Recovery Strategy for the Striped Bass (Morone saxatilis), St. Lawrence Estuary Population, in Canada
Common Name: Striped Bass (Population of St. Lawrence Estuary)
Scientific Name: Morone saxatilis (Walbaum, 1792)
Date of Assessment: November 2004
COSEWIC Status: Extirpated in 2004.
Reason for Designation: The population from the St. Lawrence Estuary has disappeared as a consequence of illegal fishing, with the last record dating from 1968.
Canadian Occurrence: Quebec
Status History: Designated extirpated in November 2004. Assessment based on a new status report.
The striped bass (Morone saxatilis) is a spiny fish with an elongated, laterally compressed body and a triangular head (Figure 1). It has two separated dorsal fins, the first of which is spiny. The caudal fin is forked. The first three rays of the anal fin are spiny. The pelvic fins are thoracic. The cheeks and opercula are covered with scales. The striped bass has a dark olive-green to black back and a white belly. On the pale or silvery sides, there are seven or eight horizontal dark stripes following the scale rows. None of these stripes extends onto the head.
This fish is well adapted to estuaries and coastal waters. It travels along the coast in compact schools of same-size fish, feeding on invertebrates and fish (see Section 1.4 Needs of the Striped Bass). In the St. Lawrence, the striped bass can live up to twenty years and reach a total length of 90 cm (Vladykov 1953).
The natural range of the striped bass (excluding areas where it was introduced by humans) extends along the Atlantic coast of North America, from the St. Lawrence River to the St. Johns River in northeast Florida. Native striped bass populations have also existed in the tributaries of the Gulf of Mexico, from the Suwannee River in northwestern Florida to Lake Pontchartrain in Louisiana (Lee et al. 1980; Bain and Bain 1982).
The species was introduced in the common estuary of the Sacramento and San Joaquin rivers, on the Pacific coast, in 1879 (Bonn et al. 1976), and gradually became established in other rivers along the west coast of the United States (Hart 1973; Lee et al. 1980; Setzler et al. 1980).
The striped bass can live in freshwater and, in certain cases, may even complete its life cycle there (Scruggs 1957). It has been introduced as a sports species in numerous lakes and reservoirs in the United States, Mexico, Ecuador, Russia, Latvia, France, Portugal, Turkey and South Africa (Lee et al. 1980; Setzler et al. 1980; Froese and Pauly 2007). In some of these locations, the populations reproduce naturally (Lee et al. 1980; Setzler et al. 1980; Froese and Pauly 2007). Elsewhere, the striped bass thrives well but cannot reproduce and on-going stocking programs are required to maintain population numbers (Lee et al. 1980).
In Canada, five native striped bass populations have existed in three distinct sectors corresponding to the three designatable units recognized by the COSEWIC (Figure 2): the Bay of Fundy, the Southern Gulf and the St. Lawrence Estuary (Robitaille 2004). The populations in the St. John, Annapolis and Shubenacadie rivers belong to the Bay of Fundy group, feeding in that bay during the summer and possibly coming into contact there. These three populations also frequent waters which, during the summer, are home to striped bass migrating from American rivers.
Figure 2 . Location of the five rivers in eastern Canada that have supported striped bass populations.
The filled-in circles indicate extant populations and the open circles indicate rivers in which no spawning activity has been observed for 20 years or more. Inset, range of North American native populations.
There is only one known spawning population in the southern Gulf, that of the Miramichi River. Striped bass have been captured in several estuaries and along the coast between Percé and Margaree, on Cape Breton Island (Melvin 1991). However, these fish all seem to originate in the Miramichi River, where the only known striped bass spawning ground in the entire southern Gulf is found (Bradford et al. 1995; Robichaud-LeBlanc et al. 1996; Douglas et al. 2003). The southern Gulf population is believed to be isolated from both the Bay of Fundy populations and the migratory bass from American rivers. All recaptures of striped bass tagged in the southern Gulf were reported in this sector, except for one in Maryland (Hogans and Melvin 1984).
The third group also contains a single population, that of the St. Lawrence Estuary, which occupied a roughly 300 km stretch of the fluvial and estuarine1 portion of the river. With respect to the striped bass population of the St. Lawrence Estuary, the distribution of recaptures in a mark-release program between 1944 and 1962 suggests that it was isolated from the other Canadian populations (Beaulieu 1962; Robitaille 2001). Of the 3,009 tagged specimens, 310 were recaptured, all within the sector between Lake Saint-Pierre and Kamouraska. It is mainly in this portion of the St. Lawrence that most of the striped bass captures were made by sports and commercial fishermen (Figure 3). Commercial captures were also regularly recorded in the St. Lawrence Estuary between 1920 and 1965, though none were recorded in the southern Gulf between 1935 and 1968 (Leblanc and Chaput 1991; Douglas et al. 2003). All available data seem to indicate that the St. Lawrence striped bass population is distinct from other Canadian populations.
Figure 3 . Range of the historic population of St. Lawrence Estuary striped bass.
The movement of three-year and older striped bass upstream seems to be linked to spawning activity. Shown are only the areas where striped bass were regularly captured each year before the start of the population decline in the 1950s which terminated in the disappearance of the population.
In 2002, following an action plan for the reintroduction of striped bass in the St. Lawrence (Comité aviseur sur la réintroduction du bar rayé 2001), a reintroduction program was developed in Quebec, which included fish breeding in Quebec hatcheries using striped bass captured in the Miramichi River in New Brunswick. Between 2002 and 2009, more than 6,300 striped bass measuring over 60 mm in length (ages2 0+ to 6+) and 6.5 million larvae, 2 to 4 mm long, were stocked in order to promote the recovery of the striped bass population of the St. Lawrence Estuary. The aim of the reintroduction program, which will stock up to 50,000 autumn fry (Comité aviseur sur la réintroduction du bar rayé 2001), is to establish a population capable of self-reproducing. Since being reintroduced, striped bass have been captured in the sector once occupied by the extirpated population, between Lake Saint-Pierre and Rivière-du-Loup (DFO 2010a, b; Pelletier et al. 2010).
The present recovery strategy is concerned with the striped bass population reintroduced in the St. Lawrence Estuary (known as the new population), intended to replace the one which disappeared in the late sixties (known as the historic population).
Within the natural range of the striped bass, the status of the different populations varies greatly. The species is globally listed as common, widespread and abundant, but at the national and subnational levels, status varies considerably (Table 1). Some eastern American coastal rivers contain abundant populations characterized by lengthy migrations between the Bay of Fundy and northern Florida. The abundance and omnipresence of these migrating fish seem to indicate a general global abundance of the species. However, several spawning populations disappeared during the 20th century, including, for example, most of those in the tributaries of the Gulf of Mexico.
*The conservation status of a species or ecosystem is designated by a number from 1 to 5, preceded by a letter reflecting the appropriate geographic scale of the assessment: G: Global; N: National; and S: Subnational (i.e., state or province). The numbers have the following meaning: 1 = critically imperilled; 2 = imperilled; 3 = vulnerable; 4 = apparently secure; 5 = secure; X: presumed extinct or extirpated; H: possibly extinct or extirpated; N: non-breeding; NA: not applicable —a conservation status rank is not applicable because the species or ecosystem is not a suitable target for conservation activities; NR: unranked—national or subnational conservation status not yet assessed http://www.natureserve.org.
In 2004, in Canada, in the three rivers where spawning populations had previously existed (the St. John, Annapolis and St. Lawrence rivers), no sign of reproductive activity had been observed and no capture of striped bass of local origin had been confirmed in over twenty years (Robitaille 2004). However, since the reintroduction of striped bass in the St. Lawrence, signs of natural reproduction were observed in 2008 (Bourget et al. 2008; Pelletier 2009). The populations in the Shubenacadie River (Bay of Fundy population) and the Miramichi River (Southern Gulf of St. Lawrence population) still appear capable of producing new individuals (Robitaille 2004).
The striped bass is an anadromous fish typical of the estuaries and coastal waters of North America (Scott and Scott 1988). Spawning, incubation and early larval development occur in freshwater in the spring. The young subsequently move downstream to brackish water and then on to salt water where they feed and grow until they reach maturity, approximately 3 years for males and 4 or 5 years for females (Berlinsky et al. 1995; Douglas et al. 2003; Powles 2003). In Canada, striped bass reproduce during three or four weeks beginning around the end of May and early June, in fresh or slightly brackish water. The spawning ground of the striped bass of the St. Lawrence Estuary has never been located, but available data seems to indicate that it lies in Lake Saint-Pierre or just downstream from there in the adjacent section of the fluvial estuary (Montpetit 1897; Vladykov and Brousseau 1957; Beaulieu 1962; Cuerrier 1962; Magnin and Beaulieu 1967; Robitaille 2001).
Of the various habitats used by the striped bass during its life cycle, the most important for the maintenance of the population appears to be the spawning, incubation and rearing habitats (Albrecht 1964; Auld and Schubel 1978; Dudley and Black 1978; Kernehan et al. 1981; Jessop 1990, 1991; Melvin 1991; Van den Avyle and Maynard 1994). Egg survival to hatching is closely tied to the physicochemical properties of the incubation habitat, particularly temperature, dissolved oxygen and the presence of a moderate current (Cooper and Polgar 1981). The duration of incubation is a function of temperature. The highest hatching rates (87%) and larval survival rates in the first 24 hours (76%) are obtained at 18oC (Morgan et al. 1981). At that temperature, the eggs hatch approximately 48 hours after fertilization (Pearson 1938; Raney 1952). Egg survival rapidly declines when the water temperature exceeds 23oC and gradually declines as water temperature drops below 17oC, with almost no eggs surviving at temperatures below 12oC (Morgan and Rasin 1973; Rogers et al. 1977). Two other factors, sufficient dissolved oxygen and the presence of a current, may have a combined effect on egg survival. The eggs are generally heavier than water and, in the absence of current, sink to the bottom, where they are more exposed to anoxia, a lack of oxygen (Chittenden 1971; Rawstron et al. 1989). The presence of a moderate current creates low turbulence levels, which keep the eggs suspended in the water column during incubation.
The survival of the larvae, like the eggs, also depends on physical variables, including temperature and dissolved oxygen. However, an additional requirement, i.e., a sufficiently abundant food supply, comes into play upon resorption of the yolk sac and the onset of feeding (Chittenden 1971; Rawstron et al. 1989). This key period occurs approximately on the eighth day of existence of the larvae, when they measure 6 to 7 mm. In natural environments, the rate of survival of larvae that have exhausted their yolk reserves is directly related to the abundance of zooplankton in their environment (Kernehan et al. 1981; Martin et al. 1985). It has been shown that in Chesapeake Bay, where the eggs and larvae are transported from several rivers where striped bass are known to spawn, the density of individuals in the first stages of development varies according to distance from the point of maximum turbidity (North and Houde 2003). Environmental characteristics and vertical migration of larvae in the water column, depending on the tides, enables them to maintain their position in the estuary, in areas where there is an abundance of prey. A zone of maximum turbidity also exists in the St. Lawrence, between Île d'Orléans and Île aux Coudres. This zone contains high densities of zooplankton, including the copepod Eurytemora affinis, and is known as a rearing ground for rainbow smelt (Osmerus mordax) and other fish species (Sirois and Dodson 2000). The striped bass of the St. Lawrence may also spend the early stages of their development there. After 35 to 50 days in the transformational larval stage, the young reach a length of 20 mm and possess the typical shape of the striped bass which they will maintain into adulthood.
Immature and adult striped bass frequent coastal and estuarine habitats (Bain and Bain 1982). During their first two years, they feed primarily on invertebrates, but gradually become piscivorous, chasing schools of soft-rayed fish, particularly juvenile clupeids (Trent and Hasler 1966; Manooch 1973; Austin 1980; Gardinier and Hoff 1982; Dew 1988). In summer, the movement of striped bass appears to follow that of their preferred prey. Adult bass tolerate and withstand variations in salinity, temperature, pH or turbidity (Talbot 1966; Auld and Schubel 1978; Setzler et al. 1980). Canadian striped bass populations typically migrate upstream in the fall and overwinter in fresh and brackish waters to avoid the cold winter ocean waters. The confined presence of striped bass in these overwintering zones may increase the risks of mortality due to environmental accidents or poaching.
The striped bass has a life expectancy of up to 30 years (Secor 2000). The largest known specimen, captured in North Carolina in 1891, weighed 56.8 kg and measured 1.82 m (Raney 1952). The growing conditions in Canadian waters are such that the maximum size of striped bass is less than 1 m. This figure is an estimate because very few individuals survive long enough to reach their maximum size. The largest striped bass caught in the St. Lawrence Estuary measured 91.5 cm (total length) and weighed 10.9 kg. After an examination of its scales, its age was estimated at 19 years (Vladykov 1953).
Typical of estuarine environments, the striped bass is highly dependent on the quality of the habitats it frequents during its life cycle, particularly the fluvial environments where it spawns. An abundant striped bass population is an indicator that a river and its estuary are in good condition and that the harvest rate is adequate (Bain and Bain 1982).
The striped bass does not build a nest and does not care for its offspring. Females discharge a large quantity of eggs into the water column. A tiny proportion of these eggs survive into adulthood. During the first weeks of their existence, most of the larvae will be preyed upon by various aquatic organisms (e.g., insects, invertebrates, fish) (Smith and Kernehan 1981; McGovern and Olney 1988; Monteleone and Houde 1992; Andreasen 1995). The survival rate of striped bass increases, however, after their first summer (Goodyear 1985).
At the adult stage, the striped bass, together with other fish, birds and mammals, occupies a high trophic level within the estuarine and coastal communities of North America (Hartman and Brandt 1995a). The species is adapted to estuaries, where it is one of the most important piscivorous species and an important component of the biodiversity of the aquatic ecosystem. It is able to withstand rapid variations in temperature, turbidity and salinity in these environments (Bain and Bain 1982). It moves along the coast in compact, same-size schools in search of food, especially at night (Koo et Wilson 1972). Consequently, the reintroduction of striped bass in the St. Lawrence would contribute to the restoration of biodiversity in this ecosystem (Comité aviseur sur la réintroduction du bar rayé 2001).
In an estuary which opens onto both fresh and salt waters, striped bass may compete with other piscivorous species (Hartman and Brandt 1995a, b). This may be the case in the St. Lawrence. According to striped bass fishermen at the wharf in Lotbinière, yellow walleye (Sander vitreus) avoid waters in which striped bass hunt in groups (C. Mélançon, undated manuscript). According to active fishermen surveyed during the 1940s, 1950s and 1960s, yellow walleye and sauger (S. canadense) were present in the St. Lawrence Estuary but captures of these species were less frequent before the disappearance of the striped bass (Robitaille and Girard 2002). The increase in abundance of yellow walleye may be explained by the fact that this species, and possibly others, have partially occupied the ecological niche vacated by the striped bass. If this is the case, the return of the striped bass may lead to a physical displacement (periodical or permanent) of walleye to other habitats and a subsequent reallocation of resources.
The known limiting factors are of particular concern during the early stages of development when fish are sensitive and less mobile. The reproductive strategy of this species is based on a very high rate of fecundity which offsets the high mortality rate during the early developmental stages. The striped bass is a highly fecund fish. Upon reaching sexual maturity at about 4 or 5 years of age, females carry approximately 53,000 eggs, a number which will grow as the fish increases in size, reaching about one and a half million eggs in ten-year-old individuals (Paramore 1998).
The existence and integrity of adequate environments for spawning, incubation and larval development, providing satisfactory water flow, temperature and water quality, are essential for the survival of a striped bass population (Albrecht 1964; Dudley and Black 1978; Kernehan et al. 1981; Jessop 1990, 1991; Melvin 1991; Van den Avyle and Maynard 1994). Survival to the end of the larval stage seems to be a key factor in year-class strength (Cooper and Polgar 1981) and thus in adult abundance several years later (Goodyear 1985; Ulanowicz and Polgar 1980). In the structure of the adult population, year classes that were produced in years in which conditions were favourable for spawning often dominate (Polgar 1981; Cooper and Polgar 1981; Goodyear 1985).
The striped bass population of the St. Lawrence Estuary may be exposed to further limiting factors because it lives at the northern limit of the species` range (Robitaille 2004). The harsher climactic conditions which the northern populations of this species must confront may result in a variable mortality according to size (Hurst and Conover 1998). It is estimated that juveniles that reach at least 100 mm in length by the end of their first growing season have a better chance of surviving the prolonged fast of their first winter under the ice than do smaller individuals (Bernier 1996; Bradford and Chaput 1997).
Another limiting factor relative to the biology of the striped bass of the northern populations is the confinement of individuals during the winter. The concentration of a high proportion of spawners in a restricted area may aggravate the repercussions of an episode of accidental mortality or increase the vulnerability of the fish to poaching. Three-year and older striped bass of the historic population used to migrate to Lake Saint-Pierre in the fall, where they would winter. Many of these individuals were the size of spawners and, consequently, naturalists at that time believed that this congregation of fish was in preparation for spawning activity, though this activity was never directly observed (Montpetit 1897; Vladykov 1947; Vladykov and Brousseau 1957; Cuerrier 1962; Magnin and Beaulieu 1967). It is impossible to foresee whether the striped bass of the new population will gather in Lake Saint-Pierre and the surrounding waters. Since the reintroduction, most of the captures of large striped bass in the Upper Estuary during the cold season have been concentrated in the plume of discharged water from the Gentilly 2 nuclear generating station (see section 1.5 Threats). This facility may be somewhat attractive for the species and could affect the winter distribution of adult striped bass. Concentrations of adult striped bass have also been observed in the spring by sports fishermen in the basin of the Rivière du Sud in Montmagny (Pelletier et al. 2010; DFO 2010a, b).
Finally, striped bass must have access to abundant food resources during the summer, without which their condition may deteriorate and the incidence of disease increase (Overton et al. 2000). They can, however, migrate to other areas to satisfy their needs.
1The St. Lawrence Estuary extends from the outflow of Lake Saint-Pierre to a line between Pointe-des-Monts and Matane.
2 Age is expressed in years.
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