ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1990.tb05014.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Evidence of the collapse and recovery of major marine fisheries for pelagic fish species is reviewed, distinguishing the influence of fishing compared with natural (environmental) effects. In one only of the best documented cases (Icelandic spring‐spawning herring) has the stock failed to reappear, after 20 years. Several others, e.g. California sardine, have persisted at 1/000th or possibly less of their peak size for some years before beginning to recover. Fishing has been the main cause of collapse in most but not all cases, due initially to the escalation of catchability as stock size decreases–a phenomenon characteristic of fisheries for pelagic species due to their shoaling habit, ease of detection and vulnerability to modern fishing methods. It is concluded that although the threat of fishing to the continuity of the species is remote, excessive depletion (although avoidable by firm and timely management) is potentially able to cause temporary disappearance of local stock and disruption of the ecosys

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1990.tb05015.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The piscivorous Nile perch was introduced into Lake Victoria some 30 years ago, since when it has completely transformed the fishing industry and the species composition of the fish fauna of the lake. The original multispecies fishery, based mostly on cichlids (haplochromines, tilapias), cyprinids (Barbus, Labeo, Rastrineobola) and siluroids (Bagrus, Clarias, Synodontis, Schilbe), has changed dramatically to one based on three species: the introduced Nile perch, the cyprinids,Rastrineobola argenrea(Pellegrin), and the introduced Nile tilapia,Oreochromis niloticus(Linnaeus).Within 25 years of its introduction the Nile perch became ubiquitous and now occurs in virtually every habitat with the exception of swamps and affluent rivers. It has preyed on all other species with profound effects, especially on the stocks of haplochromines. These originally comprised 80% of the total fish biomass in Lake Victoria, but have now decreased to less than 1% offish catches from the Kenyan waters of the lake. The fishermen of Lake Victoria have adjusted to this ecological crisis by using large‐meshed nets to catch Nile perch, which has become the most important commercial species. For the first time in the history of Lake Victoria, fish fillets are now being exported to several overseas countries: the fillets are all from Nile perc

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1990.tb05016.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The longfin sculpin,Jordania zonopeStarks, 1895, and the scalyhead sculpin,Artedius harringtoni(Starks, 1896), arecommon subtidal cottids in the San Juan Archipelago, Washington, but little of their autecology has been investigated. Comparisons of distribution, microhabitat density, foraging behaviour and diet were conducted for the two species. Even though the two species occurred close together, microhabitat use differed between them, as did foraging strategies. Jordania zonope had a broader foraging range and tended to take bites out of prey items, whereas A. harringtoni had a more limited foraging range and tended to swallow prey whole. Partitioning of spatial and nutritional resources as well as morphological differences supported the hypothesis that J. zonope and A. harringtoni minimize interspecific competition in spite of microhabitat overlap and often side‐by‐side feed

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1990.tb05923.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Populations of chum salmon,Oncorhynchus keta, are recognizable by the allelic frequencies of allozyme loci. Identification of these was used to assess the return of spawning adults to alien rivers into which they were introduced via hatchery‐reared, artificially‐fertilized eggs obtained from populations elsewhere in the Soviet Far East. Coefficients of return to spawn in the alien rivers were much lower than returns for the native fish, and in succeeding generations the alien fish disappeared from the spawning runs. It is concluded that transplanting salmonid eggs between populations is ineffective as a means of establishing new stock in territory already occupied by another stock, and the practice is deplored on grounds of conserving unique gene pools within spec

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1990.tb05017.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Compensatory growth is the phase of rapid growth, greater than normal or control growth, which occurs upon adequate refeeding following a period of undernutrition. The effect of feed cycling periods (periods of starvation followed by periods of refeeding), ration level and repetitive feed cycles on the compensatory growth response in rainbow trout were evaluated in two experiments. A feeding cycle of 3 weeks starvation and 3 weeks feeding produced better results in terms of average percentage changes in weight and length, and in specific growth rate, than either 1 week and 1 week or 2 weeks and 2 weeks feed cycles. The fish on the 3 weeks starvation and 3 weeks feeding cycle did as well as, if not better than, the constantly fed controls over one or two complete cycles, though the controls were fed more than twice the amount of feed. Three ration levels were compared using a 3‐week starvation and 3‐week feeding period. The only effect of increasing ration level was to decrease conversion efficiency, indicating overfeeding. Carcass analysis of moisture, fat, protein and ash showed no significant differences between the controls and an experimental group on a 3 weeks starvation, 3 weeks feeding cycle after one complete cycle. Possible mechanisms underlying the compensatory growth response are discus

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1990.tb05924.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

New Zealand's small freshwater fish fauna has been augmented by introductions of exotic species, primarily salmonids. Brown and rainbow trout have been successful and the chinook salmon has established anadromous populations. Although few explicit data are available, it appears that addition of large salmonids has had harmful impacts on some indigenous species, particularly several galaxiids; these appear to result from predation and competitive exclusion. Interactions may be chronic or catastrophic. It is difficult to determine causes of chronic interactions, many instances of which are likely to be occurring and escaping notice. Further, it is difficult to separate the effects of human‐induced habitat deterioration from inter‐specific interactions. Catastrophic interactions are much easier to observe but even here determining the nature of interactions and ascribing causes is fraught with difficult

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1990.tb05018.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Some physiological parameters were measured in adult rainbow trout during a 10‐day exposure to 180 μg Altotall−1in acid water (pH 4.7) with or without humic substances (10 mg l−). The fish were acclimatized to pH 5.0 for 7 days prior to the experimental treatments.Chemical analyses revealed that, in the presence of human substances, 74–80% of the A1 was organic bound, while in the absence of humic substances most of the Al(987percnt;) occurred in the inorganic form.Al bound to humic substances (13–150 μg l−1) did not alter the plasma NaCl‐concentration, nor the haematocrit value, of rainbow trout during an exposure period of 10 days. This contrasts with the high death rate obtained within 2–3 days when most of the A1 (175 μg l−1) was in the inorganic form. The lethality was accompanied by a 25% decrease in the plasmaconcentration of NaCl and a doubling of the haematocrit value. Bulk analysis revealed that when the metal was present in inorganic forms the total Al content of the gills (75 μg A1 g−1wet weight) was 15 times higher than when it was present as bound to the humic substances. These experiments showed that the accumulation of A1 at the gills was accompanied by physiological disturbances, both being a function of the ch

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1990.tb05925.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The upper Tennessee River drainage, which includes portions of the States of Virginia, North Carolina, and Tennessee, supports an exceptionally diverse fish fauna. Recent reductions in abundance and geographic ranges of several freshwater fishes have promulgated the imposition of protective measures for about 115 species among the three states, with nearly half of those species occurring in the upper Tennessee River. Most protected species are darters (Percidae: Etheostomatinae) or minnows (Cyprinidae), and are typically small, benthic invertivores. Major impacts on the fish fauna have resulted from dams, introduced species, toxic spills, mining and agriculture. An important cumulative effect of these impacts is fragmentation of the watershed; nearly 40% of the riverine habitat in major tributaries is either impounded or altered by tailwater discharges. The isolation and stress imposed on tributaries of the river have caused and will continue to cause extirpations of fishes, mussels and other aquatic fauna. Numerous federal, state, and private organizations are co‐operating in efforts to protect rare species and habitats, improve agricultural and coal‐producing practices, and enforce regulations for industrial and municipal efflue

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1990.tb05019.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The global trade in ornamental fish and associated aquarium and pond accessories is in excess of U.S. $7 × 109each year. Although the majority of freshwater fish involved in the trade are from captive‐bred sources, significant numbers are still removed from the wild. In addition, almost all of the marine fish in the trade are wild‐caught. Whilst habitat destruction, pollution and overfishing for food are the main threats facing fish populations in the wild, the ornamental fish trade may have adverse effects as a result of the introduction of nonnative organisms, and by the direct depletion of wild stocks. The ornamental fish trade is ideally placed to raise public awareness of, and actively support, fish conservation efforts, and must maintain a close liaison with legislative‐forming organizations seeking to impose further trade restri

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1990.tb05020.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY