Feeding ecology ofUrophycis brasiliensison the Uruguayan coast of the Río de la Plata estuary

Abstract

Instituto Oceanogra´fico, Universidade de Sa˜o Paulo, Sa˜o Paulo, BrasilSummaryThe Brazilian codling (Urophycis brasiliensis) is the target of animportant artisanal fishery in Uruguay. In the present study weanalysed the feeding habits of this species over a 2-year cycle.Thesampleswereobtainedfromlandingsoftheartisanalfisheryat two sites on the Uruguayan coast: one representing atransitional habitat between estuarine and marine conditions(Piria´polis), the other representing a typical marine ecosystem(La Paloma). Different approaches were considered (Index ofRelative Importance, IRI; graphical methods and multivariatetechniques of cluster analysis and Principal Component Ana-lysis). The ontogenetic changes in the diet were also assessed.Stomachcontentsof870individualswereanalysedandatotalof24 prey species identified. The shirmp Artemesia longinaris hasthe highest IRI (89.9%) score followed by Cynoscion guatucupa(IRI ¼ 4.3%). Molluscs were only marginally represented(IRI < 0.01%). Both the graphical method of Corte´s and themethod of Amundsen indicate the specialization of Braziliancodling to A. longinaris. However, a trend to a generalist dietevolves in bigger fishes, which also consume fishes in importantquantities, mainly C. guatucupa. Moreover, opportunism isoccasionallypresentbothseasonallyandspatially,andrespondsto variations of the availability of prey items throughout itsdistribution.U.brasiliensispredationplaysanimportantroleinthe trophic dynamics of the SW Atlantic ecosystem. It isdependent on shrimp for feeding, a reason for an integratedmanagement of coastal habitat and fisheries of both resources.ThedependenceofBraziliancodling,mainlywhenitissmall,onshrimp calls for an integrated management of both the coastalhabitat and fisheries.IntroductionThe coastal estuarine and marine ecosystems are of greatimportance for the fish community. During their juvenile andadultsstages,thesesystemsofferpotentialforagingareasaswellas refuge from aquatic predators. Estuarine and diadrom fishspecies usuallypreferthisenvironment forspawningbecauseofthe excellent nursery zones for their larvae (Potter and Hyndes,1999;Methven et al., 2001).This studyis focusedonthe Ri´odelaPlataestuaryanditsadjacentAtlanticOceanwaters.TheRi´ode la Plata is a very large temperate ecosystem characterised bystratified conditions with a saline wedge along the Uruguayancoast from the ocean towards the estuary head (Nagy et al.,1997;Lo´pezLabordeandNagy,1999).Thisfactallowsentranceofmarinespeciesintotheestuary.Urophycisbrasiliensis(Kaup,1858) (Brazilian codling) is a permanent and common inhabit-antoftheRi´ode laPlata(Jaureguizar et al.,2003).Thisspeciesis abundant in waters where depths are greater than 60 m(Goldstein, 1986), and its geographic distribution extends fromArgentina(40 S)toBrazil(23 S)(Cousseau,1993;Acun˜aet al.,2000).Braziliancodlingmigratesseasonallybetweenthemiddleand external regions of the Ri´o de la Plata estuary, being moreabundant at the external area in summer (12–16 m depth andsalinities between 25 and 34 psu) (Jaureguizar et al., 2003). Onthe Uruguayan coast it is associated with temperatures below19 C (Acun˜a, 2001), while in the Ri´o de la Plata U. brasiliensisoccurs in waters ranging from 9.5 C (autumn) to 21.8 C(summer) and salinities from 15 (spring) to 30 (summer)(Jaureguizaret al.,2003).Informationregardingfeeding,repro-duction, growth and fishery exploitation have been analysed byAcun˜aet al.(2000),Vianaet al.(2000)andAcun˜a(2001).ThesestudiesrevealedthatU.brasiliensisisanactivebenthic-demersalpredator, which has a slow growth and presents gonadal restduringmostoftheyear.Duetothequalityoftheirflesh,thisfishconstitutes a very attractive and valuable artisanal resource(Acun˜a and Verocai, 2001).Due to the multispecific nature of the fisheries along theUruguayan coast, proper management requires some know-ledge of the amount and direction of prey–predator ecologicalinteractions. To fully understand the sustainability and func-tionality of coastal ecosystems, detailed information on thetemporal, spatial and ontogenetical nature of prey–predatortrophic interactions are needed (Livingston, 1985; Walterset al., 1999; Hallowed et al., 2000; Whipple et al., 2000).At the study area, there is still limited background know-ledge of interrelationships, trophic connections, and trophicguild structure of the fish assemblage. Regarding the Braziliancodling some antecedents on its morphological anatomyrelated with feeding habit were focused at Montevideo(Uruguay) and the Atlantic Argentine coasts (Mora andPintos, 1980; Goldstein, 1986, 1988). The present studyprovides new and detailed information on the feeding ecologyof U. brasiliensis considering temporal and ontogenetic vari-ability along the Uruguayan coast. This information isrelevant to ascertain the consequences at the ecosystem levelthat are generated by the commercial extraction ofU. brasiliensis, thus allowing evaluation of direct and indirecteffects on and between other components of the ecosysteminhabited by this species.Materials and methods