Too many fish in the sea?

I think it is fair to say that no, there are not too many fish in the sea. However, when you are trying to survey the seabed, you really can have too many fish! In order to groundtruth our acoustic work, we have been taking video transects throughout the three sites of Pisces Reef Complex cSAC. This means that we can check exactly what the data from the acoustic methods are showing, and monitor the species and habitats that are present. The day shift duly carried out pre-defined line transects, recording video footage of what was on the seabed. One particular line, however, proved a little more tricky than the rest. 

Seabed image from Pisces Reef ©JNCC/Cefas, 2016

Holy Mackerel! A school of fish had taken up residence and were attracted by the lights and lasers from the drop camera frame, which are used to light up the pitch black seabed and provide a measure of scale.  The fish were dancing around in front of the cameras, kicking up the top layer of sediment and making our lives rather difficult. Getting a good view of the seabed, the point of the exercise, was close to impossible. Eventually we had to give up and move on to the next line, leaving the night shift to return later on to see if the fish had dispersed. Luckily, the return attempt was successful, although still with the presence of some rather over excited mackerel dancing around under the lights.  The mackerel appeared bright blue on the video, but you could clearly see the tiger-like stripes in the still images. Hopefully these young mackerel will grow on to become productive adults and help maintain stocks of one of the nation’s favourite fish.


Mackerel stirring up sediment! ©JNCC/Cefas, 2016

By Nikki Taylor
JNCC Marine Mammal Advisor

What does a dolphin look like?

JNCC and Cefas are currently on site at Pisces Reef Complex cSAC on the RV Cefas Endeavour to gather evidence for monitoring and to improve our ability to map the extent of the habitats found at each of the three reef areas in the site. In order to differentiate between exposed reef areas and those covered by a layer of mud, we’ve been using a sub-bottom profiler system known as a chirper, which uses sound to penetrate the seabed surface to identify the substrate layers within.

The chirper deployed through the ship’s ‘moon pool’. ©JNCC/Cefas, 2016

The chirper produces sounds that can interfere with cetacean species (whales, dolphins and porpoises), which rely on sound for foraging, navigation and communication. To mitigate this impact, we have on board a Passive Acoustic Monitor (PAM) and a Marine Mammal Observer (MMO). Gareth, our PAM from Gardline, takes the night shift, detecting the sounds these animals produce by using submerged underwater microphones (or ‘hydrophones’) to identify if they are in our 500m mitigation zone. During daylight hours, James, our MMO, takes the reins from the bridge to visually monitor for animals in advance of any acoustic operations. If a detection is made during the specified time prior to operations, work is paused until the animals have moved to a safe distance. If the all clear is given, the sub-bottom profiler is initiated with a ‘soft start’, using low power and slowly ramping up until the desired operating power is achieved, giving any remaining animals within earshot a chance to move away.

The first two shifts were clear, with no cetaceans gracing our presence despite the perfect conditions for spotting on the surface.  Our first detection occurred during the second PAM shift before the acoustic gear was switched on. The normally steady green sound waves on the display started dancing with shapes and colours, as dolphin whistles came through the headphones (see picture below).

So what does a dolphin look like in the world of PAM?



Screen grab from PAM software; the coloured lines and shapes shown above are produced by the whistles made by the dolphins, and in this recording, there were clearly at least two animals whistling, given the proximity of the sound profiles. ©JNCC/Cefas, 2016

 

Fortunately, the dolphins only stayed long enough to provide some excitement for the staff on board, but not so long that the work was significantly delayed. A great example of how acoustic mitigation can be applied to ensure a balance between getting the job done, but not to the detriment of our magnificent megafauna.

 

By Nikki Taylor 

JNCC Marine Mammal Adviser