Potential Spawners Research Articles

Minimum legal size of commercially important groupers in the Coral Triangle Sulawesi Sea, Indonesia

Major challenges facing grouper fisheries in Kwandang Bay within the Coral Triangle include declines in potential spawners and as well as in the abundance of juvenile fish. One measure that can be taken to maintain valuable fisheries stocks such as groupers is to regulate the minimum legal size (MLS). The aim of this research was to identify and analyse the mean size at first maturity (Lm50) as a basis for setting an MLS for three grouper species of commercial importance. A total of 525 grouper specimens (307 Variola albimarginata, 90 Variola louti, and 128 Plectropomus leopardus) were collected from January to October 2022 from grouper traders, traditional markets, and the Kwandang Fishing Port. The Lm50 for each species was calculated using the Spearman-Karber formula. The Kwandang Bay catch was dominated by immature juvenile fish and the size class contributing the most individuals was below the Lm50 for all three grouper species. The MLS should be at least 32 cm for V. albimarginata, 33 cm for V. louti and 35 cm for P. leopardus in order to enable sufficient fish to spawn at least once, increase the number of spawners, and thereby maintain stock abundance.

Overestimating management progress—modelled vs. monitored silver eel escapement in a North Sea draining river

Abstract The success of European efforts towards the recovery of the European eel (Anguilla anguilla) population will rely on accurate assessments of local stock status for the implementation of conservation measures. Yet, direct and continuous monitoring of the escapement of potential spawners (“silver eels”) is unfeasible in most habitats. Therefore, population models are widely used to estimate local silver eel escapement, but require input information on recruitment, demographic characteristics, and mortalities that are often estimated with great uncertainties. We conducted a combined mark–recapture and acoustic telemetry study across two migration seasons to quantify the actual silver eel escapement in a sub-catchment of the German river Ems. Results were compared with predictions from the demographic model used to provide stock parameters in Germany according to the EU eel-regulation. Mark–recapture results suggested an annual female silver eel escapement of ∼15–17 tons, while the demographic model predicted 90–98 tons, indicating a considerable overestimation. Our results suggest that realistic prediction of silver eel escapement is hardly feasible without high-quality input information and highlight the need for site-specific model calibrations against monitoring data. Overestimations of local stock sizes are problematic if they obscure the necessity for adequate conservation measures, hindering their implementation.

Hatchery supplementation increases potential spawning stock of Rio Grande Silvery Minnow after population bottlenecks

AbstractObjectiveSupplementation of imperiled wild fish stocks with captively raised fish is a commonly used conservation tool. Programs designed to maintain or improve fish populations through supplementation should be evaluated to determine whether they are meeting conservation objectives. The Rio Grande Silvery Minnow Hybognathus amarus is a small‐bodied, endangered minnow endemic to the Rio Grande basin of the southwestern United States. The wild population of Rio Grande Silvery Minnow has been supplemented with captive‐reared fish since 2002. Our objective was to determine whether supplementation measurably increases the number of spawning fish after years of population bottlenecks; this objective was simplified because nearly all hatchery‐released fish have been given identifying markings.MethodsWe leveraged a long‐term fish sampling data set (18 years) covering the species' contemporary range and a single‐season, high spatial coverage fish sampling data set to determine whether the number of potential spawners was increased by the addition of hatchery fish.ResultHatchery‐reared fish increased the catch rates of spawners by up to an order of magnitude in some years. We also observed that most hatchery‐reared fish were recaptured near the point of release. We were able to determine that supplementation with hatchery fish increased the abundance and distribution of Rio Grande Silvery Minnow and provided the desired demographic boost after severe population bottlenecks.ConclusionReleasing hatchery‐reared fish may be a useful tool for conservation of imperiled freshwater fishes. However, there is a need for spawning and rearing infrastructure that matches the life‐history of the species and sufficient postrelease monitoring to evaluate the effectiveness of hatchery supplementation. Use of hatchery‐reared fish has been beneficial for improving population resiliency of Rio Grande Silvery Minnow following recruitment bottlenecks; however, natural recruitment can greatly exceed hatchery supplementation and conditions promoting natural recruitment should be restored.

Captive-bred Atlantic salmon released into the wild have fewer offspring than wild-bred fish and decrease population productivity.

The release of captive-bred animals into the wild is commonly practised to restore or supplement wild populations but comes with a suite of ecological and genetic consequences. Vast numbers of hatchery-reared fish are released annually, ostensibly to restore/enhance wild populations or provide greater angling returns. While previous studies have shown that captive-bred fish perform poorly in the wild relative to wild-bred conspecifics, few have measured individual lifetime reproductive success (LRS) and how this affects population productivity. Here, we analyse data on Atlantic salmon from an intensely studied catchment into which varying numbers of captive-bred fish have escaped/been released and potentially bred over several decades. Using a molecular pedigree, we demonstrate that, on average, the LRS of captive-bred individuals was only 36% that of wild-bred individuals. A significant LRS difference remained after excluding individuals that left no surviving offspring, some of which might have simply failed to spawn, consistent with transgenerational effects on offspring survival. The annual productivity of the mixed population (wild-bred plus captive-bred) was lower in years where captive-bred fish comprised a greater fraction of potential spawners. These results bolster previous empirical and theoretical findings that intentional stocking, or non-intentional escapees, threaten, rather than enhance, recipient natural populations.

Applying a flexible spline model to estimate functional maturity and spatio-temporal variability in aurora rockfish (Sebastes aurora)

We outline a new flexible method for estimating maturity that incorporates skip spawning, which can lead to non-asymptotic behavior in the population maturity schedule. This new approach aids fisheries managers who seek to understand marine species’ responses to changing oceans. In an effort to assess shifts in maturity and spawning behavior of west coast groundfish, we used this new method to evaluate spatio-temporal trends in length at maturity, the annual reproductive cycle, and spawning behavior of aurora rockfish (Sebastes aurora). We estimated biological (presence of physiological maturity markers) and functional (potential spawners in a given year) maturity using a standard logistic and the new flexible spline model. The range in lengths at 50% maturity (biological and functional) slightly varied between the two methods (23.66–23.93 and 25.34–25.57 cm). We also investigated spatial trends in maturity and found ~ 2 cm difference in functional maturity between fish sampled north and south of Cape Mendocino, CA (26.22–26.48 and 24.38–24.74 cm). We demonstrate model sensitivity by updating the maturity estimates in the 2013 aurora rockfish stock assessment. Absolute, but not relative, spawning output, was sensitive to model choice, spatial resolution, and the updated data. This new flexible spline model can account for skip spawning, capturing potential spawners in a given year, and thus provides accurate measurements for spawning output models.

Increasing River Temperature Shifts Impact the Yangtze Ecosystem: Evidence from the Endangered Chinese Sturgeon.

Simple SummaryA river thermal regime is critically influencing the aquatic ecosystem and human-induced water temperature alteration occurs commonly worldwide. In large river systems, thermal alterations do not readily arise because of the huge water volume. The Yangtze River has the third greatest water flow, is the third longest river, and is one of the most human-influenced rivers in the world. Here, we found that the entire water temperature regime in the Yangtze River has been changed by damming and will shift further under future dam construction. We think that this, in conjunction with the impacts of global warming, means that saving the Chinese sturgeon by regulating water temperature is critically difficult. Also, river thermal shifts not only threaten fish but also affect the whole Yangtze aquatic ecosystem.The Yangtze River has the third greatest water flow and is one of the most human-influenced rivers in the world. Since 1950, this river system has experienced drastic human interventions, leading to various environmental changes, including water temperature. In this study, based on observations during the past sixty years, we found that the seasonal temperature regime has been altered, both temporally (1–5 °C variation) and spatially (>626 km distance). Temperature shifts not only delay the timing of fish spawning directly, but also lead to degeneration in gonad development. Temperature regime alterations have delayed the suitable spawning temperature window by approximately 29 days over a decade (2003–2016). It confirmed that a period of lower temperature, higher cumulative temperature, and relatively higher temperature differences promoted the maturation of potential spawners based on the correlation analysis (p < 0.05). Also, thermal alterations were highly correlated with reservoir capacity upstream (R2 = 0.866). On-going cascade dam construction and global warming will lead to further temperature shifts. Currently, rigorous protection measures on the breeding population of the Chinese sturgeon and its critical habitats is urgently needed to prevent the crisis of the species extinction. Increasing river thermal shifts not only threaten the Chinese sturgeon but also affect the entire Yangtze aquatic ecosystem.

Sexual selection leads to a tenfold difference in reproductive success of alternative reproductive tactics in male Atlantic salmon.

The precocious maturation of some male Atlantic salmon (Salmo salar L.) has become a textbook example of alternative mating tactics, but the only estimates of reproductive success available so far are either the collective contribution of precocious males to reproduction in the wild or individual reproductive success in oversimplified experimental conditions. Using genetic parentage analysis on anadromous and precocious potential spawners and their offspring, we quantified components of individual reproductive success of both tactics in a natural population. On average, precocious males produced 2.24 (variance 67.62) offspring, against 27.17 (3080) for anadromous males. For both tactics, most of the variance in reproductive success was due to mating success, with 83% of precocious males having no mate, against 50% for anadromous males. Body size increased reproductive success of anadromous males and tended to decrease precocious males' reproductive success. Although these results do not solve the coexistence of alternative reproductive tactics (ARTs) in Atlantic salmon, their inclusion in comprehensive models of lifetime reproductive success should shed light on the evolution of precocious maturation in Atlantic salmon and its effect on the selection of phenotypic traits.

Can intense predation by bears exert a depensatory effect on recruitment in a Pacific salmon population?

It has long been recognized that, as populations increase in density, ecological processes affecting growth and survival reduce per capita recruitment in the next generation. In contrast to the evidence for such "compensatory" density dependence, the alternative "depensatory" process (reduced per capita recruitment at low density) has proven more difficult to demonstrate in the field. To test for such depensation, we measured the spawner-recruit relationship over five decades for a sockeye salmon (Oncorhynchus nerka) population in Alaska breeding in high-quality, unaltered habitat. Twenty-five years of detailed estimates of predation by brown bears, Ursus arctos, revealed strong density dependence in predation rate; the bears killed ca. 80% of the salmon in years of low salmon spawning abundance. Nevertheless, the reconstructed spawner-recruit relationship, adjusted to include salmon intercepted in the commercial fishery, provided no evidence of demographic depensation. That is, in years when few salmon returned and the great majority were killed by bears, the few that spawned were successful enough that the population remained highly productive, even when those killed by bears were included as potential spawners. We conclude that the high quality of breeding habitat at this site and the productive nature of semelparous Pacific salmon allowed this population to avoid the hypothesized depressed recruitment from depensatory processes expected at low density. The observed lack of demographic depensation is encouraging from a conservation standpoint because it implies that depleted populations may have the potential to rebound successfully given suitable spawning and rearing habitat, even in the presence of strong predation pressure.

Escapement success of silver eels from a German river system is low compared to management‐based estimates

Summary The European eel (Anguilla anguilla) stock experienced a sharp decline during the last decades and is suffering from massive anthropogenic impacts on inland waters. To evaluate the benefit of management measures and to better understand the contribution of single drainage systems to spawner production, knowledge of the respective silver eel escapement is required. Furthermore, a better understanding of environmental conditions that potentially trigger the onset of spawning migration is needed to reduce anthropogenic mortalities during riverine eel migration. Investigations are also necessary to clarify whether fish protecting devices and bypasses at barriers are functional and truly increase eel survival and escapement rates. In this study, total female silver eel escapement from a northern German drainage system (Schwentine River) was assessed over a period of three consecutive years, and downstream migration patterns were compared to potential environmental triggers. Furthermore, the benefit of two fish bypasses (surface and deep) and a trash rack at the hydropower station for the survival of migrating eels was examined, and the spawner quality of escaping silver eels was determined by analysing lipid content and infection intensities with the swimbladder parasite Anguillicoloides crassus. The results indicate that silver eel escapement from the Schwentine drainage system is far below the estimated values underlying the respective eel management plan, highlighting the necessity of direct migration assessments to validate indirect estimations that include multiple assumptions and uncertainties. Major downstream migration events took place during short time periods in autumn and appear to be influenced by river discharge and water temperatures, suggesting that a precise prediction of escapement events is possible. Regarding spawner quality, fat reserves appear sufficient for escaping silver eels to migrate and spawn. However, high A. crassus prevalence and infection intensities are assumed to further reduce the number of potential spawners. Another matter of concern is the high trash rack mortality at the hydropower station that illustrates the need of fish protecting devices that fulfil eel‐specific requirements.

Estimating spatial distribution of Atlantic salmon escapement using redd counts despite changes over time in counting procedure: application to the Allier River population

AbstractIn salmonid species, such as Atlantic salmon (Salmo salar L.), the most frequent type of data set available related to adult escapements are redd counts. When collected over a broad spatio‐temporal domain, redd counts data are of great interest for tracking the variation through time of the spatial distribution of the potential spawners. This is important for management purposes when the habitat quality is variable across river sections of a catchment or when the spatial distribution can vary depending on management actions or on environmental factors. However, long‐term data sets are prone to changes in data collection methodology. In this article, we present a new hierarchical Bayesian modelling approach that allows both (i) to account for a change in the data collection procedure and (ii) to analyse the variation through time of the potential spawners’ spatial distribution. The value of the proposed approach is demonstrated by its application to the Atlantic salmon redd counts data collected in Allier (France) catchment from 1977 to 2011. The Allier can be divided into three main sections according to management and habitat considerations, and an important change occurred in the redd data collection in 1997: counts by foot or by boat were replaced by counts from a helicopter. A significant effect of this change on methodology is detected: less redds counted when using the helicopter counts. However, its explicit consideration in the modelling makes little difference with regard to the estimates of potential spawner abundance and their associated uncertainty.

Size-related variation in fecundity of European eel (Anguilla anguilla)

Abstract MacNamara, R., and McCarthy, T. K. 2012. Size-related variation in fecundity of European eel (Anguilla anguilla). – ICES Journal of Marine Science, 69: . Declining European eel (Anguilla anguilla) recruitment has focused attention on conservation of potential spawners leaving continental waters. Fecundity of wild, seaward-migrating silver-phase eels was shown to be size-related and higher than previously reported from artificial maturation experiments. Reliable information on fecundity is essential for stock modelling and future development of eel management policies.

Effect of Brook Trout Removal from a Spawning Stream on an Adfluvial Population of Lahontan Cutthroat Trout

AbstractIndependence Lake (Nevada and Sierra counties, California) harbors the only extant native population of Lahontan cutthroat trout Oncorhynchus clarkii henshawi in the Truckee River system and one of two extant adfluvial populations in the Lahontan basin. The persistence of this population has been precarious for more than 50 years, with spawning runs consisting of only 30–150 fish. It is assumed that this population was much larger prior to the introduction of nonnative brook trout Salvelinus fontinalis. Brook trout overlap with cutthroat trout in upper Independence Creek, where the cutthroat trout spawn and their resulting progeny emigrate to Independence Lake. In 2005, we began removing brook trout from upper Independence Creek using electrofishers and monitored the cutthroat trout population. Stomach analysis of captured brook trout revealed cutthroat trout fry, and cutthroat trout fry survival increased significantly from 4% to 12% with brook trout removal. Prior to brook trout removal, the only Lahontan cutthroat trout progeny emigrating to Independence Lake were fry; with brook trout removal, juveniles were found entering the lake. In 2010, 237 potential spawners passed a prefabricated weir upstream of Independence Lake. Although the results of this study suggest that brook trout removal from upper Independence Creek has had a positive influence on the population dynamics of Independence Lake Lahontan cutthroat trout, additional years of removal are needed to assess the ultimate effect this action will have upon the cutthroat trout population.Received August 26, 2011; accepted February 29, 2012

Lake sturgeon population attributes and reproductive structure in the Namakan Reservoir, Minnesota and Ontario

Summary Quantified were the age, growth, mortality and reproductive structure of lake sturgeon (Acipenser fulvescens) collected in the US and Canadian waters of the Namakan Reservoir. The hypotheses were tested that (i) age and growth of lake sturgeon in the Namakan Reservoir would differ by sex and reproductive stage of maturity, and (ii) that the relative strength of year-classes of lake sturgeon in the reservoir would be affected by environmental variables. To quantify age, growth and mortality of the population, existing data was used from a multi-agency database containing information on all lake sturgeon sampled in the reservoir from 2004 to 2009. Lake sturgeon were sampled in the Minnesota and Ontario waters of the Namakan Reservoir using multi-filament gillnets 1.8 m high and 30–100 m long and varying in mesh size from 178 to 356 mm stretch. Reproductive structure of the lake sturgeon was assessed only during spring 2008 and 2009 using plasma testosterone and estradiol-17β concentrations. Ages of lake sturgeon >75 cm ranged from 9 to 86 years (n = 533, mean = 36 years). A catch-curve analysis using the 1981–1953 year classes estimated total annual mortality of adults to be 4.8% and annual survival as 95.2%. Using logistic regression analysis, it was found that total annual precipitation was positively associated with lake sturgeon year-class strength in the Namakan Reservoir. A 10 cm increase in total annual precipitation was associated with at least a 39% increase in the odds of occurrence of a strong year class of lake sturgeon in the reservoir. Plasma steroid analysis revealed a sex ratio of 2.4 females: 1 male and, on average, 10% of female and 30% of male lake sturgeon were reproductively mature each year (i.e. potential spawners). Moreover, there was evidence based on re-captured male fish of both periodic and annual spawning, as well as the ability of males to rapidly undergo gonadal maturation prior to spawning. Knowledge of lake sturgeon reproductive structure and factors influencing recruitment success contribute to the widespread conservation efforts for this threatened species.

Upstream passage problems for wild Atlantic salmon (Salmo salar L.) in a regulated river and its effect on the population

Due to hydropower development, the upstream migration of wild anadromous salmon and brown trout is impaired in many European rivers, causing negative effects on the long-term survival of natural salmonid populations. This study identified problems for Atlantic salmon during upstream migration in a regulated river in northern Sweden, Umeälven (mean flow: 430 m3 s−1). Tagging from 1995 to 2005 involved radio tags (n = 503), PIT tags (n = 1574) and Carlin tags (n = 573) to study the spawning migration of salmon from the coast past the regulated section of the river to a fish ladder at the dam/spillway 32 km upriver. The results demonstrate that migration success from the coast to the fish ladder varied between 0% and 47% among years, indicating an average loss of 70% of potential spawners. Discharge from the turbines attracted the salmon away from the bypass route. Echo-sounding in the turbine outlet showed that salmon were normally found at 1–4 m depths. They responded with upstream and/or downstream movements depending on flow changes; increased spill in the bypass channel attracted salmon to the bypass. Once in the bypass channel, salmon could be delayed and had difficulties passing the first rapid at high spills. Additional hindrances to upstream migration were found at rapids and the area of the fish ladder, located further upstream in the regulated river section. The average migration duration was 44 days from the estuary to the top of the fish ladder, with large variation among individuals within years. Modelling the salmon population dynamics showed a potential population increase of 500% in 10 years if the overall migration success could be improved from the current 30% to levels near 75%. Consequently improved migration facilities at the regulated river section should be implemented to achieve a long-term sustainability of these threatened anadromous salmonids.

Silver eel population size and escapement in a Mediterranean lagoon: Bages-Sigean, France

Much concern has been raised about the decline in the European eel (Anguilla anguilla ) population. European management plans for the recovery of the stock are now in preparation, the main objective being to increase the escapement of the potential spawners (silver eels) in each basin to allow 40% of the pristine biomass to escape. However, there are relatively few studies on silver eel escapement and production, and no recent measurement of escapement in lagoons, habitats which support large silver eel sub-populations in the Mediterranean region. A mark-recapture study was carried out in autumn 2007 in order to estimate the number of silver eels migrating from the Bages-Sigean lagoon in the South-West of France. The migrating population, mostly males between 36 and 42 cm, was estimated to be around 1 120 000 eels (30 kg·ha–1 ). The exploitation rate by professional fishermen was around 20% (6 kg·ha–1 ), leading to an escapement level of 80% (24 kg·ha–1 ). The results are discussed regarding the available data in the literature on silver eel escapement.

Size-related habitat use, aggregation patterns and abundance of anglerfish (Lophius budegassa) in the Mediterranean Sea determined by generalized additive modelling

Spatial distribution patterns of black anglerfish, Lophius budegassa were examined in relation to size category, bathymetry, locational covariates, and season. Data were collected during a 2-y period (1998–1999) of quasi-synoptic seasonal sampling using demersal trawl surveys in the Aegean Sea. Generalized additive models (GAMs) were used to test the hypotheses that there was size-related variation in species' habitat associations and that the study area might serve as a nursery ground for black anglerfish. The current results supported these hypotheses. Data are presented that reveal size-dependent aggregation patterns of black anglerfish and an important habitat utilization of the north-eastern Aegean area. The modelled anglerfish abundances showed a strongly non-linear dependence on the explanatory covariates. The different size-classes exhibited significant seasonal effects and preferences for specific regions and distinct water depths. The present results also suggested that 1-y-old fish and potential spawners appeared to concentrate in the vicinity of the same areas. Two main areas of juvenile aggregations were detected in the deeper water regions of the study area on a seabed of around 300 m depth; both emerged in the proximity of the locations of larger fish. The bathymetric distribution of intermediate size anglerfish followed an inverse trend, with fish captured mainly in shallower waters. Results indicated a preferential aggregation of 1-y-old L. budegassa in the study area that is hypothesized to influence the supply of recruits to distant regions of the Aegean Sea.

Spawning locations and movement of Kootenai River white sturgeon

Summary The Kootenai River white sturgeon Acipenser transmontanus, an endangered species, spawns within an 18-km reach in the Kootenai River, Idaho, river kilometer (rkm) 228.0-246.0. Preliminary observations of adult white sturgeon have shown what appeared to be a progressive upstream movement during the spawning season, spawning over sand substrate seldom reaching the typical sturgeon spawning habitat of gravel and cobble located upstream of rkm 244.6. This behavior may be unusual for a white sturgeon population. The primary objecttive of this paper is to compare, within each spawning season and between seasons, the spatial and temporal pattern of egg collections (as an indicator of spawning location) and the spatial and temporal pattern of suspected spawners, as determined by their movement from 1994 to 1999. Adult white sturgeon were tagged with sonic and radio transmitters. Artificial substrate mats were deployed within three sampling reaches to determine approximate spawning locations and timing in reference to locations of spawners. Eggs were collected 207 different times from 1994 to 1999, including 123 times in the lower reach and 84 times in the middle reach. White sturgeon demonstrated a consistent temporal pattern of shifting spawning location as the season progressed, first spawning in the lower reach and then moving upstream to the middle reach. A total of 1234 contacts of potential spawners were made during May and June for the years 1994-1999. Some spawners were located in as many as four different locations from which eggs were collected within a season. There appeared to be at least five primary spawning locations, most in the vicinity of outside bends. This movement and temporal spawning pattern appears to be unique when compared with published studies on other sturgeon populations. Companion studies indicate that the species is not recruiting despite mitigative measures, and white sturgeon are thought to be spawning in unsuitable habitat. The combination of movement by white sturgeon within this sandy reach during the spawning season and spawning in unsuitable habitat may be contributing to the failure of recruitment. Present measures to recover the population may be inadequate. Further study is needed to determine if this movement pattern is caused by changing water velocities. Also, if historic spawning locations cannot be identified and rehabilitated, then we suggest consideration be given to habitat enhancement measures at the present spawning locations.

Reproduction of Aquaculture Atlantic Salmon in a Controlled Stream Channel on Vancouver Island, British Columbia

Sightings and captures of Atlantic salmon Salmo salar that have escaped from aquaculture facilities have become common in coastal British Columbia, Canada. A lack of empirical data has prevented the forecast of what effects may result from the presence of this species in the Pacific Northwest. A first step towards this objective is to evaluate the spawning potential of escaped Atlantic salmon. We report results from a study of Atlantic salmon spawning in a simulated stream channel at the Little Qualicum River, British Columbia. Adults were obtained from a local commercial marine net-pen operation; 17 of 19 males and 24 of 30 females matured sexually, and up to 9 females successfully deposited eggs in six redds, five of which yielded viable progeny when the eggs were collected and incubated in Heath trays. Results suggest Atlantic salmon escaping from aquaculture facilities are likely to experience low spawning success in coastal British Columbia. However, based on the high proportion of sexual maturation, and even though successful spawning may be limited, we conclude that adult Atlantic salmon escapees, particularly those observed in freshwater, should be considered potential spawners.

ANADROMOUS SALMONID RECOVERY IN THE UMATILLA RWER BASIN, OREGON: A CASE STUDY1

ABSTRACT: The Umatilla River Basin Fisheries Restoration Plan was initiated in the early 1980s to mitigate salmonid losses caused by hydroelectric development and habitat degradation. The objectives are to enhance the abundance of endemic steelhead and reintroduce extirpated chinook and coho salmon. The project prompted collaborative effort among federal, state, and tribal agencies, and local water users. It has incorporated habitat restoration, flow enhancement, fish passage improvements, and population supplementation through artificial production. Water exchanges have successfully increased minimum flows during spring and fall migration. While flows remain depressed compared to historic conditions, there is potential for improved habitat, passage, and homing. The mean adult‐to‐adult return rate of hatchery‐reared steelhead exceeded replacement and that of the naturally‐spawning population. Although the smolt‐to‐adult survival rates of hatchery‐reared fish fluctuate, salmonid escapement has increased in recent years, permitting steelhead and spring chinook harvest. Enumeration of potential spawners and observed redds reveals an increase in natural production of all supplemented species. Comparison of hatchery‐reared and naturally‐spawning steelhead populations revealed differences in life history characteristics (in age composition and sex ratios) though run timing and genetic stock compositions of the two components of the populations have not differed. Sustained monitoring is needed to determine benefits of integrating habitat restoration and artificial production in restoring salmonid populations.

The Vertical and Horizontal Distribution of Sea Scallop (Placopecten magellanicus) Larvae in the Bay of Fundy in 1984 and 1985

The vertical and horizontal distributions of sea scallop larvae (Placopecten magellanicus) in the Bay of Fundy were surveyed during September, October, and November of 1984 and during October of 1985. Larvae were distributed throughout the water column, although at some locations pronounced peaks in concentration associated with the thermocline occurred at depths between 5 and 20 m. Vertical stratification by size occurred, but was not consistent between stations. The horizontal distribution of larvae was compared with the distribution of commercial sea scallops (potential spawners) and the residual circulation pattern. Mean larval number per m2 was usually highest in the Outer Bay, where the greatest biomass of potential spawners was found. Some transport of larvae in the direction of the residual currents is indicated by changes in length frequency distribution. Sea scallop larvae found in the Bay of Fundy appear to originate there, rather than from the Gulf of Maine, or the Scotian Shelf. . . . ..../ II Sustained fishing ~~Oistribution,commercial ••••• quantities occur ••••••••••• occasionally ...