Showing papers on "Fishing published in 1998"

Fishing Down Marine Food Webs

Abstract: The mean trophic level of the species groups reported in Food and Agricultural Organization global fisheries statistics declined from 1950 to 1994. This reflects a gradual transition in landings from long-lived, high trophic level, piscivorous bottom fish toward short-lived, low trophic level invertebrates and planktivorous pelagic fish. This effect, also found to be occurring in inland fisheries, is most pronounced in the Northern Hemisphere. Fishing down food webs (that is, at lower trophic levels) leads at first to increasing catches, then to a phase transition associated with stagnating or declining catches. These results indicate that present exploitation patterns are unsustainable.

The effects of fishing on marine ecosystems

Abstract: We review the effects of fishing on benthic fauna, habitat, diversity, community structure and trophic interactions in tropical, temperate and polar marine environments and consider whether it is possible to predict or manage fishing-induced changes in marine ecosystems Such considerations are timely given the disillusionment with some fishery management strategies and that policy makers need a scientific basis for deciding whether they should respond to social, economic and political demands for instituting or preventing ecosystem-based management Fishing has significant direct and indirect effects on habitat, and on the diversity, structure and productivity of benthic communities These effects are most readily identified and last longest in those areas that experience infrequent natural disturbance The initiation of fishing in an unfished system leads to dramatic changes in fish community structure As fishing intensity increases the additional effects are more difficult to detect Fishing has accelerated and magnified natural declines in the abundance of many forage fishes and this has lead to reduced reproductive success and abundance in birds and marine mammals However, such donor-controlled dynamics are less apparent in food webs where fishes are the top predators since their feeding strategies are rather more plastic than those of most birds and mammals Fishers tend to target species in sequence as a fishery develops and this leads to changes in the composition of the fished communities with time The dramatic and apparently compensatory shifts in the biomass of different species in many fished ecosystems have often been driven by environmental change rather than the indirect effects of fishing Indeed, in most pelagic systems, species replacements would have occurred, albeit less rapidly, in the absence of fishing pressure In those cases when predator or prey species fill a key role, fishing can have dramatic indirect effects on community structure Thus fishing has shifted some coral reef ecosystems to alternate stable states because there is tight predator–prey coupling between invertebrate feeding fishes and sea urchins Fishing has reduced, and locally extirpated, populations of predatory fishes These reductions do not have a consistent effect on the abundance and diversity of their prey: environmental processes control prey populations in some systems, whereas top-down processes are more important in others By-catch which is discarded during fishing activities may sustain populations of scavenging species, particularly seabirds We conclude by identifying the circumstances in which new research is needed to guide managers and stress the importance of unfished control sites for studies of fishing effects We discuss the advantages and disadvantages of closed area management (marine reserves) and the conditions under which such management is likely to provide benefits for the fishery or ecosystem

Fishing, trophic cascades, and the structure of algal assemblages : evaluation of an old but untested paradigm

Abstract: Removal of important predators by fishing can result in trophic cascades and indirect effects on marine benthic communities. Indirect effects are especially evident when prey populations released from predation by fishing have the ability to modify entire benthic communities as do sea urchins Sea urchins have been shown to dramatically alter the underwater landscape by grazing, by converting stands of large erect algae into coralline barrens. In the western Mediterranean, a recent extension of coralline barrens into areas formerly dominated by erect algal assemblages has been attributed to release of predation on sea urchins by overfishing. Most suggestions concerning the transition form erect algeal assemblages to coralline barrens, however, have been speculative, and little descriptive and experimental work has been carried out to verify the hypothesis that fish predation on sea urchins (and its subsequent release by overfishing) drives this transition. Here we critically review the literature concerning the effect of fishing on sea urchin populations and its subsequent maintenance of different algal assemblages in the Mediterranean. The extant data cannot refute the fishes as important predators model. but we argue that other processes trecruitment, pollution, disease, large-scale oceanographic events, sea urchin harvesting, food subsidies, and availability of shelters) may also be important in regulating the structure of Mediterranean algal assemblages.

Large-scale disturbance and the structure of marine systems: fishery impacts on georges bank

Abstract: Georges Bank, a shallow submarine plateau located off the New England coast, has supported valuable commercial fisheries for several centuries. The region is characterized by high levels of primary productivity and, historically, high levels of fish production. Within the last four decades Georges Bank has been subjected to major perturbations that have profoundly altered levels of catch, abundance, and species composition. The arrival of distant water fleets during the early 1960s resulted in dramatic increases in effective fishing effort and the subsequent commercial collapse of several fish populations. Total fish biomass is estimated to have declined by >50% on Georges Bank during the period of operation of the distant water fleets. The implementation of extended jurisdiction (the 200-mile [370.4-km] limit) in 1977 was followed by modernization and increased capacity of the domestic fleet, resulting in a second perturbation to the system that resulted in further declines in groundfish populations to h...

The effects of fishing on marine ecosystems and communities

Abstract: Trends in world fisheries removing target species the problem of by-catch and discards effects on soft-sediment benthos fishing and nutrient dynamics coral reefs and dynamite don't mix fishing at the coastal margins.

Can shark resources be harvested sustainably? A question revisited with a review, of shark fisheries

Abstract: Sharks and other chondrichthyans are often described as long lived, slow growing and producing few offspring. These biological characteristics, together with the common assumption that recruitment is directly related to stock, and pessimistic stock prognoses obtained from application of demographic analysis, have led to doubts that sharks can be harvested sustainably. Developed over the past 40 or so years from studies of only a few shark species, these doubts have been reinforced by declining catch rates in industrial, artisanal and recreational fisheries and in fishing programmes designed to reduce the risk of sharks attacking humans at bathing beaches. However, more recent studies and application of modelling techniques allowing for density-dependent responses to the effects of stock reduction indicate that shark stocks can be harvested sustainably and, if carefully managed, can provide very stable fisheries. It is now understood that some species (such as Galeorhinus galeus, Carcharhinus plumbeus, Carcharodon carcharias and several species of dogfish) have low productivity, whereas other species (such as Mustelus antarcticus, Rhizoprionodon terraenovae, Sphyrna tiburo and Prionace glauca) have higher productivity. This paper reviews the use of shark products, the effects of fishing on shark populations of the world, and recent developments in assessment of shark fishery stocks.

Disturbance of the marine benthic habitat by commercial fishing: impacts at the scale of the fishery

Abstract: Commercial fishing is one of the most important human impacts on the marine benthic environment. One such impact is through disturbance to benthic habitats as fishing gear (trawls and dredges) are dragged across the seafloor. While the direct effects of such an impact on benthic communities appear obvious, the magnitude of the effects has been very difficult to evaluate. Experimental fishing-disturbance studies have dem- onstrated changes in small areas; however, the broader scale implications attributing these changes to fishing impacts are based on long-term data and have been considered equivocal. By testing a series of a priori predictions derived from the literature (mainly results of small-scale experiments), we attempted to identify changes in benthic communities at the regional scale that could be attributed to commercial fishing. Samples along a putative gradient of fishing pressure were collected from 18 sites in the Hauraki Gulf, New Zealand. These sites varied in water depth from -17 to 35 m and in sediment characteristics from -1 to 48% mud and from 3 to 8.5 (Lg chlorophyll a/cm3. Video transects were used for counting large epifauna and grab/suction dredge and core sampling were used for collecting macrofauna. After accounting for the effects of location and sediment characteristics, 15-20% of the variability in the macrofauna community com- position sampled in the cores and grab/suction dredge samples was attributed to fishing. With decreasing fishing pressure we observed increases in the density of echinoderms, long- lived surface dwellers, total number of species and individuals, and the Shannon-Weiner diversity index. In addition, there were decreases in the density of deposit feeders, small opportunists, and the ratio of small to large individuals of the infaunal heart urchin, Echino- cardium australe. The effects of fishing on the larger macrofauna collected from the grab/ suction dredge samples were not as clear. However, changes in the predicted direction in epifaunal density and the total number of individuals were demonstrated. As predicted, decreased fishing pressure significantly increased the density of large epifauna observed in video transects. Our data provide evidence of broad-scale changes in benthic communities that can be directly related to fishing. As these changes were identifiable over broad spatial scales they are likely to have important ramifications for ecosystem management and the development of sustainable fisheries.

Application of marine reserves to reef fisheries management

Abstract: Establishing permanent ‘no-take’ marine reserves, areas where fishing and all other extractive activities are prohibited, is an attractive but under-utilized tool for fisheries management. Marine reserves could potentially deal with many fishery problems that are not effectively addressed by other traditional management measures; they also offer numerous social, economic, and scientific benefits not directly related to fisheries. Limited but growing research has shown beneficial biological and economic effects of marine reserves on fisheries. More research is needed, especially at larger scales, to determine the ideal marine reserve size, number and location necessary to optimize fisheries productivity and resource conservation. Sufficient evidence is available to justify the expanded use of marine reserves in an adaptive approach to fisheries management.

Cephalopod and groundfish landings: evidence for ecological change in global fisheries?

Abstract: Cephalopod fisheries are among the few still with some local potential for expansion; in fact, as groundfish landings have declined globally, cephalopod landings have increased. We propose the hypothesis that, although increased cephalopod landings may partly reflect increased market demand, overfishing groundfish stocks has positively affected cephalopod populations. Data from 15 key FAO areas reveal that, with the exception of the north- east Atlantic, cephalopod landings have increased significantly over the last 25 years while groundfish have risen more slowly, remained stable, or declined. In terms of volume, cephalopods have not replaced groundfish. This is hypothesized as owing to the shorter life cycle of cephalopods, and rapid turnover and lower standing stocks than for longer-lived finfish species. Under high fishing pressure, groundfish are probably poor competitors, having less opportunity for spawning and replacement. In West Africa, the Gulf of Thailand and Adriatic there is strong circumstantial evidence that fishing pressure has changed ecological conditions and cephalopod stocks have increased as predatory fish have declined. We recommend that this hypothesis be tested thoroughly in other areas where suitable data exist. Most coastal and shelf cephalopod fisheries are likely to be fully exploited or overexploited, and current annual fluctuations in cephalopod landings are probably largely environmentally-driven.

Historical Abundance and Decline of Chinook Salmon in the Central Valley Region of California

Abstract: The Central Valley drainage of California formerly produced immense numbers of chinook salmon Oncorhynchus tshawytscha. Four seasonal runs occur in this system—fall, late-fall, winter, and spring runs. Differences in life history timing and spatial distribution enabled the four runs to use the drainage to the fullest possible extent and once made it one of the richest regions in the world for chinook salmon production. Native American fishers within the Central Valley drainage harvested chinook salmon at estimated levels that reached 8.5 million pounds or more annually. Native harvests, therefore, were roughly comparable to the peak commercial harvests taken later by Euro-American fishers, but whether or not native fishing depressed the productive capacities of the salmon populations to any substantial degree is not known. The commercial chinook salmon fishery in California started about 1850 in the San Francisco Bay and Sacramento–San Joaquin Delta region, where it formed the nucleus of the firs...

Marine Reserves: What Would They Accomplish?

Abstract: A marine reserve is defined as a subset of the area over which a fish stock is dispersed and closed to fishing. This paper investigates what will happen to fishing outside the marine reserve and to the stock size in the entire area as a result of establishing a marine reserve. Three regimes are compared: (i) open access to the entire area, (ii) open access to the area outside the marine reserve, and (iii) optimum fishing in the entire area. Two models are used: (i) a continuous-time model, and (ii) a discrete-time model, both using the logistic growth equation. Both models are deterministic equilibrium models. The conservation effect of a marine reserve is shown to be critically dependent on the size of the marine reserve and the migration rate of fish. A marine reserve will increase fishing costs and overcapitalization in the fishing industry, to the extent that it has any conservation effect on the stock, and in a seasonal fishery it will shorten the fishing season. For stocks with moderate to high migr...

Marine Reserves: from Beverton and Holt to the Present

Abstract: The idea of using marine reserves, where all fishing is banned is not new to fisheries management. It was first formally considered by Beverton and Holt but rejected in favour of approaches such as fleet and gear control. Since that analysis, many fisheries have collapsed worldwide, illustrating the vulnerability of fishery resources and the ineffectiveness of these approaches. Empirical data and modelling suggest that marine reserves would generally increase yields, especially at the high fishing mortality that occurs in most fisheries. However, the most interesting feature of reserves is their ability to provide resilience to overexploitation, thereby reducing the risk of stock collapse. Benefits from reserves come from the increase in biomass and individual size within them, resulting in adult migration and/or larval dispersal that would replenish fishing grounds. The use of marine reserves in managing fisheries necessitates a thorough understanding of critical habitat requirements, fish movement, fish behaviour, the relations between subpopulations and the critical density effect for larval dispersal. When properly designed, and coupled with other management practices, reserves may provide a better insurance against uncertainties in stock assessment, fishing control and management by protecting a part of the population from exploitation. This strategy can be used for both sedentary and migratory species.

An ecological view of the tuna--dolphin problem: impacts and trade-offs

Abstract: After a brief description of purse seining and the other methods used to catch yellowfin tuna in the eastern Pacific Ocean, some consideration s are made on the tuna--dolphin association and the solution of the problem of dolphin mortality in the eastern Pacific The association has been observed in other ocenas, but the frequency of setting in the eastern Pacific is much greater The mortalities of dolphins through fishing have declined from about 133 000 in 1986 to around 2600 in 1996 The impact of recent levels of mortality on the dolphin populations is not significant from the population point of view The mortality levels for all the stocks are less than 01%, much lower than the 2% value used as a conservative (low) estimate of net recruitment All dolphin stocks have population sizes between 400 000 and 2 200 000, and most have remained stable for a decade or more Fishing operations can cause ecological impacts of different types: bycatches, damage to the habitat, mortality caused by lost or discarded gear, pollution, generation of marine debris, etc A brief discussion follows, with a more detailed look at the bycatches For convenience we can separate the effects of the fishery on the target species, and on other species Of the different ways of purse seining for tunas, sets on dolphins catch tuna close to the optimum size to maximize yields and to allow for reproduction, and result in discards of tunas of less than 1% of the catch Sets on logs catch small tunas, and result in the highest tuna discards (20--25%) School sets fall in the middle from the point of view of the sizes caught Obviously, from the ecological point of view, sets on dolphins are the best way to harvest yellowfin tuna After a discussion of the different ecological impacts a fishery can cause to other species on the habitat, a comparison is made of the bycatches generated by the different types of purse seine sets Billfishes, sharks, mahi-mahi, wahoo and sea turtles are taken as incidental catches by purse seiners Log sets produce, by far, the largest bycatches, followed by school sets and dolphin sets in that order The bycatch levels in log sets are usually tens to hundreds of times those in dolphin sets The difference can be attributed to the selection caused by the speed of movement of the tuna--dolphin group (slow-moving species or individuals cannot keep up with the group), an effect that may be magnified by the chase that precedes the dolphin sets Log sets, on the other hand, are made on a drifting community The alternatives left to the fishers if they were forced to switch from the current fishing methods to others are briefly discussed, considering their feasibility, and comparing their ecological costs From the ecological point of view, and considering that the dolphin mortality is clearly sustainable, the impacts caused by the other types of sets, especially log sets, could be more significant than those caused by the dolphin sets Some of the species taken in log sets are endangered (eg sea turtles), others have unknown status and potential vulnerability because of their low reproductive and juvenile survival rates (eg sharks) Overall, the biodiversity of the eastern Pacific appears to be better preserved by a fishery directed to dolphin sets than the other alternatives proposed for the purse seine and for other gears

Effects of Otter Trawling on a Benthic Community in Monterey Bay National Marine Sanctuary

Abstract: Bottom trawling is one of the most disruptive and widespread human-induced physical distur- bances to seabed communities and has become a global environmental concern. We used a comparative ap- proach to test the hypothesis that persistent otter trawling decreases bottom habitat complexity and biodiver- sity, increases the abundance of opportunistic species, and benefits prey important in the diet of some commercially valuable fish. We compared two similar and adjacent fishing areas at 180 m off central Califor- nia in Monterey Bay National Marine Sanctuary: one inside the three-mile coastal zone of restricted fishing with light levels of trawling and one beyond the three-mile limit with high levels of trawling. Differences in fishing effort between the two areas were confirmed and quantified by means of data and tow number statis- tics from Pacific Fishery Management Council (PFMC) Trawl Logbook records. We used still photography, video footage, bottom grab samples, and experimental trawling to compare the physical and biological pa- rameters of the two areas. The area with high levels of trawling had significantly more trawl tracks, exposed sediment, and shell fragments and significantly fewer rocks and mounds and less flocculent material than the lightly trawled area. Most invertebrate epifauna counted were significantly more abundant in the lightly trawled area. The density of the amphinomid polychaete, Chloeia pinnata , as well as that of oligochaetes, oph- iuroids, and nematodes, were higher every year in the highly trawled area, and there were significantly fewer polychaete species every year in the highly trawled area. Content analysis of fish guts showed that C. pinnata was a dominant prey item for some of the commercially important flatfishes in both lightly and heavily trawled areas. Our study provides evidence that high levels of trawling can decrease bottom habitat complex- ity and biodiversity and enhance the abundance of opportunistic species and certain prey important in the diet of some commercially important fishes. Our work also illustrates how constraints currently imposed on fisheries research by the near universal absence of true unfished control sites severely limit our ability to de- termine appropriate levels of harvest pressure for maintaining sustainable fisheries and marine biodiversity. Valid research in these areas will require marine reserves in which fishing effort and methods can be manip- ulated in collaborative studies involving fishers, researchers, and resource agencies.

Small-scale benthic fisheries in chile: on co-management and sustainable use of benthic invertebrates

Abstract: We discuss the issues of sustainable use and management in the Chilean inshore benthic small-scale (artisanal) fisheries. The fishery benefits from two features that make it possible to overcome some of the problems of conventional management. These are: (1) major advances have been made in understanding relevant ecological processes, and (2) this knowledge has been institutionalized in the 1991 Chilean Fishing and Aquaculture Law (FAL). FAL legalizes the use of community-owned shellfish grounds, so-called “Management and Exploitation Areas” (MEA); this practice is considered to confer quasi-property rights to fishers' unions. Management plans for these areas have to be approved by the government. This co-management approach solves one of the major problem in many fisheries: overexploitation. In addition, the study of the MEAs could provide useful information, if they are considered as “replicates,” in evaluating the effect of human perturbation and different management regimes. We think that by using the different tools provided by the FAL on the spatial arrangement of the small-scale fishery and answering certain key ecological questions, the sustainable use of inshore benthic resources in Chile (e.g., gastropods, sea urchins, and algae) via an ecosystem approach can be achieved in the near future.

Short-term effects of fishing on life history traits of fishes

Abstract: An important aspect of species susceptibility to fishing are the changes in demographic characteristics of populations that fishing might induce. The purpose of this study is to show the short-term effects of fishing on growth and reproduction patterns. This assessment is made through a comparative study of key parameters (mortality, size, age and size at maturity, fecundity) among stocks subject to various levels of exploitation. Data have been assembled for 77 separate (primarily commercial) fish stocks.Trait variation is partitioned into effects attributable to size, phylogeny, and population. High adult mortality appears to lead to short-term apparently plastic changes in age and size at maturity: exploited populations are characterized by earlier age and increased size at maturity. This compensatory response to exploitation may conceal longer term selection effects, and may be worth considering in stock assessments.

Fishery‐induced changes in a marine ecosystem: insight from models of the Gulf of Thailand

Abstract: Two mass-balance trophic models are constructed to describe the Gulf of Thailand ecosystem (10–50 m depth): one model pertains to the initial phase of fisheries development, and the other to when the resources were severely depleted. The two phases are compared, and changes brought about by fishing discussed. A dynamic simulation model, Ecosim, is then used successfully to reproduce the 1980 state of the fishery based on the 1963 model and the development in catches. In addition the 1980 model is used to predict how the ecosystem groups may bounce back following marked reduction in fishing pressure. Finally, the 1963 model is used to study alternative scenarios for how the fisheries development could take place, notably the effect of exploiting only the resources of larger species. The study validates that the Ecosim model can be used to predict ecosystem level changes following changes in fishing pressure, therefore fishing induced changes can to a large extent explain the changes in ecosystem pools and fluxes observed over time.

Natural fishing experiments in marine reserves 1983 - 1993: roles of life history and fishing intensity in family responses

Abstract: This study examined the effect of fishing on the abundance and species richness of families of coral reef fish at two islands (Sumilon and Apo) in the Philippines from 1983 to 1993. Natural fishing experiments occurred in marine reserves at each island, where long term estimates of fishing intensity were available. Responses to fishing were interpreted in terms of life histories of fish. The intensity of fishing and fish life histories were generally good predictors of the differential rates of decline and recovery of abundance in response to fishing. Large predators had vulnerable life histories (low rates of natural mortality, growth and recruitment) and were subjected to high intensity fishing. They declined significantly in density when fished and increased significantly but slowly when protected from fishing. Caesionidae, a family with a life history resilient to fishing (high rates of natural mortality, growth and recruitment) but fished intensively also declined rapidly in abundance when fished. Thus, knowledge of life history alone was insufficient to predict response to fishing. Acanthuridae were fished relatively hard and had a life history of intermediate vulnerability but displayed weak responses to fishing. Thus level of fishing intensity alone was also not sufficient to predict response to fishing. For Chaetodontidae, effects of fishing conformed to expectations based on life history and fishing intensity at one island but not the other. Three families with intermediate vulnerability and subjected to intermediate to light fishing (F. Scaridae, Labridae and Mullidae) displayed predictably weak responses to fishing, or counter-intuitive responses (e.g., increasing in abundance following fishing). These counter-intuitive responses were unlikely to be secondary effects of increase in prey in response to declines of predators. Two lightly-fished families with resilient life histories (F. Pomacentridae, Sub F. Anthiinae) predictably displayed weak numerical responses to fishing except during a period of use of explosives and drive nets.

Stock enhancement in Japan : Review and perspective

Abstract: Some species typically used in stock enhancement in Japan were reviewed, and the causes of program success or failure were analyzed in an attempt to determine the best approach for future stocking. Recent successes in salmon stock enhancement are attributed to improvement of the return rate resulting from physiological and behavioral research. In scallop stock enhancement, high quality of seedlings, improvement of the environment, crop rotation, and the marketing system have supported a steady yearly increase in yield. Flounder stock enhancement in Fukushima Prefecture has achieved a 30% recapture rate, and the cost-benefit ratio is estimated to be more than 300%. In the case of red sea bream, because recreational anglers now catch a higher percentage of stocked fish than do commercial fishermen, a new method of fisheries regulation may be required, as recreational anglers now pay only little of the costs of the stocking program. Masu salmon and abalone stocks are best preserved by the protection of spawning grounds. In marine ranching of striped jack, understanding of behavioral ecology seems to be essential for the success of this project and the prevention of genetic pollution. Behavioral quality of stocked fish is a determining factor in the success of stock enhancement, so attempts have been made to improve behavioral quality in several species. Although sea farming projects have been well supported by basic research on diet, physiology, morphology, and behavior, the present authors believe that ecological research in the natural habitat of each species is indispensable for the success of stock enhancement and that the national and prefectural governments should take the initiative in protection of genetic diversity.

Extensive shrimp farming, mangrove clearance and marine fisheries in the southern provinces of Vietnam

Abstract: Within the last decade shrimp farming in the Mekong Delta of Vietnam has increased by 3500%. Shrimp farming became un-sustainable in the early 1990's due to the un-planned development of this industry and the resulting self pollution of the farms, the destruction of mangrove forest and the outbreak of viral diseases. Historical data on fisheries, fishing effort and mangrove coverage were obtained from the province Minh Hai (lately divided in Ca Mau and Bac Lieu). Analysis of catch and effort data of marine fisheries in the Mekong Delta indicated a severe danger of over-exploitation of fish stocks and further decline can be expected if fisheries management only considers the demand for fish. The relation between the total fish catch (t/year), the mangrove area (ha), the engine capacity (HP) of the fishing fleet and the social incentive for fishing could be described with the model: Total catch=0.449*Mangrove area + 0.614 Engine capacity + 654 Social factor. One hectare of mangrove forest supports a marine catch of 450 kg/year

Natural fishing experiments in marine reserves 1983–1993: community and trophic responses

Abstract: This study examined the effect of fishing on the density, biomass, species richness and overall structure of the reef fish community at two islands (Sumilon and Apo) in the Philippines from 1983 to 1993. A series of natural fishing experiments over this period involving marine reserves were monitored at each island, where estimates of fishing intensity and selectivity were available. Fishing intensity (15% and 25% of biomass removed per year at Sumilon and Apo, respectively) was high enough to affect total community biomass, but not density, significantly. Species richness was not affected significantly by fishing, except at Sumilon reserve. The fishery was relatively non-selective with most families/trophic groups caught roughly in proportion to their contribution to community biomass. Thus fishing did not alter the relative abundance of the major families/trophic groups significantly, except during a period of use of explosives and drive nets in the Sumilon reserve. At the level of family/trophic group the community displayed strong resilience of structure. There was little evidence of secondary effects e.g. declines in abundance of large predators resulting in measurable increases in abundance of their prey. This resilience of the community to the effects of fishing most likely results from three important community attributes (open nature of the component populations, likely maintenance of upstream recruitment supply and apparent lack of any obvious “keystone” species or families) and one important characteristic of the fishery (relatively non-selective with respect to the components of the community).

How Pervasive is "Fishing Down Marine Food Webs"?

Abstract: In their report ([1][1]), and in an earlier paper ([2][2]), D. Pauly et al . draw global conclusions about the effects of fishing on world fish stocks with the use of research data fitted to Ecopath models at different sites through the world's oceans, integrated with data on global fishery landings

Significance of Bottom‐Fishing Disturbance

Abstract: Since the early 1970s there has been increasing interest in the ecological effects of bottom-fishing activities on the benthic ecology of the seas of northern Europe. The majority of studies have examined the short-term effects of disturbance on benthic fauna. Some areas, however, such as the southern North Sea, have been subjected to fishing disturbance for over 50 years, which complicates predictions of long-term ecological change inferred from recent experimental studies. I highlight the importance of evaluating the ecological rele- vance of fishing disturbance versus natural perturbations, which varies among different habitats. Most exper- imental studies have shown that it is possible to detect short-term changes in community structure in response to fishing disturbance. Evidence suggests that long-term changes are probably restricted to long-lived fragile species or communities found in environments that are infrequently disturbed by natural phenomena. Un- derstanding the relative ecological importance of physical disturbance by fishing versus natural events would provide a basis for predicting the outcome of fishing activities in different marine habitats. I suggest ap- proaches that may refine attempts to correlate fishing intensity and frequency with community change, such as the use of tracking devices fitted to trawlers and surveys of fauna, such as bivalves and echinoderms, that record disturbance events of the past in their shells or body structure.

Multiyear tagging studies incorporating fishing effort data

Abstract: The Brownie models for multiyear tagging studies can be used to estimate age- and year-specific annual survival rates and tag recovery rates. The latter are composites of the exploitation rates and rates of tag reporting, tag shedding, and tag-induced mortality. It is possible to estimate the exploitation rates if the other components of the tag recovery rates can be quantified. Instantaneous rates of fishing and natural mortality can be estimated if information is available on the seasonal distribution of fishing effort. The estimated rates are only moderately dependent on the timing of the fishing; consequently, the relative effort data can be crude. Information on the timing of the catch over the course of the year can be used as a substitute for the effort data. Fishing mortality can also be assumed to be proportional to fishing effort over years; consequently, if fishing effort is known then the tag reporting rate, natural mortality rate, and a single catchability coefficient can be estimated (instea...

Marine reserves: patterns of adult movement of the coral trout (Plectropomus leopardus (Serranidae))

Abstract: Movements of Plectropomus leopardus (Serranidae), a major fisheries species, across marine reserve boundaries were investigated on the Great Barrier Reef, Australia. Mark-release-recapture and ultrasonic telemetry were used to assess movements. Mark-release-recapture used hook and line as the method of capture and underwater visual census (UVC) as the "recapture" tool. Catch rates were significantly higher in zones closed to fishing, despite UVC indicating no significant differences in density between closed and open zones. Of 183 fish marked with numerical freeze brands, 93 estimates of movements of branded fish were obtained. No branded fish was recorded to cross the reserve boundaries during the 2-month study, probably due to the initial decision to allocate capture effort evenly across the study area, rather than concentrating it on reserve boundaries. Fish carrying ultrasonic transmitters, and having home ranges straddling reserve boundaries, crossed boundaries on average 15.3 times•month⁻¹. The mean distance moved by freeze branded specimens between capture and recapture was significantly larger in areas closed to fishing than in those open to fishing. However, mean distance moved per day determined by ultrasonic telemetry did not differ between areas closed and open to fishing. This study suggests low flux rates of adult P. leopardus across marine reserve boundaries.

Assemblages and biogeography of demersal fishes of the east coast of North America

Abstract: This study describes and maps demersal fish assemblages for the east coast of North America from Cape Hatteras, North Carolina, to Cape Chidley, Labrador, evaluates evidence for interannual shifts ...