Size definition of jack chinook and coho salmon varies between systems as each population 's genetic makeup is unique. This leads to differences in management and daily quotas between systems.
Take coho salmon for example, fish in the Capilano River are considered as jacks if they are under the length of 30cm, while the same definition is used for Stave River's fish that are under the length of 35cm (probably for most Fraser Valley systems too, but most systems do not have restrictions on number of jacks and adults in a daily quota).
For chinook salmon, the size definition is not only watershed-specific, but also season-specific. Chinook salmon that bypass the Fraser River in the summer (until August 31st) are mostly Interior region bound. For these populations, fish that are under the length of 50cm are considered as jacks. For fish that are returning after August 31st, they are considered as jacks if they are under the length of 62cm because fish from fall coastal runs are larger.
For the Chilliwack River system, there were thoughts that the adult size definition should be different for the summer red chinook run and fall white chinook run. Currently the adult size definition is above 62cm for both runs.. The concern was that the summer run fish maybe smaller, so some of the adult fish are in fact under the length of 62cm. This means, if an angler keeps 4 red chinook salmon that are under the length of 62cm per day on the Chilliwack River, he or she may in fact be keeping four adults, not four jacks. In the end, I cannot exactly remember the conclusion, members of the UF SFAC agree that the adult size limit should remain the same for both runs. One reasoning is that escapement number is being met for hatchery brood collection (obviously that has not been the case for this year until the fishing boundary change). The other reasoning is that by having two different adult size definitions, anglers may mix the two up from time to time, which does not exactly make sense since the two adult size definitions are used for the Fraser River.
Jack chinook salmon do not have to be marked on your license when they are caught. Only adult chinook salmon have to be and you are only allowed to retain one adult chinook salmon per day. Jacks are also counted as part of your daily aggregated quota of four salmon.
Daily quotas and size limits for these in the Lower Mainland streams can be found at:
http://www.pac.dfo-mpo.gc.ca/recfish/Freshwater/region2_e.htmFor the Chilliwack River system, most of the info can be found at:
http://www.fishingwithrod.com/yabbse/index.php?topic=18458.0