USFWS
Wildlife & Sport Fish Restoration Program
Alaska Region   

 

Estuary Habitat Use by Juvenile Salmon

Coowe Walker seining the Anchor River Estuary. Photo credit: Sheila Cameron

 

Project Cost and Matching Funds:

$214,007  Federal
$115,234  Non-Federal Match
$329,241  Total

Partners:

U.S. Fish and Wildlife Service
Alaska Department of Fish and Game
University of Washington
Coble Geophysical Services

The Anchor River, located on the southern Kenai Peninsula supports significant populations of Chinook and Coho salmon, as well as Dolly Varden char. Five study sites within the Anchor River estuary (from the mouth of the estuary opening into Kachemak Bay and extending approximately 8 river kilometers upstream) represented a broad range of potential habitat conditions, including lower vegetated marsh, mid-marsh and three sites along the river mainstem.  Patterns of juvenile fish movement and residence in different estuary habitats were investigated through repeated fish sampling, tagging, recaptures and antenna detections. Fish were counted, identified to species, weighed, measured and returned to the channel. Habitat features related to fish occupancy, residence and feeding were identified using stationary loggers and point sampling. Sites were sampled approximately once per week from late-July to early-September, with additional sampling in October and November of 2015. In 2016, sites were sampled every other week beginning in late May through September. This project directly addresses goals of Alaska’s Aquatic Resources Implementation Plan by improving conservation and management of juvenile salmon and their invertebrate prey and salt-marsh habitat.

Alaska supports the most robust native salmon populations in the world, and yet little is known about ecosystem support for key rearing habitats of juvenile Alaskan salmon. Recent declines, particularly Chinook salmon runs, have raised concerns about the future of salmon populations on the Kenai Peninsula. Some life history types of Chinook salmon and Coho salmon spend considerable portions of their life cycle (1-3 years) in freshwater and estuarine environments before migrating to open ocean. Other life history types spend much less time in fresh water but up to several months in estuaries before entering nearshore oceanic waters as sub-yearling juveniles. It is believed that this diversity in life histories sustains the resilience of these salmon populations to environmental variability and change. Therefore, it is vital that management and conservation strategies promote resilience in ecosystems to allow the fullest potential range of habitat conditions for salmon.

Little information exists on juvenile salmon use of snowmelt, ground water supported estuaries in south central Alaska. This project identified reaches of the lower river and estuary zones of the Anchor River watershed that constitute habitats of significant influence to juvenile salmon growth and performance. Eight fish species were regularly captured including Chinook salmon, Coho salmon, Dolly Varden, Sockeye salmon, staghorn sculpin, starry flounder, steelhead, and three-spine sticklebacks. Fish community assemblages differed between the habitats. In 2016, juvenile Chinook salmon characterized the middle and upper mainstem habitats; however Chinook salmon were rarely captured in 2015, likely due to the low adult return of the previous year. After excluding highly abundant young-of-year sticklebacks, juvenile Coho salmon were the most abundant species in the estuary in both 2015 and 2016, averaging at least 25% of the total catch in all of the habitats. Small, age-0 Coho salmon continued to enter the estuary from June through November. Marsh channel habitats were utilized by juvenile Coho salmon, to a lesser degree by juvenile Chinook salmon and large numbers of staghorn sculpin and three-spine sticklebacks. Starry flounder and staghorn sculpin were most characteristic of the lower mainstem site. Data from tagged, recaptured and antenna detections revealed juvenile Coho salmon residing in the estuary for nearly 11 months and juvenile Chinook salmon residing for nearly 1 month.

Information on the timing, abundance and residence times of juvenile salmon within estuarine habitats of the Anchor River will be incorporated into conservation efforts aimed at restoring declining Chinook salmon populations. This river is located on the road system, connecting Anchorage, Alaska’s largest city, to the Kenai Peninsula, a popular recreation destination. Recreational fishing is a popular activity in the lower river, the estuary and in the nearshore environment. Salmon are immensely important to the people and ecosystems on the Kenai Peninsula. Providing salmon populations with as much resilience potential as possible will require protecting these estuarine habitats from impacts from anthropogenic modifications to the ecosystem, shifting freshwater discharge regimes, and changes in tidal influence.

The project staff pioneered the use of low energy antennas, developed by Coble Geophysical Inc. that are capable of operating remotely using power from solar panels and marine batteries. Antenna arrays were arranged 10 m apart to detect movement direction, including overwintering movements. Fish recaptured in other habitats also indicated a broad range of movement. Environmental conditions present at the different study sites ranged from fast flowing mainstem sites that are well mixed with high dissolved oxygen levels to marsh channel sites that have low flows and a high degree of stratification. Juvenile salmon take advantage of their ability to move between habitats, as evidenced by observed movement patterns. The high densities, prolonged residence, movement and growth of juvenile salmon in the Anchor River estuary support the importance of even relatively small estuaries to juvenile salmon rearing. The amount of movement among estuary habitat types supports the concept of conservation for the entire estuary to maintain full habitat potential and resilience.

 

Last updated: May 2017

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