ABSTRACT We report on the interaction between common bottlenose dolphins, Tursiops truncatus (Montagu, 1821) and cast net fishermen in southern coast of Brazil. The fishery was monitored in the mouth of the Tramandaí River Estuary to investigate the seasonality of catches and their relationships with a set of variables: presence/absence and number of bottlenose dolphins, fishing area, temperature, salinity, wind and water flow direction in the channel. The mullet, Mugil liza Valenciennes, 1836 is the target species and was the dominant fish in the catches (77% of total catch; 50% in frequency; 0.2 ind. x f-1). The use of GLM models helped to reveal that the number of the bottlenose dolphins, time of year (months) and spatial variation of fishing activity were the main factors explaining the presence and abundance of mullet in the fishermen’s catches. The presences of bottlenose dolphins in the fishing area raise the probability of fishermen catch larger number of mullets with smaller fishing effort. However, the size of the mullet is influenced basically by seasonality. The mullets are the “currency” of bottlenose dolphins and fishermen interaction. There are reasons for concern about the sustainability of the southern Brazilian M. liza stock, once the decrease of this fishing resource can lead this rare and traditional fishery to the extinction.

RESUMO Duas espécies de tainha simpátricas, Mugil curema e M. liza, usam o estuário do Rio Tramandaí como zona de berçário. Quando espécies do mesmo gênero são simpátricas, vários mecanismos podem permitir sua coexistência, incluindo segregação espacial ou temporal que resultam no uso distinto dos recursos pelos quais elas competem. Para investigar a segregação espacial nós usamos a análise de elementos químicos em otólitos inferidos por espectrometria de massas através de plasma indutivamente acoplado com amostras extraídas a laser (LA-ICPMS). Mugil curema está associada a águas de alta salinidade podendo ser classificada como Marinho Migrante sub-categoria Marinha estuarina-oportunista. Mugil liza está associada a águas menos salinas, devendo ser classificada como Marinha Migrante sub-categoria Estuarina Dependente. A variação intraespecífica no uso do habitat estuarino indica um comportamento migratório mais complexo que o previsto em tainhas.

ABSTRACT Two sympatric species of marine mullets, Mugil curema and M. liza, use the rio Tramandaí Estuary as nursing grounds. When two closely related species are sympatric, various mechanisms may permit their coexistence, including spatial or temporal segregation that results in the divergent use of the resources for which they compete. To investigate the spatial segregation, we used otolith chemistry inferred through laser ablation-inductively coupled plasma mass spectrometry. Our results indicate that in the rio Tramandaí Estuary, M. curema is associated with high salinity waters and can be classified as a Marine Migrant in the Marine Estuarine-opportunist subcategory. Mugil liza is associated with lower salinity and can be classified as a Marine Migrant in the Estuarine Dependent subcategory. The intra-specific variation in estuarine habitat use indicates that the migratory behaviors in mullets are far more complex than previously known.

Brazilian mullet Mugil liza is a schooling fish that migrates in fall and winter, leaving estuaries and coastal lagoons to spawn in ocean waters. In order to understand the reproductive migration pattern of southern stock along Brazil's coast, we analyzed data collected through the Brazilian Satellite Vessel Tracking Program (Programa Nacional de Rastreamento das Embarcações Pesqueiras por Satélite-PREPS) from 2008 to 2012. The migration period overlaps with the fishing season (May-July) when the licensed purse seine fleet fishes along the southern and southeastern coast of Brazil, motivated to capture mullet by the high value of the roe. During the five fishing seasons the average effort was of 51 active vessels. The average time per season that each vessel navigated in the Speed Compatible with Fishing Operation (SCFO) was 349.3 h, which represented an average of 17% of the total time at sea. From May to July the highest frequency (54%) of SCFO transmissions occurred in June (P < 0.05), and in 95% of the SCFO transmissions the vessels were at depths less than 50 m. The temporal and spatial displacement of the fleet in a south-north direction follows the progression of sea surface temperature SST of 19-21°C (P < 0.05). Most (60%) SCFO signals occurred in areas with this range of temperature, independent of the month and latitude. The south-north displacement of the fleets through the season was similar among the different years (P > 0.05).

La lisa Mugil liza, es una especie que forma cardúmenes, migra en otoño e invierno, saliendo de los estuarios y lagunas costeras para desovar en el océano. Para comprender la migración reproductiva del stock del Sur a lo largo de la costa de Brasil, se analizó los datos obtenidos en el Programa Nacional de Seguimiento de Embarcaciones Pesqueras por Satélite de Brasil (PREPS en portugués). El período de la migración coincide con la temporada de pesca (mayo-julio), cuando los buques cerqueros autorizados pescan a lo largo de la costa sur y sudeste de Brasil, que buscan capturar las hembras de lisas por el alto valor de sus huevos. Durante las cinco temporadas de pesca (2008-2012), el esfuerzo promedio fue de 51 embarcaciones en operación. El tiempo promedio por temporada que cada embarcación navegó de acuerdo con la Velocidad Compatible con la Operación Pesquera (VCOP) fue 349,3 h, con un promedio de 17% del tiempo total en el mar. De mayo a julio la mayor frecuencia (54%) de las transmisiones VCOP ocurrió en junio (P <0,05), y en el 95% de las transmisiones las embarcaciones operaron a profundidades menores de 50 m. El desplazamiento temporal y espacial de la flota cerquera en dirección sur-norte sigue la progresión de la temperatura superficial del mar en el intervalo de 19-21°C (P <0,05). La mayoría de las señales (60%) VCOP ocurrieron en áreas con este rango de temperatura, independiente del mes y la latitud. El desplazamiento sur-norte de la flota durante la temporada fue similar entre los diferentes años analizados (P > 0,05).

The Plata pompano, Trachinotus marginatus (Cuvier, 1832), is an endemic carangid of the Southwestern Atlantic Ocean, occurring from Rio de Janeiro to Uruguay. This study describes the reproductive period, spawning type, the size at first gonadal maturation and the length-weight relationship of individuals sampled from landings of the artisanal and commercial fishing fleets in Rio Grande that operate along the coast of Rio Grande do Sul state, southern Brazil (~ 32ºS) to the Uruguayan border (~ 34ºS). Monthly collections from September 2008 through January 2010 yielded 274 individuals ranging from 142 to 444 mm in total length (TL). The gonadal development stages were defined according to the histological examination of the ovaries and the testes. The relationship between TL (mm) and total weight TW (g) was statistically different between males (TW = 0.000463*TL2.7655) and females (TW = 0.000361*TL2.8131), showing negative allometric growth for both sexes. The sizes at first maturity were 187.2 mm and 254.9 mm for females and males, respectively. The presence of two modal groups of oocyte diameters suggested that total spawning occurred. The interpretation of the monthly variations of the condition factor and gonadosomatic index, which are associated with higher frequencies of the more advanced stages of gonadal development, identified the spring and summer months as the reproductive period, with a peak in the reproductive activity during November and January. These results suggested that the species has an opportunistic reproductive strategy.