Pit telemetry as a method to study the habitat requirements of fish populations. Application to native and stocked trout movements

Passive integrated transponder (PIT) technology was used to study the behaviour of fishes during the summer season in two headwater streams of northeastern Portugal. A total of 71 PIT tags (12 mm long x 2.1 mm diameter) were surgically implanted in 1+ stocked (39) and native (32) brown trout of two size classes (< 20.0 and ≥ 20.0 cm). Eight independent antennae, connected to a multi-point decoder (MPD reader) unit, were placed in different microhabitats, selected randomly every three days during the observation period (29 August to 9 September in Baceiro stream and 19 September to 4 October in Sabor stream). The results confirmed this method as a suitable labour efficient tool to assess the movement and habitat use of sympatric stocked and native trout populations. About 76.9% of stocked and 59.4% of native PIT tagged trouts were detected. Multivariate techniques (CCA, DFA and classification tree) showed a separation in habitat use between the two sympatric populations. Stocked trout used, mainly, the microhabitats located in the middle of the channel with higher depths and without cover. Furthermore, these fishes displayed a greater mobility and a diel activity pattern different to native trout populations

Combining radio and Pit telemetry to study the large and fine-scale movements of stocked and wild brown trout (Salmo trutta L.) in a Northeastern stream, Portugal

Radio and Passive Integrated Transponder (PIT) telemetry were used to monitor the movements of stocked and wild trout, Salmo trutta L., in a north-eastern Portuguese stream. Large scale-movement analyses using radio-telemetry showed: 1) After 14 days (September 2002), the stocked fish (270 mm in total length LT) movements were significantly higher and dispersed 1,500 m from wild trout (330 mm LT), which remained near of the stocking site; 2) At the end of 64 days (September to November 2005), 83.3% of stocked tagged trout (255-277 mm, LT) dispersed in downstream direction ranging from 200 to 4,100 m. Dispersal, daily home range and distance moved of fish that displayed higher mobility were significantly different from the more stationary fish and highly correlated (rS> 0.75) with discharge. Furthermore, even in fine-scale analysis, using PIT telemetry (12 August to 30 September 2005) stocked fish (50 individuals, 185-262 mm LT) movements were significantly greater than wild trout (25 native trout, 132-250 mm LT) and differed in the diel activity pattern, which was higher during dawn and night periods, decreasing at dusk period. Only 28% of the hatchery-reared fish survived and the lower condition and the vulnerability to predation by otter (Lutra lutra) were detected as the main causes to the mortality registered

Diet of stocked and wild trout, Salmo trutta: Is there competition for resources?

Stocked and native trout diet was assessed in two north-eastern Portugal headstreams during the summer season of three successive years (2000 to 2002). Significant differences were detected in the diet composition between stocked (age 1+) trout and distinct size-class of native trout. Stocked fish showed preference, almost exclusively, for food items captured near the surface (primarily terrestrial adult insects), emergent pupae and subimagos. In contrast, young-of-year (YOY) native trout fed predominantly on the most available aquatic prey taxa such as Chironomidae (Diptera) larvae and Baetidae (Ephemeroptera) nymphs; however, Trichoptera larvae were not taken. Native trout preference changed from benthic aquatic invertebrates to terrestrial origin organisms and this ratio increased with size, suggesting an ontogenetic diet variation. Significant diet overlap was only detected between stocked and dominant native trout, which were not displaced from the energetically profitable areas. Therefore, this study showed the absence of an evident competition for food in both streams, even when trout density was largely augmented by stocking activity. However, since no obvious benefits on space and time were obtained, stocking must be carefully evaluated and alternative approaches considered, like habitat improvement and adequate fisheries management, in order to increase the natural productivity of these systems

Acoustic and light selective behavioral guidance systems for freshwater fish

The use of non-physical barriers, particularly based on acoustic and luminous stimuli has been historically used to influence the behavior of fish, mainly for fishing purposes. Nowadays, behavioral barriers and guidance systems have been developed, not only to deter movements of fish, but also to promote behavioral responses with the objective of native fish protection, in particular the potamodromous species, reducing their mortality in the hydraulic structures of dams and guiding them towards transposition systems or to replacement habitats in regularized water bodies. This review details the use of acoustic and luminous systems and their evolution in recent years (Scopus 2012–2019) for the development of selective behavioral barriers for fish. We found that recent technologies try to identify new acoustic and luminous sensory ranges. Ambient sound, sound of predators or luminous spectral bands with different wavelengths have been used to selectively stimulate target and non-target species, in order to improve the effectiveness of repulsive/attractive systems for fish. Guidelines for future research in the area are also present.This work is supported by National Funds by FCT—Portuguese Foundation for Science and Technology, under the project UIDB/04033/2020.info:eu-repo/semantics/publishedVersio

Environmental indicators of ecological integrity and their development for running waters in northern Portugal

The recognition of deleterious effects of the destruction and loss of habitats (e.g. regularization of rivers, dredging, water diversion), chemical pollution, eutrophication, and climatic alterations on the aquatic organisms, as a result of human activities, combined with an urgent need of a more environmentally sensitive and ecologically sustainable management of Portuguese river systems , made us seek methods that assess the ecological condition of these systems. This article tries to make a revision of the concept of ecological integrity and the methods commonly used to assess it. Different approaches to establish the reference condition for bio-assessment are also indicated. Finally it shows the new methodologies that have been developed in Portugal for assessing the ecological condition of streams and new directions in the evaluation processes based on a better understanding of the entire aquatic ecosystem are also pointed out. An enormous challenge consists in the integration of various measurements of riverine attributes founded on key ecological processes, and in the development of more dynamic approaches that might together establish river condition and their dependence along multiple temporal and spatial scales.El reconocimiento de los efectos deletéreos de la destrucción y pérdida de hábitat (por ejemplo la regularización de ríos, el dragado o la extracción de agua), la polución química, eutrofización y alteraciones climáticas en los organismos acuáticos, como resultado de las actividades humanas, combinados con una necesidad urgente de una gestión ambientalmente más sensible y ecológicamente sustentable de los sistemas lóticos portugueses, nos incito a buscar métodos que evalúen la condición ecológica de estos sistemas. Este artículo intenta hacer una revisión del concepto de integridad ecológica y los métodos usados para evaluarlo. También son abordadas maneras diferentes de establecer la condición de referencia para la evaluación biológica. Finalmente muestra las nuevas metodologías que se han desarrollado en Portugal para evaluar la condición ecológica de los ríos y también son indicadas las nuevas direcciones en los procesos de evaluación basados en un mejor entendimiento de todo el ecosistema acuático. Un desafío enorme consiste en la integración de varias dimensiones de atributos fluviales fundamentada en los procesos ecológicos importantes y en el desarrollo de métodos más dinámicos que juntos podrán establecer la condición de los ríos y su dependencia a lo largo de múltiplas escalas temporales y espaciales

Conservação de recursos piscícolas em rios do Norte de Portugal: quais os impactos dos repovoamentos de truta nas populações selvagens?

A truta de rio (Salmo trutta L.) é reconhecidamente uma espécie com elevado interesse para a pesca desportiva no Norte e Centro de Portugal, constituindo um recurso económico valioso. O aumento do número de licenças de pesca nas últimas décadas (a partir de 2000 superou as 250 000 licenças, DGRF) é o reflexo de uma demanda crescente dos recursos pesqueiros dulçaquícolas por parte dos pescadores. Tal facto, tem sido motivo de apreensão relativamente à ameaça que algumas populações selvagens de truta estão sujeitas, não só pela sobrepesca mas também pelo efeito acumulado resultante da destruição do habitat, poluição da água, regularização de rios e introdução de espécies exóticas em cursos de água de aptidão salmonícola. Estudos recentes de monitorização de repovoamentos de truta (Salmo trutta L.) em cursos de água do Nordeste de Portugal, nomeadamente nos rios Baceiro e Sabor, demonstraram a existência de estratégias diferenciadas no uso de recursos disponíveis entre as trutas nativas e domésticas. Relativamente ao uso do habitat, foram usados métodos de observação sub-aquática e de PIT-telemetria (passiva) que permitiram detectar uma sobreposição muito baixa entre ambas as populações. As trutas domésticas, contrariamente à maioria das suas congéneres nativas, ocuparam preferencialmente microhabitats mais profundos, sem cobertura (refúgio), com posições focais mais elevadas e menores velocidades da corrente. Ao nível dos padrões de alimentação foram também encontrados comportamentos muito distintos, com excepção da sobreposição evidente na dieta das trutas domésticas e das trutas nativas dominantes. Os potenciais impactos negativos dos repovoamentos sobre as populações autóctones, referidos noutros trabalhos, apareceram desvanecidos e limitados em termos espaciais e temporais, como confirma a monitorização dos movimentos dos peixes, através de métodos de rádio-telemetria e marcação-recaptura, onde foi registada uma elevada dispersão, maioritariamente no sentido de jusante, dos peixes introduzidos. Foram vários os factores que contribuíram para a baixa eficácia dos repovoamentos, entre os quais se destaca a rápida diminuição da condição do peixe, a variação dos parâmetros hidrológicos, em especial o aumento dos caudais fluviais, e ainda a vulnerabilidade à predação pela lontra

Repovoamento de rios: estratégias diferenciais no uso de recursos entre trutas selvagens e domésticas

O recurso aos repovoamentos de truta (Salmo trutta L.) em rios de aptidão salmonícola de Portugal é ainda hoje uma das principais técnicas de gestão de populações piscícolas usadas no sentido de incrementar o potencial pesqueiro das massas hídricas. Apesar do longo historial de sucessivos repovoamentos, são poucos os estudos realizados ao nível dos potenciais impactos ecológicos resultantes da introdução de trutas criadas em cativeiro no meio selvagem. No presente estudo, a análise dos repovoamentos efectuados nos troços de cabeceira dos rios Sabor e Baceiro, situados no Nordeste de Portugal, revelou a existência de estratégias diferenciadas no uso de recursos disponíveis entre as trutas nativas e domésticas. Relativamente ao uso do habitat, os métodos de observação sub-aquática e de PIT-telemetria (passiva) coincidiram na detecção duma sobreposição diminuta entre ambas as populações. A profundidade total, a cobertura e a elevação do ponto focal foram as variáveis do microhabitat que mais contribuíram para a discriminação no comportamento observado. As trutas de cativeiro, contrariamente à maioria das suas congéneres nativas ocuparam preferencialmente microhabitats mais profundos, sem cobertura (refúgio), com posições focais mais elevadas e menores velocidades da corrente. Por outro lado, foram também observado padrões de alimentação distintos, tendo sido apenas detectada alguma sobreposição de dietas das trutas domésticas com as trutas nativas dominantes. Os potenciais impactos negativos dos repovoamentos sobre as populações autóctones, mostraram-se limitados em termos espaciais e temporais, como confirma a monitorização dos movimentos dos peixes, avaliada através de métodos de rádio-telemetria e marcação-recaptura, onde foi registada uma elevada dispersão, maioritariamente no sentido de jusante, dos peixes introduzidos. A diminuição rápida da condição do peixe, a variação dos parâmetros hidrológicos e a vulnerabilidade à predação foram factores que contribuíram decisivamente para a baixa eficácia dos repovoamentos

Is supplemental stocking of brown trout (Salmo trutta) worthwhile in low productive streams?

The effect of trout stocking was evaluated in two headstreams located in northern Portugal in order to assess the impact on wild trout (Salmo trutta L.) and to analyze the success of this operation. The results obtained exhibited the limitation of stocking: 1) the clumped character of the release fishes created a high mortality and limited the increasing of salmonid population to a few weeks; 2) because density-dependent factors seem to prevail in the regulation of salmonid populations, stocking is beneficial only if a population has became scarce, otherwise, the autochthonous fish may be strongly impacted; 3) the relative vulnerability of each age class of the native trout may vary according with the site

Habitat selection by native and stocked trout (Salmo trutta L.) in Northeast streams, Portugal

Underwater observations were made during the summer season in three successive years to assess the effect of supplemental stocking of brown trout (Salmo trutta L.) in two headwater streams of northeastern Portugal. Significant differences were found in microhabitat used. Focal point position, total depth and cover were the variables contributing to the discrimination between stocked and native trout. Preference curves executed for native and stocked trout of the same age (1+), exhibited a distinct pattern in the capacity to explore the available microhabitat resources. In both streams, stocked trout tended to occupy deeper pools, while holding higher focal positions. All size classes of native trout show an overlap in microhabitat use, but smaller ones (< 10.0 cm), which showed a preference for shallow habitats with fast currents, typically riffle conditions. These results do not display obvious effects of competition on habitat exploitation between stocked and native trout but additional information related to feeding, reproduction and other biotic interactions is necessary to define adequate management strategies of salmonid streams

Combining Radio and PIT-Telemetry to Study the Large and Fine-Scale Movements of Stocked and Wild Brown Trout (Salmo trutta L.) in a Northeastern Stream, Portugal

Stream-resident salmonid movements have been the subject of numerous studies and their behaviour is relatively well-known (Harcup et al., 1984; Heggenes, 1988). For example, brown trout (Salmo trutta) is described as a sedentary species based on the behaviour displayed, often associated to the strong site attachment to a territory or home range (Bridcut & Giller, 1993; Armstrong & Herbert, 1997). Other salmonids like brook (Salvelinus fontinalis) (Roghair & Dolloff, 2005) and cutthroat trout (Oncorhynchus clarki) (Hegennes et al., 1991) showed similar behaviour. However, there are studies reporting a wide range of movements for brown (Meyers et al., 1992; Young, 1994), cutthroat (Hilderbrand & Kershner, 2000) and brook (Gowan & Fausch, 1996) trout populations. Trout behaviour can be modified by natural (e.g. fish density, food availability) and especially by man induced factors (e.g. environmental degradation, harvest and stocking) responsible for major threats of wild populations (Laikre et al., 2000). Indeed, stocking of hatchery-reared brown trout is a management tool commonly used to improve the recreational fishing (Cowx, 1999). This activity is responsible for a sudden artificial increase of fish density in a particular area. Negative impacts on wild populations, such as genetic contamination, competition, predator attraction and disease transmission were often referred (White et al., 1995; Einum & Fleming, 2001; Weber & Fausch, 2003) and are potentially amplified with the dispersal failure, since many hatchery-reared trout tend to remain near of the stocking site (Cresswell, 1981; Aarestrup et al., 2005). There are also contradictory results, as reported by Bettinger & Bettoli (2002) where stocked trout dispersal reached over 12 km in the downstream direction, just 24 hours after their release. Cortes et al. (1996) found for Portuguese salmonid streams that, during three successive years (2000 to 2003), less than 20% of stocked brown trout remained in the stream segment, one month after the release. However, in this study a mark-recapture method was used that did not allow to assess the main causes of the fish depletion and was not appropriate for the observation of fish behaviour