Lakes & Reservoirs Science Policy and Management for Sustainable Use

doi: 10.1111/lre.12229pmid: N/A

Rast, Walter

doi: 10.1111/lre.12295pmid: N/A

Fukushima, Takehiko; Kitamura, Tatsumi; Komuro, Syunsuke; Nakagawa, Keita; Nagahama, Yumi; Matsumoto, Syunichi; Matsushita, Bunkei

doi: 10.1111/lre.12294pmid: N/A

To elucidate the patterns and characteristics of dissolved oxygen (DO) decline near bottom in shallow polymictic eutrophic lakes, we conducted a statistical analysis of monthly measurements for 12 years at 14 stations and hourly observation for 8 years at two stations in Lakes Kasumigaura and Kitaura. Results indicated that DO decline (hereafter, <2 mg/L) was negligible at stations with a depth of <5 m. Thus, we consider this depth to be critical depth for studying DO decline conditions in these lakes. The collected data revealed that DO decline events lasting more than 2 days occurred a few times a year. During these events, wind blew weakly (usually, <2 m/s), and diurnal stratification was formed by solar radiation. The averaged DO declining rate leading up to these events was 4.3 (±2.7) mg L−1 d−1, suggesting that within a few days, DO can fall into a declined state. The occurrence probability of DO declined events in the respective summer increased significantly with the proportion of weak wind hours (<2 m/s). Significant correlations between wind velocity and DO change rate (1 hr difference in DO) supported the importance of wind on DO changes in polymictic lakes. The influence of mean air temperature on DO decline events was insignificant.

Singh, Soubam Indrakumar; Sharma, Priyanka; Chaudhary, Savita; Sharma, Mon Gonchandra; Yegemova, Saltanat; Kumar, Rajeev

doi: 10.1111/lre.12286pmid: N/A

The water quality is one of the major criteria for the environmental evaluation based on the parametric changes in the physicochemical and biological properties of water. The distribution patterns of physicochemical and biological characteristics of the various rivers in the Imphal Valley have been studied in this work. The objective of the work is to determine the surface water quality of Imphal Valley to assess its suitability for domestic purposes. The physicochemical parameters of water such as water temperature, pH, hardness, alkalinity, EC, TDS, chloride, calcium, magnesium, sodium, potassium and nitrate were analysed for the experimentation. The biological characteristics were estimated from the Total coliform and Escherichia coli content of water. The physicochemical parameters were within the acceptable limits on the other hand Total coliform, and E. coli values were exceeding from the acceptable and permissible limits as prescribed by Bureau of Indian Standards (BIS). The study suggests untreated domestic disposal from market and household to the water body causes heavy pollution in rivers of Imphal Valley.

Okwiri, Brian; Donde, Oscar Omondi; Kibet, Caroline Jepkorir

doi: 10.1111/lre.12291pmid: N/A

The introduction and spread of non‐native fish species in Kenyan inland freshwater systems are affecting the integrity of Kenya's aquatic biodiversity and ecosystems. The present study investigated the existing knowledge of non‐native fishes in Kenyan inland freshwater systems and their consequential implications regarding fisheries management. A total of 29 non‐native fish species have been introduced to Kenyan inland freshwater systems, with 20 of these being alien fish species and nine extralimital. These introductions have increased the fish faunal compositional similarity of inland drainage systems by 4.1% to a current similarity of 26.9%, compared to a historical similarity of 22.8%. Documented impacts of this situation include displacements, predation, competition, hybridization, habitat modification and disease transmission, all of which have had negative impacts on the status and management of Kenyan freshwater fisheries. The present study addresses the taxonomic bias created by existing studies on non‐native fishes focusing on individual species, by providing more information on the status of other non‐native species about which information is limited and whose status is uncertain. The present study presents information that can be used in management efforts to control invasions and mitigate their negative impacts.

Assefa, Workiyie Worie; Wondie, Ayalew; Enyew, Belachew Getnet

doi: 10.1111/lre.12290pmid: N/A

Oreochromis niloticus is the dominant commercial fish in the Lake Tana region. However, its fishery is progressively declining over time. Little or no updated information exists on the population dynamics and exploitation patterns of the species, which is crucial to guide its sustainable management. Accordingly, the purpose of the present study was to generate essential biological parameters on the growth, mortality and stock status of O. niloticus, using length‐frequency data collected monthly from the commercial fish catches of 1 year (2014–2015). The total mortality coefficient (Z) was derived from the length‐converted catch curve. Biological reference points were predicted from relative yield‐ and biomass‐per‐recruit analyses. The estimated values of the von Bertalanffy growth parameters were L∞ = 44.1 cm, K = 0.44/year, and t0 = −0.34/year, and the growth performance index (Φ′) was 2.93. The total mortality (Z), natural (M) and fishing mortality (F) rates were 2.37, 0.98 and 1.39 per year, respectively. The current fishery exploitation rate of 0.59 exceeds the estimated biological reference points of Emax (0.52), confirming the stock of O. niloticus in the lake is being overexploited above optimum levels. Size indicators of the catches further illustrate 31% of the landed fish are harvested before reaching sexual maturity, with mega‐spawners comprising only 15%. This indicates the stock is suffering from both growth and recruitment overfishing. The logistic selection model indicated 50% of the fish vulnerable to capture was at 18.14 cm TL. The fish exhibited a year‐round recruitment pattern, with a major peak during May and June. Sustainably managing the fishery, therefore, requires increasing the fish size at first capture (Lc) towards Lopt.

Qamar, Nazia; Panhwar, Sher Khan; Awan, Khawar Parvez; Farooq, Noureen

doi: 10.1111/lre.12288pmid: N/A

Otoliths from five fish species, including Acanthopagrus latus, Daysciaena albida, Ellochelon vaigiensis, Mugil cephalus and Mystus gulio, were used to develop numerical expressions involving otolith shape indices and morphometric parameters. A total of 342 fish specimens in lagoons (24°39′ 0N, 68°50′0E) were sampled from August 2014 to July 2015. A linear model related to fish sizes, otolith sizes and weights were applied, with estimated coefficients of determinations (r2 = 0.99–0.53). Otolith shape indices, including form factor, roundness, aspect ratio, circularity, rectangularity and ellipticity for each fish species, also were analysed. The results of the present study are the first to describe relationships between otolith dimensions, fish morphometrics and shape indices of highly valued fish species and can be an important input for further trophic modelling to study food web dynamics.

Guya, Fredrick Jared

doi: 10.1111/lre.12289pmid: N/A

The Nyando River supports a large human population and an enriched biodiversity. The basin has undergone extreme modification over the last century through changes in hydrological changes and land‐use activities. The impacts of the changes have severely shifted the ecology of the river from desirable to less desirable. Of all the major rivers draining into Lake Victoria‐Kenya, the Nyando River is consistently the most turbid and exhibits the greatest phosphorus load. The present study investigated the present limnological status and sources of phosphorus loads between 2015 and 2016 through water and sediment sampling during high and low flow regimes. The samples were analysed for various phosphorus fractions, including soluble reactive phosphorus (SRP), total phosphorus in water (TPw), non‐apatite inorganic phosphorus (NAIP), apatite phosphorus (AP), inorganic phosphorus (IP), organic phosphorus (OP), total phosphorus in sediments (TPs) and elemental compositions. The measured SRP and TPw concentrations indicated hypertrophic conditions, with means for both high and low flows ranging from 79.3 to 165.7 μg P/L, and 200.0 to 243.9 μg P/L, respectively. The AP concentrations were high, with mean measurements for high and low flows being 766.9 and 790.5 mg/kg, respectively. The sources of high phosphorus loads were established to be both natural and anthropogenic, with major drivers being the industrial establishments along the river basin. Erosion of the catchment phosphorus‐enriched carbonatite rocks and river banks also contributed significant phosphorus loads. Enhanced effluent treatment, quarry dust containment, improved forest cover and regeneration of riverine buffer strips are recommended to restore the river's ecosystems.

Jayachandran, Paravanparambil Rajakumar; Bijoy Nandan, Sivasankaran; Jima, Mantodi; Sreedevi, Odassery Krishnankutty; Philomina, Joseph; Prabhakaran, Meethal Parambath

doi: 10.1111/lre.12292pmid: N/A

A comprehensive study of the macrobenthic communities in the Kodungallur–Azhikode Estuary (KAE) was conducted during 2009–2011 period. A total of 18,846 organisms were collected, with 60% being malacostracans, followed by polychaetes (20%), molluscs (9%) and ‘others’ group (11%). A total of 79 species in 71 genera belonging to 49 families were identified, with 33 spp. being polychaetes, 26 spp. being malacostracans, 11 spp. being molluscs and 9 spp. being in the ‘others’ group. A single species of opportunistic amphipod (Americorophium triaeonyx) comprised more than 62.05% of the total numerical abundance of macrobenthos. The other dominant species were Obelia bidentata, Arcuatula senhousia, Cirolana fluviatilis, Prionospio cirrifera and Capitella sp. Canonical correspondence analysis (CCA) results indicated environmental parameters such as water column salinity, turbidity, sediment Eh, substratum type, chlorophyll‐a concentration, depth and organic matter in sediment were the significant factors influencing the distribution of macrobenthic species in the KAE. The present study provides baseline information for future KAE benthic studies.

Gupta, Deepmala; Dwivedi, Arvind Kumar; Tripathi, Madhu

doi: 10.1111/lre.12287pmid: N/A

Knowledge of the length–weight relationships (LWRs) of fish is an important tool to understand fish body form, growth pattern, stock management and their conservation. The present study focused on investigating the length–weight relationships for five catfish species, Pachypterus atherinoides (Bloch, 1794), belonging to family Horabagridae; Batasio batasio (Hamilton, 1822) family Bagridae; Bagarius yarrelli (Sykes, 1839), family Gogangra viridescens (Hamilton, 1822); and Sisor rhabdophorus (Hamilton, 1822) belonging to family Sisoridae. Specimens were collected from the middle stretch of the Ganga River in India from November 2016 to May 2018. A total of 174 specimens of five fish species were collected, and their total lengths were measured to the nearest centimetre and the body weight to the nearest gram. The value of the parameter slope (b) of LWRs of the five species ranged from 2.86 (B. yarrelli) to 3.16 (G. viridescens), with a mean value of 2.99. The results of the present study documented the new maximum total length (TL) for P. atherinoides and S. rhabdophorus. The present study also provides the first reference regarding LWRs for S. rhabdophorus.