Scientists from Fisheries and Oceans Canada (DFO) and the Herring Science Council are working together to learn more about herring abundance and behaviour. The council brings together processing and harvesting industries to coordinate their contribution to DFO’s scientific data collection and assessment process.
Dr. Gary Melvin, of DFO’s St. Andrews Biological Station (SABS) in New Brunswick (N.B.), is the lead scientist for the studies. According to Melvin, “This new technology and continued collaboration with the Council will allow us to better understand and estimate the herring populations in these areas. This will be invaluable in providing improved advice for herring stock assessment and its subsequent management.”
These projects are building on a long cooperative history. Since 1998, with a hydroacoustic system developed by SABS staff, herring vessel captains have recorded the depth, density and location of herring with the simple push of a button. This information provides an assessment of herring distribution and abundance during the spawning and fishing seasons. However, this equipment does have a limited Target Strength (TS) (the acoustic signal returned from each individual fish), which is a key component in obtaining accurate abundance estimates.
The new portable equipment (i.e. eco-sounders and underwater cameras), employed since 2008, uses multi-frequency, split-beam echo sounder technology and provides better TS estimates. With this equipment, the team is investigating “acoustic blind zones” (areas close to the ocean bottom and in the water above the fishing boat hull) where traditional downward looking hydroacoustic technology can miss fish. Scientists are now questioning abundance estimates as herring have shown recent changes in behaviour. For example, herring are staying deeper and near the bottom instead of moving to the surface after dark. Underwater video cameras and the portable echo sounder are being deployed from fishing boats on the German Bank (off southwest N.S.) spawning ground to observe the fish. This information will allow for better understanding of fish behaviour and estimates of fish near the bottom.
Additionally, in the fall of 2009, the team embarked on a three-year tagging program to investigate turnover rates (movement to other areas) of individual fish on German Bank spawning grounds. In the past, during assessments and surveys, it was assumed that there was a complete turnover of spawning fish after 10 – 14 days. However, more recent tagging studies indicate that some fish remain on the spawning ground for up to five weeks, while others leave in seven days or less. This large variability could lead to estimation errors in the spawning stock abundance. With this program, fish are being tagged and returned to the water during normal fishing operations. When tagged fish are recaptured, processors are asked to return tags to the SABS along with information such as fish length, weight and catch location. Those who return tags are eligible for a $1000 draw with funding provided by the Herring Science Council.
The team is optimistic that this collaboration and use of new equipment will lead to an increased understanding of herring population estimates and behaviour, which is valuable information for effective management of the species.
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