Sustainability of bait fishing harvesting in estuarine ecosystems - Case study in the Local Natural Reserve of Douro Estuary, Portugal * Sustentabilidade da apanha de isco para pesca nos ecossistemas estuarinos - Caso de estudo na Reserva Natural Local do Estuário do Douro, Portugal

A narrow relationship between marine resources and local populations always existed in !shing communities of coastal areas. In the Portuguese estuaries bait !shing is a common practice in which gatherers collect intertidal species such as seaworms, shrimps, crabs or clams. In recent Local Natural Reserve of Douro Estuary (RNLED) this activity is fairly entrenched due to the proximity of a great !shing zone, the Afurada, and the abundance of recreational !shermen operating in the area. "is study aimed to quantify the impact of bait !shing gathering on the ecology of this estuary benthic community, in order to propose management measures for this activity, ensuring its sustainability, and to verify the in#uence this activity may have on the conservation of intertidal resources in a protected area. Between June 2010 and May 2011 monthly samples were collected in the intertidal zone, in order to quantify the density of populations of Hediste diversicolor and Scrobicularia plana at two locations in the estuary. During the same time period, weekly interviews were performed to bait !shing gatherers operating in RNLED area. In this area of Douro estuary, H. diversicolor (239.7ind/m 2 ) was the most abundant species compared to the clam S. plana (0.3ind/m 2 ). In the area of RNLED the species most collected by bait !shing gatherers was the polychaete H. diversicolor, and it is estimated that each year 9.9tons are captured, representing an annual mean catch per bait !shing gatherer of 0.3tons. However, the total annual biomass collected was substantially less than the productivity estimated for the entire intertidal area of RNLED (78.7 to 141.3tons). "e number of bait !shing gatherers varied between 0 on December 2010 and 12 in July 2010, showing a decrease in activity in the RNLED, especially during the times when surveillance occurs. "e area prospected by each gatherer was estimated to be 10m 2 /day. Considering both tides and all the e$ort done by an average of 8 men/day, the prospected area was 80m 2 /day, corresponding to 0.3% of the intertidal area. "is e$ort was mainly concentrated in about 1/3 of the available intertidal area. Results indicated the sustainable management of bait !shing activity in the referred protected area is possible. However, other aspects must be taken into account, such as the possible con#ict of this activity with biodiversity conservation in the reserve. "erefore, we suggest some possible solutions for the sustainability of this activity, along with less disturbance to birds that may feed in the reserve, such as: delimitation of a marginal area within the reserve, smaller than the current one, where the collection of organisms is allowed, as well as the oversight and control of licenses and educational procedures. Moreover, these measures would have a positive impact in the integrated management of the reserve, while enabling an activity with positive economic consequences in an underprivileged population. Also, they will contribute to lower the impact of human presence on the avifauna and on the structure of the sediments.