Ole Arve Misund

Underwater acoustics in marine fisheries and fisheries research

Underwater acoustics enables the detection and precise location of fish and is therefore a prerequisite for effective fishing methods such as pelagic trawling and purse seining. The application of acoustic instruments to detect fish and monitor gear performance in modern commercial fisheries is outlined. The latest developments in obtaining information such as bottom roughness and determining such characteristics of fish detected as size and species are presented.Echo integration is now widely used to estimate the abundance of commercially important fish stocks. The principles of the method are outlined briefly, and special emphasis is put on such effects of fish behaviour as the dramatic influence of fish orientation on its backscattering cross section, the possible effects of vessel avoidance, and the uncertainties connected with spatial variability.The use of acoustic tags, echosounders and sonar to study and quantify fish behaviour and distribution is outlined, with particular attention to new developments that provide detailed information on fish behaviour and distribution in relation to environmental parameters.Future developments and improvements in the application of underwater acoustics to commercial fisheries and fisheries research are suggested

The challenge of the herring in the Norwegian sea: Making optimal collective spatial decisions

Norwegian spring-spawning herring, Clupea harengus harengus L., are long-lived multiple spawners subject to strong variation in recruitment success. They tend to adopt low-risk, preferred-conservat...

Schooling dynamics of norwegian spring spawning herring (Clupea harengus L.) in a coastal spawning area

Abstract The behaviour of Norwegian spring spawning herring (Clupea harengus L.) was studied in a spawning ground off Kanney in southwestern Norway. A total of 47 schools were tracked from 5 to 60 minutes using multi-beam sonar and echosounder. Variables recorded included the horizontal area and vertical extent, depth, density and structure of schools and their swimming speed and direction. Herring schools were defined into five categories that differed in several respects: Immigrating schools had a large horizontal area and a more elongated shape than other schools. They swam deep and had a consistent swimming speed and direction. Searching schools were smaller and more dense and their swimming speed and direction varied. Spawning schools settled on the bottom; they had small vertical extent and low density. Emigrating schools were smaller in horizontal area and less dense than immigrating schools and they swam higher in the water column. Feeding schools were oflow density and were dynamic in their shape...

Distribution, migration and abundance of norwegian spring spawning herring in relation to the temperature and zooplankton biomass in the Norwegian sea as recorded by coordinated surveys in spring and summer 1996

Abstract The distribution and migration of Norwegian spring spawning herring (Clupea harengus) in the Norwegian Sea in spring and summer 1996 were mapped during 13 coordinated surveys carried out b...

Migration behaviour of norwegian spring spawning herring when entering the cold front in the Norwegian Sea

Abstract The distribution of Norwegian spring spawning herring when migrating to the feeding areas in the Norwegian Sea in spring was mapped by acoustic surveys in April 1995 and 1996. The schooling behaviour of the herring was recorded by a high-resolution sonar, and the swimming speed and swimming direction were quantified by tracking individual schools for up to one hour. In early April the herring migrated in the Norwegian Sea from the continental shelf off Norway, between 66° and 68°N, and westward to 2°W. When reaching the cold-water front, at about 0°, the herring turned southward along the front. During daytime the herring migrated in large schools at 300–400 m depth; at night they rose to surface and either dispersed or maintained schooling.

Reactions of penned herring and cod to playback of original, frequency-filtered and time-smoothed vessel sound

Abstract The behavioural responses of penned cod ( Gadus morhua L.) and herring ( Clupea harengus L.) to playback of original, frequency-filtered and time-smoothed sound recordings from a trawler were tested. Avoidance reactions of both cod and herring were observed during playback of the original, 60–300 Hz and 300–3000 Hz spectra, but hardly to the 20–60 Hz spectrum. The duration of responses of cod was longer to original than to time-smoothed sound. The conclusion is that the main determinant for triggering avoidance reactions of cod and herring is vessel sound level within the most sensitive frequency region, although other sound characteristics, such as temporal structure, also seem to be of importance.

Recording fish schools by multi-beam sonar: potential for validating and supplementing echo integration recordings of schooling fish

A method for comparing recordings of fish schooling near surface by a conventional echo integration unit and a multi-beam sonar system is outlined. The sonar system consists of a 95 kHz SIMRAD SA950 multi-beam sonar connected to a work station with software for reading the echo telegrams of the sonar, printing echograms, automatic detection and measurement of schools, and logging of the sonar data. This method has been employed to map sardine in False Bay, South Africa, and the abundance estimates obtained by conventional echo integration were compared to that obtained by sonar. It is concluded that the sonar method may be used to validate the recordings obtained by conventional echo integration, and also provide more precise mapping and abundance estimates of pelagic fish stocks in schools near the surface.

Avoidance behaviour of herring (Clupea harengus) and mackerel (Scomber scombrus) in purse seine capture situations

Abstract The avoidance behaviour of herring and mackerel has been quantified by means of a true motion sonar in purse seine capture situations. Schooling herring swam at an average speed of 2.5–2.8 body-lengths s −1 , and the mackerel schools about 1 bodylength s −1 faster. There were great variations in swimming speed and pattern of movement between the schools. The schools of both species usually avoided the vessel horizontally, and a relation between the avoidance and the sound emission pattern of the vessel was indicated. Shoaling herring was easy to capture at night, whereas both herring and mackerel schools escaped capture in about half of the sets in daylight. The results are discussed in relation to construction and operation of purse seines.

Survival of mackerel and saithe that escape through sorting grids in purse seines

Gear technology for the efficient size selection of mackerel and saithe in purse seines has been developed. A critical constraint for application of the technology is the survival of the fish that escape. We have conducted a series of small scale experiments in which penned mackerel and saithe have been forced through rigid grids into new storage pens in order to quantify their survival rates. Both species suffered insignificant mortality. We have also conducted full scale experiments during purse seining for mackerel off western Norway, and during purse seining for saithe in fjords in western and northern Norway. Control groups were established by transferring parts of the catch gently from the purse seine to attached net pens. Experimental groups were established by collecting the fish that escaped through the selection grids in attached net pens. The net pens were subsequently towed for up to 30 nautical miles before they were anchored inshore. In the mackerel experiments, maximum 95% of the control groups and maximum 60% of the experimental groups survived 1 month after the experiments. This indicates that the size selection process in mackerel purse seining may cause too high a mortality rate to allow it to be recommended for commercial fishing. On the other hand, the mortality in the saithe experiments was insignificant, and the use of size selection grids in saithe purse seines can therefore be recommended.

Survival of herring after simulated net bursts and conventional storage in net pens

Abstract In the herring purse seine fisheries, incidental fishing mortality may occur after net bursts, or during storage of live herring in net pens. We have simulated two net bursts by pulling up net pens until they split by the weight of the herring. In both cases, the experimental group suffered a higher mortality than the control group, and few herring exposed to a simulated net burst survived for more than 120 h. We have also quantified the mortality of herring that were captured by purse seine, transferred to net pens, and towed inshore for storing. Our study indicates that survival is primarily determined by the size of the net pen since the survival percentage was low in small net pens and high in large ones.