Effects of the fisheye bycatch reduction device (BRD) and turtle excluder device (TED) on shrimp retention and bycatch reduction were assessed, aiming to increase sustainability and attenuate the ecological impact of shrimp trawls in the Colombian Caribbean Sea. A total of 88 hauls were carried out in two different periods. The four shrimp trawl nets of the fishing vessel were each equipped with a different device configuration: BRD, TED, TED/BRD, and control (without devices). The highest reduction in incidental catch rates was recorded for the BRD-equipped net, whereas a lower reduction of fish, a higher reduction of invertebrates and discards, and a lower retention of shrimp were recorded for the TED-equipped net. Using BRD, a significant reduction in catch per unit effort was recorded for six (Lutjanus synagris, Lepophidium spp., Diplectrum spp., Synodus spp., Syacium spp., and Bagre marinus) of twelve fish species or species groups selected because of their commercial value or higher catch rates. The results indicate that widespread use of BRDs in the southern area of the Colombian Caribbean Sea would allow a decrease of 727 t of bycatch and 37 t of shrimp in the catches per year, whereas using both TED and BRD, these reductions would be 1529 t of bycatch and 128 t of shrimp per year. Some changes in the device designs currently used are considered feasible in order to increase shrimp retention and reduce the resistance of crews to adopt these devices, but at the same time attenuating the impact of fishing activities on bycatch species and recovering the abundances of the exploited demersal fish populations.

RESUMEN.A partir de muestreos realizados a bordo entre julio y septiembre de 2004, se examinaron los cambios asociados con la hora del día en las tasas de captura y estructura de tamaños de los camarones (Farfantepenaeus notialis, F. brasiliensis), las capturas incidentales, los descartes y las 12 especies de peces con mayores capturas en cada una de las dos zonas de pesca (norte y sur) en que opera la flota de arrastre de camarón en el Mar Caribe de Colombia. La tasa de captura de camarón fue significativamente mayor durante la noche, pero los individuos capturados en el día exhibieron mayor talla, lo cual ratifica la actividad nocturna que caracteriza a los camarones (Peneaidae). Especies de peces depredadores exhibieron mayores tasas de captura y menor representación de individuos grandes en horario diurno. La tasa de captura total (compuesta principalmente por especies descartadas de talla pequeña) resultó significativamente mayor en horas de la noche. La variabilidad circadiana observada en las tasas de captura y en la composición de tallas sugiere ritmos diurno -nocturno en la actividad de las especies examinadas y revela que los índices de abundancia pueden estar sesgados si los muestreos no son aleatorizados respecto a la hora del día. La elevada cantidad de individuos de talla pequeña descartados, evidencia una alta presión pesquera en la región y urge el establecimiento de medidas de manejo para mitigar el impacto de la pesca de arrastre.Palabras clave: variabilidad circadiana, tasas de captura, estructura de tallas, camarón, fauna acompañante, Colombia.Circadian variability of catch rate and size structure for shrimp and fish bycatch from Colombian Caribbean trawl fishery* ABSTRACT. Diel-associated changes of catch rates and size-structure of shrimp (Farfantepenaeus notialis and F. brasiliensis), incidental catches, discards and the twelve most caught fish species of each of the two shrimp trawling fishing zones (northern and southern) of the Colombian Caribbean Sea were examined. Data were obtained by on board observers between July and September 2004. Although individuals shrimps in daytime catches were larger in size, shrimp catch rates were significantly higher at nightime, wich confirm the nocturnal activity of the shimps (Penaeidae).Higher catch rates and few large individuals of predator fish species were observed during daytime. The total catch (mostly discarded, small-sized species) was significantly higher at night. Observed circadian variability in catch rates and size composition suggests diel rhythms in activity of examined species and indicates that the abundance indexes can be biased if sampling is not randomised by time of day. High amounts of discarded small sized individuals reveal a heavy fishing pressure in the region and indicate the urgent need for management measures to mitigate impacts of trawling.

In the Colombian Caribbean Sea the negative impacts on the bycatch cannot be only attributed to the industrial shrimp trawl flet, but also to the artisanal flet that exploits the shrimp resource by using beach seines and trawls locally called “changas”. These fihing gears capture a high proportion of juvenile fifih, which are generally discarded. Therefore, the objective of this work was to evaluate the effect of three types of bycatch reduction devices (BRD) Florida Fisheye (FF), Squared Mesh Panel (SMP), and Radial Escapement Section (RES) in the catch of this fihery. Two trials were carried out in two contrasting seasons, one in the rainy season and one in the dry one. Each test net was towed 28-30 times in parallel (one boat with a net equipped with a BRD and a control boat with a net of the same design and dimensions but no BRD), for a total of 90 paired samples in the rainy season and 84 in the dry season. Seasonal differences in the exclusion of both shrimp and bycatch were found, due to the high catch rates of jellyfih in the dry season, which affected the normal performance of all the three types of BRDs, especially of the RES. The rainy season trials showed that, opposite to the VMC and the SRE, the OP does not reduce signifiantly (p > 0.05) the discards, but only the incidental catch (p < 0.05). Although the exclusion power of the VMC and the SRE did not signifiantly differ (p > 0.05), we conclude that the VMC is a best choice for mitigating the discards of this fihery, due to its lower cost and conveniences of handling and assembly. However, some modifiations in the location and dimensions of this BRD in the codend should be tested so as to increase the retention of shrimp during the hauling of the gear by hand. Thus, adoption of this device by fihermen would be facilitated, with the consequent environmental and socioeconomic benefis.

La raya del Magdalena (Potamotrygon magdalenae) no es considerada una especie objetivo de las pesquerías de la cuenca del Magdalena. Habitualmente es descartada viva, no sin antes quebrarle la espina caudal o aguijón, por lo cual no aparece frecuentemente en los desembarcos artesanales de esta zona, de allí que se desconozca el impacto sobre sus poblaciones. Este estudio determinó la distribución espacial de la abundancia y los tamaños de P. magdalenae en el Complejo Cenagoso de Zapatosa (CCZ). A partir de una estratificación de 96 cuadrículas (4 km2 cada una), se escogieron de manera aleatoria un total de 25, las cuales fueron muestreadas en su centro geográfico utilizando redes de enmalle. Cabe mencionar que las cuadrículas adyacentes no fueron muestreadas y además se asignó por lo menos una cuadrícula de muestreo a los cuerpos de agua aparentemente independientes. Para conocer la distribución espacial de la abundancia y tamaño de la especie se utilizó ArcGIS como sistema de información geográfica, implementando la técnica hotspot. El cálculo de la captura por unidad de esfuerzo (CPUE) se estandarizó en términos de kg/lance. Los resultados indican que las mayores abundancias relativas se encontraron en el sector septentrional y central del CCZ y las menores en el sector meridional. De igual manera, los mayores tamaños fueron registrados en las cuadrículas del norte y oriente y los menores en las del sur. Otro resultado del estudio es un mapa de la distribución espacial de P. magdalenae en el CCZ, lo que constituye un insumo de interés para la implementación de medidas de manejo de una especie que, aunque hoy en día no es un recurso objetivo desde el punto de vista pesquero, desempeña una función importante en la trama trófica del CCZ.