Fishes in a changing world: learning from the past to promote sustainability of fish populations.

Populations of fishes provide valuable services for billions of people, but face diverse and interacting threats that jeopardize their sustainability. Human population growth and intensifying resource use for food, water, energy and goods are compromising fish populations through a variety of mechanisms, including overfishing, habitat degradation and declines in water quality. The important challenges raised by these issues have been recognized and have led to considerable advances over past decades in managing and mitigating threats to fishes worldwide. In this review, we identify the major threats faced by fish populations alongside recent advances that are helping to address these issues. There are very significant efforts worldwide directed towards ensuring a sustainable future for the world's fishes and fisheries and those who rely on them. Although considerable challenges remain, by drawing attention to successful mitigation of threats to fish and fisheries we hope to provide the encouragement and direction that will allow these challenges to be overcome in the future.

Environmental drivers of diurnal visits by transient predatory fishes to Caribbean patch reefs.

Video cameras recorded the diurnal visitation rates of transient (large home range) piscivorous fishes to coral patch reefs in The Bahamas and identified 11 species. Visits by bar jack Caranx ruber, mutton snapper Lutjanus analis, yellowtail snapper Ocyurus chrysurus, barracuda Sphyraena barracuda and cero Scomberomorus regalis were sufficiently frequent to correlate with a range of biophysical factors. Patch-reef visitation rates and fish abundances varied with distance from shore and all species except S. regalis were seen more frequently inshore. This pattern is likely to be caused by factors including close proximity to additional foraging areas in mangroves and on fore-reefs and higher abundances close to inshore nursery habitats. Visitation rates and abundances of C. ruber, L. analis, O. chrysurus and S. regalis also varied seasonally (spring v. winter), possibly as fishes responded to temperature changes or undertook spawning migrations. The abundance of each transient predator species on the patch reefs generally exhibited limited diurnal variability, but L. analis was seen more frequently towards dusk. This study demonstrates that the distribution of transient predators is correlated spatially and temporally with a range of factors, even within a single lagoon, and these drivers are species specific. Transient predators are considered an important source of mortality shaping reef-fish assemblages and their abundance, in combination with the biomass of resident predators, was negatively correlated with the density of prey fishes. Furthermore, transient predators are often targeted by fishers and understanding how they utilize seascapes is critical for protecting them within reserves.

Spatial distribution of nominally herbivorous fishes across environmental gradients on Brazilian rocky reefs.

Assemblages of roving herbivores were consistently different between eastern, warmer, sheltered sites and western, colder, more wave-exposed sites. At eastern sites, detritivorous-herbivorous species dominated while omnivores had the highest biomass and were dominant at western sites. Macroalgivores did not show any trends related to location. These distributional patterns, at relatively small spatial scales of a few kilometres, mirror large-scale latitudinal patterns observed for the studied species along the entire Brazilian coast, where cold water associated species are abundant on south-eastern rocky reefs (analogous to the western sites of this study), and tropical species are dominant on north-eastern coral reefs (analogous to the eastern sites). Species-level analyses demonstrated that depth was an important factor correlated with biomasses of Diplodus argenteus, Sparisoma axillare and Sparisoma tuiupiranga, probably due to resource availability and interspecific competition. Herbivorous fish assemblages in the study area have been historically affected by fishing, and combined with the variation in assemblage structure, this is likely to have important, spatially variable effects on the dynamics of benthic communities.

The ecology, behaviour and physiology of fishes on coral reef flats, and the potential impacts of climate change.

Reef flats, typically a low-relief carbonate and sand habitat in shallow water leeward of the reef crest, are one of the most extensive zones on Pacific coral reefs. This shallow zone often supports an abundant and diverse fish assemblage that is exposed to more significant variations in physical factors, such as water depth and movement, temperature and ultraviolet (UV) radiation levels, than most other reef fishes. This review examines the characteristics of reef flat fish assemblages, and then investigates what is known about how they respond to their biophysical environment. Because of the challenges of living in shallow, wave-exposed water, reef flats typically support a distinct fish assemblage compared to other reef habitats. This assemblage clearly changes across tidal cycles as some larger species migrate to deeper water at low tide and other species modify their behaviour, but quantitative data are generally lacking. At least some reef flat fish species are well-adapted to high temperatures, low oxygen concentrations and high levels of UV radiation. These behavioural and physiological adaptations suggest that there may be differences in the demographic processes between reef flat assemblages and those in deeper water. Indeed, there is some evidence that reef flats may act as nurseries for some species, but more research is required. Further studies are also required to predict the effects of climate change, which is likely to have multifaceted impacts on reef flats by increasing temperature, water motion and sediment load. Sea-level rise may also affect reef flat fish assemblages and food webs by increasing the amount of time that larger species are able to forage in this zone. The lack of data on reef flats is surprising given their size and relative ease of access, and a better understanding of their functional role within tropical marine seascapes is urgently required.

Crucial knowledge gaps in current understanding of climate change impacts on coral reef fishes.

Expert opinion was canvassed to identify crucial knowledge gaps in current understanding of climate change impacts on coral reef fishes. Scientists that had published three or more papers on the effects of climate and environmental factors on reef fishes were invited to submit five questions that, if addressed, would improve our understanding of climate change effects on coral reef fishes. Thirty-three scientists provided 155 questions, and 32 scientists scored these questions in terms of: (i) identifying a knowledge gap, (ii) achievability, (iii) applicability to a broad spectrum of species and reef habitats, and (iv) priority. Forty-two per cent of the questions related to habitat associations and community dynamics of fish, reflecting the established effects and immediate concern relating to climate-induced coral loss and habitat degradation. However, there were also questions on fish demographics, physiology, behaviour and management, all of which could be potentially affected by climate change. Irrespective of their individual expertise and background, scientists scored questions from different topics similarly, suggesting limited bias and recognition of a need for greater interdisciplinary and collaborative research. Presented here are the 53 highest-scoring unique questions. These questions should act as a guide for future research, providing a basis for better assessment and management of climate change impacts on coral reefs and associated fish communities.

Linking fishes to multiple metrics of coral reef structural complexity using three-dimensional technology.

Structural complexity strongly influences biodiversity and ecosystem productivity. On coral reefs, structural complexity is typically measured using a single and small-scale metric ('rugosity') that represents multiple spatial attributes differentially exploited by species, thus limiting a complete understanding of how fish associate with reef structure. We used a novel approach to compare relationships between fishes and previously unavailable components of reef complexity, and contrasted the results against the traditional rugosity index. This study focused on damselfish to explore relationships between fishes and reef structure. Three territorial species, with contrasting trophic habits and expected use of the reef structure, were examined to infer the potential species-specific mechanisms associated with how complexity influences habitat selection. Three-dimensional reef reconstructions from photogrammetry quantified the following metrics of habitat quality: 1) visual exposure to predators and competitors, 2) density of predation refuges and 3) substrate-related food availability. These metrics explained the species distribution better than the traditional measure of rugosity, and each species responded to different complexity components. Given that a critical effect of reef degradation is loss of structure, adopting three-dimensional technologies potentially offers a new tool to both understand species-habitat association and help forecast how fishes will be affected by the flattening of reefs.

Honduras: Caribbean Coast.

The coast of Honduras, Central America, represents the southern end of the Mesoamerican Barrier Reef System, although its marine resources are less extensive and studied than nearby Belize and Mexico. However, the coastal zone contains mainland reef formations, mangroves, wetlands, seagrass beds and extensive fringing reefs around its offshore islands, and has a key role in the economy of the country. Like most tropical areas, this complex of benthic habitats experiences limited annual variation in climatic and oceanographic conditions but seasonal and occasional conditions, particularly coral bleaching and hurricanes, are important influences. The effects of stochastic factors on the country's coral reefs were clearly demonstrated during 1998 when Honduras experienced a major hurricane and bleaching event. Any natural or anthropogenic impacts on reef health will inevitably affect other countries in Latin America, and vice versa, since the marine resources are linked via currents and the functioning of the system transcends political boundaries. Much further work on, for example, movement of larvae and transfer of pollutants is required to delineate the full extent of these links. Anthropogenic impacts, largely driven by the increasing population and proportion of people living in coastal areas, are numerous and include key factors such as agricultural run-off, over-fishing, urban and industrial pollution (particularly sewage) and infrastructure development. Many of these threats act synergistically and, for example, poor watershed management via shifting cultivation, increases sedimentation and pesticide run-off onto coral reefs, which increases stress to corals already affected by decreasing water quality and coral bleaching. Threats from agriculture and fishing are particularly significant because of the size of both industries. The desire to generate urgently required revenue within Honduras has also led to increased tourism which provides an overarching stress to marine resources since most tourists spend time in the coastal zone. Hence the last decade has seen a dramatic increase in coastal development, a greater requirement for sewage treatment and more demand for freshwater, particularly in the Bay Islands. Although coastal zone management is relatively recent in Honduras, it is gaining momentum from both large-scale initiatives, such as the Ministry of Tourism's 'Bay Islands Environmental Management Project', and national and international NGO projects. For example, a series of marine protected areas and legislative regulations have been established, but management capacity, enforcement and monitoring are limited by funding, expertise and training. Existing and future initiatives, supported by increased political will and environmental awareness of stakeholders, are vital for the long-term economic development of the country.