Stock status and current tendencies in the population dynamics of commercial fishes of Pskov-Chudskoe water body

Cyanobacteria in the genus Microcystis are dominant components of many harmful algal blooms worldwide. Their pelagic–benthic life cycle helps them survive periods of adverse conditions and contributes greatly to their ecological success. Many studies on Microcystis overwintering have focused on benthic colonies and suggest that sediment serves as the major inoculum for subsequent summer blooms. However, the contemporaneous overwintering pelagic population may be important as well but is understudied. In this study, we investigated near-surface and near-bottom pelagic population dynamics of both microcystin-producing Microcystis and total Microcystis over six weeks in winter at Dog Lake (South Frontenac, ON, Canada). We quantified relative Microcystis concentrations using real-time PCR. Our results showed that the spatiotemporal distribution of overwintering pelagic Microcystis was depth dependent. The abundance of near-bottom pelagic Microcystis declined with increased depth with no influence of depth on near-surface Microcystis abundance. In the shallow region of the lake (<10 m), most pelagic Microcystis was found near the lake bottom (>90%). However, the proportion of near-surface Microcystis rose sharply to over 60% as the depth increased to approximately 18 m. The depth-dependent distribution pattern was found to be similar in both microcystin-producing Microcystis and total Microcystis. Our results suggest the top of the water column may be a more significant contributor of Microcystis recruitment inoculum than previously thought and merits more attention in early CHAB characterization and remediation.

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The Stock Status of Skipjack Tuna (Katsuwonus pelamis) in Tomini Bay and Its Surrounding Areas, Indonesia

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/934/1/012085 ◽

2021 ◽

Vol 934 (1) ◽

pp. 012085

Author(s):

S Mardlijah ◽

A R P Pane ◽

A S Panggabean

Keyword(s):

Population Dynamics ◽

Landing Site ◽

Total Sample ◽

Utilization Rate ◽

Skipjack Tuna ◽

Katsuwonus Pelamis ◽

Stock Status ◽

Fish Recruitment ◽

Surrounding Areas ◽

And Control

Abstract Skipjack tuna (Katsuwonus pelamis) is an essential part of tuna, skipjack tuna, and mackerel tuna trades in Indonesia as the species is an economic commodity with export value. Tomini Bay is one of the areas in Indonesia with intensive skipjack tuna exploitation activities using purse seine fleets. Such a high fishing rate requires management efforts to maintain the species population’s sustainability. This study was conducted in April 2018–December 2019 at a fish landing site in Gorontalo City with a total sample of 8,833 skipjack tunas. The population dynamics, recruitment, and utilization rate were analyzed using FISAT II application and ELEFAN program. The results showed that the length at first capture (Lc) was 31.8 cmFL (in 2018) to 32.2 cmFL (in 2019) at around 1.3 year old. The fish recruitment occurred all year long, peaking in May at 16.12%. In addition, the utilization rate (E) of the species was 0.47, meaning that the species was already moderate to fully exploited. The suggested practical management efforts to maintain the population of the skipjack tunas in the area are to stop the fishing efforts from growing and control the size of the mesh for fishing.

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