Development and testing of attachment methods for pop-up satellite archival transmitters in European eel

Background: Four methods for attaching pop-up satellite transmitters to European eel were tested in the laboratory by recording long-term tag retention, growth and survival; short-term behavioral responses; and physical damage from attachments. Results: All eels survived until they lost their tag, or until end of the six-month study. Specific growth rate did not differ between tagged fish and controls. Tag retention varied from 0% to 100% among attachment methods. A tagging method that uses the strength of the eel skin by attaching the tag to the skin at three points is recommended for ocean migration studies based on a long tag retention time, minimal behavioral reactions, negligible damage to the swimming muscle, and minimal physical damage both for fish retaining and losing the tag. Although tag retention was 50% over six months, those losing their tags still retained them for 114 to 134 days. Another method had higher tag retention (100%), but required the use of steel wires that moved upwards through the muscle over time. This method was regarded as less suitable because of a strong behavioral reaction in the first two days after tagging and damage to the swimming muscle. Results from 275 silver eels released on European coasts equipped with pop-up satellite transmitters or similarly sized pop-up data storage tags to study the ocean spawning migration indicated a large premature tag release. This was partly related to mechanical tag loss, but probably mainly to a high predation rate (>20% confirmed predations of eels with pop-up satellite transmitters). Mean time to premature tag release was 14 to 21 days (maximum nine months). Conclusions: Laboratory and field data showed that pop-up satellite transmitters attached to eels can remain attached for six to nine months, but that tag retention is a challenge. Hiding behavior in a structured habitat increased the risk of entanglement and tag loss. In ocean migration studies, consideration should be given to transportation and release off shore instead of in shallower areas where they are more likely to seek the seabed and hide in structured habitats. Behavioral reactions indicate that data recorded during the first two to three days after tagging may not reflect natural behavior.Development and testing of attachment methods for pop-up satellite archival transmitters in European eelpublishedVersio

Effects of recreational angling and air exposure on the physiological status and reflex impairment of European grayling (Thymallus thymallus)

European grayling (Thymallus thymallus) is a popular recreational fish that may be lifted out of the water to facilitate hook removal or for admiration. To evaluate the effects of air exposure and angling-induced exhaustive exercise on released grayling condition, we assessed blood physiology and reflexes of grayling after angling and air exposure in the subarctic River Lakselva (Norway) at midsummer temperatures (i.e., 17–18 °C). Blood samples were drawn 30 min after angling and analyzed for lactate anions, glucose, sodium ions, and pH. Reflex impairment was determined with orientation and tail grab reflex action assessments immediately after landing, after air exposure, and after 30 min holding. Blood physiology did not indicate an exacerbating effect of air exposure relative to just angling-induced exercise, but significant and prolonged reflex impairment was associated with the 120 s air exposure interval. Anglers must take care to minimize air exposure to adhere to best handling practices.publishedVersio

Behaviour and survival of wild Atlantic salmon Salmo salar captured and released while surveillance angling for escaped farmed salmon

In many Norwegian rivers, spawning stocks are surveyed for escaped farmed salmon with surveillance fishing by rod and reel after the recreational angling season. However, the benefits of surveillance fishing depend on the ability of wild salmon to return to the spawning stock. To evaluate the impacts of surveillance fishing, we captured, radio-tagged and released wild Atlantic salmon Salmo salar in the River Lakselva, Norway, in a surveillance fishery occurring just prior to the spawning period. Among 39 salmon captured, 36 wild fish were tagged and released, whereas 3 were not released (1 bleeding from the gills, 1 farmed, 1 farmed and bleeding). Surviva

Estuarine use by spotted grunter Pomadasys commersonnii in a South African estuary, as determined by acoustic telemetry

Estuaries are important in the life history and the maintenance of the diversity of coastal fish species because of their function as nursery areas for juveniles as well as feeding grounds for adults (Cyrus 1991). The dependence of many fish species on estuaries is well documented (e.g. Wallace et al. 1984, Lenanton and Potter 1987, Blaber et al. 1989, Whitfield 1990, Hoss and Thayer 1993). Spotted grunter Pomadasys commersonnii (Haemulidae) (Lacepède 1801) is an estuarine-dependent species which spawns in the KwaZulu-Natal inshore coastal waters, between August and December (Wallace 1975b, Wallace and van der Elst 1975, Harris and Cyrus 1997, 1999). The eggs and larvae are transported southwards by the Agulhas Current, and juveniles between 20 mm and 50 mm TL recruit into the KwaZulu-Natal and south-eastern Cape estuaries (Wallace and van der Elst 1975, Whitfield 1990). Juvenile spotted grunter make use of the abundant food resources in estuaries, where they grow rapidly and remain for a period of 1–3 years (Wallace and Schleyer 1979, Day et al. 1981). Upon attaining sexual maturity (at between 300 mm and 400 mm TL), they return to the marine environment (Wallace 1975b). Some adults, however, return to estuaries to feed and to regain condition after spawning (Wallace 1975b, Whitfield 1994). The return of post-spawning fish coincides with increased catches by fishers in estuaries between July and January. These events are known as ‘grunter runs’ (Wallace 1975a, Marais and Baird 1980, Marais 1988, Pradervand and Baird 2002). It is suggested that adults spend up to several months in estuaries, before moving back to sea where they undergo gonadal development and ultimately spawn (Wallace 1975b, Wallace and van der Elst 1975). It is believed that adult fish also enter estuaries in a prespawning state to gain condition en route to their spawning grounds in KwaZulu-Natal (Webb 2002)

Assessment of the risk to Norwegian biodiversity from import and keeping of crustaceans in freshwater aquaria

Introduction The Norwegian Scientific Committee for Food and Environment (VKM) was requested by the Norwegian Environment Agency to assess the risk of negative impacts to biodiversity in Norway resulting from import of crustacean decapods for keeping in freshwater aquariums. VKM was asked to 1) list species of crayfish, crabs and shrimps that are currently kept in freshwater aquaria in Norway, and species that are likely to be kept in freshwater aquaria in Norway within the next 10 years, 2) assess the ability of the species to survive under Norwegian conditions and cause impacts on ecosystems and other species, and 3) state the potential negative effects on the biological diversity of diseases caused by pathogens, regulated under the Norwegian Food Act.Methods The risk assessment, without focus on pathogens, was performed in two steps. First, we used a pre-screening toolkit to identify species of crayfish, crabs and shrimps with potential to become invasive in freshwater habitats in Norway. Each species was given an invasiveness score based on 55 questions on biogeography, ecology, and climate change. In a second step, a full risk assessment, including the potential impacts of pathogens, was conducted on those species receiving the highest invasiveness score. This assessment included questions on the organism’s probability of entry and pathways of entry, establishment and spread, potential impacts on biodiversity, and how climate change scenarios might affect the assessment. Likelyhood and confidence was assessed for each question. In conclusion, each species was designated as either low-, moderate-, or high risk. Many crustacean decapod species are confirmed or suspected carriers of pathogens that can cause mass mortality among native crustaceans. The risk posed by crustaceans as carriers of pathogens may be independent of the environmental risk that they pose through ecological interactions. Therefore, the four crustacean disease pathogens that are regulated under the Norwegian Food Act, were assessed separately. These include Aphanomyces astaci causing crayfish plague, white spot syndrome virus (WSSV) causing white spot disease, Taura syndrome virus (TSV) causing Taura syndrome, and yellow head virus genotype 1 (YHV1) causing yellow head disease. The assessments comprised questions on the pathogen’s probability of entry (as a hitchhiker organism with imported crustaceans), pathways of entry, establishment and spread, and potential impact on crustacean biodiversity. Likelihood and confidence were assessed for each question. In conclusion, each pathogen was designated as either low-, moderate-, or high risk.In a third step, we categorized the likelihood that a crustacean species introduces a pathogen associated with a high- or moderate risk into: I) known chronic carriers, II) suspected chronic carriers, III) suspected situational carrier, IV) possible pathogen transmitters, and V) no direct or circumstantial evidence for carrier status or pathogen transmission in the genus.Results Based on information from the Norwegian Pet Trade Association, the project group listed 112 taxa (mainly species and some genera) of freshwater crayfish, crabs and shrimps that are relevant for trade in Norway. These included 38 crayfish taxa, 28 crab taxa, and 45 shrimp taxa. In addition, one marine crab was included. Sixteen species of crayfish, four species of shrimps, and two species of crabs underwent a full ecological risk assessment. The probabilities of entry both into the aquarium trade in Norway, and potentially further into Norwegian nature, were based on the prevalence of the species in the aquarium trade in Norway. We assumed that all species were equally likely to escape captivity or to be released. The four pathogens regulated under the Norwegian Food Act are either known or potential hazards to biodiversity in Norway. A. astaci is already present in Norway. It is regarded among the greatest threats to European freshwater crayfish, including noble crayfish (Astacus astacus). American freshwater crayfish are either known or suspected chronic carriers of A. astaci, while several crayfish species from other continents, as well as some species of crab and shrimp, may be situational carriers. WSSV is a "non-exotic" list 2 disease. All decapods can be infected by the virus. WSSV is primarily a problem in shrimp farming in Asia, but has spread to America and more recently to Australia. WSSV can cause 100% mortality in noble crayfish at water temperatures above 20 °C. Both TSV and YHV1 are "exotic" list 1 diseases. These can infect and cause high mortality in a limited range of saltwater shrimps. There is no evidence that TSV and YHV1 pose a risk to freshwater crayfish in the Nordic climate, nor is introduction likely through aquarium trade in freshwater crustaceans. Several other pathogens that cause crustacean dirsease are listed by the World Organization for Animal Health (OIE). These were briefly assessed, but not fully risk assessed.Conclusions VKM concluded that the risk of negative impacts on biodiversity caused by ecological interactions following import and private keeping of crayfish is high for Faxonius virilis, Faxonius spp., Procambarus clarkii, P. virginalis, and Pacifastacus leniusculus. These species can displace native crayfish, reduce the abundance of aquatic plants, and cause cascading effects that negatively influence invertebrates, fish, and birds. They can likely establish in Norwegian nature under the current climate conditions. The risk of negative consequences is moderate (with medium confidence) for the crayfish Cambarellus patzcuarensis, Procambarus alleni, Creaserinus fodiens, Cambarellus montezumae, Cherax monticola, Cherax tenuimanus, Faxonius neglectus. Perconon gibbesi of the crabs and Neocaridina davidi and Macrobrachium rosenbergii of the shrimps were associated with a moderate risk with medium confidence. Species associated with medium risk are omnivorous keystone species that will have at least moderate ecological impact on littoral freshwater ecosystems (medium confidence) if established in dense populations. None of the species associated with medium risk are likely to establish today. However, climate change will increase the risk for establishment and resulting ecological impact. The risk for negative impacts caused by the crayfish plague pathogen Aphanomyces astaci is high with high confidence. Crayfish plague can cause up to 100% mortality, and has already eradicated several noble crayfish populations in Norway. For WSSV, the risk for negative impact is moderate with high confidence. The risks associated with TSV and YHV1 are assessed as low for Norwegian crustacean biodiversity. According to the risk assessment of pathogens and the categorization of crustacean species based on their likelihood of being carriers of A. astaci and WSSV, 25 and 13 species of crayfish are associated with a high and medium risk, respectively. Four and 25 species of crabs are associated with a medium and low risk, respectively, and 14 and 31 species of shrimps are associated with medium and low risk, respectively. Notably, all species in the named genera should be regarded as belonging to the given risk category. OIE and general literature provide information of known crustacean diseases along with known susceptible crustacean hosts. However, there is a lack of information regarding carrier status of known and unknown disease pathogens for many exotic crustaceans. In this perspective, all exotic crustaceans should be regarded as potentially infected with a known or unknown pathogen. In order to reduce the risk of spreading diseases, eggs and living or dead animals should under no circumstances be disposed of in nature. The same applies for aquarium water or any material, such as gravel or ornamental plants, that have been in contact with the animals or water in the aquarium. The current permit requirement exemption for import of freshwater organisms that can only survive at temperatures above 5 °C provides no protection against the introduction, establishment, and spread of accompanying pathogens that could cause mass mortality in Norwegian crustacean populations. Finally, we can never predict how, or from which host species, a new disease might emerge. Many pandemics and plagues result from cross-continental pathogen-host jumps often facilitated by human transport, trade, introduction, release, or escape of alien species and associated alien pathogens

Global trends in aquatic animal tracking with acoustic telemetry

Acoustic telemetry (AT) is a rapidly evolving technique used to track the movements of aquatic animals. As the capacity of AT research expands it is important to optimize its relevance to management while still pursuing key ecological questions. A global review of AT literature revealed region-specific research priorities underscoring the breadth of how AT is applied, but collectively demonstrated a lack of management-driven objectives, particularly relating to fisheries, climate change, and protection of species. In addition to the need for more research with direct pertinence to management, AT research should prioritize ongoing efforts to create collaborative opportunities, establish long-term and ecosystem-based monitoring, and utilize technological advancements to bolster aquatic policy and ecological understanding worldwide