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This study investigated the level of seabird mortality caused by the domestic trawl fleet (freshies) for hake (among other less important targets) operating in waters off central Patagonia (37-481S), analyzing the effect of environmental and operational variability on the level of seabird interactions. With a total of 135 vessels, the fleet is one of the largest in Argentina. Specifically tasked seabird observers were placed onboard trawlers during the summer and winter seasons of the years 2006 and 2007. The type and number of seabird interactions (i.e. contacts with fishing gear) were recorded during shooting and hauling operations, covering 72 days of observation and 328 trawls. Black-browed albatrosses, white-chinned petrels Procellaria aequinoctialis, southern giant petrels Marconectes giganteus and southern royal albatrosses Diomedea epomophora were the most abundant species interacting with trawlers. Confirmed mortalities of black-browed and southern royal albatrosses were the result of collisions and entanglement with the warp cable while birds were scavenging. The estimated total mortality rate was 0.017 birds h À1 and 0.105 birds per vessel per day. The intensity of interactions (in terms of the number of contacts per unit time) was largely explained by the distribution of the fishing effort. Seasonality and the incidence of discards were the strongest factors explaining the occurrence of seabird interactions. The total annual mortality in the trawl fleet under investigation was roughly estimated to be from several hundred to over a thousand albatrosses. However, these figures should be considered preliminary due to the limited spatial and temporal coverage of data and the fact that estimations were based on a low number of observed mortalities. The implementation of a strategic discard management may significantly reduce the number of seabird mortalities from collisions with warp cables or improve the effectiveness of other complementary mitigation methods. Urgent implementation of mitigation measures is needed in this fleet to reduce the mortality of albatrosses and petrels along the Patagonian shelf.

SUMMARY: Seven species of the family Sciaenidae have been reported inhabiting bottom waters of the Río de la Plata estuary. Of these juvenile stripped weakfish (Cynoscion guatucupa), king weakfish (Macrodon ancylodon), whitemouth croaker (Micropogonias furnieri) and banded ground drum (Paralonchurus brasiliensis) are by far the most abundant. These species are also important prey of several top-predator species among large fishes, seabirds and mammals. In this study we provide new information regarding otolith morphology and body size relationships of juvenile sciaenid fish. The sagittae morphology of juvenile sciaenids showed strong changes in the course of their development (e.g. in overall shape and development of concrescences on the outer surface). Analysing the morphometric relationships, we concluded that otolith length and otolith mass are good indicators of fish standard length and fish weight in all species. If otolith length or mass is used to estimate fish length, the regression explained more than 97% of the variation in all species. All equations relating fish standard length and fish weight for juvenile stages of the species studied explained a very large proportion of the variance in the data. These data will help researchers studying food habits of top predators to determine size and weight of usually juvenile fish-prey from length, broad and/or weight of recovered otoliths.Key words: otolith morphology, otolith morphometry, fish prey, Cynoscion guatucupa, Macrodon ancylodon, Micropogonias furnieri, Paralonchurus brasiliensis. RESUMEN: MORFOLOGÍA DE OTOLITO Y RELACIONES DE TAMAÑO CORPORAL PARA ESCIÉNIDOS JUVENILES EN EL ESTUARIO DEL RÍO DE LA PLATA (35-36ºS). -Siete especies de la familia Sciaenidae son reportadas habitando aguas de fondo en el estuario del Río de la Plata, juveniles de pescadilla común (Cynoscion guatucupa), pescadilla real (Macrodon ancylodon), corvina rubia (Micropogonias furnieri) y córvalo (Paralonchurus brasiliensis) son por mucho los más abundantes. Estas especies son importantes presas de varias especies predadoras tope, entre ellas grandes peces, aves marinas y mamíferos. En este estudio se provee nueva información respecto a morfología de otolito y relaciones de tamaño corporal de esciénidos juveniles. La morfología de sagittae de esciénidos juveniles mostró fuertes cambios a través de su desarrollo (por ej. en la forma general y el desarrollo de concreciones en la superficie externa). Analizando las relaciones morfométricas, concluimos que el largo del otolito y la masa del otolito son buenos indicadores del largo standard y peso del pez en todas las especies. Si el largo del otolito o la masa son usados para estimar el largo del pez, la regresión explicará mas del 97% de la variación en todas las especies. Todas las ecuaciones relacionando el largo standard del pez y el peso para estadíos juveniles de las especies estudiadas explicaron una gran proporción de la varianza de los datos. Estos datos ayudarán a investigadores que estudien hábitos alimenticios de predadore...

The incidental mortality of albatrosses Diomedeidae and petrels Procellariidae by longline fishing vessels, has been assessed and analysed in several areas of the globe. We provide the first direct estimates of incidental mortality rates of albatrosses and petrels along the Argentine Shelf and shelf break. The estimated by-catch rate for the whole period analysed (1999-2001) was 0.04 birds/1,000 hooks, with a maximum of 0.20 birds/1,000 hooks observed in 1999. Annual captures averaged 1,160 birds; however, the large variation observed indicates that annual by-catch may be in the order of thousands, with around 10,000 seabirds being killed by longliners through the study period. Most of the captures were observed along the Patagonian shelf break. At least 12 bird species were incidentally taken, with Black-browed Albatrosses Thalassarche melanophris and White-chinned Petrels Procellaria aequinoctialis accounting for about 80% of total captures. The information provided in this study allowed the design and future implementation of mitigation measures and new survey methods onboard longliners operating in Atlantic waters on the Argentine shelf.

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