Disturbances In Fish Research Articles

Assessment of the Geochemical Background and Anthropogenic Load by Bioaccumulation of Microelements in Fish

Comparative characteristic of several microelements (Ni, Cu, Sr, Al, Zn, Co, Mn, Pb, Cd, Hg, As) found in fish (case study of breams in the Volga basin reservoirs) is presented. Regularities of accumulation of these elements in fish depending on their concentration in the water are analyzed. Main disturbances in fish caused by the accumulation of microelements in their organs and tissues are considered.

Physiological response of wild rainbow trout to angling: impact of angling duration, fish size, body condition, and temperature

This study evaluated the immediate physiological response of wild rainbow trout to catch-and-release angling in the Alagnak River, southwest Alaska. Information was recorded on individual rainbow trout (n = 415) captured by angling including landing time and the time required to remove hooks (angling duration), the time to anesthetize fish in clove oil and withdraw blood, fish length and weight, and water temperature at capture locations. Plasma cortisol, glucose, ions (sodium, potassium, chloride), and lactate were analyzed to determine the effects of angling duration, fish size, body condition, and temperature. Levels of plasma ions did not change significantly during the observed physiological response and levels of plasma glucose were sometimes influenced by length (2000, 2001), body condition (2001), or temperature (2001). Levels of plasma cortisol and lactate in extended capture fish (angling duration greater than 2 min) were significantly higher than levels in rapid capture fish (angling duration less than 2 min). Rapid capture fish were significantly smaller than extended capture fish, reflecting that fish size influenced landing and handling times. Fish size was related to cortisol and lactate in 2002, which corresponded to the year when larger fish were captured and there were longer landing times. Body condition (i.e., weight/length regression residuals index), was significantly related to lactate in 2000 and 2001. Water temperatures were higher in 2001 (mean temperature ± S.E., 13 ± 2 °C) than in 2002 (10 ± 2 °C), and fish captured in 2001 had significantly higher cortisol and lactate concentrations than fish captured in 2002. The pattern of increase in plasma cortisol and lactate was due to the amount of time fish were angled, and the upper limit of the response was due to water temperature. The results of this study indicate the importance of minimizing the duration of angling in order to reduce the sublethal physiological disturbances in wild fish subjected to catch-and-release angling, particularly during warmer water temperatures. It is also important to note that factors such as fish size may influence both the duration of angling and subsequent physiological response.

Factors influencing the return of submerged plants to a clear-water, shallow temperate lake

Lack of submerged vegetation was studied in a small, shallow, alkaline, clear-water lake with high nitrate concentration (mean 9 mg NO 3–N L −1) and profuse filamentous green algae (FGA) (mainly Spirogyra sp.). A laboratory microcosm and two lake enclosure experiments were carried out using Elodea nuttallii (Planchon) St John. E. nuttallii grew about 1.7 times as well in sediment from its place of origin compared with sediment from the lake. Differential water quality had no effect, and neither sediment nor water prevented growth in the lake. Nutrient addition reduced plant growth by more than 55% because of shading from epiphytic filamentous green algae (shoot dry weight versus epiphytic algal dry weight, r = −0.491, P < 0.05). Transplanted Elodea plants grew better in enclosures in the lake than in laboratory conditions with lake water and sediment ( P < 0.001, t-test). Rare Elodea individuals in the lake indicate the presence of plant propagules in the lake sediment, but excessive growth of filamentous green algae (summer mean 3.2 g dry weight m −2) significantly hamperd plant growth (shoot length reduced from 29 ± S.E.M. 1 to 25 ± 1 cm) and bird herbivory significantly reduced survival (from 82 ± 7 to 40 ± 6%) and shoot growth (from 78 ± 6 to 18 ± 5 cm) and thus eliminates establishment of even modest plant beds. Fish disturbance and sediment stability were not important. Restoration of submerged plants may require reduction of nitrate input, control of filamentous green algae and protection from birds.

Effect of phenanthrene on haematological parameters in olive flounder, Paralichthys olivaceus (Temminch et Schlegel)

Effects of phenanthrene on haematological parameters in olive flounder, Paralichthys olivaceus, were studied by exposing fish to water-borne phenanthrene (0.5, 1 and 2 μM) for 4 weeks. Red blood cell count, haemoglobin concentration, haematocrit levels decreased with increasing exposure time of phenanthrene to the fish. Plasma potassium level increased significantly in the experimental group but the levels of sodium and chloride were significantly decreased compared with control. There was no significant change in plasma magnesium, calcium and phosphate in fish of all treated groups compared with the control. The most profound physiological disturbance in phenanthrene-exposed fish was a decrease in blood osmolality. Malondialdehyde level in the plasma in the phenanthrene group (2 μM) was 1.4-fold higher following 4-week exposure compared with the control group. Acetylcholinesterase activity decreased as the concentration of phenanthrene increased, reaching 65.9% of the control value at the highest dose at the 4th week. A key finding from this study is that olive flounder exposed to phenanthrene at concentrations more than 1.0 μM are likely to experience negative impacts on haematological parameters.

Habitat structure and the survival of juvenile scallops Pecten novaezelandiae: comparing predation in habitats with varying complexity

Fishing disturbances that remove epifauna and other elements of benthic habitat struc- ture have a secondary impact on the survival of juvenile Pecten novaezelandiae, the native New Zealand scallop. We investigated habitat structure and scallop predation rates in 4 soft-sediment habitats naturally utilised by P. novaezelandiae over multiple spatial scales. We found that habitats exposed to fishing disturbance had significantly fewer elements of benthic structure and that preda- tion rates were significantly (up to 44%) higher compared to unfished habitats. Habitat complexity primarily differed at the spatial scale of site, which corresponds to the scale of fishing disturbance. Scallop predation was negatively correlated with the number of habitat elements such as sponges, horse mussels and ascidians in the immediate area, and positively correlated with predator density. Another factor that affected juvenile scallop survival was ambient scallop density, with higher pre- dation rates at the site where scallop numbers had been artificially enhanced. Although size-specific predation could not be formally tested in this study, it appeared that the predation rate was higher for larger scallops (mean size of 23 cm) compared to smaller scallops (mean size of 16 cm) in at least one of the sites but this requires further investigation. The results suggest that simplification of benthic systems by bottom-towed fishing activity degrades habitats and subsequently increases the vulnera- bility of juvenile scallops to predation. This may have important consequences for the sustainability of wild and enhanced scallop populations.

Techniques to mitigate clay turbidity problems in fertilized earthen fish ponds

An experiment was conducted in fifteen earthen ponds at the Asian Institute of Technology (AIT), Thailand, during June to November 1998 to identify the source of clay turbidity, to evaluate several clay turbidity mitigation techniques and their effects on fish growth and water quality, and to find a suitable approach for turbidity mitigation during the rainy season. There were five treatments: (A) control; (B) covering upper 50 cm pond dikes with black plastic material to prevent turbidity from run-off (edge-covered); (C) covering pond bottoms with green manure (terrestrial weeds) to alter soil texture (weed-covered); (D) covering pond bottoms with small mesh (1 cm) net to prevent turbidity from fish disturbance (bottom-covered); and (E) covering pond dikes with rice straw (straw-covered). All ponds were fertilized weekly with chicken manure at a rate of 500 kg ha −1 (dry matter basis) supplemented with urea and triple superphosphate (TSP) to provide 28 kg N per ha per week and 7 kg P per ha per week. Sex-reversed all-male Nile tilapia ( Oreochromis niloticus) were stocked at two fish per square meter at a size of 19.0±1.0 g. Results showed clearly that clay turbidity was mainly from the run-off of pond dikes but not from fish disturbance of pond bottom during the rainy season and indicated that covering pond dike was effective in mitigating clay turbidity caused by the run-off in fish ponds. No significant differences of fish survival were found among all treatments. The straw- and weed-covered treatments resulted in significantly higher fish growth and yield. In contrast, the edge- and bottom-covered treatments did not increase fish yield, compared with the control. Covering pond dikes with rice straw not only reduces clay turbidity caused by run-off but also enhance Nile tilapia growth probably through microbial biofilm developed on the rice straw. Therefore, covering pond dikes with rice straw is a cost-effective technique for clay turbidity mitigation in fish ponds during the rainy season.

Metabolic disturbances in fish exposed to sodium pentachlorophenate (NaPCP) and 3,3′,4,4′,5-pentachlorobiphenyl (PCB126), individually or combined

The Swan River Estuary is the recipient of multiple urban and agricultural contaminants which have the potential to induce liver detoxication enzymes as well as altering the metabolism of aquatic organisms. To test if altered liver metabolism would influence liver detoxication capacities, pink snapper ( Pagrus auratus) were i.p. injected with peanut oil (controls), or pentachlorobiphenyl #126 (PCB126), with sodium pentachlorophenate (NaPCP), or PCB126+NaPCP. Relative to controls, ethoxyresorufin- O-deethylase (EROD) activity was induced in the PCB126 and PCB126+NaPCP fish, but not in the NaPCP group. In the liver, cytochrome c oxidase (CCO) activity was enhanced by the treatments while citrate synthase (CS) activity remained unchanged and lactate dehydrogenase (LDH) activity was increased in the NaPCP treatment only. The results suggest that liver CCO activity may be a suitable biomarker of effect following exposure to PCBs or phenolic compounds. In the white muscle, only the PCB126+NaPCP treatment enhanced CCO activity, with all other enzymatic activities remaining unchanged. It appears that the resilience to metabolic perturbations is greater for white muscle than for liver. Low serum sorbitol dehydrogenase (sSDH) activity and histopathology of the liver indicated no significant alteration of cellular structure, albeit the lipid droplet size was increased in the PCB126 and in the PCB126+NaPCP treatments. It is concluded that the hepatic metabolic changes correspond to histopathological observations, but an altered metabolic capacity do not influence the metabolism of xenobiotics by liver enzymes, as measured by EROD activity.

Male-biased sex ratios of fish embryos near a pulp mill: temporary recovery after a short-term shutdown.

In a previous study we showed that broods from the viviparous eelpout Zoarces viviparus were significantly male biased in 1998 in the vicinity of a large kraft pulp mill on the Swedish Baltic coast. One suggested hypothesis was that masculinizing compounds in the effluent were affecting gonadal differentiation of the embryos, resulting in skewed sex ratios. In this article, we present further evidence for a causal relationship between the exposure to the effluent and the male-biased sex ratios. Analyses of historical samples showed that the eelpout produced male-biased broods close to the mill in 1997 in addition to 1998. During 1999, the mill was shut down for 17 days, coinciding with the period when the gonads of the eelpout embryos differentiate. Subsequently, in the fall of 1999, the sex ratios were no longer male biased; however, the following year (2000), a significant male bias reappeared. Investigations at 13 sites for up to 4 years showed a relatively stable sex ratio around 50/50, with the exceptions by the mill and with few observations of deviating ratios at other sites. Several reports document endocrine disturbances in fish near pulp and paper mills, including the expression of male secondary sex characters in female fish. The repeatedly identified male bias at the investigated mill, the normalization after mill shutdown, and the reappearance the following year indicate that pulp mill effluents also can affect sex ratios of nearby fish.

Modification of marine habitats by trawling activities: prognosis and solutions

AbstractFishing affects the seabed habitat worldwide on the continental shelf. These impacts are patchily distributed according to the spatial and temporal variation in fishing effort that results from fishers' behaviour. As a consequence, the frequency and intensity of fishing disturbance varies among different habitat types. Different fishing methodologies vary in the degree to which they affect the seabed. Structurally complex habitats (e.g. seagrass meadows, biogenic reefs) and those that are relatively undisturbed by natural perturbations (e.g. deep‐water mud substrata) are more adversely affected by fishing than unconsolidated sediment habitats that occur in shallow coastal waters. These habitats also have the longest recovery trajectories in terms of the recolonization of the habitat by the associated fauna. Comparative studies of areas of the seabed that have experienced different levels of fishing activity demonstrate that chronic fishing disturbance leads to the removal of high‐biomass species that are composed mostly of emergent seabed organisms. Contrary to the belief of fishers that fishing enhances seabed production and generates food for target fish species, productivity is actually lowered as fishing intensity increases and high‐biomass species are removed from the benthic habitat. These organisms also increase the topographic complexity of the seabed which has been shown to provide shelter for juvenile fishes, reducing their vulnerability to predation. Conversely, scavengers and small‐bodied organisms, such as polychaete worms, dominate heavily fished areas. Major changes in habitat can lead to changes in the composition of the resident fish fauna. Fishing has indirect effects on habitat through the removal of predators that control bio‐engineering organisms such as algal‐grazing urchins. Fishing gear resuspend the upper layers of sedimentary seabed habitats and hence remobilize contaminants and fine particulate matter into the water column. The ecological significance of these fishing effects has not yet been determined but could have implications for eutrophication and biogeochemical cycling. Simulation results suggest that the effects of low levels of trawling disturbance will be similar to those of natural bioturbators. In contrast, high levels of trawling disturbance cause sediment systems to become unstable due to large carbon fluxes between oxic and anoxic carbon compartments. In low energy habitats, intensive trawling disturbance may destabilize benthic system chemical fluxes, which has the potential to propagate more widely through the marine ecosystem. Management regimes that aim to incorporate both fisheries and habitat conservation objectives can be achieved through the appropriate use of a number of approaches, including total and partial exclusion of towed bottom fishing gears, and seasonal and rotational closure techniques. However, the inappropriate use of closed areas may displace fishing activities into habitats that are more vulnerable to disturbance than those currently trawled by fishers. In many cases, the behaviour of fishers constrains the extent of the impact of their fishing activities. Management actions that force them to redistribute their effort may be more damaging in the longer term.

Evidence of intra-specific competition for food in a pelagic seabird.

The factors affecting the population dynamics of seabirds have long intrigued biologists. Current data suggest that density-dependent depletion of prey during the breeding season may regulate population size. However, much of the evidence for this has been circumstantial, and the underlying mechanisms are unclear. Here, we show that the per capita population growth rates of northern gannet Morus bassanus at colonies in Britain and Ireland have declined with increasing population size. Furthermore, direct observations reveal that the mean foraging trip duration of breeding gannets is positively correlated with colony size, both among colonies of different sizes in the same year, and within colonies as they change in size. To understand this phenomenon, we have developed a model which demonstrates that disturbance of fish alone can readily generate conditions under which gannets at larger colonies have to travel further to obtain food.

Monitoring Natural and Synthetic Estrogens at Activated Sludge Sewage Treatment Plants and in a Receiving River Water

Sewage treatment plant (STP) effluents with primarily domestic inputs are strongly suspected to be an important source of natural and synthetic estrogens contaminating the aquatic environment. Even a few ng/L of some of these substances can provoke reproductive disturbances in riverine fish. The main purpose of this investigation has been that of ascertaining whether activated sludge STPs (ASSTPs) are able to produce significant amounts of free estrogens. For this purpose, we have monitored monthly estriol (E3), estradiol (E2), estrone (E1) and ethinylestradiol (EE2) in influents and effluents of six Roman ASSTPs for five months. To do this, we have developed an original analytical method involving analyte extraction with a Carbograph 4 cartridge and LC coupled with negative turbo ion spray tandem mass spectrometry in the selected reaction monitoring mode. Analyte recovery ranged between 86 and 91%, and limits of quantification were below 1 ng/L. Over five months, inlet concentrations of E3, E2, E1 and EE...

Effects of pre-acclimation to aluminium on the physiology and swimming behaviour of juvenile rainbow trout ( Oncorhynchus mykiss) during a pulsed exposure

Anthropogenic acidification of the freshwater environment causes aluminium to be mobilised into the aquatic environment. When pH falls below 5.5, exposure to aluminium concentrations as low as 12.5 μg·l −1 can cause serious physiological disturbances in freshwater fish. However, under constant laboratory exposures fish can acclimate and recover physiological status within 5–30 days. In reality, fish in the wild are likely to experience chronic sub-lethal exposure, with occasional elevations (pulses) to much higher levels. The experiment described here investigated the effects of an environmentally realistic, 4-day pulse exposure to a high level of aluminium (36 μg·l −1) in two groups of juvenile rainbow trout. One group was exposed to a lower level of aluminium (24 μg·l −1) for 16 days before and 10 days after the pulse (‘aluminium-acclimated’ fish). A second group was exposed to pH 5.2 alone for 16 days before and 10 days after the pulse (‘aluminium-naı̈ve’ fish). A third group exposed to pH 5.2 alone for 30 days (no aluminium added) acted as controls. Triplicate groups of 24 juvenile rainbow trout (2.3–16.7 g) were randomly allocated to one of these three treatments. Swimming behaviour was monitored throughout and samples were taken on days 14, 20, 22, 26 and 30 for assessment of physiological status. No treatment effects were recorded in the control group (pH 5.2 alone). Fish in the ‘aluminium-acclimated’ treatment became hypo-active upon initiation of the exposure to 24 μg·l −1 aluminium, but recovered after just 4 days of this exposure. Subsequent challenge on day 16 with the 36 μg·l −1 aluminium ‘pulse’ caused these fish to became hypo-active again, but they recovered normal swimming behaviour whilst still subject to the 4-day pulse. The ‘aluminium-naı̈ve’ fish also became hypo-active during the pulse exposure (36 μg·l −1 aluminium). However, they did not exhibit any recovery of swimming behaviour, either during the pulse, or even 6 days after the cessation of the pulse, despite a rapid depuration of gill aluminium load (within 2 days of the pulse finishing). Mortality was low in the aluminium-acclimated fish (4%) and significantly higher in the aluminium-naı̈ve fish (26%). Haematological disturbances were most extreme in the aluminium-naı̈ve fish and had not recovered to control levels 6 days after the end of the pulse. This study provides new evidence, using behavioural responses, that previous exposure to low levels of aluminium may be an important factor abating the impact of aluminium on fish in the natural environment.

Can shell scars on dog cockles ( Glycymeris glycymeris L.) be used as an indicator of fishing disturbance?

The use of shell damage records as an in situ indicator of past fishing disturbance was investigated using the dog cockle Glycymeris glycymeris L. Shell sections of dog cockles collected from four areas subjected to varying levels of fishing disturbance were examined for the presence of damage records or shell ‘scars’. Animals from a heavily fished area had significantly higher levels of scarring than those from three lightly fished areas. From an estimation of the age of the shells (from internal growth lines and dating of each line), the year in which scarring occurred was determined and this was compared to yearly records of fishing effort. There was a weak but significant positive correlation between the frequency of shell scars per year and the intensity of fishing effort. Our data suggest that whilst scarring in shells of G. glycymeris cannot accurately be used to estimate past fishing intensity on a year-by-year basis, it can be used to differentiate between severely impacted and lightly fished areas of the sea bed.

Chronic fishing disturbance has changed shelf sea benthic community structure

Summary 1. Bottom fishing using towed nets and dredges is one of the most widespread sources of physical disturbance to the continental shelf seas throughout the world. Previous studies suggest that degradation and ecosystem changes have occurred in intensively fished areas. Nevertheless, to date it has been difficult to attribute habitat and benthic community changes to fishing effort at a spatial scale that is truly representative of commercial fishing activities. 2. In this study we present convincing evidence that chronic bottom‐fishing disturbance has caused significant and widespread changes in the structure of two distinct soft‐sediment benthic assemblages and habitats. 3. Our study compared the benthic fauna found in areas that have been exposed to either high or low levels of bottom‐fishing disturbance over the past 10 years. We were able to validate the fishing effort data in some areas using scars in the shells of a long‐lived bivalve mollusc (Glycymeris glycymeris) which result from fishing disturbance. Shell scars occurred most frequently in bivalves collected from the area of highest fishing effort. 4. Multivariate analyses and the response of abundance/biomass curves indicated that chronic fishing has caused a shift from communities dominated by relatively sessile, emergent, high biomass species to communities dominated by infaunal, smaller‐bodied fauna. Removal of emergent fauna has thus degraded the topographic complexity of seabed habitats in areas of high fishing effort. The communities within these areas currently may be in an alternative stable state.

Burrowing behaviour and dispersion of cockles Cerastoderma edule L. following simulated fishing disturbance

Field experiments were conducted on the cockle Cerastoderma edule L. to study effects of simulated harvesting on reburrowing behaviour, displacement by tides, and recolonisation of cleared patches. The study was prompted by needs to interpret results when experimental mechanised harvesting is conducted in relatively small plots from which discards that should survive are lost or which are recolonised by immigrant adults. Simulation of machine-induced physical shocks caused delays to the normal cockle reburrowing response. Small (<20 mm) cockles were less affected than those of a size to be retained in the landed catch (>20 mm) and more of all sizes reburrowed if deposited in pools rather than on wet sand. None reburrowed into drained sand. Tagged and marked cockles failing to reburrow were transported up the shore with the flow of the flood tide, some being found again 200 m away. Many of these reburrowed at new positions. On a gently sloping macro-tidal shore the tidally mediated displacement varied with the predicted tide range. Theoretical estimates based on tide curves and extrapolations from formulae for tidal bores suggested that in the front of the flooding tide across the intertidal flat, current speeds reach 0.62 m/s on an 8.28 m spring tide. Very slight displacement took place on a neap tide, the critical speed of tide advance to displace exposed cockles being about 0.3 m/s. The majority of tagged cockles that reburrowed before the first flood tide came in subsequently remained where they had re-established themselves. Those moved to new positions stayed where they had been carried to. Extrapolation, from the slight decline in numbers still present, suggested that from a population of 80 per m 2 roughly 12 would have moved to new positions in 14 days. This compares with unmarked individuals recolonising plots, cleared at 14-day intervals, at <3/m 2/14 days.

Seasonal, Interannual, and Spatial Variability in the Concentrations of Total Suspended Solids in a Degraded Coastal Wetland of Lake Ontario

A 4-year (1993 through 1996) monitoring program examined the distribution of total suspended solids (TSS) in Cootes Paradise Marsh, a shallow (mean depth of 70 cm), degraded, drownedrivermouth marsh of Lake Ontario. Monthly meteorological and hydrographical data from 1986 through 1996 revealed a hydrologically dynamic system that exhibited large seasonal and interannual variation with respect to precipitation amount, discharge volume, and water levels; the prevailing winds were shown to be oriented along the length of the marsh. Interannual variation in TSS concentrations was inversely related to mean seasonal water levels that fluctuated 45 cm over the 11 years. In a stepwise regression analysis, planktonic chlorophyll-a concentration only explained 2% of the variation in TSS, while inorganic and non-algal organic solids explained 70% and 18%, respectively. Mean seasonal water turbidity increased significantly with mean seasonal wind speed at 17 sampling stations during 1993 and 1994. Runoff from a summer rainstorm more than doubled water turbidities at the mouth of all three creeks over the first 36 hours. In enclosure experiments, water turbidity increased proportionately with biomass of benthivorous fish (especially common carp, Cyprinus carpio). When wind and carp disturbance were compared simultaneously in the field, wind speed accounted for 41% of the variation in turbidity while presence of carp explained an additional 21%. The overall temporal and spatial distribution of TSS in the marsh reflected changes in water level, wind activities, onset of rain events, and fish disturbance that acted in concert to keep Cootes Paradise Marsh extremely turbid throughout the summer.

Inferring changes in North Sea benthos from fish stomach analysis

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 184:183-188 (1999) - doi:10.3354/meps184183 Inferring changes in North Sea benthos from fish stomach analysis C. L. J. Frid1,*, S. J. Hall2 1Dove Marine Laboratory, University of Newcastle upon Tyne, Cullercoats, North Shields, Tyne and Wear NE30 4PZ, United Kingdom 2School of Biological Sciences, Faculty of Science & Engineering, The Flinders University of South Australia,GPO Box 2100, Adelaide 5001, South Australia, Australia *E-mail: c.l.frid@ncl.ac.uk ABSTRACT: In this study we formulated a priori hypotheses for the changes in the benthos that would be expected as a result of the direct impacts of trawl fisheries. These were tested using a data set comprising stomach contents for dab Limanda limanda collected in March and August in the early 1950s and a matched sample from 1996-97. Changes in samples taken in August were consistent with the hypothesised effects of fishing, with an increased prevalence of scavengers and decreased occurrence of sedentary polychaetes in the diet. There were also marked differences between the 1950s and 1996-97 for March samples due to the high prevalence of fish remains in the contemporary samples. While our results must be treated with caution, they are consistent with the hypothesis that there have been widespread long term changes in benthic communities due to fishing. KEY WORDS: Dab · Stomach contents · Benthos · Fishing disturbance · North Sea Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 184. Publication date: July 28, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

Xenobiotics, xenoestrogens and reproduction disturbances in fish

Abstract Fish maturation and reproduction are complex biological processes that are regulated by endogenous substances (hormones), and synchronized by exogenous factors (photoperiod and temperature), thus ensuring that reproduction occurs at a time of the year optimal for survival of the offspring. The survival of any fish species is ultimately determined by the ability of its members to reproduce successfully in a fluctuating environment and thereby maintain a viable population. Several reports have documented that many compounds introduced into the environment by human activity either deliberately or unintentionally are capable of affecting reproductive processes in fish. Zonagenesis and vitellogenesis (eggshell protein and egg yolk precursor production, respectively) are two estrogen-regulated processes that are integral aspects of fish oogenesis. Several in vivo and in vitro studies have reported that some xenobiotics (xenoestrogens) possess the ability to mimic natural estrogens and therefore initiat...

Responses of benthic scavengers to fishing disturbance by towed gears in different habitats

The aggregation and feeding behaviour of invertebrate scavengers in areas disturbed by trawling was investigated at three different localities. At each site a fishing disturbance was created using a commercial 4 m beam trawl and scavenger density was quantified using a light beam trawl. At one site two diver surveys were also carried out; along a line fished with a scallop dredge or a beam trawl on two separate occasions. For all experiments the fished and adjacent unfished control areas were sampled before, and at intervals after, the initial fishing disturbance. Sampling with the light beam trawl revealed that hermit crabs Pagurus bernhardus moved into areas which had been fished with a 4 m beam trawl at an experimental site near Anglesey. The density of these hermit crabs increased significantly in the fished area after fishing had taken place, but no change in density occurred in the adjacent control (unfished) area. At two other sites (Red Wharf Bay, Anglesey and a site offshore from Walney Island) there were no detectable increases in scavenger numbers in the fished areas. Furthermore, at the site near Walney Island, numbers of hermit crabs P. bernhardus, swimming crabs Liocarcinus depurator and starfish Asterias rubens actually decreased after fishing. Thus the responses of scavengers to towed fishing gears varied considerably between different communities. At Red Wharf Bay, divers observed similar responses of scavengers to both beam trawl and scallop dredge disturbance. Four predatory species were observed feeding in the fished area; starfish A. rubens, hermit crabs P. bernhardus, brittlestars Ophiura ophiura and whelks Buccinum undatum. These predators fed on damaged bivalves, echinoderms, crustaceans, whelks and polychaetes. The proportion of starfish feeding in the fished area was significantly higher after fishing had taken place. Demersal fishing activities provide food for scavengers in the form of damaged animals which are left in the tracks of the trawl or dredge. The responses of scavengers to fishing disturbance are not always manifested as a large increase in their abundance. It is clear that the magnitude of response varies between species and between habitat types.

Opportunistic feeding by dabs within areas of trawl disturbance:possible implications for increased survival

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 152:307-310 (1997) - doi:10.3354/meps152307 Opportunistic feeding by dabs within areas of trawl disturbance: possible implications for increased survival Kaiser MJ, Ramsay K As demersal fishing gears are towed across the seabed they dig up or damage infauna. Dab Limanda limanda L. are known to aggregate in areas disturbed by trawls. We demonstrate that dab alter their diet and increase their food intake when feeding in these areas. Although dabs are frequently caught in large numbers as part of the by-catch of commercial flatfish fisheries, and a large proportion of these die, they remain the most abundant flatfish species in the North Sea. Fisheries have selectively removed species that prey upon or compete with dab. Furthermore, fishing activity increases feeding opportunities for dabs. These factors may have contributed to the observed increase in the abundance of dab in the North Sea. Dab · Fishing disturbance · Diet · Feeding behaviour · Population changes Full text in pdf format PreviousExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 152. Publication date: June 26, 1997 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1997 Inter-Research.