Marine-dumped waste tyres cause the ghost fishing of hermit crabs

Poorly managed waste tyres pose serious environmental and health risks, ranging from air pollution caused by fire, leaching of heavy metals and outbreaks of mosquitos, to destruction of vegetation and coral reefs. We report a previously unrecognized ecological risk to marine organisms from waste tyres. Over 1 year, we made monthly counts of hermit crabs ( n = 1278) invading and/or being trapped within six tyres anchored to the seabed at 8 m depth in Mutsu Bay, Japan. A complementary aquarium experiment in which hermit crabs were released into a tyre confirmed that they could not escape. We report marine-dumped waste tyres to ghost fish in a manner analogous to discarded fishing gear. Because hermit crabs play important roles in coastal food webs as both prey and scavengers, declines in their numbers as a consequence of this ghost fishing might affect coastal ecosystems.

Application of a Controlled Aquarium Experiment to Assess the Effect of Mesh Sizes and Mesh Opening Angles on the Netting Selectivity of Antarctic Krill (Euphausia superba)

Understanding the interactions between target species and netting is paramount for increasing the sustainability of trawling activities. The selectivity of the utilized netting depends on the sizes and opening angles of the mesh. The effects of the mesh size and mesh opening angle on the fishing selectivity of Antarctic krill (Euphausia superba) were assessed via micro-cosmos experiments. The results show that both the absolute abundance and the incidence of larger krill individuals passing through experimental panels are proportional to the utilized mesh size. Krill individuals larger than 35 mm passed through experimental panels at mesh opening angles larger than 50° for a 15 mm mesh size, 35° for a 20 mm mesh size and 20° for a 30 mm mesh size. Additionally, all L50 values increased with an increasing mesh size and an increasing mesh opening angle at the same mesh size. Furthermore, the selection range increased with an increasing mesh size and with an increasing mesh opening angle at the same mesh size. This paper provides scientific guidance for the choice of liner mesh sizes of krill trawl with the aim to improve fishing efficiency while minimizing fishing losses and potential negative ecosystem impacts from fisheries.

Activity, energy use and species identity affect eDNA shedding in freshwater fish

The quantitative measurement of eDNA form field-collected water samples is gaining importance for the monitoring of fish communities and populations. The interpretation of these signal strengths depends, among other factors, on the amount of target eDNA shed into the water. However, shedding rates are presumably associated with species-specific traits such as physiology and behavior. Although such differences between juvenile and adult fish have been previously detected, the general impact of movement and energy use in a resting state on eDNA release into the surrounding water remains hardly addressed.In an aquarium experiment, we compared eDNA shedding between seven fish species occurring in European freshwaters. The investigated salmonids, cyprinids and sculpin exhibit distinct adaptions to microhabitats, diets, and either solitary or schooling behavior. The fish were housed in aquaria with constant water flow and their activity was measured by snapshots taken every 30 s. Water samples for eDNA analysis were taken every 3 h and energy use was determined in an intermittent flow respirometer. After controlling for the effect of fish mass, our results demonstrate a positive correlation between target eDNA quantities as measured with digital PCR, fish activity and energy use, as well as species-specific differences. For cyprinids, the model based on data from individual fish was only partly transferable to groups, which exhibited lower activity and higher energy use.Our findings highlight the importance of fish physiology and behavior for the comparative interpretation of taxon-specific eDNA quantities. Species traits should therefore be incorporated into eDNA-based monitoring and conservation efforts.

Damselfishes alleviate the impacts of sediments on host corals

Mutualisms play a critical role in ecological communities; however, the importance and prevalence of mutualistic associations can be modified by external stressors. On coral reefs, elevated sediment deposition can be a major stressor reducing the health of corals and reef resilience. Here, we investigated the influence of severe sedimentation on the mutualistic relationship between small damselfishes ( Pomacentrus moluccensis and Dascyllus aruanus ) and their coral host ( Pocillopora damicornis ). In an aquarium experiment, corals were exposed to sedimentation rates of approximately 100 mg cm −2 d −1 , with and without fishes present, to test whether: (i) fishes influence the accumulation of sediments on coral hosts, and (ii) fishes moderate partial colony mortality and/or coral tissue condition. Colonies with fishes accumulated much less sediment compared with colonies without fishes, and this effect was strongest for colonies with D. aruanus (fivefold less sediment than controls) as opposed to P. moluccensis (twofold less sediment than controls). Colonies with symbiont fishes also had up to 10-fold less sediment-induced partial mortality, as well as higher chlorophyll and protein concentrations. These results demonstrate that fish mutualisms vary in the strength of their benefits, and indicate that some mutualistic or facilitative interactions might become more important for species health and resilience at high-stress levels.

THE INFLUENCE OF THE HIGH CONTENT OF Cа2+, Mg2+ AND Nа+ ON VARIABILITY OF THE PORES NUMBER IN LATERAL LINE CRANIAL CANALS OF ROACH FINGERLINGS

In a five-month aquarium experiment, roach Rutilus rutilus (Linnaeus, 1758) fingerlings were grown under different hydrochemical conditions. Roach eggs were collected during the spawning period in the shallow coastal waters of a small isolated and unpolluted pond and placed in laboratory for subsequent incubation. Hatched early larvae after switching to exogenous nutrition were divided into four groups for further development in control hydrochemical condition and in the water with a total mineralization increased twice relative to the control due to the addition of calcium, magnesium or sodium chloride salts. At the end of the experiment, roach fingerlings grown in the three groups in conditions of increased water mineralization differed statistically significantly from their coevals in the control group by a smaller average number of pores in the lateral line canals located on some paired dermal bones of the head. Also, these three groups of roach in comparison with the control group were characterized by an increase in the dispersion of the fluctuating asymmetry of the total values of the studied bilateral counting features. The obtained results are explained in the light of the possible influence of the above biologically significant cations on the morphogenesis of the cranial seismosensory system during the early individual development of fishes.

Influence of 17-alpha methyl testosterone on the production parameters of common carp (Cyprinus carpio L.) fry

During our research we aimed at finding an answer as to what extent the different concentrations of 17-alpha methyl testosterone incorporated in the diet of common carp fries can influence the production parameters of the species, as well as how efficient their sexreversal can be with the use of this method. To this end, an aquarium experiment was conducted in the course of which four different hormone treatments were set and monitored. The fish feed was enriched with 17-alpha methyl testosterone in 50 ppm, 75 ppm, 100 ppm, 500 ppm dosages. The obtained figures revealed that the hormone treatments had no influence on the production parameters and conservation of the common carp fries. Further on, our team is to determine the sex of the fish through the examination of gonads during autopsy when they reach the 500 g average weight. Furthermore, a male specific test method which was supposed to be of great help in our attempt to select the sex-reversed specimens in the subsequent processes was also put to the trial. During the experiment the DNA-isolation of different sample types (muscle tissue, fin, mucus) of common carp with identified sex was successfully carried out. The extracted PCR product was examined with agarose gel. Our results indicated that the ccmf2 marker was applicable, however, the obtained figures were not reliable.

Using eDNA to Detect the Distribution and Density of Invasive Crayfish in the Honghe-Hani Rice Terrace World Heritage Site

The Honghe-Hani landscape in China is a UNESCO World Natural Heritage site due to the beauty of its thousands of rice terraces, but these structures are in danger from the invasive crayfish Procambarus clarkii. Crayfish dig nest holes, which collapse terrace walls and destroy rice production. Under the current control strategy, farmers self-report crayfish and are issued pesticide, but this strategy is not expected to eradicate the crayfish nor to prevent their spread since farmers are not able to detect small numbers of crayfish. Thus, we tested whether environmental DNA (eDNA) from paddy-water samples could provide a sensitive detection method. In an aquarium experiment, Real-time Quantitative polymerase chain reaction (qPCR) successfully detected crayfish, even at a simulated density of one crayfish per average-sized paddy (with one false negative). In a field test, we tested eDNA and bottle traps against direct counts of crayfish. eDNA successfully detected crayfish in all 25 paddies where crayfish were observed and in none of the 7 paddies where crayfish were absent. Bottle-trapping was successful in only 68% of the crayfish-present paddies. eDNA concentrations also correlated positively with crayfish counts. In sum, these results suggest that single samples of eDNA are able to detect small crayfish populations, but not perfectly. Thus, we conclude that a program of repeated eDNA sampling is now feasible and likely reliable for measuring crayfish geographic range and for detecting new invasion fronts in the Honghe Hani landscape, which would inform regional control efforts and help to prevent the further spread of this invasive crayfish.

Using a multi-experimental approach to assess the fate of angled-and-released yellowtail kingfish (Seriola lalandi)

Roberts, L. W., Butcher, P. A., Broadhurst, M. K., and Cullis, B. R. 2011. Using a multi-experimental approach to assess the fate of angled-and-released yellowtail kingfish (Seriola lalandi). – ICES Journal of Marine Science, 68: 67–75. Yellowtail kingfish (Seriola lalandi) are angled throughout their global distribution and released in large numbers under the unsubstantiated assumption of few impacts. The validity of this supposition was tested for southeastern Australian stocks. In all, 54 fish were angled and released into cages with 36 controls and monitored for 5 d. Of the angled fish, 15% died, mostly as a consequence of gill-hooking and the associated physiological and mechanical damage. A biotelemetry experiment was then performed to determine if cutting the line on gill-hooked fish could improve their post-release fate. The attachment of transmitters was validated in an aquarium experiment before 12 jaw- and 10 gill-hooked fish were tagged, released, and tracked. One gill-hooked fish was detected motionless within 10 min, and another was last detected 7 min after release; both presumed dead. No jaw-hooked fish died within the first 24 h. The remaining fish were last detected between 3 and 49 d after release and, apart from subtle differences in their short-term responses, maintained similar wide-ranging movements and accelerations. The results justify cutting the line on deep-hooked fish to minimize post-release mortality and illustrate the utility of combining confinement and biotelemetry studies to assess the fate of released fish.