Phalacrocorax Auritus Research Articles

Effects of egg size on Double-crested Cormorant ( Phalacrocorax auritus) egg composition and hatchling phenotype

Maternal investment of yolk and albumen in avian eggs varies with egg mass and contributes to variation in hatchling mass. Here we use the natural variation in mass and composition of Double-crested Cormorant ( Phalacrocorax auritus) eggs to examine consequences of variation in yolk and albumen mass on hatchling phenotype. The Double-crested Cormorant, a large bird with altricial young, lays eggs ranging in mass from 40 to 60 g and containing an average of 82% albumen and 18% yolk. Variation in Cormorant egg mass arises primarily from variation in the amount of albumen and water in the eggs; yolk mass remains relatively constant, contributing only 10% to egg mass variation. Likewise, variation in hatchling mass correlates positively with albumen mass and albumen solids contribute to hatchling dry mass. Thus, variation in Cormorant egg mass is primarily the result of variation in the amount of egg albumen, which contributes most to variation in hatchling mass. Similarities in egg composition of altricial birds, along with data presented here, suggest that variation in hatchling mass of all altricial birds may depend most on the amount of egg albumen, unlike species with precocial young that hatch from eggs with substantially more yolk.

Evaluation of Aerial Cluster Sampling of Double‐Crested Cormorants on Aquaculture Ponds in Mississippi

Concern over increasing numbers of double-crested cormorants (Phalacrocorax auritus) and their impacts on channel catfish (Ictalurus punctatus) aquaculture has resulted in increased need for quantitative information to develop and evaluate depredation management efforts. We evaluated aerial surveys in a stratified cluster sampling (SCS) design to estimate and monitor abundance of cormorants on catfish aquaculture ponds in the Yazoo River Basin of Mississippi, USA (hereafter Yazoo Basin). Twice monthly abundance estimates and coefficient of variation during winter averaged 8,128 (n = 29, SE = 1,233) and 33% (n = 29, SE = 0.02), respectively. Counts of cormorants on catfish aquaculture ponds between survey years were correlated (r = 0.87, n = 28). The correlation between diurnal counts of cormorants on ponds and cormorant night roost counts was 0.64 in 2000–2001 and 0.58 in 2003–2004 (n = 20 in both years). A priori estimates of sample size indicated an average increase in sampling effort of 39% during peak periods of cormorant use would be necessary to detect a ±15% change in cormorant abundance on aquaculture ponds at α = 0.05 and β = 0.80. The sampling design we used has the potential to be an effective tool for providing quantitative information on cormorant abundance on catfish aquaculture ponds in the Yazoo Basin. However, increased sampling effort would be necessary to obtain desired levels of precision. The SCS design we evaluated represents only one of many possible survey methods, and we recommend additional evaluation of this method and related survey methods.

Examination of Factors Contributing to the Decline of the Yellow Perch Population and Fishery in Les Cheneaux Islands, Lake Huron, with Emphasis on the Role of Double-crested Cormorants

Double-crested cormorants increased exponentially in the Les Cheneaux Islands area during the 1980s and 1990s. The yellow perch fishery and population declined by the late 1990s and finally collapsed in 2000. Previous research confirmed that cormorants fed seasonally on perch. This analysis sought to use creel survey data and data from an annual gillnet collection to characterize the perch fishery and population during this time so as to explore if declines were a result of declining recruitment or increased mortality or both. Regression analysis explored six possible independent variables to account for yellow perch trends. Yellow perch abundance and its fishery declined throughout the Les Cheneaux Islands. Mean age declined which was consistent with a high mortality rate explanation. Yellow perch recruitment, as indicated by gillnet catch rate of age-2 perch, continued during this time including one very strong year class. Total annual mortality rates determined by the cohort method were as high as 85% during much of this time and increased over the time series. Cormorant abundance accounted for a total of five significant relationships with the yellow perch data, more than any other independent variable. From this, it is apparent that cormorant predation is at least one factor affecting the perch population and fishery and may be the most influential force, among those examined, during this time series.

Key Amino Acids in the Aryl Hydrocarbon Receptor Predict Dioxin Sensitivity in Avian Species

Dioxin-like compounds are toxic to most vertebrates, but significant differences in sensitivity exist among species. A recent study suggests that the amino acid residues corresponding to Ile324 and Ser380 in the chicken aryl hydrocarbon receptor 1 (AHR1) are important determinants of differential biochemical responses to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in chickens and common terns. Here, we investigate whether the identity of these amino acid residues can predict embryonic sensitivity to dioxin-like compounds in a wide range of birds. AHR1 sequences were determined in species for which sensitivity data were available. Of all the species surveyed, chickens were unique in having the Ile/Ser genotype and were also the most sensitive to dioxin-like compounds. Turkeys, ring-necked pheasants, and Eastern bluebirds (intermediate Ile/Ala genotype) were less sensitive than chickens but more sensitive than American kestrels, common terns, double-crested cormorants, Japanese quail, herring gulls, or ducks (Val/ Ala genotype). Our work suggests that key amino acids in the AHR1 ligand binding domain are predictive of broad categories of dioxin sensitivity in avian species. Given the large degree of variation in species sensitivity and the paucity of species-specific toxicity data, a genetic screen based on these findings could substantially improve risk assessment for dioxin-like compounds in wild birds.

Estimating walleye (Sander vitreus) density, gear catchability, and mortality using three fishery-independent data sets for Oneida Lake, New York

We used three long-term data sets (gill nets, trawls, and adult population estimates) for walleye ( Sander vitreus ) to simultaneously estimate density, gear catchabilities, and mortality using an age-structured, nonlinear model. Model constraints included a fixed natural mortality rate and age- and gear-specific but time-invariant catchabilities. Trawl catchability decreased with age, whereas gillnet catchability increased towards a maximum by age-4. A sensitivity analysis was conducted to investigate how the information content of the different data sets influenced parameter estimates. Estimated catchability values were relatively robust to changes in data weighting. Estimated gillnet catchability values were fairly consistent with those derived from more conventional methods. An additional mortality term was added to reflect double-crested cormorant ( Phalacrocorax auritus ) predation, and vulnerabilities associated with angling and cormorants were calculated using independent length frequency information. Estimated subadult mortality increased and the influence of fishing mortality slightly decreased during recent years when double-crested cormorants were abundant and more restrictive size limits were in place. Walleye density in Oneida Lake (New York, USA) in the last decade is estimated to be approximately half of that before 1990.

Water Regurgitation by Adult Double-crested Cormorants: A Possible Mechanism to Assist in Chick Thermoregulation

Abstract A previously undocumented thermoregulatory behavior of adult cormorants for their pre-fledged young was recorded during observations of a Double-crested Cormorant (Phalacrocorax auritus) colony in Lake of the Woods, Ontario. Many adult cormorants were observed regurgitating water over their chicks’ bodies. The authors believe that the warm temperature, intense sun, and calm winds during the observation periods were the primary factors triggering this previously undocumented thermoregulatory behavior.

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.

Male‐biased parasitism by common helminths is not explained by sex differences in body size or spleen mass of breeding cormorants Phalacrocorax auritus

In vertebrates, males are often more parasitised than conspecific females. This bias in parasitism might result from sex differences in parasite exposure and/or susceptibility to infection. Such information is important for testing hypotheses about allocation of resources to life histories of males and females and for testing hypotheses about factors thought to influence parasite fitness and parasite dynamics. We tested whether double‐crested cormorants Phalacrocorax auritus exhibit male‐biased parasitism by gut helminths. The prevalence of nematode Contracaecum spp. and trematode Drepanocaphalus spathans infections was ∼90% and 39%, respectively. Cestode, primarily Paradilepis caballeroi and acanthocephalan Andracantha gravida infections were less common (<10%). Male and female cormorants did not differ in prevalence of infection by any helminth species. However, males had twice the abundance and intensity of Contracaecum spp. infections and twice the intensity of D. spathans infections than found in females. For common parasites showing male‐biased parasitism, degree of parasitism was also unrelated to body size or mass in either sex. Males and females did not differ in spleen mass and spleen mass was unrelated to abundance of common parasites. Furthermore, abundance of trematodes and nematodes was not correlated. At present, male biases in parasitism by nematodes and trematodes in cormorants are independent patterns that remain unexplained, but are most likely attributable to sex differences in exposure and/or immunological differences not yet assessed.

Species Differences in the Sensitivity of Avian Embryos to Methylmercury

We injected doses of methylmercury into the air cells of eggs of 26 species of birds and examined the dose-response curves of embryo survival. For 23 species we had adequate data to calculate the median lethal concentration (LC(50)). Based on the dose-response curves and LC(50)s, we ranked species according to their sensitivity to injected methylmercury. Although the previously published embryotoxic threshold of mercury in game farm mallards (Anas platyrhynchos) has been used as a default value to protect wild species of birds, we found that, relative to other species, mallard embryos are not very sensitive to injected methylmercury; their LC(50 )was 1.79 microg/g mercury on a wet-weight basis. Other species we categorized as also exhibiting relatively low sensitivity to injected methylmercury (their LC(50)s were 1 microg/g mercury or higher) were the hooded merganser (Lophodytes cucullatus), lesser scaup (Aythya affinis), Canada goose (Branta canadensis), double-crested cormorant (Phalacrocorax auritus), and laughing gull (Larus atricilla). Species we categorized as having medium sensitivity (their LC(50)s were greater than 0.25 microg/g mercury but less than 1 microg/g mercury) were the clapper rail (Rallus longirostris), sandhill crane (Grus canadensis), ring-necked pheasant (Phasianus colchicus), chicken (Gallus gallus), common grackle (Quiscalus quiscula), tree swallow (Tachycineta bicolor), herring gull (Larus argentatus), common tern (Sterna hirundo), royal tern (Sterna maxima), Caspian tern (Sterna caspia), great egret (Ardea alba), brown pelican (Pelecanus occidentalis), and anhinga (Anhinga anhinga). Species we categorized as exhibiting high sensitivity (their LC(50)s were less than 0.25 microg/g mercury) were the American kestrel (Falco sparverius), osprey (Pandion haliaetus), white ibis (Eudocimus albus), snowy egret (Egretta thula), and tri-colored heron (Egretta tricolor). For mallards, chickens, and ring-necked pheasants (all species for which we could compare the toxicity of our injected methylmercury with that of published reports where methylmercury was fed to breeding adults and was deposited into the egg by the mother), we found the injected mercury to be more toxic than the same amount of mercury deposited naturally by the mother. The rank order of sensitivity of these same three species to methylmercury was, however, the same whether the methylmercury was injected or maternally deposited in the egg (i.e., the ring-necked pheasant was more sensitive than the chicken, which was more sensitive than the mallard). It is important to note that the dose-response curves and LC(50)s derived from our egg injections are useful for ranking the sensitivities of various species but are not identical to the LC(50)s that would be observed if the mother bird had put the same concentrations of mercury into her eggs; the LC(50)s of maternally deposited methylmercury would be higher.

SULFUR ISOTOPES LINK OVERWINTER HABITAT USE AND BREEDING CONDITION IN DOUBLE-CRESTED CORMORANTS

North American Double-crested Cormorant (Phalacrocorax auritus) populations have increased greatly. Both breeding and overwintering ground factors have likely contributed to these increases. However, demonstrating how overwintering conditions may affect breeding birds has not been possible because of the difficulty in linking breeding birds to their wintering grounds. Here, we demonstrate the utility of stable sulfur isotopes to elucidate overwintering habitat use by cormorants breeding on Lake Erie. Sulfur isotopes in feathers grown on overwintering grounds provided insights into the degree to which birds used freshwater vs. marine environments. The proportion of birds utilizing freshwater habitats increased through time. This change may have reflected increases in freshwater aquaculture (i.e., catfish) in the U.S. south. Examination of body condition in birds returning to breed on Lake Erie indicated that those individuals that solely used marine habitats for at least a portion of the overwintering period were in poorer condition than birds using freshwater. Enhanced foraging opportunities at aquaculture facilities may improve the fitness of individuals that have returned to breed after overwintering at such locations. This study is the first to demonstrate a linkage between overwinter habitat use and breeding ground parameters in Double-crested Cormorants. These results underscore that factors throughout the Mississippi flyway are likely acting together to regulate cormorant populations.

ECOSYSTEM-BASED MANAGEMENT OF PREDATOR–PREY RELATIONSHIPS: PISCIVOROUS BIRDS AND SALMONIDS

Predator-prey relationships are often altered as a result of human activities. Where prey are legally protected, conservation action may include lethal predator control. In the Columbia River basin (Pacific Northwest, USA and Canada), piscivorous predators have been implicated in contributing to a lack of recovery of several endangered anadromous salmonids (Oncorhynchus spp.), and lethal and nonlethal control programs have been instituted against both piscine and avian species. To determine the consequences of avian predation, we used a bioenergetics approach to estimate the consumption of salmonid smolts by waterbirds (Common Merganser, California and Ring-billed Gull, Caspian Tern, Double-crested Cormorant) found in the mid-Columbia River from April through August, 2002-2004. We used our model to explore several predator-prey scenarios, including the impact of historical bird abundance, and the effect of preserving vs. removing birds, on smolt abundance. Each year, <1% of the estimated available salmonid smolts (interannual range: 44,830-109,209; 95% CI = 38,000-137,000) were consumed, 85-98% away from dams. Current diet data combined with historical gull abundance at dams suggests that past smolt consumption may have been 1.5-3 times current numbers, depending on the assumed distribution of gulls along the reaches. After the majority (80%) of salmonid smolts have left the study area, birds switch their diet to predominantly juvenile northern pikeminnow (Ptychocheilus oregonensis), which as adults are significant native salmonid predators in the Columbia River. Our models suggest that one consequence of removing birds from the system may be increased pikeminnow abundance, which--even assuming 80% compensatory mortality in juvenile pikeminnow survival--would theoretically result in an annual average savings of just over 180,000 smolts, calculated over a decade. Practically, this suggests that smolt survival could be maximized by deterring birds from the river when smolts are present, allowing bird presence after the diet switch to act as a tool for salmonid-predator control, and conducting adult-pikeminnow control throughout. Our analysis demonstrates that identifying the strength of ecosystem interactions represents a top priority when attempting to manage the abundance of a particular ecosystem constituent, and that the consequences of a single-species view may be counterintuitive, and potentially counterproductive.

Male-biased parasitism by common helminths is not explained by sex differences in body size or spleen mass of breeding cormorants Phalacrocorax auritus

Male-biased parasitism by common helminths is not explained by sex differences in body size or spleen mass of breeding cormorants Phalacrocorax auritus

Fledgling Double-crested Cormorants Rehearse a Food Manipulation Technique with Woody Debris, Algae, and Shells

Abstract Fledgling Double-crested Cormorants (Phalacrocorax auritus) were observed practicing food manipulation techniques with large sticks, algae, and shells at their respective natal colonies in eastern Lake Ontario, North Channel of Lake Huron, and Lake of the Woods. Although practice behaviors have been documented for other species of waterbirds, this behavior has not been recorded previously for Double-crested Cormorants.

Bioenergetics and Prey Consumption of Breeding Double-crested Cormorants in the Beaver Archipelago, Northern Lake Michigan

Colonial waterbirds are an important component of Great Lakes ecosystems. In order to investigate the role these birds play in an aquatic food web, bioenergetics models, using allometric equations, were applied to breeding double-crested cormorants ( Phalacrocorax auritus) and their offspring in the Beaver Archipelago, northern Lake Michigan. These models were parameterized using detailed information collected during the 2000 and 2001 breeding seasons, as well as literature values. Each breeding season was divided into stages in the models to reflect changes in cormorant diet and population size documented in the study area. The models estimated the total prey biomass consumed as 1,445 metric tonnes (mt) of prey in 2000, and 1,585 mt of prey in 2001. Each year, the majority of the prey biomass was alewife ( Alosa pseudoharengus), with these fish comprising a greater percentage of prey biomass consumed in 2001. An increase in cormorant reproductive success in 2001 may be linked to this increase in alewife biomass consumed; the breeding bird population size, however, declined in 2001 as compared to 2000. The other prey items, which are not considered to be species of commercial or sport value, were also important contributors to bird diet and consumption of these species did tend to vary from year-toyear. Overall, the application of bioenergetics models allows for greater understanding of the role of cormorants as predators and as energy links in the system.

Comparison of sampling strategies to estimate abundance of double-crested cormorants in western Mississippi

We compared 2 sampling strategies designed to estimate abundance of double-crested cormorants (Phalacrocorax auritus, hereafter cormorants) on aquaculture ponds in western Mississippi. Cormorants are a major predator of cultured channel catfi sh (Ictalurus punctatus) in this region; thus, estimating cormorant abundance is needed to better determine their economic impact. We independently designed a species-specifi c survey (i.e., cluster sampling) and a general survey (i.e., transect sampling) based on robust probability sampling theory to estimate abundance of this target population. During winters 2002-2003 and 2003-2004, we conducted 8 pairs of surveys and compared estimates of cormorant abundance and associated precision using conventional paired t-tests and complimentary equivalency tests. Abundance estimates from sampling methods did not differ given a minimum important effect size of 1,420 individuals. Precision of estimates for both survey protocols was poor (the coeffi cient of variation (CV) was 39.5% for cluster samples and 45% for transect samples), and we were unable to defi nitively conclude if precision was similar between sampling methods (due to low sample size and high variability). We found sample sizes must increase 222% for cluster sampling and 538% for transect sampling to detect a 15% change in abundance on average. Thus, neither method met our goals of detecting a given effect size at a desired level of precision. We recommend investigating additional sampling designs that may provide precise estimates of abundance more effi ciently than the methods compared in this study.

Heat increment of feeding in double-crested cormorants (Phalacrocorax auritus) and its potential for thermal substitution

Diving endotherms inhabiting polar regions face potentially high thermoregulatory costs. Unless properly insulated, these animals will lose vast amounts of heat when diving in cold water, which has to be balanced by heat production. Heat generated as a by-product of digestion (heat increment of feeding, HIF) or from exercising muscles might be important in maintaining thermal balance under such conditions, as it would reduce the need for shivering thermogenesis. Recording the rate of oxygen consumption (V(O(2))), respiratory exchange ratio (RER), and stomach temperature, we studied the magnitude and duration of HIF in seven double-crested cormorants (Phalacrocorax auritus) following the voluntary ingestion of a single herring (Clupea pallasi) while birds rested in air. Conducting trials at thermoneutral (21.1+/-0.2 degrees C) and sub-thermoneutral temperatures (5.5+/-0.7 degrees C), we investigated the potential of HIF for thermal substitution. After the ingestion of a 100 g herring at thermoneutral conditions, V(O(2))was elevated for an average of 328+/-28 min, during which time birds consumed 2697+/-294 ml O(2) in excess of the resting rate. At sub-thermoneutral conditions, duration (228+/-6 min) and magnitude (1391+/-271 ml O(2)) of V(O(2))elevation were significantly reduced. This indicates that cormorants are able to use the heat generated as by-product of digestion to substitute for regulatory thermogenesis, if heat loss is sufficiently high. Altering meal size during sub-thermoneutral trials, we also found that HIF in cormorants was significantly greater after larger food intake. Based on these experimental results, a simple calculation suggests that substitution from HIF might reduce the daily thermoregulatory costs of double-crested cormorants wintering in coastal British Columbia by approximately 38%. Magnitude of HIF and its potential for thermal substitution should be integrated into bioenergetic models to avoid overestimating energy expenditure in these top predators.

Methodology to Quantify the Economic Impact of the Double-Crested Cormorant (Phalacrocorax auritus) to the Oneida Lake Region, New York

The economic impact of wildlife-caused damage and associated management is one of the many factors that arguably play a role in the decision-making process of wildlife managers. Often the role of an economist is to value the damage created by wildlife, or to assess programmatic efficiency to determine if changes can be made to increase return per dollar invested in management efforts. Frequently, the results of economic analyses of wildlife-caused damage are used to justify program efforts in the pursuit or maintenance of funding. The complexity of determining the economic impact of wildlife-caused damage requires that there is a clear understanding of the methodological approach used to determine impacts. Examining specific methodological approaches used in actual case studies provides a systematic replicable approach to valuing damage. This study outlines the methodology for determining the economic impact of cormorant damage to natural resources in a local economy: the Oneida Lake Region of central New York.

Effects of Roost Shooting on Double-Crested Cormorant Use of Catfish Ponds Preliminary Results

Author(s): Taylor, Jimmy; Strickland, Bronson | Abstract: Double-crested cormorants commonly depredate channel catfish at aquaculture facilities in the southeastern U.S., causing significant economic loss. Prior research has demonstrated regional night-roost harassment (i.e., “major pushes”) to be an effective technique to temporarily reduce cormorant use on aquaculture ponds; however, these efforts were extremely labor intensive and changes in impacts were difficult to quantify. We conducted a preliminary study to investigate the efficacy of site-specific, night-roost dispersal (n = 6) using lethal control on cormorant abundance by monitoring the number of birds at randomly selected aquaculture facilities for 3 days prior to and following night-roost dispersals. The effect of dispersal varied greatly by study site. At one site, the mean abundance of cormorants on catfish production ponds decreased following dispersal; however, on the other 5 sites the mean abundance of cormorants did not change on catfish production ponds following night-roost dispersal. We recommend further research to evaluate the effectiveness of night-roost dispersal using lethal control. Furthermore, we offer recommendations for the design of future large-scale studies, which include improvements to reduce large variation.

Incidental catch of seabirds in Newfoundland and Labrador gillnet fisheries, 2001-2003

Incidental catch of seabirds in gillnet fisheries in Newfoundland and Labrador, Canada, has been identified in several fisheries, but defendable estimates are unavailable. Despite reduced fishing effort in several fisheries, concern remains that catch rates might negatively impact local seabird populations. Based on data sources within Fisheries and Oceans Canada (St. John's, Canada), total numbers of incidentally caught seabirds in nearshore and offshore Newfoundland waters were estimated for the years 2001, 2002 and 2003. Incidental catch rates were derived using net-days as measures of effort, with fishing trips as sampling units. Confidence intervals were estimated using resampling techniques. Most reports originated from the nearshore gillnet fishery for Atlantic cod Gadus morhua, although many birds were captured in other fisheries. The most commonly captured seabirds were murres Uria sp. and shearwaters (genera Calonectris and Puffinus), although other species were also captured in smaller numbers. As many as 2000 to 7000 murres, over 2000 shear- waters (various species), and tens to hundreds of northern fulmars Fulmarus glacialis, gannets Morus bassanus, double-crested cormorants Phalacrocorax auritus, loons (genus Gavia), eider ducks Soma- teria mollissima, razorbills Alca torda, puffins Fratercula arctica, black guillemots Cepphus grylle and dovekies Alle alle were estimated to have been captured annually in the area during the period 2001 to 2003, although catches varied considerably from year to year. Populations of these species are not presently thought to be declining due to this incidental mortality; however, present catch levels may contribute to limited growth in these populations, and populations might be affected if fishing effort were to increase.

Incidental catch of seabirds in Newfoundland and Labrador gillnet fisheries, 2001-2003

ESR Endangered Species Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials ESR 5:149-160 (2008) - DOI: https://doi.org/10.3354/esr00094 Incidental catch of seabirds in Newfoundland and Labrador gillnet fisheries, 2001–2003 Steven Benjamins1,3,*, David W. Kulka2, Jack Lawson2 1Whale Research Group, Biology Annex, Memorial University of Newfoundland, 297 Mt. Scio Road, St. John’s, Newfoundland and Labrador A1B 3V6, Canada 2Fisheries and Oceans Canada, PO Box 5667, St. John’s, Newfoundland and Labrador A1C 5X1, Canada 3Present address: Joint Nature Conservation Committee, Monkstone House, City Road, Peterborough, Cambridgeshire PE1 1JY, UK *Email: stevenbenjamins@yahoo.com ABSTRACT: Incidental catch of seabirds in gillnet fisheries in Newfoundland and Labrador, Canada, has been identified in several fisheries, but defendable estimates are unavailable. Despite reduced fishing effort in several fisheries, concern remains that catch rates might negatively impact local seabird populations. Based on data sources within Fisheries and Oceans Canada (St. John’s, Canada), total numbers of incidentally caught seabirds in nearshore and offshore Newfoundland waters were estimated for the years 2001, 2002 and 2003. Incidental catch rates were derived using net-days as measures of effort, with fishing trips as sampling units. Confidence intervals were estimated using resampling techniques. Most reports originated from the nearshore gillnet fishery for Atlantic cod Gadus morhua, although many birds were captured in other fisheries. The most commonly captured seabirds were murres Uria sp. and shearwaters (genera Calonectris and Puffinus), although other species were also captured in smaller numbers. As many as 2000 to 7000 murres, over 2000 shearwaters (various species), and tens to hundreds of northern fulmars Fulmarus glacialis, gannets Morus bassanus, double-crested cormorants Phalacrocorax auritus, loons (genus Gavia), eider ducks Somateria mollissima, razorbills Alca torda, puffins Fratercula arctica, black guillemots Cepphus grylle and dovekies Alle alle were estimated to have been captured annually in the area during the period 2001 to 2003, although catches varied considerably from year to year. Populations of these species are not presently thought to be declining due to this incidental mortality; however, present catch levels may contribute to limited growth in these populations, and populations might be affected if fishing effort were to increase. KEY WORDS: Incidental catch · Seabirds · Newfoundland and Labrador · Canada · Murres · Shearwaters Full text in pdf format PreviousNextCite this article as: Benjamins S, Kulka DW, Lawson J (2008) Incidental catch of seabirds in Newfoundland and Labrador gillnet fisheries, 2001–2003. Endang Species Res 5:149-160. https://doi.org/10.3354/esr00094 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in ESR Vol. 5, No. 2-3. Online publication date: December 23, 2008 Print ISSN: 1863-5407; Online ISSN: 1613-4796 Copyright © 2008 Inter-Research.