Using fatty acid analysis to elucidate the feeding habits of Southern Ocean mesopelagic fish

Fatty acid biomarkers were used to investigate the feeding ecology of 17 mesopelagic fish species occurring in the Southern Ocean. Fatty acid signatures of species where little or no dietary information exists were compared to fatty acid signatures of species of known diets in order to elucidate their trophic position. Principal component analysis grouped species of known diets into two clusters with amphipods and copepods comprising the main prey species, respectively. Although the majority of species of unknown diet were grouped with either of these feeding guilds, a third cluster comprising only Gymnoscopelus bolini was identified suggesting a significantly different diet for this species. Electrona antarctica also exhibited significant changes in fatty acid signatures with size. Furthermore, discriminant analysis of the four most abundant species classified species with a 90% success rate thus validating the usefulness of fatty acid signatures when trying to resolve the trophic position of species where no or little dietary information exists.     

The role of intraguild predation in the population dynamics of small pelagic fish

In this paper, we argue that understanding marine ecosystem functioning requires a thorough appreciation of the role of intraguild predation to system dynamics. The theoretical predictions of intraguild predation models might explain some of the community features observed in marine ecosystems such as low diversity in upwelling and productive systems and species alternation in response to moderate external forcing. Finally, we argue that an ecosystem approach to fisheries requires that the size–structure of fish populations should be taken into account and that it is extremely important to account for the predators of early stages (eggs and larvae) to gain a thorough understanding of the key interactions between species.     

Density dependence in marine fish populations revealed at small and large spatial scales

Experimental manipulation of population density has frequently been used to demonstrate demographic density dependence. However, such studies are usually small scale and typically provide evidence of spatial (within-generation) density dependence. It is often unclear whether small-scale, experimental tests of spatial density dependence will accurately describe temporal (between-generation) density dependence required for population regulation. Understanding the mechanisms generating density dependence may provide a link between spatial experiments and temporal regulation of populations. In this study, I manipulated the density of recently settled kelp rockfish (Sebastes atrovirens) in both the presence and absence of predators to test for density-dependent mortality and whether predation was the mechanism responsible. I also examined mortality of rockfish cohorts within kelp beds throughout central California to evaluate temporal (between-generation) density dependence in mortality. Experiments suggested that short-term behavioral responses of predators and/or a shortage of prey refuges caused spatial density dependence. Temporal density dependence in mortality was also detected at larger spatial scales for several species of rockfish. It is likely that short-term responses of predators generated both spatial and temporal density dependence in mortality. Spatial experiments that describe the causal mechanisms generating density dependence may therefore be valuable in describing temporal density dependence and population regulation.     

Using an individual-based model to quantify scale transition in demographic rate functions: Deaths in a coral reef fish

Scientifically informed population management requires quantitatively accurate demographic rate functions that apply at the spatial scale at which populations are actually managed, but practical constraints confine most field measurements of such functions to small study plots. This paper employs an individual-based population growth model to extrapolate the death rate function in a well-studied coral reef fish, the bridled goby Coryphopterus glaucofraenum, from the scale of coral reef “cells” at which it was measured to the larger scale of an entire coral reef. Density dependence in the whole-reef function actually proves stronger than in the local function because high goby density occasionally arises in local patches with few refuges from predators, producing very high mortality there. This IBM-based approach extends the reach of scale transition theory by examining considerably more realistic models than standard analytical methods can presently handle.     

A proposed standard method for composite sampling of water chemistry and plankton in small lakes

In this paper a method for collection of vertically and horizontally integrated volume-weighted composite samples for analysis of water chemistry and plankton is presented. The method, which requires a proper knowledge of lake morphometry parameters, includes proposed standard procedures for determination of sampling interval thickness, maximum depth of sampling, selection of sampling stations, and distribution of discrete samples. An example of the outcome of the method in a lake with uncomplicated basin morphometry is given and the results are discussed against background of general lake basin morphometry data. The aim of the paper is to start a debate about optimization (statistical as well as ecological) of volume weighted composite sampling.     

Interannual fluctuations in acoustic biomass estimates and in landings of small pelagic fish populations in relation to hydrology in the Strait of Sicily

The main results of research work carried out since 1998 with regard to the application of hydro-acoustic technologies for the evaluation of biomass and distribution of small pelagic fish species off the southern coast of Sicily are presented, taking into account information from hydrology and from ecology of the fish populations targeted. The biomass estimates and the population-density charts presented concern the two main species, i.e. sardine Sardina pilchardus (Walbaum, 1792) and anchovy Engraulis encrasicolus (Linnaeus, 1758). Both the sardine and anchovy populations experienced large inter-annual fluctuations, with biomass estimates ranging from 6000 to over 36,000 tonnes (t) (sardine) and from about 7000 to 23,000 t (anchovy). Acoustic estimates are largely consistent with landings recorded in Sciacca (the main fishing port for small pelagic species in the study area) during the year following the evaluation surveys. In addition, trends in sardine and anchovy biomass estimates appears to be negatively correlated with the mean sea surface temperature calculated over the time intervals January-September (sardine) and June-November (anchovy) of the preceding year, which correspond to larval and juvenile growth periods of target species. Observed patterns would suggest the importance of enrichment processes relevant to the survival of early stages, so determining recruitment success and finally higher population sizes.     

Interannual fluctuations in acoustic biomass estimates and in landings of small pelagic fish populations in relation to hydrology in the Strait of Sicily

The main results of research work carried out since 1998 with regard to the application of hydro-acoustic technologies for the evaluation of biomass and distribution of small pelagic fish species off the southern coast of Sicily are presented, taking into account information from hydrology and from ecology of the fish populations targeted. The biomass estimates and the population‐density charts presented concern the two main species, i.e. sardine Sardina pilchardus (Walbaum, 1792) and anchovy Engraulis encrasicolus (Linnaeus, 1758). Both the sardine and anchovy populations experienced large inter-annual fluctuations, with biomass estimates ranging from 6000 to over 36,000 tonnes (t) (sardine) and from about 7000 to 23,000 t (anchovy). Acoustic estimates are largely consistent with landings recorded in Sciacca (the main fishing port for small pelagic species in the study area) during the year following the evaluation surveys. In addition, trends in sardine and anchovy biomass estimates appears to be negatively correlated with the mean sea surface temperature calculated over the time intervals January–September (sardine) and June–November (anchovy) of the preceding year, which correspond to larval and juvenile growth periods of target species. Observed patterns would suggest the importance of enrichment processes relevant to the survival of early stages, so determining recruitment success and finally higher population sizes.     

Rapid changes in growth,condition, size and age of small pelagic fish in the Mediterranean

Since 2007, the ecosystem of the Gulf of Lions has shifted to a different regime, characterised by a low anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) biomass and a remarkably high sprat (Sprattus sprattus) biomass. Surprisingly, the abundance and recruitment of anchovy and sardine remained high. To understand which processes (bottom-up or top-down control, etc.) could have caused this shift, we studied the changes in body condition, growth and size and age of anchovy, sardine and sprat over 1984–1985 and 1992–2012, using data from scientific surveys. The annual age structure of anchovy and sardine was estimated using Bayesian mixture models based on size frequency data with priors on the age–length relationship derived from independent otolith readings. The results indicated periods during which anchovy and sardine were in an average (1992–2004), good (2005–2007) or poor (2008–2012) overall state of condition. For sardine, the shift towards smaller fish observed during these past 4 years was explained by a combination of slower growth and the disappearance of older individuals (ages 2+). Despite the increase in biomass of sprat since 2008, indications were found that sprat was also smaller than in the past. As growth and condition decreased and overexploitation has not been documented or suspected for those three species in this area, we propose that the current decline in sardine and anchovy biomass could be due to qualitative and/or quantitative modifications in the planktonic production (i.e. a bottom-up control) or mass mortalities of adults due to an epidemic disease.     

Behaviour that influences dispersal and connectivity in the small,young larvae of a reef fish

Determining the scale of larval dispersal and population connectivity in demersal fishes is a major challenge in marine ecology. Historically, considerations of larval dispersal have ignored the possible contributions of larval behaviour, but we show here that even young, small larvae have swimming, orientation and vertical positioning capabilities that can strongly influence dispersal outcomes. Using young (11–15 days), relatively poorly developed (8–10 mm), larvae of the pomacentrid damselfish, Amblyglyphidodon curacao (identified using mitochondrial DNA), we studied behaviour relevant to dispersal in the laboratory and sea on windward and leeward sides of Lizard Island, Great Barrier Reef. Behaviour varied little with size over the narrow size range examined. Critical speed was 27.5 ± 1.0 cm s⁻¹ (30.9 BL s⁻¹), and in situ speed was 13.6 ± 0.6 cm s⁻¹. Fastest individuals were 44.6 and 25.0 cm s⁻¹, for critical and in situ speeds, respectively. In situ speed was about 50% of critical speed and equalled mean current speed. Unfed larvae swam 172 ± 29 h at 8–10 cm s⁻¹ (52.0 ± 8.6 km), and lost 25% wet weight over that time. Vertical distribution differed between locations: modal depth was 2.5–5.0 and 10.0–12.5 m at leeward and windward sites, respectively. Over 80% of 71 larvae observed in situ had directional swimming trajectories. Larvae avoided NW bearings, with an overall mean SE swimming direction, regardless of the direction to nearest settlement habitat. Larvae made smaller changes between sequential bearings of swimming direction when swimming SE than in other directions, making it more likely they would continue to swim SE. When swimming NW, 62% of turns were left (more than in other directions), which would quickly result in swimming direction changing away from NW. This demonstrates the larvae knew the direction in which they were swimming and provides insight into how they achieved SE swimming direction. Although the cues used for orientation are unclear, some possibilities seemingly can be eliminated. Thus, A. curacao larvae near Lizard Island, on average swam into the average current at a speed equivalent to it, could do this for many hours, and chose different depths in different locations. These behaviours will strongly influence dispersal, and are similar to behaviour of other settlement-stage pomacentrid larvae that are older and larger.     

Applying a values-based decision process to facilitate comanagement of threatened species in Aotearoa New Zealand

Ko koe ki tēnā, ko ahau ki tēnai kīwai o te kete (you at that, and I at this handle of the basket). This Māori (New Zealanders of indigenous descent) saying conveys the principle of cooperation—we achieve more through working together, rather than separately. Despite decades of calls to rectify cultural imbalance in conservation, threatened species management still relies overwhelmingly on ideas from Western science and on top-down implementation. Values-based approaches to decision making can be used to integrate indigenous peoples’ values into species conservation in a more meaningful way. We used such a values-based method, structured decision making, to develop comanagement of pekapeka (Mystacina tuberculata) (short-tailed bat) and tara iti (Sternula nereis davisae) (Fairy Tern) between Māori and Pākehā (New Zealanders of European descent). We implemented this framework in a series of workshops in which facilitated discussions were used to gather expert knowledge to predict outcomes and make management recommendations. For both species, stakeholders clearly stated their values as fundamental objectives from the start, which allowed alternative strategies to be devised that naturally addressed their diverse values, including mātauranga Māori (Māori knowledge and perspectives). On this shared basis, all partners willingly engaged in the process, and decisions were largely agreed to by all. Most expectations of conflicts between values of Western science and Māori culture were unfounded. Where required, positive compromises were made by jointly developing alternative strategies. The values-based process successfully taha wairua taha tangata (brought both worlds together to achieve the objective) through codeveloped recovery strategies. This approach challenges the traditional model of scientists first preparing management plans focused on biological objectives, then consulting indigenous groups for approval. We recommend values-based approaches, such as structured decision making, as powerful methods for development of comanagement conservation plans between different peoples.     

Predicting fish behaviour in response to abyssal food falls

Estimates of fish abundance based on arrival rates and numbers present at baited cameras allow multiple, replicate assessments where data are not available by other means. Unfortunately such estimates are strongly affected by the assumed behaviour of the fish species concerned. Three of the possible foraging strategies of deep-sea fish were modelled and the likely patterns of fish arrival calculated for the same fish density, swimming and current velocities and odour plume properties. Cross-current foraging resulted in the highest numbers of fish at bait, with arrival rates that fitted well to field data. The sit-and-wait strategy produced lower arrival rates with passive drifting animals arriving slowest. Each model produces a distinctive pattern of animal arrivals that may be diagnostic of each foraging strategy. The advantages, disadvantages and likely metabolic and sensory demands of each strategy are discussed. Published online: 17 September 2002     

Models of fish school size in relation to environmental productivity

A simple energy-balance model, relating energetic requirements of fish schools to food production, was used to predict shoal sizes. Lower limits to school size are unlikely to be set by food but rather by predation. Upper limits depend on both food and school behavior, being greater for schools that break up to feed than for schools that remain continuously cohesive. Faced with a decreasing food supply, a school could either break into smaller schools or change behavior, increasing the area available for foraging. The models suggest that environmental productivity needs to be considered when examining fishery statistics such as (catch per unit effort), where maximum catch may be limited by maximum school size.     

Growth inhibition in Japanese medaka (Oryzias latipes) fish exposed to tetrachloroethylene

A recent study in our laboratory has demonstrated that tetrachloroethylene (TCE) is acutely toxic to Japanese medaka (Oryzias latipes) larvae with a 96 hr-LC50 of 18 (17-19) mg/mL (Spencer et al., 2002). In the present study we hypothesize that TCE exposure induces a developmental effect in Japanese medaka. Growth and age specific sensitivity of Japanese medaka larvae were studied with four age groups (7, 14, 21 and 28 days old) to determine tetrachloroethylene effects on these parameters. The medaka larvae were exposed for 96 hours in a single concentration (10 mg/mL) of TCE. The toxic endpoints evaluated were larvae weight, length, water content and protein concentration. The study revealed that exposure of medaka larvae to this sub-acute concentration of TCE significantly reduced length and weight in the treated group. The difference in growth between control and treated groups was more obvious in age versus length, than in age versus weight. The dry weight-fresh weight ratio (dw/fw) was shown to be higher in the control group. Water content in TCE-treated medaka was higher than in the control group, and younger fry had more water content than older ones. A higher protein concentration was also observed in TCE-treated medaka compared to the control group. These results indicate that TCE has a profound effect on the growth and development of Japanese medaka larvae.     

再生水用于景观水体的氮磷水质标准确定

污水再生利用是解决水资源短缺问题的重要措施,其中再生水回用于景观水体是主要途径之一.而防止水华爆发则是再生水景观利用的首要任务,控制再生水中的氮磷是防止水华爆发的根本措施.目前已有的景观水体水质标准中,氮磷浓度限值要求不统一,缺乏科学依据.因此再生水处理过程中氮磷控制标准执行易出现矛盾,不利于保障再生水景观利用的水质安全.再生水景观利用的氮磷控制标准,应在藻类最大生长潜力研究的基础上,通过藻类生长的Logistic模型和Monod模型、景观水体氮磷浓度模型按拟合,并结合水体自净能力和水质保障措施等综合因素加以确定.以栅藻(Scenedesmus sp)为例,通过Logistic模型和Monod模型拟合景观水体水华控制氮磷浓度限值的确定方法.     

Ovarian changes in response to heavy metal exposure to the fish,Notopterus notopterus (Pallas)

The ovarian and hepatic protein, lipid and cholesterol content were estimated in the fish, N. notopterus after exposing it to heavy metals at sublethal concentrations. The protein, lipid and cholesterol content of ovary and liver got reduced and amongst the three exposures (mercuric chloride, cadmium chloride and their combination) it was significantly reduced in the order of (HgCl2>HgCl2>+CdCl2>CdCl2>control). The above results indicated that HgCl2 is highly toxic and its toxicity gets reduced in combination.     

Vertical distributions of euphausiids and fish in relation to light intensity in the Northeastern Atlantic

The relationship between the vertical distributions of euphausiids and fish and light intensity has been studied directly by using a photometer in conjunction with an acoustically controlled rectangular midwater trawl. Samples were taken at a position centered on 47°N; 17°W on 15 and 16 May 1978. Five species of euphausiid and six species of fish have been analysed, both groups contained migrant and non-migrant species. The population of each of these species occurred throughout a light regime spanning at least three orders of magnitude of intensity; none of them was restricted to, or followed, and isolume. There were no sexual or size differences in the distributions of the euphausiids, but the population of Argyropelecus hemigymnus was probably stratified during the day, with smaller individuals occurring shallower than large ones. The results are discussed in relation to previous observations and to the theories of photic regulation of distributions and migrations.