Fish stocks in the developing world are often depleted as a result of the application of excessive fishing effort on the part of the fishermen. A bioeconomic model with logistic growth, proportional harvesting and quadratic costs is proposed to study the effect of overcapacity on a marine fishery. Also incorporated into the model is an isoperimetric constraint to account for the annual total allowable catch (TAC). Pontryagin's maximum principle is employed to determine the necessary conditions for optimality of the model. Additionally, the sufficiency conditions that guarantee the existence and uniqueness of the optimality system are discussed. Furthermore, the relationship between the shadow price of fish stock, the shadow price of the total allowable catch and the marginal net revenue as it relates to the optimal fishing effort is explored. Numerical simulation with empirical data on the Ghana sardinella fishery is performed to validate the theoretical results. The findings of the study indicate that for a TAC equal to the maximum sustainable yield (MSY), the average fishing effort should not exceed $95\%$ of the MSY effort, provided that the initial stock size is exactly 55% of the carrying capacity.

In this study, sampling of commercial vessels of Afsoon 1 was carried out in July 2020, at a distance of more than 10 miles in longitude24 50 to 24 60 and latitude 61 03 to 61 05. At the time of the study, trawl fishing was done 13 times at different times, 8 times during the day and 5 times at night. The total catch during the study period was 12306 kg and 8720 kg were caught during the day (about 71%) and 3586 kg at night (about 29%). The average catch per fishing effort (catch per hour) of the target species was 201 kg (67%) during the day and 63 kg (33%) at night, and the average catch per fishing effort (catch per hour) discard species were 71 kg (28%) during the day and 100 kg (59%) at night (P <0.05). The mean catch per fishing effort (catch per hour) of bycatch fishing species at 18 kg during the day and 9 kg at night were not significantly different from each other (P> 0.05). The Trichiurus lepturus species (64%) had the highest catch of target species, Epinephelus coioides species (53%) had the highest catch of bycatch fishing species and Ray fish (88%) had the highest catch of discard species. The Siganidae and Megalaspis cordyla species, appear to be active during the day and pipe fish, Anguiliformes and Belonidae species of night active.

This study aimed to investigate the catch composition, length frequency, fishing effort and distribution of Sepia pharaonis caught by pot in the fishing grounds of Ramin and Konarak (Sistan and Baluchestan Province). During October, November, December, and January 2021, 387 specimens were collected in depths of 20 to 40 meters in Ramin and 368 specimens were collected in Konarak. In the Ramin region, the highest number (129 specimens) and the highest range of length (17.3-40.6cm) and weight (367.3-3847.5g) were observed in January. The highest number of squids caught belonged to the length class of 24.8-27.2cm (54 specimens) and the lowest number belonged to the length class 39.8-42.2cm (2 specimens). In the Konarak region, the highest number was observed in January (113 specimens), and the highest ranges of length (18.2-41.2cm) and weight (426.17-3886.24g) were observed in October. The highest number of caught squid belonged to the length class of 29.3-32cm (49 specimens) and the lowest number belonged to the length class of 39.9-42.4cm (6 specimens). In the Ramin region showed that 14 species were caught in October, 11 species in November, 14 species in December and 16 species in January. Also, in Konarak, 16 species were caught in October, 15 species in November, 13 species in December and 16 species in January. The values of a, b and R2 parameters of length and weight, in the Ramin region, were 0.2085, 2.6422, and 0.9791, respectively. The values of a, b and R2 parameters of length and weight, in Konarak, were 0.17038, 2.6962, and 0.9842 respectively. Comparison of CPUE values showed that the highest values in these two regions were observed in January and the lowest values were observed in October. The results of this study have enhanced comprehension of the population dynamics of Sepia pharaonis in these fishing grounds and provide valuable insights into the ecological conditions of the studied areas.

This study aimed to investigate the catch per unit effort of target and non-target species and to determine the bycatch composition in boat trawlers used in Mond and Dayyer-Nakhiloo coastal waters in Bushehr province. Field operations were carried out during the years 2020 (13 August to 15 February) and 2021 (11 April to 9 September). During the research, a 27-foot fishing boat with a 200 hp engine was used. The trawl net used was made of polyamide (PA). The sampling operation was performed in 32 steps. During this study, the amount of catch per unit effort, the ratio of by-catch to the target species, and the amount of by-catch were calculated. The highest frequency of Penaeus semisulcatus in July 2021 (96.67%), the highest frequency of Metapenaeus affinis in August 2021 (21.74%), and the highest frequency of Parapenaeopsis stylifera in July 2021 (63.75%) were recorded in Mond. 37 aquatic species were observed as a bycatch composition during fishing operations. Species including Saurida tumbil, Cynoglossus arel, Portunus segnis, Gerres filamentosus, Drepane punctata, Solea elongata, and Epinephelus coioides were permanently present in the catch composition. The highest rate of shrimp fishing effort was observed in the Mond region (58 kg/h) and the lowest rate was observed in the Dayyer-Nakhiloo (1 kg/h). Also, the ratio of by-catch to target (r) was 2.32 and the weight of by-catch during the fishing season was 1478.96 kg. The results indicate high fishing pressure on commercial and non-commercial species in this area and can be used to assess the damage caused by shrimp trawl nets on fish stocks in ecological risk assessment models. In addition, the findings showed that the deletion of some species can make the food chain longer due to their role in the food chain and reduce the resistance of the ecosystem food web, and ecological and habitat efficiency.

The gobiesare non-commercial fishes in the Iranian waters of the Caspian Sea for whichpopulation dynamics and stock status are poorly known. In this survey, we tried to define species diversity and catch per unit effort (CPUE) of Gobiidae by using beach seine nets in Salmanshahr, the southern Caspian Sea. From March 2011 to April 2012, 224 specimensrepresenting 4 gobiid species, belonging to genus Ponticola and Neogobius, were caught. The deepwater Goby, Ponticola bathybius (Kessler, 1877), was the most abundant species with 92.8% frequency. The highest catch per unit effort of gobiid fishes was obtained in spring. The species diversity was highest in spring according to Shannon’s index.

The present study was carried out in the fishing grounds of small pelagic fish on Qeshm Island (namely Ramcha, Souza, Messen, and Salakh) from September 2022 to June 2023. Field sampling was performed by double-boat purse seiners and conducting 57 netting. The length, height, and mesh size of purse seines were 300 m, 50 m, and 10 mm (STR). Data of date, time of setting, location, and weight of target species and bycatch were recorded for each setting net. The mean CPUE (±95% CI) of small pelagic fish was overally obtained at 991.23 ± 157.14 kg per set. This was 1300 ± 364.01 for Salakh, 1246.88 ± 295 for Ramchah, 669.23 ± 214.20 for Messen, and 587.5 ± 155.71 for Souza, which there was a significant difference between Salakh and Ramcha compared to Souza and Messen (P<0.01). Also, the mean CPUE (±95% CI) of target catch for warm and temperate seasons were 1227.42 ± 224.11 and 709.62 ± 174.20 kg per setting net, which was significantly differ (P<0.01). The maximum and minimum of occurrence percentages were attributed to anchovy (with 100%) and Trichiurus lepturus (with 1.75%). The highest and lowest of mean CPUE (±95% CI) for bycatch species/groups, were related to the Trichiurus lepturus (1.75 ± 3.51) and Dasyatidae (0.07 ± 0.10) kg per setting. Given that fishing efforts have increased in recent years in the region, the estimated values of CPUE for target catch were smaller than in previous studies. Therefore, the fisheries managers must take immediate action to optimize the ongoing fishing effort.

In the fishing season of 2018, fishing information, atmospheric and marine information were collected for investigating the effect of environmental factors on the amount of catch per unit effort (CPUE) of banana shrimp (Penaeus merguiensis) and Sartiz (Metapanaeus affinis) in Bandar Abbas, Qeshm and Bandar Kolahi by Means of ranking tests, permutation test and regression calculations.According to the result obtained during 49 trawl operations, the total weight of shrimp was 1932 kg, including 1379 kg of Banana shrimp with an average of 12.56 (with a 95% confidence interval of 9.68 to 15.45) kg/hour and Jinga shrimp with an average of 5.18 (with about 95% confidence was recorded (3.69 to 6.68) kg/h. The RDA ranking chart showed that the CPUE of Banana shrimp had a direct and significant relationship with the factors including depth, rainfall, and sea surface temperature. In addition, it had a slight relationship with wind speed, cloudiness, humidity, salinity, and wave height. Instead, Jinga shrimp CPUE was directly related to salinity and sea surface temperature and was inversely related to wave height and humidity. Based on the permutation test results, these relationships were not significant. The effect of environmental factors on Banana shrimp CPUE by regression calculations showed that the variables of floating speed and salinity (P<0.01) and humidity and cloudiness (P<0.05) were significant in the negative binomial regression model. The pseudo-Poisson model indicated the variables of sea surface temperature (P<0.05) and salinity (P<0.1) had a significant effect on the CPUE of Jinga shrimp. The present study shows the extent and manner of influence (direct or inverse) of environmental factors on the amount of successful shrimp fishing.

The present study aimed to determine monthly variations catch per unit effort (CPUE) of Benthosema pterotum (Myctophidea) in Iranians waters of the Oman Sea. In this survey, more than 665 cases of hauling net were analyzed from April 2011 to march 2012. CPUE in different seasons were calculated as 937±45, 1002±51, 828±51 and 640±43 kg/h in spring, summer, autumn and winter, respectively. In terms of trawling time, CPUE was calculated as 1108±60 in 2-3, 802±31 in 3-4 and 732±40 kg/h in>4 hours range. Furthermore, CPUE was calculated for different trawling depth and represented 922±33 for <250m and 791±36 kg/h for >250m depth layers. According to daytime in daybreak, CPUE was calculated as 779±37, 987±42 in the middle of the day and 805±48 kg/h in afternoon. Nonparametric Kolmogorov-Smirnov test showed normal distribution of CPUE data. The ANOVA test showed significance different between CPUE in different seasons, trawling time, trawling depth and daytime (P<0.05). Linear regression confirmed the relationship between CPUE with trawling depth and trawling time. The Pearson rank correlation showed relationship between CPUE with trawling time (p=0.0007) and trawling depth (p=0.009).

In the present study, the exploitation status of Babylon snail was evaluated by sampling four fishing areas of this species in the north of the Oman Sea (Iran) including Pasabandar, Bris, Pozm and Konarak from September 2021 to September 2022. In order to estimate the amount of catch per month, sampling was done by collecting statistics and information from the landing site, by counting at the place and sampling at the time. The amount of Babylon snail fishing effort and catch indicates that Bris and Pozm stations had the highest and lowest catch rate as well as fishing effort (day-boat) at the time of snail harvest (P < 0.05). The average catch per fishing effort post Monson and per Monson time were 183 ± 79 kg and 117 ± 25 kg, respectively (P < 0.05). In general, the fishing status of Babylon snail species has a fishing effort of 4569 days - boat fishing per year and the average catch per fishing effort (CPUE) of each boat is about 150 kg and the average catch per cage is about 0.59 kg. According to the calculations, the average of virgin biomass was obtained 971 (918-1047) tons, the average of maximum sustainable yield (MSY) less than 250 tons and maximum constant yield (MCY) less than 180 tons and total allowable catch (TAC) less from 220 tons, respectively. The amount of Babylon snails catches on the northern waters of the Oman Sea (Sistan and Baluchestan province) is more than 670 tons per year, that its seems to be higher than the optimal catch.