Phalacrocorax Carbo Sinensis Research Articles

Organochlorines and mercury in livers of great cormorants ( Phalacrocorax carbo sinensis) wintering in northeastern Mediterranean wetlands in relation to area, bird age, and gender

Wild birds are exposed to pollutants in their habitats. Top consumers of aquatic environments such as the fish-eating great cormorant ( Phalacrocorax carbo sinensis) are especially affected due to the bioaccumulation of toxic substances in their tissues. This study analysed the livers of 80 great cormorants from Greece to estimate the concentration of organochlorines and mercury and to examine their possible toxic effects and origin. The results showed that mercury (geometric mean 8089 ng g −1 dw), p,p′-DDE (2628 ng g −1 dw), ∑ HCHs (47 ng g −1 dw) and HCB (116 ng g −1 dw) concentrations can be considered high compared with those found in great cormorant livers elsewhere except in highly polluted areas, whereas ∑ PCBs occurred in relatively low concentrations (1091 ng g −1 dw). β-HCH was the dominant HCH isomer. Pollutant levels were generally unrelated to area, age and gender. However, p,p′-DDE and p,p′-DDD showed intersite differences, whilst the proportion of PCBs with 8 chlorine atoms were significantly higher in adult than 1st year great cormorants. Pollution did not reflect local patterns but rather these along the Baltic and Black Seas, whilst differences in p,p′-DDE concentration and ∑ DDTs/∑PCBs ratios between Evros, Axios or Amvrakikos, found on common migration route, suggested different bird origins. Most birds had toxic mercury concentrations; 83.7% above 4000 ng g −1 dw and 16% above 17,000 ng g −1 dw. Other pollutant levels were too low to have adverse effects.

Model comparison and assessment for multi-state capture–recapture–recovery models

The work of this paper is motivated by a study of Great Cormorants, Phalacrocorax carbo sinensis, in Denmark. The dataset is complex, involving birds in different states living in and moving between neighbouring colonies. As a consequence, the set of probability models that might describe the data is large. In order to choose between the models, we present a score test approach for moving efficiently between the members of a model set with many members. We then provide a new measure for testing the absolute goodness-of-fit of the selected model to the data. This measure may be used when a model is multi-state/multi-site, and involves age- and time-dependence, as well as integrated recovery and recapture data, which is needed for the application. An illustration is provided by data from a single colony only, but with two breeding states, and an additional emigrated state.

Stress responses of carp pond fish stock upon hunting activities of the great cormorant(Phalacrocorax carbo sinensis L.)

In addition to direct predation, cormorants can affect carp pond fish stock through disturbance and wounding of the fish. Fish stress response was evaluated by catch per unit effort (CPUE) using lift-net sampling. A significantly higher (P<0.001) CPUE was recorded in the littoral region of ponds affected by cormorant visits (43.6 ± 39.6) in comparison with a control pond (CP) without their occurrence (0.9 ± 1.1). Stress indices, spleen somatic index (SSI) and Fulton's condition coefficient (FCC) were evaluated for fish subject to two stress factors, hunting cormorants (HC) and pond harvesting (PH), and compared with levels in fish from the CP. Both SSI and FCC decreased significantly (P<0.05) in PH and HC fish in comparison with the control group, while non-significant differences were observed in both SSI and FCC indices among the HC and PH groups. Plasma biochemical indices (cortisol, glucose and lactate concentrations) were significantly higher (P<0.01) in the PH group as compared with the HC and CP groups. Concentrations in the HC and CP groups did not differ significantly. Total plasma protein levels were significantly higher (P<0.01) in HC fish compared with CP fish, but did not differ significantly from PH fish.

Changes in fish stocks in an Estonian estuary: overfishing by cormorants?

AbstractVetemaa, M., Eschbaum, R., Albert, A., Saks, L., Verliin, A., Jürgens, K., Kesler, M., Hubel, K., Hannesson, R., and Saat, T. 2010. Changes in fish stocks in an Estonian estuary: overfishing by cormorants? – ICES Journal of Marine Science, 67: 1972–1979. In Estonia, the cormorant Phalacrocorax carbo sinensis is a newcomer, and its numbers have increased rapidly since 1985. In the shallow protected (no fishery) Käina Bay in Väinameri (West Estonia), the colony was established in 1995. Gillnet sampling indicated that roach was the most abundant spawning fish species in 1995. Ten years later, when the study was repeated, the catch per unit effort was already more than 100 times lower than in 1995. The number of spawning perch decreased tenfold from 1995 to 2005. During the same period, commercial fishing effort in the entire Väinameri area decreased several times. The change in fish abundance in the Käina Bay and in the coastal fish-monitoring areas in the archipelago sea nearby, together with an analysis of food of cormorants, indicates that the decline in fish abundance might be related to the increased numbers of cormorants. The conclusion is drawn that the establishment of a cormorant colony could have seriously damaged or even prevented normal functioning of historically important spawning grounds and affected fish recruitment to adjacent areas. Therefore, expanding bird colonies might play a role similar to an expanding fishing fleet, by overexploiting the resource.

A technique to measure the volume of diving birds during voluntary dives

Buoyancy has a substantial contribution to the total mechanical cost of diving in waterbirds. Most of the techniques currently employed to estimate buoyancy are based on measuring the volume of carcasses or forcibly submerged birds using the water displacement (Archimedes) principle. In such techniques, the voluntary control the bird might have over plumage and respiratory air volumes is neglected. Here, I propose an adjustment to the water displacement measurement that allows the measurement of buoyancy in real-time from unrestrained live birds diving voluntarily. The novelty and accuracy of the technique lie in using a pressure sensor to continuously measure the water level inside the dive tank while filtering out the interference from surface waves. The error of the volume measurement in the proposed technique was only ±2.4%. Feasibility of measurement is demonstrated on captive Great Cormorants (Phalacrocorax carbo sinensis). The measured volumes of Great Cormorants exceeded predictions made based on the volume of carcasses and on average resembled values measured from live restrained birds. However the technique highlighted the high variation in buoyancy of live birds (up to 30%) as a result of small changes in the air volumes taken with the bird underwater.

Behavioural response of carp (Cyprinus carpio, L.) pond stock upon occurrence of hunting great cormorant (Phalacrocorax carbo sinensis) flocks

Besides various physiological and biological indices, stress in fish can be expressed directly by changes in their behaviour. Electrofishing point sampling approach based on CPUE (catch per unit effort) was used to evaluate fish density (escapement) into the littoral zones of four Czech ponds as a reaction to the occurrence and hunting activities of great cormorant (Phalacrocorax carbo sinensis) flocks. The behaviour of two-year-old common carp (Cyprinus carpio) before and after cormorant arrival was compared. Significant differences (P < 0.001) in CPUE were recorded in fish density before and after cormorant arrival on all of four ponds under study—Žofinský: 0.04 ± 0.18 and 22.38 ± 26.87 (mean ± SD), Starý Hospodař: 0.05 ± 0.29 and 25.49 ± 25.45, Žebrakov: 0.16 ± 0.57 and 28.58 ± 24.75 and Travicný: 0.03 ± 0.19 and 17.18 ± 18.20, respectively. The evaluation of fish wounding in the CPUE fish samples proved the proportion of fish injured by cormorant attacks ranging from 3.33 to 18.19% in the ponds under study.

Diet of the Great Cormorant (Phalacrocorax carbo Sinensis) at the Juodkrantė Colony, Lithuania

Substantial population increases in the Great Cormorant (Phalacrocorax carbo sinensis) in Lithuania since the mid 1980s have given rise to complaints by fishermen and fish farmers that the stocks of fish that they target or cultivate are being depleted. In order to test the veracity of these claims, we investigated the dietary composition of the Great Cormorant breeding colony at Juodkrantė on the Curonian Spit, Lithuania, through the analysis of 220 pellets, collected during the breeding seasons in 2005–2007. At least 25 fish taxa were identified in the sample, but only three dominated by both abundance (82.9%) and biomass (73.6%), namely Ruffe (Gymnocephalus cernuus), Perch (Perca fluviatilis) and Roach (Rutilus rutilus). The mean total length of fish prey caught was 9.5 cm and the mean weight was 16.8 g. Commercial fish species comprised a large proportion of the Great Cormorant diet (83% by biomass), predominately small, low commercial value fish, mostly Roach. Despite the proximity of the Baltic Sea ...

The use of coded wire tags to estimate cormorant predation on fish stocks in an estuary

One of the main obstacles to resolving the conflict between an increasing population of cormorants, Phalacrocorax carbo sinensis, and the fishing industry is the lack of documentation of the effect of the birds’ predation on fish stocks. Tagging and releasing fish with coded wire tags followed by intensive cormorant pellet sampling may be a viable method to measure the impact of cormorants on fish populations. To test this new method, we studied cormorant predation in a shallow estuary, where nearly 100 000 fish were tagged and more than 10 000 cormorant pellets were collected over a 3-year study period. A total of 112 tags were recovered from the collected pellets. Analyses of tag recovery data indicated considerable cormorant predation on tagged flounder, eel and salmon smolts, but the method did not deliver high-quality documentation, mainly because of limitations in pellet sampling. We conclude with recommendations to enhance the value of this method.

Experimental studies on the development of Contracaecum rudolphii (Nematoda: Anisakidae) in copepod and fish paratenic hosts

The larval development of the nematode Contracaecum rudolphii (Rudolphi, 1819), a common parasite of the proventriculus of cormorants, was experimentally studied. Within the eggs cultivated in freshwater under laboratory temperatures of 20-22 degrees C, the developing larva undergoes two moults on days 4-5, attaining the third larval stage. Most of the ensheathed third-stage larvae, 291-457 microm long, hatch spontaneously from egg shells on days 5-6. Experiments have indicated that hatched ensheated third-stage larvae and those still inside egg capsules are already infective to copepods and fishes, which both can be considered paratenic (meta-paratenic) hosts. Five copepod species, Acanthocyclops vernalis, Cyclops strenuus, Ectocyclops phaleratus, Eucyclops serrulatus and Megacyclops viridis, the isopod Asellus aquaticus and small carps Cyprinus carpio were infected by feeding them these larvae. In addition, 9 fish species, Alburnoides bipunctatus, Anguilla anguilla, Barbatula barbatula, Cyprinus carpio, Gobio gobio, Perca fluviatilis, Phoxinus phoxinus, Poecilia reticulata and Tinca tinca, were successfully infected by feeding them copepods previously infected with C. rudolphii third-stage larvae. In fishes, larvae from copepods penetrate through the intestinal wall to the body cavity, where, in a few weeks, they become encapsulated; the larvae substantially grow in fish, attaining the body length up to 4.87 mm. In carp fry, the nematode third-stage larvae survived for about 15 months (up to 18 months in fish infected directly, i.e., without copepods). One small cormorant (Phalacrocorax carbo sinensis) was successfully infected by feeding it with copepods harbouring C. rudolphii third-stage larvae.

Cormorant impact on trout (Salmo trutta) and salmon (Salmo salar) migrating from the river Dalälven emerging in the Baltic Sea

Cormorant (Phalacrocorax carbo sinensis) population increases and the resulting predation, can lead to severe effects on fish stocks. In the Dalälven River in Sweden, it was observed that the number of trout and salmon returning to spawn decreased, while the number of cormorants along the coast had increased simultaneously. This study estimated the predatory impact that cormorants had on stocked trout (Salmo trutta) and salmon (Salmo salar) populations in 2005 and 2006 by using Coded Wire Tags and Carlin tags recovered in cormorant pellets. Predatory impact on salmon was found to be low, as no tags were recovered. Impact on trout was estimated 1.9%. Additional inspections of material within and around nests for tags gave similar estimates within a low range 0.8–2.3%.

Sexual differences in the diet of great cormorants Phalacrocorax carbo sinensis wintering in Greece

Sexual differences in the diet of the great cormorant, Phalacrocorax carbo sinensis, were studied in four Greek wintering areas, the Amvrakikos Gulf, the Axios and Evros Deltas and the Messolonghi Lagoon, through the analysis of stomach contents. Great cormorants are birds sexually dimorphic in size, with males being generally larger than females. Although similar prey species were found in the stomachs of both sexes in all the studied areas, significant differences were observed with respect to the proportion of species taken. Male birds ate higher proportions of large fish species such as grey mullets, European sea bass, Dicentrarchus labrax, and Prussian carp, Carassius gibelio, while female birds took higher proportions of smaller species such as big-scale sand smelt, Atherina boyeri, and black goby, Gobius niger. As a consequence, male great cormorants were found to feed on significantly larger prey than did females by means of fish standard length and body mass. There was no significant difference between the sexes in the mass of food found in stomachs.

Creation and development of the subcolony in Cormorant Phalacrocorax carbo sinensis at the Jeziorsko reservoir, Central Poland

Creation and development of the subcolony in Cormorant Phalacrocorax carbo sinensis at the Jeziorsko reservoir, Central Poland

Habitat and Temporal Variation in Diet of Great Cormorant Nestlings in Greek Colonies

Abstract Diet of Great Cormorant (Phalacrocorax carbo sinensis) nestlings was studied during four consecutive breeding seasons (1999-2002) at three Greek colonies (Axios Delta, and Lakes Kerkini and Mikri Prespa) in order to assess variation and commercial value of prey. A variety of fish taxa were found in nestlings’ regurgitates in each area and season, but only one or two dominated by numbers or biomass. Black Goby (Gobius jozo), Round Sardinella (Sardinella aurita) and Twaite Shad (Alosa fallax) were the most important prey in the Axios Delta; Bleak (Alburnus alburnus), Giebel (Carassius auratus gibelio) and Roach (Rutilus rutilus) at Lake Kerkini; Chalcalburnus belvica and Giebel at Lake Mikri Prespa. Nestling diet varied both seasonally (but only at Lake Kerkini significantly so) and annually (significantly in the Axios Delta and at Lake Mikri Prespa). Temporal changes can be attributed to changes in prey availability and abundance and confirm this bird’s opportunistic behavior. Between-colonies, di...

Molecular evidence for the occurrence of Contracaecum rudolphii A (Nematoda: Anisakidae) in shag Phalacrocorax aristotelis (Linnaeus) (Aves: Phalacrocoracidae) from Sardinia (western Mediterranean Sea)

Specimens of Contracaecum rudolphii Hartwich, 1964 (Nematoda: Anisakidae) from Phalacrocorax aristotelis (Linnaeus) from the Archipelago of La Maddalena (Sardinia, western Mediterranean Sea) were characterised genetically and compared with C. rudolphii A sensu D’Amelio et al. 1990 and C. rudolphii B sensu D’Amelio et al. 1990 from Phalacrocorax carbo sinensis (Blumenbach) from north-eastern Italy, and with C. rudolphii C sensu D’Amelio et al. 2007 from Phalacrocorax auritus (Lesson) from west-central Florida, USA. The sequencing of the small subunit of the mitochondrial ribosomal RNA gene ( rrnS) and by polymerase chain reaction–restriction fragment length polymorphism (PCR-RFLP) analysis of the same gene and of the internal transcribed spacers (ITS) of nuclear ribosomal DNA (rDNA) allowed the identification of all specimens of C. rudolphii from P. aristotelis as C. rudolphii A. The results confirmed that the definition of genetic markers, following the analysis of nuclear ribosomal and mitochondrial DNA, provides quick and practical diagnostic tools for the detection of the 3 sibling species of C. rudolphii. The occurrence of C. rudolphii in P. aristotelis is reported for the first time from the Mediterranean area, improving the picture of the dispersal patterns of the populations of these piscivorous birds, and confirming the existence of different and isolated populations between the North and South European waters.

Prey detection by great cormorant (Phalacrocorax carbo sinensis)in clear and in turbid water

The scattering and absorption of light by water molecules and by suspended and dissolved matter (turbidity) degrade image transmission and, thus, underwater perception. We tested the effects on visual detection of prey size and distance (affecting apparent prey size) and of low-level water turbidity in hand-reared great cormorants (Phalacrocorax carbo sinensis) diving for natural prey (fish) in a forced-choice situation. The cormorants' detection of underwater prey relied on vision. The minimal tested subtending visual angle of the prey at detection ranged between approximately 34.2' (prey size constant; distance varied) and 9.5' (distance constant; prey size varied). For all tested distances (0.8-3.1 m) the mean detection success was significantly higher than the chance level. The probability of a correct choice declined significantly with increased distance, with Detection success=-0.034D+1.021 (where D is distance, r(2)=0.5, N=70, P<0.001). The combined effect of turbidity and distance on the probability of detection success was significant, with both variables having a negative effect: Detection success=-0.286D-0.224Tu+1.691 (where Tu is turbidity, r(2)=0.68, N=144, P<0.001). At prey detection threshold, the relationship between distance and turbidity was: D=3.79e(-4.55Tu). It is concluded that (i) the subtending angle of natural prey at detection was lower than that of resolution of square-wave, high-contrast grating and (ii) turbidity, at levels significantly lower than commonly used in behavioural experiments, had a pronounced effect on visually mediated behaviour patterns.

Reproductive performance of the great cormorant (Phalacrocorax carbo sinensis) in three Greek colonies

Several breeding parameters of the great cormorant (Phalacrocorax carbo sinensis) were studied in Greece in 2001 and 2002 and were found to be generally higher at Lake Kerkini than in the other colonies. Fledging success (proportion of hatched eggs that led to fledged nestlings) was significantly higher at Lake Kerkini and in the Axios Delta in both years than at Lake Mikri Prespa in 2002. Mean fledgling production (the number of young fledged per initiated clutch) was significantly higher at Lake Kerkini than at Lake Mikri Prespa in 2002. The high fledgling production (2.15–2.75 fledglings on average in this study), the high food availability and the low initial population density allowed the total Greek breeding population to grow at a fast rate (19.0% per annum) in the 1990s. Given the scarcity of information on great cormorant nesting in Greece, basic breeding parameters are important for modelling population dynamics.

Reproductive Biology of Great Cormorant (Phalacrocorax carbo sinensis ) in the Qinghai-Tibet Plateau

There have been no detailed studies on reproductive biology of the Great Cormorant (Phalacrocorax carbo sinensis) in Qinghai-Tibet Plateau. We conducted such investigations during the breeding seasons of 1999 and 2000 in Qinghai-Lake Bird Isle, China. Great Cormorants began to migrate to Qinghai-Lake for reproduction from the middle of March and left from early October at the end of reproduction. Nesting periods were from early April to mid June and took 50 days. Egg-laying occurred during the three weeks from the end of April to 20 May. Females typically laid an egg every 1-2 days until clutch completion. Mean clutch size in the study area over two years was 3.3 (SE +/- 0.13, N = 68, range 1-5) and most (66.18%) fell within the range 3-4 eggs. Length of eggs averaged 61.01 mm and breadth averaged 34.13 mm. Fresh egg weight averaged 57.34 g (SE +/- 0.36, range 46.0-73.7 g, N = 179). Hatching success was 48.7% and fledging success was 64.9% over two years. Decline of available fish resources in Qinghai-Lake might be one of main causes of lower reproductive success. The causes of chick loss were possibly high altitude, high winds and prolonged rain.

Computer-assisted image analysis in the evaluation of fish wounding by cormorant [Phalacrocorax carbo sinensis (L.)] attacks

Fish that have escaped from a cormorant’s (Phalacrocorax carbo sinensis (L.)) grasp and/or which could not be swallowed due to their size suffer from various injuries resulting in consecutive infections and subsequent increased mortality. Computer-assisted image analysis was applied to describe the extent of such injuries. Two-year-old mirror carp, Cyprinus carpio L. (TL 200–300 mm, W 200–300 g) showed injuries ranging over approximately 10% of the total body surface. Immediately after wounding, the damaged epithelium (scars) cover 5–35%, and deeper subdermal wounds caused by the beak tip pervading into muscle tissue cover an area of 1–2% of the total body surface. On the side impacted by the cormorant’s lower mandible, extensive areas of epidermal contusions (scars) occur. As time progresses, these ratios change—deeper necroses represent up to 10% of the total body surface and healing epithelial scars comprise just 1–2%. In wounded silver carp, Hypophthalmichthys molitrix Val. (300–400 mm, W 500–700 g), the share of subdermal wounds usually does not exceed 0.5% due to their compact scaly cover. During pond draining due to fish harvesting, the size spectrum of wounded fish increases and may also often include bigger fish (e.g., European catfish, Silurus glanis L.) up to 2.2 kg.

Dispersal and recruitment during population growth in a colonial bird, the great cormorantPhalacrocorax carbo sinensis

While the factors influencing reproduction and survival in colonial populations are relatively well studied, factors involved in dispersal and settlement decisions are not well understood. The present study investigated exchanges of great cormorantsPhalacrocorax carbo sinensisamong six breeding colonies over a 13‐year period when the breeding population in Denmark increased from 2800 to 36 400 nests. We used a multistate capture‐recapture model that combined multisite resightings and recoveries to examine simultaneously recruitment, natal dispersal, breeding dispersal and annual survival of first‐year, immature and breeding great cormorants. Mean survival of first‐year birds (0.50±0.09, range=0.42–0.66 among colonies) was lower than survival of breeders (0.90±0.06, range=0.81–0.97). Mean survival of immature birds over the study period was 0.87±0.08. Dispersal from a colony increased with decreasing mean brood size in the colony in both first‐time and experienced breeders. The choice of the settlement colony in first‐time breeders was affected by conditions in the natal colony and in the colonies prospected during the pre‐breeding years. In particular, first‐time breeders recruited to colonies where they could expect better breeding success. Experienced breeders relied mainly on cues present early in the season and on their own breeding experience to choose a new breeding colony. Newly established colonies resulted mainly from the immigration of first‐time breeders originating from denser colonies. Dispersal was distance‐dependent and first‐time breeders dispersed longer distances than breeders. We suggest that the prospecting behaviour allows first‐time breeders to recruit in nearby as well as more distant potential breeding colonies. Dispersing breeders preferred to settle in neighbouring colonies likely to benefit from their experience with foraging areas. We discuss the importance of these movements for growth and expansion of the breeding population.

Dispersal and recruitment during population growth in a colonial bird, the great cormorant Phalacrocorax carbo sinensis

Dispersal and recruitment during population growth in a colonial bird, the great cormorant Phalacrocorax carbo sinensis