Monitoring Condition Factorof the Dominant Fin Fishesin the Estuaries of Lower Gangetic Deltain the Backdrop of Climate Change

Ankita Mitra, Sufia Zaman, Prosenjit Pramanick and Shampa Mitra

Abstract The current global fisheries production is *160 million tonnes. Thequantum is gradually rising as a result of increases in aquaculture production.A number of climate-related threats to capture both the fisheries and aquaculture areidentified, but we have high uncertainty in predictions of the future fisheries pro-duction because of uncertainty over the future global aquatic net primary produc-tion and the transfer of this production through the food chain to humanconsumption. Recent changes in the distribution and productivity of a number offish species can be ascribed with high confidence to regional climate variability,such as the El Niño–Southern Oscillation. The future production may increase insome high-latitude regions because of warming and decreased ice cover, but thedynamics in low-latitude regions are governed by different processes, and pro-duction may decline as a result of reduced vertical mixing of the water column and,hence, reduced recycling of nutrients. There are strong interactions between theeffects of fishing and the effects of climate because fishing reduces the age, size andgeographic diversity of populations and the biodiversity of marine ecosystems,making both more sensitive to additional stresses such as climate change-inducedsalinity oscillation. The estuaries in the lower Gangetic delta at the apex of Bay ofBengal are noted for contrasting spatial variation of salinity. The Hooghly estuaryin the western sector is relatively low saline compared to the Matla estuary in thecentral sector on account of receiving the fresh water discharge from the Farakkabarrage. The central sector is hyper saline due to siltation of the Bidyadhari Riversince the late fifteenth century. The present study evaluates the condition factor offourteen commercially important fin fish species (that constitute *75 % of thefishes in the catch basket) collected from the Hooghly and Matla estuaries in thewestern and central sectors of the lower Gangetic delta, respectively. Relatively

A. Mitra (&)Department of Ecology and Environmental Sciences,School of Life Sciences, Puducherry, Indiae-mail: mitrankita92@gmail.com

S. Zaman � P. Pramanick � S. MitraDepartment of Oceanography, Techno India University,Salt Lake Campus, Kolkata 700091, India

© Springer International Publishing Switzerland 2016S. Nautiyal et al. (eds.), Climate Change Challenge (3C)and Social-Economic-Ecological Interface-Building, Environmental Science,DOI 10.1007/978-3-319-31014-5_20

347

higher values of condition factor of all the species collected from the Hooghlyestuary (compared to those collected from the Matla estuary) confirm the adverseeffect of hyper salinity on the growth and condition factor of the species.

Keywords Salinity � Condition index � Fin fish � Climate change

1 Introduction

The lower Gangetic delta at apex of Bay of Bengal sustains a wide spectrum of finfishes. The litter and detritus contributed by mangroves provide nutrition to the fishcommunity by triggering the growth of plankton. The fish fauna of the presentstudy area may be classified into residents and transients (migrants). The specieswhose individuals of different sizes are present during all the months of the year inany zone of the estuary are referred to as resident species. The important residentfinfish species are Mugil parsia, M. tade, Polynemus paradiseus, Polydactylusindicus, Otolithoides biauritus, Lates calcarifer, Hilsa toli, Arius jella, Harpodonnehereus, Setipinna taty, Ilisha elongata, Setipinna phasa, Coilia ramcarati, Pamapama and Sillaginopsis panijus. The transient or migratory fishes enter and stay inthe Bay of Bengal associated estuaries for a short period. Depending on theirmigratory pattern and direction, the migrants are divided into three categories(Jhingran 1982; Mitra 2013): (1) Marine forms that migrate upstream and spawn infreshwater areas of the estuary such as Tenualosa ilisha, P. paradiseus, S. panijusand P. pama, (2) Freshwater species, which spawn in saline area of the estuary suchas Pangasius pangasius, and (3) Marine species, that spawn in less saline water ofthe estuary such as A. jella, Osteogeneious militaris and Polydactylus indicus.

Two important estuaries in the lower Gangetic delta are the Hooghly and theMatla estuaries. These two estuaries exhibit pronounced variation with respect tosalinity. The Hooghly estuary in the western sector is relatively low saline com-pared to the Matla estuary in the central sector. This contrasting salinity may beattributed to discharge of fresh water through Farakka barrage in the Hooghlyestuary and complete closure of fresh water discharge in the Matla estuary due tosiltation of the Bidyadhari River since the late fifteenth century. The difference insalinity has profound influence on the condition factor of the fin fishes, which hasbeen attempted to study in the present programme.

Our main aim is to determine the impact of salinity variation on the conditionfactor of the selected fin fish species as the price of the fish mostly depends on theirgrowth (in terms of length and weight).

348 A. Mitra et al.

2 Materials and Methods

The entire network of the present study consists of the collection of 100 individualsof the selected species (T. ilisha, Pama pama, Pampus spp., Ilisha elongate, L.calcarifer, P. pangasius, Liza parsia, Liza tade, Tenualosa toli, P. paradiseus, O.biauritus, Tachysurus jella, Sciaena biauritus, Eleutheronema tetradactylum) fromthe two major estuaries in the study area namely Hooghly (in the western sector)and Matla (in the central sector). The sampling stations selected for the presentstudy are Diamond Harbour (in the Hooghly estuary) and Canning (in the Matlaestuary). Individual length and weight of the individuals of the selected specieswere measured to evaluate the condition factor (Chow and Sandifer 1991) as per thefollowing expression:

K ¼ �w

ðTLÞ3 � 103

where K is the condition factor, �w is the average weight (g) and TL is the averagetotal length (cm).

The secondary data of surface water salinity were obtained from the data bankcited by Ray Choudhury et al. (2014), Chakraborty et al. (2013), Mitra (2013),Sengupta et al. (2013), Mitra and Zaman (2014) and Mitra and Zaman (2015).

3 Results

It is evident that condition factor is relatively higher for the fin fish species collectedfrom the Hooghly estuary compared to those collected from the Matla estuarinewater (Table 1). This may be attributed to variation in aquatic salinity as evidencedfrom the secondary data bank. The Hooghly estuarine water is relatively hyposalineas compared to the water of Matla estuary in the central sector of the study area(Figs. 1 and 2).

Monitoring Condition Factor of the Dominant Fin Fishes … 349

Table 1 Condition factors of the selected fin fish species in the western and central sectors of thestudy area

Sl.No.

Commercially important fin fish Western sector(Hooghly estuary)

Central sector(Matla estuary)

1

Tenualosa ilisha (Family:Clupeidae)

0.942 0

2

Pama pama (Family: Sciaenidae)

1.009 0.595

3

Pampus spp. (Family:Stromateidae)

1.018 0

4

Ilisha elongata (Family:Pristigasteridae)

0.895 0

5

Lates calcarifer (Family:Centropomidae)

1.619 0.492

6

Pangasius pangasius (Family:Pangasiidae)

0.884 0.578

(continued)

350 A. Mitra et al.

Table 1 (continued)

Sl.No.

Commercially important fin fish Western sector(Hooghly estuary)

Central sector(Matla estuary)

7

Liza parsia (Family: Mugilidae)

0.986 0.713

8

Liza tade (Family: Mugilidae)

0.778 0.709

9

Tenualosa toli (Family: Clupeidae)

0.992 0.679

10

Polynemus paradiseus (Family:Polynemidae)

0.899 0.697

11

Otolithoides biauritus (Family:Sciaenidae)

1.009 0.918

12

Tachysurus jella (Family: Ariidae)

1.129 0.743

(continued)

Monitoring Condition Factor of the Dominant Fin Fishes … 351

Table 1 (continued)

Sl.No.

Commercially important fin fish Western sector(Hooghly estuary)

Central sector(Matla estuary)

13

Sciaena biauritus (Family:Sciaenidae)

1.099 0.992

14

Eleutheronema tetradactylum(Family: Polynemidae)

0.994 0.788

Note The value 0 (zero) represents the nonavailability of the species in the estuarine water

Fig. 1 Decreasing trend of surface water salinity in western sector of the study area over a periodof 31 years

Fig. 2 Increasing trend of surface water salinity in central sector of the study area over a period of31 years

352 A. Mitra et al.

4 Discussion

Climate change has both direct and indirect impacts on fish stocks which areexploited commercially preferably for the livelihood. Direct effects act on physi-ology and behaviour of fishes and alter their growth, reproduction, mortality anddistribution. Indirect effects encompass events like alteration of aquatic produc-tivity, biotic community structure and composition of the marine and estuarineecosystems on which fishes depend for food and survival. Changes in primary andsecondary production will obviously have a major effect on fisheries production,but it is not possible in the current state of knowledge to make accurate quantitativepredictions of changes in global marine primary production solely due to climatechange-induced salinity alteration (Mitra 2013).

In this paper, we used condition factor as proxy to assess the impact of salinity onthe fish community of the lower Gangetic delta complex. Condition factor is anindication of the well being of an organism and is based on the hypothesis that heavierfish of a given length are in a better condition (Bagenal and Tesch 1978; Abowei andGeorge 2009). It has been used as an index of growth and feeding intensity (Fagade1979; Abowei et al. 2009), decreases with increase in length (Bakare 1970; Fagade1979; Abowei 2009) and also influences the reproductive cycle in fish.

Our first order analysis from the data sets of two fish landing stations (DiamondHarbour in the western sector and Canning in the central sector of lower Gangeticdelta region) clearly reflect a pronounced variation between the two sectors.Significantly higher values of condition index in fin fish were observed from thefish catch of Diamond Harbour, where the aquatic phase is congenial in terms ofsalinity (Mitra 2013). This congenial salinity may be attributed to Farakka barragedischarge situated in the upstream region of Ganga–Bhagirathi–Hooghly riversystem. 10-year surveys (1999–2008) on water discharge from Farakka damrevealed an average discharge of (3.7 ± 1.15) × 103 m3 s−1. Higher dischargevalues were observed during the monsoon with an average of (3.81 ± 1.23) × 103

m3 s−1, and the maximum of the order 4524 m3 s−1 during freshet (September).Considerably lower discharge values were recorded during pre-monsoon with anaverage of (1.18 ± 0.08) × 103 m3 s−1, and the minimum of the order 846 m3 s−1

during May. During post-monsoon discharge, values were moderate with anaverage of (1.98 ± 0.97) × 103 m3 s−1 as recorded by earlier workers (Mitra2013). This hyposaline condition supports migration of T. ilisha for breeding in theupstream region of Gangetic delta and also acts as the congenial nursery ground ofseveral species of commercially important fin fish that has been reflected throughrelatively high condition factor values (Table 1).

In the central sector, the ingression of seawater and resultant salinity increase hascompletely reversed the picture with relatively low condition index values ofeconomically important fin fish species (Table 1). The unavailability of fresh waterin this sector of lower Gangetic delta due siltation and blockage of Bidyadhari Riversince the late fifteenth century (Mitra 2013; Mitra and Zaman 2014, 2015) may bethe primary cause of (i) reproductive failure of economically important fin fish

Monitoring Condition Factor of the Dominant Fin Fishes … 353

species in the hypersaline environment (ii) change in migratory route for breedingpurpose (iii) loss of primary food supply (mainly plankton) due to adverse impact ofsalinity tolerance for that organism (plankton) and (iv) direct mortality due toextreme saline condition (Mitra 2013). All these reasons directly or indirectly lowerthe condition factor of fin fish species by amplifying the environmental stress.

A long-term study of some fifty years (encompassing all the major landingstations) is, however, needed to pinpoint the impact of salinity fluctuation on thecondition factor of fin fish species in the lower Gangetic delta at the apex of Bay ofBengal.

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