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American Journal of  
Life Science and Innovation (AJLSI)

Fishing Enclosure as a Simple Approach to Stimulate Spawning Success 
of  Tenualosa ilishaTenualosa ilisha (Hamilton, 1822) in Bangladesh

Mohammad Ashraful Alam1, Flura1, Md. Moniruzzaman1, Md. Hashibur Rahman2*, Md. Abu Kawser Didar1, Md. Abul 
Bashar1, Md. Mehedi Hasan Pramanik1, Khondaker Rashidul Hasan1, Md. Anisur Rahman2, Yahia Mahmud2

Volume 2 Issue 1, Year 2023
ISSN: 2833-1397 (Online)

DOI: https://doi.org/10.54536/ajlsi.v2i1.1164
https://journals.e-palli.com/home/index.php/ajlsi

Article Information ABSTRACT

Received: January 05, 2023

Accepted: January 27, 2023

Published: January 30, 2023

The study was intended to assess the impact of  fishing enclosure during the peak breeding 
time of  hilsa, Tenualosa ilisha on its breeding success. During the last peak breeding season 
of  hilsa (October 4-25, 2021) a comprehensive investigation was attempt to evaluate the 
impact of  fishing enclosure by “MV Rupali Ilish” research vessel, speedboat and experi-
mental fishing net were deployed to demeanor a rigorous investigation in and around the 
spawning grounds areas (about 7,000 sq km, including Moulvirchar, Monpura, Dhalchar and 
Kalirchar). Additionally, data were also assumed from landing stations (via terrestrial cruises) 
near the spawning ground areas and other hilsa prone region of  Bangladesh. The percentage 
of  spent hilsa (locally called pite) and oozing hilsa were monitored following a standard pro-
tocol. Among all the hilsa captured in and around the spawning grounds, the proportion of  
male and female were 16-41% and 85-97%, respectively of  the total catch, suggesting a male 
and female sex ratio (1:2.3). The rate of  breeding success in 2021 was 51.76% i.e., 51.7% 
hilsa successfully participated in the breeding process which was 103.52% higher than the 
base year (2001-02). The approximate number of  fertilized eggs in 2021 was 7,86,314 kg. 
Increased production of  hilsa eggs and jatka indicated a positive impact of  twenty-two days 
fishing enclosure. Percentages of  gravid and oozing hilsa were also found higher compared 
to previous years. Due to the prohibition of  all types of  fishing, the percentage of  female 
hilsa in the breeding areas increased up to 83.96%. Overall, twenty-two days fishing enclo-
sure was found very effective for successful spawning of  hilsa.

Keywords

Fishing Enclosure, Tenualosa 
ilisha, Spawning Success and 
Spent Rate

INTRODUCTION
The national fish hilsa (Tenualosa ilisha, Hamilton, 1822) 
is Bangladesh’s most important open-water species, 
contributing significantly to the country’s economy, 
income, poverty alleviation, employment, and food 
security. The global average yearly production of  the 11 
hilsa fishing nations is >0.72 million tons (Hossain et 
al., 2019), of  which Bangladesh contributes about 80%, 
India 15%, Myanmar 4%, and other nations (such as 
Iraq, Kuwait, Malaysia, Thailand, and Pakistan) 1% (DoF, 
2022). In last 12 years, hilsa production in Bangladesh has 
increased about 81% that reached 5.65 lakh MT in 2020-
21 and annual growth increment in hilsa sector was 3.31% 
(DoF, 2022). Currently, hilsa contributes about 12.2% to 
overall fish production and about 1% to the country’s 
GDP (DoF, 2022). Hilsa has also wraps sociocultural and 
religious values and its non-consumptive value estimated 
approximately US$0.36 billion per annum (Mohammed et 
al., 2016). In the country, around 2.5 million individuals 
are directly or indirectly involved in the catching and 
trading of  hilsa fish (DoF, 2022). 
Hilsa is a typical anadromous shad (Jones, 1951; Pillay, 
1955; Pillay and Rao, 1962, 1963) with a complex life 
cycle. Hilsa reproduces in upstream rivers, where the 
larvae hatch from free-floating eggs. The larvae vary in 
size between 2.3 and 3.1 mm and are drifted by wave 
action and tidal currents to the nursery grounds (Rahman, 
2006). Immature early stages develop in river channels, 
then migrate to the sea to feed and grow before returning 
to the rivers as mature gravid hilsa to complete the life 

cycle (BOBP, 1987; Milton and Chenery, 2003; Hossain 
et al., 2016). Juvenile hilsa remain in the downstream of  
river, albeit they have been found to occur in the upper 
and lower estuaries, and even further down to the coastal 
areas that are far from both their spawning and nursery 
grounds (Hossain et al., 2016). The juvenile hilsa known 
as jatka remain around the nursery grounds for the next 
5-6 months and attain a maximum size of  10-16 cm (Raja, 
1985; BFRI/RS, 1994) in 8542 km2 suitable riverine 
and nearshore coastal waters in Bangladesh (Hossain et 
al.,2016). As the jatka grows bigger with an ability to adapt 
to salinity, they start migrating from brackish-freshwater 
habitats to the offshore or seawards and at 10-16 cm total 
length, all the hilsa complete their migration (BOBP, 1987; 
BFRI/RS, 1994). As the hilsa become sexually mature at 
nearly a year of  age, they start their spawning migration 
into freshwaters (Hossain et al., 2014b).
Hilsa is a high fecund fish that can lay up to 2 million eggs 
(Qureshi, 1968, Shafi et al., 1977, Quddus, 1982, Moula, 
1992, Rahman et al., 1998, Blaber et al., 2001, Haldar, 2004, 
BFRI, 2006-07, Rahman et al., 2017, Rahman et al., 2012). 
Albeit hilsa spawn all the year round, the full moon phase 
in Bengali month Ashwin-Kartik (September-October) 
(Rahman et al., 2012; Saifullah et al., 2004) coincides with 
the peak spawning season. The spawning cycle is closely 
synchronized with the lunar cycle, and intense spawning 
is observed during three-days before and after the new 
moon and the full moon (Miah et al., 1999). During the 
major spawning season, mature gravid hilsa are captured 
in large numbers from the major spawning areas. During 

1 Bangladesh Fisheries Research Institute, Riverine Station, Chandpur, Bangladesh
2 Bangladesh Fisheries Research Institute, Headquarters, Mymensingh, Bangladesh
* Corresponding author’s e-mail: hasibkhan94bfri@gmail.com

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their seaward migration, juvenile hilsa known as jatka 
have also been caught in some of  the major rivers of  the 
country (Ahmed et al., 2010; Rahman et al., 2011, 2012, 
Jaher et al., 2013). During this onward and backward 
migration, widespread unregulated capture of  mature 
and juvenile hilsa can have a serious negative impact on 
hilsa population and affect sustainable production of  the 
country.
In light of  the foregoing, the hilsa Fishery Management 
Action Plan (HFMAP) was developed for the 
management, and conservation of  hilsa, with the goals of  
safeguarding nursery and spawning sites and prohibiting 
indiscriminate killing of  illegal sized hilsa. Under the 
“Fish Protection and Conservation Act-1950”, so far six 
hilsa sanctuaries and four major spawning grounds have 
been established in the country’s coastal and freshwater 
zones for the successful conservation of  jatka and brood 
hilsa (Figures 3; Tables 3 and 4). The results of  BFRI, RS 
research showed that a high number of  matured gravid 
hilsa congregate at the spawning grounds for breeding 
during the peak spawning time, which coincides with 
the lunar periodicity, and more especially the full moon 
phase (Reuben et al., 1992; Rahman and Cowx, 2008, 
Rahman et al., 2017). At this time, matured gravid hilsa are 
indiscriminately captured, which has a negative impact 
on spawning and hilsa population BoBLME (2012). As 
a result, in accordance with HFMAP recommendations, 
fishing closure has been imposed to ensure the safe and 
successful spawning of  hilsa. This enclosure last for 22 
days, from 4th-25th October in 2021, and included a new 
moon and full moon day (Bengali month Ashwin,1427), 

(Table 1 and Figure 1). During this time, all types of  
commercial trawlers fishing in the sea, coastal regions, 
and rivers were restricted under the Marine Fisheries 
Ordinance 1983, Section 55, Sub-section 2 (D) for safe 
hilsa migration and spawning. 
Fisheries enclosures may be temporary or ongoing and have 
a variety of  justifications. For instance, fishing restrictions 
have been employed extensively in fisheries management 
to prevent overfishing and the collapse of  a fishery, restore 
depleted stocks, and limit bycatch of  protected species 
(National Oceanic and Atmospheric Administration 
(NOAA), 1985; Gell and Roberts, 2002; Farmer et al., 2016; 
Agar et al., 2019). Fishing enclosures have occasionally 
been implemented during a species’ breeding or spawning 
season in an effort to directly minimize fishing mortality 
and to increase the number of  eggs produced annually 
(Murawski et al., 2000; Arendse et al., 2007). There are 
many examples of  fishing enclosures around the world, for 
example; it has been implemented in the Gulf  of  Mexico 
shrimp fishery and Florida lobster fishery [National 
Oceanic and Atmospheric Administration (NOAA), 1985; 
Beets and Manuel, 2007], United States Virgin Islands 
grouper fishery (Beets and Friedlander, 1999) and coral 
reefs in Kenya (McClanahan, 2010).
In Bangladesh, the Department of  Fisheries (DoF) 
enacted the fishing enclosure in collaboration with law 
enforcement organizations such as the Navy, Coast 
Guards, River Police, and Air Force based on the findings 
of  BFRI, RS. The impact of  fishing enclosure seems to 
have a positive impact on the overall hilsa product of  the 
country.

Table 1: Management interventions for jatka and brood hilsa conservation in the major spawning and nursery 
grounds of  hilsa in Bangladesh.
Year Management system                                              Considering issues
2001-02                   Conventional Without any management
2002-03                Conventional Traditional (improved) management
2003-04               Jatka conservation Protection system
2004-05               Jatka conservation Protection system
2005-06             Jatka conservation+sanctuary Full Moon basis
2006-10          Jatka conservation+sanctuary+10 days hilsa fishing enclosure Full Moon basis
2011-12          Jatka conservation+sanctuary+11 days hilsa fishing enclosure Full Moon basis
2012-13         Jatka conservation+sanctuary+11 days hilsa fishing enclosure Full Moon basis
2013-14           Jatka conservation+sanctuary+11 days hilsa fishing enclosure Full Moon basis
2014-15          Jatka conservation+sanctuary+15 days hilsa fishing enclosure Full Moon basis
2015-16         Jatka conservation+sanctuary+15 days hilsa fishing enclosure Full Moon basis

Figure 1: New moon and full moon dependent fishing enclosure time in Bangladesh.
* ET= Enclosure time, FM= Full moon day, NM= New moon day

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METHODOLOGY
Preparation of  Hilsa Research Team
The Hilsa Research Team of  BFRI, RS, Chandpur carried 
out all the investigations. Two ways were selected for 
sampling and data collection such as:

a. Research vessel (M.V. Rupali Ilish with speed boat) 
trip (Figure 4) and

b. Research trip with necessary research equipment’s by 
using local transport system
Five research teams were formed to conduct a 
comprehensive investigation in the designated hilsa 

spawning and sanctuary areas (Table 2 and 3). The nursery 
grounds were chosen as sampling sites because: (a) hilsa 
shed their eggs in almost all major river systems across 
the country during the breeding season, but the spawning 
grounds (Figure 3) grasp 80-90% of  them; (b) hilsa eggs 
and larvae begin drifting and shifting to upstream rivers 
shortly after spawning; and (c) hilsa is a migratory fish 
that may travel a long distance after spawning and be 
captured there. As a result, a large sampling area was 
chosen to provide precise information on the percentage 
of  spent, oozing, and gravid hilsa.

Figure 2: Monthly GSI study of  hilsa

Figure 3: Major spawning grounds of  hilsa in the Meghna River estuary with approximate GPS point (Source: BFRI 
and GEF studies).

Table 2: Areas of  spawning grounds in Bangladesh.
Sl No. Directions Contour Areas (sq km) District
1 East-North Mayani-Mirarsorai 125 Chittagong
2 West-North Paschim Syed Aowlia-Tojumuddin 80 Bhola
3 East-South Gondamara-Bashkhali 120 Cox’s Bazar
4 West-South Latachapali-Kolapara 194 Patuakhali

Source: Bangladesh gazette 28 May, 2014, MoFL

Figure 4: Hilsa research vessel ‘MV Rupali Ilish

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Standard Formula (Rahman et al., 2009 and Rahman 
et al., 2017)
The number of  hilsa rescued and total fertilized eggs as a 
result of  the fishing enclosure were determined using the 
following formula:
No. of  hilsa saved due to fishing enclosure (TN) = Nos. 
of  fishing boat*Nos. of  haul/day*Nos. of  fish captured/ 
Nos. of  haul* ..........1
Nos. of  days TN*FF*SF*EF/1000...............(2)
Where,  

TN = Total No. of  hilsa excluded due to fishing 
enclosure;

EF = % of  female fishes in the study areas;        

SF = % of  spent/oozing fish, and 
EF = Average egg (g) per fish

Site Selection
The major hilsa spawning grounds, nursery grounds 
and fish landing sites (13 districts) in Bangladesh were 
selected for investigation (Table 5 and Figure 5). These 
sites account for the majority of  spawning hilsa during 
the peak spawning season, through which the country’s 
major river systems are flowing including the river Padma 
and Meghna. Furthermore, samples were collected from 
Chattagram and Cox’s Bazar, where the majority of  
marine hilsa are gathered for vending.

Table 3: Six established sanctuary areas of  T. ilisha.
Sl. No. Sanctuary area Length River Enclosure period District
1. Shatnol-Char Alexander 100 km Lower Meghna estuary March-April Chandpur-Laxmipur
2. Char Ilisha-Char Pial 90 km Stretch of  Shahbajpur 

Channel, tributary of  the 
Meghna River 

March-April Bhola

3. Bheduria-Char Rustam 100 km Stretch of  Tetulia river March-April Bhola-Patuakhali
4. Kalapara Golbunia- 

Confluence of  Bay of  
Bengal and Andharmanik 
river

40 km Andharmanik river November-January Patuakhali

5. Tarabunia-Vomkora 20 km Lower Padma River March-April Shariatpur
6. Habinagar, Barisal Sadar-

Hizla- Mehendigonj
82 Km Meghna River March-April Barisal

Source: Bangladesh gazette 28 May, 2014 and 17 April, 2018, MoFL

Data collection time frame
Three sequential time frames were selected for sampling 
and data acquisition by the Hilsa Research Team such as:
i) Before the enclosure period (05 days) 
ii) Whole enclosure period (22 days) 
iii) After the enclosure period (05 days)

Determination of  size, sex and percent composition 
of  gravid/berried hilsa
The length (cm) and weight (g) of  collected hilsa samples 
were measured at different sampling locations (Table 4). 

The length was measured using a wooden scale and weight 
with a digital balance, respectively. External observation 
and steady light pressure from the tip of  the ventral squat 
to the anus of  the belly were used to identify the sex of  
hilsa fish. 
The fish exhaling liquid cream while stripping was 
considered as male; on the contrary, the fish extruding 
eggs and a light reddish substance were considered as 
a female hilsa. Female hilsa were also detected with a 
potbellied reddish and larger anus. If  neither of  this milk/
eggs come out, the fish were considered as immature 

Table 4: Selected sites for sampling
SL. No. Sites District River/Sea
1. Chandpur, Katakhali, Horinaghat, Haimchar and Charvoirobi Chandpur Meghna
2. Hizla, Mehendiganj, Ulania Barishal Meghna
3. Ramgoti, Char Alexandar Laxmipur Meghna
4. Tanki Bazar, Chairman ghat, Hatia Noakhali Meghna estuary
5. Dhalchar, Moulovirchar, Daulatkhan, Monpura Bhola Meghna estuary
6. Kalirchar, Patharghata Barguna Meghna estuary
7. Mohipur, Galachipa, Kalapara Patuakhali Andharmanik
8. Tarabunia Shariatpur Padma
9. Godagari Rajshahi Padma
10. Mawa Munshigonj Padma
11. Fishery Ghat Chattagram Sea
12. BFDC Ghat Cox’s Bazar Sea
13. BFDC Ghat Khulna Sea

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Figure 5: Thirteen districts on the map of  Bangladesh 
from where data were collected during fishing enclosure.

(jatka) or partly mature. Female hilsa were often found 
larger in length than male hilsa.

Identification of  Spent (pite ‘in local language) and 
Oozing (spawning) hilsa
The spent hilsa were characterized by some external 
features like skinny, squeezed stomach, and an extended 
slender body. If  watery liquid or blood emerges with the 

alienated and malformed egg after light pressure on the 
abdomen, it was labeled as the spent hilsa (‘pite’ in the 
local language). After being captured from the river, spent 
hilsa were quite feeble. Usually fishers keep spent hilsa for 
their own household consumption and don’t bring them 
to the market because they diminish the market value 
of  other fish. Oozing hilsa were recognized by studying 
their egg-laying state, which is characterized by ripe eggs 
erupting spontaneously without any pressure on the 
abdomen (Figure 6). 

Gonadosomatic index of  hilsa
During the investigation, the sex of  at least 30 individual 
specimens were observed by abdominal incision and 
ocular examination of  the gonad. The gonads were 
meticulously stripped of  all fat, connective tissue, 
and blood vessels, and their gonadal weight (GW) was 
calculated to the nearest 0.001 g. The gonadosomatic 
index (GSI) was determined using the following formula: 
GSI = GW × 100/BW (Nikolsky, 1963)

Determining the (%) of  Spent (pite) hilsa
The Hilsa Research Team of  BFRI determined the 
number and rate of  spent hilsa primarily from hilsa 
captured using experimental nets in the breeding grounds 
and surveillance of  commercial fish landing sites around 
the breeding grounds.

Figure 6: Pictorial views of  spent and oozing hilsa.

Calculation of  Fertilized Eggs 
During the fishing enclosure, the approximate number of  
fertilized eggs (Figure 7) released by hilsa in the spawning 
grounds were estimated using the following formula:
The plausible amount of  egg production due to the 
fishing enclosure was:
Approximate Egg Production = {(54*22*15500*75/100) 
*(51.76/100*110)}/1000 = 7,86,314kg
Where, No. of  matured hilsa captured in per unit effort 

= 27 (Two haul/day; = 54); Total nos. of  enclosure 
days = 22 days; Approximate number of  fishing boats 
= 15500; Total area of  spawning ground =7000sq km, 
on an average 2 fishing boats are operated in per sq. km; 
Average percentage of  matured female during the fishing 
enclosure = 75%; Average percentage of  spent hilsa 
during the fishing enclosure = 51.76%; Average weight 
of  gonad of  matured female = 110g; One kilogram = 
1000g.

Figure 7: Pictorial views of  hilsa eggs.

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Calculation of  jatka Production
The number of  fry and jatka production were calculated 
based on 50% hatching rate of  fertilized eggs and 10% 
survival rate of  hatched larvae.

Size, Weight, Age and CPUE Calculation of  hilsa fry 
and jatka 
Hilsa larvae were collected from the spawning grounds 
and adjacent sites by means of  BFRI experimental fishing 
net (made of  glass nylon fiber) (Figure 8). A measuring 
scale and a digital balance were used to determine the 
length and weight of  hilsa larvae and jatka. The amount 
of  jatka (kg) captured in a 100 m net per hour per boat 
was delineated as the catch per unit effort (CPUE).

Observations of  Other Impacts of  Fishing Enclosure
To observe the additional benefit of  the 22-day fishing 
enclosure, larvae and juveniles of  other fish species were 
collected from the spawning grounds and adjacent sites 
using a BFRI experimental fishing net (made of  glass 
nylon fiber: mouth diameter - 15 ft, length from the 
mouth to the end - 25 ft, loop size - zero, and fishing time 
was 30 minutes) (Figure 8).

majority of  the hilsa captured in the downstream rivers 
were greater than 35 cm (>74% in Bhola and Barishal) 
(Figure 9). Furthermore, most of  the hilsa (80-90%) 
captured at the down stretches of  the Meghna estuaries 
were gravid female. Ahmed et al. (2010) found 77-84% of  
hilsa at Ramgoti and 86-92% of  hilsa at Hatia under the 
size class of  36-52 cm whereas smaller sized (18-36 cm) 
hilsa ranged between 8-23%. On the contrary, Rahman et al. 
(2009, 2013, 2015 and 2017) investigated the influence of  
fishing enclosure on hilsa spawning grounds and revealed 
larger percentage (90%, 95% and 85%, respectively) of  
hilsa comprising length groups greater than 30-35 cm in 
the Monpura and Hatia areas. Almukhtar et al. (2016) also 
found size discrepancies in T. ilisha migrating in the Shatt 
Al Arab River and Southern Al Hammar Marsh, Basra, 
Iraq. Rahman et al. (2012) categorized hilsa into four 
size groups, small (<30 cm), medium (30–39 cm), large 
(40–49) cm and extra-large (>50 cm) and found more 
than 90% hilsa within the range of  30–40 cm during their 
investigation. The data from a recent survey by phone 
to fish vendors (2013–14) conducted under the ESPA-
Deltas project in some of  the largest hilsa landing centers 
and markets of  the Bangladesh coast showed that 90% of  
the hilsa ranged from 25–75 cm (Fernandes et al., 2016). 
However, Dutta et al. (2012) found the maximum length 
of  hilsa 45.5 cm in their studies. In general, commercial 
catches in both Bangladesh and Indian waters showed a 
general size range of  about 15–52 cm (Azad et al., 1987; 
Gupta, 1989; Rahman, 2006).
Aside from the spatial variation of  L-F, an apparent 
temporal variation in the length class of  hilsa was also 
noticed. Normally, 30-35 cm length class predominated 
before and after the enclosure period, whereas mature 
hilsa (egg bearing female, >40 cm) predominated during 
the spawning time (Figure 10). Ahmed et al., 2010; 
Rahman et al., 2011, 2012, Jaher et al., 2013 and Rahman 
et al. (2017) Alam et al. (2019) also found an alteration 
of  the hilsa length class before and after the spawning 
time. The proportion of  male and female hilsa also varied 
significantly before and after the prohibition period, 
indicating an uneven hilsa sex ratio. Before and during 
the prohibition, the average proportion of  male hilsa 
was 3-14%, rising to 16-41% during the enclosure period 
(October 4-October 25). However, before and during the 
restriction period, the average proportion of  female hilsa 
was 56-89%, raised up to 85-97% during the enclosure 
period (October 4- October 25). These findings differed 

Figure 8: Experimental fishing net for collecting juvenile 
hilsa.

Data Analysis
The data were compiled and processed using Microsoft 
Excel (version 2016). Graphical representation of  data 
was also prepared by Microsoft Excel. 

Result and Discussion
Size and Sex Ratio of  hilsa
The majority of  the hilsa captured in the upstream rivers 
were smaller than 35 cm (50% in Chandpur), whereas the 

Figure 9: Percentage of  different length-classes of  hilsa at upstream and downstream of  rivers in Bangladesh.

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Figure 10: Percentage of  different length class’s male and female hilsa before, after and during the ban period in the 
major spawning grounds of  hilsa in Bangladesh

to some extent from those of  Haldar et al. (2004), who 
observed a male-female sex ratio of  1:2 in the main 
spawning sites of  hilsa. In a separate study, Islam et al. 
(1987) found a male-female sex ratio of  hilsa 1:1.08 in the 
upper stretches of  Meghna River (Chandpur). In previous 
BFRI conducted investigation, Rahman et al. (2009) 
noticed 35% male and 65% female, whereas Ahmad et 
al. (2010) found almost 4.2% male and 95.8% female in 
and around the spawning grounds among all the captured 
hilsa. During the monsoon, Quereshi (1968) observed 
a male-female sex ratio of  1:1, although the female was 
dominating in October. According to Blaber et al. (2001) 
males are more abundant among smaller fish. The bias in 
the sex ratio of  T. ilisha suggests that males may not live 
as long as females (Mahmud, 2020). 

Percent composition of  spent and oozing hilsa
Approximately, 2100 hilsa were examined throughout 
this study where a substantial number of  spent and 
oozing hilsa were found during the study period. The 

overall fraction of  oozing and spent hilsa were 32.4% 
and 51.7%, respectively (about 84%, combing both). The 
results indicated that fishing enclosure ensured successful 
breeding as also found by Ahmed et al. (2010); Rahman et 
al. (2011 and 2012); Jaher et al. (2013) and   Rahman et al. 
(2017) during their studies. 
In 2001-02, the percentage of  spent hilsa was >1%. The 
percentage of  spent hilsa has steadily increased until 
recent years (103% higher in 2020-21 than in 2009-10), 
due to the successful deployment of  a fishing closure 
during the peak spawning season (Figure 11).  
Rahman et al. (2009) found 1.51% oozing and 5% spent 
hilsa during the fishing ban period in the spawning 
grounds and it was about 2.80-3.57 times higher than 
the Global Environment Facility (GEF) and Bangladesh 
Fisheries Research institute (BFRI) studies of  2002 and 
2003. The occurrence of  spent hilsa ranged between 
5-39% in 2007-09 which was estimated 76% higher than 
the previous studies (Ahmed et al., 2010). The percentage 
of  spent hilsa was about 34% in 2010; 36% in 2011 and 

Table 5: Percent composition of  spent and oozing hilsa during the enclosure period. 
Status of  hilsa 
breeding

Sampling points
Cox’s Bazar Ramgoti Chandpur Potuakhali Monpura Average

Oozing 98 (31%) 950(62%) 72 (13%) 16 (17%) 19 (39%) 32.4%
Spent 147 (52%) 455 (31%) 287 (42%) 32 (71%) 16 (63%) 51.76%
Total Number 245 1405 359 48 35 2092

Figure 11: Percentage and change of  spent hilsa in different years in Bangladesh.

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2012; 41% in 2013; 39% in 2014; 37% in 2015; 44% in 
2016 (Rahman et al., 2017). 

Production of  fertilized eggs and jatka during the 
fishing enclosure period and spawning success
The total egg production of  hilsa was determined 
using the BFRI’s standard formula. Due to the fishing 
prohibition, approximately 7,86,314 kg of  hilsa eggs 
(Figure 12) were produced in 2021-22. If  50% of  the 
eggs produced are fertilized and hatched, and 10% of  
them survive, then approximately 7,86,314 crores of  hilsa 
fry and 39.31 crores of  jatka (Figure 12) were recruited 
into the hilsa population. These studies suggested that 
increasing the number of  enclosure days (10 days from 
2007-08 to 2010-11; 11days from 2011-12 to 2013-14; 15 
days from 2014-15 to 2015-16; and 22 days from 2016-
17 to 2020-21) had a positive impact on egg and jatka 

production. In the current year (2020-21), egg production 
augmented about 17 times, while fry and jatka production 
increased approximately 16.2 times than the year 2007-08 
when fishing enclosure during the peak spawning time 
started to be implemented. Each year, the recruitment of  
this significant number of  jatka to the hilsa population as 
a result of  the fishing restriction resulted in a consistent 
and increased production of  hilsa in Bangladesh (Figure 
14). Haldar (2004) and Ahmed et al., 2010; Rahman et 
al., 2011, 2012, Jaher et al., 2013 Rahman et al. (2017), 
Mahmud et al. (2020) stated that a total fishing prohibition 
has a significant positive impact on jatka abundance as 
well as the country’s overall hilsa production. Seasonal 
closure during the breeding or spawning period of  species 
directly reduces fishing mortality and thereby achieving 
greater annual reproductive output (Murawski et al., 2000; 
Arendse et al., 2007).

CPUE of  hilsa fry and jatka
The CPUE of  jatka (19.94 kg/100 m net/boat/hr) of  the 
current year (2021-22) demonstrated 18 times increment 
compared to the base year, and it was roughly 1.8 times 
higher in amount than the previous year (2019-20) (Figure 
13). Nevertheless, current CPUE is about four times 
greater than the study conducted by Rahman et al. (2017). 

Successful spawning of  higher percentage of  hilsa due 
to fishing closure resulted in increased CPUE of  jatka 
in the country (Alam et al., 2019a, 2019b and Mahmud et 
al. (2020). Kamal et al. (2015) found significantly higher 
CPUE while studying the effects of  seasonal closure in a 
multispecies fishery.

Figure 12: Approximate number of  eggs, fry and jatka production in the major spawning grounds.

Figure 13: CPUE of  jatka in the selected sampling sites.

Total hilsa production of  the country
The hilsa production in the country was 1,99,032 MT in 
2002-03, 2,79,189 MT in 2006-07, and in last year (2020-
21) it reached at 5,65,183 MT (DoF, 2021). The overall 
hilsa production of  the country has increased roughly 
2.77 times since 2002-03 and about 2.0 times since 2006-
07 through implementation of  fishing closure by all 

relevant government agencies (Figure 14). All previous 
investigators of  BFRI (Ahmed et al., 2010; Rahman et al., 
2011 and 2012; Jaher et al., 2013 and   Rahman et al., 2017) 
concluded that hilsa production is gradually increasing 
in the country due to the stricter implementation of  
management interventions especially fishing closure 
during the peak spawning time of  hilsa. Beets and 

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Manuel (2007) noted that, the temporal and seasonal 
closures used in fisheries management in tropical and 
subtropical regions have been useful and beneficial based 
on perceived benefits and annual production (Beets and 
Manuel, 2007). 

Availability of  hilsa and other fish’s larvae in 
experimental nets (indicator of  breeding success)
In the breeding grounds, a glass nylon fiber net was used 
to gather larvae at high and low tide (Figure 8). During 
low tide, around 29% of  hilsa larvae were detected in 

the experimental net, whereas 71% were other fish’s 
larvae. During high tide, however, hilsa larvae were 
56%, whereas other fish’s larvae were 44%. Overall, 
85% of  hilsa larvae were found during high and low tide 
(Figure 15). The total number of  larvae gathered during 
high and low tides varied significantly; at high tide, the 
number of  larvae was greater than at low tide (Figure 
16). Shrimp, chewa, poa, shillong, kakila, baim, chanda, 
kuchia, bele, and other fish larvae were found with the 
other fish’s larvae. According to the International Union 
for Conservation of  Nature’s (IUCN, 2015) biodiversity 
status of  Bangladesh and global biodiversity, many of  
these species are threatened (vulnerable, endangered, or 
least concern) (Table 6). After the breeding season, hilsa 
larvae (Figure 17) begin to migrate to the primary nursery 
grounds, where they develop into juveniles and then jatka. 

In a month, hilsa larvae develop from 2 to 2.5 cm (Haldar, 
2004). The spawning success of  hilsa is indicated by the 
presence of  hilsa juveniles (Figure 17) in various nursery 
grounds/sanctuary areas. During BFRI’s experimental 
fishing, a large number of  hilsa juveniles were found in 
the nursery grounds (Figure 17), with an estimated age of  
30-45 days. Rahman et al. (2017) found the similar positive 
impact of  fishing closure on abundance of  hilsa and other 
fish’s larvae. In another study, Kincaid and Rose (2017) 
found that biological community assemblages changed 
significantly before–after and inside–outside the closing 
time and area. Kamal et al. (2015) studied the effects of  
seasonal closures in a multi-specific fishery and found 
that depending on its timing, the closure would highlight 
some positive biological effects on some target species.

Figure 14: Total hilsa production of  the country (Freshwater and Marine)

Figure 15: Percentage of  hilsa and other’s fish larvae 
during high and low tide

Figure 16: Abundance of  hilsa larvae in the spawning 
grounds.

Figure 17: Observations of  hilsa juveniles.      

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CONCLUSION
The result obtained in this study is an approximation that 
may be adjusted for a variety of  criteria such as the number 
of  fishing boats, those who did not fish, the number of  
specimens used in the calculation of  spent hilsa, and 
the weight of  the female hilsa’s ovaries. Furthermore, 
a variety of  biotic and abiotic factors such as (plankton 
composition, temperature, dissolved oxygen, pH, carbon 
dioxide, alkalinity, hardness, turbidity, transparency, 
conductivity, rainfall, and river discharge, among others) 
may play a significant role in hilsa larvae egg production 
and hatching in different years, as well as overall breeding 
success. Furthermore, it is impossible to identify which 
elements are most relevant for hilsa breeding success and 
increased output without a controlled laboratory trial 
(successful implementation of  different management 
interventions or ecological suitability of  biotic or abiotic 
factors). However, because hilsa production is steadily 
growing with the implementation of  management 
measures, it is possible that this will have some beneficial 
effects.

RECOMMENDATIONS
The fishing closure should be continued to safeguard 
mature gravid hilsa and to protect jatka. Fishing 
enclosure should be implemented in combination with 
other management interventions like gear restrictions, 
area closure. The existing spawning grounds and nursery 
grounds should be protected and managed effectively. 
Additional research is needed to identify new hilsa 
nursery and breeding sites. The logistic support should 
be increased to conduct comprehensive on the impact of  
fishing closure.

Acknowledgement
It is also great pleasure for the investigators to express 
their sincere and deep sense of  gratitude and indebtedness 
to Bangladesh Fisheries Research Institute (BFRI) for 
providing financial support. The investigators also express 
their profound indebtedness and sincere gratitude to 
the Director General of  Bangladesh Fisheries Research 

Institute (BFRI), Mymensingh for his continuous 
support, encouragement and kind cooperation to carry 
out this research works.

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Sl. No. Local name Group name Scientific name IUCN (2015)

 BD status*
IUCN (2015) 
GB status*

1. Bele Mudskippers Glossogobius giuris LC LC
2. Chela Barbs and Minnows Salmostoma acinace LC LC
3. Cuchia Eels Monopterus cuchia VU LC
4. Red Chewa Mudskippers Odontamblyopus rubicundus LC NE
5. Vacha Catfishes Eutropiichthys vacha LC LC
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12. Khorsula Mullets Rhinomugil corsula LC LC
13. Kholisa Labyrinth fishes Trichogaster fasciata LC NE

*BD = Bangladesh; GB = Global; En = Endangered; Vu = Vulnerable; Lc = Least Concern; NE = Not endangered

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