Mar Biol (2008) 153:431–443 DOI 10.1007/s00227-007-0824-8 RESEARCH ARTICLE Diet of Neotropic cormorant (Phalacrocorax brasilianus) in an estuarine environment V. Barquete Æ L. Bugoni Æ C. M. Vooren Received: 3 July 2006 / Accepted: 17 September 2007 / Published online: 10 October 2007 Ó Springer-Verlag 2007 Abstract The diet of the Neotropic cormorant (Phala- temporary changes in diet in terms of food items, abun- crocorax brasilianus) was studied by analysing 289 dance and prey size were detected, revealing a high regurgitated pellets collected from a roosting site at Lagoa ecological plasticity of the species. Individual daily food dos Patos estuary, southern Brazil, between November intake of Neotropic cormorants estimated by pellets and 2001 and October 2002 (except April to June). In total, metabolic equations corresponded to 23.7 and 27.1% of 5,584 remains of prey items from 20 food types were their body mass, falling in the range of other cormorant found. Fish composed the bulk of the diet representing species. Annual food consumption of the population esti- 99.9% by mass and 99.7% by number. The main food items mated by both methods was 73.4 and 81.9 tonnes, were White croaker (Micropogonias furnieri) (73.7% by comprising mainly immature and subadult White croaker frequency of occurrence, 48.9% by mass and 41.2% by and Catfish which are commercially important. Temporal number), followed by Catfish (Ariidae) and anchovies variations in diet composition and fish size preyed (Engraulididae). In Lagoa dos Patos estuary the generalist by Neotropics cormorants, a widespread and generalist Neotropic cormorant fed mainly on the two most abundant species, suggest shifts according to fluctuations in the demersal fishes (White croaker and Catfish), which abundance of prey. The plasticity of this cormorant is also accounted for the low niche breadth calculated. The total revealed by their ability to adjust feeding behaviour in length of all fish preyed varied from 27.2 to 318.3 mm response to temporal or local changes in the environment, (113.5 ± 48.0 mm), and preyed White croakers’ size dif- from a generalist at the species level to a specialist at the fered between months. Neotropic cormorants seem to prey individual or local population level. on most abundant class sizes of White croaker instead of selecting similar prey size throughout the time. However, Introduction Communicated by A. Acosta. Marine organisms differ greatly in their ability to cope with V. Barquete Á L. Bugoni Á C. M. Vooren environmental changes, either natural or anthropogenic. Depto. de Oceanografia, Lab. de Elasmobraˆnquios e Aves Marinhas, Fundac¸a˜o Universidade Federal do Rio Grande In a continuum, species could benefit from changes FURG, CP 474, CEP 96207-490 Rio Grande, RS, Brazil by expanding their range and increasing population or decreasing in numbers down to the extinction point. & V. Barquete ( ) Feeding plasticity is of great adaptive value for animals Rua Alferes Poli, 381 apto 402—Centro, Curitiba, PR, Brazil e-mail: [email protected] coupling with environmental changes, as have been shown for a range of species. For instance, the Antarctic bottom- Present Address: dwelling fish (Trematomus hansoi) showed extreme feed- L. Bugoni ing plasticity, switching its feeding habits at the time of Division of Environmental and Evolutionary Biology, University of Glasgow, Graham Kerr Building G12 8QQ, fishery operations (Pakhomov 1998); and the Spitting cobra Glasgow, UK (Naja nigricollis) and Black forest cobra (N. melanoleuca) 123 432 Mar Biol (2008) 153:431–443 showed changes in the composition of diet from one habitat anchovy (Engraulis ringens) (Jorda´n 1967), and in Santa to another (Luiselli et al. 2002). On their turn, birds have Fe´, inland Argentina, they prey mainly on fish from open shown a wide range of strategies to deal with different waters and some crustacean species (Beltzer 1983). In changes (reviewed in Newton 1998). For instance, seabirds central Chile the Neotropical cormorant fed mainly upon in the North Atlantic and Barents Sea had responded dif- demersal fish and one crustacean species, but the study was ferently to the decline of pelagic fish stocks: surface- based on only 38 regurgitates and no data about size of fish feeding Kittiwakes (Rissa tridactyla) had difficulty in (Kalmbach et al. 2001), which is necessary to understand finding enough food, while pursuit diving Common guil- the ecological role of piscivorous predators on particular lemots (Uria aalge) and Puffins (Fratercula arctica) fared prey species, are available. In Galveston Bay, USA, 1,064 better (Barrett and Krasnov 1996; Carscadden et al. 2002). regurgitates were collected, with fish comprising the most Similarly, gulls (Larus spp.) and Great skua (Stercorarius of diet, and shrimp were the only invertebrate prey (King skua) increased in population size following the availabil- 1989). Thus, food requirements and diet based on large ity of fish discharges from vessels, but changed their sample sizes and a large temporal data set are not available foraging effort from scavenging to predation on seabirds, for Neotropic cormorants in their distribution areas. The after the decline of discharges (Carscadden et al. 2002; lack of detailed data on the diet of the widespread, abun- Votier et al. 2004). Optimal foraging theory predicts that an dant and generalist Neotropic cormorant preclude a clear organism will maximize its food intake rates; however, understanding of their ecological role and capacity to their ability to cope with changes in food availability dif- adjust to changing resources. fers greatly among species, and not all species are able Fish constitute the bulk of the cormorants’ and shags’ to deal efficiently with changes in food resources (Barrett diet, which are large waterbirds with cosmopolitan dis- and Krasnov 1996; Carscadden et al. 2002). In addition, tributions in marine, coastal and freshwater ecosystems predator responses can occur either in the short term, by (Barrett et al. 1990; Kirby et al. 1996; Neuman et al. changing prey species, foraging areas or delaying breeding 1997;Gre´millet et al. 2000; Nelson 2005). Their abun- season (Barrett and Krasnov 1996; Votier et al. 2004; dance in some areas raises concerns about the impacts Watanuki et al. 2004), or in the long term, by changing on fish stocks of economic value (Kirby et al. 1996), in trophic level or distribution areas (Thompson et al. 1995; commercial fisheries and aquaculture systems, such as the Newton 1998). In this study we investigate monthly vari- predation of cormorants on Catfish in the USA (Glahn and ations in the prey species and prey size of the generalist Stickley 1995), and predation upon sport fishing resources Neotropic cormorant (Phalacrocorax brasilianus) and how in North America (e.g. Ross and Johnson 1995). Cormo- they deal with variations in prey abundance. rants displace daily from colonies or nocturnal roosting The Neotropic cormorant lives in both freshwater and sites to feeding grounds, which limits their foraging range. marine environments (Harrison 1985), and they occur from For instance, 90% of radio-tracked foraging trips of southern USA to southern South America (Telfair and Neotropic cormorants in Argentina were within 2.5 km Morrison 1995). It is one of the most widely distributed of the colony (Quintana et al. 2004). As a consequence of cormorants in Americas, one of the most numerous seabird their limited foraging radius, large body size and abun- species in South America, and is remarkably versatile in its dance, cormorants could severely impact local fish stocks, use of habitats (Telfair and Morrison 1995). However, as shown by Birt et al. (1987) in Double-crested cormo- many aspects of its life history such as nutrition and rants (Phalacrocorax auritus) in Canada. Detailed study energetics, seasonal diet and population dynamics require of diet and calculations of daily food intake of the further study (Telfair and Morrison 1995; Kalmbach et al. Neotropic Cormorant are valuable information for the 2001). Neotropic cormorants are primarily generalists understanding of their role in the local environment. during breeding season, taking the most readily available A range of energetic and dietary approaches have been prey, particularly the fish that are most abundant (Telfair carried out to estimate seabird energy requirements and and Morrison 1995). They feed in protected bays and number of different fish species consumed, as well as nearshore waters along the coast by pursuit-diving from the comparison of seabird prey consumption and fishery water surface, using their feet for propulsion (Humphrey captures (Adams et al. 1991; Furness and Cooper 1982; et al. 1988; Telfair and Morrison 1995). Despite dietary Derby and Lovvorn 1997). studies being restricted to breeding season and based on In the Lagoa dos Patos estuary in southern Brazil, short-term data (reviewed by Telfair and Morrison 1995), Neotropic cormorant is present in all months, with spring the species is known to have flexible foraging techniques, (October to December) and summer (January to March) i.e. they are opportunistic rather than selective predators populations in the mouth of Lagoa dos Patos estimated (Humphrey et al. 1988; Quintana et al. 2004). For instance, at 1,400 birds (V. Barquete et al., submitted). Monthly the Neotropic cormorant in Peru prey mainly on Peruvian variations in number are poorly understood because they 123 Mar Biol (2008) 153:431–443 433 have variable breeding seasons in the area, their breeding similar food requirements were assumed to occur. Previous grounds were not fully located and their local or migratory studies on non-breeding adult and immature free-living movements are not clear. However, based on plumage cormorants elsewhere demonstrated that they typically characteristics the population is composed of post-breeding regurgitate one pellet per day, usually just before dawn and adults migrating from colonies away from the estuary and before leaving for fishing grounds (Telfair and Morrison immature birds that stay year-round in the area.