The degree of conflict between otter conservation and fish farming was assessed at Sado estuary (SW Portugal), using ecological (otter visiting rates to fish farms and consumption of commercial fish) and socio-economic (past and current instruments and policies addressing the conflict and a social impact assessment, including a discourse analysis of relevant stakeholders) parameters. The study concerned 14 fish farms producing Sparus aurata, Dicentrarchus labrax, Solea senegalensis and Solea solea. Results indicate high visiting rates in most fish farms (average: 76%), although in only 29%, species stocked were the most consumed prey. Other marine species and freshwater prey were the basis of otter diet in the remaining fish farms. The conflict is quite consensual among most fish farmers, and the results indicate that the perceived conflict by fish farmers has an ecological basis, although there are large gaps between effective and perceived predation. No specific instruments exist in Portugal to address the conflict, but some not specifically targeted can have an effect (e.g. species protection legislation and aquaculture licensing), although with limitations to effectively contribute to its mitigation (e.g. lack of enforcement and supervision). Formulating and assessing solutions is the following step, using a participatory approach to the development and evaluation of mitigation/compensation strategies, capable of providing an effective reconciliation of the conflict.

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Conflicts between the conservation of large vertebrates and the use of biological resources are common and affect many species and activities. The vast majority of the Portuguese fish farms are located in estuarine protected areas and production of marine fish species is done mostly in semi-intensive regimes and with the imposition of some restrictive rules. This exposed form of production is prone to predation by wild animals. The Eurasian otter Lutra lutra is widely distributed in Portugal and this combination of factors has led to a conflict scenario between fish farming and the conservation of otters. This study aimed to determine the influence of landscape factors in otter damages in fish farms of Sado estuary (SW Portugal) and the usefulness of visiting rates and otter diet as surrogates for damage assessment. The impact of otter predation (damage) in each fish farm was assessed by combining the percentage of consumption of reared species with otter daily food consumption, daily visitation rates, and number of otters visiting each fish farm. Landscape descriptors were recorded in the field and several landscape metrics were calculated using a geographic information system. Multiple linear regressions were used to identify key landscape factors for damage and for damage surrogates. Distance to streams and refuge cover areas were identified as key landscape features to damages. This information can be used as a management tool in landscape planning, specifically in estuaries with fish-farming activity, as highrisk farms can be identified and selectively protected.

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We measured various fish bones from 13 Iberian freshwater fish species and one hybrid species. Original total body lengths were then back-calculated using bone measurements. Bones usually found in prey remains left by piscivorous predators, were usually from the head skeleton and from the vertebral column. The 73 regressions obtained between bone length and fish length were linear for al1 species examined. Coefficients of determination ranged between 75.6 % and 99.5 %. To estimate fish biomass, length-weight relations were used for each species, too. Bone length vs. fish length relationships found in the literature for seven additional species inhabiting the Iberian Peninsula were also included, totalling 29 regression equations. The amount of dietary information available from fish predator remains can be greatly increased by using these relationships. In this paper, information is provided covering in excess of 37 YO of lberian freshwater fish fauna, including the most abundant and widespread species.