Assessment of lake sturgeon (Acipenser fulvescens) recruitment in a regulated spawning tributary of Rainy Lake,Ontario

Continued study of the relationship between lake sturgeon (Acipenser fulvescens) recruitment and hydroelectric dams and operations, in a variety of river systems and habitat types is needed to improve the ability to predict and monitor impacts of the hydroelectric industry on this species. Herein, we present results of a juvenile lake sturgeon study aimed at addressing concerns over an inferred lack of recruitment resulting from spawning downstream of a hydroelectric generating station (HGS). Two years of sampling (2015 and 2016) were conducted in five sections of a 41 km long reach of the Seine River, Ontario, a lake sturgeon spawning tributary of Rainy Lake. Using an established gillnetting method, deepwater habitat was targeted to capture juvenile lake sturgeon to assess relative abundance, recruitment (cohort strength), and growth. Deepwater habitat, defined as water depths >6 m in this system, comprised only 2.1% of the wetted area in this study area. Within these habitats, a total of 331 lake sturgeon capture events were observed over the 2-years study period. The majority of the lake sturgeon catch (85%) was comprised of age-0 to age-5 individuals (both sampling years combined). Although inter-annual variation in cohort strength was apparent, each cohort between 2006 and 2016 was represented. The spatial distribution of cohorts varied among river reaches with younger individuals (age-0 and age-1) occupying reaches proximal to the Sturgeon Falls HGS, and larger, older individuals (age-2 to age-5) occupying reaches further downstream. The rarity of age-6+ individuals can likely be explained by ongoing downstream redistribution of juveniles over time, out of the Seine River and into Rainy Lake. Growth of juvenile lake sturgeon captured in the Seine River was above average relative to conspecifics from other rivers in the Hudson Bay drainage. Unfortunately, baseline data sets required to facilitate comparisons of contemporary (post-construction Sturgeon Falls HGS) versus historical (i.e. pre- Sturgeon Falls HGS) lake sturgeon recruitment, or to evaluate the influence of the Seine River Water Management Plan (2004) on lake sturgeon recruitment, are lacking. However, juvenile Lake Sturgeon are more abundant in this system than what had been surmised based on recent studies which implemented random sampling. Results indicate that juvenile lake sturgeon may reside in spawning tributaries for several years (age-0 to age-5) prior to seeking alternate habitats and highlights the value of targeted sampling (i.e. by depth) along the flow axis of rivers downstream of spawning areas when assessing lake sturgeon recruitment patterns.     

Assessment of lake sturgeon spawning stocks using fixed-location, split-beam sonar technology

Fixed‐location, split‐beam sonar technology was used successfully to identify adult lake sturgeon Acipenser fulvescens as they moved upstream and downstream for spawning in the Sturgeon River, Michigan, May–June 2004. A Hydroacoustic Technology Inc. Model 241 Split‐Beam Echo Sounder operating at 200 kHz and a single 4 × 10° elliptical‐beam transducer with a near field range of 1.7 m set perpendicular to the river flow was used. Data collected from migrating lake sturgeon included direction of movement, swimming speed, range from transducer, time and date of passage, and target strength. The spawning population of lake sturgeon was estimated to be at 350–400 fish, with almost equal numbers of fish seen moving upstream as downstream. Most fish were recorded moving within the mid‐section of the river, 1.5–1.65 m deep, and swimming speeds upstream were slower than those for downstream moving fish. These results show that spilt‐beam sonar can be applied to lake sturgeon assessments, without the stress of actually handling these large, pre‐spawning fish.     

Seasonal variation in the diet of juvenile lake sturgeon,Acipenser fulvescens,Rafinesque, 1817, in the Winnipeg River,Manitoba, Canada

The lake sturgeon, Acipenser fulvescens, is a threatened species across most of its range. To understand any potential shifts in diet across season or habitat, stomach contents were examined from juvenile lake sturgeon caught in the Winnipeg River, Manitoba, Canada. This information will aid in assessment of environmental impacts and conservation initiatives for this threatened species. From 2006 to 2008 gut contents were collected from juvenile lake sturgeon using a non‐lethal gastric lavage methodology. Juvenile lake sturgeon were sampled from four discrete deep water habitat types (13.7–27.4 m depths), during the months of May, June, July and October. In total, 13 066 prey items belonging to 14 prey groups were collected from 345 juvenile lake sturgeon (251–835 mm TL). Overall, juvenile lake sturgeon consumed a low diversity of organisms; insect larvae from three invertebrate orders, Trichoptera, Diptera and Ephemeroptera, accounted for 97.4% of the total numeric abundance of prey items recovered. A relationship between size of juvenile lake sturgeon and prey quantity or type was not observed. Diet of juvenile lake sturgeon varied in relation to season, with Diptera (77.6%) being the most abundant prey in May, Trichoptera the most abundant in June (n = 3,056, 60.4%) and July (n = 2,055, 52.6%). During October, 96% of stomachs examined were empty. In terms of habitat type, the standardized abundance of invertebrate prey items was highest in deep water habitats characterized by medium water velocity (depths > 13.7 m) and coarse substrate (particle sizes > 0.063 mm) in May and June when compared to deep water habitats characterized by low water velocity (<0.2 m.s^?1) and fine substrate (particle sizes < 0.063 mm). However, in July, the opposite was observed and prey abundance in juvenile lake sturgeon stomachs decreased with increasing particle size. Results suggest a high degree of dietary overlap among juvenile lake sturgeon from multiple size/age classes occupying deep‐water habitats of the Winnipeg River.     

Spatiotemporal changes in juvenile lake sturgeon abundance in a large river

Monitoring trends in a long-lived species such as lake sturgeon (Acipenser fulvescens) has it challenges. Targeting the correct life stage to monitor can provide different and contrasting results. Early life stages experience high variable mortality and are often not a good predictor of population trend. Juvenile lake sturgeon (i.e., 5–10 years) experience high survival and could be a good life stage to monitor for assessing population trends. A structured, randomized gillnetting program, Broad-scale Monitoring, which was selective to juvenile lake sturgeon, was conducted over three cycles (i.e., 5 + years apart) in three contiguous Ottawa River reaches supporting lake sturgeon. In this study, we assessed spatiotemporal changes in juvenile lake sturgeon abundance among cycles, among and within the three river reaches. Density rasters based on catch records of lake sturgeon spatially were created using multilevel B-splines. Spatial differences in abundance among cycles was determined by obtaining the difference between the rasters. Three cycles of Broad-scale Monitoring sampled 334 lake sturgeon at a mean CPUE of 0.90 (0.12 SE) sturgeon • gang⁻¹ and a mean total length 673 mm (115 SD) from all three reaches. The relative abundance of juvenile lake sturgeon did not significantly vary among sample cycles, however, CPUE varied within reaches among cycles. There was a spatiotemporal change in density with a decrease in the lowest reach whereas juvenile lake sturgeon density increased the most in the upper reach. The approach used in this study has the potential to monitor spatiotemporal changes in juvenile lake sturgeon abundance populations and may prove effective when assessing rehabilitation or fisheries management efforts.     

Habitat utilization of juvenile lake sturgeon, Acipenser fulvescens, in a large Canadian river

An increased understanding of the juvenile life history stage of the lake sturgeon, Acipenser fulvescens , has been recognized as a key requirement for improving conservation efforts for this once abundant species. The objectives of the current study were to develop an effective methodology for capturing juvenile lake sturgeon in a large riverine environment; to describe the physical habitat characteristics (depth, water velocity and substrate) associated with the areas where juvenile lake sturgeon were captured; and to determine basic population parameters (length, body mass and condition factor) for juvenile lake sturgeon captured in those areas. Gillnets (mesh sizes 25–108 mm) were used to sample the Winnipeg River, a large river in the northern extent of the species range, from 12 June to 6 November 2006. A total of 2154 juvenile (<530 mm FL) lake sturgeon were captured, which represented over 74% of the total fish catch. Moderate (51–108 mm) and small (25 mm) mesh gill nets were found to be efficient for sampling juvenile lake sturgeon, with the former capturing a wider range of sizes and the latter capturing fewer fish but resulting in decreased mortality. Juvenile lake sturgeon were captured at high densities in discrete areas characterized by water depths >13.7 m, detectable water velocities >0.20 m s⁻¹, and various substrate types.     

Juvenile lake sturgeon monitoring and determinants of year‐class strength in the Rupert River,mid‐northern Québec,Canada

In 2007, Hydro‐Québec began the construction of the Rupert Diversion in conjunction with the Eastmain‐1A and Sarcelle powerhouses. The partial diversion of the Rupert River became operational in 2009. Mitigation measures to preserve lake sturgeon (Acipenser fulvescens) habitat downstream of the diversion include an instream flow, weir and spurs to maintain water levels, and fish passage channels and spawning grounds. An environmental follow‐up was done in the reduced‐flow section of the Rupert. The baseline status was established from 2007 to 2009 and follow‐up studies were conducted from 2010 through 2012, and in 2014 and 2016. Besides presenting results from Hydro‐Québec's environmental monitoring, analyses were performed to search for determinants of year‐class strength. The results of the lake sturgeon monitoring activities indicate that the abundance of juveniles ≤8‐year‐old in the reduced flow section of the river remained similar or increased. Although larval production increased in post diversion conditions, cohort strength tended to decrease as did juvenile growth. Year‐class strength was positively correlated with spring and summer flow. Also, a significant, strong negative correlation was found between estimated larval abundance and water temperature during larval drift.     

Adult lake sturgeon (Acipenser fulvescens Rafinesque, 1817) occurrence in the Muskegon River system,a Lake Michigan drowned river mouth,USA

Recent advancements in telemetry have allowed managers and researchers to conduct comprehensive studies on the movement ecology of lake sturgeon (Acipenser fulvescens), a species of conservation concern in most of the Laurentian Great Lakes basin. In Michigan waters of Lake Michigan, drowned river mouth systems (a protected lake-like habitat that connects a river to lake) support 4 of 11 remaining lake sturgeon populations. One of those remnant populations is supported by the Muskegon River, a drowned river mouth system consisting of both Muskegon Lake and the Muskegon River. The objectives of this 6-year telemetry study were to determine whether adult lake sturgeon occupied the Muskegon River system outside of the spawning season (defined as March to July), to quantify their use of the system annually, and to identify and characterize patterns in occurrence. A total of 21 adult lake sturgeon implanted with acoustic transmitters were passively monitored throughout the year during 2012–2017. Eighty-two percent of tagged fish at large were detected ≥1 day in the Muskegon River system annually, and tagged lake sturgeon were frequently detected during both spawning and non-spawning time periods. Residency index (i.e., no. detection days/365 days) values indicated that adult lake sturgeon were not only detected throughout the year but that they occupied the Muskegon River system for an average of 130 days each year (residency index = 0.36 ± 0.05 SE) during our most spatially intensive acoustic monitoring in 2016–2017. Additionally, 24% of tagged lake sturgeon were primary residents (i.e., residency index >0.5) of the Muskegon River system in both years. Adult lake sturgeon followed 1 of 3 patterns of occurrence based on individual detection histories, and those patterns varied temporally and by the relative amount of use (i.e., high, medium, and low). Our findings build on previous research that found drowned river mouth systems in Lake Michigan can be important nursery habitats for juvenile lake sturgeon by showing that these habitats also can be used extensively by adult lake sturgeon throughout the year.     

Post‐release dispersal and spawning movements of a translocated lake sturgeon (Acipenser fulvescens,Rafinesque 1817) population in the Mattagami River,Ontario

Species translocations are increasingly being used as a management tool to mitigate population losses due to such factors as habitat degradation and fragmentation, but post‐introduction follow‐up is relatively sparse. Post‐translocation telemetry can assess success by identifying activity, emigrations, survival, habitat usage, and reproductive events, aiding in the continued management of translocated populations and informing future efforts. This study assessed movement of translocated adult lake sturgeon (Acipenser fulvescens) immediately post‐release and a decade later, and tested for associations between environmental variables and spawning movements. Prior to their translocation in 2002, 13 of 51 adult lake sturgeon were surgically implanted with radio telemetry tags and tracked for 1 year. In 2011 and 2013, eight additional adults were captured within the reintroduction site and implanted with radio‐tags. Six of the 13 sturgeon tagged in 2002 dispersed downstream over a dam during the early post‐release period. In spring 2014, tagged adults were tracked to the spillway at the release area's inflow, and spawning was confirmed by larval captures. Movement data for tagged adults differed between the two tracking periods, showing marked differences in behaviour over time. Water velocity was correlated with upstream and downstream spawning movements, with water temperature also correlated with downstream movement. Research regarding post‐translocation movement and dispersal provides insight on behavioural responses following translocation, and may improve outcomes by informing future efforts.     

Migration of green sturgeon, Acipenser medirostris, in the Sacramento River

Adult green sturgeon, Acipenser medirostris, were collected in San Pablo Bay, California, and surgically implanted with ultrasonic acoustic tags from 2004 to 2006. An array of automated acoustic monitors was maintained in the Sacramento River to record movements of these fish. We presumed movements to known spawning areas (based on previous green sturgeon egg collections) or areas with potential spawning habitat (characterized by substrate, flow, and temperature criteria) represented a “spawning migration.” Three separate annual “spawning migrations” were recorded involving 15 individuals. The majority of the Sacramento River migrants entered the system in the months of March and April. Two different patterns of “spawning migration” and out-migration were observed. Six individuals potentially spawned, over-summered and moved out of the river with the first fall flow event. This is believed to be the common behavior of the green sturgeon. Alternatively, nine individuals promptly moved out of the Sacramento River before 1 September, and any known flow or temperature cue. Some green sturgeon appeared to be impeded on their upstream movement by the 15 May closure of the Red Bluff Diversion Dam, and at least five passed under the dam gates during downstream migration. A delay in the closure of the Red Bluff Diversion Dam would likely allow upstream passage of spawning green sturgeon, further, the potential mortality affects of downstream passage beneath the Red Bluff Diversion Dam should be assessed. Specific protection should be also given to the large aggregation of green sturgeon located in the reach of the Sacramento River adjacent to the Glen Colusa Irrigation District pumping facility.     

Seasonal migrations and reproductive patterns in the lake sturgeon, Acipenser fulvescens, in the vicinity of hydroelectric stations in northern Ontario

This study was conducted in order to evaluate seasonal migratory behaviour and reproductive pattern of lake sturgeon in a confined region of the Mattagami River system in northern Ontario where river flow is regulated by hydroelectric works. Radio tracking and the systematic sampling of lake sturgeon using gill nets indicated that the distribution of fish throughout the study site varied on a seasonal basis. This distribution was related to the migration of individuals to potential spawning sites in the spring, a post-spawning dispersal to feeding areas and late summer migration to an area of concentration on the Groundhog River which is a tributary of the Mattagami River. There was a high proportion of fish (about 50%), within the size range of reproductively active fish, found in the vicinity of suitable spawning habitat during early May. Measurement of the gonadosomatic index (GSI) and plasma sex steroid hormone levels revealed a divergent pattern of reproductive development between the sexes. Female sturgeon exhibited a prolonged period of ovarian regression following spawning. Resumption of ovarian development was not evident until September and was characterized by an increased GSI and plasma levels of testosterone and 17β-estradiol. In contrast, male lake sturgeon began testicular recrudescence within one month of spawning with the GSI reaching prespawning levels by September; reproductive hormones were at prespawning levels by the end of June. It seems that hydroelectric works has complex effects on sturgeon in the Mattagami system. The extensive migratory behaviour of lake sturgeon within the study area make it prone to impingement or entrainment whereas the altered river flow appears to enhance reproductive development. This revised version was published online in August 2006 with corrections to the Cover Date.     

Coral community responses to declining water quality: Whitsunday Islands,Great Barrier Reef,Australia

A five-year period (2002–2006) of below-median rainfall followed by a six-year period (2007–2012) of above-median rainfall and seasonal flooding allowed a natural experiment into the effects of runoff on the water quality and subsequent coral community responses in the Whitsunday Islands, Great Barrier Reef (Australia). Satellite-derived water quality estimates of total suspended solids (TSS) and chlorophyll-a (Chl) concentration showed marked seasonal variability that was exaggerated during years with high river discharge. During above-median rainfall years, Chl was aseasonally high for a period of 3 months during the wet season (February–April), while TSS was elevated for four months, extending into the dry season (March–June). Coinciding with these extremes in water quality was a reduction in the abundance and shift in the community composition, of juvenile corals. The incidence of coral disease was at a maximum during the transition from years of below-median to years of above-median river discharge. In contrast to juvenile corals, the cover of larger corals remained stable, although the composition of communities varied along environmental gradients. In combination, these results suggest opportunistic recruitment of corals during periods of relatively low environmental stress with selection for more tolerant species occurring during periods of environmental extremes.     

Seasonal movement, dispersal, and home range of Northern Snakehead Channa argus (Actinopterygii, Perciformes) in the Potomac River catchment

Knowledge of the movement behaviour and dispersal ability of non-native species can aid in their management by informing risk assessments and the development of control strategies. To improve understanding of the seasonal movement and dispersal behaviour of Northern Snakehead (Channa argus), we implanted 49 fish in the Potomac River with radio tags and tracked movements from October 2006 to 2007. In addition, we tested the hypotheses that activity level, dispersal ability, and home range size varied with fish size. Home range was calculated for 24 fish. Of these, 19 exhibited stable home ranges averaging 1.2 km² in size. Thirteen fish (31% of survivors) dispersed an average distance of 18 km between 30 April and 7 June, mostly upstream (92%) and across the main river channel. Fish moved greater distances during the pre-spawn season compared to the spawning season. There was no relationship between fish length and any behavioural measure. Upstream dispersal was restricted by barriers such as dams; therefore, Northern Snakehead can likely disperse greater distances than observed here. Our observations demonstrate the invasiveness of Northern Snakehead by showing that a large portion of adults dispersed over considerable distances, suggesting spread may be rapid in large, open freshwater systems.     

Spatial analysis of pallid sturgeon Scaphirhynchus albus distribution in the Missouri River, South Dakota

Movement and distribution of the endangered pallid sturgeon Scaphirhynchus albus has generally been documented using radio telemetry. However, because of the time and cost involved in tracking individual fish (i.e. small sample size), it is often difficult to evaluate spatial distribution of groups of fish over long time periods (> 3 years). Standardized sampling for pallid sturgeon, which relies on a variety of gear types, has been conducted on the Missouri River downstream of Fort Randall Dam annually since 2003. Using catch data from 2003 to 2006, the spatial distribution of juvenile pallid sturgeon was evaluated using spatial scan statistics. Presence/absence of pallid sturgeon was summarized from a variety of gear and distribution patterns were analyzed based on: (i) each gear per season, (ii) all gear pooled per season, (iii) each gear pooled across seasons, and (iv) pooled data from all gear and years combined. Three significant clusters of pallid sturgeon captures were identified when all gear and years were pooled. Distribution patterns identified using data from summer trammel nets agreed well with the overall pooled dataset and could be used to identify areas with a high probability of pallid sturgeon presence. This methodology can be used to identify areas where pallid sturgeon are likely to occur, thus improving sampling efficiency for monitoring vital statistics for this endangered species. Moreover, this approach could be applied to other reaches of the Missouri River using existing data from the Pallid Sturgeon Monitoring and Assessment Program. Once identified, these areas could then be evaluated to better understand the habitat requirements of pallid sturgeon.     

The lake sturgeon,Acipenser fulvescens,in the Menominee River,Wisconsin-Michigan

Synopsis The Menominee River is the boundary between the Upper Peninsula of Michigan and northeastern Wisconsin. It contains one of the few fishable lake sturgeon populations remaining in either state. Two sections of the river harbor naturally reproducing sturgeon stocks. Dams at either end of these sections curtail upstream movement of fish; however, some sturgeon move downstream over the dams. Surveys conducted in 1969 and 1970 and again in 1978 and 1979 intensively studied the sturgeons in a 42 km stretch of the river. Mark and recapture estimates of the number of sturgeon longer than 25 cm in this section ranged from 1884 to 2865. The number of fish longer than 107 cm ranged from 185 to 243. An estimate of 2834 sturgeon between 25 and 165 cm was made on a different 34 km stretch in 1979. Censuses on the hook and line fishery in 1969 and 1970 estimated sturgeon harvests of 59 and 48 fish, respectively. In 1974, the size limit was raised from 107 to 127 cm. Harvests of these larger fish were estimated at 19 and 41 in 1981 and 1982, respectively. Some other characteristics of the sturgeons and the fishery on the Menominee are also included.     

Seasonal variations in growth, condition and gonads of Dormitator latifrons (Richardson) in the Chone River Basin, Ecuador

Growth in length, condition, and gonads of a food fish, Dormitator latifrons , were studied in the Chone River basin, Ecuador, in 1981. The river was bordered by floodplains in the upstream freshwater zone, and by mangrove swamps and shrimp farms in the downstream estuarine zone. The climate was marked by wet (January to April) and dry (May to December) seasons. During the dry season, an earth dam in the river prevented movement of water and fish between upstream and downstream zones. At the end of the dry season, most of the upstream floodplains were dry, and the main fish refuges were in downstream areas in deep pools in the river upstream. During the floods, fish migrated from downstream areas towards upstream floodplains. Growth rates and condition increased when water levels were high or salinity was low and decreased when water levels were low or salinity was high. Seasonal changes in gonads and abundance of juveniles indicated that reproduction occurred during the floods, but there was some reproduction in the dry season. Reproduction occurred in upstream and downstream zones and appeared to be stimulated by a complex of factors, including water levels, currents and salinity. The yield in flood plain sites was estimated as c. 115 kg ha⁻¹ in 1981.     

Riverine life history of the amphidromous goby Sicyopterus japonicus (Gobiidae: Sicydiinae) in the Ota River, Wakayama, Japan

To understand the riverine life history of the amphidromous goby, Sicyopterus japonicus, studies were conducted in the Ota River, Wakayama, Japan. They were distributed from 3 to 23 km upstream from the river mouth, and abundance was higher in the middle reaches than in the upper and lower reaches. Fish were not observed in rapids during winter, suggesting a seasonal change of habitat. Body length ranged from 24 to 120 mm SL. Both females and males ranged from 1 to 6 years old, and males had larger asymptotic length than females. Condition factor showed two peaks in July and November, which appeared to correspond to the spawning season and preparation for over wintering. Gonad somatic index increased in summer with a peak in August indicating a summertime spawning season that was confirmed by collections of the newly hatched larvae migrating downstream. Eggs of 0.5 mm diameter were attached to stones and newly hatched larvae made continuous vertical movements of sinking and upward swimming and the distance of each movement was longer in freshwater than in seawater. The newly hatched larvae were collected at nighttime (19:00–24:00) mainly in August. Those larvae were very small (mean: 1.4 mm TL) with a yolk sac and no eye pigmentation. Low wintertime temperatures are likely an important determinant of the spawning and recruitment seasons and seasonal changes of activity of this species that lives at much higher latitudes than all other species of the subfamily.     

Distribution, relative abundance and movements of pallid sturgeon in the free-flowing Mississippi River

A multiyear study of pallid sturgeon distribution and relative abundance was conducted in the lower and middle Mississippi river (LMR and MMR, respectively). The LMR and MMR comprise the free‐flowing Mississippi River extending 1857 river kilometers (rkm) from its mouth at the Gulf of Mexico upstream to the mouth of the Missouri River. A total of 219 pallid sturgeon and 6018 shovelnose sturgeon was collected during the periods 1996–1997 and 2000–2006. Trotlines baited with worms were the primary collecting gear. The smallest pallid sturgeon captured on trotlines was 405 mm FL and the largest was 995 mm FL. Mean size of pallid sturgeon was statistically smaller in the Mississippi River below the Atchafalaya River near Baton Rouge, LA (621 mm FL). Mean abundance (catch per trotline night) of pallid sturgeon was highest at water temperatures around 10°C. There was a latitudinal trend in mean abundance of pallid and shovelnose sturgeon, but the pattern differed between species. Pallid sturgeon abundance was statistically (P < 0.05) higher (0.3 fish per trotline night) in the lower reach between the Atchafalaya River and New Orleans (rkm 154–507), and at the Chain of Rocks (COR), a low water dam near the mouth of the Missouri River. Pallid sturgeon abundance between these two locations was statistically the same (0.12–0.23). Shovelnose sturgeon abundance increased going upstream, but was disproportionally higher at the COR (22 fish per line compared with <6 fish per line in other reaches). Overall, the ratio between pallid and shovelnose sturgeon varied from a high of 1 : 6 at the lower reach, and gradually decreased upstream to a low of 1 : 77 at the COR. Based on differences in sturgeon abundance, size and habitat characteristics, the free‐flowing Mississippi River can be divided into two reaches in the MMR (i.e. COR is a separate location), and four reaches (i.e., including the Atchafalaya River) in the LMR where management goals may differ.     

Fish recruitment, dispersal, and trophic interactions in a heterogeneous lotic environment

I examine how dispersal of juvenile creek chubs (Semotilusatromaculatus) from beaver ponds into adjacent stream environments interacts with temporal abiotic variability to influence fish foraging, growth, and long-term persistence in the lotic ecosystem. Minnow trapping in upstream and downstream beaver ponds, along with weir traps used to monitor directional movement, indicated that most chubs colonized the stream from the downstream beaver pond. Large annual fluctuations in density of age 0 creek chubs occurred in the stream over a 10-year sampling period. Multiple regression analysis indicated that stream temperature, precipitation, and the density of reproductive creek chubs were not correlated with summer density of age 0 chubs in the stream. The factor most strongly associated with increased density of age 0 creek chubs was creation of the downstream beaver pond during the 6th–7th years of the study, suggesting dispersal from the pond was the primary factor determining age 0 fish density in the stream. Most individuals in the strong year classes neither persisted in the stream through their first winter nor resulted in an increased abundance of older age classes in later years. Comparison of age 0 fish density in summer to the proportion of fish surviving to age 1 in spring suggested that overwinter mortality was density dependent. Furthermore, a comparison of the size structure for age 0 individuals in summer to age 1 individuals the following spring indicated that winter mortality was size dependent. Experiments in an artificial stream adjacent to the natural channel revealed that fish growth was strongly density dependent, decreasing as fish density increased across both spring and summer, and elevated and low discharge. The decline in invertebrate prey captured by the fish and the subsequent decline in fish growth appeared to be particularly pronounced under low discharge in summer. Changes in juvenile creek chub density had no significant effect on benthic insect or crustacean abundance, suggesting that exploitative competition for limited invertebrate drift resources was a more important cause of density- dependent growth than depressed local benthic invertebrate abundance. These results suggest that lotic regions adjacent to beaver ponds act as potential reproductive “sinks” for dispersing juveniles confronting seasonal and flow-mediated restrictions on resource acquisition and growth, and the occurrence of seasonal bottlenecks to their survival, especially harsh winter conditions. Received: 9 September 1996 / Accepted: 8 August 1997     

Using passive sonic telemetry methods to evaluate dispersal and subsequent movements of hatchery-reared white sturgeon in the Kootenay River

A total of 35, age 1 juvenile Kootenay River white sturgeon ( Acipenser transmontanus ), were fitted with sonic tags in 2005 and released as part of larger hatchery release groups at five sites to evaluate dispersal and subsequent movements (seven tags per site). Juvenile sturgeon released at three locations within the deep, low gradient reach (typical gradient of 0.02 m km⁻¹ and velocities of <0.4 m s⁻¹) of the Kootenay River below Bonners Ferry, ID showed substantial dispersal both up and downstream; however, downstream redistribution was more common. White sturgeon from all three release locations overlapped during dispersal, with 9% of tagged fish moving from river release sites into Kootenay Lake. The three hatchery release locations in this low gradient reach produced good dispersal of hatchery progeny into available habitats. Tagged fish released above Bonners Ferry in the shallow, higher gradient reach (typical gradient of 0.6 m km⁻¹, and velocities >0.8 m s⁻¹) at two additional sites all moved downstream of the gradient break at Bonners Ferry, ID into the lower gradient reach within 2 months of release. In total, 93% of these tagged fish relocated to the low gradient section within 25 days of release, with some fish undertaking this movement within 1 day. In general, age 1 hatchery release juveniles were mobile and capable of substantial movements.     

Using stable isotope analysis with telemetry or mark-recapture data to identify fish movement and foraging

Information about animal movements has often been inferred from stable isotope analysis (SIA), but is dependent on animals assimilating site-specific isotopic signatures via diet. This potential weakness in ecological interpretation can be overcome by using other investigative tools that provide precise information about individual movement patterns. In this paper, we demonstrate the value of combining SIA with telemetry or mark-recapture data from trapping, electrofishing and remote detection of individuals to study the movement and feeding ecology of fishes in different habitats. In a fjord lake system in Newfoundland, Canada, juvenile Atlantic salmon delayed downstream migration (smolts) or actively moved into a large lake (parr) where they foraged for periods reflecting different life history strategies. In the Miramichi River (New Brunswick, Canada), SIA provided evidence of distinct foraging habitats (tributary versus large river). By tracking fish implanted with passive integrated transponder (PIT) tags, we distinguished between movements related to foraging versus seeking cool water refugia during high temperature events. Finally, site fidelity and limited mobility of slimy sculpin, a small benthic fish, was established where δ¹³C in muscle tissue showed a progressive enrichment downstream and where a median displacement of <10 m was estimated for sculpin tagged with PIT tags. Technological improvements have permitted non-destructive tissue sampling of wild fishes for SIA, and the tagging and remote detection of animals smaller than was previously possible. These advancements and the combination of investigative tools promise new insights into animal ecology.