Stew, how many Longimanus made a showing at the 'Stone? Last year their numbers were fewer than previously - maybe only half a dozen...
at Elphinstone we had 3 to ourselves for 2 dives which were way in the blue off of the southern end. other boats had them too though, so as for numbers i can only say more than 3. as a guestimate i would say 5 maybe 6. the brothers seem to have had a lot more though, which is a great sign that the fishermen have not got them yet. at the brothers on one dive we 6 circling us and again there were more around the other 8 boats so hopefully their numbers are increasing.
try and get at least one dive in out in the blue when you are there. at the end of the day, you are going there at this time of the year to see them. i am sure you have dived the walls of elphinstone before so to miss them and raise your chances of coming head to head with the longimanus isnt that bad. get your guide to go out to the furthest boat south and drop in there, put a DSMB up and go down to 5 metres. they will come to you. be patient though, we had to wait a whole 3 minutes on one dive.. 
Just to get your tastebuds going:
