Coastal Cutthroat Trout as Sentinels of Lower Mainland Watershed ...

24are sexually immature (Leider 1997), which is likely also the case for south coastal BC.Smolts and kelts subsequently migrate downstream and then into Puget Sound, wherethey have been tracked by tagging and have been shown to migrate up to 50 km fromtheir home streams.In British Columbia, comparable patterns have been documented in the Cowichan River.Another Vancouver Island stream was found to be co-inhabited by both sea-run andresident forms (Northcote 1997). The Carnation Creek watershed study provides thelongest record of cutthroat movements at this latitude. Annually, small numbers of searunspawners (about 6) enter the 10 km 2 high-rainfall watershed, and spawn in three verysmall tributaries (Hartman and Scrivener 1990). Resident fish are also present,particularly above a natural barrier to upstream fish passage. In addition, a sea-runspawner has been observed paired with a resident spawner, and there was evidence fromtagging of movement of residents into sea-run reaches (Northcote 1997). Use offloodplain habitats for overwinter refuges was well documented (Hartman and Scrivener1990). Similar patterns of sea-run and resident headwater populations have beendocumented at Musqueam Creek near the mouth of the Fraser River, and once again littleto no instream movement was detected among headwater residents (Northcote 1997).In southeast Alaska, similar migratory patterns have been documented, except lakes werecommonly utilized as over-wintering areas by sea-run stocks after they returned from theocean in the fall. Compared to Oregon, a much higher proportion (50 % versus 5 %) offirst returning adults were sexually mature in Alaska streams as reviewed by Trotter(1997).Marine knowledge of movements of sea-run smolts, sub-adults and adults in estuariesand the sea is rather limited (Pearcy 1997). In fact, detailed accounts fromknowledgeable anglers can be as illuminating as tagging studies (Raymond 1996).Although detailed descriptions are beyond the scope of this report, briefly, kelts return tothe sea in the early spring (March), followed by smolts in April to June at this latitude inBC. Returning runs of adults are as described earlier. Some return as early as August tolarge streams including the Chilliwack River (Envirocon 1986), and as late as mid-winterin other streams. Over-wintering in lakes is also documented in southeast Alaska (Jonesand Seifert 1997). Tracking at sea by tagging indicates that cutthroat follow shorelines ofthe coast rather than crossing deep open inlets, as reviewed in Pearcy (1997). Somemoved 10-46 km offshore of the open coast of Oregon (which may apply as well to theopen coast of BC).There was some evidence from scale interpretations that the first post-smolt year wasspent in the estuary of the Columbia River (which also may apply to sea-runs of theFraser River). It should be noted that climatic regime shifts are also thought to affect searuncutthroat trout, even though they are largely a coastline dweller. Predation effects aremost apt to show up in a reduced incidence of repeat spawners (Pearcy 1997). Largenumbers of predatory fishes including mackerels and Pacific hake migrate north intoPacific waters in warm years (Pearcy 1997). Repeat spawners in Oregon waters declinedfrom 32 % in the 1960s to 8 % in the 1980s (Pearcy 1997), but the incidence of repeat