MAQ Sonar’s story

Reprinted from the World Fishing Magazine May 19, 2011

In the early 1970’s the fishing industry was first introduced to Omni directional fishing sonar, designed to detect and track large schools of herring.

However the Doppler shift caused by the fish’s high speeds and relatively weak reflectivity when approaching or moving away from the fishing vessel meant that they could not “see” individual tuna.

MAQ introduced the 45 KHz Omni directional sonar in the late 1970’s, which detected and tracked Yellowfin tuna making it popular for the American, French and Spanish tuna fleets in three oceans.

In the mid 1990’s the MAQ 90 kHz sonar became available and detecting and tracking Albacore tuna at twice the distance of popular searchlight sonars of the day. The Spanish “Benito del Notre” fleet of the Bay of Biscay re-equipped with MAQ 90 KHz sonar as quickly as possible to remain competitive.

It wasn’t until 2010 that the albacore fishers of New Zealand and South Africa discovered that the MAQ 90 kHz sonar would double their catch by dragging their longlines through MAQ detected tuna schools.

Fast moving tuna approaching or moving away from the sonar have low echo strengths and high Doppler content. Using Doppler filters matched to the tuna’s speed, the MAQ sonar emphasises the fast moving echoes against the stationary background. The tuna crossing the field of view have low Doppler content but high echo strength as a result of the high cross sectional area of the fish’s side. MAQ’s latest software release characterises the Doppler filters to provide constant detectability irrespective of the tuna’s direction.

The MAQ 90 KHz sonar was designed because the near surface rays have minimal bending at this frequency. Near surface bubbles cause lower frequency sonar beams to bend upwards whereas higher frequency sonar beams bend downwards. At a frequency of 90 KHz the beams bend neither upwards nor downwards.

orld Fishing Excerpt