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Investigating the mechanisms behind changes that affect pelagic fish resources 2021.07.21

Depth-Specific Collection Nets


Pelagic fish resources, which include commonly eaten fish such as  , are said to change significantly over the spans of years or decades due to changes in the marine environment. Catch sizes have fallen for once plentiful fish, high yield fishing grounds change, and the types of fish that are caught change. Tsurumi-Seiki’s depth-specific collection nets are used to perform fishery surveys aimed at assessing these kinds of changes to marine resources and marine environments and ensuring the sustainable use of marine resources.


Collecting larval and juvenile fish to shed light on the mechanism of changes to fish resources

One of the major factors that affects catch sizes is believed to be annual changes in the survival of juvenile fish during the early stages of their life, from egg to larval fish and juvenile fish. Collecting and researching juvenile fish is an important research activity for learning more about the mechanisms behind these changes to fish resources.

The Japan Fisheries Research and Education Agency (FRA) systematically conducts research activities using survey ships to discover the change mechanisms of marine resources. It needed a collection device that could efficiently collect larval fish and juvenile fish samples over wide ocean areas within the time restrictions of ship surveys.

Depth-Specific Collection Nets are managed and operated from ships

The multi-level nets of these collection devices are managed from computers on ship decks. Information regarding dragnets that are in use (elapsed time, water depth, water temperature, filtered water volume, net open/close status) is recorded, and the nets can be opened or closed at depths where it is believed that larval fish and juvenile fish can be found.

This makes it possible to catch large larval fish and long-distance swimming juvenile fish that have been difficult to collect with previous methods. Larval fish are fish that have just hatched and whose fins and notochords have yet to fully develop. They are not long-distance swimmers, and float in the water. Juvenile fish, on the other hand, have developed fins and vertebra and can swim long distances.

The methods used to catch each differ, but the ideas used in the opening and closing of this collection device make it possible to catch both. This collection device is used in research activities aimed at discovering the connections between the initial ecologies of pelagic fish and changes in the marine environment.


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