Alewife Population Research Articles

Predator-prey interactions in Lake Michigan: model predictions and recent dynamics

Several years ago, we used a bioenergetics model to evaluate the impact of increasing salmonid stocking on the highly variable alewife forage base in Lake Michigan. At that time, we forecast an alewife population decline and the following system-wide effects: increased abundances of large zooplankton, decreased salmonid growth rates, increased diet breadth of salmonids, niche shifts among competitors of the alewife, increased alewife growth rates and increased densities of fishes suppressed by alewife. Alewives have continued to decline steadily since 1981 and are now reduced to a density similar to early outbreak levels in the early 1960s. Recent reports on fish growth rates, zooplankton size and fish community structure support our projections regarding system-wide responses to the alewife decline.

Influence of Salmonine Predation and Weather on Long-Term Water Quality Trends in Lake Michigan

Trends in Lake Michigan water quality over 1975–84 appear to reflect reduced nutrient loadings as indicated by gradual declines in spring total phosphorus (TP) and summer epilimnetic chlorophyll a (Chl a). Deviations from these trends during 1977 and 1983–84 were apparently caused by abiotic and biotic factors, respectively. Prolonged ice cover during 1977 decreased sediment resuspension resulting in lower TP, reduced Chl a levels, and increased water clarity. A similar dramatic result occurred in 1983 and to a lesser extent in 1984, but via a different mechanism. Burgeoning populations of stocked salmonines reduced populations of the planktivorous alewife (Alosa pseudoharengus), which allowed large Daphnia to flourish. Because the Daphnia are more voracious and nonselective grazers than the formerly dominant calanoid copepods, they reduced seston concentrations, causing dramatic increases in Secchi disk transparency. These exceptions demonstrate the far-reaching consequences that unusual weather conditions and fish management practices may have on water quality indicators.

Recent Major Declines in Zooplankton Populations in the Inshore Region of Lake Michigan: Probable Causes and Implications

Summer Zooplankton communities in the inshore region of southeastern Lake Michigan were dominated by small species during the 1970s, suggesting that size-selective fish predation pressures were intense. Abundances of alewife (Alosa pseudoharengus), the dominant planktivore in the 1970s, declined in recent years, especially over 1982–84. Despite decreased alewife predation, small zooplankton taxa continued to predominate. Moreover, zooplankton standing stocks declined 10-fold during 1982–84, suggesting that predatory pressures had intensified. Concurrent with the alewife population decrease was a major increase in yellow perch (Perca flavescens) abundances. As a probable consequence of intense predation pressures exerted by abundant yellow perch, zooplankton standing stocks were severely reduced. Yellow perch populations may have been adversely affected by food limitation, especially in summer 1984 when zooplankton standing stocks were only 3% of their average level over 1975–81.

Rainbow Smelt ( Osmerus Mordax) as Predators on Young Bloaters ( Coregonus Hoyi) in Lake Michigan

Examination of the stomach contents of rainbow smelt caught in bottom trawls in Lake Michigan during mid October, 1982, revealed that of 267 rainbow smelt ( Osmerus mordax) with food in their stomachs, 56% (150) had eaten young-of-the-year fish. Nearly 15% of the prey fish consumed were bloaters (Coregonus hoyi), 21 % were alewives (Alosa pseudoharengus), and the rest could not be positively identified but were probably bloaters and alewives. Although smelt predation did not appear to have affected bloater abundance, continued increases in smelt abundance and declines in alewife populations could lead to increased predator pressure on bloater stocks, which are in the process of rebuilding.

Lake Michigan's Capacity to Support Lake Trout (Salvelinus namaycush) and Other Salmonines: An Estimate Based on the Status of Prey Populations in the 1970s

We used a mass balance equation relating total mortality of age II and older alewives (Alosa pseudoharengus) to their removals by predatory fish and other sources of mortality as the basis for estimating that the forage base in Lake Michigan could support an additional 13 000 to 21 000 t of lake trout (Salvelinus namaycush) or a total lake trout biomass between 15 000 and 23 000 t. This biomass estimate is projected with biomasses of other trout and salmon held at 1979 levels. Major premises of this approach are that (1) the sustained availability of age II and older alewives to salmonines will ultimately limit the expansion of salmonine stocks, (2) the alewife population was oscillating without trend during 1973–80, and (3) additional limited predation on alewives would be compensated by a reduction in natural mortality caused by physiological stress and disease.

Ecological Shifts in Resource Use by Bloaters in Lake Michigan

In late August-early September 1979 and 1980, both juvenile (80–145 mm fork length) and adult (> 145 mm) bloaters Coregonus hoyi were abundant in bottom trawls from Lake Michigan, but few young-of-year bloaters (<80 mm) were caught near the bottom despite small cod-end mesh in the trawl. Along the bottom intersected by the metalimnion, juveniles were more abundant in warmer water than adults. Diets of both juveniles and adults were 99% benthic prey by biomass. Young-of-year bloaters were most common at the surface during the day and in the metalimnion (off the bottom) at night. They ate primarily small cladocerans and cyclopoid copepods. These ontogenetic shifts in resource use by bloaters may reduce interactions among size groups. Further, since alewives Alosa pseudoharengus became abundant in Lake Michigan in the 1960s, bloaters have assumed benthic habits much earlier in their lives. Our dietary data indicate that young bloaters now abandon small pelagic zooplankton for larger benthic prey at much smaller sizes than formerly; though we did not age our fish, available age-size data suggest this switch occurs at age 1 +, as much as 2 years earlier than before alewives became abundant. Adult bloaters also eat less zooplankton now than they did before the alewife population expanded. This shift in bloater life history toward earlier occupancy of the benthic habitat in the presence of alewives provides reasonably strong support for the hypothesis that alewife competition has been an important influence on the structure of the current Lake Michigan fish community. Received March 17, 1984 Accepted August 24, 1984

Reproduction and Early-Life Accommodations of Landlocked Alewives to a Southern Range Extension

Reproduction and first-year growth and food habits of landlocked alewives Alosa pseudoharengus in Claytor Lake, Virginia were examined and compared to descriptions for populations in the speciesˈ established New England-Great Lakes range. Alewives in mesothermal (2–27 C) Claytor Lake are shorter-lived (3 years) but grow faster, mature earlier (age 1), and have higher relative and absolute fecundities than have been reported for populations in colder northern waters. The 1979 spawning period extended from early May to early August, beginning at least 1 month earlier and lasting 4–9 weeks longer than in northern lakes. Changes in ovary condition during the spawning period suggest that alewives may be fractional spawners. Evidence of spawning was found in littoral areas throughout the lower 15 km of the reservoir. Growth in length of age-0 Claytor Lake alewives was linear through September and terminated in late autumn. Total first-year growth was reduced in 1979 (maximum of 130 mm total length, TL) from previous years (average of 160 mm TL), although it was substantially greater than recorded in the Great Lakes and the northeastern United States. The longer growing season, rather than accelerated in-season growth, appears to account for larger size achieved in Claytor Lake. High annual growth limits predation by Claytor Lake game fish on early spawned age-0 alewives by late summer. As elsewhere, larval and juvenile alewives (6–70 mm TL) fed primarily on copepods and cladocerans. Age-0 alewives longer than 35 mm TL demonstrated positive size-selection for cyclopoid copepods comparable to that shown by adults. Our findings suggest that self-sustaining alewife populations can be established in many inland waters but raise concerns regarding their forage value and community impacts.

Consequences of an Alewife Die-off to Fish and Zooplankton in a Reservoir

Alewife Alosa pseudoharengus was the principal pelagic forage species in Claytor Lake, Virginia, prior to a severe die-off in the winter of 1977–1978. Due to successful reproduction in 1978, abundance of adult alewives rebounded sharply in 1979. Changes in the size structure of the zooplankton community between summer 1978 (larger) and 1979 (smaller) were similar to differences reported for other waters between periods of low and high alewife abundance and are attributable to selective alewife predation. Alewife-induced shifts in zooplankton composition toward smaller forms represent a potentially significant adverse impact on cohabiting planktivores, including young-of-the-year sport fishes. Alewives seldom were eaten by littoral piscivores (black basses Micropterus spp. and crappies Pomoxis spp.) but were prevalent in the diets of the pelagic species (walleye Stizostedion vitreum vitreum, white bass Morone chrysops, and striped bass Morone saxatilis). When alewives were less abundant during spring and summer of 1978, pelagic predators ate more yellow perch Perca flavescens, crappies, bluegills Lepomis macrochirus, and crayfish Cambarus sp. than in 1979. Growth of adult alewives and young-of-the-year walleyes and white bass was significantly greater in 1978 than in the 2 years preceding the die-off, suggesting that both intra- and interspecific trophic competition operate when alewife density is high. Annual growth of age-2 walleyes and white bass did not differ substantially before and after the die-off; impact of the population collapse may have been mitigated by high reproductive success and rapid first-year growth of alewives in 1978. These findings indicate that alewife size-selective planktivory may have a more enduring and potentially severe impact on the reservoir fishery than does instability in the alewife population.

Evidence for a resident alewife population in the Northern Chesapeake Bay

Data developed from field sampling for age and growth, histology, and behavior patterns indicate the existence of a ‘resident’ alewife population in the northern Chesapeake Bay. Growth appeared faster and sexual maturation is 2 years earlier than larger anadromous forms. Scale analyses reveal no evidence of migration to and from salt water. It is hypothesized that a race of alewives meristically similar to the mean anadromous population but different in growth rate, sexual maturation, fecundity, and spawning period is developing in the northern Chesapeake Bay.

Depreciation of the Warmwater Fish Community in the Bay of Quinte, Lake Ontario

The sequence of fish species shifts since the 1930s in the Bay of Quinte is interpreted in terms of climatic changes and the influences of man. Among the latter, eutrophication is judged most important. The marked decrease in large piscivores in both eastern Lake Ontario and the Bay of Quinte as a consequence of these changes resulted in instability, exemplified by the explosions in populations of alewife (Alosa pseudoharengus) and white perch (Morone americana). Nutrients are imported to the bay, from Lake Ontario by way of alewife. This source has increased in the 1970s with the further decline of piscivores, and it brought about a greater fish production in the bay. We conclude that the Bay of Quinte and Lake Ontario interact significantly and should be studied as a single system.Because of its specialized feeding habits, the post-World War II rise of the walleye (Stizostedion vitreum vitreum) was related to events outside the Bay of Quinte, but its later decline was attributable to direct and indirect effects of eutrophication. Yellow perch (Perca flavescens), by contrast, were apparently not affected adversely by severe habitat changes induced by cultural eutrophication. Key words: Percidae, community ecology, species shifts, eutrophication, habitat changes

Aspects of the Population Dynamics of the Alewife, Alosa pseudoharengus (Wilson), in Cayuga Lake, New York

Parameters of size distribution, age composition, and growth were studied for the alewife, Alosa pseudoharengus (Wilson), at Cayuga Lake, New York, during 1960 and 1961. Samples enabling estimation of these parameters were taken at two locations in the lake, Taughannock and Canoga. The Canoga location was warmer and tended toward eutrophication relative to the typically oligotrophic Taughannock location. Emphasis was placed on studying the differences in size distribution, age composition, and growth between years and between locations. A major source of variation in estimates of the parameters resulted from the effect of the dominant 1959 year class. The Canoga samples exhibited a higher average and slightly faster growth rate than did the Taughannock samples. The possible effect of water temperature on this phenomenon is mentioned. Variability in size composition between locations is thought to be associated predominantly with the environmental characteristics of the two locations whereas the variability between sampling years is thought to be predominantly the effect of population structure. INTRODUCTION The alewife, Alosa pseudoharengus (Wilson), is anadromous or lacustrine-anadromous along the eastern coast of North America from Labrador (Storer, 1850) to Florida (Briggs, 1958). Aspects of the life history of the anadromous alewife are covered by Hildebrand and Schroeder (1928), Bigelow and Schroeder (1953), Havey (1961), and Cooper (1961). Strictly freshwater populations of the alewife populations which never enter a marine environment are found in Lake Ontario (Greeley, 1927), some of the New York Finger Lakes (Cayuga, Seneca, and Keuka Lakes (Eaton, 1928)), other New York lakes (Greeley, 1938; Breder and Nigrelli, 1936; Dence, 1956), lakes in glaciated northern New Jersey (Gross, 1953), and New Hampshire ponds in Rockingham County (Bailey, 1938). Man has caused an extension of the known range of the alewife by stocking (e.g., Vincent, 1960) and modification of natural waterways (Miller, 1957). The life history of the alewife in fresh water is not well known. Threinen (1958) summarizes much of the literature, but the best accounts are given by Graham (1956), Pritchard (1929), Odell, (1934b), Breder and Nigrelli (1936), and Gross (1953). Rothschild (1963a) studied the annulus on the alewife scale as a criterion of age. There are also unpublished studies by Gross (1959) and Odell (1934a) . Further investigations of alewife life history were made at Cayuga 1 Extracted from a Doctoral Dissertation submitted to Cornell University, Ithaca, New York.

Restoration and Management of the New England Alewife Fisheries with Special Reference to Maine

To augment the fish supply in New England increased attention is being accorded to the alewife. Through neglect, obstructions to migration, overfishing, and other causes, the alewife populations have been reduced greatly. A survey of the coastal streams of Maine disclosed many streams that can be returned to production by building fishways or modifying present fishways, in conjunction with a program of restocking and proper management methods. During the 1943 season, barren spawning areas (lakes) on 13 streams were stocked with alewives and observations indicated successful production and survival of young. Recommendations are made for the removal of obstructions or the construction of fishways on 17 streams.