Northern brook lamprey (Ichthyomyzon fossor) COSEWIC assessment and status report: chapter 6

Biology

Several authors have studied the biology of the northern brook lamprey. Leach (1940) examined the northern brook lamprey and its habitat in Indiana, while Vladykov (1949, 1952) studied the species in Quebec, and Purvis (1970) conducted work on the south shore of Lake Superior. Scott and Crossman (1998) also provide a review of the biology of this species.

Life cycle and reproduction

The northern brook lamprey has two stages in their development: blind, filter-feeding larvae, and non-feeding adults. About 14 days after fertilization, larvae hatch, drift downstream, and begin to burrow, forming U-shaped holes in stream substrate (Becker 1983). Burrows are made generally in soft substrate, composed of silt and sand. A small tube allows the lamprey to draw water into its burrow, from which it extracts oxygen (Sutton and Bowen 1994). Churchill (1945) found burrows occurring at depths of 0.2 – 0.6 m.

Larval densities can be very high, such as in an area in the Brule River where 153 northern brook lamprey were found in 15.6 (Churchill 1945). The larval stage of the northern brook lamprey ranges from 3 to 7 years (Purvis 1970, Scott and Crossman 1973). Larval duration is dependent on location and food availability (Scott and Crossman 1973). Their diet is made up of a ‘sestonic biofilm’, composed of diatoms, desmids, protozoans, green algae, detritus and pollen (Scott and Crossman 1973, Yap and Bowen 2003). Sutton and Bowen (1994) found almost 98% of the diet of larval sea and northern brook lampreys to be organic detritus, the remainder being algae (2%) and bacteria (0.1%). Purvis (1970) documented annual growth increments as 37 mm, 28 mm, and 15 mm for the first three years of growth, respectively, in a Lake Superior tributary.

Downward drift of the ammocoetes occurs throughout the life of the ammocoete to varying degrees, and is influenced by stream gradient, stream discharge levels, and water temperature (Potter 1980b).

After what has been termed a ‘resting period’ (Leach 1940), where feeding does not occur and a reduction in total length often takes place, the ammocoetes metamorphose into juveniles. Transformation takes place in individuals ranging in length from 12.0 to 15.0 cm. Transformation commences in August or September, and is a two to three month process (Leach 1940). During transformation, the oral hood changes to a buccal funnel with teeth, and is described in detail by Leach (1940). The onset of this process is variable, as not all lamprey of the same cohort transform in the same year (Potter 1980b). In January and February the lamprey begin to emerge fully transformed from their burrows and swim periodically (Becker 1983).

Full sexual maturity is reached in May, just before spawning. Average maturation age is 6 years (Fortin et al. 2005). The duration of the adult stage is from 4 to 6 months (Potter 1980b). As an adult, no feeding takes place. The alimentary canal is not functional. They over-winter in or near the substrate before congregating in riffle areas to spawn in the spring.

Like all lampreys, northern brook lamprey spawn only once, and adults die shortly after spawning (Leach 1940), hence the average age at maturity corresponds to generation time. Water temperature determines the timing of the spawning event (Scott and Crossman 1973). However, spawning temperatures may vary by region. In Quebec, spawning occurs in May, when water temperature is between 13 and 16°C (Vladykov 1949). In Michigan, adults were observed spawning in June, when water temperatures ranged between 16.5 and 20.5°C (Morman 1979). Reighard and Cummins (1916) published the optimal spawning temperature at between 20 and 22°C.

Males initiate the nesting, moving small stones and gravel with their mouths, creating a small depression. They also use body movements to move sand (Hardisty and Potter 1971b). The nest has a diameter from 7.6 to 10.2 cm (Scott and Crossman 1973). During nest building, the body tends to be oriented vertically rather than horizontally, as in other lamprey species.

Spawners are usually concentrated in a small area, in water 20.3 to 45.7 cm deep (Scott and Crossman 1973). Spawning usually takes place in a shallow, pool-riffle, high-gradient stretch of the stream. Nests are inconspicuously located in spaces between large stones (Morman 1979). Although typically thought to spawn in open, gravel-bottomed habitat, documentation of spawning under different types of cover has been made (Cooper 1983; Cochran and Gripentrog 1992). Usually communal spawners, northern brook lamprey exhibit behaviour very similar to that of the American brook lamprey, where groups of three to seven individuals coil their bodies around one another (Becker 1983). Cochran and Pettinelli (1987) reported four males and one female spawning together, and Morman (1979) documented an average of seven lamprey per nest. Chestnut lamprey nests have been used by northern brook lamprey spawners (Pflieger 1975).

While in the nest, the male attaches to the female, but does not wrap around the female, as occurs in most lamprey species. Vigorous vibration accompanies spawning (Scott and Crossman 1973), and after fertilization the eggs are sometimes covered with the substrate surrounding the nest (Hardisty and Potter 1971b).

Purvis (1970) analyzed sex ratios for northern brook lamprey at different life stages. He found that 49% of the larvae examined were males (n=627), 97% of the transformers from an early fall collection were males (n=33), and 75% of spawners were males (n=24). A higher proportion of males in spawning populations of lampreys is common (Applegate 1950, Hardisty 1961).

Mean fecundity of the northern brook lamprey has been estimated at 1,200 (Leach 1940), with ranges from 1,115 to 1,979 (Vladykov 1951). Schuldt et al. (1987) found the number of eggs laid is roughly proportional to the size of the female. The average egg size ranges from 1.0 to 1.2 mm (Scott and Crossman 1973).

Eggs hatch in two to four weeks (Leach 1940). The survival of northern brook lamprey eggs has not been documented.  According to Hardisty (1979) hatch rates of sea lamprey eggs likely do not exceed 5.3-7.8%; however, Manion and Hanson (1980) estimated hatch success at 90%. Mortality can be high, particularly during the early stages of ammocoete life (Potter 1980b). Larvae are sensitive to temperature fluctuations and predation when very small, but mortality declines quickly with age (Potter 1980b).

The total life span of the northern brook lamprey is up to 7 or 8 years, but this is difficult to confirm because of difficulties in aging these animals. Many studies have used length-frequency analysis to determine ages of larvae (e.g. Leach 1940, Scott and Crossman 1973, Quintella et al. 2003). Length-frequency age determination is not often applied to adults and large larvae, due to their lack of growth prior to and following metamorphosis.

Predation

As eggs and freshly hatched larvae, lamprey species are fed on by larger fish (Potter 1980b). Predation on ammocoetes is minimal due to the largely sedentary existence in burrows for extended periods. However, given the opportunity, piscivorous fishes likely consume ammocoetes, considering the historic use of ammocoetes as bait by anglers (Vladykov 1973). Predation on adult lamprey likely occurs most often during the spawning event, as egg laying usually takes place in shallow water (Manion and Hanson 1980) where the fish are vulnerable. Documented predators on adult northern brook lamprey include rainbow trout (Oncorhynchus mykiss) (Churchill 1945), rock bass (Ambloplites rupestris) (Scott and Crossman 1973), and brown trout (Salmo trutta) (Cochran et al. 1992).

Physiology

Strictly a freshwater resident, the northern brook lamprey lives in a wide range of stream sizes and alkalinity levels, as discussed in the habitat requirements section. Although little is known about the physiology of the northern brook lamprey, knowledge of other lamprey species is likely comparable. Sea lamprey eggs are very sensitive to temperature, as eggs hatch only between 15.5 and 21.1°C (Piavis 1961). It has been found that 18.4°C is the optimal rearing temperature for sea lamprey eggs (Piavis 1961), a temperature that has also been found to be conducive to rearing northern brook lamprey eggs (Smith et al. 1968). Sea lamprey larvae mortality increases markedly at 22°C (Piavis 1961).

Water depth and velocity were important factors in determining location of larval European brook lamprey (Malmqvist 1980). Sutton and Bowen (1994) reported that northern brook lamprey and sea lamprey larvae consumed from 4.2 to 5.5 mg•g-1•day-1of detritus.

Dispersal/migration

Northern brook lamprey make a short, non-synchronous movement toward spawning grounds in the spring (Leach 1940). Dispersal is limited to downstream drift by ammocoetes, where larvae passively travel short distances. This drift is seasonal and usually occurs at night, and is correlated with water temperature. Streams with higher gradients tend to have larvae distributed further from spawning grounds than do streams with lower gradients, where larvae are more closely associated with the location of the nests (Potter 1980b).

Interspecific interactions

Vladykov (1951) suggested that the high fecundity of sea lamprey may lead to competition with lampreys native to the Great Lakes. Northern brook lamprey co-exist in the same stream system with silver lamprey and sea lamprey, and occasionally American brook lamprey. Where ranges overlap, generally only one species is common (Becker 1983).

Growth of lamprey ammocoetes is affected by ammocoete density (Hardisty and Potter 1971a). The application of a lampricide called TFM (3-trifluoromethyl-4-nitrophenol) to streams to kill larval sea lamprey, and subsequent lamprey population decrease have been shown to result in increased growth rates in re-establishing year classes of larval lamprey (Purvis 1970). This is likely due to greater availability of food and space. Scott and Crossman (1973) suggested there may be competition among ammocoetes for food and habitat.

Huggins and Thompson (1970) observed another closely related pair of lampreys, the European brook lamprey and the European river lamprey, spawning on the same nest. Given that the spawning of silver and northern brook lampreys can coincide (Manion and Hanson 1980), similar interactions may occur between these two species.

In the Brule River in Wisconsin, Churchill (1945) found that northern brook lamprey burrows are often close to burrowing mayfly nymphs and small mussels. All three of these organism types feed directly on microscopic aquatic organisms and may compete with one another for food. However, Churchill dismissed the importance of this, as these three species co-exist in substantial numbers.

Adaptability

The restricted mobility and relatively low fecundity of northern brook lamprey suggest that they are not highly adaptable. However, given that another ecologically similar lamprey, the American brook lamprey, has accidentally been introduced into other streams and achieved high survival rates (D. Cuddy, pers. observ.), it is likely that there is some degree of adaptability to new areas, and that this species could be a good candidate for translocation.

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