Exploring the dynamics of small pelagic fish catches in the Marmara Sea in relation to changing environmental and bio-optical parameters

Akoğlu, Ekin

doi:10.3906/zoo-2012-23

Cited by 3 publications

(3 citation statements)

References 19 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The low throughput cycled and FCI as well as a low overhead in the 2010s model suggested that ecosystem maturity, resilience and stability have been eroded over time (Finn, 1976;Ulanowicz, 1986). A considerable decrease in the grazing flows from TL I to TL II may indicate a decreasing carrying capacity of the ecosystem due to decreased primary productivity that was possibly related to the increasing sea surface temperatures (Akoglu, 2021). Further, the decreased energy transfers from detritus to TL II indicated a degradation in the ecosystem's maturity sensu Odum (1969), as in mature ecosystem there is greater cycling through detritus and the detrital compartments The keystoneness and the relative total impact of the functional groups in the SoM models.…”

Section: Ecosystem Structure and Functioning Within Decadesmentioning

confidence: 99%

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.

View full text Add to dashboard Cite

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.

show abstract

Section: Ecosystem Structure and Functioning Within Decadesmentioning

confidence: 99%

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.

View full text Add to dashboard Cite

show abstract

“…Due to global warming, the average seawater temperature has also been increasing. Therefore, as an ecosystem, there are many concurrent stressors currently being inflicted, which combined have also contributed to decreasing catches in addition to pressure from overfishing [26].…”

Section: Pressing Issues In the Marmara Seamentioning

confidence: 99%

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

Koyun¹,

Yıldız

Ulman³

2022

Fishes

View full text Add to dashboard Cite

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.

show abstract

“…The Marmara Sea is under the influence of significant anthropogenic activities that adversely affect the well-being of its ecosystem (Akoğlu, 2021). Fish species are also influenced by the adverse impacts of anthropogenic activities (Chassot et al, 2007).…”

Section: Implications For Whiting Fishery Managementmentioning

confidence: 99%

Current Status, Management, and Future Prospects of Whiting (Merlangius merlangus) in the Sea of Marmara

Karadurmuş

2022

Acta Aquatica Turcica

View full text Add to dashboard Cite

The current status of whiting (Merlangius merlangus Linnaeus, 1758) populations in the Sea of Marmara (Turkey) was evaluated by estimating growth and mortality rates in this study. The overall sex ratio (M:F) was calculated as 1:1.36. b value of LWR computed as 2.8904 for both sex groups, and M. merlangus showed a negative allometric growth type by Pauly's t-test result. The age of individuals in the population ranged from I to VI. The growth parameters were estimated as L∞ = 35.74 cm, k = 0.124 yr -1 , and t0 = -1.338 years for all individuals. Total mortality (Z), natural mortality (M), and fishing mortality (F) rates were calculated as 1.35 yr -1 , 0.34 yr -1, and 1.01 yr -1 , respectively. The Phi-prime growth index (φ′) and exploitation rate (E) of the population were calculated as 2.20 and 0.75 yr -1 . According to the results, it is obvious that the whiting stocks in the Marmara Sea are currently used at a high capacity (E = 0.75 yr -1 ). The impact of over-fishing can have increasingly detrimental effects on the overall population size of this population. Fisheries management practices in the Marmara Sea should be regulated by taking into account the ecosystem change, fishing fleet, and unreported catch data. In addition, temporal or spatial fishing bans can be applied by increasing the selectivity of fishing gear. Keywords Age  Growth  Exploitation rate  Marmara Sea  LWR Özet: Bu çalışmada, Marmara Denizi'ndeki (Türkiye) mezgit (Merlangius merlangus Linnaeus, 1758) popülasyonunun büyüme ve ölüm oranları tahmin edilerek mevcut durumu değerlendirilmektedir. Cinsiyet oranı (E:D) 1:1,36 olarak hesaplanmıştır. LWR b değeri her iki cinsiyet için 2,8904 olarak hesaplandı ve Pauly's t-testi sonuçlarına göre mezgit popülasyonu negatif allometrik büyüme gösterdi. Popülasyondaki bireylerin yaşları I ile VI arasında değişim göstermiştir. Büyüme parametreleri, tüm bireyler için L∞ = 35,74 cm, k = 0,124 yıl -1 , and t0 = -1,338 yıl olarak tahmin edilmiştir. Toplam ölüm (Z), doğal ölüm (M) ve balıkçılık ölüm (F) oranları sırasıyla 1,35 yıl -1 , 0,34 yıl -1 and 1,01 yıl -1 olarak hesaplanmıştır. Popülasyonun Phi-prime büyüme indeksi (φ′) ve sömürü oranı (E) 2,20 ve 0,75 yıl -1 olarak hesaplanmıştır. Sonuçlara göre Marmara Denizi'ndeki mezgit stoklarının şu anda yüksek kapasitede kullanıldığı aşikardır (E = 0,75). Aşırı avlanmanın etkisi, genel popülasyon büyüklüğü üzerinde giderek daha fazla zararlı etkiye sebep olabilir. Marmara Denizi'ndeki ekosistem değişimi, balıkçı filosu ve rapor edilmemiş av verileri dikkate alınarak balıkçılık yönetimi uygulamaları düzenlenmelidir. Av araçlarının seçiciliği artırılarak zamansal veya mekânsal avlanma yasakları uygulanabilir.

show abstract

Exploring the dynamics of small pelagic fish catches in the Marmara Sea in relation to changing environmental and bio-optical parameters

Cited by 3 publications

References 19 publications

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

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

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

Current Status, Management, and Future Prospects of Whiting (Merlangius merlangus) in the Sea of Marmara

Contact Info

Product

Resources

About