Mackerel Caught Research Articles

Optimal harvest strategies with catch-dependent pricing for chub mackerel in South Korea

Chub mackerel (Scomber japonicus) is a key commercial species in South Korea. However, the catch volume of chub mackerel has experienced significant fluctuations over the past few decades, with current trends indicating a decline. Despite regulatory measures such as closed seasons, resource depletion remains a concern, thereby highlighting the requirement for effective management strategies. Numerous previous studies have proposed optimal harvest strategies by assuming constant prices. However, as large catches of mackerel tend to have lower prices, it is crucial to develop optimal harvest strategies that account for this decrease. Thus, we aim to develop a monthly optimal harvest strategy for chub mackerel that considers catch-dependent pricing. We define logarithmic, rational, and irrational catch-dependent price functions and their corresponding objective functions. In addition, we develop an optimal control system based on a discrete age-structured model. We use Pontryagin’s maximum principle to prove the necessary conditions for the optimal harvest strategy under the three catch-dependent pricing functions and perform simulations using the forward–backward sweep method. We compare the optimal harvest strategies under the three catch-dependent pricing scenarios with those under a constant price. The optimal harvest strategies with the rational and irrational price functions are similar to those with a constant price, where the fishing effort increases immediately after spawning and then gradually decreases. In contrast, the optimal harvest strategy with the logarithmic price function involves a gradual increase in fishing effort from July immediately after the spawning period, with the maximum effort in June before the next spawning season. In addition, we compare the effects of monthly closed seasons across the four pricing scenarios. A closed season in July immediately after spawning provides the highest resource recovery efficiency. In contrast, a closed season in June provides the highest catch and profit efficiencies. As the cost per unit of effort increases, the fishing effort, catch, and profit decrease, while the biomass increases, and the profit decrease is smallest under the logarithmic price function. Our method can improve monthly optimal harvest strategies for other species using catch-dependent pricing functions as well as significantly contribute to enhancing fishers’ profit.

JITU (Fish Pinch Catch Profit) Surronding Net Increases Male Mackerel Catch in Siofabanua Village, North Nias

JITU (Fish Pinch Catch Profit) Surronding Net Increases Male Mackerel Catch in Siofabanua Village, North Nias

Effects of oceanographic conditions on fishery distribution: A case study of chub mackerel (Scomber japonicus) in northeastern Taiwan

Changes in oceanographic conditions can affect species distribution in marine habitats. Global climate change may negatively influence the oceanographic factor–species distribution relationship. Here, we assessed the influence of oceanographic conditions on chub mackerel (Scomber japonicus) distribution in northeastern Taiwan by constructing and using a habitat ensemble model incorporating chub mackerel fishery, climatic oscillation, and oceanography data. Our results indicated that the chub mackerel catch was mainly influenced by the Western Pacific Oscillation. Moreover, sea-surface height and mixed-layer depth exerted the most and least significant effects on chub mackerel distribution, respectively. The chub mackerel catch rate peaked in the study area with a sea-surface temperature of 29 °C, sea-surface chlorophyll of 0.25 mg/m3, sea-surface salinity of 33.7 psμ, and SSH of 0.575 m. Chub mackerel was the most widely distributed in the area between 25°N, 120.5°E and 26.2°N, 121.5°E. Our findings can be used to develop critical adaptation plans for managing chub mackerel fisheries in the northeastern waters of Taiwan. Considering changing climate conditions globally, the incorporation of this knowledge into managerial strategies may aid decision-makers in protecting not only other ocean fisheries but also individuals dependent on them.

A multidecadal study of the Malabar upwelling system influencing Indian Mackerel landings along the coasts of Karnataka and Kerala, south-east Arabian Sea

Indian Mackerel (Rastrelliger kanagurta) is an essential small pelagic fishery resource, contributing to nearly 30 % of India's total marine fish landing. However, this species' life cycle and stock status are poorly understood and data deficient. Ocean mesoscale events are also known to influence their landing, besides the environmental factors like- salinity, chlorophyll, and sea surface temperature, affecting these small pelagic fishes' availability, migration, feeding, and reproductive activity. The Malabar upwelling region (southwest coast of India) is a significant upwelling system where upwelling occurs during the monsoon months. The nutrient-rich water increases the productivity of surface water, leading to plankton abundance. This productivity sustains a fishery for several commercially important fishes, mainly small pelagics such as sardines, mackerels, and anchovies, supporting India's most significant coastal pelagic fishery. For understanding the relationship between the target fish and the oceanographic events, in the present study, Pearson's correlation has been estimated between Indian Mackerel landing, rainfall, Sea water temperature at 0, 10, 20, 30, 45, and 50 m depths, mixed layer depth (MLD), their anomalies and occurrences of potential fishing zone (PFZ) lines along the Malabar upwelling region and corresponding coasts of Karnataka and Kerala. Mackerel landing time series showed a significant autocorrelation in four-quarter lag, correlation with rainfall anomaly in one-quarter lag, with PFZ line and MLD in three-quarter lag, and with SWT@50 (Seawater temperature@50 m depth) and SST anomaly in two-quarter lag both in Karnataka and Kerala. Upwelling events, as indicated by the presence of PFZ lines, were found to significantly impact the landings of Indian mackerel along the Karnataka and Kerala coasts. Polynomial equations were used to model the relationship between mackerel landings and these environmental factors, effectively capturing the influence of these parameters on mackerel catch trends.

Spatial characterisation and drivers of catch and effort in highly specialised recreational pelagic fisheries

Large pelagic finfish are highly mobile, distributed across broad geographical scales, and often targeted by both commercial and recreational sectors. Fishing effort in these fisheries is variable due to seasonal patterns in fish behaviour and accessibility of fishing locations. Similarly, fisher behaviour and access are likely to differ within the recreational sector, between private boat-based fishing and charter (or for hire) fishing. Here, we compare spatio-temporal patterns in catch per unit effort (CPUE), effort (boat days) and catch (total catch per fishing party) for private boat-based and charter fishing, and identify environmental variables that may influence those patterns, for two pelagic species (the tropical narrow-barred Spanish mackerel and temperate Samson fish) in Western Australia. Spatial and temporal patterns of CPUE were investigated using geostatistical indices, such as the global and local index of collocation which compares the spatial distribution of CPUE locations across years and CPUE values at common locations respectively, and the centre of gravity which calculates the mean fishing location weighted by CPUE, along with the influence of environmental variables (including rainfall and sea surface temperature) on catch using generalised additive models (GAMs). The global index of collocation showed consistency in spatial distribution of CPUE and effort between private boat-based and charter fishing for both species. In contrast, the local index of collocation showed differences in the ranges of CPUE and effort within common locations. Private boat-based fishing often occurred close to the coast and adjacent to population centres, while charter fishing occurred further offshore. Spatial shifts over time were more prominent for Spanish mackerel with an overall northerly shift. For private boat-based fishing, higher catches of Spanish mackerel were associated with higher rainfall, along with an increase in ambient air temperature. For charter fishing, higher catches of Spanish mackerel occurred with ambient air temperatures of around 30 degrees Celsius and a decrease in rainfall, where high catches of Samson fish were associated with a decrease in sea surface temperatures and austral winter months. This study highlights changes in the distributions of pelagic species over time and the potential to incorporate spatio-temporal monitoring of recreational harvest into fisheries management.

Faktor-Faktor Yang Mempengaruhi Hasil Tangkapan Ikan Kembung (Rastrelliger SPP) di Perairan Selat Makassar

This study aims to determine the factors that affect the catch of mackerel in the potential zone of fishing grounds in the Makassar Strait, namely; oceanography sea surface temperature, salinity, current velocity, depth and sea surface chlorophyll content on the catch of mackerel in the potential zone of fishing grounds in the Makassar Strait. The research method used is the survey method, which directly follows the fishing operation. The number of observations was 38 times. Data were analyzed with histogram graphs and also analyzed with multiple linear regression. The results of this study showed that mackerel were generally caught in waters with temperatures between280Cand290C; salinities of 30 ppt and 31 ppt; water depths of about 50 m and 60 m; current speeds of about 0.09 m/s and 0.12 m/s; and chlorophyll-a content of about 1.80 mg/m3 and 2.20 mg/m3. This study has explained that chlorophyll-a content is the dominant factor in relation to mackerel catch.

Enhancing Chub Mackerel Catch Per Unit Effort (CPUE) Standardization through High-Resolution Analysis of Korean Large Purse Seine Catch and Effort Using AIS Data

Accurate determination of fishing effort from Automatic Identification System (AIS) data improves catch per unit effort (CPUE) estimation and precise spatial management. By combining AIS data with catch information, a weighted distribution method is applied to allocate catches across various fishing trajectories, accounting for temporal dynamics. A Generalized Linear Model (GLM) and Generalized Additive Model (GAM) were used to examine the influence of spatial–temporal and environmental variables (year, month, Sea Surface Temperature (SST), Sea Surface Salinity (SSS), current velocity, depth, longitude, and latitude) and assess the quality of model fit for these effects on chub mackerel CPUE. Month, SST, and year exhibited the strongest relationship with CPUE in the GLM model, while the GAM model emphasizes the importance of month and year. CPUE peaked within specific temperature and salinity ranges and increased with longitude and specific latitudinal bands. Month emerged as the most influential variable, explaining 38% of the CPUE variance, emphasizing the impact of regulatory measures on fishery performance. The GAM model performed better, explaining 69.9% of the nominal CPUE variance. The time series of nominal and standardized indices indicated strong seasonal cycles, and the application of fine-scale fishing effort improved nominal and standardized CPUE estimates and model performance.

Dynamic energy budget model for the complete life cycle of chub mackerel in the Northwest Pacific

Chub mackerel (Scomber japonicus) in the Northwest Pacific is an important pelagic fishery resource and a significant target species in purse seine fisheries. However, the catch of chub mackerel fluctuates greatly from year to year, and recent studies have shown that the Tsushima stock may be overfished. Therefore, research on the biology and population dynamics of this species is required to provide sufficient scientific support for the development of reasonable management and recovery plans and for the increased sustainable use of resource fisheries. In this study, a dynamic energy budget (DEB) model was constructed based on DEB theory for the complete life cycle of chub mackerel in the Northwest Pacific by using biological data to simulate processes, including growth, reproduction, and death. The key results were as follows. 1) The DEB model accurately simulated the complete life cycle of chub mackerel, with a good fit for the relationships between age and length as well as length and weight, while accurately estimating annual absolute fecundity, aging, and death and predicting the metamorphosis time of larval fish. 2) The DEB model can incorporate the effects of temperature and food to describe the effects of marine environmental conditions on chub mackerel growth. 3) The DEB model involved multiple interrelated parameters; however, owing to a lack of observational data, there was a certain degree of uncertainty in estimated parameter values. The DEB model provides a basis for establishing correlations and intrinsically unifying biological processes, including growth, sexual maturation, reproduction, aging, and death, thereby guiding studies of growth, reproduction, and population dynamics of chub mackerel in the Northwest Pacific.

Construction of chub mackerel (Scomber japonicus) fishing ground prediction model in the northwestern Pacific Ocean based on deep learning and marine environmental variables

Accurate prediction of the central fishing grounds of chub mackerel is substantial for assessing and managing marine fishery resources. Based on the high-seas chub mackerel fishery statistics and multi-factor ocean remote-sensing environmental data in the Northwest Pacific Ocean from 2014 to 2021, this article applied the gravity center of the fishing grounds, 2DCNN, and 3DCNN models to analyze the spatial and temporal variability of the chub mackerel catches and fishing grounds. Results:1) the primary fishing season of chub mackerel fishery was April–November which catches were mainly concentrated in 39°∼43°N, 149°∼154°E. 2) Since 2019, the annual gravity center of the fishing grounds has continued to move northeastward; the monthly gravity center has prominent seasonal migratory characteristics. 3) 3DCNN model was better than the 2DCNN model. 4) For 3DCNN, the model prioritized learning information on the most easily distinguishable ocean remote-sensing environmental variables in different classifications.

The Effects of Variations in Fishing Time and Gill Nett Immersion on Mackerel Catch (Rastrelliger Spp.) in Demak Waters, Central Java, Indonesia

Gill net is included in environmentally friendly fishing gear with the main catch being mackerel (Restelliger spp.). Fishermen operate gill nets in the early hours of the morning with a long immersing period. It is feared that this can reduce the quality of the catch. This study aims to analyze the difference in fishing time, and the difference in the length of gill net immersion on mackerel catches (Restelliger spp.) in the Morodemak Fishing Port, Central Java. The method used in this study is an experimental fishing method using 2 variables, namely the difference in fishing time and the difference in immersing time with 4 repetitions. Based on tests that have been carried out on the composition of catches using Two Way Anova, the treatment of differences in the length of immersion in gill net fishing gear has a significant effect on the catch. This is shown by a significant value in the 2-way Anova test of 0.000 < 0.05. The treatment of the difference in gill net operating time also has a significant effect on the catch (significance value 0.000 < 0.05). The conclusion that can be given is that there is an interaction between the difference in fishing time and the differences in soaking duration of gill nett catches, this is shown by significant values of 0.003 < 0.05.

Experimental Mixed Gillnets Improve Catches of Narrow-Barred Spanish Mackerel (Scomberomorus commerson)

A new gillnet made from multiple mesh sizes ranging from 125 to 180 mm of stretched mesh (experimental gillnet) was tested under commercial fishing conditions to compare the fishing performance with that of conventional gillnets with a 125 mm mesh opening (control gillnet). Catch efficiency and size selectivity between the two gillnet types were evaluated throughout one year of fishing in three different locations in the waters of Vietnam. Experimental gillnets caught narrow-barred Spanish mackerel (Scomberomorus commerson), spotted mackerel (Scomberomorus guttatus), and wahoo (Acanthocybium solandri) in comparable amounts to the control gillnets, with the moon phase, month, and depth explaining some of the variation in the catch per unit effort (CPUE). An analysis of the size-dependent catch comparison rates and selectivity parameters showed that the experimental gillnets captured a wider range of narrow-barred Spanish mackerel sizes, but with a substantial proportion of individuals larger than those caught by the control gillnets. This is of higher weight per unit effort, and fishing enterprises therefore could improve their economic benefits by using modified gillnets with multiple mesh sizes. Our findings also support the biological and environmental benefits of the modified gillnet size selection, which might also extend to other species.

DIFFERENT BAIT AND HOOK SIZE EFFECT ON MACKEREL CATCHES WITH HANDLINE IN CILACAP WATERS, CENTRAL JAVA PROVINCE, JAVA ISLAND

Hand line is a fishing gear commonly used by fishermen in Cilacap Regency to catch schools of mackerel fish. Hand line is a passive fishing gear. Mackerel is a fishery commodity that has high economic value. The construction of handline fishing gear is a plastic reel, fishing line, branch line, swivel and hook. The fishing line area is in the IB fishing line. Handlines are operated in areas with a depth of 10-15 meters. Cilacap fishermen generally operate handlines not to the bottom of the waters. The purpose of this study was to determine the difference in the catch of mackerel based on the difference in bait and hook size of handline fishing gear. The experimental method in this study used 2 variables, namely differences in bait and hook size with 6 repetitions. The bait used in this study was natural (live) bait and artificial (dummy) bait in the form of squid, as well as the size of the hook, namely fishing line size 4/0 with 6/0. The overall catch on the handline fishing gear operated was 17 mackerel fish. Based on the tests that have been carried out on the catch composition using the Two Way Anova SPSS 24 test, the results show that there is no significant difference (p>0.005) on the type of bait used on catching mackerel fish. Howeever there is a significant difference (p<0.05) on the hook size used on catching mackerel fish. These results indicates that hook size acts as an important role that may affect the catching quantity of mackerel fish. The research also indicates that there is no correlation between the 2 factors (type of bait and hook size) on the overall catch of mackerel fish in Cilacap Waters.

Determination of potential fishing ground of mackerel fish (Rastrelliger kanagurta) using satellite imagery in the Malacca Strait

Mackerel fish (Rastrelliger kanagurta) is a fishery commodity in high demand by the community which is caught in the Malacca Strait. The number of mackerel catches tends to fluctuate every month because it is influenced by different mackerel fishing grounds. Determination of fishing ground tends to use traditional methods such as seeing ripples and a flock of birds flying above the water surface. This study aims to determine the effect of sea surface temperature and chlorophyll-a concentration on mackerel catches and determine the value of primary productivity of the VGPM model every month and also to determine the potential fishing ground to catch mackerel fish based on the sea surface temperature (SST) and chlorophyll-a concentration and Aqua MODIS satellite image data (SST and Chlorophyll-a) were downloaded from oceancolour.gfc.nasa.gov while the catch data were obtained from the Belawan Ocean Fishery Port, the data was taken from 2016 to 2020. The influence of SST and Chlorophyll-a concentration was analyzed and visualized on a map. It was found that every month the potential fishing ground for catching mackerel fish has a different location due to the influence of sea surface temperature and fluctuating chlorophyll-a caused by seasonal changes that occur in Indonesia, where the average SST ranged from 30.01 to 31.34°C and the concentration of chlorophyll-a ranged from 1.48 – 2.28 mg/m3 from 2016 – 2020 with a high net primary productivity ranged from 802.12 – 1.341.59 mgC/m2/day from 2016 to 2020. The potential area for catching mackerel (Rastrelliger kanagurta) caught using purse seines in the Malacca Strait is in the coordinates range of 980 10"51.6” – 1000 19"4.8” (longitude) and 30 28" 48” – 4 0 56"34.8” (latitude) and perpendicular horizontally to the Langkat Regency to Asahan Regency shoreline with a distance under 12 miles to 50 miles. Information on potential areas for catching mackerel can help fishermen in fishing activities so that they are more efficient and catch maximum results.

Assessment approach of production models to commercial pelagic catch and effort data of Indian mackerel (Rastrelliger kanagurta, Cuvier, 1816) in the Arabian Sea

Globally, Reference Points (RPs) indicators are usually lifted in the science of fisheries management for the alternative running objectives and tracking the condition of fisheries. The Fox Model (FM) and Logistic Model (LM) in A Stock Production Model Incorporates Covariates (ASPIC) estimated F = 0.062 – 0.132 and F = 0.059 – 0.126 from 2003 to 2018 with F/F MSY showing an increased inclination from 0.628 to 1.346 and 1.027 to 2.179, respectively. Estimated Starting Biomass (B) = 520800 – 263100 MT and B = 541000 – 277000 MT from population trajectory (Non-bootstrapped) sharply decreased to the ratio of biomass to B MSY (B/B MSY ) 2.810 – 1.420 and 2.075 – 1.063, respectively. Furthermore, the uncertainties reported in Maximum Sustainable Yield (MSY) (18210 – 15050 MT), F MSY (0.098 – 0.058) and B MSY (185300 – 260700 MT) from FM and LM was also estimated in ASPIC using 0.8 Initial Proportion (IP) of starting Maximum Catch (MC) that was 80 %. According to Target Reference Points (TRPs), CEDA and ASPIC (11000 – 18000 MT and 15000 – 18000 MT) range also indicate overexploitation of the Indian mackerel in the Arabian Sea of Pakistan. Estimated Predicted Yield (PY) of 28841 MT in 2003 and even Recent Catch (RC) of 19421 MT in 2018 is far away from harvested yield values of 31126 and 33658 MT and even MC of 38504 MT, pinpointing this research in a questionable and overexploitation state. Ideally, Fishing Effort (FE) should be reduced at the level of PY which is approximately 12000 fishing vessels (19421 MT) against the current engaged FE of about 19000 fishing vessels (33658 MT) in 2018 for the Indian mackerel fishery in Pakistan. In order to prevent this huge economic loss and to reduce the efforts of fisheries, it is suggested that strict and immediate measures should be followed by the policy makers and law enforcement organizations against the mesh size and illegal nets for this type of commercially important fishery.

VARIASI SUHU DAN KLOROFIL-A HUBUNGANNYA DENGAN DINAMIKA PENANGKAPAN IKAN KEMBUNG (RASTRELLIGER SP) DAN TONGKOL (EUTHYNNUS AFFINIS) DI PERAIRAN SELAT MALAKA

Indonesia's huge fishery potential has been recognized by the world. Fishing is an effort/activity that involves the exploitation of a resource in the sea or through public waters, whether commercially or not. The Malacca Strait is one of the territorial waters that is bounded by three countries, namely Indonesia in the west, Malaysia in the east and Thailand in the northeast. One of the catches of pelagic fisheries in the waters of the Malacca Strait that has important economic value is mackerel. This study aims to understand trends in fish catches, examine the effect of variations in temperature and chlorophyll-a in fish catches and provide basic information for fisheries management in the waters of the Malacca Strait. The stages of this research method consist of 3, namely first, chlorophyll-a and temperature data input from in-situ measurements and satellite data and catch production data, the second is the process stage, namely data input in the correlation test and t test and monthly CPUE production data. bloated and cob for 5 years. The results showed that the fluctuations in SST values in the Malacca Strait in 2020 ranged from 25.11 0C - 31.07 0C, the range of chlorophyll-a concentrations in the waters of the Malacca Strait from January 2015 to December 2020 was between 0.17 mg/m3 (February 2015). 2006) to 2.70 mg/m3 (December 2016). The variation in the catch of mackerel (Rastrelliger sp) in the waters of the Malacca Strait is in the range between 23,701.3 kg/trip (February 2007) to 105.47 kg/trip (March 2017). The number of tuna catches in the waters of the Malacca Strait is in the range of 2.94 kg/trip (December 2016) to 173.20 kg/trip (March 2016).

Мониторинг показателей безопасности скумбрии японской

Monitoring of the concentration of toxic elements, N-nitrosamines, pesticides, polychlorinated biphenyls and cesium and strontium radionuclides in the raw muscle tissue of the Japanese mackerel putin 2014-2019 was carried out.
 It was found that the investigated safety indicators of Japanese mackerel caught in the South Kuril fishing zone and in the Pacific subzone of the North Kuril fishing zone in 2014 – 2019 correspond to modern quality requirements. It is noted that Japanese mackerel can be used as a valuable raw material for the production of food products.

Determination of gill-net selectivity for King Fish (Scomberomorus Commerson, Lacepede 1800) using Mesh size in Sungailiat, Bangka Belitung Province

Selectivity is a fishing gear characteristic capable of catching fish of a specific size and species from the existing population distribution. Mesh size is one of the important factors that influence gillnets’ selectivity, because different length-classes of fish are caught by them. This report focuses on the selectivity of two mesh sizes of gillnets (8.89 cm and 10.16 cm) on mackerel's catch and constructing a gillnet in Sungailiat waters. Experimental fishing methods and selectivity analysis were used for the fishing gear’s more selective preparation, if the largest fishing ratio's value at the fork length (L) is high and the standard deviation value (S) is closer to 1. It is concluded that to be more selective a largest S (L) value of 0.999267194 at fork length (L=54.95 cm), and with a larger value of S (L) 0.997096071 and with (L=66.55 cm) for mesh Sizes 8.89 cm and 10.16 cm, respectively.

Information support for chub mackerel Scomber japonicus fishery in the Pacific waters of the Russian Federation

Methods of machine learning were applied for forecasting of chub mackerel fishing grounds in the South Kuril fishery district. The problem of perspective fishing area definition was reduced for a binary classification task, i.e. the sets of environmental conditions corresponded with presence or absence of fishing operations were determined for each point within the district. The fishery statistics for 2016–2020 and the data on SST with delay of 4–7 days from the date of catch, spatial SST gradients calculated using Belkin algorithm, and day-to-day SST variations were processed using LightGBM machine learning algorithm. The model was trained on the data for 2016–2019 and verified on the data for 2020. The AUC (as an aggregate measure of performance across all possible classification thresholds) varied from 0.65 to 0.92. In the fishery season of 2020, AUC was 0.69, on average, growing to 0.75 in the period of the highest catches. Approximately 75 % of the annual catch of chub mackerel was caught at the predicted sites in 2020; this portion reached 84 % in the period of the highest catches.

Effect of a Seasonal Fishery Closure on Sardine and Mackerel Catch in the Visayan Sea, Philippines

The implementation of seasonal fishery closures (SFC) can be controversial due to the frequent lack of clear objectives, monitoring and empirical evidence of management success. In the Philippines, an SFC implemented for the conservation of important fishery commodities in the Visayan Sea has been ruled a success after stricter implementation of this fishery policy in 2012. However, a comprehensive, detailed, and robust analysis of this fishery policy is lacking. Using a difference-in-differences (DID) framework, we estimated the effect of SFC on the interannual and seasonal catch for sardine and mackerel. We expanded our analysis to other species not regulated under the SFC policy. We also conducted semi-structured interviews (N= 235), focus group discussions (N= 9) and key informant interviews (N= 37) involving municipal fisheries stakeholders in the surrounding municipalities around the Visayan Sea, and representatives from the government and non-government agencies, to complement our analyses. Seasonal analyses of catch data show a significant increase in sardine catch at the end of the seasonal closure among SFC-participating provinces. However, overall, the SFC had no significant effect on sardine interannual catch among the provinces participating in the SFC. We also found no significant effect of the SFC on interannual and seasonal catch for mackerel. Furthermore, our findings show no significant changes in fishing pressure to other aquatic species. Interview results corroborate our DID findings for mackerel, but not for sardine. The varying perceptions on the outcomes of the SFC policy can be attributed to several challenges such as lack of implementing guidelines, lack of alternative livelihoods for the affected stakeholders, persistence of illegal fishing, and uneven implementation of the SFC. Since the management objective of this SFC was to conserve the regulated species, alternative management measures may be needed to achieve this goal. This could entail more consistent enforcement, improved cooperation and communication between fisheries managers and stakeholders, fish size or gear restrictions, and identification and conservation of key habitats needed to restore overexploited species.

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

The Marmara Sea has a large drainage basin that includes cities with heavy industrialisation and agricultural land use. Therefore, it is under the influence of significant anthropogenic activities that adversely affect the well-being of its ecosystem. The Marmara Sea is also an important fishing ground with many commercially important fish species. These fish species are also under the influence of the adverse impacts of anthropogenic activities. Fisheries catches in the Marmara Sea had experienced severe fluctuations since the onset of the 2000s. In this study, possible underlying reasons for these fluctuations were investigated between 2000 and 2019 using remotelysensed environmental and environmentally-influenced bio-optical parameters and fishery statistics. First, long-term inter-annual changes in the time series of sea surface temperature (SST), chlorophyll-a (Chl-a) concentration, net primary productivity (NPP), fishing effort, and catches of commercially important fish species, i.e. anchovy, sprat, Mediterranean and Atlantic horse mackerels and sardine, were scrutinised using trend analysis. Then, relationships between species? catches and the changes in the SST, Chl-a concentration, NPP, and fishing effort were investigated using correlation analysis. The results of the trend analysis showed that there were statistically significant declines in the catches of Mediterranean horse mackerel, sprat, and the total catch of the investigated species, although the decrease in the fishing effort was statistically not significant. The analysis of relationships between the environmental and bio-optical parameters and fishery statistics indicated that SST had statistically significant negative and NPP had statistically significant positive correlations with the catches of anchovy, sprat, and Mediterranean horse mackerel. Overall, the results indicated that the decreases in the fisheries catches were strongly correlated with the environmental and environmentally-influenced bio-optical parameters and fisheries management practices should consider environmental aspects of the ecosystem in addition to conventional fisheries regulations.