Forsøksdyr: Echosounder measurements of tethered fish


Godkjenningsdato 27.04.2018

This proposed experiment will be conducted in support of the NFR “MARINFORSK” funded project: “AcoSize - Direct acoustic sizing of pelagic fishes for improved catch selectivity” (Project Number: 255589/E40) (See attached project application). Novel broad band echo sounders will be used to remotely size individual fish in a set of measurement experiments. Goal is to test the feasibility of remote sizing of fish with this type of echo sounders for later proposed use on fishing vessels. The release of unwanted catch (slipping) is a common practice in purse seining for herring and mackerel and result in very high mortality among the slipped fish. Remote fish sizing that would precede fish capture/shooting the net would help to alleviate such negative effects and is currently not available. Outcomes of experiments under this project are one step in development of such a tool.

Experiment and echo sounder measurements will be performed on the aquaculture floating raft of Austevoll Research Station on adult fish of selected species and body sizes. Echo sounders will be mounted at 3m water depth just under the raft (“looking” laterally sideways), while fish suspension rig will be installed 12m away, with fish suspended at 3m water depth as well. Fish with and without swimbladder are needed for this experiment. Bladderless mackerel and bladder-bearing herring, saithe, pollock and/or cod kept in nets at Austevoll Research Station (IMR) will be used. Bladderless mackerel will be measured dead, while other species fish will be measured heavily sedated, then killed. For mackerel, single individuals will be sedated in Finquel compound solution first (100-200 mg per liter), then terminated in a second bath with a higher concentration of the same compound (500 mg per liter). For other fish, single individuals will be sedated in Finquel compound solution first (dosage and protocol for sedation will be developed), measured by echo sounder, then terminated by percussive stunning.
Individual fish will be gently suspended in water using several loops of thin nylon/fishing line. Fish then will be suspended at 3m depth under the floating raft and slowly rotated in azimuth direction while being measured by an echo sounder. One individual will be measured for period of up to 10min after which it will be taken up, killed and measured for size and body weight. This fish measurement experiment will use up to total of 500 adult individuals of Atlantic Mackerel (Scomber scombrus), Atlantic herring (Clupea harengus), saithe (Pollachius virens), pollock (Polachius polachius) and/or Atlantic cod (Gadus morhua) of various sizes.

3Rs. An experiment of same setup and location, but using a dummy fish-like objects has already been performed (2017.06), techniques of handling fish-like objects were developed, much was learned about acoustic echo properties of fish-simulating objects, next step is to measure real fish. This dummy-fish experiment helped us to refine the fish handling procedures, as well as to determine the minimum amount of fish needed to fill in the knowledge gap left after dummy-fish measurements and acoustic fish scattering modelling done on a computer.