Assessing vulnerability and adopting alternative climate resilient strategies for livelihood security and sustainable management of aquatic biodiversity of Vembanad lake in India

The present study was carried out at the Thycattussery area in Vembanad lake and assessed the ichthyodiversity, variability in climatic variables, the exploited status of predominant small-scale sector fisheries (SSFs) and impact of climatic variables upon an existing SSF. Fish, as well as clam specimens collected from the study area, were identified. Diversity indices and dominance curves helped to identify monsoon (June–September) as the diverse season in the wetland. SIMPER (similarity percentage) analysis indicated that Villorita cyprinoides (clam) was the predominant species in the wetland with a mean relative abundance of 16.1%. Canonical correspondence analysis (CCA) of variables with clam production identified calcium hardness and rainfall with axis loadings of –0.56 and 0.50 respectively as the variables predominantly contributing to clam production. Stepwise regression indicated that temperature and rainfall were the determinants of clam production. A decrease in rainfall and an increase in temperature at an annual rate of 0.02 and 0.8%, respectively, decreased the clam production by 5.37%/year in the study area. Further, the generalized linear model (GLM) indicated stagnancy in clam production until 2035 below 400,000 kg per year. The study introduced diversification of livelihood systems using clam culture in climate resilient pen structures (CRPS) as an adaptation strategy.


INTRODUCTION
Inland fisheries are declining rapidly due to the increase in anthropogenic pressures which include climate change and overexploitation (Sarkar et al. a, b). Anthropological attributes such as growth and development have significantly impacted fisheries and the various assets the system brought in to the communities (FAO ). The Understanding the response of small-scale fishers to this unprecedented challenge is critical for developing more efficient management strategies and alternative options in regional socio-ecological systems.
With this background, the present study assessed the ichthyo-diversity, the variability in hydrological and climatic variables, the exploited status of black clam fisheries and the impact of climatic variables upon the fisheries of a tropical inland wetland in India. The study provided a better adaptation strategy to improve the resilience and productivity of small-scale fisheries of Villorita cyprinoides (black clam) associated with Vembanad Lake.
Vembanad, the largest tropical wetland system which is spread over 2,033 km 2 , is bordered by the Alappuzha, Kottayam and Ernakulam districts of Kerala (Kurup et al. ). The geographical location of the wetland is explained by its extent (latitude 9.51 N-10.19 N and longitude 76.16 E-76.43 E). Vembanad Lake was designated as a wetland of international importance under the Ramsar Convention in 2002 (GOI ) and a critically vulnerable coastal area (Singh ) after recognizing its ecological significance as an indispensable ecosystem service provider and an essential habitat. The Thanneermukkom saltwater barrier, a man-made barrier, divided the lake into two sectors based on the salinity of the water as a brackish water zone (towards the north of the lake) and a freshwater zone (towards the south of the lake). The area is noted for two fishery resources (Kurup et al. ), namely black clam (Villorita cyprinoides) and Pearl spot (Etroplus suratensis).

Sampling area
The sampling area (

METHODOLOGY Data acquisition
The physical and chemical variables of water were measured monthly during the period 2016-2018. The sampled monthly data were pooled into yearly data for better analysis and interpretation to obtain a more precise estimate of the mean value of each variable (annexure).
The time-series data of climatic variables such as temperature and rainfall (in the yearly interval) procured from the Indian Meteorological Department (IMD) during the period 1987-2018 were used in the study taking into consideration its relevance in a tropical monsoon country.
The month-wise data of the various fish and clam species collected from the sampling station were pooled together into yearly data to obtain a more precise estimate of the mean value of each variable (Table 1).
The hydrological variables such as temperature, pH and conductivity were measured in-situ using a Eu-tech multiparameter probe and transparency was measured using Secchi-Disc Depth. The chemical characteristics of water, such as alkalinity, dissolved oxygen (DO) and hardness, were measured using a titrimetric method (APHA ).
Fish specimens were procured at Thycattussery by experimental fishing using gillnets (based on the number of hours of operation) and from market surveys monthly.
The specimens were then brought to the laboratory for taxonomical identification (Talwar & Jhingran ). The black clam was procured by raking (based on the number of hours of operation).

Software used
Plymouth Routines In Multivariate Ecological Research (PRIMER) is a statistical package used for analyzing species sampling data for studies pertaining to community ecology and the environment in the scientific community (Clarke & Gorley ). R is a programming language and free software environment widely used among statisticians and data miners for statistical computing and graphics (R Core Team ). The pooled year-wise data of all the collected variables in the study (hydrological and climatic variables and abundance data of fish and clam species) were analyzed using various packages in softwares such as Primer 7.0 (Clarke & Gorley ) and R (R Core Team ).

Data transformation and biodiversity indices
The study describes fish and clam abundance data as a measure of the number of fish or clam in a given area (McLachlan & Brown ). The fish and clam abundance data were normalized using log (x þ 1) transformation to moderate the influence of extreme values of fish assemblage (such as zero) on temporal scales and to estimate various indices which assess the status of fish assemblage in the area of study. Four major biodiversity indices, namely dominance index, Pielou's evenness index, Margalef's richness index and Shannon-Weiner's diversity index, were used to estimate the discrepancy of fish communities or populations in this system.
The dominance index is a uniformity index which indicates a high dominance of a species against other species (Harper ). The minimum index value is 1. The higher value indicates higher dominance of the species. This index helps to identify the dominant fish species in the selected area of study. It is calculated by the following where n i is the number of individuals of taxon i and n is the total number of individuals in the sample.
Margalef's species richness is a measure of the number of species found in a sample or community and its value ranges between 0 and 1. This index provides details about the species richness of the fish species in the study area selected. It is calculated using the following equation (Margalef ): where N is the total number of individuals; ln is the natural logarithm; S is the number of taxa; e is the natural logarithm equal to 2.718.
where H 0 is Shannon diversity index and S is the number of taxa.
The Shannon diversity index (H 0 ) is a measure of species abundance and richness to quantify the diversity of the species. The index ranges from 1.5 to 3.5 in most ecological studies (Ulfah et al. ). It is calculated as (Shannon & Wiener ): where P i is the proportion within the sample of the number of the individuals of ith species, n i is the number of individuals in ith species and N is the total number of individuals.

Data processing
A dominance curve was plotted for the study area employing the transformed data. The dominance curve remains an effective tool for measuring abundance trends in commu-

RESULTS AND DISCUSSION
The ichthyo-diversity at Thycattussery was assessed and it was found that 39 species belonging to 35 genera, 24 families and ten orders were present in the study area.

Icthyo-diversity
The ichthyo-diversity at Thycattussery was represented by 39 species belonging to 35 genera, 24 families and ten orders.
Similar studies were carried out by Narayanan et al.

Vulnerability assessment
In order to assess the importance of black clam as a critical food source and a key element in determining the food security and nutrition strategies of the local population, a vulnerability assessment was conducted using a structured schedule. The assessment indicated that Villorita cyprinoides (black clam) was a good supplier of provisioning services which was one the ecosystem services exhibited   Since the eigenvalues of axes 1 and 2 were higher compared to other axes, they were chosen for explaining the variations in the study. Table 5 Table 6.
The CCA showed that clam production was positively influenced by calcium hardness with axis loadings of -0.56 and negatively influenced by rainfall which has an axis loading of 0.50 (    The stepwise regression between the dependent variable, clam abundance and hydro-climatic variables indicated that a combination of physicochemical variables, such as specific conductivity, pH, carbon dioxide and temperature, impacted clam abundance and the relation was represented with this model: where C is clam abundance in thousand kgs, S is specific conductivity in μS, P is pH of the waterbody, CO is carbon dioxide in ppm and T is the temperature ( C).   The stepwise regression carried out in the study (Table 7)  Normally, the variable with the highest regression coefficient is the most determining independent variable in a study (Schneider et al. ) and temperature was that independent variable in this study. In India, being a monsoon based tropical country, there always existed an inverse relation between rainfall and temperature (Kamal et al.

).
Since the results from CCA indicated that rainfall was also a determining factor for clam abundance, the study has taken rainfall as a predictor to estimate the level of influence of variation in rainfall on clam production in a climate-changing context along with temperature. Thus the study identified temperature and rainfall as the predictor variables based on the analysis (stepwise regression and CCA) carried out on hydrological and climatic variables.
Changes in seasonal patterns of climatic variables will alter the hydrologic characteristics of aquatic systems, affecting species composition and ecosystem productivity (Poff et al. ). In India, being a tropical monsoon fed country, the climatic variables have predominant roles in determining the production from aquatic systems (Saud et al. ).
Trend analysis of climatic variables such as temperature and rainfall was also carried out to predict the future vari-   Table 7 | Stepwise regression in R between hydro-climatic variables and clam production Step: AIC ¼ À61.33. represented in Figure 5. Further, the trend of clam production (Clam Prod) was related to the temperature and it was found that for every 0.02% increase in temperature, the clam production decreased by 5.37% ( Figure 6).
The trend in rainfall was also investigated and is represented in Figure 7 which clearly shows that rainfall (RF) decreased at the rate of 0.8%/year during 1987-2018.
Further, the clam production in relation to rainfall is represented in Figure 8 which indicates that for every 0.8% decrease in rainfall, the clam production decreased by 5.37%.

Relevance of clam culture at Thycattussery
The Thycattussery area had a clam bed of 28 ha area with an estimated production of 296.9 kg/ha in 1988-1989 and this further reduced to 17 kg/ha (Kurup et al. ). So the clam culture was carried out at the Thycattussery area as a part of the stock replenishment programme. The trophic status of Thycattussery, which was estimated at 48.5, indicated an oligo-mesotrophic condition (CIFRI ) further suggesting that the production from this ecosystem may be enhanced using pens or cages by utilizing the multi-trophic levels in the aquatic ecosystem.

Prediction models for clam production
Taking the predominant inputs from CCA and stepwise regression (i.e. rainfall and temperature), the prediction model was fitted using the generalized linear model to identify the future status of clam production.
The prediction model (

Particulars of adaptation strategy
In this study, 650 kg of baby clams of mean size of 3 g in total weight and 3 mm in total length were stocked at the rate of 5,000 nos/m 2 in the Central Inland Fisheries Research Institute (CIFRI) fabricated CRPS for one year of culture. The annual growth rate of clams was assessed in terms of length and weight as 14.2 mm/year and 48 g/year. The average production obtained from the pen was 2,000 kg. The culture earned a revenue of $383.43 from sales of clam meat and clam shell. The meat and the shell was separated, washed and sold at $1.46/kg, whereas the shell was sold at $51.03/1,000 kg.
Thus, in a very short payback period of one year, a benefit cost ratio (BCR) of 1.26 was obtained, thereby substantiating the feasibility of the project. The BCR will act as a stimuli for other small scale sector fishers to use the technology and for researchers to improvise the system by utilizing the column niche.
This culture activity assimilated 915 kg of carbon wherein the carbon cost was estimated at $ 0.58/1,000 kg.
The advantages of the system included protection from adverse climatic events, resilience to fluctuating water levels in wetlands on account of tides and rainfall, better biosecurity compared to normal pen enclosures, tapping of natural productivity (food), environmentally viable, low maintenance cost and high shelf life, intensive utilization of space, ease of harvest and greater production in a limited space. Such culture-based fisheries fitted within an ecosystem management perspective can be a sustainable and successful food production strategy with stake-holders' participation.
This study identified this as a location specific suitable technology to support better livelihoods for the associated fisher communities and female family members in the inland aquatic system wherein double income from fish as well as black clams would be ensured. This green technology would not only provide a better livelihood but also act as a carbon sink which would help in reducing the carbon emissions from wetlands so as to curb global climate change.
We recommended the application of a participatory approach to relegate the adverse impacts of climate change and the introduction of this new adaptive strategy can withstand the current climatic situation. This clam culture in CRPS in inland waters may be recommended as a context specific and community-based adaptation strategy for sustainable tropical fisheries in India. The study also emphasizes a bottom-up approach wherein the importance of proactive planning at primary stakeholders level is ensured.