Relationship between pelagic larval duration and abundance of tropical fishes on temperate coasts of Japan

The influence of pelagic larval duration (PLD) and egg type dispersal capabilities of 35 demersal and pelagic-spawning tropical fish species is examined in relation to their abundance on the temperate coasts of Japan. The PLDs of pelagic spawners were significantly longer than those of demersal spawners, and a high occurrence of pelagic spawners on the temperate coasts suggests that these fishes are more easily transported to temperate coasts than demersal spawners. For demersal spawners, the common species on the temperate coasts had significantly longer PLDs than the rare species; this suggests that PLD is a major factor influencing the distribution patterns of tropical demersal spawners on temperate coasts. Moreover, a negative correlation between PLD and the abundance of some species of pelagic and demersal spawners suggests the presence of reproductively active fishes in northern subtropical and even in temperate waters.     

Changes in teleost yolk proteins during oocyte maturation: correlation of yolk proteolysis with oocyte hydration

Yolk proteins of prematuration occytes and postmaturation eggs were compared by SDS gel electrophoresis in several teleosts, including freshwater species that produce demersal eggs, estuarine and marine species with demersal eggs, and marine species with pelagic eggs. In certain teleosts distinct changes in yolk protein banding patterns during oocyte maturation are suggestive of extensive secondary proteolysis of yolk proteins at this time; proteolysis is most pronounced in marine fishes with pelagic eggs. In many teleosts the oocyte swells by hydration during maturation; this hydration is also most pronounced in marine fishes with pelagic eggs. The extent of yolk proteolysis is well correlated with the extent of oocyte hydration during maturation.     

Biodiversity associated with restored small-scale mussel habitats has restoration decision implications

The global loss of marine ecosystem engineers has caused an unprecedented decline in biodiversity. Although wild shellfish habitats have been shown to support biodiverse ecosystems, little is known about how biodiversity is altered by restored shellfish habitats, particularly mussels. To explore the biodiversity response to restored mussel habitats we deposited mussels on the seafloor in 1.5?×?1.5 m plots across a gradient of benthic environments. To understand a holistic community response, this study looks at the response of three faunal classifications over 1 year: infauna, epifauna, and pelagic fauna, compared with adjacent control plots (no mussels). The restored mussel habitats recorded 42 times more demersal fish than control areas, while macroalgae and mobile benthic invertebrates had over a twofold increase in abundance. Overall, the addition of mussels to the seafloor resulted in a general reduction of infaunal abundance and biodiversity, but an increase in epifaunal and pelagic faunal abundances, specifically from those species that benefit from benthic habitat complexity and an increase in food availability. From a management perspective, we highlight location-specific differences to consider for future restoration efforts, including environmental conditions and potential observed factors such as nearby sources of species, particularly predators, and relevant demersal fish ranges. Ultimately, measuring biodiversity responses in small-scale studies will serve as a valuable guide for larger scale restoration efforts and this study recommends considerations to enhance biodiversity outcomes in restored mussel habitats.

     

What can population genetics tell us about dispersal and biogeographic history of coral-reef fishes?

Abstract Coral-reef fishes, like many other marine organisms, generally possess a benthic adult stage and pelagic larval stage. What can population genetics studies tell us about the demographic, evolutionary and biogeographic consequences of this life cycle? Ten studies of geographical patterns of intraspecific genetic differentiation in reef fishes have been published. These studies have included 2t > species/species complexes (14 in the family Pomacentridae, the remaining 12 in 9 different families) and have been about equally divided between the tropical Pacific and the tropical western Atlantic. A survey of these studies shows the following: (i) the existence of the pelagic larval stage appears to have led to high levels of gene flow even among populations separated by thousands of kilometres of open ocean; (ii) an apparent pattern of increased gene flow among populations connected by intermediate 'stepping stones’; (iii) very tentative evidence for a relationship between length of pelagic larval life and gene flow; (iv) no clear relationship between egg type (pelagic rs non-pelagic) and gene flow; and (v) suggestive evidence that damselfishes (family Pomacentridae) may have more restricted dispersal (less gene flow) than other reef fishes. The application of current and future molecular tools has the strong potential to clarify some of these relationships, particularly by using relatively neutral genetic markers. Additionally, discoveries of DNA markers having very high rates of mutation may allow tracking of demographically relevant levels of larval dispersal. Molecular tools are becoming especially valuable in uncovering the biogeographic and phylogenetic history of reef fishes. The one molecular study to date has suggested that at least some speciation events may have occurred during the climate changes and sea-level regressions associated with Pleistocene glacial episodes. Molecular tools need to be used to further explore the means by which high species diversity can be generated in the face of the apparently high gene flow observed in most coral-reef fishes.     

Reproduction in the North Atlantic oceanic ichthyofauna and the relationship between fecundity and species' sizes

Synopsis The pelagic (589 spp.) and demersal (505 spp.) oceanic ichthyofaunas of the North Atlantic Basin have very different compositions at ordinal and family level. Yet the pattern of relationships between species' maximum size and maximum fecundity from data available (10% of the pelagic, 19% of the demersal species) was similar. A positive relationship between fecundity and weight was confirmed among most teleosts, but was not followed by the elasmobranchs represented. Species' reproductive styles are reviewed in ordinal groupings within a framework of the overall body size/fecundity distribution. Species size (maximum weight) spectra were synthesized for both pelagic and demersal assemblages to assess the allocation of potential reproductive effort throughout the North Atlantic oceanic ichthyofauna. The only available examples of species size spectra and biomass spectra from the pelagic and demersal ichthyofauna in this ocean basin imply geographic and bathymetric variation in overall reproductive effort among fishes whose fecundity is size dependent. Further implications concerning reproductive effort are discussed in the light of food availability.     

Population divergences despite long pelagic larval stages: lessons from crocodile icefishes (Channichthyidae)

Dispersal via pelagic larval stages plays a key role in population connectivity of many marine species. The degree of connectivity is often correlated with the time that larvae spend in the water column. The Antarctic notothenioid fishes develop through an unusually long pelagic larval phase often exceeding 1 year. Notothenioids thus represent a prime model system for studying the influence of prolonged larval phases on population structure in otherwise demersal species. Here, we compare the population genetic structure and demographic history of two sub‐Antarctic crocodile icefish species (Chaenocephalus aceratus and Champsocephalus gunnari) from the Scotia Arc and Bouvet Island in the Atlantic sector of the Southern Ocean to delineate the relative importance of species‐specific, oceanographic and paleoclimatic factors to gene flow. Based on 7 (C. aceratus) and 8 (C. gunnari) microsatellites, as well as two mitochondrial DNA markers (cytochrome b, D‐loop), we detect pronounced population genetic structure in both species (amova FSTs range from 0.04 to 0.53). High genetic similarities were found concordantly in the populations sampled at the Southern Scotia Arc between Elephant Island and South Orkney Islands, whereas the populations from Bouvet Island, which is located far to the east of the Scotia Arc, are substantially differentiated from those of the Scotia Arc region. Nonetheless, haplotype genealogies and Bayesian cluster analyses suggest occasional gene flow over thousands of kilometres. Higher divergences between populations of C. gunnari as compared to C. aceratus are probably caused by lower dispersal capabilities and demographic effects. Bayesian skyline plots reveal population size reductions during past glacial events in both species with an estimated onset of population expansions about 25 000 years ago.     

The Potential for Spatial Distribution Indices to Signal Thresholds in Marine Fish Biomass

The frequently observed positive relationship between fish population abundance and spatial distribution suggests that changes in distribution can be indicative of trends in abundance. If contractions in spatial distribution precede declines in spawning stock biomass (SSB), spatial distribution reference points could complement the SSB reference points that are commonly used in marine conservation biology and fisheries management. When relevant spatial distribution information is integrated into fisheries management and recovery plans, risks and uncertainties associated with a plan based solely on the SSB criterion would be reduced. To assess the added value of spatial distribution data, we examine the relationship between SSB and four metrics of spatial distribution intended to reflect changes in population range, concentration, and density for 10 demersal populations (9 species) inhabiting the Scotian Shelf, Northwest Atlantic. Our primary purpose is to assess their potential to serve as indices of SSB, using fisheries independent survey data. We find that metrics of density offer the best correlate of spawner biomass. A decline in the frequency of encountering high density areas is associated with, and in a few cases preceded by, rapid declines in SSB in 6 of 10 populations. Density-based indices have considerable potential to serve both as an indicator of SSB and as spatially based reference points in fisheries management.     

A phylogenetic analysis of egg size,clutch size,spawning mode,adult body size,and latitude in reef fishes

Theoretical treatments of egg size in fishes suggest that constraints on reproductive output should create trade-offs between the size and number of eggs produced per spawn. For marine reef fishes, the observation of distinct reproductive care strategies (demersal guarding, egg scattering, and pelagic spawning) has additionally prompted speculation that these strategies reflect alternative fitness optima with selection on egg size differing by reproductive mode and perhaps latitude. Here, we aggregate data from 278 reef fish species and test whether clutch size, reproductive care, adult body size, and latitudinal bands (i.e., tropical, subtropical, and temperate) predict egg size, using a statistically unified framework that accounts for phylogenetic correlations among traits. We find no inverse relationship between species egg size and clutch size, but rather that egg size differs by reproductive mode (mean volume for demersal eggs = 1.22 mm³, scattered eggs = 0.18 mm³, pelagic eggs = 0.52 mm³) and that clutch size is strongly correlated with adult body size. Larger eggs were found in temperate species compared with tropical species in both demersal guarders and pelagic spawners, but this difference was not strong when accounting for phylogenetic correlations, suggesting that differences in species composition underlies regional differences in egg size. In summary, demersal guarders are generally small fishes with small clutch sizes that produce large eggs. Pelagic spawners and egg scatterers are variable in adult and clutch size. Although pelagic spawned eggs are variable in size, those of scatterers are consistently small.     

GEOGRAPHIC POPULATION STRUCTURE AND SPECIES DIFFERENCES IN MITOCHONDRIAL DNA OF MOUTHBROODING MARINE CATFISHES (ARIIDAE) AND DEMERSAL SPAWNING TOADFISHES (BATRACHOIDIDAE)

Restriction-fragment length polymorphisms in mitochondrial DNA (mtDNA) were used to evaluate population-genetic structure and matriarchal phylogeny in four species of marine fishes that lack a pelagic larval stage: the catfishes Arius felis and Bagre marinus, and the toadfishes Opsanus tau and O. beta. Thirteen informative restriction enzymes were used to assay mtDNAs from 134 specimens collected from Massachusetts to Louisiana. Considerable genotypic diversity was observed in each species. However, major mtDNA phylogenetic assemblages in catfish and toadfish (as identified in Wagner networks and UPGMA phenograms) exhibited contrasting patterns of geographic distribution: in catfish, distinct mtDNA clades were widespread, while such clades in toadfish tended to be geographically localized. By both the criteria of species' ranges and the geographic pattern of intraspecific mtDNA phylogeny, populations of marine catfish in the western Atlantic have had greater historical interconnectedness than have toadfish. Results are also compared to previously published mtDNA data in freshwater and other marine fishes. Although mtDNA differentiation among conspecific populations of continuously distributed marine fishes is usually lower than that among discontinuously distributed freshwater species inhabiting separate drainages, it is apparent that historical biogeographic factors can importantly influence genetic structure in marine as well as freshwater species.     

Invasive lionfish drive Atlantic coral reef fish declines

Indo-Pacific lionfish (Pterois volitans and P. miles) have spread swiftly across the Western Atlantic, producing a marine predator invasion of unparalleled speed and magnitude. There is growing concern that lionfish will affect the structure and function of invaded marine ecosystems, however detrimental impacts on natural communities have yet to be measured. Here we document the response of native fish communities to predation by lionfish populations on nine coral reefs off New Providence Island, Bahamas. We assessed lionfish diet through stomach contents analysis, and quantified changes in fish biomass through visual surveys of lionfish and native fishes at the sites over time. Lionfish abundance increased rapidly between 2004 and 2010, by which time lionfish comprised nearly 40% of the total predator biomass in the system. The increase in lionfish abundance coincided with a 65% decline in the biomass of the lionfish's 42 Atlantic prey fishes in just two years. Without prompt action to control increasing lionfish populations, similar effects across the region may have long-term negative implications for the structure of Atlantic marine communities, as well as the societies and economies that depend on them.     

Age and growth of grey triggerfish Balistes capriscus from trans-Atlantic populations

Anthropogenic factors that negatively impact reef fishes can include changes in life-history patterns of fisheries-targeted species. Understanding these impacts on growth and population age structure is essential in the management of exploited populations of fishes. This is the first study to directly compare age and growth for a major fisheries species between east and west populations of a transatlantic reef fish. The main goal of this study was to document age and growth in grey triggerfish Balistes capriscus from coastal waters of Ghana in the Gulf of Guinea (GOG) and compare those with the previous growth studies from that region and with the western Atlantic population. A secondary objective of this study was to evaluate the use of otoliths to age triggerfish and to provide a preliminary comparison with spine-derived age estimates. The results obtained from this study provided an updated understanding of the growth and age structure of the eastern B. capriscus population in GOG. The authors documented that shifts in population attributes occurred for B. capriscus after its major decline in abundance. The differences in physical and biotic characteristics of the East and West Atlantic regions and the differences in collection methods of samples make direct comparisons of growth parameters difficult. Nonetheless, overall differences in maximum sizes and ages were apparent; the western Atlantic population had a larger maximum size and older maximum age. The authors also documented that sagittal otoliths can be used to provide age estimates for triggerfish species, and otoliths as an ageing structure had better between-reader precision compared to dorsal spines.     

Recovery Trends in Marine Mammal Populations

Marine mammals have greatly benefitted from a shift from resource exploitation towards conservation. Often lauded as symbols of conservation success, some marine mammal populations have shown remarkable recoveries after severe depletions. Others have remained at low abundance levels, continued to decline, or become extinct or extirpated. Here we provide a quantitative assessment of (1) publicly available population-level abundance data for marine mammals worldwide, (2) abundance trends and recovery status, and (3) historic population decline and recent recovery. We compiled 182 population abundance time series for 47 species and identified major data gaps. In order to compare across the largest possible set of time series with varying data quality, quantity and frequency, we considered an increase in population abundance as evidence of recovery. Using robust log-linear regression over three generations, we were able to classify abundance trends for 92 spatially non-overlapping populations as Significantly Increasing (42%), Significantly Decreasing (10%), Non-Significant Change (28%) and Unknown (20%). Our results were comparable to IUCN classifications for equivalent species. Among different groupings, pinnipeds and other marine mammals (sirenians, polar bears and otters) showed the highest proportion of recovering populations, likely benefiting from relatively fast life histories and nearshore habitats that provided visibility and protective management measures. Recovery was less frequent among cetaceans, but more common in coastal than offshore populations. For marine mammals with available historical abundance estimates (n = 47), larger historical population declines were associated with low or variable recent recoveries so far. Overall, our results show that many formerly depleted marine mammal populations are recovering. However, data-deficient populations and those with decreasing and non-significant trends require attention. In particular, increased study of populations with major data gaps, including offshore small cetaceans, cryptic species, and marine mammals in low latitudes and developing nations, is needed to better understand the status of marine mammal populations worldwide.     

Atlantic reef fish biogeography and evolution

Aim To understand why and when areas of endemism (provinces) of the tropical Atlantic Ocean were formed, how they relate to each other, and what processes have contributed to faunal enrichment. Location Atlantic Ocean. Methods The distributions of 2605 species of reef fishes were compiled for 25 areas of the Atlantic and southern Africa. Maximum‐parsimony and distance analyses were employed to investigate biogeographical relationships among those areas. A collection of 26 phylogenies of various Atlantic reef fish taxa was used to assess patterns of origin and diversification relative to evolutionary scenarios based on spatio‐temporal sequences of species splitting produced by geological and palaeoceanographic events. We present data on faunal (species and genera) richness, endemism patterns, diversity buildup (i.e. speciation processes), and evaluate the operation of the main biogeographical barriers and/or filters. Results Phylogenetic (proportion of sister species) and distributional (number of shared species) patterns are generally concordant with recognized biogeographical provinces in the Atlantic. The highly uneven distribution of species in certain genera appears to be related to their origin, with highest species richness in areas with the greatest phylogenetic depth. Diversity buildup in Atlantic reef fishes involved (1) diversification within each province, (2) isolation as a result of biogeographical barriers, and (3) stochastic accretion by means of dispersal between provinces. The timing of divergence events is not concordant among taxonomic groups. The three soft (non‐terrestrial) inter‐regional barriers (mid‐Atlantic, Amazon, and Benguela) clearly act as ‘filters’ by restricting dispersal but at the same time allowing occasional crossings that apparently lead to the establishment of new populations and species. Fluctuations in the effectiveness of the filters, combined with ecological differences among provinces, apparently provide a mechanism for much of the recent diversification of reef fishes in the Atlantic. Main conclusions Our data set indicates that both historical events (e.g. Tethys closure) and relatively recent dispersal (with or without further speciation) have had a strong influence on Atlantic tropical marine biodiversity and have contributed to the biogeographical patterns we observe today; however, examples of the latter process outnumber those of the former.     

Thresholds for impaired species recovery

Studies on small and declining populations dominate research in conservation biology. This emphasis reflects two overarching frameworks: the small-population paradigm focuses on correlates of increased extinction probability; the declining-population paradigm directs attention to the causes and consequences of depletion. Neither, however, particularly informs research on the determinants, rate or uncertainty of population increase. By contrast, Allee effects (positive associations between population size and realized per capita population growth rate, r_realized, a metric of average individual fitness) offer a theoretical and empirical basis for identifying numerical and temporal thresholds at which recovery is unlikely or uncertain. Following a critique of studies on Allee effects, I quantify population-size minima and subsequent trajectories of marine fishes that have and have not recovered following threat mitigation. The data suggest that threat amelioration, albeit necessary, can be insufficient to effect recovery for populations depleted to less than 10% of maximum abundance (N_max), especially when they remain depleted for lengthy periods of time. Comparing terrestrial and aquatic vertebrates, life-history analyses suggest that population-size thresholds for impaired recovery are likely to be comparatively low for marine fishes but high for marine mammals. Articulation of a ‘recovering population paradigm’ would seem warranted. It might stimulate concerted efforts to identify generic impaired recovery thresholds across species. It might also serve to reduce the confusion of terminology, and the conflation of causes and consequences with patterns currently evident in the literature on Allee effects, thus strengthening communication among researchers and enhancing the practical utility of recovery-oriented research to conservation practitioners and resource managers.     

The global decline of freshwater megafauna

Freshwater ecosystems are among the most diverse and dynamic ecosystems on Earth. At the same time, they are among the most threatened ecosystems but remain underrepresented in biodiversity research and conservation efforts. The rate of decline of vertebrate populations is much higher in freshwaters than in terrestrial or marine realms. Freshwater megafauna (i.e., freshwater animals that can reach a body mass ≥30 kg) are intrinsically prone to extinction due to their large body size, complex habitat requirements and slow life‐history strategies such as long life span and late maturity. However, population trends and distribution changes of freshwater megafauna, at continental or global scales, remain unclear. In the present study, we compiled population data of 126 freshwater megafauna species globally from the Living Planet Database and available literature, and distribution data of 44 species inhabiting Europe and the United States from literature and databases of the International Union for Conservation of Nature and NatureServe. We quantified changes in population abundance and distribution range of freshwater megafauna species. Globally, freshwater megafauna populations declined by 88% from 1970 to 2012, with the highest declines in the Indomalaya and Palearctic realms (?99% and ?97%, respectively). Among taxonomic groups, mega‐fishes exhibited the greatest global decline (?94%). In addition, freshwater megafauna experienced major range contractions. For example, distribution ranges of 42% of all freshwater megafauna species in Europe contracted by more than 40% of historical areas. We highlight the various sources of uncertainty in tracking changes in populations and distributions of freshwater megafauna, such as the lack of monitoring data and taxonomic and spatial biases. The detected trends emphasize the critical plight of freshwater megafauna globally and highlight the broader need for concerted, targeted and timely conservation of freshwater biodiversity.     

Biogeography and the structure of coral reef fish communities on isolated islands

Aim To determine the applicability of biogeographical and ecological theory to marine species at two remote island locations. This study examines how biogeography, isolation and species geographic range size influence patterns of species richness, endemism, species composition and the abundance of coral reef fishes. Location Christmas Island and the Cocos (Keeling) Islands in the tropical eastern Indian Ocean. Methods Published species lists and underwater visual surveys were used to determine species richness, endemism, species composition and abundance of reef fishes at the islands. These data were statistically compared with patterns of species composition and abundance from the neighbouring ‘mainland’ Indonesian region. Results The two isolated reef fish communities were species‐poor and contained a distinct taxonomic composition with an overrepresentation of species with high dispersal potential. Despite low species richness, we found no evidence of density compensation, with population densities on the islands similar to those of species‐rich mainland assemblages. The mix of Indian and Pacific Ocean species and the proportional representations of the various regional faunas in the assemblages were not influenced by the relative proximity of the islands to different biogeographical provinces. Moreover, species at the edge of their range did not have a lower abundance than species at the centre of their range, and endemic species had substantially higher abundances than widespread species. At both locations, endemism was low (less than 1.2% of the community); this may be because the locations are not sufficiently isolated or old enough to promote the evolution of endemic species. Main conclusions The patterns observed generally conform to terrestrial biogeographical theory, suggesting that similar processes may be influencing species richness and community composition in reef fish communities at these remote islands. However, species abundances differed from typical terrestrial patterns, and this may be because of the life history of reef fishes and the processes maintaining isolated populations.     

Warming shelf seas drive the subtropicalization of European pelagic fish communities

Pelagic fishes are among the most ecologically and economically important fish species in European seas. In principle, these pelagic fishes have potential to demonstrate rapid abundance and distribution shifts in response to climatic variability due to their high adult motility, planktonic larval stages, and low dependence on benthic habitat for food or shelter during their life histories. Here, we provide evidence of substantial climate‐driven changes to the structure of pelagic fish communities in European shelf seas. We investigated the patterns of species‐level change using catch records from 57 870 fisheries‐independent survey trawls from across European continental shelf region between 1965 and 2012. We analysed changes in the distribution and rate of occurrence of the six most common species, and observed a strong subtropicalization of the North Sea and Baltic Sea assemblages. These areas have shifted away from cold‐water assemblages typically characterized by Atlantic herring and European sprat from the 1960s to 1980s, to warmer‐water assemblages including Atlantic mackerel, Atlantic horse mackerel, European pilchard and European anchovy from the 1990s onwards. We next investigated if warming sea temperatures have forced these changes using temporally comprehensive data from the North Sea region. Our models indicated the primary driver of change in these species has been sea surface temperatures in all cases. Together, these analyses highlight how individual species responses have combined to result in a dramatic subtropicalization of the pelagic fish assemblage of the European continental shelf.     

Phylogeography and population dynamics of the white-sided dolphin (Lagenorhynchus acutus) in the North Atlantic

Highly mobile species in the marine environment may be expected to show little differentiation at the population level, but this is often not the case. Instead cryptic population structure is common, and effective conservation will require an understanding of how these patterns evolve. Here we present an assessment from both sides of the North Atlantic of differentiation among populations of a dolphin species that inhabits mainly pelagic waters, the Atlantic white-sided dolphin. We compare eleven putative populations in the western and eastern North Atlantic at mtDNA and microsatellite DNA loci and find reduced nucleotide diversity and signals for historical bottlenecks and post-bottleneck expansions in all regions. We calculate expansion times to have occurred during the early Holocene, following the last glacial maximum (LGM). We find evidence for connectivity among populations from either side of the North Atlantic, and differentiation between putative populations in the far northeast compared with all other areas sampled. Some data suggest the possibility of separate refugia during the LGM explaining this pattern, although ongoing ecological processes may also be a factor. We discuss the implications for developing effective programs of conservation and management in the context of ongoing anthropogenic impact.     

Climate and ecosystem linkages explain widespread declines in North American Atlantic salmon populations

North American Atlantic salmon (Salmo salar) populations experienced substantial declines in the early 1990s, and many populations have persisted at low abundances in recent years. Abundance and productivity declined in a coherent manner across major regions of North America, and this coherence points toward a potential shift in marine survivorship, rather than local, river‐specific factors. The major declines in Atlantic salmon populations occurred against a backdrop of physical and biological shifts in Northwest Atlantic ecosystems. Analyses of changes in climate, physical, and lower trophic level biological factors provide substantial evidence that climate conditions directly and indirectly influence the abundance and productivity of North American Atlantic salmon populations. A major decline in salmon abundance after 1990 was preceded by a series of changes across multiple levels of the ecosystem, and a subsequent population change in 1997, primarily related to salmon productivity, followed an unusually low NAO event. Pairwise correlations further demonstrate that climate and physical conditions are associated with changes in plankton communities and prey availability, which are ultimately linked to Atlantic salmon populations. Results suggest that poor trophic conditions, likely due to climate‐driven environmental factors, and warmer ocean temperatures throughout their marine habitat area are constraining the productivity and recovery of North American Atlantic salmon populations.     

Habitat specialization in tropical continental shelf demersal fish assemblages

The implications of shallow water impacts such as fishing and climate change on fish assemblages are generally considered in isolation from the distribution and abundance of these fish assemblages in adjacent deeper waters. We investigate the abundance and length of demersal fish assemblages across a section of tropical continental shelf at Ningaloo Reef, Western Australia, to identify fish and fish habitat relationships across steep gradients in depth and in different benthic habitat types. The assemblage composition of demersal fish were assessed from baited remote underwater stereo-video samples (n = 304) collected from 16 depth and habitat combinations. Samples were collected across a depth range poorly represented in the literature from the fringing reef lagoon (1-10 m depth), down the fore reef slope to the reef base (10-30 m depth) then across the adjacent continental shelf (30-110 m depth). Multivariate analyses showed that there were distinctive fish assemblages and different sized fish were associated with each habitat/depth category. Species richness, MaxN and diversity declined with depth, while average length and trophic level increased. The assemblage structure, diversity, size and trophic structure of demersal fishes changes from shallow inshore habitats to deeper water habitats. More habitat specialists (unique species per habitat/depth category) were associated with the reef slope and reef base than other habitats, but offshore sponge-dominated habitats and inshore coral-dominated reef also supported unique species. This suggests that marine protected areas in shallow coral-dominated reef habitats may not adequately protect those species whose depth distribution extends beyond shallow habitats, or other significant elements of demersal fish biodiversity. The ontogenetic habitat partitioning which is characteristic of many species, suggests that to maintain entire species life histories it is necessary to protect corridors of connected habitats through which fish can migrate.