Proportion Of Large Fish Research Articles

Downstream fish passage at small-scale hydropower plants: Turbine or bypass?

Introduction: Hydropower plants are frequently equipped with physical and behavioral fish protection barriers to prevent downstream moving fish from harmful turbine passage and to guide them to alternative bypasses. As not only diadromous but also potamodromous fish species migrate and inevitably have to pass hydropower plants, knowledge on corridor usage for a wide range of species is important to identify potential deficits and to improve bypass efficiency.Methods: In this study, the corridor usage of downstream moving fish (6,646 individuals from 42 species) was investigated at four small-scale hydropower plants with different concepts to prevent turbine entrainment and to bypass fish.Results: Despite existing bypasses and fine screens with 15 mm and 20 mm bar spacing to prevent turbine entrainment, a large proportion of fish (35%–88%) still passed the turbines. The mainly poor efficiency of the investigated bypasses was probably due to low discharge and unfavorable bypass location or detectability. The various bypass types were used by a different range of fish species and sizes due to species-specific behavior and differing fish communities between sites. The effectiveness of the investigated downstream corridors was positively correlated with the share of discharge.Discussion: To reduce the negative ecological impacts of hydropower plants on downstream moving fish, well-performing bypasses are required that consider not only current requirements regarding design, dimensioning and location, but also the site-specific fish community. Thus, bypasses should function for the widest possible range of species, which can be achieved through less selective bypass types such as full-depth bypasses, or a combination of different bypass systems. Moreover, less harmful turbine technologies and more effective fish protection systems need to be implemented, since fine screens with 15 mm and 20 mm bar spacing cannot prevent small-bodied fish species and juvenile fish <20 cm from turbine entrainment.

Timing and magnitude of climatic extremes differentially elevate mortality but enhance recovery in a fish population.

The countervailing effects of disturbances (e.g., high mortality and enhanced recovery) on population dynamics can occur through demographic processes under rapidly increasing climatic extremes. Across an extreme-event gradient, we mechanistically demonstrated how dramatic changes in streamflow have affected the population persistence of endangered salmon in monsoonal Taiwan over a three-decade period. Our modeling indicated that the dynamics of the age-structured population were attributed to demographic processes, in which extensive mortality was characterized as a function of climatic extremes and vulnerability in the young stage of fish. In the stochastic simulations, we found that the extensive mortality and high proportion of large fish resulted from extreme flooding, which caused high values of postimpact population recovery. Our empirical evidence suggests that the magnitudes and timing of disturbance can explain the population persistence when facing climatic extremes and thereby challenges the understanding of the mechanistic drivers of these countervailing phenomena under changing environmental conditions.

Feeding Hotspots and Distribution of Fin and Humpback Whales in the Norwegian Sea From 2013 to 2018

Fin whales (Balaenoptera physalus) and humpback whales (Megaptera novaeangliae) are commonly found in the Norwegian Sea during the summer months. Records from around 1995 to 2004 show that their distribution patterns were mainly associated with those of macro-zooplankton. More recent studies conducted from 2009 to 2012 demonstrate marked shifts, with fin whale distribution related to pelagic fish distribution, decreasing densities of humpbacks, and increased densities of toothed whales. During the same period, historically large abundances of pelagic planktivorous fish in the Norwegian Sea were reported. The goals of this study were to examine the summer distribution of fin and humpback whales from 2013 to 2018 and to assess the potential association between distribution and environmental impact factors. Results suggest a pronounced northerly shift in distribution for both species, a feeding hotspot for fin whales at the shelf area between Svalbard and Norway, and one near Bear Island for humpback whales. Fin whale distribution was associated with that of blue whiting (Micromesistius poutassou) and capelin (Mallotus villosus), whereas humpback whale distribution was associated with that of euphausiids (Meganyctiphanes norvegica, Thysanoessa longicaudata, andThysanoessa inermis), capelin, and herring (Clupea harengus). However, a significant negative spatial correlation was found between whale occurrence and the widely expanding population of northeast Atlantic mackerel (Scomber scombrus). The results of this study suggest that the prey composition of fin and humpback whales in recent years contain a large proportion of fish. The apparent northerly shift in the distribution of these whale species is largely determined by the availability of prey, but it likely is also impacted by direct or indirect interspecific interactions, especially with killer whales (Orcinus orca). Such large-scale pronounced changes in distribution seem to confirm a high degree of plasticity in fin and humpback whale feeding in the Norwegian Sea.

Comparison and optimization of a novel larval rearing method for bighead carp Hypophthalmichthys nobilis

Bighead carp Hypophthalmichthys nobilis is a species that is widely cultured throughout Asia, currently ranking 5th in overall global fish production. Despite the prevalence of this species culture it is considered invasive in North America and a threat to local fish communities. Investigations into the early life environmental requirements and optimization of intensive larval rearing have been limited. The present study attempts to establish most desired larval rearing conditions of bighead carp by investigating a novel static rearing method utilizing continuous light, salinity (2 parts per thousand; ppt), algal turbidity, and continuous food availability as compared to traditional recirculating culture system methods. Increased levels of salinity (3 and 5 ppt) were also examined in the novel rearing environment. A 2x2x3 full factorial ANOVA design was implemented to compare the main effects of larval rearing system, feeding regime, and stocking density (12.5, 25, and 50 fish L−1) and the interactions between the main effects on survival, biomass, length, weight, proportion of large fish (measure of heterogeneity), and specific growth rate over twenty days of feeding. A desirability function was then constructed to maximize survival (%), biomass (g L−1) and proportion of large fish to optimize larval rearing for diet nutritional requirement studies. Mortalities recorded in the experiment primarily occurred within the first ten days of feeding and leveled off during the second ten days of feeding. The desirability function identified the novel static rearing method, at high initial stocking density (50 fish L−1), and feeding with Artemia nauplii from inception as having the maximum desirability (0.733) for the selected variables. The predictions for biomass, survival and proportion of large fish from the desirability function were 2.38 g L−1 (95% CI, 2.14–2.62), 70.3% (95% CI, 60.1–80.6), and 0.768 (95% CI, 0.696–0.841) respectively. Elevated salinity, 3 and 5 ppt, was found to increase survival (51.3 ± 3.5 and 64.3 ± 10.1%, respectively) and proportion of large fish (0.76 ± 0.08 and 0.82 ± 0.02, respectively) i.e. decreased heterogeneity, as compared to 2 ppt (33 ± 3% and 0.63 ± 0.03) in the novel static rearing environment. This indicates that current results may further be improved if bighead carp are reared at higher salinities (3–5 ppt). The optimization methodology which was utilized in the current study could potentially be applied to any larval rearing program to select for treatments which meet specific desired outcomes.

Effects of temperature and water levels on dynamics of density and structure of the fish population of the channel-floodplain complex of a large river in the period of spring floods

The article discusses the features of the dynamic process of migration of ichthyofauna from wintering sites to the wetlands of a large boreal river for feeding and spawning. The influence of factors of temperature and water level on various groups of fish is estimated, and the role of water bodies of various types during fish migration in a flooded floodplain is also established. The research was performed during the spring flood in the floodplain-channel complex of the Irtysh River (Western Siberia, Russian Federation) in the water area of the conjugate water bodies: the lotic and lentic parts of the riverbed depression and the mouth of the tributary – transit section of the migration pathway of fish to the flooded floodplain. The research work was performed by “AsCor” – computerized hydroacoustic complex, hydroacoustic survey data were processed in the laboratory. The “AsCor” complex remotely performs taxonomic identification of abundant species of fish at the family level by groups (Cyprinidae, Percidae, Coregonidae–Esocidae, Acipenseridae–Lotidae). It was found that after the breakup of ice cover, maximum densities of fish were observed in the wintering sections – the initial location of the spring migration. During the 30-days observation period in the wintering sections and conjugate water bodies, the density of fish decreased from 4 to 13 times due to their migration to the floodplain. The response to a decrease in the overall density of fish in the year-round functioning lotic part of the riverbed depression to the influence of factors of water level and temperature regimes was >0.300 in general for ichthyofauna and for all groups of fish registered by hydroacoustic method (Cyprinidae, Percidae, Coregonidae–Esocidae, Acipenseridae–Lotidae). We constructed regression models of changes in the density of fish in the wintering sections of the river depending on the considered factors. Use of ANOVA analysis of variance confirmed the adequacy of the choice and the acceptability of the constructed models. We established a high statistically significant inverse correlation between the density of the fish, the water level and temperature regime for the mouth of the Konda River and the lentic part of the riverbed depression, which are transit sections of the migration pathway of fish in the floodplain. The lentic part of the riverbed depression may perform the function of a temporary station of fish during migration to the floodplain, which is beneficial from the point of view of bioenergetics resources. During the observation period, in the river flows there was a decrease in the proportion of larger fish and an increase in smaller individuals; in the lentic part of the riverbed depression, on the contrary, there was a reduced proportion of small fish and increase in the proportion of larger individuals.This pattern is explained by the reduced risk of predation by small fish in more turbulent conditions, as well as by an initial entry into the flooded floodplain of larger individuals of fish for spawning, followed by the smaller ones for feeding.

Movement dynamics of smallmouth bass (Micropterus dolomieu) in a large river‐tributary system

AbstractSmallmouth bass, Micropterus dolomieu Lacepède, movement dynamics were investigated in a connected mainstem river‐tributary system. Smallmouth bass moved large distances annually (n = 84 fish, average = 24.6 ± 25.9 km, range = 0.03 to 118 km) and had three peak movement periods (pre‐spawn, post‐spawn and overwintering). Movement into and out of tributaries was common, but the movement between mainstem river and tributary habitats varied among tagging locations and season. In general, a large proportion of fish that were tagged in tributaries moved out of the tributaries after spawning (22/30 fish). Because of the importance of fish movement patterns on population dynamics, the observed individual variability in movement, quantified using a hierarchical model, and the potential for long‐distance movements are important considerations for smallmouth bass conservation and management. In addition, mainstem river‐tributary connectivity appears to play an important role for smallmouth bass during key life history events.

Evaluación de la estructura del ensamble de peces de un arrecife costero norpatagónico sometido a diversos impactos antrópicos

Fil: Jeres, Pablo. Universidad Nacional del Comahue. Escuela de Ciencias Marinas; Argentina

Genomics and telemetry suggest a role for migration harshness in determining overwintering habitat choice, but not gene flow, in anadromous Arctic Char.

Migration is a ubiquitous life history trait with profound evolutionary and ecological consequences. Recent developments in telemetry and genomics, when combined, can bring significant insights on the migratory ecology of nonmodel organisms in the wild. Here, we used this integrative approach to document dispersal, gene flow and potential for local adaptation in anadromous Arctic Char from six rivers in the Canadian Arctic. Acoustic telemetry data from 124 tracked individuals indicated asymmetric dispersal, with a large proportion of fish (72%) tagged in three different rivers migrating up the same short river in the fall. Population genomics data from 6,136 SNP markers revealed weak, albeit significant, population differentiation (average pairwise FST =0.011) and asymmetric dispersal was also revealed by population assignments. Approximate Bayesian computation simulations suggested the presence of asymmetric gene flow, although in the opposite direction to that observed from the telemetry data, suggesting that dispersal does not necessarily lead to gene flow. These observations suggested that Arctic Char home to their natal river to spawn, but may overwinter in rivers with the shortest migratory route to minimize the costs of migration in nonbreeding years. Genome scans and genetic-environment associations identified 90 outlier markers putatively under selection, 23 of which were in or near a gene. Of these, at least four were involved in muscle and cardiac function, consistent with the hypothesis that migratory harshness could drive local adaptation. Our study illustrates the power of integrating genomics and telemetry to study migrations in nonmodel organisms in logistically challenging environments such as the Arctic.

Seasonal changes in abundance and compelling evidence of migration for 2 rockfish species (Sebastes auriculatus and S. caurinus) inhabiting a nearshore, temperate-water artificial reef

Washington Department of Fish and Wildlife 600 Capitol Way North Olympia, Washington 98501 Abstract—We used scuba over fixedwidth strip transects to monitor seasonal abundances of brown rockfish (Sebastes auriculatus) and copper rockfish (S. caurinus) on a nearshore artificial reef in Puget Sound, Washington, over a 7-year period. Spring and fall abundances were intermediate and marked transitional phases between seasons of highest (summer) and lowest (winter) abundance for both species. Analyses of length classes indicated that the numbers of seasonal juvenile recruits were not sufficient to account for the marked differences in abundance between summer and winter. For both species, the proportion of large fish (≥20 cm in total length) to the total number observed in summer and winter was significantly greater during the winter. Late-stage gravid brown rockfish occurred in greatest abundance during the spring and late-stage gravid copper rockfish were observed only in the summer. We examined auxiliary data from a genetics study of brown rockfish that was conducted concurrently at the reef and interpreted the results, along with our survey findings, as providing compelling evidence of seasonal migrations on and off the reef.

Genetic Identification of Chinook Salmon in the Columbia River Estuary: Stock‐Specific Distributions of Juveniles in Shallow Tidal Freshwater Habitats

AbstractExtensive efforts are underway to restore and conserve nearshore shallow water habitats in the Columbia River estuary with the intent of increasing the estuary's capacity to provide food, refuge, and other crucial ecosystem functions for juvenile salmon. Juvenile Chinook Salmon Oncorhynchus tshawytscha, including those from the five Evolutionarily Significant Units listed as threatened or endangered under the U.S. Endangered Species Act, are particularly expected to benefit from the habitat improvements. However, information on the temporal and spatial estuarine distributions of juveniles from specific populations or stocks is lacking and impedes restoration planning for at‐risk salmon. We conducted a series of surveys to sample juvenile Chinook Salmon occupying shallow‐water habitats with sandy beaches in six hydrogeomorphic reaches across the tidal freshwater portion of the estuary and also at one long‐term reference site near the estuary mouth. Sites were sampled bimonthly over 26 months during 2010–2012 to capture seasonal patterns of stock‐specific habitat use. Genetic stock identification analyses were conducted on the samples using microsatellite DNA loci and genotypic data representing spawning populations from throughout the Columbia River basin. We identified three tidal freshwater areas that could be distinguished by genetic stock composition. Lower tidal freshwater reaches were dominated by fall‐run juveniles from West Cascade tributaries (>70%), upper reaches had a large proportion of fish from the upper Columbia River summer–fall stock (>60%), and middle reaches were characterized by greater stock diversity with no single stock contributing more than 30% in each reach. Stock‐specific juvenile habitat use differed by season, life history type, and between natural and hatchery‐produced fish. Data from this study provide improved descriptions of the near‐shore estuary habitat use of several Columbia River genetic stocks of Chinook Salmon that can assist managers in the design and selection of estuary restoration projects.Received November 11, 2013; accepted February 18, 2014

Evaluating targets and trade‐offs among fisheries and conservation objectives using a multispecies size spectrum model

Summary Marine environmental management policies seek to ensure that fishing impacts on fished populations and other components of the ecosystem are sustainable, to simultaneously meet objectives for fisheries and conservation. For example, in Europe, targets for (i) biodiversity, (ii) food web structure as indicated by the proportion of large fish and (iii) fishing mortality rates for exploited species that lead to maximum sustainable yield, FMSY, are being proposed to support implementation of the Marine Strategy Framework Directive. Efforts to reconcile any trade‐offs among objectives need to be informed by knowledge on the consequences of alternate management actions. We develop, calibrate and apply a multispecies size spectrum model of the North Sea fish community to assess the response of populations and the community to fishing. The model predicts species' size distributions, abundance, productivity and interactions and therefore provides a single framework for evaluating trade‐offs between population status, community and food web structure, biodiversity and fisheries yield. We show that the model can replicate realistic fish population and community structure and past responses to fishing. We assess whether meeting management targets for exploited North Sea populations (fishing species at FMSY) will be sufficient to meet proposed targets for biodiversity and food web indicators under two management scenarios (status quo and FMSY). The recovery in biodiversity indicators is 60% greater when fishing populations at FMSY than if status quo (2010) fishing rates are maintained. The probability of achieving a food web target was 60% under both scenarios in spite of major community restructuring revealed by other indicators of community size structure. Synthesis and applications. Our model can be applied to evaluate indicator targets and trade‐offs among fisheries and conservation objectives. There is a significant probability that reductions in fishing mortality below FMSY would be needed in Europe if managers make a binding commitment to a proposed large fish indicator target, with concomitant reductions in fisheries yield.

A review of the biology, fisheries and conservation of the whale shark Rhincodon typus

Although the whale shark Rhincodon typus is the largest extant fish, it was not described until 1828 and by 1986 there were only 320 records of this species. Since then, growth in tourism and marine recreation globally has lead to a significant increase in the number of sightings and several areas with annual occurrences have been identified, spurring a surge of research on the species. Simultaneously, there was a great expansion in targeted R. typus fisheries to supply the Asian restaurant trade, as well as a largely un-quantified by-catch of the species in purse-seine tuna fisheries. Currently R. typus is listed by the IUCN as vulnerable, due mainly to the effects of targeted fishing in two areas. Photo-identification has shown that R. typus form seasonal size and sex segregated feeding aggregations and that a large proportion of fish in these aggregations are philopatric in the broadest sense, tending to return to, or remain near, a particular site. Somewhat conversely, satellite tracking studies have shown that fish from these aggregations can migrate at ocean-basin scales and genetic studies have, to date, found little graphic differentiation globally. Conservation approaches are now informed by observational and environmental studies that have provided insight into the feeding habits of the species and its preferred habitats. Notwithstanding these advances, there remain notable gaps in the knowledge of this species particularly with respect to the life history of neonates and adults who are not found in the feeding aggregations.

Seasonal and ontogenic migrations of meagre (Argyrosomus regius) determined by otolith geochemical signatures

Argyrosomus regius uses different water masses during its life history, being associated with estuaries for reproduction. In order to study the life history and migration patterns, variations in otolith Na, Sr and Ba were measured by laser ablation-ICPMS along transects running from the first year of life to the otolith edge, comprising up to 12 years of age. Visual and statistical modelling approaches were used to analyse both individual- and population-level patterns. Ontogenetic trends in Sr:Ca and Ba:Ca followed a sigmoidal increase over the life span, with an inflection point in Sr:Ca occurring at 5 years of age in males and 6.6 in females, suggesting respective age at maturity. Using reared young-of-year (YOY) meagre for validation, the habitat use of wild fish was characterized and our data suggest that most fish spend the first 2–4 years in offshore waters, and begin moving between water masses after age 6. Population-level analyses indicated significant seasonal variations, with a larger proportion of fish with high otolith Sr:Ca in the spring and summer. Although Sr:Ca would normally be expected to be lower after movement into estuaries, in this case the increase could mark gonad maturation and spawning activity. Alternatively, since the Sr:Ca maxima correspond to higher otolith Ba:Ca in the summer, fish would have moved into the estuarine area, especially since the Guadalquivir river drains metal-rich areas with heavy mining activities leading to elevated Sr concentrations compared to adjacent coastal waters.

Bait and the susceptibility of American lobsters Homarus americanus to epizootic shell disease

Shell disease (SD) has been observed in lobster populations for almost a hundred years, but recently, rates of an epizootic form of shell disease (ESD) have increased in the southern New England (USA) area. A large proportion of fish in the diet of American lobsters Homarus americanus has been linked to increased rates of SD. Therefore, the use of fish as lobster bait may be linked to increased ESD rates in lobsters. Lobsters from the western portion of Martha's Vineyard, MA (41 degrees N, 71 degrees W), were randomly divided into 3 groups of 16 and exposed to dietary treatments (100% herring; 48% crab, 48% blue mussel and 4% plant matter; or 50% herring, 24% crab, 24% mussel, 2% plant matter) to determine if lobster tissue delta15N levels reflected diet. The results of the feeding experiment confirmed that differences in diet are observed in the delta15N levels of lobster muscle tissue. The delta15N levels of tissue samples from 175 wild lobsters with varying degrees of ESD were unrelated to ESD severity but did indicate lobsters were eating large amounts of fish (bait). This result does not support the speculation that fish used as bait is contributing to ESD outbreaks in portions of the southern New England area.

Decline in angler use despite increased catch rates: Anglers’ response to the implementation of a total catch-and-release regulation

A mandatory total catch-and-release regulation and a bait ban were implemented on Lower Kananaskis Lake, Canada, due to the drastic decline of the native bull trout ( Salvelinus confluentus) population. In the decade following harvest-regulation changes, the adult bull trout population experienced a 28-fold increase in abundance. Two roving creel surveys of winter ice-anglers, the first conducted just prior to the regulation changes (1992) and the second 10 years later (2002), were used to compare catch rates, the size structure of fish caught, and angler effort before and after the bull trout population rebuilt. Supplementary information from voluntary creel cards (1996–2003) was used to evaluate temporal trends in summer catch-related fishery attributes as the fish population recovered. Winter catch rates were three-fold and 12-fold higher in 2002 than in 1992, for all bull trout and large (>50 cm) bull trout, respectively. The proportion of large fish in the catch also increased. Voluntary creel card information suggested summer catch rates and the frequency of large fish in the catch both increased as the population rebuilt. However, despite the increase in fishing “quality”, angler numbers were three- to 10-fold lower in 2002 than 1992, indicating reduced utilization of the fishery. We speculate that harvest-oriented anglers were displaced from Lower Kananaskis Lake because of restrictive regulations. Our study shows anglers are not necessarily attracted to high-catch-rate fisheries, suggesting angler behaviour is complex and not driven by catch rates alone. Thus, to meet management objectives, understanding angler effort responses to regulatory changes is fundamentally important.

Biodiversity of North Sea fish: why do the politicians care but marine scientists appear oblivious to this issue?

AbstractGreenstreet, S. P. R. 2008. Biodiversity of North Sea fish: why do the politicians care but marine scientists appear oblivious to this issue? – ICES Journal of Marine Science, 65: 1515–1519. Political drivers underpinning the development of an Ecosystem Approach to Marine Management (EAMM) focus on conserving and restoring biodiversity. However, the Element of Ecological Quality for Fish Communities that emerged from the 2002 Bergen North Sea Ministerial Conference relates to “Changes in the proportion of large fish and hence the average weight and average maximum length of the fish community”. How did this apparent change in direction arise? Responding to advice requests from OSPAR, ICES established seven criteria for identifying “state” indicators capable of supporting indicator-based management. Application of these criteria underlined the merits of indicators of fish size, whereas diversity indices performed poorly against four of the criteria. These difficulties are examined here. Far from being oblivious to the issue of biodiversity, marine scientists recognized that they were not in a position to recommend Ecological Quality Objectives (EcoQOs) for fish biodiversity that would have relied on the use of biodiversity indicators. The use of indicators of size structure, for which the theoretical foundation was better developed, allowed the continued development of an EAMM in the short term. However, if the issue of biodiversity is to be addressed in the longer term, then shortcomings associated with the use of biodiversity indicators need to be addressed.

Indicators of change in the size structure of fish communities: A case study from the south coast of South Africa

Heavy fishing is believed to change the size structure of fish communities through the differential removal of larger sized individuals and species. The size structure of the demersal fish communities off the south coast of South Africa is assessed using a variety of size-based indicators. The communities on this coast are subjected to different fisheries with wide ranging impacts. Changes in the size structure were assessed over the period from 1986 to 2003 for the whole south coast and two depth strata. There was a reduction in the mean length, mean maximum length ( L max), and proportion of large fish in these fish communities, and a corresponding increase in the proportion of small fish. Species with a large L max declined in mean catch rate and mean length in contrast to species with a small L max. The trend in the size-based indicators confirms that there has been a change in the size structure of the communities. This change is characterized primarily by a reduction in the abundance of larger sized individuals and a reduction in species with a large maximum length.

Dietary composition of juvenile Dissostichus eleginoides (Pisces, Nototheniidae) around Shag Rocks and South Georgia, Antarctica

A diet analysis of the Patagonian toothfish Dissostichus eleginoides, trawled in the South Georgia Islands area in March–April 1996, was carried out by frequency of occurrence (F%) and coefficient “Q” (%) methods. The samples consisted chiefly of immature specimens, with predominant length ranges of 30–70 cm (TL). Fish was by far the main food on the shelves of Shag Rocks and South Georgia, accounting for about 70% of prey. Krill appeared as secondary food, although its importance was overestimated by the frequency of occurrence method. Cephalopods and mysids were infrequent in the stomachs, and only at Shag Rocks and South Georgia, respectively. Lepidonotothen kempi, Champsocephalus gunnari and Chaenocephalus aceratus constituted the main fish prey and their variability between Shag Rocks and South Georgia depended on their local abundance. The large proportion of fish exhibiting stomachs full or close to fullness (together 62%) suggests that feeding intensity of the species was high.

Food Provisioning in Red-Necked Grebes (Podiceps Grisegena) at Common Carp (Cyprinus Carpio) Ponds

Parental feeding patterns were studied in red-necked grebe (Podiceps grisegena) broods throughout the entire period of parental care in a common carp (Cyprinus carpio) fish-pond area in SE Poland in 1993–2002. Fish formed a substantial part of prey provided to the flightless young from their second week of life. Although the numbers of large invertebrates and tadpoles, the alternative prey to fish, did not decrease during the chick rearing period, grebe parents gradually shifted from delivering predominately invertebrates to delivering fish, and the average size of fish fed to chicks increased with brood age. Broods with relatively high fledging success (at least two chicks fledged) had a larger proportion of fish in their diet than broods seriously reduced because of undernourishment. The dive duration of foraging grebe parents did not differ between carp, wild fish and non-fish prey, but carp prey required significantly more time for handling. The percentage of prey rejected by chicks increased over the prefledging period from 2 to 24%. Of the prey rejected, 82% were fish apparently too large for the young to swallow. Fish prevalence in the diet of red-necked grebe chicks at carp ponds contradicts the results of other studies on the feeding habits of the nominative subspecies during breeding season. However, the red-necked grebe is a gape-limited predator and the piscivory of the chicks is limited to small-bodied fish.

Some effects of marine reserve protection on the population structure of two spearfishing target‐fish species, Dicentrarchus labrax (Moronidae) and Sparus aurata (Sparidae), in shallow inshore waters, along a rocky coast in the northwestern Mediterranean Sea

Abstract1. The relative abundances of two highly sought after spearfishing target‐fish species, Dicentrarchus labrax (Linnaeus 1758) and Sparus aurata Linnaeus 1758, were compared using underwater visual censuses in shallow (<5 m) inshore waters along rocky shores inside and outside a marine reserve area in the northwestern Mediterranean Sea (Banyuls‐sur‐Mer region, France).2. The relative abundances of these two species were consistently lower outside the reserve area, which comprised around 40% of the 25.6 km of inshore coastal waters surveyed.3. The demographic structure of D. labrax was also different inside and outside the protected area, the proportion of larger fish being significantly higher in the marine reserve.4. The direct and indirect impacts of spearfishing are postulated to explain the distributional and population structural characteristics of these two species in the shallow waters off this rocky coast.5. Prohibition of spearfishing has favoured the persistence of these species during summer (the main spearfishing season) in the shallower inshore waters inside the area of the Cerbère/Banyuls‐sur‐Mer marine reserve.6. These preliminary results indicate the need for additional work in this area and further surveys to ascertain spearfishing impacts on target‐fish species in the vicinity of other marine protected areas.Copyright © 2001 John Wiley & Sons, Ltd.