Data for 2937 fish, collected from seven locations over five years, were analysed to evaluate the effects of sea temperature and stock biomass on size-specific ovary weight and fecundity at spawning. Ovary weight did not vary significantly between years or locations. Size-specific fecundity was higher in 1983, when coastal waters were abnormally warm because of a strong El Niño – Southern Oscillation event. The effect of location was equivocal: one stock that overwintered in warm water tended to have a higher fecundity. Mean sea temperature between 60 and 90 d before spawning (in spring) best accounted for variations in size-specific fecundity. Temperature may influence fecundity by regulating gonadotropin concentration and consequently pre-ovulatory atresia. We hypothesize that the trade-off between fecundity and egg size is adaptive. A theoretical analysis of the early life history of Pacific herring suggests that, to maximize survival to metamorphosis, egg size should decrease and fecundity increase with temperature when the larval growth rate Q 10 is less than the mortality rate Q 10 . Our model seems to explain the differences in egg size between recruit and repeat spawners, and between stocks of Atlantic herring that spawn in different seasons.
ACCARNSI Research Associate, Dan Ware from Griffith University and Dr Zsuzsa Banhalmi-Zakar from James Cook University Townsville discuss the financing options of coastal protection in Australia using three existing case studies - the Tweed River Entrance Sand Bypass Project, the City of Gold Coast A-Line Seawall and the Toogoom Seawall, presenting the rationale, the basic project parameters and the different approaches to funding each project took. They compare funding features and outcomes achieved for each project as well as discussing the implications for coastal protection funding in the future.
A new concept of recruitment is derived from bioenergetic considerations of life history phenomena. The proposed mechanism has two components, a stock-dependent process where individual reproductive effort is a decreasing function of the abundance of the mature stock, and a density-dependent mortality process which operates during the prerecruit stage. A generalized equation describing these processes yields a family of recruitment curves which vary from being asymptotic to dome-shaped, depending on the parameter values. The theory suggests that species like Atlantic herring (Clupea harengus harengus) which tend to have small density-dependent growth coefficients and which allocate most of their surplus energy to reproduction should have a small terminal body size, a high length at maturity to L ∞ ratio, and a nearly asymptotic recruitment curve. By contrast, gadoids follow a different life history strategy and therefore should have a higher L ∞ and more convex recruitment function. These consequences are shown to be in accord with observed differences in L ∞ and with the graded series of recruitment curves found for a wide range of marine fish stocks. From a more general viewpoint, analysis of the energy dynamics of natural populations suggests that (1) there is a real — as opposed to inferred — limit to growth, L ∞ , which in many species is probably determined by their reproductive effort; (2) the increase in surplus energy with body size can be linked to the theory of optimal foraging; and (3) the intensity of density-dependent growth, which influences the shape of the recruitment curve, is an increasing function of the generation time of the prey organisms of different species. Thus gadoids tend to have dome-shaped reproduction curves because they feed on slow-maturing prey, which can be overcropped by large year-classes.Key words: stock and recruitment, bioenergetics, optimal foraging, growth, reproduction, life history strategies
Abstract Developing countries face risks from natural hazards that are being amplified by climate change. Selection of effective adaptation interventions to manage these risks requires a sufficiently accurate assessment of the coastal hazard at a given location. Yet challenges remain in terms of understanding local coastal risks given the coarseness of global wave models and the paucity of locally scaled data in most developing countries, including Small Island Developing States (SIDS) like Vanuatu. The aim of this paper was to examine the differences in hazard assessment and adaptation option selections arising from analyses using globally versus locally scaled data on coastal processes. As a case study, we focused on an eroding cliff face in Port Resolution on Tanna Island, Vanuatu, which is of concern to the local community and government authorities. The coastal process modelling revealed that the global wave data generated unrealistically high predictions of wave height within Port Resolution bay. Expensive engineering adaptations designed to provide coastal protection were therefore likely to fail in preventing ongoing cliff erosion. In this case, the best adaptation solution involves changing land use to revegetate and help stabilise the cliff top. Our case study highlights the importance of accurate hazard assessment, especially in data poor regions where extrapolation of global datasets and models in the absence of local data can result in poor adaptation decision making. Furthermore, the multidisciplinary approach applied here can be applied in other data-poor regions to strengthen analyses exploring the benefits of local adaptation interventions.
During the spring of 1986, a cohort of Pacific herring, Clupea harengus pallasi, larvae was sampled for 36 d in the Strait of Georgia to measure growth rates using RNA–DNA ratios for individual larvae. Concurrent with the field study, a population of herring larvae was starved from hatching in captivity for comparison with those caught in the field. The mean RNA–DNA ratio at hatching for the starved larvae was close to 2 but it quickly rose to 3.4 by age 4 d. The mean RNA–DNA ratio subsequently dropped back to 2 and below by age 8 d, presumably reflecting the exhaustion of the endogenous food supply of the yolk sac. The mean RNA–DNA ratio at the calculated point-of-no-return was 2.06 which was very similar to the zero protein growth rate or what we define as the "critical ratio." Herring larvae from the field generally showed an increase in the RNA–DNA ratio over the 36 d from approximately 2 to 7 although the first 18 d showed more variation than the latter. There was no evidence of mass starvation ("critical period") for the 1986 year class but there was a noticeable drop in the growth rate during the change to exogenous feeding. We suggest that starvation probably only directly affected the developing larvae during a window of about 11 d. Frequency distributions of the RNA–DNA ratios are shown for larvae over time.
Small island developing states are vulnerable to the impacts of climate change, including more intense and frequent extreme weather, warming temperatures, coastal erosion, inundation, and coral bleaching. Locally-specific natural resource threats, associated with population growth and tourism, exacerbate these systemic risks, which are particularly acute where community well-being is subsistence-based and directly reliant on ecosystem services. Garden productivity is falling as the cropping/fallow cycle intensifies and culturally and there is loss of observance of traditional resource taboos, eroding the effectiveness of customary management. Ecosystem based adaptations (EbA) provide a fruitful range of interventions and are beginning to attract development funding. We undertook a social benefit cost analysis for a suite of interconnecting EbAs for Tanna in Vanuatu. We found that funds targeted at increasing the productivity of the gardens returns significant social benefit. This also reduces pressure on natural resource threats and can potentially be adopted by all households on Tanna. In addition, increasing the community’s capacity to balance formal forest and reef conservation with customary management can provide small, but nevertheless important complimentary benefits. Our programme design included interlinking activities, including a series of demonstration garden plots, extension officers, community radio, a community ranger programme and a tree nursery.
A trophodynamics model is used to estimate annual plankton and fish production for the southern British Columbia continental shelf during 1985–89. The model describes the feeding interactions among diatoms, copepods, euphausiids, juvenile and adult Pacific herring (Clupea pallasi), Pacific hake (Merluccius productus), chinook salmon (Oncorhynchus tshawytscha), and spiny dogfish (Squalus acanthias) and is forced by empirical seasonal patterns in upwelling, sea surface temperature, and solar radiation. The most important simulation results are that (1) there is an imbalance between fish consumption and euphausiid production during the summer upwelling season, (2) the biomass and arrival timing of migratory hake significantly influence plankton and fish production, and (3) about 11% of the 332 g C∙m −2 ∙yr −1 annual diatom production is transferred to copepods and euphausiids and 1.0% of the diatom production to fish, while 27.5% of the 11.9 g C∙m −2 ∙yr −1 euphausiid production is consumed by herring and hake. The high plankton and fish production on the southern British Columbia shelf is comparable with other productive coastal upwelling regions.
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