Octopus fisheries are an integral part of the diet and economy of coastal communities and are threatened by multiple stressors including climate change, overfishing, illegal fishing and habitat destruction (Barnes-Mauthe et al., 2013; Muttenzer and Andriamahefazafy, 2021; Cooke, 2022; Farquhar et al., 2022). Octopuses play an important ecological role as both predator and prey in the marine food web, thus contributing to the overall health and balance of the coastal ecosystem (Yarnall, 1969; Forsythe and Hanlon, 1997; Guard, 2009). The emergence of global markets has shifted many small-scale fisheries from primarily subsistence-based to trade-focused, consequently exposing marine resources to the peril of overexploitation (Iida, 2005; Cripps and Gardner, 2016). Moreover, declining traditional finfish catches have compelled fishers to shift their attention to invertebrates, often leading to cascading impacts on the marine food web (Anderson et al., 2011). Today, octopus fisheries are expanding worldwide to meet demand and fill market gaps left by overexploited fish species, such as tuna, grouper and snapper (Sauer et al., 2021; Ospina-Alvarez et al., 2022). From East Africa to Hawaii, small-scale octopus fisheries produce upwards of 88,000 tons of catch a year (Willer et al., 2023). Octopus cyanea, also known as the day or big blue octopus, is a steadily harvested resource from Indo-Pacific reefs (Norman, 1991; Loganimoce et al., 2023; Willer et al., 2023). Approximately 3,000 tons of octopus are exported annually from the West Indian Ocean (WIO), worth an estimated value of US$12.2 million per year (Rocliffe and Harris, 2016).

Small-scale fisheries in the coastal villages of southwest Madagascar are estimated to employ 87% of the adult population and generate approximately 82% of household income (Barnes-Mauthe et al., 2013; Oliver et al., 2015). Fishers from Madagascar are part of a larger market of buyers and exporters that supply octopus to foreign markets (Humber et al., 2006). The Barren Isles fishery is seasonal, with fishers migrating annually to the islands from April to November following local weather patterns (Muttenzer and Andriamahefazafy, 2021). The arid climate and soil profiles of western Madagascar do not support large agricultural production, one of many reasons why the cultural identity and economy of the Vezo (‘people of the sea’) are naturally intertwined with the highly productive marine systems of the Mozambique Channel (Astuti, 1995). Throughout the Comoros Islands, local fish consumption can constitute as much as 50% of landings, with large pelagic fish making up approximately 75% of the country’s overall fish consumption (Breuil and Grima, 2014). Comoros lacks the capacity for octopus storage and transportation to support larger export markets and hence remains a subsistence-based fishery with most fishers also maintaining other sources of income (Ahamada et al., 2008; Hauzer et al., 2013a; Freed and Granek, 2014).

As the demand and price of octopus have risen, the once predominantly female fishers that glean for octopus in the rocky intertidal at low tide have been joined by more male fishers that spear dive at deeper depths, impacting catch across all regions (Guard and Mgaya, 2002; Doherty et al., 2015; Rocliffe and Harris, 2016). Both male and female fishing associations exist in Comoros, where men historically fished for pelagic and reef fishes on small-scale fleets of pirogues and motorboats (Doherty et al., 2015). However, interviews with local fishers reported declines in catch abundance and mean fish sizes in recent decades (Hauzer et al., 2013a, b), suggesting more fishers may now be participating in the octopus fishery and ‘fishing down’ marine food webs (Rocliffe and Harris, 2016; Sauer et al., 2021).

The small-scale octopus fisheries of Madagascar and Comoros are managed both nationally and locally. Seasonal octopus closures banning all octopus harvesting on the west coast of Madagascar (from December 15 to January 31) and on the east coast of Madagascar (from June 1 to July 15) were established by the national government in 2005. A minimum size limit of 350g was also established by the national government for O. cyanea (Rocliffe and Harris, 2016). However, since the most common method of fishing (gleaning) is unselective, size limits are difficult to implement and enforce. As an additional measure to safeguard well-established traditional fishing grounds, local management groups and fishing associations implement community-level periodic closures of a predefined fishing ground that can vary in duration and size, typically occurring outside or in complement to the national closure ( Supplementary Table 1 ). These closures typically represent approximately one-fifth of a village’s total fishing grounds. When implemented in conjunction with other management strategies like size limits, gear restrictions, species bans and limited access, periodic closures can expedite population recovery and maximize catch (Johannes, 1982; Cohen and Foale, 2013; Carvalho et al., 2019).

In Madagascar, the first locally-led periodic closure was implemented in the village of Ankereo, Atsimo Andrefana, in 2004. Initial success of this management initiative catalyzed the establishment of the first locally managed marine area (LMMA) in Madagascar and inspired neighboring villages to establish similar management structures with closure implementations. Today, independent civil society network initiatives such as MIHARI, a national Malagasy network of LMMAs, connects fishers across the country by supporting workshops, advocating for community rights and fisheries reform. The research results and best practices shared through these network forums have prompted numerous management measures across the country, including the initial Barren Isles octopus closures in 2018. Subsequently, the Vezo Miray Nosy Barren Association was founded as an officially recognized legal entity entrusted with the responsibility of overseeing the LMMA in this area. The management associations in southwest Madagascar and Barren Isles are legally created and empowered to set and enforce local rules known as Dina and manage local resources in their designated areas. In the Comoros archipelago, periodic closures were first established in 2016 supported by the Moheli National Park and governmental (WorldBank) projects. While LMMAs have not been created in Comoros as of yet, locally managed male and female fishing associations exist in some villages and implement periodic closures in collaboration with local authorities.

Considering octopus life history traits when designing closure parameters such as duration, season, habitat and size can increase the probability of octopus reaching reproductive age, enabling fishers to capture larger octopus with comparable effort (Humber et al., 2006; Emery et al., 2016; Goetze et al., 2018). This, in turn, can lead to increased income for fishers (Oliver et al., 2015; Silas et al., 2022). Periodic closures are argued to be most advantageous to this fast-growing invertebrate during reproduction and brooding seasons to protect larval cohorts (Cohen and Foale, 2013; Emery et al., 2016), as well as the post-settlement stage, when growth rates are maximized (Benbow et al., 2014; Oliver et al., 2015). Females are known to brood in the deep rocky subtidal (~100m) (Van Heukelem, 1976; Herwig et al., 2012). O. cyanea paralarvae can spend approximately 30 to 60 days in the water column traveling more than 100 km before settling in a benthic coral environment (Wells and Wells, 1970; Van Heukelem, 1973; Bower et al., 1999; Casu et al., 2002; Murphy et al., 2002). Local environmental conditions such as wind speed, sea surface temperature (SST) and chlorophyll-a can affect octopus landings; often on a time lag due to their influence on food availability at the paralarval stage (Chande et al., 2021). Growth and maturation can vary greatly based on latitude and local environmental factors (Guard and Mgaya, 2002; Herwig et al., 2012; Raberinary and Benbow, 2012; Silas et al., 2021). Based on the life-history study of O. cyanea, researchers in Tanzania have recommended (April-July) periodic closures to protect growth periods; or the use of rotational closures for these cyclic spawners (Guard and Mgaya, 2002; Chande et al., 2021). Past studies from Madagascar recommended closures from June to August and September to November to protect settlers from recruitment peaks during maximum growth periods (Raberinary and Benbow, 2012; Oliver et al., 2015). The high plasticity of octopus life history traits and opportunistic feeding regimes are ideal for managing adaptive octopod populations via closures amid modern fishery and climate stressors (Caballero-Alfonso et al., 2010; Quetglas et al., 2013; Rodhouse, 2013; Rodhouse et al., 2014). Studies suggest that octopus fisheries could be benefiting from a changing ocean environment; octopuses were found to grow quicker and mature earlier at increased temperatures (Forsythe and Hanlon, 1988; Caverivière et al., 1999; Semmens et al., 2004; André et al., 2009; Uriarte et al., 2012; Caamal-Monsreal et al., 2016). These plastic and condensed biological stages make octopus fisheries adaptable to future climate scenarios and suitable for dynamic closure schedules.

While there is evidence suggesting that periodic closures of octopus fisheries have effectively enhanced fisher catch and income, further research is required to explore optimal closure design parameters and formulate long-term management strategies (Benbow and Harris, 2011; Oliver et al., 2015; Silas et al., 2022). Here, we examine long-term trends in octopus catch (> 4 years) and short-term effects of periodic octopus closures (7 and 30 days) across Madagascar and Comoros. Our analyses establish baselines for octopus catch, identify major drivers of positive closure outcomes and provide management recommendations for designing effective closures. Additionally, we examine the ongoing use of closures in the Atsimo Andrefana region of Madagascar.

We observed short-term positive effects following periodic octopus closures across our three study regions in Madagascar and Comoros, and positive long-term trends (increasing or maintained landings) across two of our study regions. Significant increases in median CPUE (octopus kg/fisher-day) and daily total catch (kg/day) were observed when examining catch within both 7- and 30-days post-closure. On average, fishers across the three study regions caught 0.5 kg more octopus 30 days after a closure compared to 30 days before a closure (from 2.0 ± 0.12 kg/fisher-day to 2.5 ± 0.12 kg/fisher-day) and 0.7 kg more octopus 7 days after a closure compared to 7 days before a closure (from 2.1 ± 0.16 kg/fisher-day to 2.8 ± 0.17 kg/fisher-day). Change in daily total catch per village diminished over time when comparing 7- and 30-days post-closure. Median daily total catch increased by 156% in the 7-day period and increased by 95% in the 30-day period. This can be explained by an observed decrease in the mean number of fishers recorded per day, from an average of 24 fishers/day to 16 fishers/day.

CPUE recorded from fishers across Comoros showed consistent catch levels from 2017 to 2022 ( Figure 2 ). In comparison to the two study regions in Madagascar, CPUE and daily total catch are notably lower across Comoros. Fishers in these villages rely heavily on the extraction of marine resources, however, absence of an export market and refrigeration facilities keeps the octopus fishery local and subsistence based (Hauzer et al., 2013a). The highest median CPUE was observed in the Barren Isles, where the catch has shown consistent growth since 2018, most likely driven by sales to export markets. The uncompromising weather patterns and geographical location of these islands prohibit human populations from permanently settling and restricts fishing activity to only seven months out of the year (April to November). Thus, a naturally occurring 4-month closure takes place here every year in addition to the austral summer closures, enhancing benefits to fishers and contributing to the high pre-closure values.

Oliver et al. (2015) found that median CPUE increased by approximately 87% in the 30 days after a closure relative to 30 days before (from 2.37 ( ± 0.33) kg/fisher-day to 4.42 ( ± 0.51) kg/fisher-day) across 36 closures implemented between 2004 and 2011 in the Atsimo Andrefana region. We observed a lower pre-closure median CPUE (2.1 ± 0.09 kg/fisher-day) and an approximate increase in CPUE of 19% across 72 closures between the years of 2008 and 2019. Our data indicated that median CPUE across Atsimo Andrefana increased between 2004 and 2006, followed by a consistent decline beginning in 2011 ( Figure 2 ). Thus, while we did not observe a consistent decline in daily total village catch on average, individual fishers caught more between 2006 and 2011 compared to 2022. This is likely due to the 26% increase in the mean number of fishers recorded each day from the periods 2005-2010 to 2015-2020 ( Supplementary Figure 3 ). Our findings are consistent with previous studies, finding that the mean harvestable sizes and weights of octopus landings in the region have declined (Guard and Mgaya, 2002; Guard, 2009; Sauer et al., 2011).

Though periodic closures are suitable for managing short-lived and rapidly growing taxa like octopus, the design of closures is crucial for their effectiveness. We identified three primary drivers of closure success, defined as increased octopus CPUE and total daily catch: 1) baseline conditions, 2) closure duration and 3) seasonality (closure start month). Relationships between each of these closure variables and catch outcomes suggest the potential for maximum benefits when closures are placed in areas with lower baseline catch, have a duration of at least 13 to 16 weeks and commence in June or November. While we observed positive closure effects across all baseline conditions, the villages with lower baseline CPUE (or lower fishing pressure) have the greatest returns ( Figure 6D , Supplementary Figure 1 ). Based on our analyses, we defined lower baseline catch as approximately 2 kg/fisher-day and 20 kg/day at the village level.

Our findings indicate that there is a predominantly positive change in CPUE across villages linked to closure durations of at least 13 weeks, with maximum benefits observed at approximately 16 weeks ( Figure 7A ). This aligns with findings of previous studies demonstrating benefits from closures with durations ranging from 10 days to 3 months (Guard and Mgaya, 2002; Fernández-Rueda and García-Flórez, 2007; Oliver et al., 2015). Closure duration is closely associated with increased growth capacity in octopuses. An O. cyanea individual can gain 100 to 200 g over a period of approximately two weeks (Van Heukelem, 1973). This implies that conservatively, fishing protection through closures has the potential to contribute an estimated 600-1200 g per octopus in 12 weeks or 800-1600 g in 16 weeks. Longer closure durations may be required if pre-closure fishing pressure is particularly high resulting in low overall octopus biomass.

Managers can also maximize growth potential by aligning closures with reproductive cycles, thereby, providing protection during critical spawning and recruitment periods. In our assessment of post-closure CPUE within the 7 days following a closure opening, 49 out of 61 closures initiated in June (n=38) and November (n=11). In Atsimo Andrefana an increase in CPUE of approximately 97% was observed across villages associated with closures commencing in November; all occurring between the years of 2008 and 2009 with a duration of 12 or more weeks (n = 8). After 2010, most closures in Atsimo Andrefana occurred between the months of June and August in response to studies for a duration of approximately two months. Raberinary and Benbow (2012) also suggested closure periods between September and November. On average, we observed an increase in CPUE of only 18% across villages associated with closures that started in June after 2010. Based on our results, this gain could be maximized by extending the duration of June closures to at least 13 weeks and/or potentially implementing additional closures in November. While our data indicates a more pronounced change in CPUE linked to November closures as opposed to June closures; the imbalance in sample size makes it difficult to conclusively recommend closures start in one month versus another when positive short-term benefits in octopus catch were observed for both.

Although closure size was not identified as a primary factor influencing positive management outcomes in our models, our breakpoint analysis suggests an optimal closure size of 50 to 100 hectares. Within this range the majority of closures exhibit an increase in CPUE after the closure period ( Figure 7B ). As closure size increased from 100 hectares to approximately 200 hectares, we observed a more varied change in CPUE. Large closure areas may be difficult to enforce, minimizing positive closure effects. However, here in our study region compliance was often successful, with records indicating very few infractions. The impact of closure areas is contingent on the availability of suitable habitat, such as rocky coral reefs. Closures in our analysis that were of the suggested optimal size (50-100 ha) contained on average 68% suitable habitat. Across our study area, closures with at least 50 hectares of suitable habitat were associated with increases in CPUE. O. cyanea has relatively small home ranges compared to other marine resources (e.g., fish) and has been reported to have dens distributed approximately 30 m apart and forage on average 81 m each trip from the den (Forsythe and Hanlon, 1997). Our recommended closure size has the potential to provide protection for octopus as well as other species with similar home ranges. Larval connectivity was also not a major driver of closure success. Mean larval import values across four fish species was used to represent general connectivity and applied to octopus which may underestimate variation in octopus connectivity across our study area. A spatial network of periodic closures that protects key larval source and sink areas would facilitate population connectivity and recovery via the export from brooders and the import of settling larvae (Krueck et al., 2022). In the future, we suggest the development of larval dispersal models for octopus to improve our understanding of how connectivity influences octopus population dynamics and the outcomes of periodic closures.

Periodic closures have demonstrated success in delivering short-term benefits for fishers and fostering engagement in locally led management practices. However, this strategy alone is not likely to ensure the long-term sustainability of the fishery. Our findings underpin the importance of a comprehensive ecosystem-based management approach that optimizes closure duration, season, size and habitat coverage for octopus. In addition, we suggest that minimum size limits, gear restrictions and limited access be considered when areas are open to fishing to support reproduction potential and population growth. Management recommendations derived from the response of O. cyanea fisheries to periodic closures in Madagascar and Comoros can be used to inform comprehensive management approaches that incorporate diverse and complementary strategies for adaptive management, ensuring the long-term sustainability of this highly prized and adaptive invertebrate.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

MM: Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Investigation, Formal analysis, Data curation, Conceptualization. LM: Writing – review & editing, Writing – original draft, Visualization, Validation, Formal analysis, Data curation. TR: Writing – review & editing, Validation, Supervision, Resources, Project administration, Methodology, Investigation, Funding acquisition, Data curation, Conceptualization. NR: Writing – review & editing, Validation, Supervision, Resources, Project administration, Investigation, Data curation. FV: Writing – review & editing, Validation, Supervision, Resources, Project administration, Data curation. RR: Writing – review & editing, Validation, Supervision, Project administration, Investigation, Data curation. FS: Writing – review & editing, Validation, Supervision, Resources, Project administration, Investigation, Data curation. FR: Writing – review & editing, Validation, Supervision, Resources, Project administration, Data curation. TR: Writing – review & editing, Validation, Supervision, Project administration, Investigation, Data curation. SB: Writing – review & editing, Supervision, Resources, Project administration, Funding acquisition, Conceptualization. CC: Writing – review & editing, Writing – original draft, Visualization, Supervision, Resources, Project administration, Funding acquisition, Formal analysis, Conceptualization.