toward halting and reversing the decline of these critically important species. The urgency of this task is underscored by the IUCN’s designation of all commercial Caspian sturgeon as Critically Endangered and the ongoing decline of spawning stocks .
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