Southern Residents are, as their name suggests, the southern cousins of the Northern Residents.
SRs (the easier way to say it :) live around the border between Canada and the USA. They live in both Washington and British Columbia. They spend most of the summer near the San Juan Channel and the San Juan Islands, and in the winter move into Puget Sound, and go out to sea.
While the northerns may be the most studied orcas, the Southerns are probably the best known ones in the wild. They are adoptable through the Whale Museum in Friday Harbour. When an orca is born or dies, or is even named, local newspapers feature it. Since the SRs are right near big cities (and small ones) they are easier to find, see and love than the hard-to-reach northerns.
The SRs were the Pacific orcas who were most hit by the captures. Their easy-to-find habitat worked against them when people despised orcas, and at one point a branch of the US Army used them for target practice. This may have wiped out entire pods!
It was around the time the northerns were first having the study done on them when Kenneth Balcomb went down to photo-ID the southerns as well. He set up their own study, which became the Center for Whale Research. The Center still researches and photo-IDs the whales, with help from researchers and volunteers.
The SRs all belong to the same community and share dialects. They have never been seen interacting (peacefully at least) with the other three communities (northerns, transients and offshores). They also belong to the same clan, J-Clan.
The SRs spend most of their time all together. They are made up of 3 large pods. The L-Pod is the largest pod known. Each pod tends to keep all its matrilineal families together, and they are rarely seen spending time apart, even in winter. Also, the three pods spend a lot of time all together.
The three pods are:
-J Pod
-K Pod
-L Pod
There is another level of society in the southerns. They are also put in 'subgroups', before matrilines. This is because the southerns travel together in larger groups so much. Officially, subgroups are a social unit containing one or more matrilines and are nearly always together, although like with the pod, this isn't always necessarily true. Subgroups are often made up of matrilines closely related to each other; for instance, if two sisters had three kids each, when their mother died, it's entirely possible they both go off with their own matriline. However, they'd probably stay in the same subgroup. While originally, before we really had a grasp on the concept of matrilines, all the communities had subgroups (later changed to matrilines or pods, appropriately), researchers still use the SR subgroups, as they travel together so often, whereas Northerns often go off into their smaller matrilines.
There are 6 subgroups in the Southern Residents, as of 1994:
-J2 Subgroup (all of J1 Pod)
-K7 Subgroup (K3, K7 and K4 Matrilines)
-K18 Subgroup (K18 Matriline)
-L12 Subgroup (L12, L32, and L28 Matrilines)
-L25 Subgroup (L25, L37, L26, L21, L2, L4, L9 and L45 Matrilines)
-L35 Subgroup (L35 Matriline)
Finally, there's the matrilines. While matrilines are of course the core unit of their social system, SRs actually don't put much use to the word. They travel as large groups so much, and all the whales interact so much, that they are rarely, if ever, seen in just matrilines. The matrilines are more to keep track of who has who for a mom, but unlike the northerns, they aren't the most important part.
There are matrilines in the Southern Residents, as of 2005:
In J1 Pod:
-J8 Matriline
-J16 Matriline
-J9 Matriline
In K1 Pod:
-K3 Matriline
-K4 Matriline
-K7 Matriline
-K18 Matriline
-*K30 Matriline* (?)
In L1 Pod:
-L12 Matriline
-L32 Matriline
-L28 Matriline
-*L15 Matriline* (?)
-L25 Matriline
-L37 Matriline
-L26 Matriline
-L21 Matriline
-L2 Matriline
-L4 Matriline
-L9 Matriline
-L45 Matriline
-L35 Matriline
*Both these matrilines have died out (they did long ago) and I really don't have information on them.