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Implications of an extensive salt water barrage on the distribution of black clam in a tropical estuarine system, Southwest coast of India

Nagarathinam Arunpandi, Retnamma Jyothibabu, Loganathan Jagadeesan, Singaram Parthasarathi, Madam Savitha Mohanan Kannampally, Jose Albin Konnakkamannil, Subramanian Pandiyarajan Rethinam

Oceanologia

2021

No. 63 (3)

343--355

Based on a monthly field sampling over a year in the Kochi backwaters (KBW), this study presents the larval ecology of black clam and discusses how an extensive saltwater barrage [Thannermukkom barrage (TB)] impacted the natural black clam resource distribution. Spatial variations in salinity were found minimal during the Southwest Monsoon (June-September) due to the predominance of the freshwater associated with heavy monsoonal rainfall. Conversely, significant spatial changes in salinity were evident during the Pre-Southwest Monsoon (March-May) and Post-Southwest Monsoon (October-February). Monthly sampling exercises revealed that the black clam stock in the KBW breeds throughout the year, as their larvae were found (8 indiv. m-3 -494 indiv. m-3) in all the locations. This observation is the modification of the traditional belief that black clam in the KBW breeds only twice a year. Mesohaline condition (salinity 5-18) is the most conducive for peak spawning and larval production. There were two peaks of larval production in the KBW over a year, mainly associated with the prevalence of the optimum salinity conditions on different spatial scales. The closing of the TB after the Southwest Monsoon (September) causes shrinkage of the area of the oligohaline and mesohaline conditions, the most conducive environment for the peak spawning and larval production of black clam in the KBW. This study presents a clear case of how human alterations of the natural environment impact valuable biological resources, which may apply to many similar aquatic ecosystems across the globe.

Age, growth and reproductive biology of the saddled seabream (Oblada melanura) in the North Aegean Sea, Eastern Mediterranean

Daban Ismail Burak, Ismen Ali, Ihsanoglu Mukadder Arslan, Cabbar Koray

Oceanological and Hydrobiological Studies

2020

Vol. 49, No. 1

13--22

This study determines the length distribution, length–weight relationship, age, growth parameters, mortality rate, sex ratios, length at first maturity and reproduction of saddled seabream (Oblada melanura) collected monthly by fishermen around the Northern Aegean Sea between November 2017 and October 2018. The length–weight relationship was calculated as W=0.0091×L 3.11 (R 2=0.95) and positive allometric growth was found. The condition factor and GSI varied between 0.81–1.58 and 0.01–9.61, respectively. The spawning season extended from May to July and peaked in June. Total lengths at 50% maturity were 18.97 cm for males and 18.83 cm for females. Parameters of the von Bertalanffy growth equation were: L∞ =29.91 cm, K =0.27 per year, t0=−0.82 year and age varied between 1 and 8. The instantaneous rates of total mortality (Z) and natural mortality (M) were 1.36 and 0.58 per year, respectively. Rates for fishing mortality F and exploitation E were 0.78 and 0.57 per year, respectively. The mean absolute fecundity (F) was 117 075±23 243 oocytes, ranging from 19130 to 470 132.

Charakterystyka wiekowo-wzrostowa tarłowych migrantów łososi (Salmo salar L.) Wieprzy

Pilecka-Rapacz M.

Rocznik Ochrona Środowiska

2011

Tom 13

1441-1452

Spośród wędrownych ryb łososiowatych Polski najliczniej w rzekach występowała i występuje troć wędrowna, natomiast łososie miały stosunkowo niewielki udział [1]. Występowały w Wiśle, Odrze (Drawie) oraz w małym procencie w rzekach pomorskich [2]. Jako ryba atrakcyjna biologicznie i gospodarczo był badany przed drugą wojną światową [3]. Dokładniejsze badania wzrostu i struktury wiekowej łososi prowadzone były w latach powojennych [1÷8]. Natomiast dyskusja dotycząca wzrostu obecnych łososi, występujących w naszych rzekach jest trochę skomplikowana. W latach 80. zanikły nasze ostatnie łososie [9]. Potem rozpoczęła się odbudowa populacji i obecnie opiera się ona na stadzie z rzeki Daugawy (Łotwa) [10]. Głównie na tej bazie oparta jest aktualna restytucja łososia w Polsce, którym zarybia się rzeki pomorskie i Wisłę z dobrymi wynikami restytucyjnymi [3, 11]. Dlatego wydawało się celowym, dokonanie analizy wiekowo-wzrostowej na podstawie oceny łusek ryb migrujących z morza do Wieprzy na tarło.

Atlantic salmon is a biologically and economically attractive fish. A detailed study of salmons' growth and age structure were carried out in post-war years. In the 80s our last salmon disappeared, and in the 90s the reconstruction of the salmon population (restitution) has started. It was based on salmon from the Daugawy River (Latvia). Salmon from Wieprza River came from stocking conducted by staff of the Polish Angling Association. Therefore, it seemed advisable, to examine age and growth of fish based on scales from salmon migrating from the sea to Wieprza River to spawn. In the study 363 fish were obtained, caught in late autumn from 1998 to 2005 (excluding 2004) in Darlowo. All fish were measured, weighed, identified for the condition factor, age and gender. Most spawners were caught from 2000 to 2002, then their number was decreasing. Females were caught more than twice as often as males. Length of fish ranged from 34 to 126 cm, with an average of 87 cm, weight ranged from 0.4 to 20 kg, with an average of 6.3 kg and the condition factor KF ranged from 0.76 to 1.09, with average 0.91. Fish got to the sea as 1-2 years old smolts, while in the majority smolts were 2-years old and accounted for almost 96% of the total population. In the system of gender, 2-year old female smolts were accounted for higher percentage, almost 98%, but in males it was lower - 90%. The average length in the system of gender and groups of rivers' age were similar. At the sea age we highlighted 4 key groups, from 1+ to 4+. The largest was the group of A.2+ - 78% of the population and next one was A.3+ - 17.3% of the population. Dependence on gender, age group system was similar.