Lake Fisheries Research Articles

Climate change projections for lake whitefish ( Coregonus clupeaformis ) recruitment in the 1836 Treaty Waters of the Upper Great Lakes

Abstract Lake whitefish ( Coregonus clupeaformis ) is an ecologically, culturally, and economically important species in the Laurentian Great Lakes. Lake whitefish have been a staple food source for thousands of years and, since 1980, have supported the most economically valuable (annual catch value ≈ US$16.6 million) and productive (annual harvest ≈ 7 million kg) commercial fishery in the upper Great Lakes (Lakes Huron, Michigan, and Superior). Climate changes, specifically changes in temperature, wind, and ice cover, are expected to impact the ecology, production dynamics, and value of this fishery because the success of recruitment to the fishery has been linked with these climatic variables. We used linear regression to determine the relationship between fall and spring air temperature indices, fall wind speed, winter ice cover, and lake whitefish recruitment in 13 management units located in the 1836 Treaty Waters of the Upper Great Lakes ceded by the Ottawa and Chippewa nations, a culturally and commercially important region for the lake whitefish fishery. In eight of the 13 management units evaluated, models including one or more climate variables (temperature, wind, ice cover) explained significantly more variation in recruitment than models with only the stock–recruitment relationship, using corrected Akaike's Information Criterion comparisons (ΔAICc > 3). Isolating the climate–recruitment relationship and projecting recruitment with the Coupled Hydrosphere-Atmosphere Research Model (CHARM) indicated the potential for increased lake whitefish recruitment in the majority of the 1836 Treaty Waters management units. These results can inform adaptive management strategies by providing anticipated implications of climate on lake whitefish recruitment.

The integration of social science information into Great Lakes fishery management: Opportunities and challenges

Fishery management is increasingly moving toward management that accounts for environmental and social dimensions. Such an approach requires the integration of natural and social science information into planning and decision-making processes. The actual integration of social science information, however, remains limited in many policy and decision-making processes within fisheries. Our study provides insights into factors that influence the intention to use social science information among fishery managers and the actual integration of such information into fishery management. Based on interviews with fishery managers in the Great Lakes, we find that the lack of social science expertise in fishery management agencies leads to multiple negative beliefs and attitudes, and subsequently a low intention to use social science information in decision-making processes. At the same time, the paper finds that more expertise in decision-making tools and basing social science on equal footing with natural sciences within fishery management institutions appears critical to advance the actual integration of social science information in fishery management.

Reviews of Science for Science Librarians: The Great Lakes Fishery—Current Status, Human Impacts, and Literature

The Laurentide Great Lakes are the single largest fresh water system in the world and home to a significant fishery. This article reviews the research and literature on the Great Lakes fishery and describes how a history of overfishing, habitat change, aquatic nonindigenous species (ANS), and compromised water quality caused population declines for several native fish species and reduced commercial fishery productivity. While recreational fishing remains both a popular activity and a significant industry in the Great Lakes region, understanding the ecosystem interactions within the Great Lakes is a key to understanding the decline in fishery production and provides insight into how best to maintain other freshwater fisheries facing similar challenges.

Lake Huron's Entangled Eden: Fish, Fisheries, and Lost Opportunities in Freshwater Borderlands, 1900–1940

Lake Huron’s Entangled Eden: Fish, Fisheries, and Lost Opportunities in Freshwater Borderlands, 1900-1940 By Kent LaCombe Lake Huron is both a dynamic, interconnected ecosystem and a politically divided international borderland between Michigan and Ontario. However, even as it serves as a barrier and dividing line, the lake concurrently fosters exchange and migration. The international boundary between Canada and the United States is often referred to as a permeable border.1 In the nineteenth century, the Great Lakes fueled increasing market linkages between the two nations. Agricultural products, fishes, and other goods were shipped across the lakes; human migrations were common. Despite the interchange, commercial fishing was an increasingly competitive venture. The Lake Huron fisheries story is one of the contentious nature of managing borderlands resources, the pernicious influence of short-term thinking, and the tendency of stakeholders to focus on economic selfinterest as fisheries stakeholders successfully blocked the adoption of new regulations to the detriment of their own industry. Any critical management plan for fishing was ultimately stalled and derailed, leading to further adverse environmental changes. Although there have been a good number of environmental and scientific histories of the Great Lakes, any systematic historical investigation of Lake Huron’s commercial fisheries remains woefully incomplete. As present day environmental managers struggle to address new and evolving challenges in aquatic environments, a careful analysis of past assumptions, motivations, mistakes, and other modes of destructive resource exploitation can aid in the formation of improved conservation 1 For an excellent explanation of the term’s applicability to the region, see John J. Bukowczyk et al., Permeable Border (Pittsburgh: University of Pittsburgh Press, 2005), 1-9. THE MICHIGAN HISTORICAL REVIEW 41:1 (SPRING 2015): 25-56© 2015 Central Michigan University. ISSN 0890-1686 All rights reserved 26 The Michigan Historical Review and preservation strategies.2 Today economic priorities and anthropocentric considerations continue to provide the foundations of freshwater environmental management. Yet it was those same priorities which earlier drove decisions on how to manage the Great Lakes commercial fisheries, ultimately to their detriment. The period from 1900 to 1940 is especially noteworthy in the histories of the Great Lakes due to the numerous examples of lost opportunities at cooperative international management, particularly within the interwar period. With the outbreak of World War II, a wartime shift toward maximum food production and the successful formulation of the Great Lakes Fishery Commission after the war further wove a vibrant historical tapestry that lies outside the scope of this work. Few records provide a better historical reconstruction of the state of international fishery than the accumulated testimonies of individual commercial fishermen, scientists, and government officials concerning the utilization and management of critical freshwater resources. Catch records are also a useful, though incomplete, resource. Michigan did not adopt comprehensive catch reporting until 1929 and Ontario waited until the 1940s.3 Even considered as minimum totals, the incomplete catch data of the nineteenth and early twentieth centuries chronicled dramatic declines.4 Canada took the lead in developing broad regulatory legislation. While its international negotiations remained in the hands of the British Crown until the 1931 Statute of Westminster, federal governance of domestic resources was a reality following the Constitution Act of 1867. 2 See William Ashworth, The Late, Great Lakes: An Environmental History (New York: Alfred A. Knopf, 1987); Arthur F. McEvoy, The Fisherman’s Problem: Ecology and Law in the California Fisheries, 1850-1980 (New York: Cambridge University Press, 1986); Margaret Beattie Bogue, Fishing the Great Lakes: An Environmental History, 1783-1933 (Madison: The University of Wisconsin Press, 2000); Michael J. Chiarappa and Kristin M. Szylvian, Fish for All: An Oral History of Multiple Claims and Divided Sentiment on Lake Michigan (East Lansing: Michigan State Press, 2003); Milo M. Quaife, ed., The American Lakes Series (Indianapolis: The Bobbs-Merrill Company, 1944-1949); Arthur F. McEvoy, The Fisherman’s Problem: Ecology and Law in the California Fisheries, 1850-1980 (New York: Cambridge University Press, 1986); Robert Doherty, Disputed Waters: Native Americans and the Great Lakes Fishery (Lexington: The University Press of Kentucky, 1990). 3 Travis O. Brenden et al., “Great Lakes Commercial Fisheries: Historical Overview and Prognosis for the Future,” in Great Lakes Fisheries Policy and Management...

Influence of macrophyte-induced hypoxia on fish communities in lakes with altered hydrology

Altered flow regimes in lakes can change macrophyte habitats from dynamic, species-rich communities to dense, monotypic communities that can change the physicochemical environment available to fish. We tested whether fish community composition, fish density, fish species richness, and fish species diversity changed across a range of dissolved oxygen concentrations (DO; mg/L) in dense stands of several macrophyte species that are commonly the target of macrophyte control efforts in Florida lakes. We sampled fish communities within growths of 5 emergent macrophyte species including cattail (Typha spp.), pickerelweed (Pontedaria cordata), smartweed (Polygonum spp.), torpedograss (Panicum repens), and water primrose (Ludwigia spp.) at lakes Kissimmee and Istokpoga, Florida. Fish communities were sampled using 3 different enclosure gears treated with rotenone, and DO was measured in mid-water column at each site. Macrophyte biomass and DO concentrations were inversely related. Poeciliids accounted for 90% of the catch composition, and density was inversely related to DO. Centrarchid, cyprinodontid, and sport fish densities were highest at DO >4 mg/L. Restoration efforts should reduce dense emergent macrophyte biomass to reestablish habitats with greater habitat heterogeneity, which will increase DO concentrations. These efforts should increase fish species diversity, fish species richness, and improve recreational fisheries in lakes with stabilized water levels.

Fish assemblage of a Pampean shallow lake, a story of instability

Pampean lakes are characterised by the alternation of flood and drought periods, but little is known about its effects on fish assemblage in an extended temporal scale. This study analyses the temporal variability of the fish assemblage in Chascomus Lake, and discusses the role of temperature and precipitation as potential drivers of fish composition shifts. Data acquisition was based on experimental fishing performed from 1999 to 2013 and from historical fishing records. Two alternative fish assemblage configurations were identified by cluster analysis. Odontesthes bonariensis, Parapimelodus valenciennis and Cyphocharax voga were the dominant species, which accounted for 70–80% of the relative abundance. The species O. bonariensis showed temporal fluctuations in its representativeness, changing from dominant to almost absent, whereas C. voga and P. valenciennis changed their abundance following a similar pattern along time. When historical data were considered, Platanichthys platana appeared as the fourth most relevant species. Precipitation, critical temperatures and fish mortalities were identified as the main drivers of species abundance shifts. This study highlights the importance of long-term assessments to understand the influence of climatic factors and the need to maintain or restore natural ecological processes as the basis to support dynamic sustainable fisheries in Pampean shallow lakes.

Kenya Research Station and its Research Activities

The Institute of Tropical Medicine Kenya Research Station of Nagasaki University (NUITM) was established in 2005 with Japan’s Ministry of Education, Culture, Sports, Science and Technology (MEXT) funds. The station involves clinical and epidemiological research programs focusing on tropical medicine and emerging infectious diseases based on education and research exchanges between Africa and Japan. This project is supported by about 22 Japanese staff members, including short-termers, in addition to 85 Kenyan staff members. It has at least 12 research groups studying the prevention of tropical and emerging diseases in collaboration with stakeholder institutions. The station also implements a JICA grassroots technical cooperation project since 2012. In April 2010, the Nagasaki University Africa Research Station was incorporated into the Kenya Research Station, enabling other faculties to conduct research in Kenya. The Nagasaki University School of Dentistry then started an oral health survey in Mbita and the Schools of Fisheries, Engineering, and Health Sciences have started joint research projects conserving and managing Lake Victoria basin water and fishery resources. Our aim is to develop a foundation enabling researchers from all different fields to conduct research for improving local community health and living standards. The NUITM was invited to become an associate member of the Japan Initiative for Global Research Network on Infectious Diseases (J-GRID) in 2011.

Consequences of fish stocking density in a recreational fishery

Density-dependent processes resulting from fish stocking were demonstrated to have a significant impact on recreational fishery performance, and this case study will be of use to guide fish stocking decisions in other fisheries. We evaluated a put-grow-and-take lake fishery stocking program for Chinook salmon (Oncorhynchus tshawytscha) located in south-western Victoria, Australia. We hypothesised that recreational fishery performance would show significant density-dependent relationships with fish stocking. To test this hypothesis, we used Wald F tests in a general linear regression model to evaluate relationships between a long-term historical fish stocking program and fishery performance, including angler and net catch rates and weight, length, and condition of caught fish. Our results yielded (i) significant positive relationships between angler and net catch rate of Chinook salmon with the number of Chinook salmon stocked in the same year and (ii) significant negative relationships between the weight of angler-caught Chinook salmon with both the number of Chinook salmon stocked in the same year and total number of fish stocked (apart from Chinook salmon) over the previous three year period.

Environment, Culture, and The Great Lakes Fisheries

The commercial fisheries of the United States and Canadian Great Lakes are in a long period of decline. Detailed statistics kept for well over a century document a fluctuating pattern of harvests of the major commercial species. In the 1940s, sea lamprey began to devastate the fisheries, an effect that has not been fully countered. Overfishing, nonnative species, declining nutrient levels, and chemical pollution have contributed to reduced catches. Court decisions in the United States and Canada during the past thirty years have awarded a sizable share of commercial fishing rights to Native North Americans for their own support and sustenance. The Lake Erie yellow perch and walleye fishery, based mainly in Ontario, is the most successful commercial fishing operation in the region. Despite the many environmental and cultural challenges, the Great Lakes fisheries live on.

Management of Great Lakes fisheries: Progressions and lessons

Fishery resources include the fishes, the other biota they interact with, and the habitats they occupy. The historical sequences in the use and management of these resources may be considered as a series of interacting sequences of change. These sequences can span from social, economic, institutional and landscape changes, through water quality, habitat supply, and climate changes, to biotic composition changes, introductions and extinctions, and species harvest changes. A selection of these sequences is examined for the St. Lawrence-Great Lakes which has been subjected to intense development and study over the last 200 years. While the whole basin is considered, some detailed attention is given to Lake Ontario and, within it, the Bay of Quinte. Brief selective development histories are given for the three areas as context. The management history is outlined and critiqued. While much progress has been achieved in cleaning up the load-driven problems in the basin, little secure progress toward rehabilitation and sustainability has been achieved. In the current period of economic problems, governments, particularly Canada’s, are undoing past ecosystem management progress. The development of St. Lawrence-Great Lakes’ ecosystem science has drawn heavily from both oceanography and limnology. A brief, selective overview of several progressions in ecosystem science illustrates how knowledge and understanding of this ecosystem has expanded over the last 60 years, providing an improved basis for management action. As with use and management, the science of fishery resource management has consisted of many historical progressions. The many sequences in the St. Lawrence-Great Lakes management and science histories lend support for recognition of (i) the importance of taking an ecosystem approach to renewable resource management, (ii) the value of adaptive management practices and, particularly, (iii) the vital complementary roles of long-term monitoring and mathematical modelling.

Fishing down or fishing up in Chinese freshwater lakes

AbstractChanges in mean trophic level (MTL) of catches have been widely used to reflect the impact of industrial fisheries on aquatic ecosystems because this measure represents the relative abundance of fished species across the trophic level spectrum. In this study, fisheries data from six important freshwater lakes at the middle‐lower Yangtze River and Huaihe River reach of Southern China from 1949 to 2009 were used to evaluate changes in catch MTL. After fishery markets opened at 1985, fish catches increased significantly in all the lakes. Lakes Poyang and Dongting, which were dominated by omnivores and connected to the Yangtze River, showed no significant change in catch MTL before and after 1985. Catch MTL in lakes Taihu and Hongze increased significantly due to an increase in the proportion of pelagic zooplanktivorous. Catches in Lake Chaohu were dominated by zooplankton‐feeding lake anchovy, Coilia ectenes Temminck & Schlegel and icefish, Neosalanx taihuensis Chen, while Lake Donghu was dominated by phytoplanktivorous carps. Due to low biodiversity, catch MTL of these two lakes showed no significant change before and after 1985. Both fisheries‐based and human activities‐based drivers influenced the structure and catch MTL of fisheries in Chinese freshwater lakes.

An empirical analysis of the consequences of zebra mussel invasions on fisheries in inland, freshwater lakes in Southern Ontario

With increasing human use of North American inland lakes for recreational purposes, there is a greater probability of the incidental transfer and introduction of aquatic invasive species within them. This raises concern over the potential ecological and economic impacts that invasive species could have in these highly valued freshwater ecosystems. In this study, we focus our interests on 63 inland lakes distributed across the Southern Ontario landscape in order to evaluate whether concerns are warranted over potential adverse impacts of a well-known aquatic invasive species (the zebra mussel (Dreissena polymorpha)) on native fish assemblages and targeted game species (i.e., walleye (Sander vitreus), smallmouth bass (Micropterus dolomieu), lake trout (Salvelinus namaycush), and northern pike (Esox lucius)). Through the analysis of a comprehensive and multivariate dataset comprising lake morphometric, water chemistry, fish assemblage, fish metric, and zooplankton haul data, we examined the potential consequences of zebra mussel invasions in inland lakes. It was found that condition, growth, and relative abundance of some of the most highly valued game fish in inland lakes significantly varies among lakes with and without zebra mussel, though the nature of such effects differed for each of the fish species examined. In addition, it was shown that the species composition (i.e., identity and relative abundance) of active, large-bodied fish assemblages within a lake can indicate zebra mussel presence/absence with a high degree of certainty. Finally, while correlations between zebra mussel presence and the richness, abundance, growth, and condition of certain fish species were found, the results of this study indicate that the potential consequences of this well-known aquatic invader to fisheries in inland lakes may be less dramatic than those reported within the Great Lakes.

Identifying useful climate change information needs of Great Lakes fishery managers

There is mounting evidence that climatic changes have altered physical conditions in the Laurentian Great Lakes and will continue to do so. In the face of this challenge, fishery managers require useful information to support decision making. We utilized a mixed methods approach, including an email survey and focus groups with fishery managers, to identify information gaps in understanding the impacts of climate change on fishery management. The fishery managers perceived climate change to be a threat to the fishery and identified specific climate change information that would be most useful for their work. This includes information on how climate change will affect fish populations, trophic interactions, and habitat conditions, as well as how climate change will interact synergistically with other management concerns. Our findings indicate that future research efforts should focus on species of commercial or recreational interest and species for which restoration plans already exist. Although modeling efforts that incorporate both biotic and abiotic factors may be useful to fishery management stakeholders, to enhance utility for managers, researchers should work with the information users to understand the pertinence of various temporal and spatial scales when designing studies and presenting information. Many fishery managers believe that valuable information related to climate change, particularly long-term datasets, already exists but has not been made easily accessible or brought to their attention. Finally, in order to increase the awareness and use of their climate research, researchers should present at relevant meetings in addition to just emailing reports and publishing scientific manuscripts.

Elucidation of ecosystem attributes of two Mackenzie great lakes with trophic network analysis

The Mackenzie Basin in northwestern Canada is a high-latitude region, with one of the largest watersheds in the world. The Mackenzie great lakes, consisting of Great Bear Lake, Great Slave Lake and Lake Athabasca form the large lake complex. The human presence in the area is small in terms of population and industry and thus these ecosystems remain comparatively pristine and show no major changes in the fish communities. Ecopath with Ecosim (EwE), the most important and most used ecosystem trophic network modelling tool to study the ecosystem-level responses to changes, and information available in the scientific literature together with traditional knowledge about Great Slave Lake and Great Bear Lake was used to elucidate the ecosystem attributes. Our models give a cohesive view of these two ecosystems that will allow researchers and decision makers to explore questions regarding the stability of fisheries and future ecological change. The moderate trophic level of fish catch along with the small percentage of primary production required to sustain fisheries in both lakes demonstrated that fisheries were sustainable during the time period modelled. The ecosystem indices and attributes of the comparatively pristine Mackenzie great lakes were compared with those of two Laurentian Great Lakes having similar types of Ecopath ecosystem models. The metrics utilized to assess comparatively the ecosystem's maturity, stability and health indicated a decline in ecosystem maturity and stability from pristine Great Bear Lake to transitioning Lake Ontario.

Qarun Lake fisheries; Fishing gears, Species composition and Catch per unit effort

Qarun Lake is a closed salty basin located about 90km southern Cairo Egypt, cover an area of 230km 2 with annual production of about 3000 tonnes. The present study assessed the lake fishery for better management purpose. Data, information and samples were collected through 42 field trips and 311 fishermen interviews during fishing season (2010-2011). The lake was divided into three sub-areas, east, middle and west. It was found that the fishing gears used in the lake were; 1-Trammel nets with four types differed in their dimensions, mesh sizes and mainly targeting Mugil cephalus, Tilapia zillii, Solea spp. and Liza spp. 2- Seine nets with three types that were targeting M. cephalus, anchovy and shrimp. 3- Others fishing methods (Fishing aggregation system, traps and hooks) targeting mainly T. zillii. For each gear and methods used, the species composition (target and by-catch) and catch per unit effort were estimated according to sub-area and season. It is realized that middle area was more productive with higher species diversity. The present study recommends prohibiting traps in spring and all seine nets except Gahzl Zardina during summer in west and improving the fish catch and effort statistics for sustainable management of this valuable resource.

Response to Dettmers et al. (2012): Great Lakes Fisheries Managers Are Pursuing Appropriate Goals

ABSTRACTAfter reading the article by Dettmers et al. in the November 2012 issue of Fisheries (“Management of Alewife Using Pacific Salmon in the Great Lakes: Whether to Manage for Economics or the Ecosystem?”), we feel compelled to respond and to present a different perspective on this important management issue. Despite the generally positive contribution to Great Lakes literature made by this article, it contains several inaccuracies concerning the past and current state of Great Lakes ecosystems. Dettmers et al. present an oversimplification of options currently available to Great Lakes fisheries managers; a false dichotomy describing only two future options for management of these fisheries. We submit that managers could strive to “… maintain a diverse salmonid community, [while proceeding] (to the extent possible) with native species rehabilitation” and we conclude that, “… on each of the Great Lakes, managers are pursuing appropriate goals, managing the aquatic resources of the lakes for the greatest public good, given the variability in conditions and likelihood for success specific to each lake.”

Growth and Survival of Sea Lampreys from Metamorphosis to Spawning in Lake Huron

AbstractLarval Sea Lampreys Petromyzon marinus live burrowed in stream bottoms and then metamorphose into their parasitic stage. Among larvae that metamorphose in a given year (i.e., parasitic cohort), autumn out‐migrants (October–December) to the Laurentian Great Lakes can feed on fish for up to 6 months longer than spring out‐migrants (March–May), which overwinter in streams without feeding. We evaluated whether the season of out‐migration affected growth or survival of newly metamorphosed Sea Lampreys in Lake Huron. Newly metamorphosed individuals (n = 2,718) from three parasitic cohorts were netted during their out‐migration from Black Mallard Creek, Michigan, to Lake Huron during autumn 1997 through spring 2000; each out‐migrant was injected with a sequentially numbered coded wire tag and was released back into the creek. After up to 18 months of feeding in the Great Lakes, 224 (8.2%) Sea Lampreys were recaptured (in 1999–2001) as upstream‐migrating adults in tributaries to Lakes Huron and Michigan. Recovery rates of autumn and spring out‐migrants as adults were 9.4% and 7.8%, respectively, and these rates did not significantly differ. Overwinter feeding (i.e., as parasites) by autumn out‐migrants did not produce adult mean sizes greater than those of spring out‐migrants. Because we detected no growth or survival differences between autumn and spring out‐migrants, the capture of newly metamorphosed Sea Lampreys at any point during their out‐migration should provide equal reductions in damage to Great Lakes fisheries. The absence of a difference in growth or survival between autumn and spring out‐migrants is an aspect of Sea Lamprey life history that yields resiliency to this invasive parasite and complicates efforts for its control in the Great Lakes.

Coupled human and natural system dynamics as key to the sustainability of Lake Victoria’s ecosystem services

East Africa's Lake Victoria provides resources and services to millions of people on the lake's shores and abroad. In particular, the lake's fisheries are an important source of protein, employment, and international economic connections for the whole region. Nonetheless, stock dynamics are poorly understood and currently unpredictable. Furthermore, fishery dynamics are intricately connected to other supporting services of the lake as well as to lakeshore societies and economies. Much research has been carried out piecemeal on different aspects of Lake Victoria's system; e.g., societies, biodiversity, fisheries, and eutrophication. However, to disentangle drivers and dynamics of change in this complex system, we need to put these pieces together and analyze the system as a whole. We did so by first building a qualitative model of the lake's social-ecological system. We then investigated the model system through a qualitative loop analysis, and finally examined effects of changes on the system state and structure. The model and its contextual analysis allowed us to investigate system-wide chain reactions resulting from disturbances. Importantly, we built a tool that can be used to analyze the cascading effects of management options and establish the requirements for their success. We found that high connectedness of the system at the exploitation level, through fisheries having multiple target stocks, can increase the stocks' vulnerability to exploitation but reduce society's vulnerability to variability in individual stocks. We describe how there are multiple pathways to any change in the system, which makes it difficult to identify the root cause of changes but also broadens the management toolkit. Also, we illustrate how nutrient enrichment is not a self-regulating process, and that explicit management is necessary to halt or reverse eutrophication. This model is simple and usable to assess system-wide effects of management policies, and can serve as a paving stone for future quantitative analyses of system dynamics at local scales.

Laurentian and African Great Lakes--Different Strategies in the Fight Against Invasive Species

Invasive exotic species are a reality in all ecosystems. These biological invaders disrupt ecological patterns and cause billions of dollars in economic damage. Justifiably, governments are stepping up their response. However, while many invaders are considered unmitigated ecological disasters, a number of species have become important and controversial parts of the regional economy. In the Laurentian Great Lakes, the invasive species issue has been addressed through a number of unilateral and multilateral attempts at the state, national, and international level. This “law of the lakes” has evolved towards the implementation of the Great Lakes Water Quality Agreement of 2012, which uses a framework-protocol basis to combat the problem through a preservation-focused ecosystem approach. The management of water and fisheries in the African Great Lakes has similar problems addressing invasive species. However, states in this region have responded to the threat differently, particularly as it pertains to economically viable invasive fish species. Various state-level legislation and policy shows that the invasive threat is acknowledged, but follows a conservation management approach, which hopes to maintain the essential economic opportunities that the invasive species provide for area residents. The experiences of the Laurentian Great Lakes in moving their invasive species management forward can be used as a template to update and focus the response in the African Great Lakes.

Economic effectiveness of stocking lakes in Poland

This paper was based on survey data regarding stocking and fish catches from the 1995-2007 period that was collected from enterprises licensed to manage lake fisheries in Poland. An average of 70 questionnaires were collected annually from lake fisheries enterprises exploiting a combined lake surface area of 228,102 ha. The eleven species of fish analyzed were those that were the most intensely stocked. The effectiveness of stocking in Polish lakes in this period was analyzed by calculating the mean annual stocking effectiveness coefficient, i.e, the value in PLN ha -1 of catches of a given species per 1 PLN ha -1 of stocking this species in a given year. The highest mean annual stocking effectiveness coefficient was noted for pikeperch Sander lucioperca (L.) (4.21 PLN ha -1 ) and bighead carp Aristichthys noblilis Rich. together with silver carp Hypophthalmichthys molitrix Val. (4.02 PLN ha -1 ); however, these values were unstable. A similar situation was noted for eel Anguilla anguilla (L.), which had the next highest stocking effectiveness coefficient at 2.32 PLN ha -1 . The stocking effectiveness coefficient was stable for tench Tinca tinca (L.) (2.16 PLN ha -1 ), vendace Coregonus albula (L.) (2.09 PLN ha -1 ), and pike Esox lucius L. (1.31 PLN ha -1 ). The stocking of whitefish Coregonus lavaretus (L.), Wels catfish Silurus glanis (L.), crucian carp Carassius carassius (L.) together with Prussian carp Carassius auratus gibelio Bloch., common carp Cyprinus carpio L., and grass carp Ctenopharyngodon idella Val., were ineffective economically from the viewpoint of the size of commercial catches.