scholarly journals Population dynamics of Ruditapes philippinarum in the man-made seashores of Tokyo Bay

2004 ◽  
Vol 30 (1) ◽  
pp. 193-198 ◽  
Author(s):  
Takayuki TANAKA ◽  
Yusuke SUGAMOTO ◽  
Ikumi MIYAZAKI ◽  
Yuta ITOU ◽  
Masami HAMAGUCHI ◽  
...  
Keyword(s):  
Population Dynamics ◽  
Ruditapes Philippinarum ◽  
Tokyo Bay

Production of asari (Manila) clams, Ruditapes philippinarum, during the period of harvest decrease in the 2000s in the Banzu tidal area, Tokyo Bay

2020 ◽  
Vol 33 ◽  
pp. 14
Author(s):  
Mitsuharu Toba ◽  
Jun Kakino ◽  
Kazuo Tada ◽  
Yutaka Kobayashi ◽  
Hideharu Tsuchie
Keyword(s):  
Field Investigation ◽  
Ruditapes Philippinarum ◽  
Management Style ◽  
Seed Stock ◽  
Tokyo Bay ◽  
Yearly Variation ◽  
Culture Area ◽  
Stock Biomass ◽  
Tidal Area ◽  
High Level

In Tokyo Bay, the harvestable quantity of asari (Manila) clams Ruditapes philippinarum has been decreasing since the late 1990s. We conducted a field investigation on clam density in the Banzu culture area from April 1988 to December 2014 and collected records spanning January 1986 to September 2017 from relevant fisheries cooperative associations to clarify the relationship between the temporal variation in stock abundance and the production activities of fishermen. The yearly variation in clam abundance over the study period was marked by larger decreases in the numbers of larger clams. A large quantity of juvenile clams, beyond the biological productivity of the culture area, may have been introduced as seed stock in the late 1980s despite the high level of harvestable stock. The declines in harvested quantity began in the late 1990s and may have been caused by decreases in harvestable stock despite the continuous addition of seed stock clams. The harvested quantity is likely to be significantly dependent upon the wild clam population, even within the culture area, as the harvestable quantity was not correlated with the quantity of seed stock introduced during the study period. These declines in harvested quantity may have resulted from a decreasing number of operating harvesters due to the low level of harvestable stock and consequently reduced profitability. Two findings were emphasized. A certain management style, based on predictions of the contributions of wild and introduced clams to future stock biomass, is essential for economically-feasible culturing. In areas with less harvestable stock, actions should be taken to maintain the incomes of harvesters while avoiding overexploitation, even if the total harvest quantity decreases.

scholarly journals Population dynamics of a commercially harvested, non-native bivalve in an area protected for shorebirds: Ruditapes philippinarum in Poole Harbour, UK

2019 ◽  
Vol 32 ◽  
pp. 10 ◽  
Author(s):  
Leo John Clarke ◽  
Luciana S. Esteves ◽  
Richard A. Stillman ◽  
Roger J.H. Herbert
Keyword(s):  
Population Dynamics ◽  
Marine Protected Area ◽  
Condition Index ◽  
Ruditapes Philippinarum ◽  
Ecological Interactions ◽  
Fishing Season ◽  
Before And After ◽  
Harvesting Efficiency ◽  
The Uk ◽  
Lower Biomass

The Manila clam Ruditapes philippinarum is one of the most commercially valuable bivalve species worldwide and its range is expanding, facilitated by aquaculture and fishing activities. In existing and new systems, the species may become commercially and ecologically important, supporting both local fishing activities and populations of shorebird predators of conservation importance. This study assessed potential fishing effects and population dynamics of R. philippinarum in Poole Harbour, a marine protected area on the south coast of the UK, where the species is important for oystercatcher Haematopus ostralegus as well as local fishers. Sampling was undertaken across three sites of different fishing intensities before and after the 2015 fishing season, which extends into the key overwintering period for shorebird populations. Significant differences in density, size and condition index are evident between sites, with the heavily dredged site supporting clams of poorer condition. Across the dredge season, clam densities in the heavily fished area were significantly reduced, with a harvesting efficiency of legally harvestable clams of up to 95% in this area. Despite occurring at significantly higher densities and growing faster under heavy fishing pressure, lower biomass and condition index of R. philippinarum in this area, coupled with the dramatic reduction in densities across the fishing season, may be of concern to managers who must consider the wider ecological interactions of harvesting with the interest of nature conservation and site integrity.

scholarly journals Population Dynamics of a Clam, Ruditapes philippinarum, on an Artificially-created Sand Cover on the Tidal Flats at the River Mouth of Midorikawa River.

2002 ◽  
Vol 57 ◽  
pp. 177-187 ◽  
Author(s):  
Hiroaki TSUTSUMI ◽  
Kouko ISHIZAWA ◽  
Miho TOMISHIGE ◽  
Midori MORIYAMA ◽  
Kaori SAKAMOTO ◽  
...  
Keyword(s):  
Population Dynamics ◽  
River Mouth ◽  
Ruditapes Philippinarum ◽  
Tidal Flats

Population dynamics of naturalised Manila clams Ruditapes philippinarum in British coastal waters

2007 ◽  
Vol 151 (6) ◽  
pp. 2255-2270 ◽  
Author(s):  
John Humphreys ◽  
Richard W. G. Caldow ◽  
Selwyn McGrorty ◽  
Andrew D. West ◽  
Antony C. Jensen
Keyword(s):  
Population Dynamics ◽  
Coastal Waters ◽  
Ruditapes Philippinarum

Impact of sea spider parasitism on host clams: susceptibility and intensity-dependent mortality

2017 ◽  
Vol 98 (4) ◽  
pp. 735-742
Author(s):  
Katsumasa Yamada ◽  
Katsumi Miyazaki ◽  
Takeshi Tomiyama ◽  
Gen Kanaya ◽  
Yoshifumi Miyama ◽  
...  
Keyword(s):  
Clearance Rate ◽  
Adductor Muscle ◽  
Ruditapes Philippinarum ◽  
Mass Mortality ◽  
Manila Clam ◽  
Tokyo Bay ◽  
Sea Spiders ◽  
Sea Spider ◽  
Massive Scale ◽  
The Impact

Nymphonella tapetis (Pycnogonida, Ascorhynchidae) is an endoparasitic sea spider affecting bivalves. Recently, sea spiders have been found on a massive scale in the commercially important Manila clams (Veneridae, Ruditapes philippinarum) in Japan (Tokyo Bay). Simultaneously, mass mortality has occurred in this area. Local fishers assumed that this mass mortality was caused by the parasitic sea spider, despite the effect of the parasite and parasite intensity on the host being unknown. To evaluate the susceptibility of the Manila clam to sea spider infestation and the impact on mortality levels, we established six treatments at different infection intensities (density of newly hatched larvae of sea spiders) over a 6-month long laboratory experiment. We monitored mortality and three susceptibility indices (clearance rate, sand-burrowing speed and adductor muscle strength) under sufficient food conditions. Parasitization by sea spider affected clearance rate and sand-burrowing speed. The pattern of parasitic intensity effects on survival of Manila clam hosts was shown to be dependent on the levels of parasite numbers, i.e. clams with lower parasitic levels (total of <200 hatching larvae of sea spider given to a host) have a higher survival rate, and high mortality of host clams was shown in excessively higher parasitic densities (400–4000 individuals). Such pattern of parasitic effects on host survival might be one of the causes of mass mortality of Manila clams occurring in the field.

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