Alosa pseudoharengus
(alewife)

A. pseudoharengus is native to the western Atlantic Ocean off the coast of North America, where it occurred historically from Labrador, Nova Scotia, and northeastern Newfoundland, Canada south to South Carolina, USA (ASMFC, 2009). It is anadromous, ascending rivers and streams to spawn, and the young naturally occur in many coastal lakes and streams (Scott and Crossman, 1973). Although A. pseudoharengus is a valued fish in its native range, where there are numerous projects aimed at restoring anadromous populations (Maine DMR, 2009; USFWS, 2009), when introduced into lakes and reservoirs, they can become invasive. They can complete their life cycle in freshwater, they are fecund (Norden, 1967; Bronte et al., 1991), they can spawn successfully in a wide variety of habitats (ASMFC, 2009), and, they are relatively long lived with a maximum age of 11 having been reported from the Laurentian Great Lakes of North American (O’Gorman et al., 1987, 1997; Madenjian et al., 2003). In land-locked waterbodies A. pseudoharengus can become overabundant, altering the zooplankton community by size-selective predation (Brooks and Dodson, 1965; Wells, 1970; Warshaw, 1972), affecting native fishes by preying on their young (O’Gorman and Stewart, 1999; Madenjian et al., 2008; O’Gorman et al., in press) and, sometimes, causing a thiamine deficiency among the fishes that eat them (Brown et al., 2005). Dense populations are subject to periodic die-offs and the dead fish washing ashore create odour and sanitation problems (Greenwood, 1970).

Established populations of A. pseudoharengus in North American waterbodies are mainly in the United States and in the easternmost part of the continent. All but a few are located east of the Mississippi River (USGS, 2009). The lone exceptions are in the north part of the state of Nebraska. Although there are records of alewife in the western state of Colorado (Minckley, 1973; USGS, 2009), the fish was not recently listed as being present in that state (Johnson and Nomanbhoy, 2005).

Introduction of A. pseudoharengus is unlikely without a concerted effort unless the receiving waterbody is in a watershed where A. pseudoharengus are already established. A. pseudoharengus can move within a watershed through rivers and canals, even through canals with navigation locks. There is a large body of literature on the adverse affects of introducing alewife to freshwater ecosystems (O’Gorman and Stewart, 1999; Madenjian et al., 2008; O’Gorman et al., in press) so natural resource management agencies are vigilant against further introductions. The greatest risk for introduction appears to be from illicit releases by individuals seeking to “improve” fishing, followed by accidental introduction by release of A. pseudoharengus, illegally used for live bait. A. pseudoharengus are somewhat fragile and are therefore not used in the aquarium trade or transported live for human consumption.

A. pseudoharengus is a pelagic fish that occupies open waters. In the northwestern Atlantic Ocean, A. pseudoharengus favour a depth range of 56 to 110 m (Neves, 1981). In the Laurentian Great Lakes, the depths occupied by A. pseudoharengus change seasonally and vary somewhat among lakes due to differences in bathymetry and temperature regimes (Wells, 1968; O’Gorman and Schneider, 1986; O’Gorman et al., 2000). In general, A. pseudoharengus overwinter offshore in deep water and move shoreward into shallower water in spring to spawn, after which they move back to open waters where they remain throughout the summer, occupying mid to upper levels in the water column (Bergstedt and O’Gorman, 1989; O’Gorman et al., in press). In autumn, as the lakes cool, A. pseudoharengus descend to greater depths. The depth distribution of A. pseudoharengus within a lake can change, however, as it did in Lake Ontario following changes in the lake ecosystem (O’Gorman et al., 2000).

Reproductive Biology

A. pseudoharengus spawn in spring, at night, near the surface, throughout nearshore areas including bays, harbours, and in tributaries (Scott and Crossman, 1973). The minimum temperature at which Atlantic A. pseudoharengus spawn is 10ºC (Cianci, 1965) and spawning peaks at 13-16ºC (Richkus, 1974; Tyus, 1974). In landlocked populations, the spawning period is protracted, lasting more than a month (Odell, 1934; Norden, 1967; Hlavek and Norden, 1978). Mean fecundity of Lake Michigan A. pseudoharengus was 11,150 for fish averaging 160 mm total length, 16,140 for fish averaging 176 mm, and 22,400 for fish averaging 192 mm (Norden, 1967; Hlavek and Norden, 1978). The non-adhesive eggs are demersal and are broadcast at random over any type of bottom (Odell, 1934; Mansueti, 1956). Optimum temperature for egg incubation is 17.8ºC and incubation time varies from 15 days at 7.2ºC to 3.7 days at 21.1ºC (Edsall, 1970). Alewife larvae average 3.8 mm at hatching, 5.1 mm at yolk sac absorbtion, and, when held at 20ºC, they begin feeding two days after hatching (Norden, 1967; Heinrich, 1981). The larvae are positively phototropic and pelagic (Odell, 1934).

Nutrition

Land-locked A. pseudoharengus eat zooplankton throughout their life (Morsell and Norden, 1968; Mills et al., 1992, 1995; Stewart et al., 2009). They are size-selective feeders, preferentially eating the largest available zooplankters (Kohler, 1980). Indeed, the movements of A. pseudoharengus around a large lake or the magnitude of an alewife population can sometimes be tracked by the size and species composition of zooplankton (Wells, 1970; Warshaw, 1972; O’Gorman et al., 1991). The first food of larval alewife is cyclopoid copepodites and as the larvae grow they incorporate larger zooplankton in their diet (Heinrich, 1981). When the fish grow to about 110-119 mm they begin to feed on larger invertebrates (Morsell and Norden, 1968) - amphipods, insects, and, in the Laurentian Great Lakes, the opossum shrimp Mysis diluviana and the bloody-red shrimp Hemimysis anomola (Walsh et al., 2008; Stewart et al., 2009; Lantry et al., 2010). A. pseudoharengus are adept at capturing prey in mid-water but have difficulty capturing prey located on or near the lake bottom (Janssen, 1978a). They can feed in the dark (Janssen, 1978b; Janssen et al., 1995; Kelso and Ney, 1983) and they have three modes of feeding: particulate, filtering, and gulping (Janssen, 1976). Nocturnal movement of A. pseudoharengus to nearshore areas of lakes to feed has been recorded (Kelso and Ney, 1983). Conversely, A. pseudoharengus have been found feeding at night far offshore in the Great Lakes on vertically migrating Mysis (Boscarino et al., 2009). A. pseudoharengus also eat their own larvae (Odell, 1934; Rhodes et al., 1974) as well as the larvae of other fishes and small young-of-year fishes (Kohler and Ney, 1980; Brandt et al., 1987; Kreuger et al., 1995).

Environmental Requirements

A. pseudoharengus in Lake Michigan begin spawning when water temperatures reach about 15.6ºC; spawning is interrupted when water temperatures exceed 27.8ºC (Edsall, 1970). Eggs hatch when incubated at 6.9 to 29.4ºC but not at lower or higher temperatures. About 69% of the larvae from eggs incubated at less than 10.6ºC are deformed and not likely to survive. Alewife young-of-year (YOY) have been found at 16 to 29ºC in Lake Michigan (Brandt, 1980; Dufour et al., 2008). Laboratory studies show a YOY temperature preference range of 21 to 31ºC (Otto et al., 1976; Spotila et al., 1979) and critical thermal maximum range of 32 to 34ºC for YOY acclimated to 20-25ºC (Otto et al., 1976). In the Laurentian Great Lakes, A. pseudoharengus must grow to a total length of 60 mm or longer if they are to survive the winter (O’Gorman and Stewart, 1999). A. pseudoharengus are rare in Lake Superior, the northern-most Great Lake, presumably because the short growing season does not allow most young A. pseudoharengus sufficient time to grow to a size that would allow successful overwintering (O’Gorman et al., 1997; O’Gorman et al., in press). In summer, adult A. pseudoharengus in the Great Lakes avoid the cold hypolimnetic waters and occupy the warm epilimnetic waters although under certain conditions they some can be found in the thermocline (Wells, 1968; Olson et al., 1988; Johannsson and O’Gorman, 1991; but see Janssen and Brandt, 1980). Laboratory temperature preferences for adult A. pseudoharengus were 21ºC in spring, 16-19ºC in summer, and 16 -20ºC in autumn (Otto et al., 1976; Spotila et al., 1979). Ultimate upper lethal temperatures were 31-34ºC for adult alewives acclimated to 20-27ºC (Otto et al., 1976; McCauley and Binkowski, 1982).

A. pseudoharengus are severely stressed by temperatures lower than 3ºC (Colby, 1973). In the Great Lakes A. pseudoharengus are in water at 1 to 3ºC during most winters. In severe winters, as water temperature may be at or below 1ºC (Mortimer, 1971; Rodgers, 1987), mass mortalities of A. pseudoharengus sometimes occur (O’Gorman and Schneider, 1986; Bergstedt and O’Gorman, 1989; O’Gorman et al., in press). Low-temperature mortalities appear to be due to osmoregulatory failure caused by a loss of homeoviscous adaptation (altering the lipid composition of biomembranes to compensate for temperature-induced changes in membrane fluidity; Stanley and Colby, 1971; Snyder and Hennessey, 2003). Homeoviscous adaptation can be influenced by diet (Synder and Murray, 2009) and inter-annual variation in diet may be the reason for discrepancies in the severity of die-offs among years with similar winter weather (O’Gorman et al., in press). When held in ponds where water temperatures were < 2ºC for more than six weeks, A. pseudoharengus experienced sublethal immunosuppression, increasing their susceptibility to disease (Lepak and Kraft, 2008).

Animal feed, fodder, forage

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Human food and beverage

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A. pseudoharengus is similar in appearance to the blueback herring Alosa aestivalis. Indeed, due to their similarity, the two species are often harvested and managed together as “river herring” in the USA or as “gaspereau” in Canada (Mullen et al., 1986; NOAA, 2009). The eye of A. pseudoharengus is large with a diameter greater than the length of the snout whereas the eye of the blueback herring is small with a diameter equal to or less than the snout length (Mullen et al., 1986). Internally, the peritoneum of the alewife is pearly to white, sometimes with grey flecks, whereas that of the blueback herring is sooty to black (Scott and Crossman, 1973; Owens et al., 1998). Landlocked populations of A. pseudoharengus are common and occur across a broad geographic range whereas landlocked populations of blueback herring are uncommon and are confined to the southern USA (Owens et al., 1998).

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Once established in a waterbody, an alewife population cannot be eradicated although it can be reduced by increasing the number of piscivorous fishes (O’Gorman et al., in press). Invasive populations of alewife were established by movement of alewife through navigation canals (O’Gorman and Stewart, 1999) and by introduction, either accidental or intentional. Stocking of alewife was once done to augment prey fish populations but once the deleterious effects of establishing a population became known, it was no longer sanctioned. Illicit, intentional introductions are now the primary means of movement and they are most likely done by anglers who view A. pseudoharengus favourably because of the well-advertised, large size of piscivorous fishes in some lakes where A. pseudoharengus are abundant (Marsden and Hauser, 2009). Populations may also become established by anglers releasing the fish they are using for bait, some of which may be A. pseudoharengus. The state of New York, as well as other states, prohibit or greatly limit the use of A. pseudoharengus for live bait in inland waters.

13/04/10 Original text by:

Robert O'Gorman, Lake Ontario Biological Station, USGS7 Lake Street, Oswego, NY 13126, USA