Sampling errors and variability in video transects for assessment of reef fish assemblage structure and diversity
Video monitoring is a rapidly evolving tool in aquatic ecological research because of its non-destructive ability to assess fish assemblages. Nevertheless, methodological considerations of video monitoring techniques are often overlooked, especially in more complex sampling designs, causing inefficient data collection, processing, and interpretation. In this study, we discuss how video transect sampling designs could be assessed and how the inter-observer variability, design errors and sampling variability should be quantified and accounted for. The study took place in the coastal areas of the Galapagos archipelago and consisted of a hierarchical repeated-observations sampling design with multiple observers. The results confirm the suitability of the technique to study reef fish assemblages, but also highlight the importance of a sound methodological assessment since different biological responses and sampling designs are associated with different levels of sampling variability, precision and ecological relevance.
Fishers’ Local Ecological Knowledge to Support Mangrove Research in the Galapagos
Mangroves provide multiple ecosystem services to coastal communities and their fisheries. In the Galapagos, mangroves have been primarily prized for their role as nursery grounds; though, the importance of cultural benefits, including the development of knowledge systems among fishers, needs to be further explored. Fishers’ local ecological knowledge (LEK) has been employed in the past to answer questions about the marine environment; not yet about mangroves. In such regard, this ethnoecological approach can contribute to unveil mangrove habitat-dependence relationships among fishery taxa across the life cycle, connectivity among habitats, and productivity spatial patterns across the archipelago. To access fishers’ LEK, we conducted 35 semi-structured interviews and 2 facilitated community workshops comprising 3 activities. Despite having an explorative focus, our work already showcases the potential of fishers’ LEK in improving mangrove research in the Galapagos, and the arising opportunities for ecosystem-based fisheries management and mangrove protection.
Polluted paradise: Occurrence of pesticide residues within the urban coastal zones of Santa Cruz and Isabela (Galapagos, Ecuador)
Although pesticides are frequently used for agriculture in the Galapagos Islands (Ecuador), there are, to date, no investigations of pesticide occurrences in its coastal waters. We examined the presence of pesticide residues in the coastal waters of urban areas in two islands of the Galapagos archipelago using a repeated sampling design. In total, sixteen pesticides were detected, including three persistent organic pollutants. This study provides insights into the need to regulate, monitor and assess the presence of pesticides in the islands.
Assessing the Drivers behind the Structure and Diversity of Fish Assemblages Associated with Rocky Shores in the Galapagos Archipelago
The Galapagos archipelago is well known for its fish diversity, but the factors that structure communities within and between its islands remain poorly understood. In this study, water quality, physical habitats and geographical distance were assessed as potential predictors for the diversity and structure of fish assemblages. A wide variety of species with different geographical origins were distributed over the different islands, which indicates that most fish species are able to reach the islands of the archipelago. Since pollution is a clear pressure on the fish assemblages of oceanic islands, environmental management of the coastal areas is of paramount importance.
Vulnerability and Decision-Making in Multispecies Fisheries: A Risk Assessment of Bacalao (Mycteroperca olfax) and Related Species in the Galapagos’ Handline Fishery
Marine fish populations can be vulnerable to overfishing, as a response of their life history, ecology, and socio-economic aspects. Vulnerability assessments, in this regard, can be used to support fisheries decision-making by aiding species prioritization. Using this method, we assessed local vulnerability of the Galapagos grouper (‘bacalao’; Mycteroperca olfax) and compared it with other phylogenetically-related species caught in the Galapagos’ handline-fishery. Bacalao is an overfished regionally endemic fish species, characterized by low resilience, high market and cultural value and high spatial overlap with the fishery. Our results suggested that bacalao is a species of high management priority, requiring urgent measures to prevent fisheries’ collapse.
Spatial Characteristics and Temporal Evolution of Chemical and Biological Freshwater Status as Baseline Assessment on the Tropical Island San Cristóbal (Galapagos, Ecuador)
The fragility of geographically isolated islands stresses the necessity of evaluating the current situation, identifying temporal trends and suggesting appropriate conservation measures. To support this, this study assessed the freshwater quality of three stream basins on San Cristóbal (Galapagos) for two consecutive years. Spatial analysis via principal component analysis (PCA) illustrated that abiotic differences between stream basins were mostly related to turbidity, pH, dissolved oxygen (DO), and conductivity. Biotic differences were less clear due to masking by anthropogenic disturbances and dispersal limitations, yet indicated a negative effect of reduced pH and DO on Atyidae presence. In 2017, significantly narrower ranges were found for turbidity, temperature, pH, and diversity (p < 0.01), suggesting a decrease in habitat variability and a need for conservation measures, including mitigating measures related to dam construction for water extraction. As such, further follow-up is highly recommended for the sustainable development and environmental protection of this unique archipelago.