What to throw away had to be balanced with what might be of historic value in the future, he said.
"I am taking some books and things home, but I have had to give quite a lot away.''
Technical books about archiving theory had been donated to the Hocken; other material given to his colleagues.
Mr Strachan (64) has worked with archives for 40 years, 32 of them within the Hocken's walls and the past 23 as its head librarian.
Between 1977 and 1985, he was senior archivist with the National Archives in Wellington.
The Hocken played an important part in his private life - he met his wife, Jean, when both were on the staff there. Mrs Strachan now heads the Dunedin Public Libraries' McNab research library.
The Hocken Collections are named after Dr Thomas Morland Hocken, who in 1907 donated his lifetime collection of about 4300 books and about 5500 other items, including maps, paintings, photographs and artefacts, to the University of Otago, to be held in trust for the people of
New Zealand.
Mr Strachan began as a library assistant in September 1968 under head librarian Michael Hitchings. The starting salary was $41 a week - he knows that because he still has his first pay slip and his letter of appointment.
At that time, the collections were housed in the Hocken wing attached to the Otago Museum.
Mr Strachan said he was "immediately enchanted'' by the combined workroom and storage area with its floor-to-ceiling shelves overflowing with books, papers and registers. There were even piles of books on the floor.
"I was all enthusiasm. This was the real stuff of history. It was like an Aladdin's cave, so overwhelming was the sense of riches.''
Conditions for the staff were primitive, he said. Water to boil the kettle for morning and afternoon tea had to be hauled upstairs in buckets from the men's toilet, and the slops disposed of in reverse.
Unlike today, conservation standards then were "lamentable'', he recalled.
By 1968, the collections had grown to about 32,000 items and 1000 linear metres of shelving, but the backlog of material waiting to be properly catalogued and archived was large.
The collections were not held in climate-controlled storage areas and the staff were not trained in how to look after them properly.
Mr Strachan became New Zealand's first trained archivist when he completed a course at University College, London, in 1970, returning to Dunedin to become the Hocken's curator of manuscripts.
Mr Strachan said the biggest change he had seen through the years was technology. The "labour-intensive'' card-catalogue systems of past decades were replaced in the 1980s by computers.
The arrival of photocopiers, the Internet, online catalogues and digitised versions of much of the Hocken's material had made the collections accessible to people all over the world who did not need to visit in person, at least in the early stages of their research.
But technology also brought challenges, he said. "The issues of preservation, management and resourcing [of electronic material] is very great indeed, and has yet to be fully faced up to.
"A recent study has shown it is cheaper and easier to keep a book on a shelf than it is to preserve it digitally.
"However, so much now exists in this form that even within New Zealand it is claimed that the digital world is larger than that of physical texts.''
Specialist electronic repositories had to be developed, he said, otherwise the risk of losing material was "extreme''.
The other dilemma for the Hocken and other archives was whether to keep on collecting at the same pace.
Mr Strachan said he was a "committed adder'' in his early years on the staff and was particularly proud of acquiring extensive records from the National Mutual Assurance company, the Plunket Society, and New Zealand Paper Mills.
During one summer holiday, he had also brought back a "massive'' collection of New Zealand Women's Weeklies, dating back to the 1950s, from his mother-in-law's house in Nelson.
But now, when the Hocken's collections contained more than one million photographs, 250,000 books, 13,500 original works of art, 15,000 sound recordings, 10,000 maps and more than 8000 linear metres of shelving, there was "continuing tension'' between preservation and access.
He said it raised the question of whether it was better to save as much as possible while it still existed to be saved, even though it might not be possible to provide access to it for a considerable time, or whether it was best to concentrate on making what was already held more accessible.
"In the past, I never had any doubts - save what you can and then let access follow when it is able . . . However, this view no longer holds universal sway.
"Readers and staff are frustrated if access if denied to what is already held.
"Consequently, in the past few years, the emphasis has moved away from collecting to cataloguing . . . and making records available online.''
Asked what he would miss most about the Hocken, Mr Strachan said his direct contact with the material in the collections, his contact with his colleagues, and his contact through the years with many literary figures, such as James K. Baxter, Janet Frame, Charles Brasch and Roger Hall.
However, he would not miss his management and administration responsibilities.
Mr Strachan and his wife will stay in Dunedin, although they are planning a trip next year to visit their lawyer daughter Helen, who lives in London.
Mr Strachan will also continue his involvement with several national bodies, including the Archives Council of New Zealand.
With more time to himself, Mr Strachan also hopes to progress a research project of his own, editing the diary of the 1840s surveyor J.W. Barnicoat.
That means he will be back at the Hocken.
"But not too soon, and not every day,'' he said with a laugh.
