juvenile fish communities
Fyke Net sampling –
Fyke net sampling is used to evaluate changes in migration timing, body sizes, and age composition of sockeye salmon smolts. We have continued to use the same sampling design and similar gear described by Burgner (1962). Gear is set at the outlet of Lake Aleknagik from 21:00 to 23:00 every other night, and continuing from 23:00 to 01:00 if no fish are caught. Fish are returned to the lab, measured, weighed, and a fin clip is taken for genetic analysis. Genetic stock identification techniques were used to assign the population of origin of fish migrating over the course of the season in 2008-2009 (McGlauflin et al. 2011). Genetics samples have been collected and archived from migrating smolts in all subsequent years, but have not yet been analyzed.
Fyke net sampling for outmigrating smolts from the Wood River system began in 1954 and continued to 1958. In 2008, we re-initiated the FRI sockeye smolt sampling program at the outlet of Lake Aleknagik (Mosquito Point) and have continued this sampling. ASP smolt sampling in the Chignik system has been sporadic and is generally associated with thesis and/or dissertation work (2005-2006).
Beach seine sampling –
The goal of our long term beach seine sampling is to assess the relative abundance of juvenile salmonids and their resident competitors (sticklebacks and sculpin). The littoral juvenile fish community is sampled with a beach seine at set locations on Lake Aleknagik, Chignik Lake, Black Lake, Chignik Lagoon, and, historically, Iliamna Lake. Fish are counted, measured, and occasionally weighed. It is important to note that, because of variation in emergence timing, it is difficult to assess the growth rates of salmonids with this type of sampling. Additionally, the sampling is not designed to estimate absolute abundance, but can be used to calculate catch per unit effort (CPUE), an index of abundance.
Beach seine sampling occurs approximately every seven days throughout the summer growing season at Lake Aleknagik and Chignik/Black Lakes. Data from beach seine sampling at Lake Aleknagik is continuous from 1962. Data from other lakes in the Wood River system are sporadic. Sampling at Chignik and Black Lakes has been continuous since 1956. Iliamna Lake was sampled between 1962-1983 and again between 2004-2009.
Tow net sampling –
Around August 3, juvenile sockeye and their resident competitors migrate from the nearshore littoral zone to the pelagic zone of lakes, where they avoid predators by hiding in the darker depths during the day, then migrate up the water column to feed on zooplankton at night. We sample these fish in the last days of August by towing a 3m x 3m net between two boats at the surface of the water (tow net, or surface trawl). The net is set for 5-20 minutes, then is hauled in by the crew. Five to 16 sets are made on each lake we sample, spanning the entire lake for all lakes but Iliamna. Fish are returned to the lab, measured, weighed, and occasionally sampled for diet or genetics.
Tow net data have been collected continuously since 1958 from Aleknagik, Nerka, and Little Togiak lakes in the Wood River system. Beverley and Kulik were sampled between 1958-1988, the again beginning in 2006-present. Iliamna Lake tow net sampling has been continuous since 1961. Chignik and Black Lakes have also been continuously sampled since 1961.
Spawning ground surveys and age composition
The longest continuously maintained dataset is our adult sockeye spawning ground surveys and spawning ground age composition. Spawning adult sockeye are counted on the ground, by researchers walking upstream and counting individuals or groups of 10 on tally clickers. Historically, only total counts of salmon were recorded, occasionally parsed out to live and dead. As interests grew, we expanded our counts to include sex (male, female, jack), status (live, dead), and mode of death (senescent, bear killed). Since 2005, counts are recorded in 200m sections, and many streams are counted three to five times per spawning season, allowing for spatially and temporally explicit analyses. Other species are counted when present (pink, chum, Chinook, coho, rainbow trout, grayling, etc). Otoliths are collected from dead sockeye and ages read back in the lab.
Both spawner abundance and age composition data from the Wood River system are more or less continuous and date back to 1947, while data from the Kvichak system extend back continuously to 1964. We have sporadic data on age composition in the Chignik system beginning in 1922. Included in these spawning ground surveys is information on water temperature, water height and visibility.
Our core limnology sampling is a programmatic priority. One striking feature of these long-term records is the large change in environmental conditions associated with climate warming during the last century. Climate warming has been notable throughout Alaska, and it appears to be having a wide array of effects on the physical and biological aspects of the spawning and nursery habitats of salmon and other aquatic species. During a typical limnology survey, we sample a broad suite of physical and biological variables:
Zooplankton (density and species composition)
Phytoplankton (chlorphyll-a and pheophyton concentration)
Secchi depths (water clarity)
Temperature profiles (0-60m)
Limnology surveys occur approximately every 10 days throughout the summer at the Wood River lakes and in the Chignik system. Currently, sampling begins mid-July on Lake Iliamna, but historically data span the entire summer growing season. Most data have been collected continuously since 1961 from all core lakes (Aleknagik, Nerka, Little Togiak, Beverley, Kulik, Iliamna, Chignik, and Black).
Stream and lake temperatures
Since 2008, the ASP has devoted much research effort to monitoring summer and year-round temperature in streams, rivers, and lakes in Southwest Alaska. We have deployed remote temperature loggers at nearly all of our regularly surveyed spawning locations, as well as in rivers and at spawning beaches. In certain streams we have multiple loggers deployed in various habitat types. These data are part of a collaborative effort between the University of Washington, the University of Alaska, and the US Fish and Wildlife service.
The Alaska Salmon Program began collecting temporally consistent hydrology data in 2008. Stream water discharge rates and water heights are monitored both manually (summer only) and with continuously recording loggers (year round). Numerous streams and rivers draining into the Wood River lakes, Iliamna Lake, Chignik Lake and Black Lake are included.
As part of our long-term monitoring efforts, the Alaska Salmon Program collects a variety of environmental data.
Ice breakup – The timing of ice breakup has important affects on the biology and ecology of lake ecosystems. We have been recording the date of ice breakup on Lake Aleknagik since 1946 and on Lake Iliamna since 1969.
Lake level – Lake level is an indicator of precipitation/snowmelt, and can have important effects on the ability of salmon to entered their natal spawning streams. Lake level has been recorded since 1958 on Lake Nerka, since 1961 on Iliamna Lake, since 1998 on Lake Aleknagik, and since 2008 at Black Lake.