Predation on small juvenile fishes in shallow estuarine nursery areas: Reply to Baker & Sheaves (2021)

2021 ◽  
Vol 662 ◽  
pp. 209-214
Author(s):  
A Whitfield
Keyword(s):  
South Africa ◽  
Juvenile Fish ◽  
Fish Predation ◽  
Estuarine Waters ◽  
Fish Nursery ◽  
Piscivorous Fish ◽  
Small Juvenile ◽  
Nursery Habitats ◽  
High Predation ◽  
Counter Argument

The key criticism by Baker & Sheaves (2021; Mar Ecol Prog Ser 662:205-208) of the Whitfield (2020; Mar Ecol Prog Ser 649:219-234) estuarine littoral predation paradigm review is that shallow water fish nursery habitats contain abundant predator assemblages which may create high predation pressure on the juvenile fish cohorts that occupy these areas. The primary arguments supporting Baker & Sheaves’ criticism arise from a series of papers published by them on piscivorous fish predation in certain tropical Australian estuaries. The counter-argument that shallow littoral areas in estuaries do indeed provide small juvenile fishes with refuge from small and large piscivorous fishes is provided by published papers from 4 different estuary types in South Africa, covering both subtropical and warm-temperate systems. Based on the overall published information, the argument for shallow (<1 m depth) estuarine waters providing major protection for newly settled juveniles appears to be weak in northern Australia but strong in South Africa. The global situation, as outlined in this response, is more supportive of low piscivorous predation in shallow nursery habitats, but further targeted research is needed before we can confirm that littoral estuarine waters are indeed a universal keystone attribute in this regard.

Size-selective predation by river otter (Lontra canadensis) improves refuge properties of shallow coastal marine nursery habitats

2008 ◽  
Vol 86 (11) ◽  
pp. 1324-1328 ◽  
Author(s):  
D. Cote ◽  
R. S. Gregory ◽  
H. M.J. Stewart
Keyword(s):  
Shallow Water ◽  
Atlantic Cod ◽  
Prey Availability ◽  
Juvenile Fish ◽  
Lontra Canadensis ◽  
River Otter ◽  
Fish Nursery ◽  
Piscivorous Fish ◽  
Risk Of Predation ◽  
Nursery Habitats

Young fish often avoid deep water to reduce predation risk from larger fish. Less clear are explanations for the avoidance of shallows by large piscivorous fish; however, one hypothesis suggests that this distribution reduces contact with depth-limited semi-aquatic mammal and bird piscivores. We determined prey size selection of the river otter ( Lontra canadensis (Schreber, 1777)) to test the hypothesis that larger fish are at elevated risk in shallow coastal waters in Newman Sound, Newfoundland, during June–November 2001 and May 2002. We compared otter diet (scat analysis) and prey availability (seine sampling) to test this hypothesis. Five fish taxa (Atlantic cod ( Gadus morhua L., 1758), Greenland cod ( Gadus ogac Richardson, 1836), shorthorn sculpin ( Myoxocephalus scorpius (L., 1758)), cunner ( Tautogolabrus adspersus (Walbaum, 1792)), and winter flounder ( Pseudopleuronectes americanus (Walbaum, 1792))) dominated the shallow-water fish community and were sufficiently abundant in otter scats to examine feeding preferences. Larger, piscivorous fish were selected by otters, suggesting that they were at greater risk of predation than smaller fish, consistent with our hypothesis that depth-limited, diurnally active predators restrict large fish from hunting in shallow water during daytime. We suggest that depth-limited air-breathing predators may reduce the presence of such predatory fish in shallow-water juvenile fish nursery habitats.

Littoral habitats as major nursery areas for fish species in estuaries: a reinforcement of the reduced predation paradigm

2020 ◽  
Vol 649 ◽  
pp. 219-234 ◽  
Author(s):  
AK Whitfield
Keyword(s):  
Fish Species ◽  
Juvenile Fish ◽  
High Energy ◽  
Global Scale ◽  
Nursery Areas ◽  
Fish Nursery ◽  
Piscivorous Fish ◽  
Dominant Component ◽  
Littoral Habitats

For many decades, the role of estuaries as important nursery areas for fishes was accepted as fact by scientists and environmental managers. At the turn of the 21st century, a question mark was raised in relation to the reduced predation component of the nursery function, with some scientists contending that both large and small piscivorous fish species had access to the estuarine habitats that juvenile fishes in estuaries occupied. If true on a global scale, the nursery designation for these habitats would be compromised and the long-held paradigm that estuaries are important nursery areas for fishes would need to be revised. In this review, I examine the nature of fish nursery areas in estuarine littoral habitats from a mainly predation perspective and, based on a variety of ichthyofaunal and avifaunal studies, come to the conclusion that apart from a few selected estuarine systems, there is limited predation on juvenile fishes in these particular areas. This, coupled with the abundant suitable food resources for juvenile fish from different trophic categories, shelter from high-energy marine wave action and biological connectivity between a variety of submerged and emergent macrophyte communities, renders shallow estuarine littoral areas ideal nursery areas for the juveniles of mostly euryhaline marine fish species, the dominant component of estuarine ichthyofaunas globally. In addition, there are strong indications from the fossil record that these littoral estuarine nursery areas have been functioning since the Devonian, more than 350 million years ago.

scholarly journals Unusually High Predation on Chacma Baboons(Papio ursinus)by Female Leopards(Panthera pardus)in the Waterberg Mountains, South Africa

2012 ◽  
Vol 83 (3-6) ◽  
pp. 353-360 ◽  
Author(s):  
E. Jooste ◽  
R.T. Pitman ◽  
W. van Hoven ◽  
L.H. Swanepoel
Keyword(s):  
South Africa ◽  
Panthera Pardus ◽  
Papio Ursinus ◽  
High Predation ◽  
Chacma Baboons

scholarly journals Fish nursery value of algae habitats in temperate coastal reefs

PeerJ ◽  
2019 ◽  
Vol 7 ◽  
pp. e6797 ◽  
Author(s):  
Hilmar Hinz ◽  
Olga Reñones ◽  
Adam Gouraguine ◽  
Andrew F. Johnson ◽  
Joan Moranta
Keyword(s):  
Juvenile Fish ◽  
Strong Association ◽  
Late Summer ◽  
Early Spring ◽  
Rocky Reef ◽  
Term Survival ◽  
Fish Nursery ◽  
Prey Biomass ◽  
Reduced Height ◽  
Time Of Year

The nursery function of coastal habitats is one of the most frequently mentioned and recognized ecosystem services in the valuation of coastal ecosystems. Despite its importance our understanding of the precise habitat parameters and mechanisms that make a habitat important as a nursery area is still limited for many species. The study aimed to establish the importance of different algae morphotypes in providing shelter and food for juvenile coastal fish during the main settlement peaks, in early spring and late summer, in littoral rocky reef systems in the Northwestern Mediterranean. The results of our study showed strong seasonal differences in algae cover, composition and height between the two sampling periods. Overall, during spring the algae were well developed, while in late summer, both density and height, of most algae decreased considerably. Equally, prey biomass, in form of suitable sized invertebrate fauna associated to the algae, decreased. Accordingly, the shelter and food for the fish settling in this habitat during late summer were less abundant, indicating a mismatch between the observed presence of juvenile fish and optimal habitat conditions. Differences in prey densities were detected between algae morphotypes, with structurally more complex algae, such as Cystoseira spp. and Halopteris spp. consistently containing more prey, independent of season, compared to simpler structured morphotypes such as Dictoytales. The study furthermore related juvenile fish density to habitats dominated by different algae morphotypes. Out of the three-study species (Diplodus vulgaris, Symphodus ocellatus, Coris julis) only S. ocellatus showed a significant association with an algae habitat. S. ocellatus related positively to habitats dominated by Dictoytales which provided the highest cover during late summer but had the lowest prey densities. A strong association of this species with Cystoseira, as reported by other studies, could not be confirmed. Cystoseira was abundant within the study area but in a state of dieback, showing loss and reduced height of foliage, typical for the time of year within the study area. It is therefore likely that algae-fish associations are context-dependent and that several algae species may fulfil similar functions. We also discovered that prey biomass did not appear to have an important effect on juvenile abundances. Nevertheless, the availability of prey may influence juvenile fish condition, growth performance and ultimately long-term survival. We therefore suggest that future studies on habitat quality should also include, besides abundance, indicators related to the condition and growth of juveniles.

Potential Usefulness of Chlorine for Controlling Pacific Salmon Leeches, Piscicola salmositica, in Hatcheries

1985 ◽  
Vol 42 (12) ◽  
pp. 1986-1993 ◽  
Author(s):  
S. M. Bower ◽  
L. Margolis ◽  
R. J. MacKay
Keyword(s):  
Logistic Regression Model ◽  
Coho Salmon ◽  
Pacific Salmon ◽  
Juvenile Fish ◽  
Gill Tissue ◽  
Residual Chlorine ◽  
Lethal Effects ◽  
Small Juvenile ◽  
Wide Range ◽  
Low Levels

Susceptibility to the lethal effects of low levels of total residual chlorine (TRC) differed between juvenile coho salmon (Oncorhynchus kisutch) and the salmon leech (Piscicola salmositica), the vector for the haemoflagellate salmonid pathogen Cryptobia salmositica. There was no salmon mortality at concentrations below approximately 50 μg TRC/L for the maximum exposure time of 24 h. Some damage to gill tissue (hypertrophy, fusion, oedema, and some necrosis), was observed at the highest concentrations of TRC that did not kill any of the fish (approximately 50 μg/L for 24 h, and approximately 100 μg/L for 8 h). This damage was repaired by the fish within 4 d of exposure, although evidence of past irritation was noted in 6 of 12 fish. All small juvenile leeches exposed to 44 μg TRC/L for 24 h died, and over half of such leeches exposed to 44 μg/L for 8 h and 21 μg/L for 24 h died. Below TRC concentrations that were lethal to the fish (approximately 50 μg/L), contours of constant leech mortality derived from a logistic regression model fitted to the data offered a wide range of concentrations and exposure times that would result in high mortality of juvenile leeches. Larger subadult and adult leeches were more resistant to chlorine than the smaller leeches but were more sensitive than the juvenile fish. Thus, chlorine may prove useful for controlling P. salmositica in salmonid hatcheries.

Effects of juvenile fish predation (Cyprinus carpio L.) on the composition and diversity of free-living freshwater nematode assemblages

Nematology ◽  
2016 ◽  
Vol 18 (1) ◽  
pp. 39-52 ◽  
Author(s):  
Sebastian Weber ◽  
Walter Traunspurger
Keyword(s):  
Species Composition ◽  
Cyprinus Carpio ◽  
Juvenile Fish ◽  
Natural Habitat ◽  
Fish Predation ◽  
Trophic Levels ◽  
Free Living ◽  
Food Web Ecology ◽  
Freshwater Pond ◽  
Predation Effects

Free-living nematodes are well recognised as an abundant and ubiquitous component of meiobenthic communities, where they serve as a link between microbial production and higher trophic levels. However, the effect of fish predation on nematode assemblages is almost unknown. In this study, the predation effects of the benthivorous juvenile carp (Cyprinus carpio) on nematode abundance, biomass, diversity and species composition in the littoral zone of a natural freshwater pond were examined over 310 days using field enclosures and exclosures. Fish predation altered the abundance and biomass of nematodes, and especially of the dominant species Tobrilus gracilis, Eumonhystera filiformis and Monhystera paludicola/stagnalis. Species richness and species composition, but not the diversity and feeding type of nematode assemblages, were affected by fish predation. Our study provides insights into the food-web ecology of lakes and the first evidence of freshwater fish predation effects on nematode assemblages in a natural habitat.

Does the quantity and timing of fresh water flowing into a dry tropical estuary affect year-class strength of barramundi (Lates calcarifer)?

2004 ◽  
Vol 55 (8) ◽  
pp. 787 ◽  
Author(s):  
Jonathan Staunton-Smith ◽  
Julie B. Robins ◽  
David G. Mayer ◽  
Michelle J. Sellin ◽  
Ian A. Halliday
Keyword(s):  
Fresh Water ◽  
River Flow ◽  
Juvenile Fish ◽  
Early Life History ◽  
Relative Strength ◽  
Estuarine Fish ◽  
Causal Mechanism ◽  
Lates Calcarifer ◽  
Nursery Habitats ◽  
Class Strength

The influence of fresh water flowing into estuaries on biological processes, such as recruitment of juvenile fish, is poorly understood, but important if freshwater resources are to be managed sustainably. Typically, lagged correlations between freshwater flows and fisheries production (i.e. catch) are used to support speculation that flows affect the survival of fish (and thus year-class strength) during their first year of life. The present study compares the relative strength of year classes in an estuarine fish population with two indices of fresh water flowing into the estuary, river flow and coastal rainfall. Year-class strength was estimated from a subset of the age structure of commercially caught adult barramundi (Lates calcarifer), which were sampled at seafood processors for three consecutive years. Strong and coherent fluctuations in year-class strength were observed. Positive correlations were found between the abundance of year classes (accounting for age) and quantity of fresh water flowing into the estuary during spring and summer, when barramundi spawn and young-of-the-year recruit to nursery habitats. Regression analysis was used to explore the relationships between year-class strength and environmental variables. A possible, but unproven, causal mechanism for the relationship is that the quantity of fresh water flowing into the estuary during spring and summer influences the survival of early life-history stages of barramundi (i.e. juvenile recruitment) by altering accessibility, productivity and or carrying capacity of nursery habitats.

scholarly journals Investigating the Need to Reintroduce a Ballot Requirement for a Protected Strike in South Africa

Obiter ◽  
2019 ◽  
Vol 40 (2) ◽  
Author(s):  
Mlungisi Tenza
Keyword(s):  
South Africa ◽  
The Other ◽  
Bill Of Rights ◽  
Labour Relations ◽  
Other Hand ◽  
Long Run ◽  
Meaningful Role ◽  
Counter Argument

The issue of violent and protracted strikes has been a source of debate on many labour platforms in South Africa. Unions believe that if a ballot is introduced as one of the requirements for a protected strike in South Africa, it will be abused by employers and manipulated as was the case under the old Labour Relations Act. A counter- argument is that no one can take away a right in the Bill of Rights unless the prescribed procedure in the Constitution is followed. A right in the Bill of Rights can also not be limited unless the limitation is in terms of section 36 of the Constitution. Of particular importance to this issue is not the number of strikes in South Africa but their nature (which has been violent) and their duration (which has been unreasonably long). The violent nature of strikes is a major concern for employers, society and non-striking employees. Violent and lengthy strikes are dangerous to both employers and employees. The employer suffers loss of profit and loss of clients with the possibility of reducing its workforce or closing its business. Employees, on the other hand, face retrenchments if the business is not making a profit. The article argues that the reintroduction of a ballot requirement will play a meaningful role in reducing the number of strikes and their duration. Balloting employees prior and during the course of a strike will help test whether employees have the appetite for the strike. The article further argues that if long strikes can be reduced through ballots, dismissal on the basis of operational requirements could be avoided. In the long run, poverty arising from high levels of unemployment could be avoided.

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