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Maximum Sustainable Yield (msy) Estimates for Industrial Finfish Fishery in Marine Waters of Bangladesh Using Trawl Catch Log

SUMAN BARUA
Department of Fisheries, Marine Fisheries Office, Chattogram, Bangladesh

Abstract/ Executive Summary:

A time series of annual catch per unit effort (CPUE) is derived from commercial logbook data from 2007 to 2018 and used as a tuning series for a Schaefer biomass model. The estimated maximum sustainable yield (MSY) reference points are optimal biomass B_MSY = 206,082 t and optimal harvest rate u_MSY = 38%. The current stock size is estimated to be around 211,000 t and the annual harvest rate around 55%, slightly higher than the estimated optimal stock size and much higher than optimal harvest rate respectively. The average annual catch in last five years was 95,924 t, higher than the estimated MSY of 79,325 t. Overall, the stock is therefore estimated to be in an overfishing state. The catch rate of high value and large demersal species have gradually declined whereas low valued species such as small pelagic and miscellaneous groups have been appeared as major percentage in catch composition for the last couple of years.

Keywords: Finfish, MSY, Trawl catch log, Bay of Bengal

Location: Department of Fisheries, Marine Fisheries Office, Chattogram, Bangladesh

Start Date: 00-00-2017

End Date: 00-00-2018

Program Area: Animal Health and Management

Commodity: Finfish

Objectives:

To estimate the maximum sustainable yield of offshore finfish resources, which may provide information for fishery administrators and fishery biologists in achieving management goals and to take appropriate management strategy for their sustainable exploitation.

Methodology:

Data sources: The time series data (catch and effort) of industrial finfish stock in Bangladesh marine waters since 2007 to 2018 were taken from logbook datasheet from Marine Fisheries Office. Trawl fishing has been restricted by ordinance to operate beyond 40 meters depth contour. Fish trawlers are of two kinds including wooden body and steel hull engaged in fishing in the EEZ of Bangladesh. All wooden body trawlers have chilling facilities and almost all steel hull trawlers have freezing facilities for processing of caught fish. The industrial fishing fleet has a capacity of gross tonnage ranged between 56 to 148 t for wooden body and 251 to 668t for steel hull trawlers. The overall length is ranged from 18.5 to 26.50 meters for wooden body trawlers and 34 to 54 meters for steel hull trawlers. The engine powers are varied from 420-600 BHP for wooden body and 716-1850 BHP for steel hull, but mostly fall within 500-1000 BHP. Industrial trawlers were mainly engaged in harvesting demersal fish and shrimp, but in recent years mid-water trawlers have been added to the fleet coupled with conversion of demersal trawlers into mid-water trawlers for fishing pelagic or epi-pelagic species. There is no bycatch in true sense as almost all fish caught are brought ashore as alternate use of fishes which are not consumed directly. Discarding of trash fish/by-catch at sea is forbidden by Rule 7 of the Marine Fisheries Rules, 1983 (The Bangladesh Gazette 1983). The fin fish trawlers use mostly high opening bottom trawls from the stern side with 60 mm mesh size at the cod-end. The head-rope length in the fish trawler fleet varies from 18m to 32m. The smaller wooden trawlers approved to sail for 14 days and steel-hull vessels for 30 days per trip. They usually complete 5-6 hauls in a day taking 3-3.5 hours per haul. Almost all the trawlers are equipped with modern navigations, communication and fish finding equipment (Barua et. al. 2014). Shrimp trawlers catch finfish too as non-target species. Shrimp trawlers usually have 150-250 t gross tonnage capacity including main engine power of 500-900 BHP. The maximum days of fishing per trip is 30 days. Every day each trawler usually completes 5-6 hauls for a period of 3-4 hours. Though, the fishing days and number of hauling fully depends upon weather and sea worthiness of the vessel itself (Uddin et. al. 2012). Sparre and Venema (1992) suggested a method in which the quantities of yield and CPUE are proportional to effort, where related different types of boats which fished at the same time and in the same fishing ground (Sparre and Venema 1992). The quantity of effort thus estimated is called relative effort. The relative CPUE for each gear and each year was calculated by dividing the CPUE for that year by the mean CPUE of the gear during the studied period. The relative effort is calculated by dividing the total yield of all gears by the sum of relative CPUE weighted by the yields each year. Here, catch (t) and effort (fishing days) of wooden body, steel hull and shrimp trawlers were used for standardizing CPUE in respective years.

Source of Information: Bangladesh J. Fish. (2019) 31(2) : 313-324

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Observed and expected index of industrial finfish catch fitted to the CPUE used for tuning the SPM model. The residue sum of square (RSS) was 0.340and negative log likelihood was -4.35, which are all indicated the fairly precision between observed and expected fit. The standing stock biomass was always above the biomass reference point (206,082 t) since 2009, when the standing stock biomass was almost close to the reference point. The highest biomass was observed 313,478 t in the year 2012. Then, it has gradually been down pace up to the last of the year studied. In 2018, the standing stock biomass was the lowest (211,413 t) since after 2010. The harvest rate was always well below the reference point (0.38) since the inception of population studied. The lowest harvest rate (0.12) was observed in 2010. Then it has gradually increased for rest of the study periods. In 2015-16, its urpassed the reference point and followed same trend in rest of the years. In 2017-18 it rose to the highest up to the period studied (0.55). The catch was well below the MSY reference point since the beginning of the period studied to 2011. From 2012 to 2014, the catches were close to the MSY reference point (79,325 t). Then, the catch had taken increasing trend and it was sharply raised to 116,405 t in the year of 2018. Within a decade, lowest quantity caught by lowest efforts fishery has given the highest catch over the years studied by applying highest efforts. The abundance of large commercial species such as cat fish, croaker, grunters, scads, pomfrets, snappers etc. was higher in catch composition of Lamboeuf report (Lamboeuf 1987). In recent years, the major catch is small pelagic species such as sardine, Indian mackerels and miscellaneous in catch composition.

Knowledge Management: Journal