Study Area

The Alagnak Wild River, a conservation unit partially within Katmai National Park and Preserve in southwest Alaska, originates at the outlet of Kukaklek Lake and flows 120 km into the Kvichak River which drains into Bristol Bay (see Map 1). A major tributary is the Nonvianuk River which originates at Nonvianuk Lake south of Kukaklek Lake. Numerous tributaries feed into Kukaklek and Nonvianuk Lakes, the largest of which are Kulik River, Battle Creek, and Moraine creeks. The Alagnak River is extensively braided downstream of the Nonvianuk River confluence and eventually becomes tidally influenced near its union with the Kvichak River. All but the downstream-most 29 km of the Alagnak River are managed by Katmai National Park. The majority of the upper watershed is within the Katmai National Preserve or Katmai National Park.

Map of the Alagnak River Watershed

Background and issues addressed:

Concerns have been raised about the health of Alagnak River rainbow trout population(s) because of the dramatic increase in fishing pressure beginning in the early 1990’s. Angler complaints of poor fishing and a decrease in the size of rainbow trout throughout the watershed have become a concern. It is difficult to assess the relative impacts of the increasingly popular sport fisheries because knowledge of basic life history characteristics and habitat use for this species in Alaska is limited. USGS research is designed partly to determine whether rainbow trout in the various rivers, lakes, and tributaries of the watershed are a single, well mixed population with interbreeding spawning groups, or whether there are discrete, independent spawning populations. Our research is also focused on identifying the detailed movement patterns and seasonal migrations made by rainbow trout in the watershed, and to identify critical habitat for the species. This study was designed to assist state and federal fisheries managers with improved technology for decisions to maintain healthy trout populations and sport fisheries.

Prized Trophy Rainbow Trout Fishery

The Alagnak River rainbow trout fishery has a reputation of being a world-class fishery and therefore attracts large numbers of anglers. It is considered to be one of the most popular fly-in fishing destinations in southwest Alaska, also supporting important salmon (chinook, sockeye, pink, chum, and silver), Arctic grayling, Arctic char, and lake trout sport fisheries.

Several lodges on the main stem Alagnak, at the outlet of Nonvianuk Lake, and one on the Kulik River provide guided fishing services. Together these lodges support the majority of the visitation for fishing because there are no roads to the Alagnak; all access is by air. A lesser number of parties are flown to strategic locations and then use rafts to drift the river, fishing as they go. Few natives use the river to harvest salmon and a small amount of trout for subsistence use.

Increased Angler Use

• Over 30,000 trout caught and released in the early 1990’s

The Alaska Department of Fish and Game reports that visitor use for fishing has increased from approximately 1,900 angler days per year (a 4-month fishing season) in 1981 to over 13,000 in 1995. Angler, guide, and lodge owner complaints of poor fishing and a decrease in the average size of rainbow trout throughout the watershed are common. The degree to which sport fishing has influenced Alagnak River rainbow trout population structure is presently unknown. These statistics and concerns prompted emergency regulatory changes to catch-and-release fishing only for the Alagnak River rainbow trout sport fishery in 1996, becoming permanent in 1998.

Hooking Injuries Affect Aesthetics of Fishery

• Over 30% of rainbow trout captured in recent surveys show past hooking injuries

Because of the high angler use of this trout sport fishery, it is possible that hooking injuries and mortality are significantly affecting Alagnak rainbow trout population structure. Angling is one of the most physically demanding forms of exercise in fish, and recovery from the physiological disturbance in response to capture by angling may influence feeding behavior, migratory behavior, and reproductive function. Although the anatomical hooking location with associated bleeding has been indicated in many studies as the primary cause of initial mortality of angler caught fish, non-lethally injured fish may have a foraging disadvantage due to an eye or jaw injury, and may require more time for recovery than uninjured fish. A recent study completed in 2003 by USGS on factors affecting the physiological disturbance of trout subjected to catch-and-release angling indicate the duration of angling and water temperature to be the factors most influential to the initial physiological response. Barbed hooks were found to cause more hooking injuries than barbless hooks, and took longer to remove. Angler experience was found to influence landing rates and the frequency of hooking injuries. Follow this link for detailed information on catch-and-release angling research of Alagnak River rainbow trout:
http://www.absc.usgs.gov/research/Fisheries/Alagnak/catch_and_release.htm

Seasonal movement and migrations determined by radio telemetry

Radio transmitters were surgically implanted into 135 rainbow trout during 1997 and 1998, however, only 58 fish were included in the final analysis because they had the most consistent relocations over time to allow us to draw conclusions about movement patterns. Results from radio telemetry in 1997-1999 revealed a high degree of seasonal movement made by rainbow trout throughout the watershed (see Map 2). The telemetry data indicated the existence of unique, life-history based, seasonal movement behavior that suggest discrete, within-basin population structure of Alagnak River rainbow trout. The observed groups, or ecotypes, consisted of lake residents, a lake-river group, and a riverine group with fish exhibiting both migratory and nonmigratory behavior.

Map of Alagnak River watershed showing the use of the drainage
by multiple rainbow trout ecotypes.

Lake-resident ecotype. Trout within this ecotype used a combination of one lake (Kukaklek or Nonvianuk lakes) and the respective lake outlet and inlet tributaries (see Maps 1 and 2 of drainage). During the spawning (April-June) and postspawning or feeding season (July-September), radio-tagged fish either remained at the lake outlets or migrated upstream through the lakes to the inlet tributaries, where sockeye salmon begin spawning activity in August and September. All fish overwintered (October-March) in the lakes or lake outlets. Fish within the lake-resident ecotype exhibited both migratory and nonmigratory behavior and sockeye salmon apparently influenced the movement of trout during the postspawning and winter seasons. The presence of fish at the lake outlets and inlet tributaries during the spawning season indicate that there may be both inlet and outlet spawners within the same lake basin.

Lake-river ecotype. Trout within this ecotype used the lakes, inlet tributaries, and the Alagnak River main stem. Fish within this group were generally caught at the lake outlets, and during the spawning season migrated downstream to the braided reaches of the main stem. Some of the fish remained in the braided reaches during the postspawning or feeding seasons, which coincided with spawning activity of chum, pink, and chinook salmon in the same reaches. Some of the fish returned to the lakes after the spawning season and used the inlet tributaries in the postspawning season, which coincided with sockeye salmon spawning activity. All lake-river fish migrated back to their respective lake basins to overwinter in the lakes or lake outlets. Fish within this group made longer migrations than any other ecotype, and there was no recorded of movement between lakes indicating lake basin fidelity. The desirable spawning habitat in the braided reaches of the main stem influenced the extensive downstream migrations made by lake-river fish during the spawning season, the spawning activity of salmon influenced movement during the postspawning season, and the distance fish moved to suitable winter habitat was influenced by the location of feeding habitats.

Riverine ecotype. This group of fish represented the largest group of radio-tagged trout from this study, most likely because the majority of fishing was focused in the main stem river because it was the most accessible. Fish within this ecotype exhibited both highly variable seasonal migratory behavior, as well as nonmigratory behavior. The general pattern for river migratory fish was to migrate upstream to the braided reaches of the main stem during the spawning season, to make another upstream migration to the braided reaches during the postspawning season, and to move back downstream to overwinter in the lower and middle portions of the river. The areas where river migratory fish were located during the spawning season overlapped with the areas lake-river fish were located during the same season. During the postspawning season, the areas where river migratory fish were located coincided with salmon spawning activity in the braided reaches. The majority of river nonmigratory fish were located in the braided reaches of the main stem during all seasons. These fish made upstream migrations during the spawning and postspawning seasons, but on a relatively smaller scale in comparison to migratory fish. We believe that the highly diverse migratory strategies of riverine fish represent a continuum of fluvial rainbow trout movement behavior.

Noteworthy variation in movement patterns was found within lake-resident, lake-river, and river migratory groups. Migratory behavior similar to that demonstrated by each ecotype has been documented previously, but this is the first study we are aware of that has detected all three distinct, life-history-based, seasonal rainbow trout migratory ecotypes in the same watershed. The periodic, simultaneous use of the main stem braided reaches by lake-river and river migratory and nonmigratory trout suggests that these areas may be critical spawning and postspawning habitat for all groups of rainbow trout, and may provide winter refugia for the nonmigratory group. Because of their importance to multiple ecotypes from throughout the watershed, the braided reaches of the main stem should be considered critical habitat for Alagnak River rainbow trout. The presence of salmon spawning grounds in the Alagnak drainage appears to determine the temporal and spatial aggregations of rainbow trout during the summer, and ultimately influences the amount of movement necessary to reach overwinter habitat from feeding habitat.

Basin-wide Population Structure - Genetics and local adaptation

Little is known about rainbow trout population structuring in the Alagnak drainage. Past population studies utilizing allozyme variation on rainbow trout from other drainages have indicated that there is usually little genetic divergence among populations. Although rainbow trout from multiple ecotypes apparently spawned in the braided reaches, we have no definitive information demonstrating whether there was reproductive mixing among the ecotypes. Some implications may be drawn from an ongoing study of Alagnak River rainbow trout genetics based on microsatellite DNA variation in non-lethal tissue samples collected from radio-tagged fish and from trout caught in the braided reaches during the spawning seasons of 1999 and 2000. Preliminary results from the 1999 analysis have thus far revealed no significant genetic differences among groups. Trout that used the braided reaches of the main stem during the spawning season may have been interbreeding spawning groups, yet spatiotemporally different during the post-spawning and winter seasons. It is also possible that ecotypes are spawning separately, but in the same physical reach. Collecting tissue samples from known ecotype members appears to be the only method to fully resolve this issue. However, because the three ecotypes in this study have demonstrated separable behavioral strategies, a conservative interim management approach would be to consider trout within each ecotype as separate populations units. Until unknowns about the sources of behavioral differences are resolved, the ecotypes should be considered irreplaceable and managed accordingly.

Publications

Meka, J. M., E. E. Knudsen, D. C. Douglas, and R. B. Benter. 2003. Variable migratory patterns of different adult rainbow trout life history types in a southwest Alaska Watershed. Transactions of the American Fisheries Society 132:717-732.

Meka, J. M., E. E. Knudsen, and D. C. Douglas. 2000. Alagnak watershed rainbow trout seasonal movement. Pages 35-42 in J. H. Eiler, D. J. Alcorn, and M. R. Neuman (editors). Biotelemetry 15: Proceedings of the 15th International Symposium on Biotelemetry. Juneau, Alaska, USA. International Society on Biotelemetry. Wageningen, The Netherlands. [PDF file - 52 kb]

For more information, please contact: Julie Meka USGS - Alaska Science Center - Biological Science Office 1011 E. Tudor Rd., MS 701 Anchorage, AK  99503 (907) 786-3917 (907) 786-3636 FAX email: julie_meka@usgs.gov