Uncovering ecological regime shifts in the Sea of Marmara and reconsidering management strategies

Demirel, Nazlı; Akoğlu, Ekin; Ulman, Aylin; Ertör-Akyazı, Pınar; Gül, Güzin; Bedikoğlu, Dalida; Yıldız, Taner; Yılmaz, I. Noyan

doi:10.1016/j.marenvres.2022.105794

Cited by 14 publications

(6 citation statements)

References 55 publications

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“…The Marmara Sea was chosen as the study site due to its small, enclosed area, its high incidence of fishing activity and directed capacity, and its cumulative environmental concerns that are underrepresented in current research (see Pressing Issues in Marmara Sea). Other similar directed research in this sea has been on the economics of the purse seine fisheries in Turkey [39,40], and the variables behind its regime shifts [41]. This is the first study to investigate the perceptions of purse seine fishers towards the fisheries and fisheries management tactics, and also investigates the economics of this fishery.…”

Section: Three Ongoing Debatesmentioning

confidence: 99%

The Rich Get Stronger: The Purse Seine Fishery of the Turkish Straits System

Koyun¹,

Yıldız

Ulman³

2022

Fishes

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Purse seiners generally try to maximize their revenues by targeting multiple species, starting with the most valuable ones available. The technology and capacity of purse seiners can be exceptionally high for the stocks found in the Marmara Sea, Turkey’s only inland sea, due to its small size and nearly totally enclosed nature. Due to their large capabilities, they are responsible for the majority of catches and hence declines from this sea and thus should be held responsible for the poor state of marine stocks in the region. This study examines the catch compositions, expenses, and revenue sharing of purse seiners by using one representative vessel class for each of the four vessel length categories in the Marmara Sea. Surveys were also conducted with purse seine fishers to assess their perceptions related to fisheries management strategies along with their ideas for transitioning towards sustainable fisheries. As purse seiners are prominent stakeholders in the Marmara Sea fisheries, they should be incorporated into management guidance for effectiveness, along with other stakeholders. This study provides novel socio-economic data along with their perspectives, which may assist in improving policy decisions and capabilities. Our results demonstrate that purse seiners do not consider that their actions are a contributing factor to the current state of the fisheries, they trust in their amassed historical local knowledge, and seem to want to rebuild the resources, however only with minimal rules imposed on their sector.

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Section: Three Ongoing Debatesmentioning

confidence: 99%

The Rich Get Stronger: The Purse Seine Fishery of the Turkish Straits System

Koyun¹,

Yıldız

Ulman³

2022

Fishes

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“…The distribution patterns and abundance of sharks and rays are intricately linked to a combination of environmental factors, ecological interactions, and human activities. Therefore, variations in abundance across stations could also reflect the varying degrees of human disturbances or conservation efforts in those areas (Demirel et al, 2023;Kabasakal, 2020;Öztürk, 2018). The observed high abundance in regions such as Prince Islands and Yalova suggests a notable dominance of elasmobranchs within these areas.…”

Section: Dipturus Batismentioning

confidence: 99%

Distribution and diversity of elasmobranchs in the Sea of Marmara: A 2023 status report

Karadurmuş,

Sarı

2024

Aquatic Conservation

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Elasmobranchs, encompassing an array of sharks and rays, confront a threat of extinction on a global scale. The Sea of Marmara (SoM) stands out as a critical refuge for these endangered species. This study harnesses data derived from comprehensive trawl surveys, representing the first area‐based evaluation of the elasmobranchs inhabiting the SoM. Sampling protocols were carried out at 10 separate stations along the 980‐km coastline of the SoM, each bounded by different ecological characteristics and anthropogenic influences. A total of eight shark species and six ray species were caught in the towed area of the entire the SoM. Notably, Scyliorhinus canicula and near‐threatened Raja clavata constitute more than 50% of the total abundance. Additionally, rare, and critically endangered species, including the Oxynotus centrina, Squatina squatina, Dipturus batis, and Myliobatis aquila, were documented, expanding our knowledge of their presence in the region. Spatial distribution heterogeneity was pronounced within species. Size distributions were species‐specific, and the presence of both juvenile and adult individuals suggested successful reproduction and growth. Records expand the known size range in the SoM for six shark and three ray species. It also provides first‐size information based on the total length of the S. stellaris and D. batis. Additionally, the urgent need for field‐based conservation efforts is highlighted, citing a previously unidentified important sensitive areas located in the southern part of the SoM.

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“…The SoM is surrounded by the Marmara geographical region which is the most populated and most urbanized region in Turkey including Metropolitan city of Istanbul with a population of nearly 15.5 million, located in the northeast, and Gulf of I ̇zmit in the east with the center of industrial activities. Over the last 30 years, the marine ecosystem of the SoM was changed by human induced pressures and it lost its large pelagic and demersal predator species (Demirel et al, 2023). In the 2000s, carnivorous pelagic species seriously decreased, 22 marine species with high trophic levels including swordfish (Xiphias gladius), leerfish (Lichia amia), angelshark (Squatina squatina) and picked dogfish (Squalus acanthias) have become commercially extinct, and biodiversity has evolved towards the dominance of planktivorous fish species (Ulman et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

“…In the 2000s, carnivorous pelagic species seriously decreased, 22 marine species with high trophic levels including swordfish (Xiphias gladius), leerfish (Lichia amia), angelshark (Squatina squatina) and picked dogfish (Squalus acanthias) have become commercially extinct, and biodiversity has evolved towards the dominance of planktivorous fish species (Ulman et al, 2020). Unhealthy conditions such as harmful phytoplankton blooms (Tas et al, 2020), population increase of gelatinous organisms (I ̇sinibilir and Yılmaz, 2016), and the effect of climate change via increasing sea surface temperatures (Demirel et al, 2023) have been observed since the late 1990s. Being a continuously degraded ecosystem over the last thirty years, the SoM is in severe need of understanding the changes in the structure and functioning of its ecosystem under these multiple stressors for the development of EAF as well.…”

Section: Introductionmentioning

confidence: 99%

“…Here, we have developed for the first time a food-web model of the SoM by investigating the changes since the 1990s using trophodynamic mass-balance models set up to represent three decades separately; the 1990s, the 2000s and the 2010s. While we set up three models for each decade, we considered a series of changes reported in the SoM (Demirel et al, 2023); i) the 1990s are characterized with fast development of urbanization and industrialization especially in the Istanbul and surrounding area, ii) the 2000s are mainly dedicated to overfishing and serious eutrophication and pollution including increase in the frequency of harmful algal blooms, and iii) the 2010s are dedicated to public awareness and starting of pollution monitoring activities, a buyback programme in fisheries which lowered active number of fishing boats. In line with the different characteristics of the three decades, we first aimed to understand the state of the SoM ecosystem and then to compare outputs of the three models.…”

Section: Introductionmentioning

confidence: 99%

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Fisheries impact on the Sea of Marmara ecosystem structure and functioning during the last three decades

Saygu

Akoğlu²,

Gül³

et al. 2023

Front. Mar. Sci.

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The Sea of Marmara (SoM), without doubt, is one of the most disturbed marine ecosystems of the Mediterranean basin. As a semi-enclosed and a recognized eutrophic basin, it has a unique natural characteristic by permanent stratification at ~25 m depth. The SoM ecosystem is under threat by multiple stressors from excessive nutrient enrichment, overfishing, invasive species, habitat loss to the climate change. Within this study, an assessment on the SoM ecosystem structure and functioning and its changes over time have been achieved. Hence, we firstly evaluate the SoM ecosystem over a period of three decades from the 1990s to the 2010s by using three mass-balance Ecopath models, secondly, we delineate the prevailing ecosystem structure and functioning in each period, thirdly we determine how the fishing impact contributed to the changes in the SoM since the 1990s and finally establish a baseline for the management and future studies of the ecosystem. The comparison of the models’ results for three consecutive time periods of the SoM showed that the energetic capacity of the ecosystem decreased significantly over the three decades while the decrease in cycling indices indicated that the SoM ecosystem became fragile to anthropogenic disturbances. According to ecosystem theory indices, the SoM is an immature ecosystem at a stage of autotrophic succession, with a very high total primary production, much more above unity that greatly exceeds total respiration. Our results highlighted that the SoM ecosystem was under bottom-up control exerted by mesozooplankton; however, anchovy was a bottleneck in energy transfers to higher trophic levels creating also a wasp-waist control in the food-web. The bycatch of demersal species with long life span, sharks and rays, brought them to the brink of going commercial extinction. Overall, the changes in the SoM ecosystem were due to the trophic cascades exerted by fisheries exploitation in addition to the changes in the productivity of the system. We conclude that the concomitant impacts of stressors on the SoM have been so diverse that an immediate action plan is required. Therefore, we propose a tentative outlook that will help in ecosystem monitoring and better management of the SoM.

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Uncovering ecological regime shifts in the Sea of Marmara and reconsidering management strategies

Cited by 14 publications

References 55 publications

The Rich Get Stronger: The Purse Seine Fishery of the Turkish Straits System

The Rich Get Stronger: The Purse Seine Fishery of the Turkish Straits System

Distribution and diversity of elasmobranchs in the Sea of Marmara: A 2023 status report

Fisheries impact on the Sea of Marmara ecosystem structure and functioning during the last three decades

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