Conference Paper

Spawning Migrations of American Shad in the Columbia River

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We sampled American shad, Alosa sapidissima, in the Columbia and Snake Rivers during 2005-2007 & 2010 to characterize basic migration biology of the population, as a model system to test general migration ecology hypotheses, and to determine if dam passage metrics for shad in the Columbia River are better than those for eastern United States populations, which are imperiled. We PIT-tagged and released 2496 adults during the 2005-2007 study period. We simultaneously determined length, mass, sex, age and spawning history (from scales) and energetic status (using a Fatmeter) for a subset of PIT tagged fish in an effort to relate individual traits to migration behavior. Collections of adults at Bonneville and Lower Granite dams and of juveniles at six lower Columbia and Snake river dams characterized seasonal and longitudinal patterns during upstream and downstream migration, respectively. Analyses demonstrated that: 1) individual adults returned to the Columbia Basin spawn in multiple years; 2) the adult populations at Lower Granite Dam (rkm 695) were younger and male-biased compared to adults at Bonneville Dam (rkm 235); 3) that mean initial lipid content of adults detected at McNary Dam (rkm 470) was higher than adults detected only at Bonneville Dam; and 4) juvenile growth rates were higher in upstream reaches of the basin, particularly in the Snake River reservoirs. In 2010, we radio- and PIT-tagged 234 adult fish to estimate individual passage behavior and success at the four lower Columbia River dams. A total of 26% of the tagged fish passed Bonneville Dam. A total of 78% of the fish passing Bonneville Dam passed The Dalles Dam, 45% of those passed John Day Dam, and 48% of those passed McNary Dam. A seasonal effect was evident, with 57% of the fish tagged in the early part of the run passing Bonneville Dam, compared to 18 and 4% during the middle and late parts of the run. Collectively, the results suggest that: 1) shad passage behavior and performance at dams differ from salmonids; 2) that adult upstream migration behavior appears to be relatively flexible, may be dependent on life history stage and/or initial condition of individuals, and may affect offspring growth and survival; 3) the ecological effects of adults in reservoirs differs longitudinally; and 4) indicate greater passage success than observed in East Coast rivers.

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Habitat use by spawning adults, eggs, and larvae of Alosa sapidissima was determined and published habitat suitability index models evaluated through field studies in the middle-to-upper Delaware River. The surface-water temperature model for spawning adults (maximum suitability of 14-20°C) was supported at its lower but not upper limit, where relatively high spawning activity was observed to 24.5°C. Maximum suitabilities for the water velocity model for spawning adults (0.3-0.9 m/sec) were higher than those observed in the field (0.0-0.7 m/sec). Run habitats produced the highest spawning activity, and pools the lowest. The HSI model describing egg and larval abundance in relation to surface-water temperature (maximum suitability of 15-25°C) was supported for eggs but not larvae because no reduction in larval density occurred at the upper thermal limit (>25°C). Only postlarvae appeared to select riffle pools as habitat. -from Authors
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American shad Alosa sapidissima from the Hudson River, New York, were introduced into the Sacramento River, California, in 1871 and were first observed in the Columbia River in 1876. American shad returns to the Columbia River increased greatly between 1960 and 1990, and recently 2-4 million adults have been counted per year at Bonneville Dam, Oregon and Washington State (river kilometer 235). The total return of American shad is likely much higher than this dam count. Returning adults migrate as far as 600 km up the Columbia and Snake rivers, passing as many as eight large hydroelectric dams. Spawning occurs primarily in the lower river and in several large reservoirs. A small sample found returning adults were 2-6 years old and about one-third of adults were repeat spawners. Larval American shad are abundant in plankton and in the nearshore zone. Juvenile American shad occur throughout the water column during night, but school near the bottom or inshore during day. Juveniles consume a variety of zooplankton, but cyclopoid copepods were 86% of the diet by mass. Juveniles emigrate from the river from August through December. Annual exploitation of American shad by commercial and recreational fisheries combined is near 9% of the total count at Bonneville Dam. The success of American shad in the Columbia River is likely related to successful passage at dams, good spawning and rearing habitats, and low exploitation. The role of American shad within the aquatic community is poorly understood. We speculate that juveniles could alter the zooplankton community and may supplement the diet of resident predators. Data, however, are lacking or sparse in some areas, and more information is needed on the role of larval and juvenile American shad in the food web, factors limiting adult returns, ocean distribution of adults, and interactions between American shad and endangered or threatened salmonids throughout the river.
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The anadromous American shad Alosa sapidissima (Wilson) ranges from the St. Lawrence River, Canada, to the St. Johns River, Florida. Once the major commercially fished species in the USA, catches went from a high of nearly 23,000 metric tons (1896) through a series of cascading declines to present-day levels in the hundreds of metric tons. These declines have been attributed to overfishing, habitat loss, and pollution over the past 170 years. Despite the success of some fishways, major modern spawning rivers have lost approximately 4,000 km of habitat due to dams. American shad exhibits biological variation along its geographic range. This variation includes juvenile growth rates (counter gradient), fecundity, and degree of iteroparity. Good information exists on adult migration trends, migration physiology, and young-of-the-year ecology. Whereas many aspects of American shad biology have been well studied in certain systems, complete population profiles from its entire range, including key population parameters, are lacking. This paper synthesizes available data and points out gaps in information that would aid in restoration and management of this valuable species.
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We examined spawning site selection and habitat use by American shad Alosa sapidissima in the Pee Dee River, North Carolina and South Carolina, to inform future management in this flow-regulated river. American shad eggs were collected in plankton tows, and the origin (spawning site) of each egg was estimated; relocations of radio-tagged adults on spawning grounds illustrated habitat use and movement in relation to changes in water discharge rates. Most spawning was estimated to occur in the Piedmont physiographic region within a 25-river-kilometer (rkm) section just below the lowermost dam in the system; however, some spawning also occurred downstream in the Coastal Plain. The Piedmont region has a higher gradient and is predicted to have slightly higher current velocities and shallower depths, on average, than the Coastal Plain. The Piedmont region is dominated by large substrates (e.g., boulders and gravel), whereas the Coastal Plain is dominated by sand. Sampling at night (the primary spawning period) resulted in the collection of young eggs (≤1.5 h old) that more precisely identified the spawning sites. In the Piedmont region, most radio-tagged American shad remained in discrete areas (average linear range = 3.6 rkm) during the spawning season and generally occupied water velocities between 0.20 and 0.69 m/s, depths between 1.0 and 2.9 m, and substrates dominated by boulder or bedrock and gravel. Tagged adults made only small-scale movements with changes in water discharge rates. Our results demonstrate that the upstream extent of migration and an area of concentrated spawning occur just below the lowermost dam. If upstream areas have similar habitat, facilitating upstream access for American shad could increase the spawning habitat available and increase the population's size.Received March 22, 2011; accepted July 14, 2011
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Despite millions of dollars expended on restoration efforts for depleted North American stocks of alosine fishes, rangewide abundance levels for multiple species have continued to decline to historic lows. Stocking practices aimed at rebuilding spawning runs have been deemed “successful” when numerical abundance levels are shown to increase in response. However, these practices may only yield short term gains in abundance at the ultimate expense of population genetic integrity, and do not ensure the long term persistence and evolutionary potential of species. Although molecular methods are now widely employed in fisheries management and provide a suite of powerful management tools, these approaches have not been well integrated in alosine management strategies. We review the net effects of stocking practices to population genetic integrity and species long term persistence as it is currently understood, and highlight what is known in this regard for alosines in North America, with particular focus on American shad. We find that stocking practices carry a substantial risk to the persistence of genetically distinct alosine spawning runs, and suggest that future restoration efforts should proceed by providing access to historical spawning grounds, either through dam removal or by providing effective fish passage, followed by natural recolonization of reclaimed habitat. We also identify important areas of research relevant to future alosine restoration that require exploration, and identify recent developments that may alter future restoration decisions in an adaptive management framework.
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Ecologists have become increasingly aware of the combined effects of habitat disturbance and climate change on the establishment and proliferation of invasive species. Long-term data on the population of the invasive American Shad Alosa sapidissima in the U.S. portion of the Columbia River basin provide an opportunity to examine how habitat disturbances affect the abundance and spatial distribution of an invasive species in a heavily modified environment. After the establishment of American Shad in the Columbia River in the late 1800s, the drainage was transformed from its natural lotic state to a series of reservoirs, with concomitant changes to discharge and temperature regimes, which are confounded by climate change. As the Columbia River was dammed, American Shad extended its range and increased in abundance. A large and rapid increase in spawning population abundance (recruits per spawner = 63) followed completion of The Dalles Dam in 1957, which inundated Celilo Falls, a natural barrier to upriver American Shad migration. Regressions revealed that the annual percentage of American Shad migrating upstream from McNary Dam varied with water temperature and discharge (R2 = 0.72), but not population density. When Atlantic coast rivers were dammed, however, American Shad lost spawning habitat and declined in abundance. Understanding the rapid colonization of the Columbia River by American Shad may reveal ways to help American Shad recolonize rivers where they are native. Understanding the roles of water temperature and discharge may allow us to project effects of climate change on the future distribution and abundance of American Shad in the Columbia River basin. Our results suggest that dam construction and alterations to the temperature and discharge regimes of the Columbia River have contributed to the increase in abundance and spatial distribution of American Shad. These changes might have improved the reproductive success of American Shad by providing access to additional spawning grounds and creating suitable juvenile rearing conditions.
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We investigated the population size and the proportion of the population of American shad Alosa sapidissima that passed through the New Savannah Bluff Lock and Dam, a low-head lock and dam on the Savannah River in South Carolina and Georgia. We fitted 110 American shad with radio transmitters in 2001 and 2002. All but two fish moved downstream after transmitter implantation. In 2001, a smaller proportion of American shad implanted with radio transmitters earlier in the season returned to the dam than fish released later. Of the fish that returned to the dam, over 50% in 2001 and 9% in 2002 passed through the lock and continued migrating upstream. In both years, the modal daily movement distance was less than 1 km. Movements greater than 5 km/d were generally associated with fish rapidly returning upstream after their initial downstream movement. Continuous diel monitoring indicated that movements greater than 0.1 km/h were more frequent at night than during the day. In both years, American shad were not uniformly distributed over the study area but were predominantly grouped just below the dam and in a relatively large pool approximately 6 km below the dam. We estimated the population size of American shad that reached the New Savannah Bluff Lock and Dam at 157,685 in 2001 and 217,077 in 2002.
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The movements of 18 radio-tagged American shad (Alosa sapidissima) were studied in 1980 and 1981 as they attempted to locate the upstream fish collection facilities of two fish lifts at Holyoke Dam on the Connecticut River in Massachusetts. Nine fish (50%) were passed by the lifts during the 2 years and, in 1980, the efficiency of the tailrace lift was estimated at 42%. The mean delay time of the seven fish passed by the tailrace lift during the 2 years was 3.3 d (range 2-5 d); the delay of the two fish passed by the spillway lift in 1981 was 6 and 7 d. Fish were repelled by the turbulence caused by the turbine discharge into the head of the tailrace and only entered the vicinity of the tailrace lift during 55% of all upstream trips in 1980 and 67% of the trips in 1981. During high river flows, fish were attracted to the spillage over the dam, not the flow from the tailrace. The inefficiency of either lift to pass early migrating American shad and of the tailrace lift to pass fish efficiently at any time may limit upstream passage during some years. The situation at Holyoke Dam, together with similar problems at other upstream dams, prevents many fish from reaching the historical upstream limit of their range and creates a poor or, at best, an unpredictable sport fishery upstream.
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Of 5074 adult American shad, Alosa spidissima, tagged in the Annapolis River, Nova Scotia, during the 1981 and 1982 spawning runs, 292 (5.8%) were recaptured, 180 in the river during the same year, 56 in the river in subsequent years, 53 at distant marine sites, and 1 in another Nova Scotia river. Recovery from 6124 adult shad tagged in a marine environment (Cumberland Basin, Bay of Fundy) was similar (395 recaptures, 6.5%) but distribution was markedly different. Thirty-five were taken in the Basin during the same year, but only 7 in subsequent years. Conversely, 139 were recaptured at distant marine sites, and 214 in rivers from the St. Lawrence River, Quebec, to the St. John's River, Florida. Assuming equal probabilities for recapture within this species' geographical range, Annapolis River freshwater recaptures were specific for the Annapolis River but Cumberland freshwater recaptures were nonspecific. Except for two returns, possible strays, fidelity to the Annapolis was 97%.
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Humans have been damming rivers for millennia, and our more ambitious efforts over the past century have arguably altered river ecosystems more extensively than any other anthropogenic activity. Effects of damming on river biota include decimation of migratory fauna (e.g., diadromous and potamodromous fishes and crustaceans), lost fisheries, and imperilment of obligate riverine taxa. Although effects of dams on biota have been widely documented, ecosystem-level consequences of faunal depletion caused by dams are only beginning to be appreciated. We discuss consequences to river ecosystems of altering distributions and abundances of migratory fauna, which often provide trophic subsidies and may strongly influence the structure of local habitats and communities. It is well documented that anadromous fishes can provide a major input of nutrients and energy to freshwater systems when spawning adults return from the sea. Other less-studied taxa that migrate between distinct portions of riverine systems (e.g., acipenserids, catostomids, and prochilodontids) may similarly provide trophic transfers within undammed river systems in addition to modifying local communities and habitats through feeding and spawning activities. Experimental faunal exclusions have demonstrated strong potential effects of some amphidromous shrimps and potamodromous fishes on benthic organic matter and algal and invertebrate communities. Depletion of these animals above dams is likely to significantly affect ecosystem processes such as primary production and detrital processing. The decline of freshwater mussels isolated by dams from their migratory fish hosts has likely lowered stream productivity, nutrient retention, and benthic stability. Greater focus on effects of dams on ecosystem processes, as mediated by faunal change, would improve our ability to assess the costs and benefits of future river management strategies.
Striped bass Morone saxatilis and American shad Alosa sapidissima in the Neuse River, North Carolina, historically migrated up to 435 km upriver to spawn. However, migration was impeded in 1952 by the construction of Quaker Neck Dam at river kilometer 225 (measured from the point where the Neuse River enters Pamlico Sound). To determine the fraction of tagged fish that migrated upstream of this low-head dam and the characteristics of selected spawning habitat, we implanted sonic transmitters in 25 striped bass and 25 American shad during 1996 and 1997. We determined preferred depth, water velocity, and substrate composition by measuring those characteristics at both randomly selected sites and sites where spawning was observed. Of 13 striped bass and 8 American shad with transmitters that migrated to the base of Quaker Neck Dam, only 3 striped bass passed the structure, indicating that the dam was an impediment to migration. Striped bass spawning was observed only in the area directly below (within 1.5 km of) Quaker Neck Dam. Although none of the telemetered American shad passed Quaker Neck Dam, American shad spawning was observed from the base of the dam to 1.5 km downstream as well as 3 km above the dam. Striped bass spawned at sites with significantly higher water velocity and significantly larger substrate than on average was found at randomly sampled locations. American shad spawned at sites that were significantly shallower and had significantly larger substrate than was found in random samples. The type of spawning habitat selected by both species is more abundant above than below Quaker Neck Dam, indicating that improved access to upstream reaches would benefit both species.
The rate of evolution and the scope for phenotypic plasticity can be assessed by studying the adaptation of an introduced population to a new habitat and the response of established populations to progressive environmental change. Adult American shad (Alosa sapidissima), an introduced species, and sockeye salmon (Oncorhynchus nerka), a native species, migrate up the Columbia River (northwestern United States) in late spring and early summer to spawn. Based on records from Bonneville Dam, the river's spring warming has occurred progressively earlier since approximate to 1950, coinciding with a reduction in spring discharge. The date when 50% of the shad migrated past the dam is correlated with this shift in thermal and flow regimes; they now ascend the river approximate to 38 d earlier than they did in 1938. However, the mean temperature that they experience has actually decreased by 1.8 degrees C in 45 yr, indicating that the change in their migratory timing has outstripped the rate of environmental change. The upriver migration of sockeye salmon is also earlier than in past years, but their change in timing (approximate to 6 d since 1949) lags behind the rate of environmental change, and they are now experiencing approximate to 2.5 degrees C warmer temperatures than in past years. We hypothesize that the differences in response to changing environmental conditions between these species arise from differences in their migration patterns and early life histories. Shad spawn soon after they enter the river in its main stem where environmental conditions of the larvae will closely mirror those experienced by upstream-migrating adults. They may therefore have evolved a migratory pattern that allows greater behavioral response to environmental fluctuations than sockeye salmon, which spawn in distant locations many months after their upriver migration. Sockeye salmon migration may be more strongly controlled by innate responses to photoperiod, migrating at the time of year which is best on average because conditions in the lower river will not be indicative of those to be experienced by incubating embryos and juveniles.
We provide a detailed description of the migratory and reproductive behaviour of allis shad (Alosa alosa L.), a species that is in decline in Europe. Adult swimming behaviour during the last part of upstream migration and on a spawning ground downstream of an insurmountable dam was studied in detail and its main features identified. "characterized" in this context. Mobile telemetry and a fixed telemetry system were used to record fish positions and to monitor 23 acoustically tagged individuals (17 females and six males) during the 2001 and 2002 reproductive seasons. Allis shad showed considerable exploratory behaviour, and a rest area was observed 1.5 km downstream of the spawning ground. Thirteen individuals were observed on the spawning area, though both males and females spent most of their time (70-99%) away from it. Male and female residency times on the spawning area were, respectively, 1-11 days and 1-7 days, and females were observed during both day and night on the spawning ground. In 2002, an analysis of the 3D swimming behaviour on the spawning ground of six individuals allowed us to estimate the number of spawning events per fish. Males participated in more spawning acts (up to 60) than females (0-2). (C) 2004 International Council for the Exploration of the Sea. Published by Elsevier Ltd. All tights reserved.
The American oyster, Crassostrea virginica, is an important commercial and mariculture species. Spawning occurs repeatedly during warmer months with millions of eggs released. Embryos and larvae are carried by currents throughout the estuaries and oceanic bays where they occur. The few surviving larvae cement themselves to a solid object, where they remain for the remainder of life. Unable to move, they must tolerate changes in the environment that range from -1.7° to 49°C, 5 to 30 ppt salinity, and clear or muddy water. 88 references, 2 figures, 1 table.
Cating's method of using scales to age American shad (Alosa sapidissima) has been the standard for more than 50 years. However, the only validation of this method is for ages 4–6 in the Connecticut River. To test the method for these—and older—age classes in another river, we obtained scales from 52 known-age fish from two Pennsylvania rivers and had 13 experienced biologists estimate ages using Cating's method. Each biologist read the scale impressions twice, and these readings were then assessed in terms of precision, accuracy, and bias. Percent agreement between estimates for the same scale set (precision) ranged from 50.0 to 76.5%. Percent agreement between estimated age and known age (accuracy) was highest for ages 3–6 (33.7–48.5%), markedly lower for age-7 (12.1%), and lowest for age-8 fish (3.9%). Ages of the youngest fish were often overestimated, and those of the oldest fish were typically underestimated (bias). Therefore, Cating's method is not applicable to American shad in these Pennsylvania rivers. In fact, this scale-ageing method has never been validated across all ages for any American shad stock. Thus, we recommend against using age-based techniques to assess stocks of American shad until further age-validation studies have been completed.
The intra-population tissue weight dynamics and bioenergetics of American shad (Alosa sapidissima) were studied during the freshwater migration in the Connecticut River. Emphasis was on the extent and significance of temporal differences in the magnitude and rate of depletion of stored body reserves. This was accomplished by the comparison of body reserves of shad sampled at various locations and times along the migratory route. Somatic weight loss and associated energy depletion was extreme (45–60%); up to 50 and 70% of available body protein and lipid, respectively, were used to fuel the migration. The extent of reserve depletion was sex- and size-specific. Small individuals and males suffered the greatest tissue depletion. High water temperatures accounted for the reduced energy efficiency of late migrant shad (average of 42 vs. 24 KJ∙kg−1∙km−1 expended by earlier migrants), and resulted in, greater depletion of total body reserves. More extensive depletion may contribute to the higher mortality reported among this component of the population. Gonad development was complete prior to entry into the river. This may spare somatic reserves during the freshwater fast and hence maximize survival. The pattern and extent of energy utilization in other anadromous fish species are discussed with reference to possible influence on demographic parameters, especially the repeat spawning habit.Key words: American shad, Alosa sapidissima; energetics, allocation, weight loss, temporal differences, Connecticut River, migration
The reproductive characteristics of five populations of American shad (Alosa sapidissima) on the Atlantic coast were studied. The proportion of repeat spawners increased with the latitude of the home river. Relative and absolute fecundities decreased as the proportion of repeat spawners increased. These reciprocal trends in reproductive characteristics are independent of growth parameters. The principal factor influencing reproductive strategies in shad appears to be variability in the thermal regime of the home river which influences egg and larval survival. Northern populations, spawning in environments that are thermally harsh and variable, allocate a greater proportion of their energy reserves to migration thereby ensuring higher postspawning survival. This is accomplished by reducing the energy allocated to gonads. The pattern of reproductive responses of shad to the thermal environment of the natal river is consistent with existing ecological theory concerning the evolution of reproductive strategies in response to differing environmental conditions. Available literature for several other fishes suggests that fine tuning of reproductive strategies to local environmental conditions may be widespread among fish and may be the ultimate basis for the evolution of homing. Key words: American shad, Alosa sapidissima, reproductive strategies, fecundity, frequency of reproduction, energy allocation, latitudinal variation, theoretical ecology
We present a simulation model in which individual adult migrant American shad (Alosa sapidissima) ascend the Connecticut River and spawn, and survivors return to the marine environment. Our approach synthesizes bioenergetics, reproductive biology, and behavior to estimate the effects of migratory distance and delays incurred at dams on spawning success and survival. We quantified both the magnitude of effects and the consequences of uncertainty in the estimates of input variables. Behavior, physiology, and energetics strongly affected both the distribution of spawning effort and survival to the marine environment. Delays to both upstream and downstream movements had dramatic effects on spawning success, determining total fecundity and spatial extent of spawning. Delays, combined with cues for migratory reversal, also determined the likelihood of survival. Spawning was concentrated in the immediate vicinity of dams and increased with greater migratory distance and delays to downstream migration. More research is needed on reproductive biology, behavior, energetics, and barrier effects to adequately understand the interplay of the various components of this model; it does provide a framework, however, that suggests that provision of upstream passage at dams in the absence of expeditious downstream passage may increase spawning success - but at the expense of reduced iteroparity.
The relationships among behavior, environment, and migration success in anadromous fishes are poorly understood. We monitored migration behavior at eight Columbia and Snake river dams for 18 286 adult Chinook salmon (Oncorhynchus tshawytscha) and steelhead (sea-run Oncorhynchus mykiss) over 7 years using radiotelemetry. When statistically controlling for variation in flow, temperature, fisheries take, and other environmental variables, we observed that unsuccessful individuals - those not observed to reach spawning areas - had longer passage times at nearly all dams than fish that eventually reached tributaries. In many cases, times were also longer for unsuccessful adults passing through a multiple-dam reach. Four ecological mechanisms may have contributed to these patterns: (i) environmental factors not accounted for in the analyses; (ii) inefficient responses by some fish to passage conditions at dams that resulted in slowed passage, energetic depletion, and unsuccessful migration; (iii) ongoing selection for traits needed to pass obstructions; and (or) (iv) passage rate was not directly linked to migration success, but rather, both resulted from relatively poor phenotypic condition upon river entry in unsuccessful migrants. Overall, these results illustrate the need for a mechanistic understanding of the factors that influence migration success and the need for fitness-based criteria to assess the effects of dams on anadromous fishes.
Use of navigation locks represents a low-cost alternative to the construction of fishways or lifts at low-elevation (<5 m) dams. We used sonic tracking to assess the passage efficiency of adult American shad Alosa sapidissima in 1996-1998 through the navigation locks at Lock and Dam 1 on the Cape Fear River, North Carolina. We also tested the passage efficiency at a steeppass fishway installed in 1997. Eighty-six tagged American shad were released below the dam over the 3-year study; passage efficiency ranged from 18% in 1997 (a year of high discharge during the tracking period) to 61% in 1998. During low flows, we were able to improve passage efficiency by (1) operating the lock to pass fish through until mid-June, (2) increasing attraction flows emanating from the lock entrance, (3) conducting as many lockages (i.e., use of locks to pass fish upstream) as possible in a day, and (4) closing one of the lower lock gates to better retain fish in the lock chamber after they had entered. The steeppass fishway was not as effective as the navigation locks for passage of American shad. Only three tagged fish (8%) used the fishway in 1998, probably because of design deficiencies and the lack of attraction flow at the fishway entrance.
Analysis of scales taken at the times of tagging and recapture from 74 Dover soles Microstomus pacificus collected off Oregon demonstrated that scales were inadequate aging structures for this species. This contradicted earlier work that used marginal growth of scales and age–length observations as indirect validation methods. Errors in scale-age determinations were found for fish assigned scale ages of 5 years and greater. For female Dover soles, the probability of increment (“annulus”) formation was greater for younger than for older fish. Relationships between expected scale age and actual age indicated that maximum longevity of this species off Oregon may be in the range of 48–52 years, in contrast to the maximum scale age of 28 observed for this species.
Runs of the anadromous American shad Alosa sapidissima in the Lehigh River, a major tributary to the west shore of the Delaware River, were blocked by construction of dams during the 1820s. Completion of two fish ladders in 1994 opened up the lower 39 km to migratory fish. Hatchery-reared American shad larvae, marked by immersion in tetracycline antibiotics, have been stocked in the Lehigh River since 1985. From 1995 to 2000, hatchery-origin (marked) American shad made up 73–98% of the adult shad collected in the Lehigh River upriver of the first dam. The contribution of Lehigh River hatchery-marked adult shad in the Delaware River was 5–15% at Raubsville, 10 km downriver from the mouth of the Lehigh River, and 0–4% at Smithfield Beach, 53 km upstream from the mouth of the Lehigh River. These results demonstrated that American shad migrating into the Lehigh River were not a random assortment of shad from the Delaware River population. When the downstream Delaware River samples were segregated laterally on the east and west sides of the river, the sample on the west side had a significantly higher proportion of Lehigh River marks (8–15%) than the sample on the east side (2–7%), indicating that the returning Lehigh River hatchery-marked adults preferred the side of the Delaware River influenced by the Lehigh River. Our results suggest that efforts to restore American shad above dams should include some transplant strategy to expedite recolonization.
We examined the status of diadromous (migratory between saltwater and freshwater) fishes within the North Atlantic basin, a region of pronounced declines in fisheries for many obligate marine species. Data on these 24 diadromous (22 anadromous, 2 catadromous) species are sparse, except for a few high-value forms. For 35 time series, relative abundances had dropped to less than 98% of historic levels in 13, and to less than 90% in an additional 11. Most reached their lowest levels near the end of the observation period. Many populations persist at sharply reduced levels, but all species had suffered population extirpations, and many species are now classified as threatened or endangered. Habitat loss (especially damming), overfishing, pollution, and, increasingly, climate change, nonnative species, and aquaculture contributed to declines in this group. For those diadromous fishes for which data exist, we show that populations have declined dramatically from original baselines. We also discuss the consequences of these changes in terms of lost ecosystem services.
Four methods were used to determine the energy content of somatic tissues of Perca fluviatilis. Two forms of direct calorimetry (both adiabatic and non-adiabatic) and wet (dichromate) oxidation gave similar results. When energy contents were calculated from proximate analysis using accepted conversion factors (9.45 cal mg−1 for lipid, 5.65 cal mg−1 for protein) results were higher than those from the other methods. The discrepancy was eliminated when a lower, directly determined energy content for the extracted lipid fraction was used. Some historic and technical aspects of the comparison are discussed.
Traditional methods for determining the energy content of fish involve either chemical assays of lipid and protein levels (proximate analyses) or tissue combustion (bomb calorimetry). In studies of migrating Pacific salmon Oncorhynchus spp., entire fish need to be homogenized prior to analysis, as energy reserves are stored along a head-to-tail gradient and change along this gradient depending on the stage of upriver migration. The logistics and costs associated with transporting carcasses to the laboratory can be prohibitive. Also, many populations of Pacific salmon are at risk of extinction, so lethal sampling is often not an option. Few reliable and practical methods exist that enable rapid and nonlethal energy determinations of large fish in the field. We evaluated a handheld microwave energy meter as a means of estimating whole-body energy concentrations. In 2002 and 2003, we collected sockeye salmon O. nerka from several stocks during their coastal and upriver migration through the Fraser River watershed (British Columbia). For each stock, we sampled fish from various locales ranging from ocean to spawning areas. Fish somatic tissues were interrogated at four body positions; however, the two most anterior positions produced the most accurate energy information. It took less than 30 s per fish to collect these data. We found strong regression relationships between somatic lipid percentage (R2 = 0.93; P < 0.001) and gross somatic energy density (R2 = 0.94; P < 0.001) measured by whole-carcass proximate analyses and loge transformed energy meter readings. The slopes and intercepts of these relationships did not differ among stocks or years.
Maltais E, Daigle G, Colbeck G, Dodson JJ. Spawning dynamics of American shad (Alosa sapidissima) in the St. Lawrence River, Canada–USA. Ecology of Freshwater Fish 2010: 19: 586–594. © 2010 John Wiley & Sons A/SAbstract –  The most northerly population of American shad (Alosa sapidissima), located in the St. Lawrence River, is considered vulnerable because of low population abundance and limited spawning habitat located at the upstream extent of the population’s anadromous migration. Here, we aimed to establish the temporal and spatial extent of spawning based on a novel hatch-date analysis of juveniles. Spawning activity lasted from early May to early July. We found that juveniles captured downstream during the summer hatched later in the year than those captured further upstream. As a result, younger juveniles were distributed somewhat further downstream. In addition, we found significant multimodality in hatch-date distributions at midstream and downstream sampling stations. Together, these results provide evidence that the 2-month spawning period involved numerous spawning events that progressed in a downstream direction as the season advanced, rather than being restricted to upstream sites over the spawning season.
Adaptive fishway design: a framework and rationale for effective evaluations. Monitoring, Funktionskontrollen und Qualitätssicherung an Fischaufstiegsanlagen. 2. Kolloquium zur Herstellung der ökologischen Durchgängigkeit der Bundeswasserstraßen
  • T Castro-Santos
Castro-Santos, T. 2012. Adaptive fishway design: a framework and rationale for effective evaluations. Monitoring, Funktionskontrollen und Qualitätssicherung an Fischaufstiegsanlagen. 2. Kolloquium zur Herstellung der ökologischen Durchgängigkeit der Bundeswasserstraßen. 76-89. Koblenz, Germany, Bundesanstalt für Gewässerkunde.
A fishway that shad ascend
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