scholarly journals Influence of macroalgal mats on abundance and distribution of dunlin Calidris alpina in estuaries: a long-term approach

2006 ◽  
Vol 323 ◽  
pp. 11-20 ◽  
Author(s):  
RJ Lopes ◽  
MA Pardal ◽  
T Múrias ◽  
JA Cabral ◽  
JC Marques
Keyword(s):  
Calidris Alpina ◽  
Abundance And Distribution ◽  
Macroalgal Mats

scholarly journals Trends in numbers of Cape gannets (Morus capensis), 1956/1957–2005/2006, with a consideration of the influence of food and other factors

2006 ◽  
Vol 64 (1) ◽  
pp. 169-177 ◽  
Author(s):  
Robert J. M. Crawford ◽  
Benedict L. Dundee ◽  
Bruce M. Dyer ◽  
Norbert T. W. Klages ◽  
Michael A. Meÿer ◽  
...  
Keyword(s):  
South Africa ◽  
South African ◽  
Conservation Status ◽  
Fish Prey ◽  
Management Measures ◽  
Fur Seals ◽  
Long Term Changes ◽  
Influence Of Food ◽  
Abundance And Distribution

Abstract Crawford, R. J. M., Dundee, B. L., Dyer, B. M., Klages, N. T., Meÿer, M. A., and Upfold, L. 2007. Trends in numbers of Cape gannets (Morus capensis), 1956/57–2005/06, with a consideration of the influence of food and other factors – ICES Journal of Marine Science, 64, 169–177. Cape gannets (Morus capensis) breed at six colonies in Namibia and South Africa. Population size averaged about 250 000 pairs over the period 1956/1957–1968/1969 and about 150 000 pairs from 1978/1979 to 2005/2006. Over the whole 50-y period, numbers at the three Namibian colonies fell by 85–98%, with greater proportional decreases in the south. There were increases at two South African colonies between 1956/1957 and 2005/2006. The colony at Lambert's Bay increased between 1956/1957 and 2003/2004, but attacks by Cape fur seals (Arctocephalus pusillus) on birds at nests caused abandonment of the entire colony in 2005/2006. Long-term changes at colonies are thought to be largely attributable to an altered abundance and distribution of prey, especially sardine (Sardinops sagax) and anchovy (Engraulis encrasicolus). In both Namibia and South Africa, the numbers of Cape gannets breeding were significantly related to the biomass of epipelagic fish prey. Over the 50-y period, there was also a marked similarity in the proportions of gannets and epipelagic fish in the Benguela system, which were present in Namibia and South Africa. In the 2000s, there was an eastward shift in the distribution of sardine off South Africa and a large increase in the number of gannets breeding at South Africa's easternmost colony. When sardine were scarce off South Africa, gannets fed on anchovy, but off Namibia anchovy only temporarily and partially replaced sardine. Ecosystem management measures that might improve the conservation status of Cape gannets are considered.

Krill (Euphausiacea) demography and variability in abundance and distribution

2000 ◽  
Vol 57 (S3) ◽  
pp. 151-167 ◽  
Author(s):  
Volker Siegel
Keyword(s):  
Energy Flow ◽  
Environmental Changes ◽  
Population Level ◽  
Survival Strategies ◽  
Detailed Knowledge ◽  
Species Survival ◽  
Flow Through ◽  
Abundance And Distribution ◽  
Geographical Locations

Among euphausiids, there are many species that are represented by enormous numbers of individuals and are of considerable importance to various ecosystems, as well as to human exploitation. Considerable progress has been made regarding quantitative aspects of krill biology. This detailed knowledge about krill population parameters is necessary to answer questions about the importance of euphausiids to energy flow through certain ecosystems. This information also helps in assessing the importance of seasonal or long-term climate effects on variation in euphausiid populations because variability is not simply noise. Hypotheses have been developed as to how large seasonal or latitudinal environmental changes affect species survival strategies in poor conditions and maintenance of a stable population level. This paper discusses aspects of the spatial distribution with regard to seasonal and interannual changes, developments to define genetically distinct populations, and results of long-term variability in krill abundance and biomass for various species in different geographical locations.

scholarly journals Long-term patterns of abundance, residency and movements of bull sharks (Carcharhinus leucas) in Sydney Harbour, Australia

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Amy F. Smoothey ◽  
Kate A. Lee ◽  
Victor M. Peddemors
Keyword(s):  
Spatial Distribution ◽  
Austral Summer ◽  
Diel Pattern ◽  
Water Users ◽  
Carcharhinus Leucas ◽  
Nearshore Environments ◽  
Sydney Harbour ◽  
Bull Shark ◽  
Abundance And Distribution

AbstractBull sharks (Carcharhinus leucas) are known to frequent nearshore environments, particularly estuaries, resulting in interactions with humans. Knowledge of the behaviour of large individuals in temperate, estuarine environments is limited. This acoustic telemetry study reports on residency and movement patterns of 40 sub-adult and adult bull sharks in Sydney Harbour, a large temperate estuary, over seven years. Bull sharks exhibited clear seasonal patterns in their occurrence during the austral summer and autumn, with abundance peaking in January and February. This pattern was consistent between sexes and across all sizes. Bull sharks displayed weak diel differences in their spatial distribution, with individuals using areas further from the Harbour entrance more frequently during the day and at low tides. A diel pattern in depth use was apparent, with sharks utilising deeper water during daytime and moving shallower at night. Bull sharks had high individual inter-annual variability in their spatial distribution, however, when data were aggregated among all individuals and years, two locations of increased use were identified. Water temperature was the key predictor for seasonal movements and return behaviour to this estuary, suggesting that increasing water temperatures as a result of climate change may lead to higher shark abundance and possibly longer periods of residency in Sydney Harbour. Understanding the drivers for bull shark abundance and distribution will hopefully facilitate better education and shark smart behaviour by estuarine water-users, especially during summer and autumn months.

Long-term shifts in abundance and distribution of a temperate fish fauna: a response to climate change and fishing practices

2010 ◽  
Vol 20 (1) ◽  
pp. 58-72 ◽  
Author(s):  
Peter R. Last ◽  
William T. White ◽  
Daniel C. Gledhill ◽  
Alistair J. Hobday ◽  
Rebecca Brown ◽  
...  
Keyword(s):  
Climate Change ◽  
Fish Fauna ◽  
Abundance And Distribution ◽  
Temperate Fish ◽  
Fishing Practices

scholarly journals Population status, structure and distribution of the greater one-horned rhinoceros Rhinoceros unicornis in Nepal

Oryx ◽  
2013 ◽  
Vol 47 (3) ◽  
pp. 352-360 ◽  
Author(s):  
Naresh Subedi ◽  
Shant Raj Jnawali ◽  
Maheshwar Dhakal ◽  
Narendra M.B. Pradhan ◽  
Babu Ram Lamichhane ◽  
...  
Keyword(s):  
National Park ◽  
Null Model ◽  
Closed Population ◽  
Rhinoceros Unicornis ◽  
Detection Probabilities ◽  
Potential Habitats ◽  
Chitwan National Park ◽  
Wildlife Reserve ◽  
Abundance And Distribution

AbstractWe assessed the abundance and distribution of the greater one-horned or Indian rhinoceros Rhinoceros unicornis in all its potential habitats in Nepal, using block counts. In April 2011 5,497 km were searched in 3,548 elephant-hours over 23 days. The validity of the block count was assessed by comparing it with counts obtained from long-term monitoring using photographic identification of individual rhinoceroses (ID-based), and estimates obtained by closed population sighting–mark–resighting in the 214 km2 of Chitwan National Park. A total of 534 rhinoceroses were found during the census, with 503 in Chitwan National Park (density 1 km−2), 24 in Bardia National Park (0.28 km−2) and seven in Suklaphanta Wildlife Reserve (0.1 km−2). In Chitwan 66% were adults, 12% subadults and 22% calves, with a female : male ratio of 1.24. The population estimate from sighting–mark–resighting was 72 (95% CI 71–78). The model with different detection probabilities for males and females had better support than the null model. In the Sauraha area of Chitwan estimates of the population obtained by block count (77) and ID-based monitoring (72) were within the 95% confidence interval of the estimate from sighting–mark–resighting. We recommend a country-wide block count for rhinoceroses every 3 years and annual ID-based monitoring in a sighting–mark–resighting framework within selected subpopulations. The sighting–mark–resighting technique provides the statistical rigour required for population estimates of the rhinoceros in Nepal and elsewhere.

Divorce and breeding dispersal in the dunlin Calidris alpina: support for the better option hypothesis?

Behaviour ◽  
2012 ◽  
Vol 149 (1) ◽  
pp. 67-80 ◽  
Author(s):  
Donald Blomqvist ◽  
Lars-Åke Flodin
Keyword(s):  
Reproductive Success ◽  
Egg Laying ◽  
Male Reproductive Success ◽  
Breeding Dispersal ◽  
Social Monogamy ◽  
Calidris Alpina ◽  
Pair Bonds ◽  
Mate Change ◽  
Term Data

AbstractSocial monogamy is a rare mating system among animals, occurring commonly only in birds. In long-lived birds, pair bonds may persist for several seasons in some species, while in others mate change occurs even when both partners are still alive. Here, we test predictions from the adaptive hypotheses for divorce, using long-term data (15 years) on mate change and reproductive success in a long-lived shorebird, the dunlin Calidris alpina. We found that about one quarter of the pairs divorced (23% of 126 breeding attempts). Among the divorcing females, six changed partner more than once (one female changed partner three times). Following divorce, females dispersed longer than males. Start of egg-laying (presumably reflecting arrival time to the breeding ground), previous breeding success, and male age or size did not seem to influence the occurrence of divorce. However, females that changed mate between consecutive breeding attempts achieved higher reproductive success. Moreover, this improvement appeared independent of breeding experience. Since we were unable to detect any effect of divorce on male reproductive success, our results suggest that divorce in the dunlin is best explained by the better option hypothesis.

scholarly journals Population Viability of Endangered Lost River Sucker and Shortnose Sucker and the Effects of Assisted Rearing

2018 ◽  
Vol 9 (2) ◽  
pp. 582-592 ◽  
Author(s):  
Josh E. Rasmussen ◽  
Evan S. Childress
Keyword(s):  
Population Viability ◽  
Recruitment Failure ◽  
Assessment Approach ◽  
Upper Klamath Lake ◽  
In The Wild ◽  
Klamath Basin ◽  
Abundance And Distribution ◽  
The U.S ◽  
Klamath Lake

Abstract The Lost River Sucker Deltistes luxatus and Shortnose Sucker Chasmistes brevirostris are two narrowly endemic fish species in the upper Klamath Basin of southern Oregon and northern California. Both species have been federally listed as endangered pursuant to the U.S. Endangered Species Act since 1988 because of dramatic declines in abundance and distribution. In Upper Klamath Lake, Oregon, both species have only recruited a single cohort to the adult populations since that time. Most individuals in this population are at or older than the expected life span of the species. Consequently, the U.S. Fish and Wildlife Service and the Klamath Tribes have initiated assisted rearing efforts to stabilize the population. However, it is unclear how quickly these populations might become extirpated and how assisted rearing might alter population trajectories. We modeled the potential for extinction and recovery of the populations of endangered Lost River Sucker and Shortnose Sucker in Upper Klamath Lake. We simulated population trajectories over the next 50 y with a stochastic population viability assessment approach. Projections indicate that if population trajectories do not change, the Shortnose Sucker population may decline by 78% to number < 5,000 in 10 y and become completely extirpated within the next 30 (18.6% probability) to 40 y (99% probability). The two Lost River Sucker populations have a greater likelihood to remain extant after 50 y, with only 1% probability of extinction given our scenarios and assumptions, but the populations are likely to number fewer than 1,000 individuals. Our results also suggest that rearing of Klamath Lake sucker species in a controlled environment for augmenting the natural population will be effective in reducing extirpation probabilities over the next 50 y if survival to recruitment can be achieved, but a long-term effort of at least 40 y will be required. The necessity of long-term augmentation to ensure population persistence in the absence of natural recruitment underscores the urgent need to determine and address the causes of recruitment failure in the wild.

Interactions Between the Amphipod Corophium Volutator and Macroalgal Mats on Estuarine Mudflats

1991 ◽  
Vol 71 (4) ◽  
pp. 899-908 ◽  
Author(s):  
D. Raffaelli ◽  
J. Limia ◽  
S. Hull ◽  
S. Pont
Keyword(s):  
Coastal Areas ◽  
Data Sets ◽  
Low Oxygen ◽  
Corophium Volutator ◽  
Intertidal Mudflats ◽  
Capitella Capitata ◽  
Term Data ◽  
Macroalgal Mats

One of the most obvious effects of eutrophication in sheltered coastal areas and estuaries is enhanced growth of opportunistic macroalgae, which may form extensive mats over intertidal mudflats during the spring and summer. In the Ythan estuary, densities of the amphipod Corophium volutator (Pallas) in the sediment underlying weed mats were significantly lower than those in weed-free sediments, and are dominated by species characteristic of organically enriched, low oxygen environments such as Capitella capitata. Long-term data sets on Corophium abundance in the Ythan suggest that this species has declined dramatically throughout those parts of the estuary affected by weed mats.

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