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- 1. When a species is identified for conservation, often the only way to effect recovery is to reduce the harm imposed by stressors threatening the survival of the species. Ideally all threats would be removed; however, this is often not feasible or practical. Within this context, a demographic approach is presented to assess how much human‐induced harm could be allowed without impairing the persistence of the species. Harm is defined as a negative perturbation that can target one or more vital rates and life stages simultaneously.
- 2. Allowable harm, defined as a level of harm that will not jeopardize survival or recovery, will be a function of the vital rates affected by human actions, the sensitivity of population growth to changes in these vital rates (their elasticities), the population growth rate prevailing before harm occurs, and the set of demographic parameters considered safe for long‐term persistence. This life‐history based approach requires minimal data, can link demography with habitat‐explicit information, is flexible enough to encompass complex life histories, and follows a precautionary approach.
- 3. Quantification of allowable harm could be applied to any species at risk. This approach is introduced by applying it to a Canadian population of a freshwater fish, the black redhorse (Moxostoma duquesnei), demonstrating that in the absence of habitat constraints population dynamics of this species are most sensitive to the survival of young adults, but population fitness is particularly sensitive to the loss of habitat used by young‐of‐the‐year fish under current levels of habitat supply.
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Andrzej Kamocki Maria Urbańska Urszula Biereżnoj-Bazille Małgorzata Ożgo 《水产资源保护:海洋与淡水生态系统》2021,31(7):1918-1924
- Local extinctions break species interactions and have cascading effects throughout ecosystems; parasites are often severely affected. The European bitterling, Rhodeus amarus, is a cyprinid fish that parasitizes unionid mussels by laying eggs into the mussel gill cavity, where embryos develop and emerge as active juveniles; this relationship is obligatory for the bitterling.
- This article describes a field experiment aimed at averting the secondary extinction of the European bitterling after a complete die-off of a freshwater mussel community, as a result of habitat destruction.
- Approximately 5,000 unionid mussels were reintroduced within the short time frame in which the remnant bitterling population was still present at the site. Mussel survival was high, and bitterling resumed reproduction, with vigorous courtship observed within 24 hours of mussel release. Recruitment was successful, as evidenced by increased occupancy, densities, and relative frequencies in the fish assemblage. The frequency of sub-adults and young-of-the-year changed from 0% before mussel reintroduction to 80% a year later, and 50% 2 years later, when young-of-the-year contributed to about half of the young fish. No bitterling were observed at two control sites where mussels were not reintroduced.
- This study exemplifies how the timely restitution of affiliate species can avert co-extinction. It also shows how the conservation of the bitterling within its historical distribution range can serve mussel conservation, including species that although not legally protected, are important keystone species and ecosystem engineers, shaping the structure and function of a broad range of freshwater habitats.
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- 1. Carassius auratus, a primary freshwater fish with bisexual diploid and unisexual gynogenetic triploid lineages, is distributed widely in and around the Eurasian continent and is especially common in East Asia. East Asian C. auratus diverged genetically to form local endemic populations in different regions, and those distributed in the Ryukyu Archipelago form a local endemic population that can be regarded as an evolutionarily significant unit because of its high phylogenetic independence and evolutionary distinctiveness. Although the evolutionary uniqueness of this population should be conserved, its distribution area and population size are decreasing rapidly, and some island populations are currently considered endangered or already extinct.
- 2. To develop effective conservation measures to stop the current decline of Ryukyuan C. auratus, ecological data need to be collected. In this study, life history data for a C. auratus population distributed in the Hiji River system were collected by estimating age, growth, and spawning season.
- 3. The spawning season of C. auratus in the Hiji River extended from March to September, peaking during March–May. Females became sexually mature in their second year, but males reached maturity and were able to spawn as early as in the late spawning season of their year of hatching. Once having reached sexual maturity, males probably continuously stay ripe throughout their life.
- 4. Sagittal otoliths of C. auratus proved to be useful ageing structures because one annual increment is formed on the sagittal otolith before the spawning season in each year. The oldest fish observed were a 10‐year‐old female and an 11‐year‐old male. Females showed faster somatic growth and higher final standard length than males, and a sexual size dimorphism was observed.
- 5. The standard length at each age class did not differ between diploid and triploid C. auratus, suggesting that triploid growth rates were almost equal to those of diploids. Copyright © 2009 John Wiley & Sons, Ltd.
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- 1. In rearing experiments performed between 1997 and 2007, captive‐bred juvenile mussels were harvested shortly after they had dropped off their host fish, and exposed to different types of cages and holding systems.
- 2. Survival of juveniles ranged from 0 to 92% in the first 4 months, but the mean annual mortality was high in all trials and with all systems. In three trials with sheet cages and sediment boxes exposed to mussel rivers from an initial number of 1440 to 1660 only one to eight mussels reached 4 years of age.
- 3. With the exception of mussels kept in spring water no relationship between growth and survival was observed.
- 4. Low survival rates were obtained in sheet cages exposed to very oligotrophic and highly eutrophic brook stretches. Several natural sites that were lacking recruitment in the wild nevertheless showed good results in the cages.
- 5. All holding systems showed irregular variations in survival rates. Pairs of sheet cages showed no correlation between the survival of mussels in the adjacent cages. In contrast, growth rates were correlated.
- 6. No relationship could be found between the growth or survival in sheet cages at different sites and brooks and the corresponding data on water chemistry.
- 7. The systems tested for rearing young mussels involving a minimal time and effort in the natural habitat were not successful due to the elevated mortality rates of juveniles.
- 8. The rearing success of young pearl mussels in cages in the water flow of mussel rivers gives no information about the suitability of these sites for natural reproduction. Thus, to find potential natural habitats for Margaritifera, it is imperative to survey water quality, sediments and habitat structure. Copyright © 2010 John Wiley & Sons, Ltd.
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- 1. An internationally important population of the freshwater pearl mussel (Margaritifera margaritifera) was rediscovered in a small river in north‐west Russia.
- 2. A survey of visible mussels in 2008/2009 indicated an estimated population of 40 000 individuals. This is the largest population currently known in the Leningrad oblast and is comparable with the entire pearl mussel population of some western European countries.
- 3. The average density of visible mussels was 29.6 individuals m?2 in the middle part of the river. In the four largest mussel beds maximum densities of 1000+ individuals m?2 were recorded. Such densities are exceptional and have not been reported elsewhere in Europe during the last 100 years.
- 4. Live juvenile mussels were recorded, indicating that that this population is viable, although further investigation is required to establish its status.
- 5. Analysis of the population age structure, based on the measurement of empty shells, showed an age class distribution similar to those reported for other healthy Margaritifera populations.
- 6. Only two live juveniles were found. However, this is likely to be due to the survey being restricted to counts of visible mussels only, and the age structure being based on the analysis of dead shells.
- 7. The population's current status and possible reasons for its survival in this river are discussed. Conservation measures should include the construction of a fish ladder to make fish migration through the culvert possible, removal of a metal screen preventing fish migration from the upper reaches of the river to the lake, reduction of recreation activities, and providing the local children's camp with water treatment facilities. Copyright © 2011 John Wiley & Sons, Ltd.
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Simone Tenan Noelia Hernndez Holly Fearnbach Renaud de Stephanis Philippe Verborgh Daniel Oro 《水产资源保护:海洋与淡水生态系统》2020,30(5):949-958
- The Strait of Gibraltar is an important habitat for cetaceans due to its high marine productivity. However, it is also the second most navigated channel in the world, subjecting cetaceans to a high level of vessel traffic, including an established whale‐watching fleet. Both maritime traffic and whale‐watching activities have been shown to impact the behaviour of cetaceans, but little is known about their impact on the demography and dynamics of cetacean populations.
- The aim of this study was to evaluate the impacts of both ferry traffic and whale‐watching vessels on the apparent survival probability of a bottlenose dolphin (Tursiops truncatus) population that occurs in the Strait.
- A Bayesian hierarchical mark–recapture modelling approach was applied to 8 years of photo‐identification data (2002–2009). Apparent annual survival probability was negatively correlated with ferry traffic, which explained >70% of temporal variation in survival, in contrast to whale‐watching, the effect of which was almost negligible. Despite these results, other natural and human‐related factors are likely to drive apparent survival in the study area.
- Abundance increased between 2002 and 2005, and then decreased between 2006 and 2009, while local per‐capita recruitment decreased from 2004 until the end of the study period. These shifts correlated temporally with the construction of a large harbour on the Moroccan coast, which increased maritime traffic significantly, including a 40% increase in ferry traffic that regularly transited the Strait.
- These results highlight the need to better understand the impact of maritime traffic on the demography of the dolphin population in the Strait, in order to implement evidence‐based conservation regulations in a region of high cetacean occurrence.
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B. G. Clynick 《水产资源保护:海洋与淡水生态系统》2008,18(5):483-492
- 1. Artificial structures are becoming increasingly important in conserving biodiversity in urban ecosystems, by providing habitat for endangered or rare species. Their role in providing habitat for such species has, however, been largely unexplored.
- 2. In Sydney Harbour, Australia, seahorses were observed among the netting used to keep sharks out of swimming enclosures. Over a 2‐year period, the relative densities of two species of seahorses observed on netting was measured at swimming enclosures with permanent netting and at swimming areas that were only enclosed with netting during the summer months.
- 3. The rate of colonization by seahorses to new netting was also examined over a period of 10 months.
- 4. Numbers of seahorses on permanent swimming enclosures were 10 to 100 times greater than numbers present on swimming enclosures that were only set up during the summer months.
- 5. This large difference may have been attributed to the slow rate of colonization of seahorses to new habitat. Seahorses were not observed at experimental nets that were deployed in two areas in the harbour until at least 4 months after the netting was deployed.
- 6. Swimming pool nets are a habitat for species of seahorses in Sydney Harbour and, consequently, the removal or disturbance of swimming nets may impact the survival of these fish. Management of these artificial habitats may therefore best be focused on providing a permanent habitat that may help to compensate for the loss of netting during winter months.
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Jean‐Marie Ballouard Pauline Priol Jean Oison Alexandre Ciliberti Antoine Cadi 《水产资源保护:海洋与淡水生态系统》2010,20(7):756-761
- 1 Despite conservation programmes (India 1975, Nepal 1978) gharial populations (Gavialis gangeticus) have declined over their entire distribution range. Information about the current status and main threats is needed to implement effective conservation measures.
- 2 This study presents a survey (2003/2004) of the largest Nepalese gharial population in the Chitwan National Park that has benefited from regular re‐introduction of young gharials since 1981.
- 3 Population size estimates fluctuate between 34 (2003) and 38 (2004). The reintroduction programme, although of limited success, has helped to maintain the gharial population.
- 4 Gharials bask preferentially in large sand banks, and these sites must be protected.
- 5 The main threats are from a dam that causes fish depletion and flushes gharials from the protected area, sand mining and grazing that destroy basking sites, fishing that causes food shortage, drift nets that kill gharial, and water pollution.
- 6 Improvement in the survival of reintroduced gharials is needed. Strict protection of preferred basking sites and prohibition of fishing in the main settling zones are the principal conservation measures while in the long term, education and participatory management by local people are also necessary. Copyright © 2010 John Wiley & Sons, Ltd.
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- 1. Habitat suitability criteria that fail to incorporate temporal variability in habitat preferences of stream fish may mis‐represent critical habitat requirements and lead to setting of inappropriate flow targets when used in instream flow assessments. Developing suitability criteria from daytime observations alone relies on the assumption that habitat preferences are constant over the diel cycle. Few studies have tested these assumptions, particularly for small‐bodied, cryptic, benthic species.
- 2. During summer in two gravel‐bed rivers, bluegill bullies (Gobiomorphus hubbsi), torrentfish (Cheimarrichthys fosteri) and upland bullies (Gobiomorphus breviceps) exhibited strong preferences with respect to water depth, velocity and substratum size. All three species underwent a diel shift in microhabitat preference for at least two of these variables.
- 3. Microhabitat preferences were generally weaker when fish were active at night; bluegill bullies, upland bullies and especially torrentfish were observed over a broader range of depths, velocities and substratum sizes at night than during the day. Observations of fish in a stream simulator confirmed that bluegill bullies and torrentfish showed a preference for runs at dusk and return to riffles before dawn, but habitat preferences of upland bullies remained static across the diel cycle.
- 4. Diel microhabitat shifts affected the assessment of flow requirements. Instream habitat analysis of the Waipara River using separate day and night suitability criteria predicted differing amounts of habitat available at a given flow, and the relationships between fish abundance, fish density and flow. The presence of diel microhabitat shifts in stream fishes suggests that instream habitat analyses will produce more effective and defensible flow recommendations when patterns of nocturnal microhabitat preferences are known and critical habitat bottlenecks can be identified. Copyright © 2011 John Wiley & Sons, Ltd.
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