Management Plan for the Grass Pickerel (Esox americanus vermiculatus) in Canada
1.4 Needs of the Grass Pickerel
1.4.1 Habitat and biological needs
Grass Pickerel habitat is typically characterized as shallow (< 2 m), heavily vegetated, slow moving, lowland streams and overflow ponds of large streams and stream expansions with mud or muck bottoms (organic soils) and clear- to tea-coloured water that is mildly alkaline to slightly acidic (Scott and Crossman 1998, Crossman and Holm 2005, Marson et al. 2007). Although Canadian Grass Pickerel populations are usually associated with mud substrates, they have been found in areas of gravel and rock (Crossman and Holm 2005). Some specific observed habitat features in Indiana streams include aquatic macrophytes, logs and woody structure and slow moving water (Cain et al. 2008). Grass Pickerel have also been associated with shallow vegetated areas in lakes and ponds (Kleinert and Mraz 1966, Foster 1979), dense beds of vegetation in headwaters of Oklahoma streams (Ming 1968), and with sheltered coastal wetlands with abundant vegetation in lakes Ontario and Erie (Brousseau et al. 2005). In Quebec, Grass Pickerel are most frequently associated with vegetated areas in large waterbodies.
Vegetation types that are typically associated with Grass Pickerel include pondweed (Potamogeton spp.), water lilies (Nymphaea and Nuphar sp.), muskgrass (Chara sp.) and coontail (Ceratophyllum sp.) (Crossman and Holm 2005). In Long Point Bay, Grass Pickerel were captured in habitats containing the following plant species: Common Reed Grass (Phragmites australis), cattail spp. (Typha spp.), bulrush (Scirpus sp.), wild rice (Zizania sp.), muskgrass (Chara sp.), Common Waterweed (Elodea canadensis), watermilfoil sp. (Myriophyllum spp.), Wild Celery (Vallisneria americana) and water lilies (Nymphaea and Nuphar sp.) (OMNR, unpubl. data).
Based upon a survey of 75 wetlands along the American shoreline of the Laurentian Great Lakes, Trebitz et al. (2007) determined that the Grass Pickerel was moderately turbidity-intolerant, which they defined as multiple occurrences at < 10 nephelometric turbidity units (NTU) and at most one occurrence at < 25 NTU.
In lakes, adult Grass Pickerel have been observed in shallow (< 5 m) water, with submergent and emergent vegetation, logs (Crossman 1962, Becker 1983) and fine grain sized (clay/silt/sand) substrates (Lane et al. 1996a). In riverine habitats, juvenile Grass Pickerel have been associated with shallow water (< 60 cm) (Leslie and Gorrie 1984) and with silt/clay substrates and vegetation (Scott and Crossman 1998). Juveniles have also been found to be intolerant of turbidity (Trautman 1981) and to be most common in pools (Crossman 1962, Scott and Crossman 1998).
Grass Pickerel appear to be tolerant of a wide temperature regime (5°C - 32°C) (Ming 1968, Cain et al. 2008), although they are classified as a warmwater species with a preferred temperature of 26°C (Wismer and Christie 1987) and upper avoidance of 29°C (Scott and Crossman 1998). Additionally, the species is adapted to low dissolved oxygen environments (< 1.0 mg/l) (Scott and Crossman 1998, Cain et al. 2008); this allows them to survive in shallow, densely vegetated habitats that can become oxygen depleted during the night due to plant respiration. In Ohio, Grass Pickerel populations declined or were extirpated wherever ditching, dredging or other forms of channelization destroyed their habitat (White et al. 1975; cited in Cain et al. 2008, Trautman 1981). Leslie and Timmins (1997) observed the presence of Grass Pickerel in disturbed locations (e.g., drainage ditches) in Long Point Bay; however, it is possible that a sufficient length of time had elapsed since the streams were last disturbed to allow the regeneration of aquatic macrophytes that provide the necessary cover for Grass Pickerel.
Little knowledge exists with respect to the spawning habitat requirements of Grass Pickerel (Portt et al. 1999), but spring spawning does appear to be associated with flooded terrestrial vegetation at temperatures ranging from 4 to 12°C (Keast 1977, Becker 1983, Lane et al. 1996b, Scott and Crossman 1998). Spawning in Ontario waters has been recorded from late March to early May with a period of approximately two weeks to egg hatch and a further two to five weeks to initiate feeding (Crossman 1962). In still-water habitats, Grass Pickerel spawning grounds appear to be in shallow (< 1 m) waters with emergent and partially or completely flooded terrestrial vegetation to which the eggs can adhere (Crossman 1962, Goodyear et al. 1982). Young-of-the-year are also associated with shallow (< 2 m) waters, submergent and emergent vegetation, and silt substrates (Goodyear et al. 1982, Dombeck et al. 1984). There is some evidence to suggest that Grass Pickerel may spawn more than once a year and late-summer to winter spawning may occur (Crossman 1962, Kleinert and Mraz 1966). Eggs are broadcast over aquatic vegetation to which they then adhere; no parental care is given to the eggs or young of this species (Becker 1983). Egg diameters range from 1.5-2.5 mm with a hatching length of 5-6 mm (Carlander 1969, Scott and Crossman 1998). In Ontario, sexual maturity is reached during the second year, and estimated maximum longevity is approximately seven years (Crossman 1962).
This species likely only travels over short distances in search of food and cover (Crossman 1962), although spawning aggregations have been reported in lakes (Kleinert and Mraz 1966). In winter, the species may burrow in mats of fallen leaves (Etnier and Starnes 1993).
The Grass Pickerel is a solitary species that, along with other esocids, is typically an ambush predator (Foster 1979) with prey dominated by fishes and, to a lesser extent, aquatic insects and crayfishes (frogs and tadpoles were infrequently eaten in Ontario, despite being abundant) (Crossman and Holm 2005). When Grass Pickerel reach 50-150 mm TL, generally during their first year, they switch from consumption of aquatic insects to piscivory, after which fishes constitute 60-80% of their diet (Becker 1983, Keast 1985). Dietary studies of Grass Pickerel residing in Wisconsin lakes have observed a shift in food preference from zooplankton in individuals with a TL of 9.5-15 mm, to aquatic insects (15-40 mm TL) and finally to piscivory in maturity (Kleinert and Mraz 1966). Grass Pickerel residing in Indiana streams demonstrated a diet shift during their life-history from one dominated by fishes when they were 57-95 mm TL to fishes and crayfishes (96-150 mm TL) and finally to larger crayfishes (>150 mm TL) (Weinman and Lauer 2007). Grass Pickerel appear to be opportunistic feeders, which enables them to exist on a wide variety of prey within their area of occupancy (Weinman and Lauer 2007).
1.4.2 Ecological role
Many piscivorous fish species may act as keystone species (e.g., Carpenter and Kitchell 1993, Mittlebach et al. 1995, Carpenter et al. 2001). Grass Pickerel are predominantly piscivorous in nature and may be functioning as a keystone species in some systems. It is often the top predator in communities of which it is characteristic (Crossman and Holm 2005, Weinman and Lauer 2007) and may play a significant role in controlling populations of small fishes (Jenkins and Burkhead 1993). During the summer in the Niagara region, Grass Pickerel are typically found within remnant pool habitat of headwater streams, where they are often the top predator. Weinmann and Lauer (2007) speculated that if Grass Pickerel populations were to decline or disappear in the Indiana headwater streams they were studying, altered ecosystem dynamics may result. Yellow Perch (Perca flavescens), catfish spp. (Ictaluridae) and sunfish spp. (Centrarchidae) have been observed to prey on Grass Pickerel (Becker 1983) indicating that Grass Pickerel may be a significant food source for some species.
The Grass Pickerel can tolerate a wide range of water temperatures and water quality conditions (Cain et al. 2008), which may allow the species to utilize habitats that would be unsuitable for larger top predators (e.g., densely vegetated, shallow habitats).
1.4.3 Limiting factors
The Grass Pickerel is at the northern limit of its range in Canada and is limited by cooler water temperatures. This species has a specific habitat requirement for abundant aquatic vegetation, which may be limited in some areas. Since the Grass Pickerel is smaller than other esocid species (i.e., Muskellunge, Northern Pike), it may be particularly vulnerable to predation and/or competition from these species, which could result in the loss or decline of Grass Pickerel from habitats frequented by other esocids.
Hybridization between Grass Pickerel and other esocids, including Redfin Pickerel, Chain Pickerel and Northern Pike is known to occur in nature (McCarraher 1960, Crossman and Buss 1965, Serns and McKnight 1977). The probability of hybridization would likely be higher with species that are more closely related to the Grass Pickerel (i.e., Chain Pickerel and Redfin Pickerel). Offspring produced as a result of hybridization are sterile with the exception of Redfin Pickerel x Grass Pickerel offspring, which are fertile (Scott and Crossman 1998).
1.5 Threats
1.5.1 Threat classification
Current and anticipated threats to the Grass Pickerel are listed in Tables 3 and 4 for Ontario and Quebec, respectively. Threats were ranked based on their relative impact, spatial extent and expected severity. The threats have been prioritized starting with the greatest perceived threat to the survival of the species based on the strongest evidence. There may be some variability in the severity and level of concern for some threats for individual populations. Threat assessment, particularly where evidence is limited, is an ongoing process linked to both species assessment and, where applicable, management. The threat classification parameters are defined as follows:
Extent – spatial extent of the threat in the species range/waterbody (widespread/localized);
Occurrence – current status of the threat (e.g., current, imminent, anticipated);
Frequency – frequency with which the threat occurs in the species range/waterbody
(seasonal/continuous);
Causal Certainty – level of certainty that it is a threat to the species (High – H, Medium – M, Low - L);
Severity – severity of the threat in the species range/waterbody (H/M/L); and,
Overall Level of Concern – composite level of concern regarding the threat to the species, taking into account the five parameters listed above (H/M/L).
* The impacts of Damage/Destruction of Aquatic Vegetation are described under several other threats listed below due to the high degree of overlap that can occur between these threats.
* The impacts of Damage/Destruction of Aquatic Vegetation are described under several other threats listed below due to the high degree of overlap that can occur between these threats.
1.5.2 Description of threats
The primary threat affecting this species appears to be the destruction and degradation of wetland habitat. Industrial, urban and agricultural developments have reduced the quality and quantity of habitat available to Grass Pickerel and pose a significant threat to their continued survival. For example, in the Niagara region, there may have been an 80% loss of suitable Grass Pickerel habitat since human settlement (Crossman and Holm 2005). As the Grass Pickerel is a visual ambush predator, activities that result in increased turbidity and the removal or destruction of aquatic and riparian vegetation (e.g., through channelization, dredging, ditching and clear-cutting) will likely have negative impacts on Grass Pickerel survivability.
Drainage: Local modification of natural hydrological regimes including the realignment of watercourses, excavation of channels and ditches, drainage measures, back-filling, diking of floodplains, maintenance, and any other local modification of the natural hydrological regime in Grass Pickerel habitat can be harmful to the species. In Ontario, municipal drainage activities are one of the primary threats to the Grass Pickerel; in the Niagara Region, surveys indicated that Grass Pickerel abundance immediately declined following drainage works in the Point Abino Drain (Crossman and Holm 2005, A. Yagi, pers. comm. 2008). Municipal drainage practices alter flow characteristics, which results in reduced in-stream habitat complexity, reduced pool and wetland habitat, increased drainage rates (thereby leaving intermittent streams dry and inaccessible), reduced and/or eliminated riparian cover, and increased turbidity and sedimentation. Additionally, flow velocity and peak discharge increase in channelized watercourses during periods of heavy precipitation or snowmelt, subjecting the banks to greater erosion.
A decrease in water level can also influence recruitment and cause mortality by stranding young and adult fish (Kleinert and Mraz 1966). During low water periods in summer and winter, in areas that have been extensively drained, the groundwater reserves that feed streams are reduced, leading to lower water levels and unfavourable conditions for aquatic life. Some watercourses are completely dry during these low flow periods while others are intermittent. Fishes then become trapped in trenches where water temperature rises and dissolved oxygen is reduced, often resulting in mortalities (Société de la faune et des parcs du Québec [FAPAQ] 2002). If a watercourse is sufficiently deepened, or the substrate altered during channelization, the aquatic macrophyte community may not regenerate to its original quantity or quality. Additionally, activities resulting in low water levels and lowering of stream temperatures are also threats to Grass Pickerel (Crossman and Holm 2005). Water level reductions, particularly in nursery areas, may result in reduced Grass Pickerel recruitment (Kleinert and Mraz 1966). It should be noted that Grass Pickerel have demonstrated some ability to tolerate disturbed habitat if sufficient cover is present (Leslie and Timmins 1997).
Sediment loading/turbidity: Excessive sediment loading can affect aquatic habitats by decreasing water clarity, increasing siltation of substrates, and may have a role in the selective transport of pollutants, including phosphorous (Vachon 2003, Essex-Erie Recovery Team [EERT] 2008). Additionally, sediment loading may impact the entire food web (Vachon 2003). The impacts on aquatic organisms such as fishes may be direct (e.g., physiological disorders, behavioural modifications, physical injury) or indirect (e.g., destruction or degradation of habitat and of food resources) (Vachon 2003). This can result in stunted growth, population decline and problems associated with reproductive capability. The sensitivity of individuals to sedimentation and turbidity is different in the various stages of the life cycle; however, in most cases the indirect effects of sedimentation through the destruction of food resources, eggs and larvae and/or habitat degradation are clearly noticeable before the adult fish are directly affected (Vachon 2003).
The Grass Pickerel is moderately intolerant to turbidity (Trebitz et al. 2007); high levels of turbidity in the Dunnville Marsh (lower Grand River) have been implicated in the decline of aquatic macrophytes and may have contributed to the apparent decline of Grass Pickerel in the Grand River. Increasing turbidity reduces the depth to which sunlight can penetrate into the water, thereby limiting photosynthesis and the amount of aquatic vegetation that can establish. This can have detrimental impacts on species that rely on dense growths of aquatic vegetation, such as the Grass Pickerel. Trautman (1981) reported that the species declined or was locally extirpated wherever an increase in turbidity destroyed aquatic vegetation. Increased turbidity negatively impacted Grass Pickerel feeding in Long Point Bay (Crossman and Holm 2005).
Nutrient loading: Nutrients (nitrates and phosphates) enter waterbodies through a variety of pathways, including manure and fertilizer applications to farmland, manure spills, sewage treatment plant outputs and faulty domestic septic systems. Nutrient enrichment of waterways can negatively influence aquatic health through algal blooms and associated reduced dissolved oxygen concentrations. Although Grass Pickerel is apparently tolerant of low dissolved oxygen levels (Crossman and Holm 2005), it is possible that extended periods of low dissolved oxygen could negatively impact the species. Additionally, low dissolved oxygen levels may have an indirect affect on Grass Pickerel by negatively impacting prey abundance.
Damage/destruction of riparian vegetation: The removal of stream and riverbank vegetation as a result of forestry, agricultural, and urban development practices (e.g., through rock-fill, lawns, crops, shorewalls) reduces the quality and quantity of habitat available to Grass Pickerel. Riparian vegetation stabilizes water temperatures, and minimizes soil erosion and filter runoff from watershed lands that contain fertilizers, pesticides and sediments (FAPAQ 2002, Vachon 2003). As riparian vegetation is degraded or destroyed, waterbodies become vulnerable to direct sun exposure and impacts from other environmental elements. As a result, water temperatures increase and higher rates of overland runoff transporting sediment and nutrients into the water are experienced. Poor land management practices in agricultural areas have been a significant anthropogenic cause of siltation and increased turbidity in watercourses. Certain practices are especially destructive, for example, the trampling of banks and stream-beds by livestock can destroy riparian vegetation and damage aquatic habitat by re-suspending sediments (Crossman and Holm 2005). The ploughing of fields, the spreading of solid and liquid manure, and crop harvesting all contribute to increases in sediment input in streams, especially where riparian buffers are inadequate or non-existent. The presence of well vegetated, adequately wide riparian buffers promotes the maintenance of water quality in the waterbodies frequented by Grass Pickerel.
In Quebec, Grass Pickerel is very rare and likely endangered by the development of intensive agriculture and the resulting degradation of small rivers and streams (P. Dumont, pers. comm., 2008). In accordance with the Règlement sur les exploitations agricoles of the Loi sur la qualité de l’environnement, livestock access to watercourses is prohibited. Moreover, the protection of shoreline and stream and river banks is managed by municipal by-laws in Québec. These by-laws must conform to a provincial policy, The Protection Policy for Lakeshores, Riverbanks, Littoral Zones and Floodplains:
Section 2.1 of the Environment Quality Act (L.R.Q, c.Q-2) requires the Ministre du Développement durable, de l'Environnement et des Parcs to develop, implement and coordinate the application of a policy to protect rivers, littoral zones and floodplains. This obligation was fulfilled by the adoption of the Protection Policy for Lakeshores, Riverbanks, Littoral Zones and Floodplains (Decree 468-2005). This Policy establishes a minimum level of protection for rivers, littoral zones and floodplains. Under the An Act respecting land use planning and development (L.R.Q., c.A-19.1) the Ministre du Développement durable, de l'Environnement et des Parcs may request the amendment of a metropolitan plan or a regional county municipality’s (RCMs) plan if the plan is not consistent with the Protection Policy for Lakeshores, Riverbanks, Littoral Zones and Floodplains.
In areas around watercourses and lakes citizens can carry out private works, but those works must conform to municipal by-laws or by-laws of RCMs. Before commencing work, applicants must secure a permit, authorization or certificate in accordance with provincial legislation and applicable municipal by-laws, the requirements of which largely come from the Protection Policy for Lakeshores, Riverbanks, Littoral Zones and Floodplains. Other laws, such as the An Act Respecting the Conservation and Development of Wildlife (L.R.Q., c.C-61.1)might also require authorizations for works near water courses and lakes. Finally, according to s.104 of the Municipal Powers Act (L.R.Q. c.C-47.1), RCMs have the power to adopt by-laws regulating waterflow of water courses.
In 2003, a survey conducted by Environment Québec and the Department of Municipal Affairs, Sports and Recreation found that the level of conformity of municipal by-laws to this policy was very low (Sager 2004). It is doubtful whether the situation has changed since that time. Apart from the initiatives of a few municipalities and some reclamation projects, there has been a noticeable general deterioration of the quality of riparian zones in both urban and agricultural areas.
Contaminant inputs:The sources and types of contaminant inputs in Grass Pickerel habitat vary, as do their effects on the survival of the species. In general, the effects of contaminants on the Grass Pickerel are not well known, but several studies have shown that certain chemical compounds can have a lethal effects, others can disrupt the endocrine system of exposed organisms, cause deformities, and create problems in reproduction and growth in many fish species including the White Sucker (Catostomus commersonii), the Copper Redhorse (Moxostoma hubbsi) and the Spottail Shiner (Notropis hudsonius) (de Lafontaine et al. 2002, Jobling and Tyler 2003, Aravindakshan et al. 2004, Environment Canada [EC] 2009).
Pesticides and herbicides used in agriculture can impact Grass Pickerel habitat to the point where survival of the population is at risk. Herbicides that are commonly used can alter the composition and abundance of the aquatic vegetation, which is an essential component of Grass Pickerel habitat. For example, atrazine found in streams and rivers in agricultural areas is harmful to aquatic life and the entire ecosystem, causing reductions in zooplankton abundance, phytoplankton photosynthesis and aquatic plant growth (FAPAQ 2002).
Water level fluctuations (beyond natural seasonal variability): Natural water level fluctuations and flow regimes are necessary and beneficial to maintain pool habitat and wetland floodplain features that are important elements of Grass Pickerel habitat. Control structures (dams/weirs), channelization and drainage alters natural flow dynamics and degrades available habitat.
The fluctuations in water levels in the Great Lakes and St. Lawrence River are a result of the combined action of several natural factors (e.g., climate and climatic variations), but also of human activity. Water levels are affected by water-control structures that are used to prevent flooding in the spring, augment flows downstream during low flow conditions, facilitate commercial navigation, and produce hydroelectric power. Great Lakes and St. Lawrence River water flow is managed by the International Joint Commission (Canada and United States) whose goal is to provide wise management of lake and river systems along the border (International Joint Commission 2009).
Development of the St. Lawrence Seaway has also modified the river’s flow regime (EC 1999). The dredging of the shipping channel and shallows has altered habitat and water levels, concentrating water flow in the main river channel and reducing current velocity in the shallower areas. Species, such as Grass Pickerel, that live in the shallower waters could be significantly affected by reductions in water levels in the Great Lakes and the St. Lawrence River. More specifically, some habitat areas may be temporarily drained leading to a deterioration of aquatic vegetation and precluding fish access to these areas, or these areas may be permanently dewatered, reducing available habitat for some Grass Pickerel populations.
Certain water level management activities may be beneficial to the long-term survival of Grass Pickerel. For example, in NWAs water levels may be managed and some aquatic vegetation may be removed to maintain hemi-marsh conditions (50/50 emergent/open water habitat). Big Creek NWA has been diked and has had ongoing water level management (approximately once a decade) for the past 25 to 60 years (J. Robinson, Canadian Wildlife Service, pers. comm. 2008). This management appears to result in improved habitat conditions for Grass Pickerel in the long term; however, the impacts to the population and its viability are unknown and require investigation.
Disease: The introduction of pathogens can also constitute a threat for Grass Pickerel. For example, viral hemorrhagic septicaemia (VHS) is a contagious viral disease that affects, to varying degrees, more than 65 fish species (including Northern Pike and Muskellunge). First identified in the Great Lakes in 2005 and 2006, this potentially fatal disease has been linked to mass mortalities in several species of fish in the region, including Ontario. To date, no cases of VHSL have been detected in Quebec. There is presently no treatment for this disease. The Canadian Food Inspection Agency (CFIA) implemented a biennial plan to monitor the presence of the VHSL virus in Canadian wild fish in 2007 (CFIA 2009). Given the low population abundance of Grass Pickerel in Canada, mass mortalities associated with this disease could be highly detrimental to the conservation of the species.
Barriers to movement: Dams and other water-regulating structures (e.g., locks) can transform lotic (flowing water) habitat into lentic (still water) habitat and inhibit the movement of fishes, denying them access to different habitats, fragmenting their distribution, and isolating populations. Guenther and Spacie (2006) have shown that the fragmentation of lotic habitat causes important changes in the distribution and abundance of species, especially piscivorous species. For example, the Redfin Pickerel was less abundant in fragmented streams than in non-fragmented streams. Additionally, in the fragmented streams, the average size of captured fish was smaller (Guenther and Spacie 2006).
In Quebec, historic Grass Pickerel populations occurred in three disjunct areas that have no connection with each other or with the populations in Ontario. Two of the three populations of Grass Pickerel in Quebec were found in the St. Lawrence River on both sides of the Beauharnois locks and the Beauharnois-Les Cèdres hydroelectric station, and the third population was found in the original riverbed near Coteau-du-Lac. Though there is no evidence at the present time of any genetic or reproductive isolation (Crossman and Holm 2005), habitat fragmentation may be detrimental to the maintenance of genetic diversity and re-colonisation in the event that one of these populations becomes extirpated.
Exotic species: Dextrase and Mandrak (2006) suggested that while habitat loss and degradation is the predominant threat affecting aquatic species at risk, exotic species are the second most prevalent threat, affecting 26 of 41 federally-listed species across Canada. There are now at least 185 exotic species that have invaded the Great Lakes basin since 1840 and 88 in the St. Lawrence River (Y. De Lafontaine, Environment Canada-Centre Saint-Laurent, pers. comm. 2009). Some of these species will likely impact the Grass Pickerel. Exotic species may affect the Grass Pickerel through several different pathways, including direct competition for space, habitat and food, and the restructuring of aquatic food webs.
Alteration of wetland habitat by species such as the Common Carp (Cyprinus carpio), Eurasian Watermilfoil (Myriophyllum spicatum) and Common Reed Grass may pose a threat to Grass Pickerel populations. Jolley and Willis (2008) have shown that increased Common Carp biomass in a Nebraska lake led to reductions in the quantity of aquatic vegetation and in the quality of Grass Pickerel habitat. Consequently, Grass Pickerel population density and individual growth rates were lower than in the other populations that were surveyed (Jolley and Willis 2008). Eurasian Watermilfoil, an aquatic plant that was first introduced to Ontario and Quebec in the 1960s (EC 2003), could have a negative effect on aquatic macrophyte beds available for or used by the Grass Pickerel. When Eurasian Watermilfoil invades a body of water it generally crowds out the other aquatic plants that are present. This plant creates changes in several physical and chemical parameters (e.g., pH, oxygen, temperature). These changes then impact on the different biological communities present in the waterbody, including aquatic insects and fishes (Auger 2006).
Climate change: Climate change is expected to have significant effects on aquatic communities of the Great Lakes basin through several mechanisms, including increases in water and air temperatures, lowering of water levels, shortening of the duration of ice cover, increases in the frequency of extreme weather events, emergence of diseases and shifts in predator-prey dynamics (Lemmen and Warren 2004). Additionally, warming trends, as a result of climate change, may favour the establishment of potentially harmful exotic species that may currently be limited by cooler water temperatures. Climate change may specifically affect Grass Pickerel through the alteration of water levels and vegetation communities. Mortsch et al. (2006) investigated potential impacts of climate change on Great Lakes coastal wetland communities, including areas where the Grass Pickerel is resident. The possibility exists for loss of diversity among aquatic vegetation communities resulting from modified hydrologic and thermal regimes. As the Grass Pickerel is highly associated with the presence of aquatic vegetation, factors altering aquatic communities may have profound impacts on Grass Pickerel populations. The Grass Pickerel was deemed a highly vulnerable species (ranked 26th most vulnerable of 99 species considered) under various climate change scenarios (Doka et al. 2006).
In southern Quebec, one of the major impacts of climate change would be a reduction in water flow in the St. Lawrence River. If concentrations of atmospheric carbon dioxide double over the course of the next century, the atmospheric general circulation models forecast a 30C rise in temperature along the St. Lawrence River within 50 years and up to 50% reduction in water flow from Lake Ontario. The ensuing decrease in water levels in the western part of the St. Lawrence would entail increased dredging operations, deterioration of water quality, and a loss of wetlands (EC 1999).
Interspecific interactions: Hybridization between esocid species is a natural occurrence and cases have been reported from Canada (e.g., Crossman and Buss 1965, Serns and McKnight 1977); however, should the frequency of hybridization increase above natural rates, the genetic integrity of the Grass Pickerel could be at risk. Grass Pickerel is more likely to hybridize with Redfin Pickerel or Chain Pickerel as it is more closely related to these two species and is of a similar size and life-history (N. Mandrak, pers. comm. 2009).
In Canada, Chain Pickerel and Redfin Pickerel are found together with Grass Pickerel exclusively in Quebec, although the Chain Pickerel has recently been captured in the Bay of Quinte region (Lake Ontario). The Redfin Pickerel is rare, small in number, and limited to the area of the St. Lawrence River between the Contrecoeur Islands and the mouth of the Godefroy River, and the river system of the Richelieu (including Lake Champlain), Godefroy (including Lake St. Paul), Yamaska and François rivers. Reports of Redfin Pickerel presence in the Contrecoeur Islands are relatively recent (1994) and it is the first time that this sub-species has been observed so far upstream from the mouth of the Richelieu River. Its distribution appears to be expanding westward, an expansion that may eventually be facilitated by various programs aimed at restoring and enhancing wetlands. Therefore, there is a risk that the ranges of both sub-species will overlap (Lachance 2001). The potential effects on Grass Pickerel (e.g., competition, predation) of an overlap in distribution with Redfin Pickerel are unknown, but the two sub-species could hybridize and Redfin Pickerel could eventually replace Grass Pickerel in Quebec (Crossman and Holm 2005).
It is not known if interactions with other esocid species may be negatively impacting the Grass Pickerel. In the Niagara region, preliminary results of recent surveys suggest that when Grass Pickerel are abundant, Northern Pike are present in low densities or absent (A. Yagi, pers. comm. 2008). Further research is required to determine the potential impacts on Grass Pickerel, if any, of interspecific competition with other esocid species.
Fishing pressure: The Essex-Erie recovery strategy identifies fishing pressure (incidental capture in commercial/recreational activities) as a speculative threat for Grass Pickerel in the Essex-Erie region (EERT 2008); however, further research is required to determine possible impacts this may have on the species. In Quebec, during two studies to determine the impact of baitfish fisheries on five species at risk, no Grass Pickerel were found in bait buckets or baitfish stores that were visited in autumn 2005 (Boucher et al. 2006) and summer 2007 (Garceau et al. 2008).
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