Recovery Strategy for the Striped Bass, St. Lawrence Estuary Population, Canada [Final] 2011: Threats

According to the COSEWIC status report (Robitaille 2004), Canadian striped bass populations may be threatened by overfishing, modifications to spawning habitat due to changes in water flow, and by pollution. In addition, as mentioned in the preceding section, they may be exposed to further limiting factors because they are at the northern limit of the species` range (Robitaille 2004).

The following evaluation of threats to the survival and recovery of the striped bass combines two main sources: observations of factors which seem to have had a negative effect on the historic population; and phenomena which are presently active in the estuary and which affect fish populations in that environment. At present, the analysis of these two sources and the assessment of the relative importance of the different threats are based on the practical experience and the judgement of the members of the Recovery Team. Over the next five years, new information on the recovering population and the consequences of any new incidents which may occur will be incorporated in the threats classification.

The Recovery Team has assessed each threat according to six parameters (Table 2):

1.5.2.1. Threats to Habitat

Fish habitat is comprised of the spawning grounds and nursery, rearing, food supply and migration upon which the survival of the fish depends, directly or indirectly. It includes the physical, chemical and biological attributes of the environment which are essential in the life cycle of the fish. It identifies the freshwater, estuarine and marine environments which, directly or indirectly, support fish stocks which are or could be the object of commercial, subsistence and recreational fisheries. The Recovery Team has identified a number of threats which may have a negative effect on the habitat of the striped bass of the St. Lawrence.

Habitat Disturbance Due to Dredging: Data and observations indicate radical changes in the distribution of immature striped bass before the disappearance of the species, coinciding with dredging and maintenance operations in the Traverse du Nord, the section of the shipping lane adjacent to Île d'Orléans (Robitaille 2001; Robitaille and Girard 2002; G. Labrecque, extirpated population technicians/biologists, pers. comm. 1990). According to project workers and local residents who observed the work being done, the dredged material was deposited in the area immediately surrounding the channel and on the banks of the nearest islands (Robitaille and Girard 2002). In the 1950s, analysis of recaptures of tagged fish by biologists of the Marine Biology Laboratory of the Department of Marine Fisheries (Vladykov 1945; Beaulieu 1962) revealed a change in the distribution of immature individuals aged from 1 to 2 years, previously abundant along the southern section of Île d'Orléans. Beginning in 1957, recaptures of these fish were only recorded along the South Shore, between Saint-Vallier and Rivière-Ouelle (Robitaille 2001). Observations by fishermen at the time corroborate this change in distribution: according to them, striped bass very rapidly became scarce around Île d'Orléans, Île Madame and Île au Ruau. Striped bass could only be caught on the South Shore or around the Montmagny Islands (Robitaille and Girard 2002) (Figure 4).

Changes to the aquatic environment which may have resulted from dredging and the dumping of dredged materials were reported over an extensive area, from Île Madame to the downstream end of Île aux Oies (Robitaille and Girard 2002). In several locations, an accumulation of silt or sand was observed on the river bottom, gradually decreasing water depth (Figure 4). Some of the channels between the islands, used by smaller vessels during low tide (for example, the passage between Île Madame and Île Ruau) were no longer navigable after the widening of the Traverse du Nord (Robitaille and Girard 2002). Over the years, shoals, such as the banks at Île au Ruau, also began to appear at ebb tide (Robitaille and Girard 2002).

Figure 4 . Map of a section of the St. Lawrence Estuary where, according to local fishermen, the accumulation of sand may have reduced water depth between Île Madame and Île aux Grues (in pink).
Adapted from Robitaille and Girard (2002).

Maintenance work on the shipping lane is still required on an annual basis in order to remove the sand which accumulates there. Several locations within the striped bass range must be dredged, particularly in Lake Saint-Pierre, near Bécancour, and at the Traverse du Nord. However, dredging practices have changed in recent decades; dredged material is now deposited in designated areas, chosen according to their dispersion capacity. The maintenance of the shipping lane continues, nevertheless, to have an impact on aquatic wildlife. Studies have revealed the negative effects which the dumping of dredged material has on benthic fauna and on the feeding grounds of Atlantic sturgeon (Acipenser oxyrinchus) and lake sturgeon (A. fulvescens)(Hatin et al. 2007; Nellis et al. 2007; McQuinn and Nellis 2007). In the estuary, the shipping lane is the largest area which is regularly dredged. This activity may increase in the coming years with the increase in marine traffic, the presence of increasingly larger vessels and decreasing water levels due to climate change. In addition, a great number of sites (docks, marinas, access channels) also require periodical dredging.

Consequently, the Recovery Team believes that this threat warrants a high level of concern and that additional research is necessary on the effects that dredging has on the striped bass.

Disturbance and Destruction of Habitat: The loss and destruction of habitats (bank-hardening, construction of walls, roads and docks, flood-plain and swamp infilling) may significantly modify the habitat of aquatic species. Practices such as these are still common and may be detrimental to the recovery of the striped bass in the St. Lawrence Estuary, particularly in Anse Sainte-Anne at La Pocatière, identified as critical habitat.

In 2004, an inventory was conducted of several sites³ where juvenile striped bass had been captured before the disappearance of the species and this revealed that some of these sites had undergone major changes. The most remarkable seems to be the fishing zone in Saint-Grégoire de Montmorency, where striped bass of all sizes had once been caught (A. Michaud, extirpated population technician/biologist, pers. comm.1990). This area is just downstream of what was once the Maizerets Flats and the Bay of Beauport, an important wetland adjacent to Quebec City. Between 1945 and 2008, in the area between the Saint-Charles River and the Île d`Orléans bridge, an estimated 360 ha of aquatic and riparian habitat was lost due to backfilling for the port of Quebec City and the construction of a highway in the 1970s (Robitaille et al. 1988). A major portion of one location where striped bass were caught in abundance disappeared beneath the highway (Robitaille 2005) and one section of the wetland is now cut off from the river by an embankment and the flow of water, regulated by the tides, must pass through concrete culverts.

Not all the encroachment on the riparian environment is so extensive, but the Recovery Team deems that the cumulative loss of these important habitats for juvenile development may reduce the estuary`s carrying capacity for the reintroduced striped bass population and the entire aquatic community, warranting a high level of concern.

Discharge from the Gentilly 2 Nuclear Station (thermal attraction and decompression of gases): The Gentilly nuclear station (located near Trois-Rivières), which has been operating since 1983 on the south shore of the upper estuary, discharges hot water which attracts several fish species during the cold season. Reintroduced adult striped bass were regularly captured in this area between 2006 and 2009, during the fall, winter and spring (Hydro-Québec Production 2007; Alliance Environnement inc. 2008). In comparison, in 2009, no winter captures of the species were reported in the fishing zones around the power station, in places such as the dock in Bécancour, in Sainte-Angèle-de-Laval or in Lake Saint-Pierre and its archipelago, where the recreational fishery was monitored from January to March. It is impossible to determine with certainty whether the striped bass are spawning in the plume of warmer water and, consequently, whether the eggs and larvae are being transported to the colder neighbouring waters where they are exposed to a thermal shock (Donaldson et al. 2008). However, among the specimens captured in this area in March, females were present that required only a slight pressure on the abdomen to discharge their eggs. At this stage, females are ready to spawn and the eggs survive in the environment only briefly (DFO 2010a, b). The thermal attraction created by the discharged water from the power station may thus have important consequences if a high proportion of spawners from the reintroduced striped bass population frequent this area, though this is not yet confirmed by the available data (DFO 2010a, b).

Furthermore, the discharged water from the power station is saturated with gas, which produces symptoms of gas disease in some fish species (Mikaélian 1999; Lair 2006, 2007). In the subcutaneous tissue of channel catfish (Ictalurus punctatus), gas bubbles which lead to inflammation and possible infection have been observed (Lair 2006). It is impossible to gauge, from the available data, the significance and the scope of this phenomenon outside the channel of discharged water. Striped bass captured in this area have presented no signs of gas disease (Aecom Tecsult inc. 2009).

It is presently impossible to determine whether a significant percentage of adult striped bass frequents this area during the winter months, but it will be important to study how the striped bass use this area. Studies are presently under way. In light of the uncertainty as to a possible impact on the survival and recovery of the striped bass, the Recovery Team, as a precautionary measure, has judged the level of concern of this threat as moderate.

Contamination: Many industrial, municipal and agricultural contaminants from the entire St. Lawrence Basin and the Great Lakes reach the estuary. They are able to accumulate in the food chain and, through bio-amplification, reach high levels in the flesh of organisms at the top of the food chain, including striped bass. Some of the effects of these contaminants, either direct or synergetic, have been observed in aquatic organisms. Among the substances considered to be contaminants, the focus initially was on those that produce primary toxic effects (Korn and Earnest 1974; Hall 1991). However, it has since been shown that the introduction into aquatic environments of several families of synthetic compounds (e.g., antioxidants, detergents, organometallics, steroids, organochlorines, organo-nitrates) can cause hormonal disruptions in aquatic organisms, leading to such things as femininization and inhibition of gamete production (Aravindakshan et al. 2004).

Bioassays of mercury in the scales of specimens from the historic population revealed that the exposure of striped bass to this metal reached a peak in the mid-1940s, decreased during the following decade and then increased again during the 1960s (Desjardins et al. 2003, 2006). However, there exists no information to suggest that the level of mercury in the historic and the new populations could affect the viability of the species. As for the other contaminants likely to affect the striped bass, information is either incomplete or unavailable.

The Recovery Team is unable to assess the gravity of the threat which contaminants pose for the new population of striped bass but, as a precautionary measure, considers the level of concern to be moderate.

Obstacles to Migration: Obstacles to the free movement of striped bass may: 1) fragment the habitats used by the fish over the course of a year; and 2) isolate populations from one another. Before the disappearance of the species, 1+ year-old striped bass often traveled along the coast in schools searching for food during the summer (Beaulieu 1962; Robitaille 2001). In October, mature striped bass from the St. Lawrence began a migration towards the Upper Estuary and Lake Saint-Pierre, in preparation for spawning (Montpetit 1897; Vladykov 1947; Vladykov and Brousseau 1957; Magnin and Beaulieu 1967; Robitaille 2001). Construction projects or the introduction of obstacles along these routes may affect the migration of the new population. The effects that the obstacles may have can vary depending on the nature of the construction projects and their location relative to the migration route of the striped bass.

The Recovery Team considers the level of concern of this threat to be low because there presently exist no major obstacles to the movement of striped bass within their distribution range.

Eutrophication: Domestic sewage systems and the spread of manure and fertilizers on agricultural land contribute to the eutrophication of aquatic environments. This can disrupt local biological communities through the spread of stringy algae and of cyanobacteria, habitat degradation (e.g., the spawning grounds of rainbow smelt), the prevalence of tolerant species, incidences of anoxia, and other phenomena. Eutrophication may alter aquatic habitats in the tributaries which drain agricultural lands and in the alluvial fans where they empty into the river.

Besides the degradation of local habitat and an indirect effect stemming from a decrease in the abundance of certain prey species, according to the Recovery Team this factor does not appear to constitute a serious threat to the recovery of the striped bass in its entire distribution area. It has thus been given a low level of concern.

Climate Change: In the medium and long term, the St. Lawrence Estuary may undergo many changes brought on by climate warming: decreases in freshwater flows, a rise in sea level, advance of the saline front, lengthening of the growth season, changes in the biological community of the estuary, etc. An increase of 0.7 ºC in air temperature during the last century has been recorded (Environment Canada 2001, Lemmen and Warren 2004, Environment Canada 1999). According to the different climate forecast models for 2050, average air temperature during the summer may rise by 2 to 4 ºC in Quebec (Bourque and Simonet 2007). In the long term, these changes may affect the aquatic habitats in the estuary and, consequently, the striped bass.

The Recovery Team considers it unlikely that, based on inter-annual variations in weather conditions, there will be negative impacts on striped bass due to climate change. The level of concern for this threat is thus low. If necessary, the situation will be reviewed and considered in the future action plan.

1.5.2.2. Threats Due to the Harvesting of Individuals

The historic striped bass population was subjected to intense commercial and recreational fishing, and poaching, right up to the time of its disappearance (Caron 1877; Montpetit 1897; Beaulieu 1985; J. Brousseau, A. Michaud, G. Labrecque, extirpated population technicians/biologists, pers. comm. 1990; Robitaille and Girard 2002). At that time, the number of catches was not regulated and size limits, introduced near the end, were not generally respected (A. Michaud, extirpated population technician/biologist, pers. comm. 1990). The use of fixed fishing gear, extensive throughout the estuary, resulted in abundant captures of juveniles that would die at low tide (G. Labrecque, extirpated population technician/biologist, pers. comm. 1990). Mortality due to fishing, already high, increased after habitat modifications reduced the range of immature striped bass (Robitaille 2001).

Today, the management of fisheries resource exploitation is much more structured. In 2005, sports fishing for striped bass was prohibited in the St. Lawrence downstream of the Quebec City bridge and the prohibition was extended to cover all of Quebec in 2007. Furthermore, the directed commercial fishery of striped bass is no longer sanctioned. However, there is still a by-catch of striped bass by commercial and sports fishermen. Under the Quebec Fishery Regulations of the Fisheries Act, striped bass must be immediately released when caught, in the area where they are caught and with due precaution not to injure the fish if it is still alive.

In order to assess and monitor the impact of the fisheries, a network to monitor accidental captures of striped bass has been created. This network is composed mainly of commercial fishermen who have been issued a permit for the capture of wildlife for scientific, educational and wildlife management purposes (SEG) ⁴. They are authorized to keep striped bass that are accidentally captured, in order to give them to the biologists of the ministère des Ressources naturelles et de la Faune du Québec (MRNF) for analysis. Since 2009, any live striped bass over 20 cm long that are captured must be released. In addition to the information gathered by this network, there are observations of caught and released striped bass which sports fishermen report to the Centre de données sur le patrimoine naturel du Québec (CDPNQ⁵). In 2005, the Fédération québécoise des chasseurs et pêcheurs (FédéCP), in collaboration with the MRNF, conducted a widespread awareness campaign to inform commercial and sports fishermen about the reintroduction of striped bass, the mandatory catch and release regulation, and the importance of reporting captures to the CDPNQ. Between 2003 and 2009, 507 striped bass were brought to MRNF biologists for analysis and 163 observations were recorded. These data made it possible to compile the first biological status report on the reintroduced population (Pelletier 2009) and to better identify habitat use (Pelletier et al. 2010).

In 2009, the DFO conducted an analysis of the possible impact of accidental captures in the commercial and recreational fisheries on the survival and recovery of the striped bass population of the St. Lawrence Estuary (DFO 2009). The analysis concluded that: “overall, freshwater and marine environment fisheries as they are currently carried out, are not very likely to have an impact on survival and recovery of the striped bass population in the St. Lawrence Estuary”. The Recovery Team has thus determined that the level of concern for this threat is low in all three areas: commercial fishery, recreational fishery and poaching.

Accidental Captures in the Recreational Fishery: Sports fishermen in the estuary may accidentally catch striped bass but they are obliged to release them immediately. Analysis of the impact of the fisheries has concluded that the mandatory release of captured fish, together with the awareness campaign carried out, makes it unlikely that recreational fishing will harm the survival and recovery of the striped bass (DFO 2009).

Accidental Captures in the Commercial Fishery: The risk of accidental capture of striped bass in commercial fishing gear varies according to location and season. The greatest risk for the new population, as it was for the historic population, comes from fixed gear designed to trap American eels (Anguilla rostrata) in the Middle Estuary. Since being reintroduced, some striped bass have been caught in fixed nets set for American shad (Alosa sapidissima) and in fyke nets, but these captures are negligible according to the commercial fishery monitoring reports (DFO 2009).

The number of eel traps in the St. Lawrence Estuary has declined dramatically since the 1950s. Presently, most of them are set in the Middle Estuary in September. In 2009, the number of authorized traps in the river and in the estuary saw a 73% drop, from 190 to 51 traps (about 35 are set each year). There are now only 21 commercial eel fishermen operating within the distribution range of the striped bass between Saint-Romuald and Rimouski (one fisherman near Quebec City and 20 others between Île d'Orléans and the mouth of the Saguenay River on the North Shore and Rimouski on the South Shore). As mentioned in the analysis of the impact of accidental catches (DFO 2009: "the sector where juvenile striped bass were very vulnerable prior to their disappearance is no longer a sector where the fishing effort is significant".

Analysis of the impact of the fisheries has concluded that all the freshwater and marine commercial fisheries have no or almost no impact on the survival and recovery of the striped bass except for the fyke nets and eel traps whose impact was deemed low and moderate respectively (DFO 2009). Should an increase in by-catches present a problem, measures may be implemented to redress the situation (e.g., closure of selected fishing zones).

Poaching: This activity is much harder to evaluate because of the lack of reliable data. According to the available information, there is no indication of an illegal fishery specifically targeting striped bass since its reintroduction.

1.5.2.3. Biological Threats

Exotic Invasive Species: Several exotic species have established themselves in the St. Lawrence River and Estuary. Exotic species can alter ecosystems and their ecological functions and may represent a threat to the striped bass (e.g., competition for habitat and food resources, restructuring of the food chain, predation).

The introduction of non-native organisms seems to have begun in the 19th century and has accelerated dramatically during the last decades. It is estimated that at least 185 exotic species have colonized the Great Lakes Basin since 1980, 88 of which have moved into the St. Lawrence River (Ricciardi 2006; NCRAIS 2009; De Lafontaine, Environment Canada, pers. comm. 2009). Several fish species have been introduced including the tench (Tinca tinca) and the round goby (Neogobius melanostomus). The latter has rapidly become quite abundant in several sections of the St. Lawrence, including the area once used by the striped bass.

The impact of invasive species on the new striped bass population has not yet been determined and is not currently known. The Recovery Team consequently considers this threat as a low level of concern because no major impact on the striped bass population is foreseen.

Parasites and Pathogens: Necropsies performed on striped bass of the historic population revealed that several specimens had unidentified parasitic worms in their digestive tracts and abdominal cavities (J. Brousseau, laboratory notes). One of these worms may be the Philometra sp. (Séguin et al. 2007), a parasite which was also found in wild striped bass transferred from the Miramichi River to the St. Lawrence in 2005. In the southern Gulf of St. Lawrence, striped bass are often carriers of the Philometra sp. nematode and their general condition does not appear to be affected (S. Douglas, DFO, pers. comm. 2005).

The new population of striped bass will likely be host to a number of parasites, as are other fish species in the St. Lawrence, and may be exposed to certain pathogens, such as viral hemorrhagic septicemia (VHS) which is present in the Great Lakes Basin and in the Maritimes. VHS was first identified in 2005 and 2006 in the Great Lakes and is associated with mass mortalities in numerous fish species in the area. To date, no case of VHS has been detected in Quebec (C. Brisson-Bonenfant, MRNF, pers. comm. 2009). Several analyses were conducted prior to the implementation of the action plan for the reintroduction of striped bass from the Miramichi River. They showed that the risk of introducing new parasites or pathogens in the St. Lawrence was low (Robitaille 2000). After striped bass infected with VHS were discovered in the Miramichi River, captures of fish from that river ceased as part of the reintroduction program. Additional analyses at the hatchery confirmed that the individuals kept for reproduction in captivity were not carriers of VHS.

Parasites and pathogens do not presently appear to constitute a threat to the survival and recovery of the population, the Recovery Team considers this a low level of concern. It is however important to take the necessary precautions to ensure that the stocking of striped bass does not introduce new parasites and pathogens in the St. Lawrence.

The Comité aviseur sur la réintroduction du bar rayé (2001), composed of striped bass and fisheries specialists, released a statement supporting the introduction of this species in the St. Lawrence (Appendix 2). An agreement was signed between DFO - Gulf Region, and the MRNF to allow the sampling of up to 2,000 juvenile striped bass each year in the Miramichi River in New Brunswick. Representatives from the recreational and commercial fisheries and from aboriginal communities were then consulted to obtain their approval for the reintroduction project.

In 1999, and from 2002 to 2006, juvenile striped bass were captured in the Miramichi River and transported to the Baldwin-Coaticook hatchery in Quebec in order to develop and serve in artificial reproduction. The survival rate of the transferred striped bass in hatcheries proved to be greater than anticipated. Beginning in 2002, the St. Lawrence River was stocked with surplus fish from this program (Table 3), usually as part of a media event advertising the reintroduction of striped bass. As previously mentioned, between 2002 and 2009 more than 6,300 striped bass, over 60 mm long (age 0+ to 6+), and almost 6.5 million larvae, 2 to 4 mm long, were released into the St. Lawrence between Saint-Pierre-les-Becquets and Rivière-Ouelle. The stocking of striped bass produced in hatcheries began in 2006; these were initially surplus larvae that could not develop in hatchery environments because the necessary installations were not yet available. The Baldwin-Coaticook hatchery was renovated to permit the production of this species and, after a few years of trials and readjustments, is very close to success in producing fry, the preferred stage for stocking. The goal of the reintroduction program is to stock 50,000 autumn fry yearly with the objective of reaching a population capable of self-reproduction (Comité aviseur sur la réintroduction du bar rayé 2001). Methods of tagging larvae (chemical tagging), juveniles and adults (microchips) will provide the means to identify which of the striped bass captured in the St. Lawrence were stocked and which are of natural origin and to track abundance levels over time.

In 2005, fishing of this species was prohibited downstream of the Quebec City bridge and the prohibition was extended to cover all of Quebec in 2007. In 2005, the FédéCP and the MRNF launched an awareness program informing sports fishermen how to identify the species and advising them to release all catches immediately and report captures to the Centre de données du patrimoine naturel du Québec (CDPNQ). Hundreds of notices were posted around docks, marinas and boat ramps, all along the river and the estuary.

In 2004, a network to monitor accidental catches of striped bass in commercial fishing gear was established, supplemented by observations reported to the CDPNQ (Bourget et al. 2008). Various biological and morphometric parameters of striped bass conserved at the MRNF are being analyzed in laboratories. The data gathered by this network have confirmed that the reintroduced striped bass are developing well in the St. Lawrence and are occupying a distribution range similar to that of the historic population. In 2008, this data helped show that natural spawning had occurred in the estuary because 38 striped bass individuals born that year (age 0+) were captured, and no stocking had occurred for this age group that year (Pelletier 2009). A report on the biology of the new striped bass population was produced (Pelletier 2009) and new information became available on habitat use (Pelletier et al. 2010). In addition, necropsies ensured regular monitoring of diseases and parasites (Guy Verreault, MRNF, pers. comm. 2010).

The results of analyses of the data and specimen collections of the extirpated population will also be used to facilitate the reintroduction of the striped bass. These data were used to document the biology and exploitation of the extirpated population (Robitaille 2001), the food sources of juveniles (Robitaille 2005), and the population`s exposure to mercury contamination (Desjardins et al. 2003, 2006).

When the striped bass population of the St. Lawrence Estuary disappeared at the end of the 1960s, it had been the object of scant research, focused primarily on its movements (Beaulieu 1962), its feeding habits (Brousseau 1955) and its development (Magnin and Beaulieu 1967). Further analyses were made possible through the additional collection of data and specimens (Robitaille 2001, 2005, 2010; Desjardins et al. 2003, 2006). It is not possible at the present time to determine to what extent the biological descriptors of the historic population may apply to the reintroduced population. Regular monitoring of the latter is first required.

Recovery activities are difficult to plan due to the lack of information on present day spawning grounds, the reproductive process, and the early stages of development. It will be necessary to locate the various habitats used during the different stages in the life cycle, particularly the habitats vital for spawning and larval development. This will make it possible to ensure the protection of these habitats and to accumulate measurements on abundance and survival during these critical stages. It will also enable the identification of the environmental parameters which influence the vitality of cohorts of the new striped bass population.

It is equally important to offer a description of the interspecific relationships of striped bass with other aquatic organisms, particularly prey, predator and competing fish species. A better understanding of this network of interactions will provide valuable indicators of the health of the striped bass population and of the species it interacts with. This will ensure that the recovery of the striped bass will not be achieved at the cost of other species endemic to the estuary. Finally, special attention should be paid to the threats listed above (see Section 1.5), particularly the ones of greatest concern, in order to formulate precise assessments of the risks they present and, if need be, to develop the appropriate mitigation measures.

³ In the St. Lawrence Estuary, specimens of juvenile striped bass captured in fixed gear between 1946 and 1962, from Neuville and Rivière Ouelle, were preserved (Robitaille 2005).

⁴ A special permit issued by the MRNF for the capture of animals for scientific, educational or wildlife management purposes (SEG permit).

⁵ Centre de données sur le patrimoine naturel du Québec