Showing papers in "Reviews in Fish Biology and Fisheries in 1997"

Structuring dynamic models of exploited ecosystems from trophic mass-balance assessments

Abstract: The linear equations that describe trophic fluxes in mass-balance, equilibrium assessments of ecosystems (such as in the ECOPATH approach) can be re-expressed as differential equations defining trophic interactions as dynamic relationships varying with biomasses and harvest regimes. Time patterns of biomass predicted by these differential equations, and equilibrium system responses under different exploitation regimes, are found by setting the differential equations equal to zero and solving for biomasses at different levels of fishing mortality. Incorporation of our approach as the ECOSIM routine into the well-documented ECOPATH software will enable a wide range of potential users to conduct fisheries policy analyses that explicitly account for ecosystem trophic interactions, without requiring the users to engage in complex modelling or information gathering much beyond that required for ECOPATH. While the ECOSIM predictions can be expected to fail under fishing regimes very different from those leading to the ECOPATH input data, ECOSIM will at least indicate likely directions of biomass change in various trophic groups under incremental experimental policies aimed at improving overall ecosystem management. That is, ECOSIM can be a valuable tool for design of ecosystem-scale adaptive management experiments

Egg quality in fish: what makes a good egg?

Abstract: Factors affecting egg quality are determined by the intrinsic properties of the egg itself and the environment in which the egg is fertilized and subsequently incubated. Egg quality in fish is very variable. Some of the factors affecting egg quality in fish are known, but many (probably most) are unknown. Components that do affect egg quality include the endocrine status of the female during the growth of the oocyte in the ovary, the diet of the broodfish, the complement of nutrients deposited into the oocyte, and the physiochemical conditions of the water in which the eggs are subsequently incubated. In captive broodfish, the husbandry practices to which fish are subjected are probably a major contributory factor affecting egg quality. Our knowledge of the genetic influences on egg quality is very limited indeed. We know that parental genes strongly influence both fecundity and egg quality, but almost nothing is known about gene expression and/or mRNA translation in fish oocytes/embryos. This is surprising because the products synthesized in ovoand the mechanisms controlling their expression are likely to play a central role in determining egg quality. The genetic mechanisms underpinning oocyte and embryo growth and development are a priority for research

Fisheries stock assessment and decision analysis: the Bayesian approach

Abstract: The Bayesian approach to stock assessment determines the probabilities of alternative hypotheses using information for the stock in question and from inferences for other stocks/species. These probabilities are essential if the consequences of alternative management actions are to be evaluated through a decision analysis. Using the Bayesian approach to stock assessment and decision analysis it becomes possible to admit the full range of uncertainty and use the collective historical experience of fisheries science when estimating the consequences of proposed management actions. Recent advances in computing algorithms and power have allowed methods based on the Bayesian approach to be used even for fairly complex stock assessment models and to be within the reach of most stock assessment scientists. However, to avoid coming to ill-founded conclusions, care must be taken when selecting prior distributions. In particular, selection of priors designed to be noninformative with respect to quantities of interest to management is problematic. The arguments of the paper are illustrated using New Zealand's western stock of hoki, Macruronus novaezelandiae (Merlucciidae) and the Bering--Chukchi--Beaufort Seas stock of bowhead whales as examples

Microsatellite DNA in fishes

Abstract: For the last 30 years, attempts have been made to discriminate among fish populations by using molecular markers. Although some techniques have proved successful in certain circumstances, the consistent trend to newer markers among fishery geneticists highlights the general lack of resolving power observed with older technologies. The last decade has seen the increasing use of satellite DNA in investigations of genetic variability and divergence. Applications to fish and fisheries-related issues initially concentrated on minisatellite single-locus probes. Although minisatellites have successfully addressed a number of fishery-related questions, this class of satellite DNA has not been widely adopted by fishery geneticists. Most of the current research effort is concentrated on another class of satellite DNA called microsatellites. The large interest in microsatellite loci is largely due to the very high levels of variability that have been observed and the ability to investigate this variation using PCR technology. The isolation and application of microsatellites to research fields as diverse as population genetics, parentage analyses and genome mapping are reviewed. Despite the undisputed advantages that the marker possesses, there are a number of potential problems associated with investigating variation at microsatellite loci. Statistical considerations (e.g. appropriate sample sizes, number of loci and the mutation model assumptions on which the estimate is based) have not been considered in detail yet and the problems are often exacerbated in fish species, as some species show very large numbers of alleles at microsatellite loci. These issues and others, e.g. null alleles, are reviewed and possible solutions are proposed

Metapopulations and the Atlantic herring

Abstract: Two opposing concepts of Atlantic herring, Clupea harengus L., population structure are critically reviewed with the objective of unifying these divergent views under the metapopulation concept. It is concluded that neither the discrete population concept nor the dynamic balance concept adequately explains all the data associated with herring population structure and dynamics, including meristic and morphometric measurements, life- history traits, homing, year-class twinning, and biochemical analyses. However, the available information does suggest that Atlantic herring population structure and dynamics are well described within the metapopulation concept. The example of sympatric seasonal-spawning populations is used to illustrate the strategy, opportunity and mechanism by which local population integrity and persistence are maintained within the adopted- migrant hypothesis. Local population integrity is maintained through behavioural isolation, i.e. repeat rather than natal homing to spawning areas, while local population persistence is ensured through the social transmission of migration patterns and spawning areas from adults to recruiting individuals

The pineal organ of teleost fishes

Abstract: The pineal organ of teleost fish is a directly photosensory organ that contains photoreceptor cells similar to those of the retina. It conveys photoperiod information to the brain via neural pathways and by release of indoleamines, primarily melatonin, into the circulation. The photoreceptor cells respond to changes in ambient illumination with a gradual modulation of neurotransmission to second-order neurons that innervate various brain centres, and by modulation of indoleamine synthesis. Melatonin is produced rhythmically, and melatonin synthesis may be regulated either directly by ambient photoperiod, or by an endogenous circadian oscillator that is entrained by the photoperiod. During natural conditions, melatonin is produced at highest levels during the night. Although the pineal organ undoubtedly influences a variety of physiological parameters, as assessed by experimental removal of the pineal organ and/or administration of exogenous indoleamines, its role in any physiological situation is not clear cut. The effects of any interference with pineal functions appear to vary with the time of year and experimental photothermal regimes. There are strong indications that the pineal organ is one component in a central neural system that constitutes the photoperiod-responding system of the animal, i.e. the system that is responsible for correct timing of daily and seasonal physiological rhythms. It is important to envisage the pineal organ as a part of this system; it interacts with other photosensory structures (the retina, possibly extraretinal non-pineal photoreceptors) and circadian rhythm generators

Neuroendocrine regulation of ovulation in fishes: basic and applied aspects

Abstract: This review summarizes the major neuroendocrine mechanisms regulating ovulation, thus providing a basis for understanding the various environmental and hormonal techniques for induction of ovulation of cultured teleosts. The secretion of gonadotrophin-ii(GtH-ii) is stimulated by gonadotrophin-releasing hormone (GnRH), and, although some teleosts have three different forms of GnRH regionally distributed in the brain, in most species investigated, only one form is present in the pituitary and apparently involved in GtH-ii secretion. In nearly all species investigated, dopamine (DA) inhibits GtH-ii secretion by direct actions on gonadotrophs, as well as by inhibition of GnRH release. Sex steroids act at both brain and pituitary levels to regulate GtH-ii secretion through a combination of positive and negative feedback actions; one important positive feedback action is that sex steroids enhance the responsiveness of the pituitary to GnRH and an important negative feedback action is to increase DA turnover, thereby increasing the overall DA inhibitory tone on GtH-ii secretion. The preovulatory surge of release of GtH-ii is stimulated by a surge release of GnRH. A decrease in DA turnover also occurs to disinhibit GnRH and GtH-ii release. Environmental factors including photoperiod, temperature and spawning substrate may cue ovulation and spawning. Social and pheromonal interactions play a very important role in synchronizing preovulatory endocrine changes, ovulation and spawning behaviour in many species. A widely used technique for inducing ovulation of cultured fishes is injection of the combination of a GnRH superactive analogue, to stimulate GtH-ii release, and a DA receptor antagonist, to block the inhibitory actions of DA. This is termed the Linpe technique and has proven particularly useful with those species having synchronous or group synchronous follicular development and a large preovulatory surge of GtH-ii. In other groups of teleosts, particularly those species having asynchronous ovarian development and multiple spawnings over an extended period, treatment with a sustained-release preparation of a GnRH superactive analogue to cause a prolonged, somewhat enhanced release of GtH-ii has proven highly successful in inducing multiple ovulations and spawnings. However, the lack of specific radioimmunoassays for GtH-ii in many of these species has hindered progress, as the precise pattern of GtH-ii release necessary for the recruitment of vitellogenic oocytes into final maturation and ovulation in these multiple spawners remains an intriguing neuroendocrine question

The evolution of diadromy in fishes (revisited) and its place in phylogenetic analysis

Abstract: Diadromy is a term used to describe migrations of fishes between fresh waters and the sea; these migrations are regular, physiologically mediated movements which occur at predictable life history phases in each diadromous species, they involve most members of a species' populations, and they are usually obligatory. Around 250 fish species are regarded as diadromous. A review of the life history strategies amongst families of fishes that include diadromous species provides little support for a suggested scenario for their evolution that involves: (1) evolution of anadromy via amphidromy from fishes of marine origins, and (2) evolution of catadromy through amphidromy from fishes of freshwater origins, even though these scenarios seem intuitively reasonable. The various forms of diadromy appear to have had multiple independent origins amongst diverse fish groups. There is increasing confidence that behavioural characteristics of animals are heuristic in gener ating and interpreting phylogenies. However, examination of fishes shows wide variability of diadromous life histories within closely related families and genera, within species, and there is even ontogenetic variation in patterns of behaviour by individual fish. In addition, there is multiple loss of diadromy in many diadromous fish species in which the life history becomes restricted to fresh waters. This variation suggests that diadromy is a behavioural character of dubious worth in determining phylogenetic relationships. Moreover, it appears to have been an ancestral condition in some fish families, such as Anguillidae, Salmonidae, Galaxiidae, Osmeridae, and others, and perhaps in the whole salmonoid/osmeroid/galaxioid complex of families. This, too, makes diadromy of dubious worth in phylogenetic analysis

Underwater acoustics in marine fisheries and fisheries research

Abstract: Underwater acoustics enables the detection and precise location of fish and is therefore a prerequisite for effective fishing methods such as pelagic trawling and purse seining. The application of acoustic instruments to detect fish and monitor gear performance in modern commercial fisheries is outlined. The latest developments in obtaining information such as bottom roughness and determining such characteristics of fish detected as size and species are presented.

Effects of pollution on reproductive behaviour of fishes

Abstract: This review attempts to integrate pollution research with behavioural ecology by focusing on reproductive behaviour of fishes. A search of Aquatic Sciences and Fisheries Abstractsand other sources showed that only 0.1% of 19 199 studies of aquatic pollution and fishes during the past 20 years have made this link. Effects on parental care and courtship have been investigated using a variety of pollutants (e.g. acidification, herbicide, thermal effluent) in several fish families (e.g. Cichlidae, Poeciliidae, Gasterosteidae, Cyprinidae).

Relationships of the Chimaeriformes and the basal radiation of the Chondrichthyes

Abstract: The origin and early evolution of the cartilaginous fishes (Chondrichthyes) has been the subject of considerably more debate than of data. The two modern groups, Chimaeriformes and Elasmobranchii, differ so radically in morphology that in the past they have often been considered unrelated -- descended from some remote and unknown common ancestor. The current consensus promotes the Chimaeriformes and Elasmobranchii as sister taxa of the Class Chondrichthyes which are linked by an assemblage of Palaeozoic fossil taxa, but no taxonomic or phylogenetic scheme has been accepted for the Class. Of the two groups, the Chimaeriformes is the less understood. The few species of Chimaeriformes existing today are enigmatic, principally deeper-water fish that are not readily accessible for study. In the past the fossil record of both groups has been relatively scanty, primarily due to the poor potential for skeletal fossilization, and so has provided little useful input into fundamental discussions of vertebrate diversification. However, these situations are changing. Chimaerids are increasingly becoming the subject of renewed biological and limited fisheries interests. Regarding extinct chondrichthyans, the last 30 or so years have entailed discoveries of new fossils that illuminate our view of Palaeozoic life and are eliciting dramatic changes in our understanding of these early fishes, their relations, and the origins of jawed conditions. Morphological examination of fossil chondrichthyans indicates that the plesiomorphous state of the gnathostome suspensorium is autodiastylic and that complex labial cartilages are primitive and likely to have been critical to the mechanical architecture of the first jaws. Analysis of cranial morphology, cranial proportions, the phyletic and developmental history of calcified tissues, and postcranial data including the evolution of the prepelvic tenaculum are now feasible. Cumulatively, when the results of these analyses are subject to cladistical evaluation, the result is one predominant cladogram supporting two monophyletic subclasses: the Elasmobranchii and the Euchondrocephali. The latter subclass contains a monophyletic group of holocephalans including the Cochliodontomorpha, and within this taxon, the restricted Chimaeriformes. Alternative cladograms of the non-holocephalan Euchondrocephali are dependent upon whether whole-body or cranial characters alone are employed in the analysis, or the additive or non-additive treatment of characters. Otherwise, only the discovery and description of additional members of this diverse assemblage are expected to alter these patterns of associations

Points of view: The trouble with fisheries science!

Abstract: Marine ®sheries management has passed through turbulent times in the past decade (Royce, 1996). Management has been unable to sustain ®sheries and curb population declines in commercial species in many jurisdictions (Hannesson, 1996). Although management dif®culties often stem from unrealistic visions of `managing' marine resources in dynamic ocean systems, with biological goals compromised by political, economic and social considerations, the failure of ®sheries science and scienti®c institutions to provide adequate stock information upon which to base management must be acknowledged (Finlayson, 1994; Walters and Maguire, 1996). Several recent publications examined ®sheries science problems (Parsons and Seki, 1995; Parsons, 1996; Ulltang, 1996; Walters and Maguire, 1996). In general, these authors suggest that in past decades, ®sheries science has lost touch with the realities of ®sheries, management and ocean ecosystem dynamics. Much of this can be attributed to an obsession with quantitative methods, which relegated these realities, and ecological science, to the back burner, and spawned unwarranted faith in population and bioeconomic model outputs (Symes, 1996). As a corollary, where statistical primness outranked experienced observation, so-called anecdotal views of ®shermen (and scientists) were discounted (e.g. small boat northern cod ®shermen: Rose, 1992). However, the above articles do not consider why ®sheries science took this path (except Finlayson, 1994, who ascribes problems to sociological pressures within science). In my view, the problems are simpler. They arise because too many ®sheries scientists have become `keyboard ecologists', who seldom if ever go to sea or work directly with real ®sheries. It is not simply that of®ce-bound scientists do not contribute to new knowledge of the ®sheries. Data are sometimes bountiful. However, wisdom to interpret those data, comprising ` Knowledge and good judgement based on experience'' (Avis et al., 1972), is often scarce. Wisdom is a hard-won property, and one unlikely to be garnered at the keyboard. The argument that statistics replaces wisdom is counterfeit in the face of an inexact science with poor data. Fisheries science has fallen to the Doon (1996) condition, whereby ` a scientist who lacks familiarity with nature will have dif®culty interpreting any kind of results realistically''. In our haste to free ourselves from descriptive naturalism we have embraced clever but naive abstractions of reality, and ultimately, ignorance. Reviews in Fish Biology and Fisheries 7, 365±370 (1997)

Putting fisheries management back in places

Abstract: Except, miraculously, for Jules Verne’s, scientific predictions always turn out to be wrong. However, the 3rd Millennium is coming, fisheries resources are going, and it is impossible to resist the urge to take the plunge and make a few predictions about the future of fisheries management, and of the scientific discipline. And no, the ‘s’ at the end of the title is not out of place: I shall suggest that in the future, fisheries management and its associated science will have to deal with ‘places’ far more than they have in the recent past. Indeed, I shall suggest that they will have to return, in many cases, to ancient modes of allocating fisheries resources to local communities, rooted in physical places. The trend now is going somewhere else, toward privatization of fisheries resources through Individual Transferable Quotas (ITQs) and similar instruments (Pauly, 1996), and there are also attempts to privatize the research scientists and the detailed assessment work that these instruments require (see e.g. Annala, 1996, and other contributions in Munro and Pitcher, 1996). However, this trend will crest when it is realized that, while eminently compatible with the acquisitive mood of our times, selfinterested exploitation schemes do not resolve, any more than the open-access schemes they might replace, the basic discrepancy between human and natural time scales. Many fisheries resource species, e.g. demersal fish in temperate waters and large predators on coral reefs, are long-lived, with natural mortalities of 0.1–0.2 yeary1, and often less (Pauly, 1980). This implies that, for exploitation to be sustainable, fishing must not extract more than about 10% of the stock biomass per year, especially in datasparse situations (Walters and Pearse, 1996). Even such low level of fishing mortality is sufficient, however, to quickly remove accumulations of large, old females – the source of most of the eggs and subsequent recruitment to stocks of long-lived fishes. This is so because the relationship between fish size and egg production is highly non-linear, with large females being far more fecund than an equivalent weight of small ones. Indeed, this non-linearity is so pronounced that for example one single ripe female red snapper, Lutjanus campecheanus, of 61 cm and 12.5 kg, contains the same number of eggs (9 300 000) as 212 females of 42 cm and 1.1 kg each (Bohnsack, 1990). The massive reduction of egg production, relative to unexploited stocks, coincident with the removal of such females, that occurs even when a very low fishing mortality is applied, is one of the reasons why exploited stocks fluctuate as much as they do, Reviews in Fish Biology and Fisheries 7, 125–127 (1997)

Points of view: Introduction of spawning potential: improvement in the threshold management theory

Abstract: To avoid overfishing, we must maintain sufficient productivity of the fish population. Threshold or limit reference point management is widely used for this purpose. In many cases, a minimum biomass level is used in conjunction with other management measures that control exploitation above the threshold (Myers et al., 1994). In this study, I explore a possible threshold other than biomass, which to the best of my knowledge has never been examined.