BRUV and other studies (telemetry) in the same site

[Frida Lara]

 Hi everyone,

I am Frida from Mexico. I would like to know your opinion, 

What could be the effect of BRUV on telemetry studies? 

Do the receptors close to the BRUVs would receive more presence of sharks than normally do?

Shall I take some precautions, in order to, don't affect the results of other projects in the same sites?

Thank you!

[Tim Langlois]

Hey Frida

Interesting question - I am not sure.

If you could combine the BRUV sampling with telemetry recordings though - that could be interesting to investigate how far away certain fish species travel to the BRUV.

I don't really think that sharks are all that attracted to BRUV that are baited with standard baits such as pilchards - but if you use tuna or something the sharks in your area are likely to prey on - you could indeed increase shark visitation - but of course depends on the species of shark.

Repetitive BRUV sampling in the same locations has been demonstrated to alter fish behaviour - see Birt et al 2013.

Cheers

Tim

[Jordan Goetze]

Hey Frida,

I am going to disagree with Tim a little here. I think we do get quite a few sharks on BRUVs that use pilchards (sardines) it just depends on the area and how healthy the shark populations are. For example my work in Fiji I was getting 1 shark every two BRUV drops and the work in the Chagos they were getting a lot more than that. On the other hand some work that was done off Saudi Arabia (with a much greater fishing pressure for sharks) they couldn't get a single shark so resorted to experimenting with all sorts of crazy bait. I also agree with Tim that Tuna and other baits would increase the number of sharks. However, I would recommend you standardise your bait to what the majority of other people use (~1kg of pilchards/sardines) as it will make your work more comparable to other studies. For example, Steve Lindfield and I have plans to compare shark populations on BRUVs across countries and if people start using things like whole tuna to attract sharks we won't be able to use their data.

If a receptor is close to a BRUV I think it would definitely increase the chances of detecting sharks so definitely take some precautions! This will obviously depend on how close, i.e. if it is 10m away it would definitely increase the chances while say 500m maybe not. Unfortunately we don't know how far the bait plume travels yet so can't give you a set distance. We try to separate each BRUV by about 250m as a precaution so maybe that could be a starting point.

Hope this helps

[Frida Lara]

Hi,

Thank you for your answers. I already talked with my supervisor, we are going to consider your thoughts in order to reduce bias in the telemetry study undertaken in the same area. I am about to start my project in Revillagigedo Islands (Pacific Ocean), this is a very healthy system. We set a couple of BRUVs, and in some areas there are 10-12 sharks in an hour. Therefore, the effect could be important.

Regards,

Frida.

[Tim Langlois]

Hey Frida

Jordan has some good advice there. Using a standardised method to allow comparison between regions is a great thing to bear in mind.

That sounds like quite a lot of sharks - is that a MaxN?

Jordan may have had similar numbers in the protected areas in Fiji - but I don't think so?

See his note published in Coral Reefs.

Cheers

Tim

[Frida Lara]

Hi Tim,

I think the MaxN is most likely 5 Galapagos sharks and so on. I will read the note, Thank you.

Cheers,

Frida

[Lachlan Fetterplace]

Hi Tim and Frida

On Lord Howe BRUVs it is also quite common to get a MaxN of 5+ Galapagos sharks around a pilchard bait, I have seen videos with MaxN of more like 10+. Then again their abundances are quite high there anyway so perhaps the BRUVs are just being dropped right on top them and they are inquisitive enough that if the BRUV is close they will investigate regardless of bait type

Cheers
Lachlan