Spawning Population Research Articles

Co-occurrence of European sardine (<i>Sardina pilchardus</i>), anchovy (<i>Engraulis encrasicolus</i>) and sprat (<i>Sprattus sprattus</i>) larvae in southern North Sea habitats: Abundance, distribution and biochemical-based condition

Spawning populations of European sardines (Sardina pilchardus) and anchovies (Engraulis encrasicolus) have become re-established in the southern North Sea after a ~30-year absence and now co-occur with sprat (Sprattus sprattus). Consequently, little is known concerning potential interactions among these three species in this region. Based upon parallel cruises conducted in June/July 2005, we compared the larval abundance, size-distributions and biochemical-based condition of these species among 1) nearshore (Wadden Sea) areas and offshore (German Bight) areas that were 2) vertically mixed, 3) frontal zones, or 4) stratified waters. In general terms, larval condition (RNA:DNA) was relatively high at all stations. Although fronts clearly acted to concentrate larvae, larval condition was not necessarily higher. For example 9% of sardines captured at the tidal mixing front were categorised as starving, while no starving larvae were sampled in the stratified water masses. Habitats of sardine and sprat larvae were similar, whereas anchovies were primarily restricted to nearshore areas. This is the first study examining the potential role of near- and offshore habitats as nursery areas and the extent to which resource (habitat) partitioning exists among the larvae of sprat and newly established anchovy and sardine in the North Sea.

Intercalibration of hydroacoustic and mark–recapture methods for assessing the spawning population size of a threatened fish species

Hydroacoustic counting and a three-year mark-recapture study with passive integrated transponders (PIT tags) were used to estimate the size of a spawning population of nase Chondrostoma nasus, a threatened potamodromous cyprinid that undertakes annual spawning migrations into a tributary of the Danube River. In 2005, the estimates of the size of the spawning population from the hydroacoustic counts (N = 2234, 95% CL 1929-2538) and from the Jolly-Seber model (N = 1198, 95% CL 461-5842) corresponded well. Estimates from the jackknife-estimator based on the hydroacoustic counts yielded slightly higher values (N = 2783, 95% CL 2529-3037), but were still in the same order of magnitude as those from the hydroacoustic and mark-recapture approach. At low run-size, hydroacoustic counting was more time consuming and technically demanding than mark-recapture studies. At the same time, it was non-invasive, provided real-time data on a fine temporal scale, and estimates showed less variability than the Jolly-Seber model. Mark-recapture of fish in spawning streams involved substantial disturbance at a sensitive stage of the life cycle. Hence, hydroacoustics is highly suited for population estimates of threatened potamodromous fishes, where interference needs to be minimized.

Unaccounted mortality in salmon fisheries: non‐retention in gillnets and effects on estimates of spawners

Summary 1. Effective and sustainable natural resource management is enhanced when the consequences of exploitative practices are fully understood and acknowledged. Commercial fisheries devote considerable resources to maximize the harvest of target species and minimize interference with non‐target stocks. Appropriately, bycatch and discard of non‐target stocks are recognized as critical economic and conservation concerns. Few studies, however, have examined non‐retention mortality in target stocks. Non‐retention, where fish are engaged by fishing gear but not landed, is rarely quantified and the effects on stocks are unknown. Mortality due to non‐retention may have important effects on the dynamics of exploited populations. 2. We surveyed spawning populations of sockeye salmon Oncorhynchus nerka that had traversed commercial fisheries in Bristol Bay, Alaska, to estimate the incidence of non‐retention in gillnets and the severity of injuries associated with entanglement. To better understand how gillnet injury affects spawning success, we tagged and monitored stream‐spawning fish and applied a maximum likelihood model to mark–recapture data. 3. A substantial portion (11–29%) of spawning sockeye salmon exhibited clear signs of past entanglement with commercial gillnets. Survival among such fish was significantly reduced. More than half of the fish that reach natal spawning grounds with fishery‐related injuries fail to reproduce. This suggests that estimates of spawning stocks are inflated by 5–15% at minimum. 4. Synthesis and applications. Our analyses indicate that non‐retention in gillnet fisheries is an important and under‐appreciated consequence of the exploitation of salmon. Stock estimates for exploited populations that do not account for non‐retention mortality overestimate the number of reproductively viable fish. Unaccounted mortality and interannual variation in the magnitude of this mortality may prevent accurate estimates of viable spawners, confound our understanding of the relationship between stock size and recruitment, impede optimal management and obscure the ecosystem impacts of migratory stocks in coastal watersheds. Given the magnitude of non‐retention in this fishery, explicit consideration of non‐retention mortality may be warranted across a wide range of exploited populations.

Spatial patterns of hybridization between bull trout, Salvelinus confluentus, and brook trout, Salvelinus fontinalis in an Oregon stream network

Hybridization with introduced species represents a serious threat to the persistence of many native fish populations. Brook trout (Salvelinus fontinalis) have been introduced extensively throughout the native range of bull trout (S. confluentus) and hybridization has been documented in several systems where they co-exist and is seen as a significant threat to the persistence of bull trout populations. We identified a group of diagnostic microsatellite loci to differentiate bull trout and brook trout and then used these loci to examine the spatial distribution of hybrids in the Malheur River basin, Oregon USA. In random samples of approximately 100 fish from each of three creeks we identified 181 brook trout, 112 bull trout and 14 hybrids. Although bull trout, brook trout and hybrids were found in all three creeks, they were not evenly distributed; brook trout were primarily found in the lower sections of the creeks, bull trout further upstream, and hybrids in the areas of the greatest overlap. One creek with a population of brook trout in a headwater lake provided an exception to this pattern; brook trout were found distributed throughout the creek downstream of the lake. Several post-F1 hybrids were identified suggesting that hybrids are reproducing in the Malher River Basin. Mitochondrial DNA analysis indicated that both female bull trout and brook trout are involved in hybridization events. Analysis of population structure suggested that brook trout have established multiple spawning populations within the Malheur system. Data presented in this study suggest that relative abundance of brook trout and habitat quality are important factors to consider when evaluating the threat of hybridization to bull trout populations.

Dynamic micro‐geographic and temporal genetic diversity in vertebrates: the case of lake‐spawning populations of brown trout (Salmo trutta)

Conservation of species should be based on knowledge of effective population sizes and understanding of how breeding tactics and selection of recruitment habitats lead to genetic structuring. In the stream-spawning and genetically diverse brown trout, spawning and rearing areas may be restricted source habitats. Spatio-temporal genetic variability patterns were studied in brown trout occupying three lakes characterized by restricted stream habitat but high recruitment levels. This suggested non-typical lake-spawning, potentially representing additional spatio-temporal genetic variation in continuous habitats. Three years of sampling documented presence of young-of-the-year cohorts in littoral lake areas with groundwater inflow, confirming lake-spawning trout in all three lakes. Nine microsatellite markers assayed across 901 young-of-the-year individuals indicated overall substantial genetic differentiation in space and time. Nested gene diversity analyses revealed highly significant (< or =P = 0.002) differentiation on all hierarchical levels, represented by regional lakes (F(LT) = 0.281), stream vs. lake habitat within regional lakes (F(HL) = 0.045), sample site within habitats (F(SH) = 0.010), and cohorts within sample sites (F(CS) = 0.016). Genetic structuring was, however, different among lakes. It was more pronounced in a natural lake, which exhibited temporally stable structuring both between two lake-spawning populations and between lake- and stream spawners. Hence, it is demonstrated that lake-spawning brown trout form genetically distinct populations and may significantly contribute to genetic diversity. In another lake, differentiation was substantial between stream- and lake-spawning populations but not within habitat. In the third lake, there was less apparent spatial or temporal genetic structuring. Calculation of effective population sizes suggested small spawning populations in general, both within streams and lakes, and indicates that the presence of lake-spawning populations tended to reduce genetic drift in the total (meta-) population of the lake.

Spawning season, spawning grounds, and egg production of red sea bream in Hiuchi-nada, Seto Inland Sea

The spawning season and grounds of red sea bream in Hiuchi-nada, the central part of the Seto Inland Sea, were described using a new method based on monoclonal antibodies for identifying Pagrus major eggs, and the daily egg production (standardized by the incubation time and survival rate) was estimated. At the peak of spawning (May), the ranges of sea temperature, salinity, and chlorophyll a where red sea bream eggs occurred were 14.8–17.4°C, 32.0–33.0, 0.5–4.4 μg/L, respectively. The main spawning grounds of the red sea bream were confirmed as being the areas near the Geiyo Islands, Misaki Peninsula, Saijyo, Niihama. The spatial spread of red sea bream eggs increased with the egg developmental stage. The ranges of daily egg production in 2005 and 2006 were 0.3–19.3 and 0.2–6.7 × 109 eggs/day, respectively. In Hiuchi-nada, aquaculture farms are located close to the spawning grounds, and the potential spawning population from the aquaculture farms equaled or exceeded that of the estimated spawning population obtained by the egg production method. Red sea bream eggs in Hiuchi-nada might be produced by both wild and aquaculture-based spawning populations.

Continental-scale variation in otolith geochemistry of juvenile American shad (Alosa sapidissima)

We assembled a comprehensive atlas of geochemical signatures in juvenile American shad ( Alosa sapidissima ) to discriminate natal river origins on a large spatial scale and at a high spatial resolution. Otoliths and (or) water samples were collected from 20 major spawning rivers from Florida to Quebec and were analyzed for elemental (Mg:Ca, Mn:Ca, Sr:Ca, and Ba:Ca) and isotope (87Sr:86Sr and δ18O) ratios. We examined correlations between water chemistry and otolith composition for five rivers where both were sampled. While Sr:Ca, Ba:Ca, 87Sr:86Sr, and δ18O values in otoliths reflected those ratios in ambient waters, Mg:Ca and Mn:Ca ratios in otoliths varied independently of water chemistry. Geochemical signatures were highly distinct among rivers, with an average classification accuracy of 93% using only those variables where otolith values were accurately predicted from water chemistry data. The study represents the largest assembled database of otolith signatures from the entire native range of a species, encompassing approximately 2700 km of coastline and 19 degrees of latitude and including all major extant spawning populations. This database will allow reliable estimates of natal origins of migrating ocean-phase American shad from the 2004 annual cohort in the future.

Demographic Analysis of Lost River Sucker and Shortnose Sucker Populations in Upper Klamath Lake, Oregon

AbstractWe used 13 years (1995‐2007) of capture‐mark‐recapture data to assess population dynamics of endangered Lost River suckers Deltistes luxatus and shortnose suckers Chasmistes brevirostris in Upper Klamath Lake, Oregon. The Cormack‐Jolly‐Seber method was used to estimate survival, and information theoretic modeling was used to assess variation due to time, gender, species, and spawning subpopulations. Length data were used to detect multiple year‐class failures and events of high recruitment into adult spawning populations. Average annual survival probability was 0.88 for Lost River suckers and 0.76 for shortnose suckers. Mean life span estimates based on these survival rates indicated that Lost River suckers survived long enough on average to attempt reproduction eight times, whereas shortnose suckers only survived to spawn three to four times. Shortnose sucker survival was not only poor in years of fish kills (1995‐1997) but also was low in years without fish kills (i.e., 2002 and 2004). This suggests that high mortality occurs in some years but is not necessarily associated with fish kills. Annual survival probabilities were not only different between the two species but also differed between two spawning subpopulations of Lost River suckers. Length composition data indicated that recruitment into spawning populations only occurred intermittently. Populations of both species transitioned from primarily old individuals with little size diversity and consistently poor recruitment in the late 1980s and early 1990s to mostly small, recruit‐sized fish by the late 1990s. A better understanding of the factors influencing adult survival and recruitment into spawning populations is needed. Monitoring these vital parameters will provide a quantitative means to evaluate population status and assess the effectiveness of conservation and recovery efforts.

Use of Microsatellites to Determine Population Structure and Migration of Pacific Herring in British Columbia and Adjacent Regions

AbstractThis study assessed genetic population structure of Pacific herring Clupea pallasii in British Columbia and adjacent regions by analyzing microsatellite variation; the utility of microsatellites for stock identification applications was also evaluated. Variation at 14 loci was surveyed in approximately 26,000 Pacific herring from 90 sampling locations. Estimates of the genetic differentiation index FST by locus varied between 0.000 and 0.014, and the mean across all loci was 0.003. Four stocks of Pacific herring were defined in British Columbia, and stocks were also identified in southeast Alaska, Washington, and California. In British Columbia, differences in timing of spawning are the main isolating mechanisms among stocks, although geographic isolation of the spawning populations may also have some effect in maintaining the genetic distinctiveness of each stock. The limited genetic differentiation among Pacific herring populations in British Columbia is consistent with among‐population straying rates that are sufficient to homogenize allele frequencies over broad areas. Analysis of simulated mixtures from fishery sampling suggested that acceptable estimates of stock composition were achieved by use of the microsatellites. Mixed‐stock samples (∼1,700 individuals) were collected during research vessel surveys from 14 locations in British Columbia. Analysis of summer mixed‐stock samples from the Strait of Georgia and adjacent waters indicated that resident fish on the west side of the strait were mainly derived from primary‐spawning populations (i.e., those that spawned during the primary period in March) that failed to migrate to traditional summer feeding grounds. On the east side of the strait, Pacific herring of mainland inlet origin were found in higher proportions and presumably did not move in appreciable numbers to feeding areas off the west coast of Vancouver Island. In northern British Columbia, fish from northern late‐spawning populations dominated fishery samples collected in waters adjacent to the mainland until the end of June; however, by late July, this group had been replaced almost entirely by primary‐spawning Pacific herring of British Columbia origin.

Comments on ‘Weak population differentiation in northern European populations of the endangered anadromous clupeid Alosa fallax’

In a recent paper, Volk et al. (2007) reported statistically significant, but weak genetic differentiation among ‘spawning populations’ of the endangered twaite shad Alosa fallax (Lacepede). The authors state that this suggests ‘substantial gene flow among the majority of individual estuary–river spawning locations’, an assertion that could have implications for the management of this endangered species. The sampling regime upon which this study is based is flawed, however, and may underestimate the degree of population differentiation for A. fallax from northern Europe. A fundamental precept of genetic studies of fish population structure is that samples need to come from spawning aggregations on the spawning grounds in order for clear interpretations of population structuring to be reached. Volk et al. (2007) state that A. fallax ‘spawning biology and habitat requirements are not well described’. Aprahamian et al. (2003), however, provide a comprehensive overview of A. fallax biology, including spawning biology and spawning habitat requirements within specific rivers. Alosa fallax is an anadromous clupeid, which are believed to home to their natal river, and are known to spawn in tidal fresh water and non-tidal portions of rivers as far as 400 km upstream (Aprahamian et al., 2003). Similarly, the congeneric allis shad Alosa alosa (L.) (Bagliniere et al., 2003) and American shad Alosa sapidissima (Wilson) (Limburg et al., 2003) are known to make extensive upstream spawning migrations. Despite a reportedly high degree of spawning-site fidelity (Melvin et al., 1986), A. sapidissima are known to exhibit forays into multiple estuaries along the Atlantic coast during their annual spawning migration. Adults tagged in the Connecticut River have been captured in the subsequent annual spawning migration in estuaries ranging from Pamlico and Albemarle Sounds (North

A Range Extension of the Atlantic Silverside, Menidia menidia, to Coastal Waters of Southwestern Newfoundland

Previous literature documents Atlantic Silverside, Menidia menidia, as occurring from the southern Gulf of St. Lawrence to northeastern Florida. Beach seining in St. George’s Bay, Newfoundland, revealed the presence of this species in coastal waters of southwestern Newfoundland. This is the first documented report of M. menidia in Newfoundland waters. This report extends the range of this species north of the Laurentian Channel, a significant biogeographic barrier to small coastal fishes. All M. menidia collected were young-of-the-year, less than 90 mm SL (Standard Length). These fish may be representative of a larger relict population originating from the Mid-Hypsithermal Interval (7000 years ago) that spawn in St. George’s Bay and migrate offshore for winter. Alternatively, these M. menidia may be survivors of a more southern spawning population carried northward by ocean currents.

Seasonal and interannual variations of sockeye salmon (Oncorhynchus nerka) microsatellite DNA in two Kamchatka lake-river systems

Seasonal and interannual variations in the sockeye salmon populations from two lake-river systems of the East and West Kamchatka were studied. Stability of allele and genotypic frequencies of six microsatellite DNA loci in the adjacent generations and spawning populations of the sockeye salmon of the Bol'shaya River was confirmed experimentally. The pairwise intersample differentiation (F(st)) of the local sockeye salmon populations from the southwestern Kamchatka coast (Ozernaya and Bol'shaya Rivers)was almost 7 times higher than the corresponding values for the spawning populations of the Bol'shaya River sockeye salmon of the adjacent years; 15 times, for the adjacent Bol'shaya River sockeye salmon generations; and four times, for the seasonal races within the Kamchatka River.

Progress Toward the Rehabilitation of Lake Trout ( Salvelinus namaycush) in South Bay, Lake Huron

Our objective was to evaluate the status of lake trout Salvelinus namaycush rehabilitation in South Bay, Lake Huron. Standardized surveys were conducted to quantify natural recruitment, annual mortality, and the contribution of wild-versus hatchery-origin lake trout. Some indicators suggest a high level of natural recruitment. The spawning population was comprised of multiple ages, and the mean age of spawners (8.4 years for females, 7.9 years for males) was at least 1 year older than the age at 50% maturity (5.8 years). Estimated annual total mortality rates (0.20–0.25) and sea-lamprey induced mortality rates (0.02) were less than maximum allowable values. The proportion of wild-origin fish captured was high among spawners but varied among sampling programs (42% in fall trap nets, 70% in fall gill nets, and 88% in summer gill nets). A strong year class (1997) could be tracked from 2001 to 2005. Few fish were captured from early (< 1996) or later (1999–2002) year classes. Possible explanations for low natural recruitment during these later years include declining spawning habitat quality caused by low water levels and/or invasion of non-native mussels ( Dreissena spp.) and/or direct or indirect effects of alewife ( Alosa pseudoharengus).

Population Size and Relative Abundance of Adult Alabama Shad Reaching Jim Woodruff Lock and Dam, Apalachicola River, Florida

AbstractWe estimated the population size of migrating Alabama shad Alosa alabamae below Jim Woodruff Lock and Dam in the Apalachicola River (located in the central panhandle of northwestern Florida) using mark–recapture and relative abundance techniques. After adjustment for tag loss, emigration, and mortality, the population size was estimated as 25,935 (95% confidence interval, 17,715–39,535) in 2005, 2,767 (838–5,031) in 2006, and 8,511 (5,211–14,674) in 2007. The cumulative catch rate from boat electrofishing averaged 20.47 Alabama shad per hour in 2005, 6.10 per hour in 2006, and 13.17 per hour in 2007. The relationship between population size (N) and electrofishing catch per unit effort (CPUE) was modeled by the equation N = −9008.2 + (electrofishing CPUE × 1616.4). Additionally, in 2007 the hook‐and‐line catch rate averaged 1.94 Alabama shad per rod hour. A predictive model relating the population size and hook‐and‐line CPUE of spawning American shad A. sapidissima was applied to Alabama shad hook‐and‐line CPUE and produced satisfactory results. Recent spawning populations of Alabama shad in the Apalachicola River are low relative to American shad populations in other southeastern U.S. rivers.

Facultative semelparity in capelin Mallotus villosus (Osmeridae)-an experimental test of a life history phenomenon in a sub-arctic fish

Two alternative reproductive modes are present in fishes and reflect the age-specific mortality encountered through ontogenesis. Life-history hypotheses suggest that semelparity (i.e. death after a single reproductive event) evolves when the ratio of juvenile to adult survival is relatively high. Conversely, a relatively low ratio of juvenile to adult survival will favour iteroparity (i.e. death after two or more reproductive events). Fisheries management associates capelin ( Mallotus villosus) spawning with mass mortality and semelparity even though life history models developed for this species suggest that females may follow an iteroparous trajectory. Capelin may spawn either inter-tidally on the beach or offshore in deeper, ocean waters but post-spawning survival and potential iteroparity has been notoriously difficult to assess in natural populations. Through a series of aquarium experiments we tested post-spawning survivability in a beach spawning and an ocean spawning population. The findings demonstrate that capelin which spawn offshore are absolute semelparous (death of both genders) while beach spawning capelin are iteroparous irrespective of sex. Beach spawning capelin regenerated ripe gonads from one spawning season to the next and provides the first conclusive evidence that capelin is physiologically capable of an iteroparous reproductive mode. The potential physical and biological processes which generate certain reproductive patterns in capelin are summarized and discussed in relation to life history hypotheses. We suggest that capelin is a facultative semelparous species in which dynamic changes within the semelparity-iteroparity continuum may occur as a result of subtle interactions between the spawning habitat, physical forcing, and predatory pressure.

Gametic conflict versus contact in the evolution of anisogamy

Anisogamy refers to gametes that differ in size, and characterizes the difference between males and females. The evolution of aniosgamy is widely interpreted as involving conflict between gamete producers with small sperm parasitizing on the investment made by the eggs. Using a population genetic model for evolution at a locus that codes jointly for sperm and egg sizes of a hermaphrodite, we show that the origin of anisogamy in an externally spawning population need not involve conflict between gamete producers. Gamete size dimorphism may be an adaptation that increases gamete encounter rates when large zygotes are selected, and we show this in a mechanistically general individual selection model. We use the Vance survival function without specific allometric assumptions to model the zygote fitness dependence on its size, and hence obtain ecological and life-history correlates of isogamy and anisogamy, which we successfully compare with data from Volvocales.

Enhancing the Recovery of Depleted Tripneustes gratilla Stocks Through Grow-Out Culture and Restocking

Grow-out culture in sea cages and restocking were undertaken to help rebuild the spawning population of Tripneustes gratilla in Bolinao, Philippines. Higher population densities and incidence of recruits in 2004–2006, as well as steady increase in the catch per unit effort of gatherers, indicate that the sea urchin population is recovering. Growth of reseeded, hatchery-produced sea urchins in two sites was high and comparable to those in grow-out cages. However, natural mortalities were very high (91–99%). Good growth, high survivorship, and potential reproductive output of sea urchins in grow-out cages, aside from immediate socio-economic benefits, demonstrate that grow-out culture is a cost effective option for reestablishing effective spawning populations. Higher recruitment success in Lucero, compared to other sites, may be attributed to local favorable biophysical conditions and to maintenance of an effective spawning population due to enforcement of marine sanctuary rules, size regulation, and the presence of broodstock cages. Results suggest that the establishment of a network of marine protected areas in tandem with grow-out culture may be strategic in enhancing the recovery of depleted populations by maintaining larval exchange to sustain the productivity of sea urchin fishery stocks along NW Luzon.

Genetic Assessment of Lake Sturgeon Population Structure in the Laurentian Great Lakes

AbstractMany populations of lake sturgeon Acipenser fulvescens have decreased in size throughout the Great Lakes basin. To implement management strategies such as stocking, it is important to understand the genetic structure of lake sturgeon spawning populations. Lake sturgeon from 27 spawning locations (25 from the Great Lakes basin and 2 from the Hudson Bay drainage) were analyzed using 12 microsatellite loci. Population structure was detected at different spatial scales. At the largest scale, consistent genetic breaks were observed among three clusters of spawning populations: (1) Hudson Bay–northern Lake Superior, (2) southern Lake Superior, and (3) the rest of the Great Lakes. These clusters were identified using a Bayesian approach that does not define the populations a priori. Within each of the three clusters, sublevels of genetic structure were detected. These sublevel clusters accounted for 8.82% of the genetic variation (P &lt; 0.000), while differences among populations within the clusters accounted for 3.72% of the genetic variation (P &lt; 0.000). At the smallest scale, significant genetic differentiation was detected between most sampled locations through pairwise genetic differentiation index (FST) tests and pairwise contingency tests. Lake sturgeon showed greater genetic differentiation in Lake Superior than elsewhere, which could be due to the lake's bathymetry. The lower genetic resolution observed elsewhere in the Great Lakes could be due to more recent colonization events. The results can be used to delineate management units and to select appropriate donor populations for supplementation or reintroductions.

Population assessment and movement patterns of lake sturgeon (Acipenser fulvescens) in the Manistee River, Michigan, USA

Summary Lake sturgeon (Acipenser fulvescens) population characteristics and migration patterns were evaluated in the Manistee River system, Michigan. Sturgeon (n = 102) were captured using gillnets, tagged and released in the system between 2001 and 2005. Biological data (weight, length, age, sex and spawning status) were collected to calculate length–weight relationships and relative condition factor (Kn), determine age structure, and estimate the annual spawning population size. Sturgeon were also implanted with radio and sonic transmitters, and migration patterns of 22 sturgeon were determined. The weight–length equation for sturgeon in the Manistee River system was log10 W = 3.17log10TL−5.52 and did not differ by sex. Kn equaled 0.72 and did not differ by sex or spawning status. Ages ranged from age 5 to age 54. Sexually mature male and female sturgeon were captured over the course of the study, and the size of the spawning population ranged from 21 to 66 spawners. Sturgeon migration movements up and down the Manistee River varied with date, water temperature, and discharge. The sturgeon appeared to use two different spawning sites in the Manistee River. The Manistee River system supports a remnant lake sturgeon population; the presence of a wide range of age classes and availability of a limited number of suitable spawning sites suggest continued recruitment to the population.

Weak population differentiation in northern European populations of the endangered anadromous clupeid Alosa fallax

Examination of genetic structure among different spawning populations of the endangered twaite shad Alosa fallax showed statistically significant but weak differentiation estimated using nine microsatellite loci. Results point to substantial gene flow among the majority of individual estuary/river spawning locations, and no evidence that habitat disruption has led to increased local genetic drift.