Collapse and Recovery of the European Smelt (Osmerus Eperlanus) Population in a Small Boreal Lake — an Early Warning of the Consequences of Climate Change
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Boreal environment research 17: 398–410 © 2012 issn 1239-6095 (print) issn 1797-2469 (online) helsinki 28 september 2012 collapse and recovery of the european smelt (Osmerus eperlanus) population in a small boreal lake — an early warning of the consequences of climate change tapio Keskinen1)*, Juha lilja2), Pia högmander1), John a. holmes3), Juha Karjalainen1) and timo J. marjomäki1) 1) Department of Biological and Environmental Science, P.O. Box 35, FI-40014 University of Jyväskylä, Finland (*corresponding author’s e-mail: [email protected]) 2) Finnish Game and Fisheries Research Institute, Jyväskylä Game and Fisheries Research, Survontie 9, FI-40500 Jyväskylä, Finland 3) Fisheries and Oceans Canada, Pacific Biological Station, 3190 Hammond Bay Road, Nanaimo, British Columbia V9T 6N7, Canada Received 8 July 2011, final version received 16 Mar. 2012, accepted 16 Mar. 2012 Keskinen, t., lilja, J., högmander, P., holmes, J. a., Karjalainen, J. & marjomäki, t. J. 2012: collapse and recovery of the european smelt (Osmerus eperlanus) population in a small boreal lake — an early warning of the consequences of climate change. Boreal Env. Res. 17: 398–410. We used warm summer temperatures as an analogue of climate change to estimate the potential impacts on a population of smelt (Osmerus eperlanus) in a boreal lake. A combi- nation of hydroacoustics, seine and gillnet catches with temperature and dissolved oxygen profiles was used to study the changes in the abundance, vertical distribution and age struc- ture of the smelt population. Smelt were squeezed between their temperature and dissolved oxygen tolerance limits during most summers. Conditions in 2002 were, however, extreme and mean surface-water temperatures exceeded 21 °C while at the same time waters below 6 m had low (< 0.5 mg l–1) dissolved oxygen concentration. Pelagic fish density during summer declined from 5000 to 200 fish ha–1. However, some young-of-the-year smelt survived in 2002, leading to a recovery in abundance to 4500 fish ha–1 by 2004. A similar recovery is not likely if the high temperature and low oxygen conditions persist during critical periods over a generation time. Introduction the distribution and movements of many aquatic organisms are related to the timing of seasonal Future scenarios of global warming resulting temperature cycles, which are strongly affected from increasing atmospheric greenhouse gas con- by atmospheric temperature and winds. Lakes centrations anticipate increases in average annual in temperate and boreal regions of the world air temperature of 2–4 °C, with more intense are generally dimictic and exhibit strong ther- warming occurring in northern latitudes (IPCC mal stratification during the summer months. 2007). These kinds of increases have important During stratification, the epilimnion is warm, implications for aquatic ecoystems, particularly well mixed, and oxygenated and the hypolimnion small boreal lakes (Forsius et al. 2010), since is cold and cut-off from mixing and reoxygena- Editor in charge of this article: Outi Heikinheimo Boreal env. res. Vol. 17 • European smelt population and climate change 399 tion by the temperature gradient in the thermo- occurs typically at the age of 2 years and smelt cline. Fish distributions during stratification typi- spawn during the spring in tributaries or shallow cally reflect thermal preferences and tolerances, littoral areas when water temperature is between with coldwater fish (e.g., coregonids, salmonids) 4 and 8 °C (Nellbring 1989). Embryos hatch in the hypolimnion and cool water fish (e.g., 10–20 days after spawning. There are only a few cyprinids, percids) in the epi- and metalimnion estimates of European smelt abundances in small (Jurvelius 1991, Vašek et al. 2009, Rydell et al. lakes owing to the absence of recreational and 2010). Decreased recruitment in cold-water fish commercial catch data and the low catchability species and increased recruitment of cool-water of smelt in standard gillnet sampling (Olin and species (Casselman 2002, Winfield et al. 2008, Malinen 2003, Olin et al. 2008). Peltonen et 2010), changes in distributions and loss of popu- al. (1999) stated that echo sounding gives more lations (Sharma et al. 2007, Lehtonen 1996), and reliable estimates of smelt stocks than gillnet changes in growth potential of certain fish species sampling especially small smelts having low (Brandt et al. 2002) have all been reported as the catchability with the multimesh gillnet. potential impacts of the climate change on the During the summer of 2003, central Europe northern freshwater ecosystems. was exposed to an unusually severe heat wave, Eutrophication as a result of increased nutri- which also directly affected the hydrology of ent loading due to poor land-use practices in many lakes (Jankowski et al. 2006). In Finland, catchment areas is common in many boreal temperature in lakes was in the end July even lakes. Over 2000 lakes are currently classified 4–6 °C higher than average. However, in 2002 as eutrophic in Finland (Tammi et al. 1999). The the warm period was even longer, surface water increased nutrient supply accelerates primary temperatures being 2–3 °C higher than average production and the rate of oxygen-consuming till the end of August (Korhonen 2007). The decomposition, leading to more rapid and pro- main objectives of this study were to describe longed oxygen depletion in the hypolimnion. the population responses of European smelt in a Appropriate water temperature and dissolved small boreal lake to warmer than normal summer oxygen (DO) levels, which generally varies temperatures. We used these data and findings with local climate, is among the most important as an analogue of the likely effects of climate attributes of habitat quality affecting survival change on coldwater fish population in a small of fish in lakes (Tonn 1990, Jackson et al. boreal lake ecosystem. In this study, we explore 2001, Lucas and Baras 2001). Hypoxia is more whether the thermal niche–dissolved oxygen likely in lakes where water is slow moving, squeeze hypothesis (Coutant 1985) could explain poorly mixed, and is rich in nutrients (e.g. the observed substantial reduction in population Kramer 1987). Consequently, the combination abundance of smelt during the summer of 2002 of increasing water temperature and decreasing in the study lake. dissolved oxygen levels in eutrophic lakes may significantly increase the risk of local extinc- tions of some fish species (Magoulick and Kobza Material and methods 2003). Yet, there are only few recent studies of oxygen and temperature combination in relation Study area to climate or other long-term changes (Jones et al. 2008, Elliott and Bell 2011). Alvajärvi is a lake located in central Finland The European smelt (Osmerus eperlanus) is (62°19´N, 25°43´E) and has a surface area of a short-lived (usually 1–3 years) pelagic omni- 200 ha, maximum depth 16.5 m and mean depth vore and is a key species in the pelagic food web 3.8 m (Fig. 1). The lake discharges into the of many temperate and boreal lakes (Ivanova Päijänne system, but upstream fish migrations 1982, Nyberg et al. 2001, Sandlund et al. 2005). are blocked by a hydroelectric dam about 10 km This makes smelt a good species for the study downstream from Alvajärvi. Several small lakes of population abundance changes in response to upstream of Alvajärvi are connected by creeks. changes in environmental conditions. Maturity The lake is dimictic and the main basin is 400 Keskinen et al. • Boreal env. res. Vol. 17 5°E 20°E 35°E daytime and ascend to warm epilimnetic waters 70°N at dusk and dawn for feeding. During night, smelt are dispersed throughout the hypolimnion, even in areas with relatively low oxygen concen- Alvajärvi SWE FIN trations (Malinen et al. 2005). 500 m 60°N F G Hydroacoustic data E1 D 1 B A Echo sounding data were collected with a cali- 3 C 10 brated single-beam 70-kHz Simrad EY-M echo 6 15 sounder (full beam angle 11°, pulse duration 0.6 ms, ping rate 3 pings s–1, time-varied gain 40 log R). During data collection carried out at the end of August or the beginning of Septem- ber annually from 2001 to 2006, N–S transects 6 E2 Kitusjärvi established in the main basin were followed using a global positioning system (GPS) (Fig. 1). Because of the diurnal vertical migration pat- Jääsjärvi tern of smelt, hydroacoustic data collection was commenced at least one hour after sunset. Each survey took about one hour. Echo counting 3 N (MacLennan and Simmonds 1992) was used to estimate smelt density and distribution because D2 smelt are uniformly dispersed at night and most of the acoustic scatters are single fish. A ver- Fig. 1. location of alvajärvi, Kitusjärvi and Jääsjärvi tically aimed transducer approximately 0.5 m in central Finland. the bathymetric map (isobaths in below the surface on a side of the boat was used metres) of alvajärvi shows the hydroacoustic transects (a–G) and the main basin sampling site for hydrologic for all surveys. All acoustic data were collected –1 data (×). at a constant boat speed of 7–8 km h . Analysing threshold value of target strength was set to –56 dB. In the years 1994 and 1997, the echosound- fully stratified by late summer. The average ing protocol was similar apart from the location chlorophyll-a concentration during the summers of transects. During these two years, the survey 2001–2006 at 2 m depth was 19 µm l–1. Thus, the was done by sailing along a zigzag route in the lake is eutrophic as a result of nutrient loading areas with depth > 3 m for about one hour with- from agriculture in the watershed. Water colour out fixed transects. The covered area of the lake is high (average 146 mg Pt l–1), average pH is was however about the same as in 2001–2006.