5:15 PM - 6:45 PM
[ACG39-P04] Field Experiment on Promoting Increases in Organisms on Which of Fish Feed at Suttsu Fishing Port, Hokkaido
Keywords:nursery function, feeding ground function, attached substrate, sea floor substrate, benthic ecosystem
Given the recent depletion of fisheries resources, the Fisheries Agency has been promoting the development of habitats that are well-integrated with the life history of fisheries organisms, toward raising the productivity of the entire sea area by fostering rich ecosystems. Coastal facilities such as fishing ports allow for the safe unloading of fish from fishing vessels and for the protection and nurturing of fisheries organisms (as spaces for feeding grounds and for shelter from high waves). These facilities need to increase their ability to offer such protection and nurturing.
Previous studies have proved that calm fishing ports, including those located in rock reef areas, excel at providing locations for organism to feed, because the sand and gravel seabed within the harbor provides habitats for benthic organisms. There are more benthic primary producers and benthic animals within harbors than outside of harbors. These benthic organisms provide food for fish, so expanding habitat spaces for benthic organisms to structures such as existing blocks is expected to further enhance the habitat’s ability to serve as a location for feeding.
To investigate methods for enhancing the ability of fishing ports to serve as locations for feeding, field experiments were conducted with two types of substrates, each serving as a habitat for benthic organisms, including attached organisms: (1) an attached substrate and (2) a seabed substrate. The experiments were conducted at Suttsu Fishery Harbor in southwestern Hokkaido, with the aim of gaining knowledge on how to increase the amount of feed organisms through the installation of substrates.
(1) Attached substrate experiment: Aligned polyvinyl chloride plates were installed on foot protection blocks and left for approximately two years. Samples were taken periodically. Microalgae and attached animals were observed on the surface of the plates. Furthermore, more zooplankton were found around the specimen than in the water column at the anchorage in the port. The dominant attached animals and zooplankton were annelids and arthropods, on which fish are regarded as feeding.
(2) Seabed substrate experiment: Net sacks filled with gravel were installed on foot protection blocks. The sacks were collected after 12, 18, and 30 months of installation. Macrozoobenthos collected from the sacks are regarded as organisms on which fish feed, and macrozoobenthos (particularly annelids), which are the dominant organisms in the harbor, were found to be more abundant in population and wet weight on substrates within the harbor than outside the harbor. The population and weight of annelids in the harbor were similar to those in the anchorage in the port. The types, number, and wet weight of macrozoobenthos increased over time. Both omnivorous and carnivorous annelid species were confirmed to increase.
From this, it was suggested that the addition of attached substrates and seabed substrates will help to increase spaces which serve as habitats for benthic organisms and that the development of a stable benthic ecosystem will enhance the ability of fishing ports to serve as locations for the feeding of fishes.
Previous studies have proved that calm fishing ports, including those located in rock reef areas, excel at providing locations for organism to feed, because the sand and gravel seabed within the harbor provides habitats for benthic organisms. There are more benthic primary producers and benthic animals within harbors than outside of harbors. These benthic organisms provide food for fish, so expanding habitat spaces for benthic organisms to structures such as existing blocks is expected to further enhance the habitat’s ability to serve as a location for feeding.
To investigate methods for enhancing the ability of fishing ports to serve as locations for feeding, field experiments were conducted with two types of substrates, each serving as a habitat for benthic organisms, including attached organisms: (1) an attached substrate and (2) a seabed substrate. The experiments were conducted at Suttsu Fishery Harbor in southwestern Hokkaido, with the aim of gaining knowledge on how to increase the amount of feed organisms through the installation of substrates.
(1) Attached substrate experiment: Aligned polyvinyl chloride plates were installed on foot protection blocks and left for approximately two years. Samples were taken periodically. Microalgae and attached animals were observed on the surface of the plates. Furthermore, more zooplankton were found around the specimen than in the water column at the anchorage in the port. The dominant attached animals and zooplankton were annelids and arthropods, on which fish are regarded as feeding.
(2) Seabed substrate experiment: Net sacks filled with gravel were installed on foot protection blocks. The sacks were collected after 12, 18, and 30 months of installation. Macrozoobenthos collected from the sacks are regarded as organisms on which fish feed, and macrozoobenthos (particularly annelids), which are the dominant organisms in the harbor, were found to be more abundant in population and wet weight on substrates within the harbor than outside the harbor. The population and weight of annelids in the harbor were similar to those in the anchorage in the port. The types, number, and wet weight of macrozoobenthos increased over time. Both omnivorous and carnivorous annelid species were confirmed to increase.
From this, it was suggested that the addition of attached substrates and seabed substrates will help to increase spaces which serve as habitats for benthic organisms and that the development of a stable benthic ecosystem will enhance the ability of fishing ports to serve as locations for the feeding of fishes.