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Species at Risk Act - Legal Listing Consultation Workbook, Striped bass, St-Lawrence Estuary Population

Background information on striped bass: St. Lawrence Estuary population.

Status : extirpated

Last COSEWIC assessment :   November 2004

2.1. Description of the species

Part of the Moronidae family, the striped bass, Morone saxatilis, is a species typical of eastern North American estuaries and coastal waters. It has an elongated body, a triangular head and a mouth with a protruding lower jaw. It has two separated dorsal fins, the first of which is spiny. It has a dark olive-green to black back, paling on the sides to silvery, and a white belly. It has seven or eight easily distinguishable contrasting horizontal stripes.

2.2. Species distribution

The natural range of the striped bass extends along the Atlantic coast of North America, from the St. Lawrence River to the St. Johns River in northeast Florida. The striped bass populations that are recognized in Canada are found in the northern portion of this species distribution range. Historical data confirms that striped bass used to spawn in five eastern Canadian rivers: the St. Lawrence River (Quebec), the Miramichi River (New Brunswick), and in the St. John, Annapolis and Shubenacadie rivers (Nova Scotia). The only two rivers where they still spawn are the Miramichi and Shubenacadie rivers, and their respective populations seem to be isolated and distinct from one another. All available data (from sport and commercial fishery studies between 1944 and 1965) appear to indicate that the St. Lawrence Estuary population, which is addressed in this document, was isolated from other Atlantic groups. The Estuary’s striped bass population extended along a 300 km stretch of the River, from Lake Saint-Pierre (Sorel) to Kamouraska. There have been no reports of recaptures downstream from Kamouraska of bass tagged in the St. Lawrence. This does not rule out the possibility of contacts, but they appear to be the exception.

2.3. Biology of the striped bass

2.3.1. Spawning

Like salmon, the striped bass is an anadromous species that moves between freshwater or slightly brackish spawning habitats (spawning, incubation, initial rearing) and brackish or salt water feeding sites to complete its life cycle, and sexual maturity is reached after a few years. Females reach sexual maturity at about 5 years of age and 40 cm in length. Males on the other hand reach maturity at about 3 years and 30 cm. Adult bass usually spawn towards the end of May or beginning of June. Males reach the spawning areas first, followed by the females who are usually fewer in numbers. Spawning can last 3 to 4 weeks when the number of spawners is high and begins when water temperatures rise above 10 °C. The fecundity of females between the ages of 4 and 11 ranges from 53,000 to 1,464,000 eggs, making it a prolific fish species. Spawning occurs near the surface, at twilight. Striped bass can spawn several times during their lives, with sometimes a year of rest between successive contributions. In some rivers, active spawners of 14 years of age have been observed. The striped bass spawning ground in the St. Lawrence Estuary has never been located, but various sources suggest that it is in Lake Saint-Pierre or downstream from it, in the adjacent section of the upper estuary.

2.3.2. Incubation and rearing

The fertilized eggs remain suspended in water during the entire incubation period (2-3 days). A week after hatching, and after exhausting their own reserves (egg yolk), larvae move up the water column to find their food. After 35 to 50 days, young-of-the-year (of around 20 mm) take their typical bass adult form. The growth of one-year-olds depends on the quantity of food ingested (invertebrates first then fish gradually). Contrary to the rather static larvae, juveniles can travel several tens of kilometres to satisfy their feeding needs. Younger bass then move towards brackish and saltwater to feed and grow.

2.3.3. Movements and migration

The migration of striped bass is related to their development, feeding, spawning and overwintering. Spawning of St. Lawrence striped bass occur in or around LakeSaint-Pierrefrom mid-May to mid-June. Afterwards, downstream migration of young-of-the-year occur over several weeks, from mid-July (near Neuville, around the Orléans Island and in the Montmagny archipelago) to early September (Rivière-Ouelle and Saint-Jean-Port-Joli). They are found along the banks of the St. Lawrence River and around several estuarine islands between the Madame and Aux Oies islands.

In the fall, spawners that lived in saltwater return to the river to winter, as far as Lake Saint-Pierre. The young (3 years and younger) winter in the estuary, downstream from Quebec City, in the river’s freshwater plumes. After the spring spawning period, spawners travel to the estuary where they feed and gather strength throughout the summer. Striped bass travel in schools made up of individuals from the same age class (cohort).

2.3.4. Diet

The larvae diet changes as it grows: beginning with the yolk, they then feed on immature micro-crustaceans, followed gradually by adult micro-crustaceans. Young-of-the-year feed mostly on small invertebrates. When they reach two years of age, young bass begin eating fish. St. Lawrence bass of two years and older appear to feed on Atlantic tomcod, rainbow smelt, American shad, alewife, herring and flounder.

2.3.5. Population size

Population distribution and seasonal movements in the St. Lawrence Estuary was described in detail towards the end of the 19th century. However, biological data on this species was systematically collected by scientists between 1944 and 1962 only.

The St. Lawrence bass population appears to have declined significantly since the mid-1950s. Even though the St. Lawrence striped bass were being heavily exploited, there was no population size assessment. Only indirect abundance indices exist, such as recording the number of commercial and sport fishery catches. Beginning in 1957, landings, which had always fluctuated between 5 and 50 tons annually since 1920, dropped under 3 tons and remained there until 1965, the last year commercial catches were recorded for this species. Similarly, the sport fishery, heavy around the Orléans Island and in the Montmagny archipelago, particularly in July and August, appears to have followed the same trend: a few occasional catches were made between 1963 and 1968, but no other evidence of spawning has been observed since then.

It was briefly believed that the local population had recovered around the early 1980s, when some 100 bass were caught around the Gaspé Peninsula and in the lower estuary. However, it appears they were actually bass from the Miramichi River.

2.3.6. Habitat

Of the various habitatsused by striped bass, the most important to the maintenance of a population seems to be its spawning, incubation and rearing habitat. The incubation period depends on water temperature as eggs only survive well between 17 and 23 °C. A sufficient level of oxygen and a moderate current creating light turbulence help with survival. If the current stops, eggs drop to the bottom under their own weight, into an inhospitable environment in which they could die due to the lack of oxygen. Larvae are also dependent on water temperature and dissolved oxygen, but they also require a steady micro-crustacean supply. Immature and adult striped bass frequent sheltered bays, estuaries and coastal habitats where they feed during summer, and their movements are primarily associated withthose of their preferred prey.

Because the species requires high quality spawning and rearing habitats and abundant aquatic fauna for food, maintaining an abundance of bass indicates to a certain extent the good quality of a river and its estuary. The striped bass represents a significant component of the biodiversity of aquatic ecosystems.

2.4. Why has COSEWIC given the striped bass an extirpated species status?

Here is the reason for the striped bass status designation by COSEWIC:

COSEWIC revealed that the St. Lawrence Estuary population disappeared because of illegal fishing; the last observation took place in 1968. The report also mentioned that the alteration of spawning and rearing habitats  also contributed towards this situation.

2.5. What are the threats to the species?

Canadian studies on striped bass have shown that overfishing by commercial and recreational fishermen may have decimated some populations such as the one in the St. Lawrence River. The alteration of spawning, incubation or rearing habitats may have also compromised reproduction of the Laurentian striped bass. The fact that the Estuary population was located at the northern edge of the American distribution range may have exposed it to additional limiting factors. The concentration of fish in small areas in rivers during wintering could for example make them vulnerable to poaching and various other mortality factors. Changes in flow conditions and pollution are contributing factors in the decline of abundance.

2.5.1. Geographic and biological characteristics

Susceptibility of age groups

An abundant production of new individuals, for a given number of spawners, depends closely on favourable weather and environmental conditions that do not occur every year. However, high fecundity of bass along with their capacity to reproduce several times during their lives diminishes the effects of variable recruitment.

Because eggs and larvae have specific needs, their survival varies according to the annual conditions in their immediate environment. Once their yolk reserves are exhausted (about the eighth day) larvae begin a critical period: their survival during this stage is a guarantee of adult abundance a few years later. Juvenile and adult bass are more tolerant and handle changes better (salinity, temperature, pH, turbidity); they have the capacity to move to coastal or estuarine habitats to meet their needs.

Canadian populations migrate in fresh or brackish water, avoiding lower sea temperatures during winter. However, for young-of-the-year, fish of less than 10 cm are less likely to survive their first winter of prolonged fasting than larger fish. Their growth over the first summer is therefore another significant condition.

2.5.2. Traditional, commercial and sport fishing

Subsistence fishery

The striped bass was fished by First Nations, and later by the first European settlers. Archaeological digs on First Nations sites and colonial settlements uncovered striped bass bones near Lanoraie (Quebec) (14th century) and colonial sites in Quebec City (17th century, French regime). Until 2000, in the southern Gulf of St. Lawrence, some catches were allowed to First Nations for ceremonial and social purposes. These allocations were then suspended.

Striped bass was sought out by commercial and sport fishermen because of its delicate white flesh and its combatitiveness.

Commercial fishery, accidental catches and poaching

Some biologists believe that heavy fishing can either cause or amplify variations in the abundance of bass populations. Fisheries, according to their intensity, can limit the number of individuals that reach maturity, or for those that do, reduce the probabilities of reproducing several times. The impact the fisheries have on bass populations has long been underestimated.

In the St. Lawrence Estuary, commercial striped bass catches mostly occurred in fall. Bass catches were lucrative enough so that fishermen from certain areas invested particular time and effort on this species. Bass commercial catches in the Estuary reached a high of 53 tons in 1943. Lake Saint-Pierre appears to have long been a winter bass fishing area. When the ice melted, an increase in fishing for this species could be observed in the Lake. Landings reached a high at the end of April and in early May. Bass that were displaced by dredged material dumping activities (see section 2.5.3) became an easy catch for fishermen.

Mortality due to accidental catches was observed on the St. Lawrence, particularly around the Orléans Island: large numbers of bass fry died in fixed gear.

Finally, illegal catches could also be a significant cause of mortality that is impossible to measure. Bass confinement in wintering areas would have increased the risks of mortality due to environmental accidents or poaching. When a significant drop in abundance occurred in the mid-1950s, regulations were strengthened (1951) in order to limit the number of bass caught during summer (protection just before spawning and minimum size allowed (30 cm) increased to 40 cm in 1960) and winter (ice fishing prohibited between December 31st and May 1st). Many were those who openly defied the regulations by continuing their activities. At the Quebec City market, bass of sizes smaller than the legal limit could regularly be found on the stands. In Quebec, between 1975 and 1984, there were no regulations prohibiting striped bass commercial fishery. It was only banned in 1984.

Sport fishery

Striped bass is a highly prized species by sport fishermen. In the St. Lawrence Estuary, the best angling sites are between the Batture au Loup-Marin, in front  of L’Islet, and the Cap Tourmente. In the 1940s, 1950s and 1960s, the striped bass was subject to an intense seasonal sport fishery in several communities along the estuary (Montmagny, Rivière-Ouelle, Château-Richer, Orléans Island). This fishery was only banned starting in 1993.

2.5.3. Habitat changes and alterations

Certain characteristics help increase the number of fish in favourable areas: the tolerance of adults to variations in salinity, temperature, pH, or turbidity; species prolificacy (number of eggs per laying); feeding opportunism; and rapid growth. However, several human-induced modifications in the aquatic environment could cause an increase in mortality, particularly during the first life stages (eggs, fry). But the study of scientific data indicates that the eradication of the St. Lawrence River population is the consequence of the reduction of its distribution range, because of habitat encroachment. The areas where bass have converged rapidly became areas of heavy fishing. For twelve years, the population has remained in low abundance, until all catches were stopped in 1968.

Dredged material dumping activities

The disappearance of the St. Lawrence bass population appears to be associated to a change in habitat; the immature bass summer rearing areas, located around several islands in the St. Lawrence, would have been modified by the dumping of dredged material. As a result of these habitat changes, striped bass became concentrated at several locations along the south shore that quickly became exploited and then exhausted (see section “T raditional, commercial and sport fishing”).

Flow conditions and pollution

The effects of flow condition changes in reproductive areas can lead to a displacement of eggs from a site that is favourable to their development to another place where conditions could be fatal. However, a collection of specimens gathered by biologists until 1962 shows that young-of-the-year were produced in the St. Lawrence as long as there were spawners. This leads to consider that flow conditions may have not caused bass reproduction to cease in the St. Lawrence River.

Based on laboratory studies, contaminants such as polychlorinated biphenyls (PCBs), aromatic hydrocarbons (PAH), pesticides, heavy metals and several other chemicals would reduce egg and larval survival. However, their effect on recruitment has not been clearly demonstrated in the field.

Other factors such as changes in the quality of water, dumping of waste from pulp and paper mills, from communities (wastewater), pesticides from agricultural activities, as well as changes to spawning grounds brought on by the construction of dams are all potential disruptive factors.