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Shark depredation, whereby hooked fish are partially or completely consumed before they can be retrieved, occurs globally in commercial and recreational fisheries. Depredation can damage fishing gear, injure sharks, cause additional mortality to targeted fish species and result in economic losses to fishers. Knowledge of the mechanisms behind depredation is limited. We used a 13 yr dataset of fishery-dependent commercial daily logbook data for the Mackerel Managed Fishery in Western Australia, which covers 15° of latitude and 10000 km of coastline, to quantify how fishing effort and environmental variables influence depredation. We found that shark depredation rates were relatively low in comparison with previous studies and varied across the 3 management zones of the fishery, with 1.7% of hooked fish being depredated in the northern Zone 1, 2.5% in the central Zone 2 and 5.7% in the southern Zone 3. Generalized additive mixed models found that measures of commercial fishing activity and a proxy for recreational fishing effort (distance from town centre) were positively correlated with shark depredation across Zones 1 and 2. Depredation rates increased during the 13 yr period in Zones 2 and 3, and were higher at dawn and dusk, suggesting crepuscular feeding in Zone 1. This study provides one of the first quantitative assessments of shark depredation in a commercial fishery in Western Australia, and for a trolling fishery globally. The results demonstrate a correlation between fishing effort and depredation, suggesting greater fishing effort in a concentrated area may change shark behaviour, leading to high rates of depredation.

Este artículo contiene 16 páginas, 5 figuras, 1 tabla., Aim The influence of niche and neutral mechanisms on the assembly of ecological communities have long been debated. However, we still have a limited knowledge on their relative importance to explain patterns of diversity across latitudinal gradients (LDG). Here, we investigate the extent to which these ecological mechanisms contribute to the LDG of reef fishes. Location Eastern Atlantic Ocean. Taxon Reef-associated ray-finned fishes. Methods We combined abundance data across ~60° of latitude with functional trait data and phylogenetic trees. A null model approach was used to decouple the influence of taxonomic diversity (TD) on functional (FD) and phylogenetic (PD) diversity. Standardized effect sizes (SES FD and SES PD) were used to explore patterns of overdispersion, clustering and randomness. Information theoretic approaches were used to investigate the role of large- (temperature, geographic isolation, nitrate and net primary productivity) and local-scale (human population and depth) drivers. We further assessed the role of demographic stochasticity and its interaction with species trophic identity and dispersal capacity. Results Taxonomic diversity peaked at ~15°–20°N, with a second mode of lower magnitude at ~45°N; a pattern that was predicted by temperature, geographic isolation and productivity. Tropical regions displayed a higher proportion of overdispersed assemblages, whilst clustering increased towards temperate regions. Phylogenetic and functional overdispersion were associated with warmer, productive and isolated regions. Demographic stochasticity also contributed largely to community assembly, independently of ecoregions, although variation was dependent on the trophic identity and body size of species. Main conclusions Niche-based processes linking thermal and resource constraints to local coexistence mechanisms have contributed to the LDG in reef fishes. These processes do not act in isolation, stressing the importance of understanding interactions between deterministic and stochastic factors driving community structure in the face of rapid biodiversity change., This study was partially supported by Portuguese national funds from FCT—Foundation for Science and Technology through project UIDB/04326/2020. C.R. and P.N. were financially supported by the Oceanic Observatory of Madeira Project (M1420-01-0145-FEDER-000001—Observatório Oceânico da Madeira-OOM). D.A.S. was supported by a UKRI Future Leaders Fellowship (MR/S032827/1). P.J.M. was supported by a Marie Curie Career Integration Grant (PCIG10-GA-2011-303685). T.W. received funding from the Australian Research Council (DP170100023).

Global warming is facilitating the range expansion of tropical herbivores, causing a tropicalization of temperate marine ecosystems, where tropical herbivores can suppress habitat‐forming macrophytes, supporting the resilience of canopy‐free ecosystem states. However, currently we lack a thorough understanding of the mechanisms that, on one hand, support the persistence of tropical herbivores and on the other support the recovery of temperate foundation species in tropicalized ecosystems, a required knowledge to predict potential regime shifts and reversals to the baseline state of the ecosystem. This study tested processes behind the persistence of the tropicalization of temperate reefs which experienced a complete loss of their kelp forests and an influx of tropical herbivores following a marine heatwave in 2011. For this, we assessed the feedback mechanisms that maintain turf‐dominated states (recruitment of tropical herbivores, browsing and grazing rates and turf cover) and those that resist it (kelp recruitment, survival and reproductiveness). We found that the reefs remained tropicalized with high abundances of turf and tropical herbivores after 9 years from the regime shift. The rabbitfish Siganus fuscescens and the chub Kyphosus bigibbus were the most important herbivores whose persistence was supported by the adjacent reef lagoon, where seagrass meadows and the backreef habitats hosted juveniles of both species, particularly rabbitfish. Tropical herbivores exerted a strong top–down control on turf seaweed and kelp during herbivory assays, rapidly consuming kelp individuals in open areas. However, in topographical refuges in the reefs, herbivory was low and kelp individuals survived, with some having reproductive tissue. Synthesis. Our findings incorporate the importance of nursery grounds for tropical herbivores and herbivory refugia for kelp individuals into the tropicalization model, where the former increases the resilience of canopy‐free states and the latter might facilitate recovering kelp populations. The restoration of abundant warm‐resistant kelp populations in shelters could provide local sources of propagules to recolonize open spaces; however, our results suggest that the reduction of herbivory and the provision of turf‐free substratum would be necessary to boost the recovery of kelp forests.

The arrival of non-indigenous species into new areas is one of the main processes altering the oceans globally. Macrorhynchia philippina is a large-sized colonial hydrozoan of an invasive nature. To obtain a deeper understanding of the process of colonization of new areas, it is essential to describe the ecological pattern through scales of temporal and spatial variation. In this study, we describe the colonization by M. Philippina of an oceanic island (Gran Canaria Island, Canary Islands, eastern Atlantic). We describe the abundance and size structure patterns of M. Philippina in three nearshore habitats, rocky reefs, seagrass meadows and rhodolith seabeds, at times before (2014), during (2016) and after (2017) the demographic explosion of this species. On rocky reefs and rhodolith seabeds, the abundance of colonies increased dramatically in 2017 rel­ative to 2014, e.g. from 0 to 138 colonies/100 m2. On seagrass meadows, however, the colonies were smaller. In summary, M. Philippina shows an ecological plasticity to rapidly colonize different types of nearshore habitats, but with varying success. La aparición de especies exóticas es uno de los principales factores que alteran los océanos de forma global. Mac­rorhynchia philippina es un hidrozoo colonial de tamaño grande y naturaleza invasora. Para tener un mejor conocimiento del proceso de colonización es fundamental describir los patrones ecológicos a escalas de variación temporal y espacial. En este estudio, describimos el proceso de colonización por M. Philippina en una isla oceánica (Gran Canaria, Islas Canarias, Atlántico oriental). Se describen los patrones de abundancia y estructura de tallas de M. Philippina en tres hábitats costeros: arrecifes rocosos, praderas de fanerógamas marinas y fondos de rodolitos, antes (2014), durante (2016) y después (2017) de la explosión demográfica de la especie. Sobre arrecifes rocosos y en fondos de rodolitos, la abundancia de las colonias se incrementó drásticamente en 2017 con relación a 2014, e.g. desde 0 hasta 138 colonias/100 m2; este incremento fue menor en las praderas de fanerógamas marinas. En las praderas marinas, la longitud de las colonias fue más pequeña que sobre ar­recifes rocosos y fondos de rodolitos. Consecuentemente, la colonización rápida por M. Philippina demuestra su plasticidad ecológica para colonizar diferentes tipos de hábitats costeros, aunque con diferente éxito.

Sharks play a key role in the structure and functioning of marine ecosystems. More ecological information is essential to implement responsible management and conservation actions on this fauna, particularly at a regional level for threatened species.

The conservation of coastal seascapes requires a better understanding of how different dimensions of biodiversity are represented between juxtaposed habitats. We explored patterns of taxonomic, functional, and phylogenetic diversity of fishes between four habitats (sandy bottoms, rocky reefs of high and low relief, and mixed bottoms) within a semi-lagoon seascape (Las Canteras beach) in Gran Canaria Island. Data on fish presence in each habitat were provided by weekly snorkeling tours, at day and night, from August 2015 to August 2018. Indices that measured ‘how much’ biodiversity, i.e., ‘how many species’ (species richness), ‘how much functional dissimilarity’, and ‘how much evolutionary history’ were larger on rocky bottoms. However, indices that measured phylogenetic differentiation, i.e., ‘how different’, via the taxonomic distinctiveness and the Mean Pairwise Distance index were particularly high on sandy bottoms, because of the presence of elasmobranchs, which were absent from rocky bottoms. The ‘phylogenetic signal’, whether phylogenetically related species are functionally similar, was significant on rocky bottoms, but non-significant on sandy bottoms, reflecting phylogenetic ‘overdispersion’ on sandy bottoms and phylogenetic ‘clustering’ on hard bottoms. From a conservation perspective, sandy bottoms cannot be underrated, particularly in the context of maximizing indices that measure ‘how phylogenetically different’ biodiversity is.

Marine fisheries in coastal ecosystems in many areas of the world have historically removed large-bodied individuals, potentially impairing ecosystem functioning and the long-term sustainability of fish populations. Reporting on size-based indicators that link to food-web structure can contribute to ecosystem-based management, but the application of these indicators over large (cross-ecosystem) geographical scales has been limited to either fisheries-dependent catch data or diver-based methods restricted to shallow waters (20 m) that can misrepresent the abundance of large-bodied fished species. We obtained data on the body-size structure of 82 recreationally or commercially targeted marine demersal teleosts from 2904 deployments of baited remote underwater stereo-video (stereo-BRUV). Sampling was at up to 50 m depth and covered approximately 10,000 km of the continental shelf of Australia. Seascape relief, water depth, and human gravity (i.e., a proxy of human impacts) were the strongest predictors of the probability of occurrence of large fishes and the abundance of fishes above the minimum legal size of capture. No-take marine reserves had a positive effect on the abundance of fishes above legal size, although the effect varied across species groups. In contrast, sublegal fishes were best predicted by gradients in sea surface temperature (mean and variance). In areas of low human impact, large fishes were about three times more likely to be encountered and fishes of legal size were approximately five times more abundant. For conspicuous species groups with contrasting habitat, environmental, and biogeographic affinities, abundance of legal-size fishes typically declined as human impact increased. Our large-scale quantitative analyses highlight the combined importance of seascape complexity, regions with low human footprint, and no-take marine reserves in protecting large-bodied fishes across a broad range of species and ecosystem configurations.Las pesquerías marinas de los ecosistemas costeros en muchas áreas del mundo históricamente han removido a individuos de gran tamaño, potencialmente perjudicando el funcionamiento ambiental y la sostenibilidad a largo plazo de las poblaciones de peces. Los reportes sobre los indicadores basados en el tamaño que se vinculan con la estructura de la red alimenticia pueden contribuir al manejo basado en el ecosistema, aunque la aplicación de estos indicadores a grandes (inter-ecosistemas) escalas geográficas ha estado limitada a datos de captura dependientes de las pesquerías o métodos basados en el buceo restringidos a aguas someras (20 m), lo cual puede representar erróneamente la abundancia de peces de gran tamaño capturados para la pesca. Obtuvimos los datos de la estructura del tamaño corporal de 82 teleósteos marinos demersales focalizados por razones recreativas o comerciales tomados de 2,904 despliegues de video estéreo subacuático remoto con cebo (stereo-BRUV, en inglés). El muestreo se realizó hasta los 50 metros de profundidad y abarcó aproximadamente 10,000 km del talud continental de Australia. El relieve marino, la profundidad del agua y la gravedad humana (es decir, un indicador de los impactos humanos) fueron los pronosticadores más sólidos de la probabilidad de incidencia de los peces de gran tamaño y de la abundancia de peces por encima del tamaño legal mínimo de captura. Las reservas marinas de protección total tienen un efecto positivo sobre la abundancia de los peces que están por encima del tamaño legal, aunque el efecto varió según el grupo de especies. Como contraste, los peces de tamaño sublegal fueron pronosticados de mejor manera usando gradientes de la temperatura de la superficie marina (media y varianza). En las áreas con un impacto humano reducido, los peces de gran tamaño corporal tenían hasta tres veces mayor probabilidad de aparecer y los peces de tamaño legal eran aproximadamente cinco veces más abundantes. Para los grupos de especies conspicuas con afinidades contrastantes de hábitat, ambiente y biogeografía, la abundancia de peces de tamaño legal normalmente declinó conforme aumentó el impacto humano. Nuestros análisis cuantitativos a gran escala resaltan la importancia conjunta que tienen la complejidad marina, las regiones con una huella humana reducida y las reservas marinas de protección total para la protección de los peces de gran tamaño corporal en una extensa gama de especies y configuraciones ecosistémicas. Efectos de la Huella Humana y los Factores Biofísicos sobre la Estructura del Tamaño Corporal de Especies Marinas Capturadas para la Pesca.

Marine reserves are a key tool for the conservation of marine biodiversity, yet only ~2.5% of the world's oceans are protected. The integration of marine reserves into connected networks representing all habitats has been encouraged by international agreements, yet the benefits of this design has not been tested empirically. Australia has one of the largest systems of marine reserves, providing a rare opportunity to assess how connectivity influences conservation success. An Australia‐wide dataset was collected using baited remote underwater video systems deployed across a depth range from 0 to 100 m to assess the effectiveness of marine reserves for protecting teleosts subject to commercial and recreational fishing. A meta‐analytical comparison of 73 fished species within 91 marine reserves found that, on average, marine reserves had 28% greater abundance and 53% greater biomass of fished species compared to adjacent areas open to fishing. However, benefits of protection were not observed across all reserves (heterogeneity), so full subsets generalized additive modelling was used to consider factors that influence marine reserve effectiveness, including distance‐based and ecological metrics of connectivity among reserves. Our results suggest that increased connectivity and depth improve the aforementioned marine reserve benefits and that these factors should be considered to optimize such benefits over time. We provide important guidance on factors to consider when implementing marine reserves for the purpose of increasing the abundance and size of fished species, given the expected increase in coverage globally. We show that marine reserves that are highly protected (no‐take) and designed to optimize connectivity, size and depth range can provide an effective conservation strategy for fished species in temperate and tropical waters within an overarching marine biodiversity conservation framework., An Australia‐wide dataset was collected using baited remote underwater video systems deployed across a depth range from 0 to 100 m to assess the effectiveness of marine reserves for protecting fished species. A meta‐analytical comparison of 73 fished species within 91 marine reserves found that, on average, marine reserves had 28% greater abundance and 53% greater biomass of fished species compared to adjacent areas open to fishing. We show that marine reserves that are highly protected (no‐take) and designed to optimize connectivity, size and depth range can provide an effective conservation strategy for fished species in temperate and tropical waters.

In recent decades, numerous marine species have changed their distribution ranges due to ocean warming. The Spotfin burrfish, Chilomycterus reticulatus, is a reef fish with a global distribution along tropical, subtropical and warm-temperate areas of the Pacific, Indian and Atlantic oceans. In this work, we analyzed the presence of this species, between 1990 and 2019, at two islands of the Canarian Archipelago under varying oceanographic conditions: El Hierro (the westernmost island, under more tropical conditions) and Gran Canaria (a central-east island, under more cooler conditions). We expected that, under increased ocean temperatures in recent decades, the number of sightings has increased in Gran Canaria relative to El Hierro. We compiled information from different sources, including interviews and local citizenship databases. A total of 534 sightings were reported: 38.58% from El Hierro and 61.43% from Gran Canaria. The number of sightings on Gran Canaria has significantly increased through time, at a rate of 0.1 sightings per year, at El Hierro, however, the number of sightings has not significantly changed over time. Sea Surface Temperature has linearly increased in both El Hierro and Gran Canaria islands over the last three decades. Positive Sea Surface Temperature anomalies, particularly in 1998 and 2010, including high winter minimum temperatures, provide an ideal oceanographic context to favour the arrival of new individuals and, consequently, the increase in the number of sightings in Gran Canaria. Still, potential donor areas of fish recruits remain unknown.

Understanding changes in biodiversity requires the implementation of monitoring programs encompassing different dimensions of biodiversity through varying sampling techniques. In this work, fish assemblages associated with the "outer" and "inner" sides of four marinas, two at the Canary Islands and two at southern Portugal, were investigated using three complementary sampling techniques: underwater visual censuses (UVCs), baited cameras (BCs), and fish traps (FTs). We firstly investigated the complementarity of these sampling methods to describe species composition. Then, we investigated differences in taxonomic (TD), phylogenetic (PD) and functional diversity (FD) between sides of the marinas according to each sampling method. Finally, we explored the applicability/reproducibility of each sampling technique to characterize fish assemblages according to these metrics of diversity. UVCs and BCs provided complementary information, in terms of the number and abundances of species, while FTs sampled a particular assemblage. Patterns of TD, PD, and FD between sides of the marinas varied depending on the sampling method. UVC was the most cost-efficient technique, in terms of personnel hours, and it is recommended for local studies. However, for large-scale studies, BCs are recommended, as it covers greater spatio-temporal scales by a lower cost. Our study highlights the need to implement complementary sampling techniques to monitor ecological change, at various dimensions of biodiversity. The results presented here will be useful for optimizing future monitoring programs. FCT-Foundation for Science and Technology [CCMAR/Multi/04326/2013] info:eu-repo/semantics/publishedVersion

The ecology of reef fish varies with depth, although patterns in diversity remain largely undescribed, in particular the complementarity of their taxonomic, functional and phylogenetic facets. In the present study we investigated patterns of taxonomic, functional and phylogenetic diversity of fish on 21 reefs, at depths ranging from 3 to 31m, at Príncipe Island (Gulf of Guinea). Taxonomic and functional diversity decreased monotonically with depth; the pattern was less accentuated for phylogenetic diversity. Functional diversity was saturated at high levels of taxonomic diversity, reflecting redundancy in species traits, particularly at the shallower reefs. Functional diversity increased linearly with phylogenetic diversity; thus, increasing niche availability seems to translate into a larger diversity of phylogenies. Dissimilarities in the structure and composition of fish assemblages among reefs were correlated with differences in depth, including a progressive turnover in species. Depth affected the functional traits of nearshore reef fish. Trophic breadth decreased with depth; carnivores and planktivores increased with depth, whereas herbivores decreased with depth. Small-sized fusiform fish dominated on the shallowest reefs. In summary, the present study demonstrated decays in biodiversity, from different perspectives, of reef fish with depth, which are connected with shifts in fish traits.