Nazli Demirel

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• PhD
• Professor at Istanbul University

The Mediterranean Sea is classified as a “data-poor” region in fisheries due to its low number of assessed stocks given its biodiversity and number of exploited species. In this study, the CMSY method was applied to assess the status and exploitation levels of 54 commercial fish and invertebrate stocks belonging to 34 species fished by Turkish flee...

The invasive Rapa whelk, Rapana venosa in the Black Sea presents a complex governance problem posing a diverse set of positive and negative impacts on marine ecosystems as well as on coastal communities. While some marine scientists perceive the Rapa whelk as a fishery to be sustainably managed, others are more concerned about the threats it poses...

Ecosystem regime shifts can alter ecosystem services, affect human well-being, and trigger policy conflicts due to economic losses and reductions in societal and environmental benefits. Intensive anthropogenic activities make the Sea of Marmara ecosystem suffer from nearly all existing available types of ecosystem pressures such as biological degra...

Understanding the dynamics of pelagic fish fluctuations is crucial to ecosystem well-being and sustainable fishery. Here, inter-and intra-annual landing dynamics of small and medium pelagic fish were delineated between 2000 and 2022 in the landlocked Sea of Marmara. Time series of environmental variables and fisheries landings were analyzed for the...

Over the past two decades, environmentally harmful fishing subsidies, particularly capacity-enhancing ones, have posed significant threats to marine fish stocks worldwide, including the Mediterranean Sea. Despite the global attention paid to harmful fishing subsidies, studies focusing on their impacts in specific regions, especially in the Mediterr...

Islands are diversity hotspots and vulnerable to environmental degradation, climate variations, land use changes and societal crises. These factors can exhibit interactive impacts on ecosystem services. The study reviewed a large number of papers on the climate change-islands-ecosystem services topic worldwide. Potential inclusion of land use chang...

Islands are diversity hotspots and vulnerable to environmental degradation, climate variations, land use changes and societal crises. These factors can exhibit interactive impacts on ecosystem services. The study reviewed a large number of papers on the climate change-islands-ecosystem services topic worldwide. Potential inclusion of land use chang...

This study evaluates the stock status of Scomberomorus commerson in the southern Arabian Gulf, particularly in Abu Dhabi waters, using length-based models to address data limitations in fisheries assessments. The findings contribute critical insights into management practices using four length-based models, namely, LBI, LBB, LBSPR, and LIME, to ana...

Coastal and shelf regions play an extraordinary role with their rich marine resources and ecosystem services for human use. As an important transition zone, the Sea of Marmara (SoM) and its two narrow straits connect Mediterranean and Black Seas, and also support a diverse and rich ecosystem for many fish species. This chapter aims to examine the i...

Globally, all marine ecosystems are under pressure by anthropogenic stressors. However, semi-enclosed seas are at a greater risk of degradation due to their limited connectivity to open seas. This leads to a greater accumulation of pollutants and abrupt regime shifts triggered by unsustainable exploitation of living resources, as ecosystems exhibit...

Simple Summary Invasive alien species are a global threat to biodiversity, ecosystem services (e.g., tourism and fisheries) and human health. Pufferfishes are notorious for their toxicity and may also display aggressive behavior, thus posing a threat to human health. In this work, we collected records of attacks, poisonings and fatalities, due to L...

Some comments on the suitability of stocks for analysis with CMSY++ It is important to realize that every method, when applied to unsuitable data, will fail to provide reasonable results. Thus, this document attempts to provide some insights into the applicability of the data-limited CMSY++ method, by taking a closer look at the features of some st...

Following an introduction to the nature of fisheries catches and their information content, a new development of CMSY, a data-limited stock assessment method for fishes and invertebrates, is presented. This new version, CMSY++, overcomes several of the deficiencies of CMSY, which itself improved upon the “Catch-MSY” method published by S. Martell a...

Following an introduction to the nature of fisheries catches and their information content, a new development of CMSY, a data-limited stock assessment method for fishes and invertebrates, is presented. This new version, CMSY++, overcomes several of the deficiencies of CMSY, which itself improved upon the “Catch-MSY” method published by S. Martell a...

The highly toxic orange-spotted toadfish Torquigener hypselogeneion (Bleeker 1852) [conspecific Torquigener flavimaculosus Hardy & Randall, 1983] is now a very common invasive fish in the Eastern Mediterranean. Its small size, well under 20 cm, may have concealed the danger it represents, and little is known about its biology or ecology. Here, the...

Fisheries are of immense importance to Mediterranean countries, for protein, employment and livelihoods. Studies addressing the factors affecting fish price dynamics are of interest to examine their drivers as prices often dictate target fisheries. This study investigates fish market prices in relation to landings and fish sizes from Türkiye's larg...

This Frontiers Research Topic (RT) “Fishing Effort and the Evolving Nature of its Efficiency” explores the evolution of fishing effort, notably in coastal artisanal fisheries presenting time series analyses of fishing effort and their impact on coastal habitats or on the functioning of those ecosystems. Overall, 10 articles were authored by 54 rese...

Various studies have recently been carried out to assess the condition of the Sea of Marmara's ecosystem and fish stocks. In this section, i) The results obtained from these studies are synthesized to reveal the ecosystem change and fisheries status; ii) The relationship between the mucilage event and the fisheries, and the status of the important...

The presence, bioconcentration, and health risk via seafood consumption of 11 pharmaceutical compounds belonging to different therapeutic groups (anti-inflammatory, antiepileptic, lipid regulators, and hormones) were investigated in the muscle tissues of fish and the meat of shrimp in the Sea of Marmara. Six biota species (Merlangius merlangus, Tra...

Diet studies are critical for ecosystem-level understanding of fish populations and a move toward ecosystem-based management of marine resources. European hake, Merluccius merluccius, a demersal mesopredator species, is one of the most important commercial fish in the Mediterranean, and as a predatory species it controls the food web. Here, we char...

Stock assessment for Mullus barbatus using catch-based (CMSY) and length based (LBB, LBSPR and LIME) data limited models were performed by using official catch statistics and commercial length frequency data from northeastern Mediterranean. The CMSY model results showed that the catch amount did not exceed MSY, and the fisheries reference points (B...

Son yıllarda, Marmara Denizi ekosistemi ve balık stoklarının durumunu ortaya koymak için önemli çalışmalar yapılmıştır. Bu bölümde, i) Bu çalışmalardan elde edilen sonuçlar sentezlenerek Marmara Denizi’nin ekosistem değişimi ve balıkçılığının durumu ortaya konmuş, ii) Marmara Denizi’nde gerçekleşen müsilaj olayının balıkçılıkla ilişkisi ve bu deniz...

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, overfi...

Groupers (Epinephelidae) are ecologically, commercially, and culturally important carnivorous fishes found throughout the world’s tropical, subtropical, and temperate coastal marine waters. Due to various life history traits (e.g., late maturity, sequential hermaphroditism) and behavior (e.g., sedentary, small home ranges) groupers are susceptible...

In the Mediterranean Sea, European pilchard Sardina pilchardus and European anchovy Engraulis encrasicolus are the most important small pelagic fish regarding their ecological role, and revenue. Here, we perform a comprehensive assessment of length-based methods for those small pelagics from İzmir Bay, Aegean Sea. Therefore, the Length-based Bayesi...

Trophic ecology studies on predator–prey interactions reveal insights into ecological communities and help understand a species’ role in the food web by contributing to improved fisheries management and conservation capabilities. Understanding the ecological role of overexploited and endangered predators is essential to deciphering how their feedin...

The angular roughshark, Oxynotus centrina (Linnaeus, 1758), is a rarely encountered deep‐sea demersal shark species. It is listed as “Critically Endangered” in the IUCN's regional assessment for the Mediterranean. Like other sharks and rays, the angular roughshark is subject to by‐catch in demersal trawl and longline fisheries. This study contribut...

Zooplankton is an essential component of marine ecosystems, with Copepoda and Cladocera being the most important zooplankton groups in all the world's seas. In the Sea of Marmara, Cladocera has the highest participation in zooplankton abundance. Here we investigated reproductive strategies and population characteristics of four Cladocera species; P...

Invasive species pose threats to either human health or inflict ecological and/or economic damage. The silver-cheeked toadfish (Lagocephalus sceleratus), a Lessepsian species, is one of the most harmful species in the Mediterranean Sea, because of its potent neurotoxin, impacts on marine biodiversity, and the increased costs and labor they inflict...

Mesopredator species play an essential role in balancing and sustaining ecosystems through their interactions with various species and with their habitats. In ecosystems that have been subjected to overfishing, it is essential to obtain information on the trophic ecology of such predators. Based on this motivation, this study aimed to investigate t...

The silver-cheeked toadfish (Lagocephalus sceleratus, from the pufferfish family Tetraodontidae) and the Pacific red lionfish (Pterois miles, family Scorpaenidae) have recently invaded the Mediterranean Sea. Lagocephalus sceleratus has spread throughout this entire sea with the highest concentrations in the eastern basin, while more recently, Ptero...

CMSY++ is an advanced state-space Bayesian method for stock assessment that estimates fisheries reference points (MSY, Fmsy, Bmsy) as well as status or relative stock size (B/Bmsy) and fishing pressure or exploitation (F/Fmsy) from catch and (optionally) abundance data, a prior for resilience or productivity (r), and broad priors for the ratio of b...

This study uses surplus production model-based methods to assess data-poor stocks and estimate key reference points for Atlantic bonito (Sarda sarda) and bluefish (Pomatomus saltatrix) in the Black Sea. Our results demonstrate that the catch maximum sustainable yield (CMSY) method, using catch data only, yields similar results to the more accurate...

Seasonal fishery closures, are an input control measure to reduce fishing pressure on spawning stocks in fisheries management. Despite the huge foregone economic losses from such closures, the efficacy of them has yet to be examined in Turkey. This study compares the monthly landed catch distribution for commercial marine species averaged for 12 ye...

A timeline of commercial fisheries extinctions and a list of threatened or extirpated marine species are presented to document the rapidly declining abundance of marine resources in the Turkish part of the Black Sea and Marmara Sea. Turkish nationally reported fisheries data were compared over a 50-year period from 1967 (the first year data were sp...

This contribution presents the detailed responses to the peer-review of Froese et al. (2019) "Estimating stock status from relative abundance and resilience" (ICES J. Mar. Sci. 2019) which outlined a method called "AMSY" for inferring biomass trends for stocks for which only catch-per-unit-effort and limited ancillary ('priors') data are available....

Supplementary material of the article entitled "First large-scale Eastern Mediterranean and Black Sea stock assessment reveals a dramatic decline" published in Frontiers in Marine Science. Here, we present, all outputs of CMSY stock assessment analysis for 54 stocks from Black, Marmara and Levantine Seas. Each stocks represented with graphs in two...

The Law of the Sea and regional and national laws and agreements require exploited populations or stocks to be managed so that they can produce maximum sustainable yields. However, exploitation level and stock status are unknown for most stocks because the data required for full stock assessments are missing. This study presents a new method [abund...

There is a recognized need for new methods with modest data requirements to provide preliminary estimates of stock status for data-limited stocks (e.g. Rudd and Thorson, 2018). Froese et al. (2018)provide such a method, which derives estimates of relative stock size from length frequency (LF) data of exploited stocks. They show that their length-ba...

Besides being an exceptional marine ecosystem, Turkish Straits System (TSS) is a very important marine transportation route. However, the heavy maritime traffic through TSS gives rise to accidents and consequently oil spills, which can toxify this peculiar environment. There have been over 40 heavy accidents occurred in the İstanbul Strait since 19...

The aim of ecosystem-based fisheries management is to provide the maximum sustainable take of target organisms with the minimum impact on other ecosystem components. The challenge of the approach is that in the developing countries, including Turkey stock assessments have been made only for a tiny minority of stocks with the rest of these being cat...

This study presents a new method (LBB) for the analysis of length frequency data from commercial catches. LBB works for species that grow throughout their lives, such as most commercially-important fish and invertebrates, and requires no input in addition to length frequency data. It estimates asymptotic length, length at first capture, relative na...

Since January 2014, the reformed Common Fisheries Policy (CFP) of the European Union is legally binding for all Member States. It prescribes the end of overfishing and the rebuilding of all stocks above levels that can produce maximum sustainable yields (MSY). This study examines the current status, exploitation pattern, required time for rebuildin...

This study presents a Monte Carlo method (CMSY) for estimating fisheries reference points from catch, resilience and qualitative stock status information on data-limited stocks. It also presents a Bayesian state-space implementation of the Schaefer production model (BSM), fitted to catch and biomass or catch-per-unit-of-effort (CPUE) data. Special...

The approach to fisheries termed “balanced harvesting” (BH) calls for fishing across the widest possible range of species, stocks, and sizes in an ecosystem, in proportion to their natural productivity, so that the relative size and species composition is maintained. Such fishing is proposed to result in higher catches with less negative impact on...

Fisheries management reference points used for stocks in the Northeast Atlantic were investigated as to the appropriateness of their current levels based on three practical limits of exploitation in fisheries management: (i) the smallest sustainable size of the fished stock (SSBpa), (ii) the maximum sustainable rate of exploitation (Fmsy), and (iii...

In a recent publication (Froese et al., ICES Journal of Marine Science; doi:10.1093/icesjms/fsv122), we presented a critique of the balanced harvesting (BH) approach to fishing. A short section dealt with the size-spectrum models used to justify BH, wherein we pointed out the lack of realism of these models, which mostly represented ecosystems as c...

AbstractThis manuscript reports the first observations of three species of Hydrozoa (Podocorynoides minima, Koellikerina fasciculata and Gastroblasta raffaelei) and one species of Scyphozoa (Discomedusa lobata) in the Marmara Sea that were sampled in 2006?2011. Their possible introduction pathways, some ecological and distributional details are bri...

Spatio-temporal distribution and composition of ichthyoplankton assemblages were studied in the Golden Horn estuary (Istanbul) over a 10-month period. Environmental parameters were considered to determine the environmental status in different parts (upper, middle and lower) of the estuary. The ichthyoplankton composition of the Golden Horn estuary...

Seasonal changes in the distribution of an important commercial and recreational fish species, Trachurus mediterraneus (Steindachner, 1868), from the family Carangidae were investigated in the Golden Horn Estuary of İstanbul. Environmental conditions were also considered to evaluate distributional patterns in the region. Sampled fish size ranged be...

In this study the spawning frequency of Trachurus mediterraneus was estimated for the first time in the Mediterranean basin. The presence of the late-migratory nucleus stage oocytes and post ovulatory follicles (POFs) in the same ovaries were observed continuously during the sampling period. The daily percentage of spawning females with ovaries con...

Turkish booklet of the basic definition on Ecosystem Based Management of the Sustainable Fisheries.

The reproductive biology of Mediterranean horse mackerel Trachurus mediterraneus was investigated in the Sea of Marmara over a one-year period. Duration and timing of the spawning season, gonad histology, oocyte development and size at sexual maturity were determined. The presence of all stages of oocytes without any distinct size hiatus indicated...

Weight−length relationships (WLRs) for 28 fish species were investigated in an enclosed basin in the Sea of Marmara. Due to low sample sizes (<15), 11 species were not taken into account, but length results were represented. WLR information for 8 species was taken for the first time in the Sea of Marmara, and these 8 species were examined according...

Thirty of the 33 alien decapod crustacean species that have been reported off the Turkish Mediterranean coast are believed to have invaded the region via the Suez Canal, but only three of the species have been recorded along the Turkish Aegean coast. The marine biota of Gökova Bay, Datça Peninsula and Gulf of Fethiye, on the southern Aegean coast o...