There is increasing evidence that fish gain energetic benefits when they swim
in a school. The most recent indications of such benefits are a lower tail (or
fin) beat at the back of a school and reduced oxygen consumption in schooling
fish versus solitary ones. How such advantages may arise is poorly understood.
Current hydrodynamic theories concern either fish swimming side by side or in a
diamond configuration and they largely ignore effects of viscosity and
interactions among wakes and individuals. In reality, however, hydrodynamic
effects are complex and fish swim in many configurations. Since these
hydrodynamic effects are difficult to study empirically, we investigate them in
a computer model by incorporating viscosity and interactions among wakes and
with individuals. We compare swimming efficiency of mullets of 12.6 cm
travelling solitarily and in schools of four different configurations at
several inter-individual distances. The resulting Reynolds number (based on
fish length) is approximately 1150. We show that these fish always swim more
efficiently in a school than alone (except in a dense phalanx). We indicate how
this efficiency may emerge from several kinds of interactions among wakes and
individuals. Since individuals in our simulations are not even intending to
exploit the wake, gains in efficiency are obtained more easily than previously
Since 2000, virtually every major assessment of ocean policy has called for implementing an ecosystem approach to managing marine resources, yet crafting such an approach has proved difficult. Ecosystems today exhibit little of the abundance and complexity found in the past, and populations of over-fished species have declined dramatically world-wide, yet historical evidence has been difficult to assimilate into complex ecosystem models. Here, we look to the testimony of Gulf of Maine fishermen for insights on the abundance of Atlantic cod (Gadus morhua) and the environment that once supported such large numbers of them. Using logbook data from Frenchman’s Bay, Maine, and other New England communities at the time of the Civil War, we estimate cod landings in the Gulf of Maine in 1861, establish a population structure for cod at that time, and map the geographical distribution of fishing effort of a fleet that minimized risk and cut expenses by fishing inshore where cod and bait species were plentiful. Log entries list the pelagic and bottom-dwelling invertebrate species these fishermen used for bait, when and how they acquired it, and what species they looked for in the water to signify the presence of cod. Ranked descriptions of both cod and bait abundance were found to be statistically significant indicators of cod catch. Frenchman’s Bay fishermen 140 years ago provided a minimum set of ecosystem requirements for abundant cod, conditions that may inform management plans aimed at restoring both the species and the Gulf of Maine marine ecosystem.
This paper aims to describe the state of crayfish farming technology in the USA, Australia and Europe, and to discuss some of the prerequisites for this industry. Data from Europe are partly based on replies from a questionnaire sent out to scientists in all European countries. For other parts of the world, the crayfish literature has been reviewed and data from the August 2000 meeting of the International Association of Astacology are also included. Issues addressed in this review are cultivated species, production and productivity figures, production technique with regard to enclosures, reproduction and feed items, disease problems, predators, pond vegetation and water quality.
Fewer than a dozen crayfish species are cultivated. The most attractive ones for culture and stocking in natural waters have been transferred to more than one continent. Pond rearing techniques predominate in all countries, and the technology required to achieve the spawning and rearing of juveniles is relatively simple. Pieces of fish, carrots and potatoes are frequent supplementary feed items; plants, cereals, pieces of meat, zooplankton and pellets are also common. Diseases are not usually a major concern, except in Europe where the American plague fungus , Aphanomyces astaci , has eradicated many European crayfish populations. Predators identified as common include insects and amphibians, as well as fishes, birds and mammals. Many water macrophytes are common in crayfish farms. These may either serve a useful function or cause problems for the crayfish farmer. Water temperature is the crucial factor for crayfish production. Water parameters such as pH and certain inorganic ion concentrations may also be of concern. Acidic waters that occur in some areas are generally detrimental to crayfish.
The total yield from crayfish production from farming and fishery is in the order of 120 000–150 000 tonnes, more than four times the quantity given by FAO statistics. The largest crayfish producer is the Peoples’ Republic of China, followed by the USA (70 000 and 50 000 tonnes in 1999, respectively). Of the quantity produced in the USA in 1999, about 35 000 tonnes was farmed. The yield in Europe was about 4500 tonnes in 1994, and of this quantity only 160 tonnes came from aquaculture. There are no official statistics for crayfish fishery production in Australia, but about 400 tonnes came from aquaculture in 1999.
Ghoti aims to serve as a forum for stimulating and pertinent ideas. Ghoti publishes succinct commentary and opinion that addresses important areas in fish and fisheries science. Ghoti contributions will be innovative and have a perspective that may lead to fresh and productive insight of concepts, issues and research agendas. All Ghoti contributions will be selected by the editors and peer reviewed.
Etymology of Ghoti
George Bernard Shaw (1856–1950), polymath, playwright, Nobel prize winner and the most prolific letter writer in history, was an advocate of English spelling reform. He was reportedly fond of pointing out its absurdities by proving that ‘fish’ could be spelt ‘ghoti’. That is: ‘gh’ as in ‘rough’, ‘o’ as in ‘women’ and ‘ti’ as in palatial.
Man has been domesticating plants and animals for 10 000 years. Domestication increased so that 2000 years ago, following the ‘Neolithic’ or ‘food‐producing’ revolution, the overwhelming majority of people were making a living by farming. Nowadays hunting, an uncertain way of collecting food, has shifted from a survival activity to a secondary (and most often recreational) activity. Within less than a century, marine fisheries, which constitute the last major world industry exploiting wild animal resources, have reached many ecological and economic limits and they face many uncertainties. In the context of generalised overexploitation, fishing could rapidly follow the same history as hunting and become a marginal activity for the collection of luxury items. This is not only a major concern for the future of an important food source, it also seriously questions our ability to preserve our last and unique relationship with renewable wild animal resources. If we do not want fisheries to be the counterpart of hunting, fisheries and fisheries research need to be ‘modernised’ in a way amenable to integrating new objectives, paradigms and ethical concerns. As scientists, we must direct our efforts toward reconciling long‐term environmental objectives and short‐term constraints by defining new indicators and reference points for management. Will we be able to initiate a ‘human and wild food reconciliation’ revolution?
Maintaining or restoring fish stocks at levels that are capable of producing maximum sustainable yield is a legal obligation under the United Nations Convention on the Law of the Sea (UNCLOS) and has been given the deadline of no later than 2015 in the Johannesburg Plan of Implementation of 2002. Here, we analyse stock assessment data of all major fish stocks of the Northeast Atlantic to determine whether Europe will be able to deliver on this commitment, which it has helped to bring about. The analysis shows that, if current fishing pressure continues, 91% of the European stocks will remain below target. If European ministers in charge of fisheries were serious about meeting their obligations, they would have to reduce drastically fishing pressure and halt fishing completely on some stocks. But even if fishing were halted in 2010, 22% of the stocks are so depleted that they cannot be rebuilt by 2015. If current trends continue, Europe will miss the 2015 deadline by more than 30 years. We argue that, from a legal perspective, such repeated enactment of fisheries management measures, which are incapable of maintaining or restoring Bmsy, does not comply with the requirements contained in UNCLOS and may constitute a breach of the precautionary principle of European Community law.
A long-term (1907–98) virtual population analysis (VPA) was made for Norwegian spring-spawning herring (NSSH), which is a huge pelagic fish stock in the north-east Atlantic. It shows that this herring stock has had large fluctuations during the last century; these fluctuations have mainly been determined by variations in the temperature of the inflowing water masses to the region. The spawning stock biomass (SSB) increased from a rather low level in the early years of this century and reached a high level of around 14 million tons by 1930. The spawning stock biomass then decreased to a level of around 10 million tons by 1940, but increased again to a record high level of 16 million tons by 1945. The stock then started to decrease and during the next 20-year period fell to a level of less than 50 000 tons by the late 1960s. Through the 1970s and 1980s, the stock slowly recovered and after the recruitment of strong year classes in 1983 and 1990–1992 the stock recovered to a spawning stock biomass of about 10 million tons. The long-term fluctuation in spawning stock biomass is caused by variations in the survival of recruits. It is found that the long-term changes in spawning stock abundance are highly correlated with the long-term variations in the mean annual temperature of the inflowing Atlantic water masses (through the Kola section) into the north-east Atlantic region. The recruitment is positively correlated with the average temperature in the Kola section in the winter months, January–April, which indicates that environmental factors govern the large-scale fluctuations in production for this herring stock.
The interaction between environmental forces and dispersal characteristics is largely responsible for the patterns of population structure in marine fish. Yet, crucial gaps in knowledge on life-histories and the relative contributions of numerous environmental factors still hinder a thorough understanding of marine population connectivity. One life-history trait so far overlooked by most fish population geneticists is sequential hermaphroditism, whereby individuals first mature as one sex and later in life reverse into the other sex. Population genetic theory predicts that sex-changing fish will present a higher potential for more spatially structured populations than gonochoristic species, as a result of their naturally skewed sex ratio, which is expected to reduce effective population size and hence increase genetic drift. We gathered published data on genetic population structure in marine fish, as summarized by the popular FST index, and – after controlling for several potentially confounding factors – we tested the hypothesis that sex-changing species are more genetically structured than gonochoristic ones. Although we found no evidence to support the theoretical expectations, our results suggest new working hypotheses that can stimulate new research avenues at the intersection between physiology, genetics and fisheries science.
The dramatic declines in abalone Haliotis spp. fishery production have been documented all over the world. Release of hatchery-reared juveniles into natural habitats has been considered as one measure to sustain and/or augment the current fishery production of abalone, as well as to restore collapsed abalone stocks. However, attempts at abalone release programmes have only been undertaken at experimental scales, except for Japan, where large-scale stock enhancement programmes for abalone have been undertaken since late 1960s. To evaluate the potential of stock enhancement for abalone, we analysed the release surveys of 13 case studies in Japan in terms of the overall recapture rate (number of recaptures through a lifetime/number of juveniles released), yield per release (YPR, yields from released individuals), the economic efficiency of releases (ratio of income from recaptured abalone to release cost) for each release year, and the contribution of hatchery releases to total catches for each fishing year. The average estimates for overall recapture rates (0.014–0.238) and YPR (3.1–60.3 g/individual) varied between locations and release years. The economic efficiency was estimated at 0.4–6.2. The released abalone contributed 6.9–83.5% to total catches. Hatchery releases could augment total production at some locations, but the success of release programmes would be limited by the carrying capacity at release areas, because density-dependent mortality occurred following releases in some cases. Throughout Japan, the annual catch of abalone has continuously declined from ∼6500 t in 1970 to ∼2000 t in the mid-1990s, despite the increase in the number of hatchery releases. Based on the estimates for YPR, the magnitude of the abalone releases on a national scale has not been sufficiently large to sustain the total production of Japanese abalone, which has primarily fluctuated according to the abundances of wild populations. Our results suggest that releases should be targeted at local populations in regions where stock enhancement is predicted to have the greatest chance of success, and the magnitude of releases should be considered carefully and determined for each region by taking the local carrying capacity into account. We also address the future prospects of abalone stock enhancement.
Mortality in longline fisheries is a critical global threat to most albatross and large petrel species. Here we identify key principles and approaches to identify and achieve broad use of effective seabird by-catch avoidance methods. Despite the availability of highly effective and cost-saving seabird avoidance methods, few longline fleets employ them. Given the political context and capacity of management authorities of the majority of longline fisheries, it is critical to identify seabird avoidance strategies that are not only highly effective, but are also economically viable and commercially practical. Adoption of an international performance standard for longline baited hook–sink rate, and prescribing minimum gear weighting designs that meet this standard that are achievable by all longline fisheries, would be an important step forward towards resolving low use of seabird avoidance methods by vessels, including those in illegal, unregulated and unreported fisheries. Due to differences between fleets, no single seabird avoidance measure is likely to be effective and practical in all longline fisheries. Therefore, testing of seabird avoidance methods in individual fleets is needed to determine efficacy and economic viability. Longline fishers should directly participate in these trials as they have a large repository of knowledge and skills to effectively develop and improve seabird by-catch avoidance techniques, and this provides industry with a sense of ownership for uptake of effective by-catch reduction methods. Establishing protected areas containing seabird colonies and adjacent waters within a nation's EEZ can be an expedient method to address seabird by-catch. However, establishing high seas marine protected areas to restrict longline fishing in seabird foraging areas, which would require extensive and dynamic boundaries and large buffer zones, may not be a viable short-term solution because of the extensive time anticipated to resolve legal complications with international treaties, to achieve international consensus and political will, and to acquire requisite extensive resources for surveillance and enforcement. Analysis of results of research on seabird avoidance methods reveals that the most reliable comparisons of the efficacy of alternative strategies are from comparing the effectiveness of methods tested in a single experiment. Benefits from standardizing the reporting of seabird by-catch rates to account for seabird abundance are described. To provide the most precise inputs for seabird population models, estimates of seabird mortality in longline fisheries should account for seabird falloff from hooks before hauling, delayed mortality of seabirds caught but freed from gear, and mortality caused by hooks discarded in offal.
Genetic and environmental factors may interact to control sex determination in fishes. A common pattern of initial female differentiation and subsequent male transformation before maturation in non-hermaphroditic fishes and after maturation in sequentially hermaphroditic fishes has suggested that changes in developmental timing may be responsible for the evolution of various expressions of sexual lability. Sequential hermaphroditism is rare in freshwater fishes, but investigators report degrees of sexual lability at four distinct life stages in cichlid fishes. Some cichlids undergo genetic sex determination and are not labile. Lability at the larval stage allows temperature or pH to determine sex. Social interactions apparently determine sex at the juvenile stage in the Midas cichlid (Amphilophus citrinellus). Most reports of post-maturational sex change in cichlids are anecdotal or unsubstantiated. The common occurrence of same-sex spawning suggests that many species are incapable of sex change. Sequential hermaphroditism is concluded not to be typical, except for the checkerboard cichlid (Crenicara punctulata), which regularly undergoes functional female-to-male transformation. Expression of sexual lability at four life stages in one family of fishes corroborates a role for developmental timing in the evolution of sequential hermaphroditism as well as environmentally controlled sex determination. The broad phylogenetic distribution of sexual lability in cichlids indicates that processes capable of producing sex change are generally present. The rarity of sequential hermaphroditism in cichlids and possibly other freshwater fishes is likely due to unpredictability of food and therefore potential mate distributions compared with coral reef habitats.
Originally developed to assess the relative abundance of ≥1+ fishes in large rivers, point abundance sampling by electrofishing (PASE) was adapted for 0+ fishes in the mid-1980s. Being both economical and widely applicable, PASE for 0+ fish has become a commonly used sampling approach in Europe, but its use for estimating 0+ fish density and species richness has attracted particular concern because of size and species selectivity. As such, this review is both timely and necessary. It summarizes the development of PASE and evaluates its various applications: studies of 0+ fish community composition, relative abundance and density, species richness (S), population size structure, larval and juvenile growth dynamics, microhabitat use, diel dynamics of species–species and species–microhabitat interactions, and the analysis of data emanating from PASE databases. The use and potential misuse of replicate sampling in estimates of S are examined, with PASE data from various European rivers re-analysed to assess geographical patterns in 0+ fish S. Comparisons of PASE and other approaches for estimating 0+ fish density and species richness have all demonstrated PASE to be cost-effective and relatively reliable, but sampling accuracy and precision do decrease as fishes enter the juvenile period of development.
Views expressed on the potential impact of ocean acidification range from wholesale degradation of marine ecosystems through to no discernable impact with minimal consequences. Constraining this range of predictions is necessary for the development of informed policy and management. The direct biological impacts of acidification occur at the molecular and cellular level; however, it is the expression of these effects at the population and ecosystem level that is of societal concern. Here, we consider the potential impact of ocean acidification on fisheries with particular emphasis on approaches to scaling from physiological responses to population- and ecosystem-level processes. In some instances, impacts of ocean acidification may lead to changes in the relative species composition at a given trophic level without affecting the overall productivity, whilst in other instances, ocean acidification may lead to a reduction in productivity at a given tropic level. Because of the scale at which ecological processes operate, modelling studies are required. Here, ocean acidification is situated within ongoing research into the ecological dynamics of perturbed systems, for which many models have already been developed. Whilst few existing models currently explicitly represent physiological processes sensitive to ocean acidification, some examples of how ocean acidification effects may be emulated within existing models are discussed. Answering the question of how acidification may impact fisheries requires the integration of knowledge across disciplines; this contribution aims to facilitate the inclusion of higher trophic level ecology into this ongoing debate and discussion.
Atmospheric carbon dioxide (CO2) emissions from human industrial activities are causing a progressive alteration of seawater chemistry, termed ocean acidification, which has decreased seawater pH and carbonate ion concentration markedly since the Industrial Revolution. Many marine organisms, like molluscs and corals, build hard shells and skeletons using carbonate ions, and they exhibit negative overall responses to ocean acidification. This adds to other chronic and acute environmental pressures and promotes shifts away from calcifier-rich communities. In this study, we examine the possible implications of ocean acidification on mollusc harvests worldwide by examining present production, consumption and export and by relating those data to present and future surface ocean chemistry forecast by a coupled climate-ocean model (Community Climate System 3.1; CCSM3). We identify the ‘transition decade’ when future ocean chemistry will distinctly differ from that of today (2010), and when mollusc harvest levels similar to those of the present cannot be guaranteed if present ocean chemistry is a significant determinant of today’s mollusc production. We assess nations’ vulnerability to ocean acidification-driven decreases in mollusc harvests by comparing nutritional and economic dependences on mollusc harvests, overall societal adaptability, and the amount of time until the transition decade. Projected transition decades for individual countries will occur 10–50 years after 2010. Countries with low adaptability, high nutritional or economic dependence on molluscs, rapidly approaching transition decades or rapidly growing populations will therefore be most vulnerable to ocean acidification-driven mollusc harvest decreases. These transition decades suggest how soon nations should implement strategies, such as increased aquaculture of resilient species, to help maintain current per capita mollusc harvests.
Fishing affects the seabed habitat worldwide on the continental shelf. These impacts are patchily distributed according to the spatial and temporal variation in fishing effort that results from fishers' behaviour. As a consequence, the frequency and intensity of fishing disturbance varies among different habitat types. Different fishing methodologies vary in the degree to which they affect the seabed. Structurally complex habitats (e.g. seagrass meadows, biogenic reefs) and those that are relatively undisturbed by natural perturbations (e.g. deep-water mud substrata) are more adversely affected by fishing than unconsolidated sediment habitats that occur in shallow coastal waters. These habitats also have the longest recovery trajectories in terms of the recolonization of the habitat by the associated fauna. Comparative studies of areas of the seabed that have experienced different levels of fishing activity demonstrate that chronic fishing disturbance leads to the removal of high-biomass species that are composed mostly of emergent seabed organisms. Contrary to the belief of fishers that fishing enhances seabed production and generates food for target fish species, productivity is actually lowered as fishing intensity increases and high-biomass species are removed from the benthic habitat. These organisms also increase the topographic complexity of the seabed which has been shown to provide shelter for juvenile fishes, reducing their vulnerability to predation. Conversely, scavengers and small-bodied organisms, such as polychaete worms, dominate heavily fished areas. Major changes in habitat can lead to changes in the composition of the resident fish fauna. Fishing has indirect effects on habitat through the removal of predators that control bio-engineering organisms such as algal-grazing urchins. Fishing gear resuspend the upper layers of sedimentary seabed habitats and hence remobilize contaminants and fine particulate matter into the water column. The ecological significance of these fishing effects has not yet been determined but could have implications for eutrophication and biogeochemical cycling. Simulation results suggest that the effects of low levels of trawling disturbance will be similar to those of natural bioturbators. In contrast, high levels of trawling disturbance cause sediment systems to become unstable due to large carbon fluxes between oxic and anoxic carbon compartments. In low energy habitats, intensive trawling disturbance may destabilize benthic system chemical fluxes, which has the potential to propagate more widely through the marine ecosystem. Management regimes that aim to incorporate both fisheries and habitat conservation objectives can be achieved through the appropriate use of a number of approaches, including total and partial exclusion of towed bottom fishing gears, and seasonal and rotational closure techniques. However, the inappropriate use of closed areas may displace fishing activities into habitats that are more vulnerable to disturbance than those currently trawled by fishers. In many cases, the behaviour of fishers constrains the extent of the impact of their fishing activities. Management actions that force them to redistribute their effort may be more damaging in the longer term.
Interactive governance theory proposes that fisheries can be compared according to their governability, or their overall capacity for governance. Central to governance capacity in fisheries is institutional adaptability, the ability of humans to modify their organizations and reflect on the rules and values that guide them in response to change. In this paper, I suggest a preliminary synthesis of interactive governance theory, resilience thinking and adaptive co-management in order to refine the understanding of institutional adaptation as a key component of fisheries governability. I use the case of patron–client relationships in the Junagadh fishery to show how governability analysis is a valuable perspective from which to understand institutional characteristics that have contradictory implications for adaptation in fisheries.
One of the most challenging problems in evolutionary biology is linking the evolution of the phenotype with the underlying genotype, because most phenotypes are encoded by many genes that interact with each other and with the environment. Further, many phenotypes are correlated and selection on one can affect evolution of the other. This challenge is especially important in fishes, because their evolutionary response to harvest, global warming and conservation actions are among the least understood aspects of their management. Here, we discuss two major genetic approaches to studying the evolution of complex traits, multivariate quantitative genetics and molecular genetics, and examine the increasing interaction between the two fields. These interactions include using pedigree-based methods to study the evolution of multivariate traits in natural populations, comparing neutral and quantitative measures of population structure, and examining the contribution that the two approaches have made to each other. We then explore the major role that quantitative genetics is playing in two key issues in the conservation and management of fish populations: the evolutionary effects of fishing and adaptation to climate change. Throughout, we emphasize that it is important to anticipate the availability of improvements in molecular technology and statistical analyses by creating research populations such as inbred lines and families segregating at fitness traits, developing approaches to measuring the full range of phenotypes related to fitness, and collecting biological material and ecological data in natural populations. These steps will facilitate studies of the evolution of complex traits over informative temporal and spatial scales.
There are a small number of fish species, both marine and freshwater, that exhibit a truly amphibious habit that includes periods of aerial exposure. The duration of emersion is reflected in the level of physical and physiological adaptation to an amphibious lifestyle. Fish that are only briefly out of water retain predominantly aquatic attributes whereas there are semi-terrestrial species that are highly adapted to prolonged periods in the aerial habitat. Desiccation is the main stressor for amphibious fish and it cannot be prevented by physiological means. Instead, amphibious fish resist excessive water loss by means of cutaneous modification and behavioural response. The more terrestrially adapted fish species can tolerate considerable water loss and may employ evaporation to aid thermoregulation. The amphibious habit is limited to fish species that can respire aerially. Aerial respiration is usually achieved through modification to existing aquatic pathways. Freshwater air-breathers may respire via the skin or gills but some also have specialized branchial diverticula. Marine species utilize a range of adaptations that may include modified gills, specialized buccopharyngeal epithelia, the intestine and the skin. Areas of enhanced respiratory activity are typified by increased vascularization that permits enhanced perfusion during aerial exposure. As with other adaptations the mode of nitrogenous elimination is related to the typical durations of emersion experienced by the fish. Intertidal species exposed on a regular cycle, and which may retain some contact with water, tend to remain ammoniotelic while reducing excretion rates in order to prevent excessive water loss. Amphibious fish that inhabit environments where emersion is less predictable than the intertidal, can store nitrogen during the state of emersion with some conversion to ureotelism or have been shown to tolerate high ammonia levels in the blood. Finally, the more amphibious fish are more adapted to moving on land and seeing in air. Structural modifications to the pectoral, pelvic, dorsal and anal fins, combined with a well-developed musculature permit effective support and movement on land. For vision in air, there is a general trend for fish to possess close-set, moveable, protruberant eyes set high on the head with various physical adaptations to the structure of the eye to allow for accurate vision in both air and water.
Mbuna, the dominant fishes on the rocky shores of Lake Malawi, have become a major ‘model system’ for the study of rapid speciation and adaptive radiation. At least 295 putative species are known, of which more than 200 remain undescribed. There is no good evidence for monophyly in the mbuna, rather mitochondrial DNA phylogenies indicate that they are polyphlyetic with respect to benthic feeding cichlids of the genera Aulonocara, Alticorpus and some species of Lethrinops. Male mbuna hold territories for 18 months or more and breed year-round. All species are maternal mouthbrooders, but females do not guard free-swimming young. Mbuna are polygamous (both sexes). There is sexual dimorphism in size, colour and fin length, and many species show within-population colour polymorphism. Mbuna genera are largely differentiated on the basis of head, jaw and tooth morphology, but congeneric species are generally distinguished by male colour. Many morphologically specialized forms have broad diets and often feed on common easily obtainable resources. While it is likely that dietary and habitat niche partitioning contributes to species coexistence, this has never clearly been demonstrated under experimental conditions. Populations on spatially separated habitat patches are often genetically differentiated, probably because most species are specialized for life on rocky shores, and lack a dispersal phase in their life histories. Males seem to disperse more than females, but are able to home several kilometres back to their territories. Some closely related ecologically equivalent allopatric populations are differentiated in male colour. Those tested have been shown to mate at least partially assortatively. Sexual selection acting on male colour seems the most plausible mechanism for initial species divergence. The same colour forms seem to have arisen several times, suggesting frequent parallel evolution. The main conservation threat to mbuna at present seems to be translocation of species within the lake as a result of the aquarium trade. However, deleterious effects on indigenous populations are not documented. In the long run, sedimentation, pollution, introduction of alien species and the development of targeted food fisheries could be more serious threats.
Anadromy and homing are two traits found widely amongst teleost fishes. They co-occur in salmonid fishes, and probably also in other fish families. Anadromy provides fish with the opportunity for more rapid growth, larger size, and higher fecundity through the exploitation of rich food resources and favourable growing temperatures in the sea, but may result in higher predation mortalities and has the tendency to disperse stocks very widely. Homing fosters adaptation of stocks to favourable local spawning conditions, but the dispersive effects of anadromy, in the absence of homing, may tend to break down such local adaptation. A low percentage of straying in species that home may have long-term evolutionary advantages. This paper explores the question of whether homing may be a preadaptation for successful evolution of anadromy, or whether the two attributes have coevolved.
Several diadromous New Zealand and Australian species of Galaxias are now known, or suspected, to deposit their eggs amongst riparian vegetation or substrates either supratidally in estuaries or in forested streams in locations that are only temporarily submerged by elevated water levels. The eggs develop in a humid atmosphere and hatch when the egg deposition sites are resubmerged; a significant role for agitation in stimulating hatching seeming likely. There are risks from the eggs becoming dehydrated, and also from a failure by water to resubmerge the eggs before they have exhausted their energy resources. Hatching is triggered by elevated flows, perhaps being an outcome of agitation of the eggs. Elevated flows may also increase the rate of downstream transport of the larvae, facilitating survival during dispersal to sea from spawning sites in streams that may be long distances inland. Hatching during flood events may favour survival of the larvae because turbid flows may provide ‘cover’ for the larvae as they emigrate to sea. Risks from egg predation by aquatic predators may be replaced by risks from terrestrial predators.
More than 120 surveys over 25 years suggest that appropriate use of the daily egg production method (DEPM) provides unbiased but rather imprecise estimates of spawning biomass (coefficient of variation generally above 30%). Knowledge of species reproductive biology and early life history and a survey design adapted to local population dynamics are required to optimize DEPM performance in terms of bias, precision and cost. Clupeoid applications dominate worldwide (mainly for anchovies and sardines) and estimates are often used to tune indirect assessment models or to calibrate other fisheries-independent methods. The method seems better adapted to the life history of anchovies than of sardines, leading to more precise estimates of anchovy spawning biomass and facilitating extensions of the method to estimate total biomass and numbers at age. The continuous underway fish egg sampler is often used as a secondary sampler in the ichthyoplankton survey of the DEPM to reduce the cost and improve the precision of egg production. Multinomial models were recently developed to analyse egg incubation data and used in a Bayesian procedure for egg ageing and delimitation of daily cohorts. These were incorporated in model-based estimators to get spatially explicit estimates of egg production, daily fecundity parameters and spawning biomass that can improve the precision of DEPM. Uncertainty in daily fecundity estimation of clupeoids is mainly because of spawning fraction estimation by the post-ovulatory follicle (POF) method. Exploration of recent histological and molecular techniques for POF characterization and laboratory experiments to test the effect of temperature on POF degradation can help to improve spawning fraction estimation. Available estimates of egg production and mortality, daily fecundity, spawning area and biomass from different populations, species and ecosystems are being used to improve the understanding of clupeoid spawning dynamics, their relation with ecosystem productivity and to build comprehensive population models. Finally, a counter-intuitive finding of this review is that, although the DEPM is almost exclusively applied to clupeoids, recent evidence indicates that it may be easier and cheaper to use in other teleost families, including demersal species.
Although genetic approaches to questions in fisheries management have been very useful in the past, they have encountered consistent hurdles despite the development of new marker systems. However, recent technological advances in molecular genetics will help to overcome many of these hurdles and are likely to revolutionize fish and fisheries biology. DNA-sequencing costs have been decreasing exponentially, and recent breakthroughs have led to rapid increase in throughput that allows sequencing the entire expressed genome of a non-model organism with standard project budgets. Increase in screening throughput and number of available markers, reduction in costs and improved insights into gene function and control of gene expression will allow applications that were impossible until recently. Here, we briefly recount the recent history of fisheries genetics, provide an outlook on near-term and long-term developments in genetic technology and consider their applications and implications for fisheries science and education.
Scientists hold different views about environmental management. These views may drive their interest in the subject and help them to address a wide range of research issues, but they can also affect the ways in which research results are interpreted and reported. Studies that mix science and perspective can compromise public and scientific understanding of fishing effects, as perceived differences in evidence may actually reflect differences in interpretation. To improve the rigour of ‘fishing effects’ science, it would help if the benchmarks used to assess whether fishing effects ‘matter’ were always made explicit. These benchmarks might be the objectives set by the management authorities and/or a series of alternate objectives proposed and stated by the scientist. To demonstrate how the reported significance of fishing effects can depend on objectives, I use a simple model to predict the response of fish populations and communities to fishing. Fishing effects that would be reported as negative in relation to preservation or biodiversity objectives, such as declines in size, abundance and trophic level, occur at lower fishing intensities than those associated with meeting sustainability objectives for target species. When fishing pressure is so high that both conservation and fisheries objectives are not being met, the initial management actions to meet a range of objectives are likely to be compatible (e.g. reduce capacity, support alternate livelihoods).