Fish stock assessments in Lake Konnevesi

In 1977, the average fish yield in the oligotrophic and oligohumic lake Konnevesi was 6.4 kg ha^–1 (2.6 kg vendace, 1.3 kg perch, 0.7 kg whitefish, 0.5 kg roach, 0.3 kg pike and 0.3 kg burbot). In that year the stock of vendace was exceptionally poor. A study was made to determine the optimum strategy for exploiting the stocks. The field work included test fishing (1970–78), sampling of catches (1977–80) and collection of catch per unit effort data (1978–80), and catch statistics (1969, 1970, 1977). The stocks were assessed by the Beverton and Holt method. Whitefish is exploited at a proper level. Fishing of vendace and roach can be increased, and the yield of pike would be greater, if the recruiting age were higher than at present.     

Fluctuations in food supply drive recruitment variation in a marine fish

Reproductive rates and survival of young in animal populations figure centrally in generating management and conservation strategies. Model systems suggest that food supply can drive these often highly variable properties, yet for many wild species, quantifying such effects and assessing their implications have been challenging. We used spatially explicit time series of a well-studied marine reef fish (black surfperch Embiotoca jacksoni) and its known prey resources to evaluate the extent to which fluctuations in food supply influenced production of young by adults and survival of young to subadulthood. Our analyses reveal: (i) variable food available to both adults and to their offspring directly produced an order of magnitude variation in the number of young-of-year (YOY) produced per adult and (ii) food available to YOY produced a similar magnitude of variation in their subsequent survival. We also show that such large natural variation in vital rates can significantly alter decision thresholds (biological reference points) important for precautionary management. These findings reveal how knowledge of food resources can improve understanding of population dynamics and reduce risk of overharvest by more accurately identifying periods of low recruitment.     

Standing on the Shoulders of Giants: Learning from Experience in Fisheries

Progress in any field depends primarily on our ability to synthesize previous experience – to stand on the shoulders of the giants who have worked before us. In fisheries management we have learned a great deal from past experience, but we have also failed to do so. Most stock assessments use no quantitative information derived from previous experience on other fish stocks, and often fix parameter values at some best estimates rather than admit uncertainty in their value. Meta-analysis provides a method to admit the uncertainty in most model parameters while using experience from other populations to provide an estimate of the distribution of the parameter. We demonstrate the application of meta-analysis for the intensity of depensation in spawner–recruit relationships in two species of Pacific salmon, and we discuss the potential of, and limitations to, meta-analysis in fisheries stock assessment.     

Self-sustaining populations, population sinks or aggregates of strays: chum (Oncorhynchus keta) and Chinook salmon (Oncorhynchus tshawytscha) in the Wood River system, Alaska

Small populations can provide insights into ecological and evolutionary aspects of species distributions over space and time. In the Wood River system in Alaska, USA, small aggregates of Chinook (Oncorhynchus tshawytscha) and chum salmon (O. keta) spawn in an area dominated by sockeye salmon (O. nerka). Our objective was to determine whether these Chinook and chum salmon are reproductively isolated, self-sustaining populations, population sinks that produce returning adults but receive immigration, or strays from other systems that do not produce returning adults. DNA samples collected from adult chum salmon from 16 streams and Chinook salmon from four streams in the Wood River system over 3 years were compared to samples from large populations in the nearby Nushagak River system, a likely source of strays. For both species, microsatellite markers indicated no significant genetic differentiation between the two systems. Simulations of microsatellite data in a large source and a smaller sink population suggested that considerable immigration would be required to counteract the diverging effects of genetic drift and produce genetic distances as small as those observed, considering the small census sizes of the two species in the Wood River system. Thus, the Wood River system likely receives substantial immigration from neighbouring watersheds, such as the Nushagak River system, which supports highly productive runs. Although no data on population productivity in the Wood River system exist, our results suggest source-sink dynamics for the two species, a finding relevant to other systems where salmonid population sizes are limited by habitat factors.     

Habitat and Fish Fauna Structure in a Subtropical Mountain Stream in Taiwan before and after a Catastrophic Typhoon

Habitats and fish populations of a subtropical mountain stream in Taiwan were surveyed before and after the hit of super-typhoon Herb in July 1996. There was a significant decrease in total pool area and an increase in total riffle area. Upper stream habitat was more susceptible to the disturbance. Relative abundance of the species was significantly correlated before and after the typhoon (rs=0.89, p<0.001). Morisita's index of similarity for the fish communities in June 1996 and October 1997 ranged between 0.82 and 1.02 for seven out of nine stations. Most common cyprinids decreased in densities after Herb, but recovered seventeen months after the typhoon. There were only minor changes in fish community fourteen months after the typhoon. Cyprinids that are smaller in size, such as Candidia barbata and Abottina brevirostris alticorpus were affected the most. Gobiid Rhinogobius nantaiensis that is well adapted to riffle habitat was unaffected throughout the surveys. The results of this study suggested that in subtropical mountain stream, severe typhoon may significantly alter the habitats, but the impact on fish populations could be relatively small due to features of these mountain species.     

The non-indigenous freshwater fishes of Flanders (Belgium): review, status and trends over the last decade

Fourteen non-indigenous fish species have been successfully introduced to the wild within the territory of Flanders; nine are considered naturalized. Most of the introductions occurred prior to 1950, with six species introduced since then. This paper reviews the available, hitherto scattered, information (including 'grey literature') on these 14 non-indigenous fish species introductions, and evaluates a decade of data from fisheries surveys to assess the recent development of these non-indigenous populations. Gibel carp Carassius gibelio and topmouth gudgeon Pseudorasbora parva are the most widespread of the non-indigenous species in Flemish waters, and both continue to expand their ranges. A reduction in range has been observed in brown bullhead Ameiurus nebulosus only. A case is presented for not including European catfish Silurus glanis , sunbleak Leucaspius delineatus and European bullhead Cottus gobio on the list of non-indigenous freshwater fishes in Flanders. Also discussed are non-indigenous fish species that are likely to colonize Flanders inland waters in the near future.     

Acoustic assessment of the number of pelagic fish in Lake Kinneret,Israel

The pelagic fish stock (mostly lavnun, Mirogrex terraesanctae) of Lake Kinneret was assessed using HADAS, a newly developed echo-counting analysis system. Total fish numbers (during Mar–Apr) were estimated to be 61 million in 1987, 218 million in 1988, 120 million in 1989, and 69 million in April 1990. The total fish number for March 1981 was recalculated from published data and estimated at 170 million. The decline in total numbers between 1988 and 1990 resulted primarily from a decrease in the relative abundance of the smallest size classes of fish. Since fish abundance apparently declined between 1981 and 1990, the decline in zooplankton standing stocks documented during these years cannot be attributed to higher fish predation caused by larger fish stocks. The HADAS estimates of lavnun population size are large enough to account for the known catch of lavnun.Contribution from Israel Oceanographic & Limnological Research, Ltd. This research was supported in part by the Israeli Water Commissioner, the Israeli Electric Company, and by a grant from the U.S. Agency for International Development.     

Invasion of an intermediate predator: Fish population dynamics in a mathematical model of a trophic chain (As applied to Syamozero lake)

A mathematical model is presented for the dynamics of a spatially heterogeneous predator-prey population system; a prototype is the Syamozero lake fish community. We show that the invasion of an intermediate predator can evoke chaotic oscillations in the population densities. We also show that different dynamic regimes (stationary, nonchaotic oscillatory, and chaotic) can coexist. The “choice” of a particular regime depends on the initial invader density. Analysis of the model solutions shows that invasion of an alien species is successful only in the absence of competition between the juvenile invaders and the native species.     

The Humphead Wrasse,Cheilinus Undulatus: Synopsis of a Threatened and Poorly Known Giant Coral Reef Fish

The humphead wrasse, Cheilinus undulatus, is the largest living member of the family Labridae, with a maximum size exceeding 2 m and 190 kg. Its geographic range covers much of the Indo-Pacific. The species is not common, recorded maximum adult densities rarely exceeding 20 fish/10,000 m². Small individuals are typically associated with high coral cover; larger fish are found mainly on outer or deep reefs, steep slopes and passes, singly or in small groups and seagrasses. However, for reproduction the species forms small spawning aggregations of tens to more than one hundred fish. The diet of the humphead wrasse includes large invertebrates and small fishes. The species attains at least 30 years and reaches sexual maturation at about 35–50 cm total length and <5 years of age. Most small adults are female while mainly males exceed 1 m and there is evidence of female to male sex change. The humphead wrasse is of considerable cultural value in some Pacific countries and is among the most prized in the live reef food fish export trade, for which it is often taken in its juvenile size range, either directly for sale or, increasingly, for grow-out to market size. It is also marketed chilled. The species is particularly sensitive to fishing pressure. In most fished areas, density and body size have dropped substantially. It appears to be particularly heavily targeted and depleted in SE Asia and in some places faces extirpation. The humphead wrasse is often taken by night spearfishing and by cyanide, with protection typically weak or non-existent, despite regulations and by a vulnerable assessment on the 1996 IUCN Red List. The humphead wrasse has not been reared successfully in hatcheries. Other giant reef fish share many similar problems and detailed study of the humphead wrasse contributes to a better understanding and conservation of all such species. This review examines and evaluates published and gray literature, original unpublished research and correspondence with almost 50 knowledgeable workers. It examines the value of such sources for quickly, but adequately, assessing the conservation and management status and key data gaps in species that are little known, vulnerable, difficult and expensive to study and may require urgent management or conservation action.     

New Zealand triplefin fishes (family Tripterygiidae): contrasting population structure and mtDNA diversity within a marine species flock

Triplefin fishes (Family Tripterygiidae) dominate the New Zealand temperate coastal fish fauna in diversity (26 endemic species, 14 genera). Most species appear to have evolved as a local radiation and mostly occupy sympatric distributions throughout New Zealand. To investigate the forces driving current gene‐flow patterns and past evolutionary histories, we searched for common patterns of population genetic subdivision within eight species sampled throughout their distributions [mitchochondrial DNA (mtDNA) control region, n = 1086]. We hypothesised that common phylogeographical and population differentiation patterns would reveal past or ongoing physical processes, with differences reflecting stochastic or species‐specific processes. Striking differences between species were apparent, with strong phylogeographical structure detected in Grahamina capito and the estuarine species G. nigripenne. G. capito fell into three distinct geographically restricted lineages. G. nigripenne largely separated into northern and southern lineages (Φ_ST 0.834). Strong population structuring and isolation by distance was evident in Bellapiscis medius, B. lesleyae and Forsterygion lapillum (Φ_ST 0.686, 0.436 and 0.115, respectively). High gene flow was apparent in G. gymnota and Ruanoho whero, and F. varium. However, for the latter species, isolation was apparent with samples collected from the offshore Three Kings Islands. Overall, a strong relationship was found between habitat depth and population structure among species, and species inhabiting shallower water habitats showed lower genetic diversity with higher levels of population subdivision. High‐latitude populations generally showed low haplotype and nucleotide diversity. These data suggest that processes resulting from intraspecific differences in habitat preference, climatic histories and/or larval ecologies have subdivided populations of shallow water triplefin species.     

Fish parasitism in a new impoundment and differences upstream and downstream

The parasitic fish fauna in Guelph Lake, a four-year old impoundment, were compared with those in upstream and downstream localities. The lacustrine assemblage of the young mesotrophic to eutrophic impoundment was dominated by the cestodes, Ligula intestinalis and Proteocephalus ambloplites, and the nematode, Philometra sp. The acanthocephalan, Neoechinorhynchus saginatus, and the nematode, Rhabdacona cascadilla dominated the rheophilous assemblage of fish parasites, but the prevalence rate and intensity of R. cascadilla was significantly reduced downstream.     

Fish cell lines: Establishment of a line from ovaries of channel catfish

Summary A cell line was established from the ovaries of a healthy, juvenile channel catfish,Ictalurus punctatus. These cells, designated CCO, have been passed 130 times during 3 years. The cells grow well in Eagle's MEM-10 at a temperature of 30°C. Species of origin of the cells was confirmed by a cytotoxic dye exclusion test. The cells were found to be free of bacterial and fungal contamination. A study of chromosome preparations indicated that the karyotype is still in a state of flux. The CCO line replicated channel catfish virus but was refractory to 12 other viruses, 4 from fish, 1 from birds, and 7 from mammals. This research was supported by the Southeastern Cooperative Fish Disease Project, Sport Fish Restoration Funds and Regional Research S-83 Funds.     

Seasonal and inter-stream variations in the population dynamics, growth and secondary production of an algivorous fish (Pseudogastromyzon myersi: Balitoridae) in monsoonal Hong Kong

1. Balitorid loaches are widespread and highly diverse in Asian streams, yet their life history and ecology have received little attention. We investigated seasonal (wet versus dry season) and spatial variation in populations of algivorous Pseudogastromyzon myersi in Hong Kong, and estimated the magnitude of secondary production by this fish in pools in four streams (two shaded and two unshaded) over a 15‐month period. 2. Mean population densities of P. myersi ranged from 6.0 to 23.2 individuals m⁻², constituting more than half (and typically >70%) of benthic fishes censused. Abundance was c. 25% greater in the wet season, when recruitment occurred. Significant density differences among streams were not related to shading conditions and were evident despite small‐scale variations in P. myersi abundance among pools. Mean biomass varied among streams from 0.85 to 3.87 g ash‐free dry weight (AFDW) m⁻². Spatial and seasonal patterns in biomass and density were similar, apart from some minor disparities attributable to differences in mean body size among populations. 3. All four P. myersi populations bred once a year in June and July, and life spans varied from 24 to 26 months. Populations consisted of three cohorts immediately after recruitment but, for most of the study period, only two cohorts were evident. Cohort‐specific growth rates did not differ significantly among streams but, in all streams, younger cohorts had higher cohort‐specific growth rates. 4. Secondary production of P. myersi estimated by the size‐frequency (SF) method was 2.7–11.5 g AFDW m⁻² year⁻¹ and almost twice that calculated by the increment‐summation (IS) method (1.2–6.6 g AFDW m⁻² year⁻¹). Annual P/B ratios were 1.17 – 2.16 year⁻¹ (IS) and 2.73 – 3.22 year⁻¹ (SF). Highest production was recorded in an unshaded stream and the lowest in a shaded stream, but site rankings by production did not otherwise match shading conditions. Wet‐season production was six times greater than dry‐season production, and daily production fell to almost zero during January and February. Cool temperatures (<17 °C) may have limited fish activity and influenced detectability during some dry‐season censuses. Estimates of abundance and annual production by P. myersi are therefore conservative. 5. Comparisons with the literature indicate that the abundance and production of P. myersi in Hong Kong was high relative to other benthic fishes in tropical Asia, or their temperate counterparts in small streams. Manipulative experiments are needed to determine the influence of P. myersi, and algivorous balitorids in general, on periphyton dynamics and energy flow in Asian streams.     

Food-web studies in shallow eutrophic lakes by the Netherlands Institute of Ecology: Main results,knowledge gaps and new perspectives

For more than 20 years scientists of the ‘Food-chain studies’ Group of the former Limnological Institute have been studying interactions within the pelagic food web. Purpose of research was to explain the structure and dynamics of the zooplankton and fish communities in lakes and reservoirs in relation to biotic and abiotic environmental factors. A so-called multi-species approach was used, in which all common and abundant species within a specific ecosystem were studied on the individual and population level with the same degree of detail. The recent results and the scientific approach used are evaluated and the main gaps in knowledge about food-web dynamics in shallow eutrophic lakes are identified and discussed. It is concluded that instead of the purely functional approach used so far, future studies should also include evolutionary aspects which determine the success of an organism in a given environment and that more attention should be paid to central questions in ‘community ecology’. This paper is based on a lecture given by the first author for the Netherlands Society of Aquatic Ecology on May 12th, 1992, in Amsterdam, The Netherlands.     

长江上游特有种长鳍吻鮈种群数量和资源利用评估

长鳍吻鮈(Rhinogobio ventralis)为长江上游特有种, 由于过度捕捞和大坝建设, 其种群生存受到极大威胁。为了解三峡工程蓄水后、金沙江一期工程蓄水前该物种的种群动态, 作者利用2007-2009年长江上游江津和宜宾江段调查获取的体长频率数据, 评估了其生长和死亡参数、种群数量及资源利用情况。结果表明, 长江上游长鳍吻鮈渔获群体体长范围为52-250 mm, 体重范围为2.7-307.2 g, 平均体长为150.8 ± 40.7 mm, 平均体重为72.3 ± 49.7 g。江津江段长鳍吻鮈平均体长(168.6 ± 29.5 mm)显著大于宜宾江段(125.6 ± 41.2 mm)。长鳍吻鮈体长-体重关系为: W = 6.06 × 10^-6L^3.20 (R² = 0.98, P < 0.01, n = 436)。由体长频率法拟合出渐近体长(L_∞)为338 mm, 生长系数(k)为0.24/yr。由Pauly公式、Gunderson和Dygert公式、Jensen公式等3种方法估算出其平均自然死亡系数为0.43。由长度转渔获物曲线估算出江津和宜宾江段长鳍吻鮈的总死亡系数分别为2.26和2.09。江津和宜宾江段长鳍吻鮈资源开发率分别为0.81和0.79, 已超过由Beverton-Holt动态综合模型估算出的最大开发率0.57和0.62。由体长实际种群分析估算出2007、2008和2009年江津江段长鳍吻鮈种群数量分别为68,247、67,432和176,266尾, 平均为103,982尾; 宜宾江段种群数量分别为22,953尾、46,340尾和34,021尾, 平均为34,438尾, 表明江津江段种群数量高于宜宾江段。长鳍吻鮈资源已被过度开发, 建议加强种群动态监测, 延长禁渔期及开展栖息地修复等措施保护这一特有物种。     

Endocrine Toxicants and Reproductive Success in Fish

There is compelling evidence on a global scale for compromised growth and reproduction, altered development, and abnormal behaviour in feral fish that can be correlated or in some cases causally linked with exposure to endocrine disrupting chemicals (EDCs). Attributing cause and effect relationships for EDCs is a specific challenge for studies with feral fish as many factors including food availability, disease, competition and loss of habitat also affect reproduction and development. Even in cases where there are physiological responses of fish exposed to EDCs (e.g., changes in reproductive hormone titres, vitellogenin levels), the utility of these measures in extrapolating to whole animal reproductive or developmental outcomes is often limited. Although fish differ from other vertebrates in certain aspects of their endocrinology, there is little evidence that fish are more sensitive to the effects of EDCs. Therefore, to address why endocrine disruption seems so widespread in fish, it is necessary to consider aspects of fish physiology and their environment that may increase their exposure to EDCs. Dependence on aquatic respiration, strategies for iono-osmotic regulation, and maternal transfer of contaminants to eggs creates additional avenues by which fish are exposed to EDCs. This paper provides an overview of responses observed in feral fish populations that have been attributed to EDCs and illustrates many of the factors that need consideration in evaluating the risks posed by these chemicals.     

新疆濒危野生樱桃李的种群结构与动态

为了解野生樱桃李种群结构和种群生态现状,采用“空间序列代替时间变化”的方法,对新疆天然分布区内的野生樱桃李不同种群的径级结构、冠幅结构及株高结构进行了分析,运用静态生命表描述了野生樱桃李种群年龄结构的动态变化规律.结果表明,樱桃李天然种群的株高和冠幅结构呈现为一定的衰退趋势,冠幅在总体呈现为近乎对数型的衰减趋势;种群的径级结构趋于稳定型,但种群结构表现出较强的波动性,种群衰退风险较高;同时,不同样地种群因所处微环境等的差异,在径级、株高和冠幅结构上表现出一定差异.野生樱桃李种群的存活曲线接近于B1型(台阶型),说明幼龄的死亡率较高,且不同生活史时期的死亡率差异较大.新疆的野生樱桃李天然种群表现出一定的不稳定性,亟待补充低龄级的个体,并减少对成年树的砍伐破坏,从而为种群的保育和恢复提供保障.     

Population biology and stock assessment of Pristipomoides filamentosus on the Mahe Plateau, Seychelles

The population of P. filamentosus around the periphery of the Mahe Plateau was studied using data derived from commercial handline fishing operations between November 1989 and December 1990. Sex ratio was close to one. Fork length was in the range 25.6–79.8 cm: at first sexual maturity, 36–38 cm for females and 40–42 cm for males. Spawning occurred from October to April peaking between February and April and in November.
The length ( f.l. , cm)–weight (kg) relationship was W =0.00005353 × f.l. ^2.7004. The von Bertalanffy growth parameters, estimated from length frequency data, were K =0.2875 and L _inf=81.7 cm. Mortality rates, estimated from length converted catch curve analysis, were Z =0.811, F =0.277 with M =0.534 derived from Pauly's empirical formula. Jones' length cohort analysis gave an estimate of F= 0.294 for the fully exploited part of the stock, and a density of 2.59 t km⁻² for the periphery of the plateau from 75 to 150 m depth. The Lesley constant catchability model, applied to the results of intensive fishing around isolated banks, derived a mean density estimate of 2.99t km⁻². The sustainable yield was estimated to be 233–268 tonnes per annum and the catch in 1990 was 200 tonnes.     

A conceptual mathematical model of the aquatic communities of lakes Naroch and Myastro (Belarus)

A conceptual mathematical model of the dynamics of fish and zooplankton (rotifer) populations of connected lakes Naroch and Myastro (Belarus) is built and examined with parameters based on field data. It is shown that community coupling and trophic interactions give rise to both regular and irregular oscillations in population numbers.     

Pacific Coral-reef Fishes: The Implications of Behaviour and Ecology of Larvae for Biodiversity and Conservation, and a Reassessment of the Open Population Paradigm

The two-phase life history of most marine fishes and invertebrates has enormous implications for dispersal, population connectivity, and resource management. Pelagic dispersal larvae of marine animals traditionally thought to ensure that populations are widespread, that chances of local extinction are low, and that marine protected areas (MPA) can easily function to replenish both their own populations and those of unprotected areas. Traditionally, dispersal is considered to depend primarily on two variables: pelagic larva duration and far-field currents. These conclusions arise from the open population paradigm and are usually accompanied by a simplifying assumption: larvae are distributed passively by far-field currents. Unfortunately, they ignore the complex reality of circulation and hydrological connectivity of reefs, and do not consider newly-demonstrated behavioural capabilities of coral-reef fish larvae. Far-field circulation varies with depth and often excludes water bodies where propagules are released, and this has important implications for predicting trajectories of even passive larvae. However, larvae are not passive: late-stage larvae of coral-reef fishes can swim faster than currents for long periods, can probably detect reefs at some distance, and can actively find them. This behaviour is flexible, which greatly complicates modelling of larval fish trajectories. Populations at ecological (as opposed to evolutionary) scales are probably less open and more subdivided than previously assumed. All this means that dispersal predictions based solely on far-field water circulation are probably wrong. An emerging view of larval-fish dispersal is articulated that takes these new data and perspectives into account. This emerging view shows that re-evaluation of traditional views in several areas is required, including the contribution of larval-fish biology and dispersal to biodiversity patterns, the way reef fishes are managed, and the way in which MPA are thought to operate. At evolutionary and zoogeographic scales, reef-fish populations are best considered to be open.