The SSP (Or US Zoos,or both) do claim to be managing their surplus male population successfully and without having to resort to castration. However, I am not sure how completely they have really 'solved' this issue and whether all surplus males in the US are now held in good situations(as far as any male groupings can be ideal) or how many of them are still actually held solitary/living offshow etc.
The reference to the surplus males issue was just an example (when arguing in favour of a collaboration between the EEP and SSP), and I agree the SSP has not 'solved' this issue in the strict sense of the word (apart from avoiding castrations, if that's a criteria). Indeed there are some solitary males under their management, and (my guess) not all are suitable for a recommendation to join a mixed or an all-male group.
Some interesting figures from a January 2014 SSP paper: (a) 77 males are in all-male groups (number of members: 2 - 5). (b) 14 males are being singly housed; however, two of them have been introduced to a mixed group since. [One of the remaining 12 is
Wanto in Knoxville. He had lived solitary for 20 years and joined a band of females earlier this year, but the introduction failed.] (c) As a side note, also two females are kept solitary, one of them being the iconic Colo.
Of the 12 solitary males, some of them have at least visual access to other gorillas (5), and the majority is recommended to join either a bachelor group (6) or to lead an existing group of females (3). Admittedly, in some cases a 'recommendation', for the time being, doesn't imply much more than having 'good intentions' to socialise these males at some point in the future – reflected in the paper's diction that "attempts should be made" to join X with Y.
However, the paper as well as my impressions at the Gorilla Workshop in Atlanta last June suggest that the SSP doesn't give up on any of these solitary males, and tries to socialise them wherever possible. An attitude that also includes the above-mentioned
Wanto – on him the paper states, "Consider integration with an older female to house as a pair at Knoxville if his introduction to the zoo’s 0.3 doesn’t succeed."