ABSTRACT Fisheries interactions with non-target marine vertebrates are a worldwide problem. The impact of coastal bottom trawl fisheries on marine mammals has never been evaluated before in the Río de la Plata Estuary and the adjacent Atlantic Ocean. Our aim was estimating the bycatch per unit effort (BcPUE) and incidental mortality rates of marine mammals caused by the industrial coastal bottom trawl fisheries fleet. We evaluated the mortality of three species (i.e., franciscana dolphin Pontoporia blainvillei, South American sea lion Otaria flavescens, and the South American fur seal Arctocephalus australis); these species are facing conservation problems either at the regional or local scale. We conducted an onboard data collection program of marine mammals’ bycatch involving crew members of 10 vessels (30%) of the Uruguayan coastal bottom trawl fleet between January 2009 and April 2012. A total of 102 marine mammal individuals were bycaught during 490 fishing trips involving 2,398 fishing days. Mortalities estimated for franciscana dolphin were the highest among the species affected, with values adding up to ~100 individuals for year (with scenarios of population decline in the area), followed by South American sea lion with ~77 individuals by year (0.8% of local population) and the South American fur seal with an annual mortality estimate of ~25 individuals (~0.02% of local population). BcPUE showed significant temporal variation, with franciscana dolphin BcPUE varying seasonally and those of otariids according to their breeding season. Our estimates of marine mammal bycatch by bottom trawl fisheries should constitute an important input for the sustainable management of fisheries and the conservation of marine biodiversity in the southwestern Atlantic Ocean.

Artisanal fisheries in Uruguay involve directly or indirectly more than 5000 people and constitute the main source of income in several coastal communities. However, and despite its economic and environmental importance, this activity is poorly documented. As such, this scarcity of information constrains the understanding and effective management of artisanal fisheries. This study aims to characterize different strategies of marine artisanal fisheries on the Uruguayan Atlantic coast and describe the spatial distribution of fishing effort. Based on a Principal Components Analysis we identified four fishing strategies targeting different species (mainly whitemouth croaker Micropogonias furniert, narrownose smooth-hound shark Mustelus spp., angel shark Squatina spp. and Brazilian codling Urophycis brasiliensis), exhibiting different seasonal patterns and fishing gear usage. Finally, the above outlined strategies showed differences in spatial utilization of the fishing area. Our results provide a spatially explicit framework for the management of Uruguayan marine artisanal fisheries.

En Uruguay las pesquerías artesanales involucran, directa e indirectamente, a más de 5.000 personas, constituyendo la principal fuente de ingresos en varias comunidades costeras. Sin embargo, a pesar de su importancia económica y ambiental, dicha actividad está muy poco documentada. De esta forma, la falta de información restringe la comprensión y el manejo efectivo de las pesquerías artesanales en el país. Los objetivos de este trabajo son caracterizar las diferentes estrategias de la pesquería artesanal de la costa atlántica uruguaya y describir la distribución espacial de su esfuerzo pesquero. En base a un Análisis de Componentes Principales se identifican cuatro estrategias de pesca dirigidas a diferentes especies objetivo (principalmente corvina Micropogonias furnieri, gatuzo Mustelus spp., angelito Squatina spp. y brótola Urophycis brasiliensis), que presentan diferentes patrones estacionales y del tipo de arte utilizado. Finalmente, las estrategias anteriormente descritas muestran diferencias en el uso espacial de las áreas de pesca. Los resultados proporcionan un marco espacialmente explícito para el manejo de las pesquerías artesanales en la costa atlántica de Uruguay.

Foi estudado a dinâmica sazonal da comunidade de peixes em relação as variáveis ambientais do estuário Pando, localizado na costa uruguaia. Os peixes foram amostrados mensalmente entre maio de 2002 e junho de 2003. Os indivíduos coletados foram identificados e classificados em estágios (jovens, adultos) e grupos funcionais. Relações entre a dinâmica da comunidade e as variáveis ambientais foram avaliadas utilizando-se técnicas uni- e multivariada. Vinte e uma espécies foram coletadas, principalmente visitantes de água doce, estuarinas e marinhas migratórias, sendo as mais abundantes e representadas por juvenis: Micropogonias furnieri, Mugil platanus, Paralichthys orbignyanus e Brevoortia aurea. A comunidade variou sazonalmente com rápidas mudanças na primavera e no outono, associadas à variações de temperatura e salinidade. Correlações significativas entre abundância e temperatura parecem estar relacionadas com a sincronizaçao de eventos dos ciclos de vida. Neste estuário a salinidade parece desempenhar um papel-chave na estrutura funcional e uso do habitat por juvenis. Este fato é relevante para a definição dos estuários como áreas de criadouro e pela influencia da salinidade sobre o ciclo da ictiofauna local.

The seasonal dynamics of the fish community in the Pando estuary on the Uruguayan coast were studied in relation to environmental sampled monthly between May 2002 and June 2003. Individuals collected were identified, and classified into stages (juveniles, adults) and functional groups. Relationships between community dynamics and environmental variables were evaluated using uni- and multivariate techniques. Twenty-one species, mostly freshwater stragglers, estuarine and marine migrants were collected. The most abundant species were Micropogonias furnieri, Mugil platanus, Paralichthys orbignyanus and Brevoortia aurea and were represented by juveniles. The community varied seasonally with rapid shifts in spring and autumn associated with changes in temperature and salinity. Significant correlations between abundance and temperature may be related to the timing of life cycle events. In this estuary, the salinity appears to play a key role in the functional structure and in the use of the habitat by juveniles. This is relevant for the definition of estuaries as nursery areas: this definition is context-dependent and is determined by the salinity conditions.