Hi Snooty,
If you are on the latest version of MAC , then Nikon will not tether with Lightroom.
Please check the following article : https://helpx.adobe.com/lightroom/kb/lightroom-and-el-capitan---mac-os-10-11.html
Incase it is not Latest MAC, please follow the article : https://helpx.adobe.com/lightroom/kb/troubleshoot-tethered-capture-lightroom-4.html
Regards,
Tanuj