Hideaki Tanoue

Possible change in distribution of seaweed, Sargassum horneri, in northeast Asia under A2 scenario of global warming and consequent effect on some fish

Global warming effects on seaweed beds are already perceptible. Their geographical distributions greatly depend on water temperatures. To predict future geographical distributions of brown alga, Sargassum horneri, forming large beds in the northwestern Pacific, we referred to future monthly surface water temperatures at about 1.1° of longitude and 0.6° of latitude in February and August in 2050 and 2100 simulated by 12 organizations under an A2 scenario of global warming. The southern limit of S. horneri distribution is expected to keep moving northward such that it may broadly disappear from Honshu Island, the Chinese coast, and Korean Peninsula in 2100, when tropical Sargassum species such as Sargassum tenuifolium may not completely replace S. horneri. Thus, their forests in 2100 do not substitute those of S. horneri in 2000. Fishes using the beds and seaweed rafts consisting of S. horneri in East China Sea suffer these disappearances.

Assessing bottom structure influence on fish abundance in a marine hill by using conjointly acoustic survey and geographic information system

Acoustic survey and a geographic information system (GIS) were used conjointly to estimate the significance of bottom substrate to explain fish abundance distribution in the complex topography context of a marine hill. The survey was conducted in the Hachirigase hill, off southwestern Honshu Island in the Sea of Japan. Analysis of acoustic data focused on a 10-m thick layer beginning at the bottom, assuming that bottom influence does not exceed this distance. Area backscattering strength (Sa) values were rescaled in order to reflect real differences before being analyzed. Results show that the influence of the different parameters taken into account (bottom depth, bottom substrate and water temperature) varies widely from one place to another. Bottom substrate is above all important in the zone located to the west of the peak. The kriging and stratification methods were applied to the Sa distribution for estimating the total Sa in the hill. Differences between results are discussed. Conjoint use of acoustic survey and GIS is an effective method for analyzing and estimating fish abundance distribution in a marine hill.

Mapping is a Key for Sustainable Development of Coastal Waters: Examples of Seagrass Beds and Aquaculture Facilities in Japan with Use of ALOS Images

Sound coastal ecosystems provide important ecological services such as food supply, nutrient cycling, and stabilizing effects of environments (Costanza et al., 1997). They are indispensable for sustainable development of coastal areas. However, human impacts such as fisheries or reclamation destroy coastal environments and ecosystems (e.g. Huitric et al., 2002). To conserve or restore sound coastal ecosystems, it is necessary to know present situation of coastal areas including coastal ecosystems such as seagrass beds, seaweed beds, coral reefs and tidal flats, and also human activities such as fisheries related facilities and reclamation. Diving and observation from the boat are usually used for checking bottom habitats. However, these methods are laborious and time consuming (Komatsu et al., 2002a). If a boat is employed to survey a broad area with many aquaculture facilities, it requires a long time to survey it due to obstruction of rafts against navigation. The survey with the boat is unsuccessful to localize many aquaculture facilities with GPS in the cases that the boat can’t easily approach to the aquaculture facilities due to ropes and rafts. Thus, it is desired to develop efficient mapping and monitoring systems of coastal areas.

Relation Between Body Tilt Angle and Tail Beat Acceleration of a Small Fish, Parapristipoma trilineatum (Threeline Grunt), During Mobile and Immobile Periods Measured with a Micro Data Logger

Recently, data loggers that can measure acceleration of two- or three-dimensional axes have been downsized to 5 cm length and 1 cm width.

Costs and benefits of biparental mucus provisioning in discus fish (Symphysodon aequifasciatus)

We tested the manner in which the number of fry influences the costs and benefits of mucus provisioning in discus fish (Symphysodon aequifasciatus) via two experiments. In experiment-1, we found that fry grew more rapidly when they were raised with parents than when raised without parents, suggesting that fry benefits from the mucus provisioning by parents. In experiment-2, a reduction in the body weight of parents correlated with brood size. The growth rate of fry did not linearly correlate with brood size. We discuss the functions, costs, and benefits of mucus provisioning in discus fish.

New Monitoring Method to Assess the Marine Algae Distribution and Fish School in Marine Ecosystems: The Hachiri-ga-se Hill (Off Mishima, Hagi, Japan) Case Study

The importance of seamounts ( 500 m height) situated on the continental shelves are smaller than seamounts, even though they contribute significantly to coastal ecosystems by enhancing the supply of prey and providing resting grounds for numerous fish populations, they have not been fully recognized. Therefore, lately, the importance of sea-hills as a spawning and nursery ground and migration area for marine resources has been pointed out.