The effect of fishing period and the cod-end mesh size of the beach seine net on the size structure and length frequency of two species of mullet in the Caspian Sea

Rezaee Shirazi, Ali; Paighambari, Seyyed Yousef; Zare, Parviz

doi:10.22113/jmst.2024.432377.2571

The effect of fishing period and the cod-end mesh size of the beach seine net on the size structure and length frequency of two species of mullet in the Caspian Sea

Document Type : Original Manuscript

Authors

Ali Rezaee Shirazi

Seyyed Yousef Paighambari

Parviz Zare

Department of Aquatic Production and Exploitation., Faculty of Fisheries and Environment, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran.

10.22113/jmst.2024.432377.2571

Abstract

The present study aimed to investigate the effect of fishing period and mesh size on the size structure and length frequency of two species of Caspian mullet. The length ranges of the fish caught in the cod-end and cover for golden grey mullet were 13.9-56.1 cm and 10.5- 50.6 cm and for leaping mullet were 13.8-31.2 and 8.5-31.1 cm, respectively. The peak frequency of length in the cod-end for the two species was the same in the two fishing periods and the two meshes, while in cover It depended on the two mentioned factors for golden grey mullet. From October to January, smaller fish of both species accounted for a relatively higher percentage. The proportion of medium-sized leaping mullets in the cod end was consistently lower than that of large fish, but this pattern was reversed in the cover. golden grey mullet, the percentage of medium-sized fish was consistently higher than the percentage of large fish, both in the cod-end and in the cover. The results showed that the average fork length of both species trapped in the cod-end was significantly greater than their length in the cover. There was a significant difference in the average fork length of the leaping mullet between two cod-end with mesh sizes of 30 and 33 mm, but it was not significant for the golden grey mullet. This pattern was also observed in the cover. There was a significant difference in the mean length between the two fishing periods for both species trapped in the cod end and the cover. The results also indicated that a significant percentage of large leaping mullets escape from the cod end, making them inaccessible to fishermen. This may indicate the ineffectiveness of the mesh size commonly used in the beach seine net for catching this species.

INTRODUCTION

After Caspian white fish (Rutilus kutum), mullet is the most important species in the coastal catch composition of the Caspian Sea and plays a significant role in the production of marine protein and the economy of the northern provinces of Iran (Pourgholami Moghaddam, 2016). Analysis of size structure and length frequency is one of the most common methods of aquatic catch assessment. Hence, length frequency data provide useful information about the population dynamics of different fish species and help identify issues such as cohort strength, slow growth, or excess mortality (Anderson and Neumann, 1996). Therefore, the main aim of the present study was to investigate the effect of standard size (30 and 33 mm) of seine net using cover in two different fishing periods on the size structure and length frequency distribution of two species of golden mullet and leaping mullet caught in the Miankale area of Golestan province.

MATERIAL AND METHOD

This study was conducted during the 2022 fishing season at the Parah Fisheries Cooperative located in the Miankaleh region of Golestan province. The samples were collected using two beach seine with mesh sizes of 30 and 33 mm in the bag part and a cover with an 18-millimeter mesh size during two fishing time intervals (October to December and February to March). Fish were obtained separately from the main bag and the cover during 54 seine-haul fishing. After species identification based on morphological characteristics such as caudal peduncle, snout, head shape, and caudal fin (Pourgholami Moghaddam, 2016), as well as skin color, the samples were biomaterial. Data were analyzed using t-test, ANOVA, and chi-square. All statistical analyses and charts were performed using R and Excel software.

RESULTS

Out of 10,647 pieces of mullet caught, 7,010 pieces were leaping mullet (Chelon saliens) and 3,637 pieces were golden grey mullet (Chelon auratus). The length ranges of the fish caught in the cod-end (main bag) and cover for golden grey mullet were 13.9-56.1 cm (with an average of 32.2 cm) and 10.5-50.6 cm (with an average of 24.1 cm), respectively. For leaping mullet, the range was 13.8- 31.2 cm (with an average of 25.7 cm) and 8.5-31.1 cm (with an average of 22.6 cm) in the main bag and the cover, respectively. The peak frequency of length in the cod-end for two species, leaping mullet and golden grey mullet, was 26.5-29.5 cm and 32.5-36.5 cm, respectively. This pattern was consistent during two fishing periods and with two different mesh sizes. The leaping mullets trapped in the cover were most abundant in the length group 20.5-23.5. The catch of golden mullet, however, varied depending on the fishing period and the mesh size of the cod-end net. These were divided into two groups: 20.5-23.5 and 24.5-28.5. During the period from October to January, smaller fish of both species accounted for a relatively higher percentage. The proportion of medium-sized leaping mullets in the cod end was consistently lower than the proportion of large fish, but this pattern was reversed in the cover. For golden grey mullet, the percentage of medium-sized fish was consistently higher than the percentage of large fish, both in the cod end and in the cover. However, in the cover, the percentage of large fish was significantly lower compared to medium-sized fish. The results showed that the average fork length of both leaping mullet and golden grey mullet trapped in the cod-end was significantly greater than their length in the cover. There was a significant difference between the average fork length of leaping mullet in two bags with mesh sizes of 30 and 33 mm, but it was not significant for golden grey mullet. This pattern was also observed in the cover. The average length between two fishing time intervals for both species caught in the main bag and cover showed a significant difference.

CONCLUSION

In general, the results indicate that the mesh size and fishing period should be taken into account in the analysis of stock assessment and catch management. The results also indicated that a significant percentage of large leaping mullets escape from the cod end of the beach seine net, making them inaccessible to fishermen. This may indicate the ineffectiveness of the mesh size commonly used in the beach seine net for catching this species.

REFERENCE
Anderson, R.O., and Neumann, R.M., 1996. Length, weight, and associated structural indices. In Fisheries Techniques. Bethesda, M.D: American Fisheries Society. pp. 447–482.
Pourgholami Moghaddam, A., 2016. Investigation of fish stocks in the Iranian shores of the Caspian Sea. Project Report, Iranian Fisheries Research Institute, Tehran, Iran. 43 P. (In Persian).

Keywords

Chelon auratus

Chelon saliens

beach seine net

Length analysis

Subjects

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