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Year first Published: 2019
Language: English

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Dynamics of Octopus Catch per Unit Effort in Zanzibar: Implications for Octopus Fisheries Management

 Ali M. Ussi*
Department of Natural Sciences
State University of Zanzibar
P.O.Box 146, Zanzibar, Tanzania.

Received Date: March 07, 2025; Accepted Date: March 18, 2025; Published Date: April 08, 2025.
^*Corresponding author: Ali M Ussi, Department of Natural Sciences, State University of Zanzibar, P.O.Box 146, Zanzibar, Tanzania; Email: amau04@gmail.com

Citation: Ussi AM [2025] Dynamics of Octopus Catch per Unit Effort in Zanzibar: Implications for Octopus Fisheries Management. Jr Aqua Mar Bio Eco: JAMBE-151.

DOI: 10.37722/JAMBE.2025103

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Abstract

      Octopus fisheries play a vital role in Zanzibar's economy and food security, supporting livelihoods through artisanal fishing activities. The increasing demand for octopus and environmental and anthropogenic pressures necessitates an in-depth understanding of catch dynamics to inform sustainable management. This study investigated the dynamics of Catch Per Unit Effort (CPUE) in Zanzibar's octopus fishery, assessing the implications for sustainable management. Data were collected from two landing sites, Unguja Ukuu and Uroa, over 12 months in 2020. A total of 4,379 octopuses (3,588.63 kg) were recorded at Unguja Ukuu, and 3,759 octopuses (2,719.03 kg) at Uroa, revealing spatial differences in catch rates and octopus sizes. The average octopus weight at Unguja Ukuu (0.82 kg) was significantly higher than at Uroa (0.72 kg) (p = 0.023), suggesting habitat quality and fishing pressure variations. CPUE analysis showed variability across fishing grounds, with daily catches ranging from 0.03 kg to 8.40 kg per fisher at Unguja Ukuu (average 1.28 kg/fisher/day) and 0.06 kg to 7.60 kg at Uroa (average 1.26 kg/fisher/day). Monthly CPUE variations were significant (p < 0.005), peaking in May due to seasonal closures during Ramadhan. Fishing method and gear type influenced CPUE, with on-foot fishers having the highest efficiency (2.29 kg/fisher/day at Unguja Ukuu and 1.94 kg/fisher/day at Uroa, p << 0.0001). The results emphasise the need for site-specific management strategies, such as rotational closures, size limits, and gear regulations, to balance ecological sustainability and economic benefits. Adaptive management approaches are recommended to ensure the long-term viability of the fishery.

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Keywords: Dynamics, Octopus, Catch per unit effort, Zanzibar.

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Introduction

     The coastal waters of Zanzibar support vibrant ecosystems teeming with diverse marine life. Among these, the octopus plays a crucial ecological role and is a vital resource for the local fishing industry (A Staehr, 2018). Octopus fisheries contribute significantly to the local economy and food security (Thyresson et al., 2013). Octopus fishing is predominantly artisanal, relying on traditional methods passed down through generations (Guard, 2014). This inheritance makes it an integral part of the local culture and places it at the intersection of sustainability and traditional practices.

      The dynamics of octopus fisheries in Zanzibar are critical for understanding the sustainable management of marine resources (Jiddawi & Öhman, 2002). Different studies focused on various aspects of octopus fisheries, such as the CPUE and the Maximum Sustainable Yield (MSY) of artisanal fishing in Tanzania, found notable differences in CPUE across different sites, with significantly lower CPUE in areas like Tanga and Mtwara compared to Mafia, suggesting potential overfishing in the former sites (Guard & Mgaya, 2002). Likewise, the maximum sustainable yield of artisanal fishery in Zanzibar revealed that the catch was only about 40% of the estimated MSY, with an effort of about twice the estimated optimum (Mkenda & Folmer, 2001). The findings of these studies highlight the existing complexities and challenges in managing octopus fisheries in Zanzibar and the need for strategies that balance ecological sustainability with the economic needs of local communities.

      Recently, concerns have been raised about the sustainability of octopus populations in the face of increasing fishing pressure and environmental changes (Action, 2024; Silas et al., 2023). S. Catch per unit effort (CPUE), defined as the amount of catch obtained per unit of fishing effort, is a key metric helpful tool for fisheries management (Maunder & Punt, 2004; Pauly, 1983)  for assessing health, sustainability, and resource abundance. A decline in CPUE could indicate overfishing, habitat degradation, or shifts in ecological dynamics, triggering a need for effective management strategies. Understanding the dynamics of octopus CPUE is thus becoming vital for sustaining the octopus fisheries and the communities they support.

      In Zanzibar, fishers access fishing grounds at designated sites through two primary methods: using vessels, which can be fibreglass boats, wooden boats and dhow, or traversing on foot, described as "paddling." The predominant fishing gears employed include spearguns (locally termed as mshare or bunduki), metal rods (locally referred to as umangu) and wooden sticks (also called uchokoo) (Jiddawi & Öhman, 2002). This study aimed to comprehensively analyse octopus CPUE in Zanzibar, where octopus fishing holds ecological and economic significance, using catch data from octopus landings at Unguja Ukuu and Uroa. The study highlights key issues in octopus resource management, sustainability, and the complex interactions between human activities and ecological systems. Ultimately, the findings emphasise the importance of CPUE as a critical tool for managing octopus fisheries and ensuring their long-term viability.

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Methodology
Study area     

      This study was conducted on Unguja Island, located about 35 kilometres off the coast of Tanzania mainland (Fig. 1). octopus catch data were collected from two landing sites: Unguja Ukuu, situated on the southwest of the island, and Uroa, located on the southeast. Both sites are home to popular fish markets, where buyers from various parts of the island gather for fish auctions. Among the common fisheries products landed are octopuses, which are harvested from nearby fishing grounds and typically accessed by paddling or using vessels such as fibre boats, wooden boats, dhows and canoes. The time required to reach these fishing grounds ranges from 0.5 to 1.5 hours.

Figure 1: Map of Unguja Island showing the study sites: Unguja Ukuu and Uroa. 

Data collection    

      Octopus catch data were collected for twelve months at Unguja Ukuu (from January 2020 to December 2020) and eleven months at Uroa (from February 2020 to December 2020), using prepared data sheets for their respective sites. (Fig. 1). Three trained data collectors were employed in catch data gathering for each site. A mixed approach was used to obtain reliable and representative data that involved registering special fishers and randomly selecting landings. The registered approach was meant to maintain consistency in data quality, as the same fishers are likely to follow standardised reporting and measurement methods. It also allowed for longitudinal data collection from the same participants, which could help analyse trends over time. Randomly selecting fishers during landing intended to acquire greater representativeness and help accurately reflect the variations in CPUE across the respective sites. It was also designed to reduce the likelihood of voluntary reporting bias, as fishers did not know beforehand that they would be selected for data collection. At each site, at least twenty fishers were registered to report their daily catch consistently. Similarly, at least twenty landings were randomly selected for catch measurements per day. Each site was sampled for ten days a month during a spring tide (full moon (five days) and new moon (five days), considering that the fishing habitats become exposed during these days of the respective months. Catch information gathered included the number of octopuses and weights landed and was recorded with seven categorical variables describing the respective catch. The key categorical variables were (i) landing site, (ii)the date of sampling, fishing ground, (iii) type of fishing vessel, (iv) number of fishers in a fishing vessel, (v) travel time to fishing, (vi) fishing time, (vii) fishing gear type.  

Data processing

      Catch data were structured into a sheet with all-categorical variables describing the respective catch. The mean weight of the octopus of each catch was computed from the total catch weight divided by the number of octopuses. The CPUE (kg/fisher/day) was calculated from the total catch as the total weight of the catch (in kilogram) divided by the fishing effort (number of fishers * actual time used for fishing on that day (hours)) (Guard & Mgaya, 2002). The sum of the mean weight (kg) was computed for each fishing ground from the mean weight of octopuses caught, which was then summarised into a fishing site and monthly average (Maunder & Punt, 2004).

Data analysis

      CPUE assessment data were presented as average weight in kilograms per fisher per day. All statistical analyses were performed with Statistica 7 for Windows (Esaki et al., 2012). Levene's test was used to test the homogeneity of variance of mean weight catches among Uroa and Unguja Ukuu fishing grounds. Following the data's non-normality and variance heterogeneity, mean weight data for Unguja Ukuu were log-transformed to meet the parametric test requirements. One-way analysis of variance (ANOVA) and the Kruskal Willis H-test were used to test for the difference in mean weight among fishing grounds for Unguja Ukuu and Uroa, respectively. Likewise, the Kruskal-Wallis H-test was used to test the significance of variations among months, fishing grounds, type of fishing vessels and fishing gear. The Mann-Whitney U test compared the average catch between sites. 

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Results

Catchweight distribution

      A total of 4,379 individual octopuses weighing 3,588.63 kg were measured from a total of 1,057 catches, and 3,759 individual octopuses weighing 2,719.03 kg were measured from 984 catches landed at Unguja Ukuu and Uroa, respectively, representing eighteen fishing grounds for each site. The average weight of a single octopus landed at Unguja Ukuu was 0.82 ± 0.031 kg, and 0.72 ± 0.021 kg for the octopus landed at Uroa. The average weight of a single octopus landed at Unguja Ukuu was significantly greater than that of Uroa (p = 0.023).  

      Catch assessments across fishing grounds within sites revealed substantial variability in octopus capture rates and biomass (Table 1). In Unguja Ukuu, a significant variation was documented among 18 fishing grounds, with Pungume exhibiting the highest harvest, capturing 1,327 octopuses totalling 1,183.685 kg, with an average mass per catch of 1.095 kg, albeit with considerable size variability (SE = 0.078 kg). In contrast, Kijini and Shungi reported notably lower yields, with mean weights per octopus of 0.900 kg and 0.393 kg, respectively, and less variability in catch sizes. Other sites like Kwale, Nyemembe and Vijambani demonstrated more consistent catch sizes with substantial activity levels (Table 1a). In Uroa, Michamvi emerged as the most productive site, yielding 1,346.55 kg from 1,698 catches with moderate octopus sizes (mean catch weight = 0.955 kg). Other sites like Dikoni and Bungwe displayed significantly lower total weights. At the same time, Pongwe and Bimbi ndogo maintained a notable activity level with 564.88 kg from 969 catches and 457.06 kg from 562 catches, respectively (Table 1b).

Table 1b: Octopus catch summary in kilograms (kg) from fishing grounds in Uroa. SE represent the Standard Error. 

Catch per unit effort (CPUE) distribution

      The daily catch rates revealed marked variability within sites. Unguja Ukuu fishing grounds exhibited daily catches ranging from 0.03 kg to 8.40 kg per fisher, averaging 1.28 kg per fisher per day. Uroa recorded catches from 0.06 kg to 7.60 kg per fisher, averaging 1.26 kg per fisher per day. Subsequent mapping and analysis of CPUE across fishing grounds within sites highlighted further differences; in Unguja Ukuu, CPUE varied from 0.3 kg to 3.0 kg per fisher per day across the Komonda and Kotemoto grounds, respectively (Fig. 2). Similarly, Uroa's CPUE ranged from 0.63 kg to 2.83 kg per fisher per day from Miamba miwili to Ndudu (Fig.3). The variability among fishing grounds within sites was significant (p << 0.0001), with Unguja Ukuu recording higher CPUEs over 2 kg per fisher per day at Vijambani, Tindije, Ushanza, Kijini, and Kotemoto, and lower CPUEs below 1kg at Komonda, Majanini, and several others. Uroa also showed significant disparities with higher catches at Fungufungu and Ndudu and lower yields at sites like Miamba miwili and Dikoni (Fig. 3).

Figure 2: Mean CPUE (kg/fisher/day) for octopus harvested in Unguja Ukuu fishing grounds. Error bars denote the standard error (SE) of the mean. The numbers above the error bars are the respective sample sizes.

Figure 3: Mean CPUE (kg/fisher/day) for octopus harvested in Uroa fishing grounds. Error bars denote the standard error (SE) of the mean. The numbers above the error bars are the respective sample sizes.

      Distinct monthly fluctuations, with substantial variations in catch rates documented across different months (Fig. 4), with both sites exhibiting significantly higher catches in May (p < 0.005). Specifically, CPUE ranged from a low of 0.53 kg per fisher per day in September to a high of 2.19 kg in May at Unguja Ukuu and from 0.87 kg in September to 1.91 kg in May at Uroa. The average monthly CPUE was relatively consistent between the sites, measuring 1.01 kg per fisher per day at Unguja Ukuu and 1.04 kg at Uroa, indicating no significant spatial variation (p = 0.744).

Figure 4: CPUE (kg/fisher/day) monthly variation for octopus harvested in the Uroa fishing grounds. Error bars represent the standard error (SE) of the mean. Numbers above the error bars indicate the respective sample sizes (N).

The analysis of fishing vessel efficiency on CPUE across sites revealed significant differences among four primary vessel types (p << 0.0001, Fig. 5a). On-foot fishers recorded the highest CPUE in both locations, averaging 2.294 kg/fisher/day in Unguja Ukuu and 1.944 kg/fisher/day in Uroa, with higher catch variability in Unguja Ukuu (SE = 0.093) compared to Uroa (SE = 0.065). Fibre boats, the most commonly used vessels (N = 563 in Unguja Ukuu, N = 566 in Uroa), exhibited moderate and consistent CPUEs of 0.945 kg/fisher/day and 0.891 kg/fisher/day, respectively. Dhows displayed lower efficiency, with CPUEs of 0.791 kg/fisher/day in Unguja Ukuu and 1.054 kg/fisher/day in Uroa. Wooden boats had the lowest performance, yielding 0.517 kg/fisher/day in Unguja Ukuu and 0.573 kg/fisher/day in Uroa.

Figure 5a: Mean CPUE (kg/fisher/day) variations among means of access to fishing sites for octopus within sites. Error bars represent the standard error (SE) of the mean. Numbers above the error bars indicate the respective sample sizes (N). 

      In both Unguja Ukuu and Uroa, the Kruskal-Wallis test revealed significant differences in CPUE among the three fishing gears (p < 0.001; Fig. 5b). Spear was the most frequently used gear in both sites, with an average CPUE of 1.3827 kg/fisher/day in Unguja Ukuu (N=826) and 1.3423 kg/fisher/day in Uroa (N=765), indicating consistent efficiency. Wooden sticks, though used less frequently (N=36 in Unguja Ukuu, N=38 in Uroa), recorded the highest CPUE in both sites (2.7241 kg/fisher/day and 2.1803 kg/fisher/day, respectively), suggesting selective use in high-yield areas. Metal road consistently exhibited the lowest CPUE (0.5889 kg/fisher/day in Unguja Ukuu, 0.7438 kg/fisher/day in Uroa), highlighting its lower efficiency.

Figure 5b: Mean CPUE (kg/fisher/day) variations across different means of access to octopus fishing grounds within study sites. Error bars represent the standard error (SE) of the mean, and numbers above the error bars indicate the respective sample sizes (N).

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Discussion

      The observed variability in catch distributions and CPUE across different fishing sites, months, fishing methods, and gear types highlights the complex interplay of ecological and anthropogenic factors shaping octopus fishery performance. Possible drivers of this variability include habitat quality, fishing intensity, and local environmental conditions, all of which influence catch rates and octopus population structure (Boyle & Rodhouse, 2007). Fishing grounds such as Pongwe (Uroa) and Vijambani (Unguja Ukuu), which recorded higher CPUEs, are likely characterised by more suitable habitats, such as rocky reefs or coral-rich substrates, which support greater octopus densities by providing essential feeding and sheltering conditions (Rosa et al., 2019). In contrast, sites like Komonda and Majanini, where CPUEs were lower, may be affected by suboptimal habitats or heightened fishing pressure, leading to reduced stocks (Guard & Mgaya, 2002). Additionally, the spatial differences in octopus size distribution, with larger individuals found in Unguja Ukuu (mean weight: 0.82 kg) compared to Uroa (mean weight: 0.72 kg), further underscore the influence of environmental variability and exploitation intensity on fishery dynamics (Boyle & Rodhouse, 2007). The predominance of larger octopuses in Unguja Ukuu suggests more favourable habitat conditions and potentially lower fishing pressure. In contrast, the comparatively smaller sizes in Uroa may indicate higher fishing pressure, limiting octopus growth (Forsythe & Hanlon, 1997a; Rosa et al., 2019). This interplay between habitat quality, fishing effort, and exploitation rates underscores the necessity for site-specific fisheries management strategies, including minimum size limits and spatial management measures, to ensure the sustainable harvesting and long-term viability of octopus stocks (FAO, 2020).     

      Among the eighteen fishing grounds surveyed at Unguja Ukuu, four grounds, Pungume, Nyemembe, Kwale, and Vijambani, accounted for a significant portion of octopus catches, collectively contributing over 85% of the total catch weight and more than 80% of the total number of octopuses captured (Table 1a). Similarly, at Uroa, three out of the eighteen fishing grounds, Bimbi Ndogo, Michamvi, and Pongwe, demonstrated a marked dominance in octopus yields, with these sites collectively representing 87% of the total weight and 86% of the total number of octopuses captured (Table 1b). Moreover, an analysis of total catch weights relative to mean individual weights revealed that Pungume (Unguja Ukuu) and Bimbi Ndogo (Uroa) had the highest mean individual weights, exceeding 1 kg per octopus. These disparities in catch rates and biomass across different fishing grounds suggest that certain areas exhibit consistently high yields, potentially placing them at risk of overexploitation. This finding further emphasises the productivity of these specific fishing grounds, highlighting the need for targeted management strategies to safeguard these particularly productive sites from overexploitation. Conversely, lower-yielding fishing grounds may reflect degraded habitat conditions, possibly due to prior overfishing or environmental stressors. The concentration of catches in a limited number of high-yield areas indicates that such sites could benefit from rotational fishing practices or temporary closures to mitigate the risk of stock depletion using low-yield grounds as buffers (Silas et al., 2022). Implementing these management strategies would allow for periodic recovery phases to low-yield grounds while promoting the long-term sustainability of octopus populations in high-yield grounds.

      Tanzania established the size limit for octopus harvesting at 0.5 kg, which is higher compared to Kenya and Madagascar (0.35 kg) and lower than that of Comoro (1 kg) (Mtonga et al., 2022). In a study of 18 fishing grounds at Unguja Ukuu, 78% reported average weights exceeded the 500 g threshold, with only Kotemoto, Majanini, Vijijini, and Shungi recording mean catch sizes below this limit (Table 1a). Conversely, Uroa, Dikoni and Likoni were the only grounds where the average octopus weight fell below the size limit, indicating that over 89% of the sites surveyed recorded weights above the regulatory threshold (Table 1b). Despite these figures, the mean weights at Uroa and Unguja Ukuu were 0.72 kg and 0.82 kg, respectively, which are still below the estimated first maturity size for female octopus in Tanzania, ranging between 1.5 kg and 2.6 kg, compared to a significantly lower range for males (500-640 g) (Emery et al., 2016; Guard & Mgaya, 2002). Harvesting octopuses that exceed legal size limits yet remain below maturity sizes presents significant ecological and management challenges. From an ecological standpoint, this practice compromises reproductive potential, potentially reducing population sizes as immature individuals do not contribute to reproduction(Sreeja et al., 2015). Furthermore, it may impact genetic diversity, removing larger, potentially more genetically fit individuals before they reproduce, which could lead to populations that mature at smaller sizes and possess suboptimal survival traits (Pliego-Cárdenas et al., 2016). This alteration in genetic composition can shift population dynamics, affecting the age and size structure of the population and ultimately destabilising the ecosystem (Quetglas et al., 2016).

      When comparing CPUE values exceeding an average of approximately 1.3 kg per day (Figs. 2 and 3) with the corresponding fishing pressure indicated by sample size, it becomes evident that sites such as Pongwe (Uroa) and Vijambani (Unguja Ukuu) which recorded higher CPUEs are likely characterised by more suitable octopus habitats. These sites are associated with critical environmental features, such as rocky reefs or coral-rich substrates, which are essential for octopus density, feeding, and shelter (Forsythe & Hanlon, 1997b). The name "Vijambani" in Unguja Ukuu refers to the rocky substrate found in this area. At the same time, Pongwe, located along the fringing reef, further supports the suitability of these fishing grounds for octopus populations. In contrast, Komonda and Majanini, which exhibited lower CPUEs, may be influenced by suboptimal habitats or increased anthropogenic pressures, such as overfishing and habitat degradation.

      Regarding overall CPUE performance, only 38.8% of the observed fishing grounds in Unguja Ukuu surpassed the average CPUE threshold of 1.28 kg per fisher per day. In comparison, approximately 50% of the fishing grounds in Uroa recorded average CPUEs above the site-specific threshold of 1.26 kg per fisher per day. These values highlight a significant variability in fishing success across the sites, with most fishing grounds exhibiting CPUEs below these thresholds, indicating varying productivity levels.

      Comparable CPUE values have been reported by (Hamad et al., 2025) for the Nungwi and Kizimkazi sites in Zanzibar, aligning with the findings of this study. These results suggest that octopus fisheries in Zanzibar are experiencing significant harvesting pressures, underscoring the urgent need for effective fisheries management interventions. Given the substantial variation in CPUE and the potential ecological risks posed by overfishing and habitat degradation, management strategies should focus on improving habitat protection, regulating fishing intensity, and incorporating adaptive measures to ensure the sustainability of octopus populations.

      The significant differences in CPUE between different vessel types (foot fishers vs. fibre boats, dhows, and wooden boats) suggest that the method of fishing directly impacts efficiency. Foot fishers, who achieved the highest CPUE, are likely able to target specific areas, more specifically in shallow intertidal and sub-tidal areas, with greater precision and less disturbance, allowing them to capture octopuses that might be missed by skin divers who use more mechanised fishing methods (McCabe et al., 2024; Raberinary & Benbow, 2012). Higher catches for on-foot fishers relative to other means to access fishing sites have been widely reported, for instance, by (Hamad et al., 2025; Kombo et al., 2024). The finding implies that the choice of fishing method plays a crucial role in catch efficiency and resource sustainability. This suggests that management strategies should consider the advantages of low-impact, selective fishing techniques like foot fishing to promote sustainable harvesting. Additionally, the higher CPUE observed among foot fishers highlights the need to assess the potential ecological impacts of different fishing practices, ensuring that resource use remains balanced and does not lead to localised depletion. These dynamics can inform policy decisions, such as regulating fishing gear or access to particular habitats, to optimise conservation and economic outcomes.

      The observed high variability in CPUE across different months, with notable increases in May for both study sites, correlates strongly with the imposition of the automatic temporal closure of octopus fishing during the holy month of Ramadan, which, in 2021, occurred in April. This temporal alignment suggests a significant seasonal influence on octopus yields, particularly marked by the spike in catches following Ramadan. The Ramadhan period traditionally sees a reduction in fishing activities as divers abstain from underwater fishing, a practice believed to invalidate their fast. This cessation likely serves as a crucial recovery phase for octopus populations, which is substantiated by the recorded increase in average size by as much as 200g in only 15 days and up to 12 kg in weight following the closure period (Guard & Mgaya, 2002; Raberinary & Benbow, 2012), thus highlighting the ecological advantages of temporal fishing closures synchronised with cultural practices. Other studies reported findings that coincide with the positive impact of temporary closure during Ramadhan; for instance,  (Hamad et al., 2025) reported higher CPUEs in July and October for Kizimkazi and Nungwi in Zanzibar, based on data collected in 2019. Notably, the timing of Ramadan in 2019 was June, suggesting a similar influence on octopus populations due to reduced fishing activity during the holy month. This consistency in findings between the two study periods reinforces the conclusion that integrating biological cycles and cultural practices into fisheries management can significantly enhance the sustainability of marine resources.

      The octopus fisheries in Zanzibar are significantly affected by the prevailing socioeconomic situation. For instance, the role of gender in the octopus fishery has evolved from the 1990s to the present. Previously, women and children dominated the fishery, gleaning octopuses along exposed shores and reefs during low tide using sharp sticks (Mtonga et al., 2022). However, recent trends indicate that, of the 7,313 octopus fishers, only 30% are female (Rocliffe and Harris, 2016). The increasing dominance of males in octopus fisheries is attributed to factors such as rising market demand driven by the development of the tourism industry, which accounts for over 90% of the octopus market (Pandu, 2014; Rocliffe and Harris, 2016). Male fishers typically collect octopuses through skin and scuba diving, allowing them to access deeper waters and achieve higher catches than female fishers. However, this shift raises concerns about the sustainability of octopus stocks, as increased harvesting pressure could contribute to resource depletion. Understanding these changes is crucial for developing gender-inclusive and sustainable fishery management strategies that balance economic benefits with conservation efforts.

       Climate variability can significantly impact Catch Per Unit Effort (CPUE) trends in Zanzibar's octopus fisheries through various environmental and ecological mechanisms. Octopuses are highly sensitive to sea surface temperature fluctuations. Warmer waters can affect their physiology, such as growth rates, reproductive success and metabolism, and may drive the change in migration patterns (Xiang et al., 2024). If climate variability becomes less favourable for spawning, future stock recruitment may decline, influencing CPUE trends. Likewise, climate-related stressors such as coral bleaching and ocean acidification can degrade essential octopus habitats. Loss of shelter and foraging areas may result in population declines, impacting CPUE trends. Understanding the effects of climate variability on CPUE trends is crucial for adaptive fisheries management in Zanzibar. Implementing climate-resilient strategies, such as seasonal closures, habitat restoration, and diversified fishing practices, can help mitigate negative impacts and ensure the sustainability of octopus fisheries in the island.

     Octopus fishery in Zanzibar has not received much attention in establishing and enforcing regulatory policies, a prominent challenge across the country. Currently, a licensing system exists for fishers (Rocliffe and Harris, 2016), along with a voluntary minimum size limit of 500g in some areas and voluntary closures during Ramadan and local closed seasons in Chwaka Bay (Indian Ocean Commission, 2014). These regulatory measures are not operative as octopuses have been witnessed to be caught to as low as 100g (Ussi et al., 2025). The lack of specific octopus fishery regulatory frameworks highlights the gaps in regulatory frameworks governing Zanzibar's octopus fishery, emphasising the reliance on voluntary measures that may not be sufficient to ensure sustainability. A structured and enforced management approach, including seasonal closures and local governance, could help mitigate overfishing, promote stock recovery, and enhance long-term economic benefits for coastal communities.

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Implications for Management

      The observed patterns of high dominance in specific fishing grounds at Unguja Ukuu and Uroa underscore the potential for targeted management interventions. Specifically, the four high-yielding fishing grounds at Unguja Ukuu (Pungume, Nyemembe, Kwale and Vijambani) and the three at Uroa (Michamvi, Bimbi ndogo and Pongwe) could serve as focal areas for sustainable octopus fisheries management, ensuring that productive grounds continue to generate viable catches while less productive grounds are given time to recover. In summary, adopting a management framework that incorporates rotational closures, habitat restoration, and monitoring of high-yielding grounds could strike a balance between exploitation and conservation, ensuring the long-term sustainability of the octopus fishery in these regions.

      From a management perspective, the recorded size of octopus being harvested below maturity sizes necessitates a comprehensive review and adjustment of size limits to better align with octopus maturity sizes. Reviewing and adjusting limits is vital in ensuring individuals have at least one reproductive opportunity before harvest (Rodhouse et al., 2014) and enhances the size and number of octopuses caught post-closure, thereby restoring populations and benefiting local fisheries economically. Another measure that can be beneficial is seasonal closures during peak breeding periods and establishing spatial closures to create refuges for immature octopuses, which is crucial (Rogers-Bennett et al., 2013). Such strategies would support reproductive output and the replenishment of surrounding fishing grounds, underscoring the urgent need for updated management practices in Zanzibar.

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Conclusion

      A notable difference in CPUE across sites, months, fishing gears, and vessel types highlights octopus fisheries' complex dynamics. The low CPUEs across fishing grounds reveal the extensive harvesting pressure on the octopus fisheries in Zanzibar, raising the need for close management attention. The significant variability in CPUE across sites, months, and fishing methods underscores the need for adaptive and localised fishery management strategies. Site-specific management measures, ranging from gear regulation to seasonal and spatial closures, are critical for balancing ecological health and economic sustainability in octopus fisheries. Spatial short-term closure can be considered in reefs that are of little importance to fishers to minimise the impact of the closure on fishers.

Authorship contribution statement: Ali M. Ussi: Conceptualization, Methodology, Investigation, Formal Analysis and Writing – original draft.

Animal ethics: Research permission was obtained from the office of the Second Vice-President office of the revolutionary government of Zanzibar. The Department of Fisheries was aware of the collection of fisheries data.

Funding: The World Bank funded this research through the Southwest Indian Ocean Fisheries Governance and Shared Growth (SWIOFish) project under the current Ministry of Fisheries and Blue Economy, Zanzibar.

Declaration of Interest: I, Ali M. Ussi, declare that I have no conflict of interest regarding this manuscript or any part.

Acknowledgement: The authors is thankful to the Zanzibar SWIO Fish project for the financial support. I sincerely thank the ZAFIRI staff for their support in data collection.

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