Chapter 8 Freshwater Ecosystems and Fisheries Lead Authors Frederick J.Wrona,Terry D. Prowse, James D. Reist Contributing Authors Richard Beamish, John J. Gibson, John Hobbie, Erik Jeppesen, Jackie King, Guenter Koeck, Atte Korhola, Lucie Lévesque, Robie Macdonald, Michael Power,Vladimir Skvortsov,Warwick Vincent Consulting Authors Robert Clark, Brian Dempson, David Lean, Hannu Lehtonen, Sofia Perin, Richard Pienitz, Milla Rautio, John Smol, Ross Tallman,Alexander Zhulidov Contents Summary . .354 8.5. Climate change effects on arctic fish, fisheries, and aquatic 8.1. Introduction . .354 wildlife . .393 8.1.1. Challenges in projecting freshwater hydrologic and ecosystem 8.5.1. Information required to project responses of arctic fish . .393 responses . .354 8.5.1.1. Fish and climate parameters . .394 8.1.2. Quantifying impacts and likelihood . .356 8.5.1.2. Ecosystems, habitat, and fish: climate change in the 8.1.3. Chapter structure . .356 context of multiple stressors . .400 8.2. Freshwater ecosystems in the Arctic . .356 8.5.1.3. Effects of climate-induced changes on physical habitat .402 8.2.1. General features of the Arctic relevant to freshwater 8.5.1.4. Issues at the level of fish populations . .403 ecosystems . .356 8.5.2.Approaches to projecting climate change effects on arctic fish 8.2.2. Freshwater inputs into arctic aquatic ecosystems . .357 populations. .403 8.2.3. Structure and function of arctic freshwater ecosystems . .358 8.5.2.1. Physiological approaches . .404 8.2.3.1. Rivers and streams, deltas, and estuaries . .358 8.5.2.2. Empirical approaches . .404 8.2.3.2. Lakes, ponds, and wetlands . .361 8.5.2.3. Distributional approaches . .405 8.3. Historical changes in freshwater ecosystems . .365 8.5.3. Climate change effects on arctic freshwater fish populations . .406 8.3.1. Ecosystem memory of climate change . .365 8.5.3.1. Region 1: European percids . .406 8.3.1.1. Lentic archives . .365 8.5.3.2. Region 2: Fishes in Siberian rivers . .406 8.3.1.2. Lotic archives . .366 8.5.3.3. Region 3:Alaskan game fish . .407 8.3.1.3.Terrestrial and wetland archives . .366 8.5.3.4. Region 4: Northern Québec and Labrador salmonid 8.3.2. Recent warming: climate change and freshwater ecosystem and pike populations . .407 response during the Holocene . .366 8.5.4. Effects of climate change on arctic anadromous fish . .408 8.3.2.1. Region 1:Arctic Europe, eastern Greenland, the Russian 8.5.5. Impacts on arctic freshwater and anadromous fisheries . .410 European North, and the North Atlantic . .367 8.5.5.1. Nature of fisheries in arctic freshwaters . .410 8.3.2.2. Region 2: Siberia . .368 8.5.5.2. Impacts on quantity and availability of fish . .411 8.3.2.3. Region 3: Chukotka, the Bering Sea,Alaska, and western 8.5.5.3. Impacts on quality of fish . .412 Arctic Canada . .369 8.5.5.4. Impacts on access to and success of fisheries . .413 8.3.2.4. Region 4: Northeastern Canada, Labrador Sea, Davis 8.5.5.5. Impacts on specific fishery sectors . .416 Strait, and West Greenland . .371 8.5.5.6. Impacts on aquaculture . .417 8.3.3. Climate change and freshwater ecosystem response during the 8.5.6. Impacts on aquatic birds and mammals . .417 Industrial Period . .371 8.6. Ultraviolet radiation effects on freshwater ecosystems . .419 8.4. Climate change effects . .372 8.6.1. Climate effects on underwater ultraviolet radiation exposure . .419 8.4.1. Broad-scale effects on freshwater systems . .372 8.6.2. Ultraviolet radiation effects on aquatic biota and ecosystems . .420 8.4.2. Effects on hydro-ecology of contributing basins . .376 8.6.3. Impacts on physical and chemical attributes . .423 8.4.3. Effects on general hydro-ecology . .379 8.6.4. Impacts on biotic attributes . .424 8.4.3.1. Streams and rivers, deltas, and estuaries . .379 8.6.4.1. Rivers and streams . .424 8.4.3.2. Lakes, ponds, and wetlands . .381 8.6.4.2. Lakes, ponds, and wetlands . .425 8.4.4. Changes in aquatic biota and ecosystem structure and 8.7. Global change and contaminants . .427 function . .384 8.7.1. Contaminant pathways and arctic freshwater ecosystems . .427 8.4.4.1. Effects on biological communities, biodiversity, and 8.7.2. Persistent organic pollutants in arctic catchments . .427 adaptive responses . .384 8.7.3. Mercury in arctic catchments . .432 8.4.4.2. Effects on food web structure and dynamics . .386 8.8. Key findings, science gaps, and recommendations . .433 8.4.4.3. Effects on primary and secondary production . .388 8.8.1. Key findings . .433 8.4.4.4. Effects on carbon dynamics . .391 8.8.2. Key science gaps arising from the assessment . .437 8.8.3. Science and policy implications and recommendations . .438 Acknowledgements . .438 References . .438 Appendix. Scientific names of arctic fishes alphabetically listed by common name used in the text and boxes . .452 354 Arctic Climate Impact Assessment Summary iad of smaller permanent and semi-permanent lakes and ponds; vast areas of wetlands and peatlands; and coastal Changes in climate and ultraviolet radiation levels in the estuarine and river delta habitats. In turn, these fresh- Arctic will have far-reaching impacts, affecting aquatic water systems contain a wide diversity of organisms that species at various trophic levels, the physical and chemi- have developed adaptations to cope with the extreme cal environment that makes up their habitat, and the environmental conditions they face. Examples include processes that act on and within freshwater ecosystems. life-history strategies incorporating resting stages and Interactions of climatic variables, such as temperature diapause, unique physiological mechanisms to store and precipitation, with freshwater ecosystems are highly energy and nutrients, an ability to grow and reproduce complex and can propagate through the ecosystem in quickly during brief growing seasons, and extended life ways that are difficult to project.This is partly due to a spans relative to more temperate species. poor understanding of arctic freshwater systems and their basic interrelationships with climate and other Thus, given the regional complexity of climate and land- environmental variables, and partly due to a paucity of scape and the diversity of freshwater ecosystems and long-term freshwater monitoring sites and integrated their associated biota, projecting the potential impacts of hydro-ecological research programs in the Arctic. future climate change and ultraviolet (UV) radiation exposure presents significant challenges.What is certain This chapter begins with a broad overview of the general is that the responses are likely to be quite variable and hydrological and ecological features of the various fresh- highly specific to particular freshwater ecosystems, their water ecosystems in the Arctic, including descriptions of biota, and the ecological and biophysical circumstances each ACIA region, followed by a review of historical in which they occur. changes in freshwater systems during the Holocene. The chapter continues with a review of the effects of 8.1.1. Challenges in projecting freshwater climate change on broad-scale hydro-ecology; aquatic hydrologic and ecosystem responses ecosystem structure and function; and arctic fish, fish- eries, and aquatic wildlife. Special attention is paid to The first and most significant challenge in projecting changes in runoff, water levels, and river- and lake-ice responses of freshwater systems to climate change relates regimes; to biogeochemical processes, including carbon to the limited understanding of how the climate system is dynamics; to rivers, lakes, ponds, and wetlands; to coupled to, and influences, key physical and biophysical aquatic biodiversity and adaptive capacities; to fish popu- processes pertinent to aquatic ecosystems, and in turn lations, fish habitat, anadromy, and fisheries resources; how these affect ecological structure and function. and to aquatic mammals and waterfowl. Potential syner- Figure 8.1 summarizes the complex and often hierarchi- gistic and cumulative effects are also discussed, as are the roles of ultraviolet radiation and contaminants. The nature and complexity of many of the effects are illustrated using case studies from around the circum- polar north, together with a discussion of important threshold responses (i.e., those that produce stepwise and/or nonlinear effects).The chapter concludes with a summary of key findings, a list of gaps in scientific understanding, and policy-related recommendations. 8.1. Introduction The Arctic, which covers a significant area of the Northern Hemisphere, has a number of prominent and unique climatic, geological, and biophysical features. The region is typified by extreme variability in climate and weather, prolonged darkness in the winter and con- tinuous daylight in the summer, the prevalence of vast areas of permafrost, and the dominance of seasonal ice and snow cover.The Arctic also has a diversity of terrains that contain a significant number and diversity of fresh- water ecosystems. Fig. 8.1. Climate–ecosystem interactions.The interactions The Arctic has some of the largest rivers in the world among and within components tend to be sequential but com- (e.g., the Lena, Mackenzie, Ob, and Yenisey); numerous plex. However, complex feedbacks also exist both within major permanent and semi-permanent streams and rivers classes of components (e.g., trophic structure linkages with bio- geochemical cycling), as well as between components (e.g., ice draining mountains, highlands, and glaciated areas; large duration and timing feedbacks to the regional climate system), lakes such as Great Bear, Great Slave, and Taymir; a myr- but are not illustrated above for visual clarity. Chapter 8 • Freshwater Ecosystems and Fisheries 355 cal interactions between climatic variables (e.g., radia- hampers the ability to make accurate and reasonable pro- tion, precipitation, and temperature), their influence on jections regarding such effects within arctic freshwater the biophysical features of freshwater ecosystem habitat, ecosystems with high levels of certainty.