Bioeconomic Approach for Assessing Status of Trawl Fishery in the Straits of Malacca

The Straits of Malacca provides half of Malaysia’s total marine fish and seafood supply. Due to depleted fish stock, the Malaysian Government has established a comprehensive legal framework to reduce overfishing in the Straits over the last five decades. However, there are limited scientific studies on the current status of stock recovery. This paper aims to use bioeconomic approach to determine the current trawl fishery status in the Straits. Various statistical tests showed that the Clarke-Yoshimoto-Pooley model was better than the Schnute model in predicting and thus used to estimate the crucial bioeconomic parameters. The current yield and standardised effort of 239,692 tonnes and 931,692 standard fishing days were very close to the estimated biological maximum sustainable yield (239,915 tonnes) and above 18 % of the standardised effort (763,649 standard fishing days) to achieve it. The maximum economic yield was estimated at 201,542 tonnes while the corresponding standardised effort was 396,799 standard fishing days indicating serious economic overfishing in the Straits. If the current effort can be reduced by 57 %, fish biomass and economic rent will increase by 97 % and 835 %, respectively. A price sensitivity analysis predicted that demand-pull fish price inflation could exacerbate the overfishing problem, particularly under unrestrained environment. A 50 % increase in price could lead to a 132 % increase in fishing effort from the base case. The findings of this paper provide valuable insights for fishery managers to refine their existing fishery management program to achieve sustainable fishery for the future.

Finfish Bycatch Diversity of Trawl Fishery of Nagapattinam Coast, Tamil Nadu, South India

Background: The present study was undertaken to analyse the monthly and seasonal finfish bycatch diversity of trawler fishery of Nagapattinam coast situated in the state of Tamil Nadu, South India from January 2017 to August 2019. Methods: Samples of finfish bycatch were collected fortnightly from the commercial shrimp trawlers operating in the coastal waters off Nagapattinam. The collected bycatch of finfish species was identified and month-wise and season-wise trawl finfish bycatch occurrence data collected were subjected to univariate and multivariate analysis using PRIMER Version 6.1.7. software. Result: In this study, the annual average total landing was estimated at 15,414.41 tonnes with an annual average fishing effort of 9327 boat days. Of this total landing, commercial catch constituted 70.75% (10,905.78 tonnes), whereas finfish bycatch formed 21.12% (3,256.14 tonnes) and rest by other groups. The peak fishing effort was observed in every March during the study period. A total of 210 finfish species belonging to 15 orders, 79 families and 153 genera were recorded, in which the order, Perciformes alone shared 53.81% of the total number of species. The monthly univariate analysis revealed that bycatch diversity was the highest in every September and the lowest in every June during the study period, while the season-wise analysis revealed the highest diversity during monsoon seasons. Likewise, the month-wise multivariate analysis performed through cluster analysis divulged the highest similarity between September’17 and September’18, while the season-wise analysis revealed the highest similarity between postmonsoon’17 and postmonsoon’18. Further, the K dominance plot divulged that the highest density of finfish species was in every September and in monsoon seasons during the study period.

A Deep Learning Approach to Assist Sustainability of Demersal Trawling Operations

Bycatch in demersal trawl fisheries challenges their sustainability despite the implementation of the various gear technical regulations. A step towards extended control over the catch process can be established through a real-time catch monitoring tool that will allow fishers to react to unwanted catch compositions. In this study, for the first time in the commercial demersal trawl fishery sector, we introduce an automated catch description that leverages state-of-the-art region based convolutional neural network (Mask R-CNN) architecture and builds upon an in-trawl novel image acquisition system. The system is optimized for applications in Nephrops fishery and enables the classification and count of catch items during fishing operation. The detector robustness was improved with augmentation techniques applied during training on a custom high-resolution dataset obtained during extensive demersal trawling. The resulting algorithms were tested on video footage representing both the normal towing process and haul-back conditions. The algorithm obtained an F-score of 0.79. The resulting automated catch description was compared with the manual catch count showing low absolute error during towing. Current practices in demersal trawl fisheries are carried out without any indications of catch composition nor whether the catch enters the fishing gear. Hence, the proposed solution provides a substantial technical contribution to making this type of fishery more targeted, paving the way to further optimization of fishing activities aiming at increasing target catch while reducing unwanted bycatch.

Comparing size selectivity and exploitation pattern of diamond-mesh codends for Southern velvet shrimp (Metapenaeopsis palmensis) in shrimp trawl fishery of the South China Sea

In this study, size selectivity and exploitation pattern of six diamond-mesh codends with different mesh sizes, ranging from 25 to 54 mm, for Southern velvet shrimp (Metapenaeopsis palmensis) were tested and compared in a shrimp trawl fishery of the South China Sea (SCS). We used a codend with a mesh size of 25 mm (D25) as a starting point, which is the minimum mesh size (MMS) currently regulated in the studied area. Four different fishing population scenarios were applied to quantify and compare how mesh sizes of codends used would impact the size selectivity and exploitation pattern for the target shrimp species. The results demonstrated that the D25 codend was not proper for protecting juvenile shrimp at the studied area. By applying this legal codend, L50 (50% retention length) of the target shrimp species was below its minimum conservation reference size (MCRS, 7.0 cm total length), the retention probability of shrimp with a length of MCRS was above 95% CI [91–99] and more than 43% of undersized shrimp was retained. To mitigate the bycatch issue of undersized shrimp, increasing the mesh size in the diamond mesh codend is a simple and effective option. However, the loss of catch efficiency for marketable shrimp is a major concern while increasing the mesh size. A good compromise between releasing undersized shrimp and maintaining the legal individuals is manifested by using the codend with 35 mm mesh size (D35). Our study will be beneficial for the management of shrimp trawl fisheries in the SCS.