Risks Associated with Lake Trout stocking on Lake Champlain's Food Web and Fishing Industry

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1 Risks Associated with Lake Trout stocking on Lake Champlain's Food Web and Fishing Industry Chris Blazek Justin Forster Danny Hopkins Ben Katz Cassie McGoldrick Lake trout (Salvelinus namaycush) stocking efforts in Lake Champlain are associated with many direct and indirect ecological and economical issues. Stocking lake trout has a strong influence on the natural food web interactions by introducing another top predator to the aquatic system. There is pressure on rainbow smelt (Omserus mordax), a native forage fish, by not only lake trout, but by the presence of invasive alewives (Alosa pseudoharengus). These two species are similar in terms of diet and habitat. The alewives have foreseeable impacts on native rainbow smelt populations due to this competition. The dynamics that play out between lake trout, smelt and alewife populations will have a large influence on the food web in the lake. A significant impact is the alterations to zooplankton and phytoplankton populations, which in turn affect the potential for algal blooms. Overstocking fish can lead to ecological issues such as higher waste produced, increased demand for oxygen and nutrients from the water and a higher demand for food resources. In addition, overpopulation can increase the risk of spread of pathogenic organisms to wild fish stocks due to higher densities. This risk assessment will explore the interactions among these species in order to evaluate the issues associated with stocking lake trout into Lake Champlain. The evaluation of lake trout stocking will incorporate the economic implications associated, which will be assessed alongside of the ecological impacts. It is recommended that further study and analysis be done on alewife and smelt interactions, along with long term monitoring of the lake trout growth rates to accurately determine adequate stocking numbers and how to appropriately respond in events of overstocking.

2 Introduction The goal of this report is to assess the impacts of stocking lake trout in terms of its ecological and economical implications. Stocking of lake trout has many ecological effects on predator prey dynamics in Lake Champlain. If stocking numbers are not regulated and lake trout become overpopulated, the forage base and food web interactions will become severely altered in Lake Champlain. Overstocking lake trout would have several ecological repercussions, potentially leading to unstable food webs and the loss of desired native species in the lake. As a forage species, rainbow smelt are particularly vulnerable to an overabundant lake trout population. Lake trout live for about 10 years, and may cause compounding effects if overstocking were to occur. Smelt are also under pressure due to their overlapping feeding habits with alewives. This interspecific competition, in combination with lake trout predation, leaves smelt at a significant risk of extirpation in Lake Champlain. Alewives pose their own set of interspecific threats to the aquatic food web. Their selective feeding habits often cause the zooplankton community to shift from predominantly larger species (cladocera) to smaller species (copepods and rotifers). Cladocera (~1-2 mm) are larger than copepods (~1 mm) and rotifers ( um), and have different foraging habits. The larger zooplankton are able to eat larger sized particles of phytoplankton than the smaller species can. The shift in sizes is likely to have effects on the balance of phytoplankton in the lake, which may lead to an increased risk of algae blooms. Economically, overstocking lake trout would result in wasted time and an unnecessary cost of production at the fish hatcheries and those that fund the stocking efforts such as the State Departments of Fish and Wildlife. There may also be financial loss in restocking efforts of species of other fish populations that have decreased due to the influx of lake trout predation. Finally, State Fish and Wildlife agencies rely on a consistent flow of income from sport anglers and fishing licenses. Thus, if the population of lake trout in Lake Champlain change, then the demand for fishing licenses may change as well. Our objectives are to: (1) Examine the life history traits of the lake trout and rainbow smelt to better understand how these species interact. (2) Determine whether the lake trout in Lake Champlain are a self-sustaining, reproductive population. (3) Analyze lake trout annual stocking data. (4) Seek the knowledge of experts in the field, including Ellen Marsden of the Rubenstein School of Environment and Natural Resources, and Dave Tilton and Brian Chipman of the Vermont Department of Fish and Wildlife. Methods Information regarding this analysis was gathered primarily via web searches and interviews with a few experts in the field. We spoke with Ellen Marsden of the Rubenstein School of Environment and Natural Resources and Dave Tilton of the Vermont Department of Fish and Wildlife to gain insight on their personal knowledge regarding lake trout s role in the aquatic food web. Furthermore, we contacted The Ed Weed Fish Culturing Station in Grand Isle, VT to discuss their methods for determining the stocking population of lake trout per stockcycle. Due to the full-text inaccessibility of many of the potentially resourceful scientific papers found on ISI Web of Science, much of the content was found using precise keywords in the Google search engine. Keyword phrases such as, alewife + lake trout interactions, alewife + algal blooms and lake trout stocking + Lake Champlain led us to many other full-text scientific journals.

3 Lake Trout History Lake trout (Salvelinus namaycush) are a freshwater char living mainly in lakes in northern North America. Other names for it include mackinaw, lake char (or charr), touladi, togue, and grey trout. The Lake trout are the largest of the Char family and has been recorded to weigh upwards of 101 lbs (Dehring, T & Krueger, D 1987). They were once native to all great lakes, smaller lakes in New England and over a wide range of Canada. Lake trout were a self-sustaining native fish of Lake Champlain up to the beginning of the 20th century. The main reason for their extinction in Lake Champlain was over harvesting and exploitation. Female lake trout lay their eggs in the fall when the water temperatures are between 10 and 12 degrees Celsius. When spawning, they will generally choose water that is 2 to 3 meters in depth and within close proximity of shoreline. The most active spawning time is about one hour after dusk. Lake trout generally have small spawning areas that are only a few square meters in size. The most common spawning habitat is on coarse gravel that serves as protection for their eggs and where there is enough water movement to create a steady supply of oxygen. Lake trout lay large eggs, and in lower amounts than many other lake fish species. Some female lake trout spawn every year once they reach maturity, and other lake trout will spawn every other year (Johnson, 2011). Often with heavy winter ice cover due to geographic location, the eggs will hatch under a layer of ice in February and the young lake trout will survive off of their yolk sack until the spring melt. Similar to other salmonids, both males and females will tend to return to the spawning beds in which they were hatched from when they have reached reproductive age. Marsden et al. (2005) studied lake trout spawning habitat and distinguished prime habitat using lake bottom topography and substrate composition. The study collected egg bags at multiple site locations on Lake Champlain to investigate lake trout reproduction. Figure 1 is a diagram of the sample locations from the study. Figure 1: Lake Trout Spawning Habitat Studied (Ellrott & Marsden 2005)

4 Figure 2 is the summary of lake trout egg deposition in Lake Champlain, Eggs were collected in egg traps or in egg bags buried in the substrate. Collections in egg traps are reported as mean number of eggs trap1 day-1; collections from egg bags are reported as mean number of eggs m-2± SD.(Ellrott and Marsden, 2005) this table indicates that lake trout reproduction is occurring in lake Champlain and is most prevalent in the Grand Isle location. Figure 2: Sampling locations, sampling methods and total amount of eggs present in the indicated time period. (Ellrott and Marsden, 2005) Lake Champlain Gear Type No. traps/bags Collection Dates Number of Eggs Number m-2 or trap- 1 day-1 Grand Isle Bags Nov 39,593 9,623 ± 1,658 Burlington Break wall (N) Burlington Break wall (S) Bags 15 3 Dec 0 0 Bags Nov 0 0 Shelburne Point Traps Oct-29 Nov ±0.03 Willsboro Bay Bags 19 5 Dec 0 0 Allen Hill Bags Nov 0 0 Saxton Cove Bags Nov ± 59 Cannon Point Bags 15 4 Dec 0 0 Whallon Bay Bags 60 4 Dec 2, ± 158 Thompson s Point Traps 30 8 Nov- 13 Nov 0 0 Iron Bay Bags 15 4 Dec ± 1.3 Arnold Bay Bags Nov ± 289

5 Lake trout growth rates are high in their first five years and reach maturity between five and ten years of age. Major predators of lake trout when they are in the egg stage include whitefish, burbot and sculpin. As the lake trout matures and grows to juvenile size it is vulnerable to predation by larger carnivorous fish, which in Lake Champlain would include mature adult lake trout, brown trout, northern pike, and walleye. As lake trout reach maturity, predators become less numerous and are limited to humans and lamprey eels (T. Dehring and C. Krueger, Wisconsin Department of Natural Resources). Lake trout populations disappeared from Lake Champlain by After sporadic stocking of lake trout in the late 19th century and in the 1950s and 1960s, a sustained stocking program began in 1973 focused on re-establishing a fishery. The specific objective developed in 1977 was to re-establish a lake trout fishery by 1985 that will annually provide at least 45,000 additional man-days of fishing with an approximate yield of 18,000 lake trout averaging 5 lb. (2.3 kg) each (Fisheries Technical Committee 1977), these stocking efforts now support a sport fishing industry. Starting in 1999, a search for evidence of reproduction by stocked fish revealed numerous sites where spawning and egg survival to hatch occurred, but recruitment of wild fish has been low (Ellrott and Marsden 2004). Therefore this demonstrates a need for lake trout stocking in the lake in order to produce fish for the sport fishing industry. Several different lake trout strains have been stocked, with the majority of Vermont s recent stockings focused on the Lake Champlain strain (progeny of feral lake trout from Lake Champlain). In the state of New York, the recent stockings have focused on the Finger Lakes strain, more specifically the Seneca Lake strain. Because of their close genetic similarities wild-caught Seneca Lake Trout are used for their egg source for rearing yearlings for stocking(johnson 2011).

6 Figure 3 describes the percentage of unclipped lake trout from adult populations collected annually in a 2005 study by Ellrott & Marsden. Before hatchery reared lake trout are released into Lake Champlain a fin is clipped indicating to fisheries biologists that that fish had indeed been stocked. Therefore, all fish that are sampled with no fin clips are determined to be born in Lake Champlain. The line at 2% represents the estimated level of missed fin clips or unidentified hatchery fish, and above which recruitment is presumed to be accumulating. The results show that through the late 1990 s, unclipped lake trout sampled increased, indicating higher natural reproduction and the beginning of a self sustaining population. In 2001, there is a decline in the unclipped finned lake trout sampled due to newly introduced invasive species. If this graph were to continue to present day, there would be a similar declining trend due to alewive introduction in 2003 (Figure 3). Figure 3: Percentage of Unclipped lake trout collected in adult population assessment in Lake Champlain.

7 An Introduction to Alewife and Rainbow Smelt Alewives (Alosa pseudoharengus) are considered a clupeid species (a schooling forage fish) in their native breeding range (Klauda et al. 1991). The majority of alewives found in the United States are anadromous, meaning they spend the majority of their life at sea and only travel up freshwater tributaries to spawn. Landlocked alewives, such as the species found in Lake Champlain and considered in this paper, are those that have been stocked in freshwaters (Alewife 1954). Unlike anadromous alewives, which reach sizes of up to 15 inches, landlocked alewives typically range from only 3-6 inches, with a maximum length of 9 inches. Landlocked alewife spawning activity begins in April, when large numbers of alewife migrate from the deep limnetic zone towards the shallow littoral zone located along beaches and shoals. Once in shallow waters, spawning will occur both day and night between June and August and will peak in mid- July. Female alewives lay demersal, non-adhesive eggs and provide no care to them before heading back to deep waters. The eggs hatch in between four and six days. Once the fish reach about 6 mm during their fry stage, they become planktivores and begin feeding on small copepoda and cladocera. As alewives mature into adulthood they begin feeding on larger crustaceans and zooplankton, as well as insect and fish larvae (US Fish 2002). Rainbow smelt (Omerus mordax) are a small, pelagic (lives primarily in the surface waters), schooling species that typically grow between 7-9, and about 3 ounces in weight. In Lake Champlain, rainbow smelt are a preferred forage for trout and salmon and are also popular amongst ice fishermen. The rainbow smelt populations in Lake Champlain are landlocked, similar to the alewife. There are reports of two different species of rainbow smelt in Lake Champlain. However, there is little reproductive data on these species, but it is interesting to note although not included in this study (Simion et. al 2011). The life history of the rainbow smelt is important to understand in order to gain insight into the big picture of food web dynamics between species. The landlocked species of smelt in Lake Champlain are found in the cooler, deeper portions of the lake, with preferable temperatures ranging from 4-20 degrees Celsius (Stritezel et al. 2010). Shortly after ice-out, females produce eggs in the thousands, which will be laid and hatched within 1-4 weeks (Simonin et al. 2011). During the summertime, young smelt prefer a warmer temperature and are separated from adults by the thermocline. The young smelt will occupy the epilimnion for the entire day, whereas the adults will follow a diel migration pattern to warmer water during nighttime. This separation plays an important role in decreasing age-0 smelt mortality due to cannibalism, allowing the juveniles to develop and grow properly in their first year of growth. Being a clupeid (schooling) species, rainbow smelt growth rates are limited by density. It was found that high densities of age-0 smelt result in reduced growth, increasing the amount of time vulnerable to predation and cannibalism (Strietzel et al. 2010). As previously stated, the separation of the two age classes reduce cannibalism. With increases in alewife populations, it will be important to look into roles of predation between the two species, especially at young ages where there is a higher risk of predation. The introduction of alewife was first recognized in Lake Champlain s Missisquoi Bay in 2003 (Marsden et al. 2006). They did not appear in the Northeast Arm or the Main Lake segments until 2004, and possibly entered from Lake St. Catherine, which drains into Lake Champlain 80 miles south. Alewives can cause tremendous ecological changes in the food web. This is due to their tendency to outcompete other small foraging species for zooplankton, as well as their ability to cause thiamine deficiency complex (TDC) in lake trout.

8 Interactions and Impacts of Alewife and Rainbow Smelt on Lake Trout: Kircheis et al (2004) examines the interspecific interactions between alewife and rainbow smelt in Lake George. The study explores the interactions between these species within aquatic food webs and how they influence it. During the first three years of alewife introduction, young-of-the-year (YOY) rainbow smelt populations grew significantly faster. This growth rate could be caused by alewive s selective feeding habits, which restructure plankton communities. Since smelt and alewives feed on similar sized zooplankton, it is possible that the alewives altered the smelt s feeding habits and decreased the density among smelt. Figure 5 supports that the size of zooplankton decreased in Oswego Lake after alewive introduction. Adult and juvenile alewives inhabit the warmest water, or epilimnion layer, of the lake, which is also where age-0 rainbow smelt reside during the summer months. Figure 4 shows temperatures where adult and age-0 smelt and alewives are most dense in the main part of Lake Champlain from June- October. Age-0 alewives were not collected until July (Simonin et. al 2010). In the summer juvenile rainbow smelt are interacting with both adult and juvenile alewife. This causes high levels of competition between juvenile rainbow smelt and juvenile alewife for food and space, and it also increases the predation on juvenile smelt from adult alewife. Rainbow smelt and alewife are both opportunistic visual feeders, meaning that they will both eat what is most available in their sight range. By decreasing the size of zooplankton available, there is a reduction in the visual spectrum of what plankton the smelt can see and feed on (Simonin et. al. 2011).This is another compound effect on smelt populations due to the increasing size of alewife populations (Simonin et. al. 2011). With a higher juvenile mortality of smelt due to predation and competition on top of cannibalism, there are going to be smaller smelt populations in future summers, having altering effects on both sides of the food web. Figure 4: Adult Rainbow smelt and alewife interactions with age-0 rainbow smelt and alewife

9 Adult alewives are efficient and selective predators which filter for only large species of zooplankton (High 2003). According to a study performed on the interaction between lake trout and alewife in Otsego Lake, NY, this selective feeding has led to a shift in the zooplankton community from larger crustaceans (cladocera), to smaller rotifers (Figure 5). The possible explanation behind this selective feeding behavior is thought to be caused by population divergence and a lack of gene flow in landlocked alewives (Palkovacs et. al, 2008). A decrease in larger zooplankton such as cladocerans, which are more efficient algae feeders, lead to an increased algal biomass (Marsden 2006). In general, this means that nothing is keeping the phytoplankton in balance, allowing them to grow without predators. Phytoplankton use copious amounts of dissolved oxygen at night for growth, leading to very low levels available for lake trout and other aquatic species (Dissolved Oxygen, 2012). Figure 5: Zooplankton sizes in Oswego Lake, NY before and after Alewife introductions (Marsden, 2006) In conjunction with the alewives ability to increase the risk of algal blooms there are also seasonal factors we must take into consideration. During the summer, lake trout prefer the cool temperatures of the deep hypolimnion zone of the lake, which under normal conditions will contain a suitable level of dissolved oxygen (Biological Differences 2010). However, this zone is particularly vulnerable to algal blooms during the summer. During summer stratification, the epilimnion (surface layer) warms up. Since warm water is less dense and therefore lighter than cold water, the epilimnion remains at the surface and does not mix with the hypolimnion due to the formation of the thermocline. In

10 the early summer months, prior to thermocline development, bottom dwelling plants decompose and release nutrients which travel up through the hypolimnion, into the epilimnion zone (Hudson 1997). The warm water and ample amount of sunlight in the epilimnion creates optimal conditions for these nutrients to trigger algal blooms. Taking into consideration the impact that alewives have on increasing algal bloom potential, as well as the tremendous stress lake trout endure during summer stratification, it is of high importance to keep alewife populations in check. Due to the natural ability of lake trout to keep alewife populations under control, it is imperative that we continue to monitor both the stocking and recruitment rate of lake trout. The way in which alewives and smelt have the most direct impact on lake trout is due to a naturally occurring enzyme found in their body tissues called thiaminase (USGS Fish Health Research). Once ingested by an adult lake trout, this chemical will begin to break down thiamine concentrations in the body and cause thiamine deficiency complex (TDC). Thiamine plays a crucial role in the development of lake trout between the hatch and fry stage (Carvalho et al. 2009). Because of this, the signs of TDC in lake trout aren t apparent until eggs are laid and have begun to develop. TDC plays an especially crucial role to development in the swim-up fry stage. The swim-up stage occurs when the larvae have absorbed the yolk sac and begin to ascend toward the surface of the water. At this point, they are negatively buoyant because their air bladder is not inflated. Upon reaching the surface, they will gulp enough air as to fill their air bladder and are from then on referred to as fry. TDC pose two major threats to these underdeveloped swim-up fry. For one, they do not develop a properly working immune system which makes them susceptible to bacterial infection and may lead to early mortality syndrome (EMS), essentially premature death (Thiamine Deficiency Complex 2008). Secondly, if the swim-up fry are able to survive EMS, they are highly unlikely to mature past the age of one and are still likely to suffer several neurological effects. It has been found that TDC leads to a decrease in visual acuity, foraging abilities, predator avoidance and loss of swimming equilibrium, therefore putting young lake trout at a severe disadvantage for survival.

11 Economic Findings Lake Champlain is considered a premier fishing destination. State Fish and Wildlife agencies rely on the flow of revenue from sport angler and fishing licenses. Thus, if the population of lake trout in Lake Champlain change, the demand for fishing licenses may change as well. In 1958, Lake Champlain started stocking lake trout populations annually and sometimes semi-annually to account for the total number harvested through the sport fishing season. Theoretically, the number of lake trout stocked will account for the total lake trout harvested, the mortality, trophic level interactions, and habitat fragmentation (Marsden 2012). At this time however, hatcheries have used the same stocking number annually since the 1990 s. Brian Chipman, a fisheries biologist in the VT Department of Fish and Wildlife, stated that this stocking number was determined using predator prey dynamics and bioenergetics modeling. Currently, approximately 80,000 lake trout are stocked annually; 57,000 are stocked in Vermont and 23,000 are stocked in New York (Chipman 2012). However, plans to refine the process of stocking number determination is currently in motion. New measurements such as predator fish consumption on the forage base, the girth and health of the food web should be taken into account when annual stocking numbers are decided. In addition, Chipman said that if lake trout are severely overstocked, you could expect to see a decrease in forage fish population and a decrease in growth rate in predators. Economic implications have been associated with the appropriate stocking of lake trout. First, lake trout are considered a large game fish that many sport anglers travel to Lake Champlain to catch. A number of charter boats rely on the constant population of lake trout to support their business (Marsden 2012). Due to the fact that lake trout is a native game species, substantial management effort are assigned ensuring its sustained population. Some may argue that angling of lake trout in Lake Champlain is severe enough to inhibit population restoration (Oosten 1993). Trophic economics is a term created by Ney (1990) to describe the relationship between consumer demand and prey resource supply. Lake Champlain hatcheries that manage lake trout introduction must find a balance between predator consumption and prey supply. The chosen annual lake trout population must be appropriate in regards to trophic economics. Lake trout overstocking would result in a unsustainable management system and additional expenses (Johnson 2000). Ney states that to find the desired balance the following tools must be used by Fishery managers: vigorous and adaptive monitoring, adjusting stocking rates, and manipulating harvest mortality by means of fishing regulations (Ney 1990). At this time, hatcheries that support Lake Champlain do not use these theories in determining lake trout stocking numbers.

12 Discussion & Recommendations Lake trout overstocking could critically impact the food web. Extreme overstocking of lake trout would cause considerable damage to the rainbow smelt population. The over-predation on the smelt population would therefore have compounding effects on zooplankton populations. Along with over predation of the smelt population there is an issue with alewife causing a shift in the size of the present zooplankton population, alewife are highly competitive with rainbow smelt for food and space. Since smelt and alewives consume similar sized zooplankton, the influence of both species present causes the zooplankton community to shift to primarily small-bodied rotifers because of the over predation on larger zooplankton. These smaller zooplankton are less efficient algae grazers, therefore causing potential increases in algal biomass in the lake. Economically, overstocking lake trout would increase the short term revenue generated through sport fishing licenses. However, the revenue generated over an extended period of time would decrease due to the lack of sustainable management programs and hatchery expenses used to supplement the altered populations of smelt and alewives. Therefore, based on the economic findings of the assessment, it is recommended that the hatcheries that stock lake trout into Lake Champlain avoid long term overstocking. Another factor to consider in the economic assessment is the potential need of funding for algal bloom clean up. Therefore we suggest that the Lake Champlain Committee continue their monitoring efforts for algal outbreaks. In order to provide ecologically sound stocking there needs to be more data surrounding the lake trout populations annually. Currently the stocking numbers are kept consistent with no consideration into the previous year's efforts. This would require more data on the lake trout s primary feeding habits, stressors present, and their reproductive success. We recommend following Ney s theory on trophic economics which includes adjusting stocking rates annually through vigorous and adaptive monitoring, and manipulating harvest mortality by means of fishing regulations (Ney 1990). More information on each aspect will allow more concrete, effective management plans to be implemented in the future. When over-stocking figures are established, we can attempt to control the populations by increasing the daily limits and/or decrease size limits for lake trout. On the other side, if there is a drastic decrease in smelt populations due to either lake trout predation or alewife competition, we can implement a limit on the rainbow smelt daily takes. In order to further understand impacts on prey rainbow smelt populations, extensive data must be collected on all sides surrounding the issue. Additional research must occur on the Lake Champlain rainbow smelt in terms of their basic function and roles. These studies can be implemented through the Rubenstein School and perhaps performed as part of undergraduate service learning fisheries or wildlife biology classes. In terms of the alewife issue, we recommend that further research go into the eradication or at least population control of the alewives. The alewife being present in the lake will alter future conditions and will ultimately have to be considered amongst any future stocking plans. Acknowledgments We d like to thank Ellen Marsden from the Rubenstein School of Natural Resources for her insight on different aspects of lake trout stocking and also for providing us with some journals to use as research. We would also like to thank Brian Chipman a fisheries biologist from the Department of Vermont Fish and Wildlife for his information on the current status of Lake Champlain stocking efforts and our current understanding of the role stocking plays in the lake.

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14 Maine River Herring Fact Sheet. Maine DMR, River Herring (Alewife and Blueback Herring) Information. US Fish and Wildlife Service, 16 Dec Web. 30 Mar Manley, T. O., & Manley, P. L. (2000). Lake champlain in transition. (pp ). Washington DC: American Geophysical Union. Marsden, Ellen J. et al. (2006). Lake Champlain Alewife Impacts. Workshop Summary: Marsden, Ellen J. et. al. (2012). The History and Future of Lake Champlain s Fishes and Fisheries. Journal of Great Lakes Research. 38: Mihuc, T. (2011). Long-term patterns in lake champlain's zooplankton: Journal of Great Lakes Research, 38(1), Retrieved from Ney, J. J. (1990). Trophic Economics in Fisheries: Assessment of Demand Supply Relationships Between Predators and Prey. Reviews in Aquatic Sciences 2: Palkovacs, E. P. et al. (2008). Independent evolutionary origin of landlocked alewife populations and rapid parallel evolution of phenotypic traits. Molecular Ecology 17: Simonin, Paul W. et. al. (2011). Native rainbow smelt and nonnative alewife distribution related to temperature and light gradients in Lake Champlain. Journal of Great Lakes Research. 38: Thiamine Deficiency Complex & Early Mortality Syndrome." USGS: Science for a Changing World. Great Lakes Science Center. Web. 26 Apr USGS Fish Health Research in the Great Lakes: Thiamine Deficiency Complex and Fish Mortality." USGS: Science for a Changing World. Web. 26 Apr Walsh, M. R. (2012). Evolutionary consequences of alewife divergence. Journal of Evolutionary Biology 25: Van Oosten, J. (1933). Resume of the History of the Atlantic salmon in the United States with special reference to its re-establishment in Lake Champlain. Unpublished report.