Salinity ranges of some southern African fish species occurring in estuaries     

A.K. Whitfield  S.J.M. Blaber  D.P. Cyrus 《African Zoology》2013,48(3):151-155

The recorded salinity ranges of 96 fish species occurring in southern African estuaries are documented. Factors influencing the tolerance of fishes to low and high salinity regimes are discussed, with most species tolerant of low rather than high salinity conditions. This is important since most systems are subject to periodic freshwater flooding, especially during summer. The penetration of freshwater teleosts and elasmobranchs into estuaries is examined and the occurrence of marine fishes in rivers documented. Mortalities arising from salinity extremes in southern African estuaries are discussed, with temperature a key factor initiating such fish kills. Only eight fish species have been recorded spawning in estuaries although the fry of many species are attracted to estuarine waters. It is concluded that a small percentage of southern African fishes have succeeded in utilizing estuaries and this may be attributed to the paucity of strong osmoregulators  相似文献   

Factors Influencing the Recruitment of Juvenile Fishes into the Mhlanga Estuary     

A. K.Whitfield 《African Zoology》2013,48(3):166-169

The migration of juvenile fishes (<5 cm) into the temporarily open Mhlanga estuary was monitored to determine the effects of different opening periods on immigration. The estuary opened at the end of January 1978 following a nine month closed phase. Only two marine species were recorded entering the estuary in February, compared to 11 species in November 1978. The estuary was closed between April and September. The large November recruitment may be attributed to the abundance of juvenile fishes in the sea adjacent to the estuary, whereas by February very few juveniles were present in Natal inshore waters. Estuarine and freshwater fish species were found to breed inside the estuary during the closed phase when environmental conditions were relatively stable. Mechanisms employed by these species to prevent eggs and larvae from being swept out to sea are discussed, as are strategies used by marine species to ensure recruitment during the very short open phase of the estuary.  相似文献   

Birds as major predators of fishes in the East Kleinemonde Estuary     

Paul D Cowley  Anja I Terörde  Alan K Whitfield 《African Zoology》2017,52(3):147-154

This study provides a quantitative account of fish predation by piscivorous birds in the temporarily open/closed East Kleinemonde Estuary and represents the first global attempt to simultaneously relate such consumption to production by a fish community in the same estuary. Cormorants and herons were the dominant predators and seasonal variations in the avifaunal community composition were noted. Based on comprehensive counts over three years, the piscivorous bird population was estimated to have consumed a maximum of 4 414?kg of fish in 1994, 2 400?kg in 1995/96 and 2 960?kg in 2004/05. In 1995/96 fish production in the East Kleinemonde Estuary (55.89?g m^?2 a^?1) was estimated at 9 780?kg and maximum bird predation amounted to 25% of annual fish production within the system over the same period, assuming that all birds counted on the estuary foraged there and that the diet of these birds comprised only fish. The above 1995/96 figures, together with an estimate of fish predation by the dominant piscivorous fish Lichia amia of 696?kg suggests that birds are probably the single most important natural predator of fishes within this estuary. An unusual mass invasion by marine Cape Cormorants Phalacrocorax capensis during July 1994 was responsible for large-scale predation of fish (2 155?kg) and resulted in the population of estuary-associated marine fishes declining from approximately 63 300 to about 18 600 individuals during the 1994 closed phase. Given that little or no marine fish recruitment was possible while the estuary mouth was closed, piscivorous birds are likely to have a higher predatory impact on populations of juvenile marine fishes in small temporarily closed estuaries than in larger permanently open systems.  相似文献   

The ways in which fish use estuaries: a refinement and expansion of the guild approach          下载免费PDF全文

Ian C Potter  James R Tweedley  Michael Elliott  Alan K Whitfield 《Fish and Fisheries》2015,16(2):230-239

This study refines, clarifies and, where necessary, expands details of the guild approach developed by Elliott et al. (2007, Fish and Fisheries 8 : 241–268) for the ways in which fish use estuaries. The estuarine usage functional group is now considered to comprise four categories, that is, marine, estuarine, diadromous and freshwater, with each containing multiple guilds. Emphasis has been placed on ensuring that the terminology and definitions of the guilds follow a consistent pattern, on highlighting the characteristics that identify the different guilds belonging to the estuarine category and in clarifying issues related to amphidromy. As the widely employed term ‘estuarine dependent’ has frequently been imprecisely used, the proposal that the species found in estuaries can be regarded as either obligate or facultative users of these systems is supported and considered in the guild context. Thus, for example, species in the five guilds comprising the diadromous category and those in the guilds containing species or populations confined to estuaries are obligate users, whereas those in the marine and freshwater estuarine‐opportunistic guilds are facultative users.  相似文献   

Could movement of neonates from non-host plants affect the potential of polyculture to reduce crop colonisation by pest insects?     

D.R. George  R. CollierC. Whitfield  G. Port 《Crop Protection》2011,30(8):1103-1105

Existing and impending constraints to the use of synthetic pesticides, along with changing legislation in favour of an integrated approach to pest management, are driving uptake of ‘alternative’ approaches to pest control. Polyculture is one such approach, often relying upon the presence of non-host plants within the crop to reduce colonisation by pest insects. The diamondback moth, Plutella xylostella (L.), is known to oviposit on non-host plants and the present study showed that neonates were able to move relatively large distances, enabling them to relocate from non-host natal plants to nearby hosts. Although fewer larvae were found on host plants when they hatched on non-hosts, it is concluded that even a low level of re-location of neonates could potentially reduce the potential for polyculture to control this pest. It is proposed that non-host oviposition and neonate movement could explain why polyculture sometimes fails in controlling pest insects.  相似文献   

Modes of ingress by larvae and juveniles of marine fishes into estuaries: From microtidal to macrotidal systems     

Alan K. Whitfield  Ian C. Potter  Francisco J. Neira  Edward D. Houde 《Fish and Fisheries》2023,24(3):488-503

We review published research on the ingress of larvae and early juveniles of marine fishes into estuaries subjected to different tidal regimes and provide perspectives on the abilities and responses of these early-life stages to the physico-chemical, hydrodynamic and biological drivers that facilitate such ingress. We focus on documenting ingress and the mechanisms employed by early-stage fishes from coastal waters to enter different types of microtidal and macrotidal estuaries but also include information on ingress into mesotidal systems. Spawning localities for estuary-associated marine fishes are assessed with respect to ontogeny of larvae and their ability to ingress estuaries during the preflexion and postflexion stages. The processes and physico-chemical cues employed by larvae and early juveniles to locate estuaries are reviewed, with olfactory cues being recognised as especially important. Particular emphasis is directed to vertical migratory behaviours and selective tidal stream transport (STST) employed by many larvae ingressing macrotidal estuaries, contrasting with mainly passive flood-tide entry and active swimming modes typically used by larvae and early juveniles that enter microtidal estuaries and estuarine lakes and lagoon systems.  相似文献   

Effects of stage of growth,irrigation frequency and gypsum treatment on CO2 exchange of lucerne (Medicago sativa L.) grown on a heavy clay soil     

D. M. Whitfield  G. C. Wright  O. A. Gyles  A. J. Taylor 《Irrigation Science》1986,7(3):169-181

Summary Effects of weekly (W) and fortnightly (F) irrigation schedules on CO₂ assimilation by lucerne grown on untreated (C) and gypsum-ameliorated (G) heavy clay soil were investigated. Leaf area limited rates of assimilation during the initial stages of regrowth, but rates of up to 9 g CO₂ m^–2 h^–1 were measured once full ground cover was achieved after approximately two weeks. High rates were maintained until the fifth week of regrowth (one week after full flower), after which there was a marked decline.During the fourth week of regrowth, afternoon rates of canopy photosynthesis under less frequent irrigation were less than those measured at similar irradiance during the morning. This was evidenced as hysteresis in the light response curves and was apparent in all treatment during the final stages of the experiment.For the first five weeks of regrowth, daytime integrals of photosynthesis were directly related to the amount of light intercepted by the crops. The mean efficiency of utilisation of light in CO₂ assimilation was 6.2 g CO₂ MJ^–1 in all treatments apart from that on untreated soil under the fortnightly irrigation regime (treatment F_C). Its mean efficiency was 5.1 g CO₂ MJ^–1. The amounts of CO₂ assimilated exceeded the growth and respiratory requirements of the above-ground components of the crops, and it was estimated that 25% and 40% of the assimilated carbon was partitioned to and retained in the roots and crowns of the weekly and fortnightly irrigated crops, respectively.Results are appraised in terms of the response of lucerne to moisture deficits. Implications for above-ground dry matter production are also discussed.  相似文献   

Gene expression profiles in the brain predict behavior in individual honey bees   总被引：2，自引：0，他引：2  

Whitfield CW  Cziko AM  Robinson GE 《Science (New York, N.Y.)》2003,302(5643):296-299

We show that the age-related transition by adult honey bees from hive work to foraging is associated with changes in messenger RNA abundance in the brain for 39% of approximately 5500 genes tested. This result, discovered using a highly replicated experimental design involving 72 microarrays, demonstrates more extensive genomic plasticity in the adult brain than has yet been shown. Experimental manipulations that uncouple behavior and age revealed that messenger RNA changes were primarily associated with behavior. Individual brain messenger RNA profiles correctly predicted the behavior of 57 out of 60 bees, indicating a robust association between brain gene expression in the individual and naturally occurring behavioral plasticity.  相似文献   

A weight‐of‐evidence approach to determine estuarine fish health using indicators from multiple levels of biological organization     

N. Richardson  A. K. Gordon  W. J. Muller  A. K. Whitfield 《水产资源保护:海洋与淡水生态系统》2011,21(5):423-432

The guild approach to categorizing estuarine fish assemblages: a global review   总被引：5，自引：0，他引：5  

Michael Elliott  Alan K Whitfield  Ian C Potter  Stephen J M Blaber  Digby P Cyrus  Frank G Nordlie  & Trevor D Harrison 《Fish and Fisheries》2007,8(3):241-268

Many studies have recently described and interpreted the community structure and function of fishes inhabiting estuaries and other transitional waters in terms of categories or guilds. The latter describe the main features of the fishes’ biology and the way in which they use an estuary. However, the approach has been developed by different workers in different geographical areas and with differing emphasis such that there is now a need to review the guilds proposed and used worldwide. The previous wide use of the guild approach has involved increasing overlap and/or confusion between different studies, which therefore increases the need for standardization while at the same time providing the opportunity to reconsider the types and their use worldwide. Against a conceptual model of the importance of the main features of fish use in estuaries and other transitional waters, this review further develops the guild approach to community classification of fish communities inhabiting those areas. The approach increases the understanding of the use of estuaries by fishes, their interactions and connectivity with adjacent areas (the open sea, coastal zone and freshwater catchments) and the estuarine resources required by fishes. This paper gives a global perspective on this categorization by presenting new or refined definitions for the categories, lists the synonyms from the literature and illustrates the concepts using examples from geographical areas covering north and central America, north and southern Europe, central and southern Africa, Australia and the Indo‐Pacific.  相似文献