46 research outputs found
The associative behaviour of silky sharks, Carcharhinus falciformis, with floating objects in the open ocean
No full textThe silky shark Carcharhinus falciformis forms the primary elasmobranch
bycatch in tuna purse seine fisheries using fish aggregating devices (FADs)
in all of the world’s tropical oceans. Its life-history traits of slow growth,
late maturation and low fecundity make it vulnerable to over exploitation,
as is apparent from historical bycatch trends. Very little is known about the
associative behaviour of this species with floating objects, information which is
essential in formulating effective mitigation and management measures. This
study aims to address this knowledge gap through the use of various electronic
tagging techniques in conjunction with dietary analysis. Dietary data were
collected from 323 silky sharks incidentally caught at FADs. Approximately
40 percent of the diet consisted of prey associated with FADs while the remaining
60 percent were non-associated species of crustaceans, cephalopods and fishes.
These results suggest that the associative behaviour is not primarily driven
by trophic enhancement, but is likely a combination of predator avoidance,
social interactions and feeding. Fine-scale behavioural data from silky sharks
associated with drifting FADs were collected through the use of acoustic
telemetry techniques. Acoustic tags were implanted into 38 silky sharks (69-
116 cm TL) at eight FADs. FADs were equipped with satellite linked acoustic
receivers and abandoned to drift freely. Presence/absence and swimming
depth data were telemetered via the Iridium satellite system. A total of 300 d of
behavioural data were collected from 20 tagged individuals. Individuals remain
associated with the same FAD for extended periods (min = 2.84 d, max = 30.60
d, mean = 15.69 d). Strong diel patterns were observed in both association and
swimming depth. Typically individuals moved away from FADs after sunset and
return later during the night, then remain closely associated until the following
evening. Vertical behaviour also changed around sunset with sharks using
fairly constant depths, within the upper 25 m, during the day and switching
to rapid vertical movements during the night, with dives in excess of 250 m recoded. Broader scale movement behaviour was investigated using pop-up
archival satellite tags (PSATs). Tags were deployed on 46 silky sharks (86-224.5
cm TL) for a total of 1495 d. Light data were used to calculate geolocation
estimates and reconstruct the sharks’ trajectories. Movement patterns differed
between animals and according to deployment duration. Several extensive
horizontal movements were observed, with an average track length of 3240 km
during an average tag deployment of 44.02 d. Horizontal movement patterns
were found to correlate very closely with drift patterns of FADs. Consequently,
it appears that the movement behaviour of juvenile silky sharks is strongly
influenced by the movement of drifting FADs in this region. Ghost fishing
of silky sharks through entanglement in FADs was also investigated using
data derived from PSATs as well as underwater visual censuses. Thirteen per
cent of the tagged sharks became entangled in FADs and entangled sharks
were observed in 35 percent of the 51 FADs surveyed. Using this information in
conjunction with estimated time that sharks remained entangled in the FAD
(from depth data from PSATs), and scaling up according to estimates of FAD
numbers, it was found that between 480 000 and 960 000 silky sharks are
killed annually in this manner in the Indian Ocean. Subsequent management
measures in this region prevent the deployment of FADs with netting that could
lead to entanglement. Overall, floating objects appear to play a significant role
in the juvenile life stages of silky sharks in this region. While their association
with floating objects is clearly advantageous in an evolutionary sense, under
current tuna fishery trends, this behaviour is certainly detrimental for the
population
Movements of sub-adult sicklefin lemon sharks Negaprion acutidens in a remote Indian Ocean atoll
No full textThe sicklefin lemon shark Negaprion acutidens is a large-bodied (> 3m) coastal shark
species, widely distributed in tropical and sub-tropical Indo-Pacific waters. Despite its
large size and wide distribution, very little is known about its movement behaviour
throughout ontogeny. The primary aim of this thesis was to gain an understanding of the
movements of sub-adult N. acutidens, in and around the St. Joseph Atoll, Republic of
Seychelles, to facilitate the effective conservation of this vulnerable species. A total of
22 sharks (139 – 202 cm TL) were equipped with coded acoustic transmitters and
passively monitored using moored acoustic receivers for a period of 20 month from
March 2009 to October 2010.
The use of passive acoustic telemetry arrays to study behavioural ecology has increased
in popularity in recent years and been successfully applied to study a host of teleost and
elasmobranch species in a diversity of habitats, ranging from sheltered estuaries to the
offshore pelagic environment. However, the practicalities of designing an effective
network of receivers to optimally monitor animal movements can be challenging. In this
study the receiver array was optimised through a series of incremental steps to achieve
an efficient design that allowed for the specific objectives to be addressed.
The specific objectives of this study were to i) gain an understanding of the long term
space use patterns and site fidelity of sub-adult N. acutidens within degree of use of the
St. Joseph Atoll lagoon and surrounding habitats, and ii) investigate their short term
behavioural patterns in response to natural rhythmic cycles.
The important role the atoll plays in the sub-adult stage of this species was
demonstrated by the very low numbers of detections outside the atoll compared to the
very large numbers of detections inside the atoll. Over the course of a year the tagged
sharks showed a high degree of site fidelity to the atoll, with 79 – 100% of the
individuals detected during each month and 50% being detected on a near daily basis.
This result provides testimony of the nursery role of the atoll and importance of these
habitats in the early life history for this species. Individual area use was generally found
to be restricted to the eastern part of the atoll incorporating a portion of the central deep
lagoon and a nearby adjacent area of the sand flats. The movements of sub-adult N.
acutidens on and off of the shallow flats surrounding the central lagoon (likely for
foraging) were found to be strongly influenced by the tidal height and the diel cycle.
Tagged sharks were found to utilise the flats more regularly when the tidal height was
greater than 90 cm and particularly more so during the night and early morning than
during daylight times.
The combined results of this study expose the vulnerability of this species to rapid local
depletion. Similarly, the effectiveness of spatial management measures, such as no-take
marine protected areas is highlighted as an efficient tool for the future conservation of
this species. In the St. Joseph Atoll in particular, the use of a multi-levelled protection
approach, where the eastern portion on the atoll is completely restricted while the
remaining area is utilized for non-consumptive tourism activities, could be highly
effective. Future research should investigate changes in area use throughout the
ontogeny of this species as well improve the understanding of the breeding site fidelity
and population size of reproductive females using the St. Joseph Atoll
Management strategies of dysglycaemia in critically ill adult patients : a scoping review
No full textDissertation (MNurs)--University of Pretoria, 2023.Management strategies of dysglycaemia in critically ill adult patients: a scoping review.
Background: Dysglycaemia comprises of hypoglycaemia, hyperglycaemia and glycaemic variability. It is a biomarker of disease severity and my lead to increased mortality in critically ill patients. Dysglycaemia is common in critically ill patients and also presents in non-diabetic patients. However, blood glucose/dysglycaemia management strategies for critically patients remain ad hoc, which increases the risks for complications associated with dysglycaemia.
Objective: The objective of the study was to explore, identify and map the evidence available on management strategies of dysglycaemia in critically ill adult patients in the critical care unit, and to identify evidence gaps relating to the management of dysglycaemia in critically ill adult patients.
Design: A Scoping review was done according to the Joanna Briggs Institute (JBI) methodology.
Data source and search strategy: Medline and CINAHL databases were searched to identify articles that examine glucose control in the critical care unit (CCU). Articles that were published from 2001 until 2023 were evaluated and the search was limited to articles published in English. We used the following search terms: Glucose monitoring OR glucose control OR glycaemic control OR dysglycaemia NOT Diabetes mellitus OR Diabetes OR Diabetic AND Critically ill OR intensive care patients OR critical care patients. Only original articles were included while case reports as well as editorial letters, opinion papers, and surveys were excluded. The search strategy was compiled by the author and an experienced information specialist executed the search.
Eligibility criteria and study selection: Population - (i) patients 18 years or older, (ii) female and male patients, (iii) patients of any race and ethnicity, (iv) patients admitted to the critical care unit following a medical or surgical diagnosis, (v) studies from 2001 up to 2023. Concept – Sampling method of blood glucose, frequency monitored, target range of blood glucose guiding treatment (hypo or hyper), method of Insulin or Dextrose administration, evaluation. Context – Critical care units and high care units.
All publications were screened by the researcher and a supervisor. Results were discussed, and the screening and data extraction process was amended as necessary, before making final decisions. Titles, abstracts, and full texts of all the publications were screened by the researcher and supervisor independently to ascertain inclusions. Disagreements were settled without the need for a 3rd party involvement.
Once the results were available, it was exported into EndNote and Rayyan, an online systematic review software. Duplicates were removed by the researcher, and articles were reviewed for inclusion and exclusion. Additional relevant material was not deemed necessary, so no authors were contacted during this period. Lastly, reference lists were searched and screened for potential sources.
Data extraction: A data charting form was created in Excel and data extraction variables were drawn up as columns. This was done to ensure important details were not omitted and to ensure that the data captured were in line with the study’s objectives and inclusion criteria. The data charting form was continuously updated. With the aid of a data extraction tool created for this study, the data from the eligible studies were then charted. The form was used to capture all the relevant data and specific key characteristics regarding included variables of blood glucose control. Only one reviewer charted the results independently and these were reviewed by another reviewer. Disagreements were solved through discussion.
Results: The primary search strategy identified 2261 potentially relevant papers (see Figure 2). Duplicates were removed at this stage (in Rayyan), and a total of 1908 articles remained. Articles which had restricted access to full text was 160. A total of 1748 records remained at this stage. The titles and abstracts, as well as full-text articles were screened, of which 1732 were excluded. The selection at this stage included 16 studies. Two (2) additional studies were identified through a manual search of the reference lists of these studies. Uncertainty existed over the optimum treatment goal for glycaemia in the critically ill population. The largest prospective multicenter trial, which revealed an increase in mortality in patients receiving intense insulin therapy, could not duplicate the findings of randomized controlled trials from the early 2000s that showed a benefit of very tight glucose control. The present research largely focused on the clinical benefit and hypoglycaemia risk of intensive insulin therapy; however, there was no consensus on the ideal blood glucose control range, the patients who should receive it, when to initiate treatment, and how to minimize the risk.
Conclusion: There’s more to blood glucose measurement than meets the eye. It is much more comprehensive and is not as simple as sampling blood for testing, and a lot of factors need to be taken into consideration. There are many diverse and different views regarding target range of blood glucose, frequency of testing, and sampling of blood. Conclusions cannot simply be drawn from the articles as there were too many diverse views and results.Nursing ScienceMNursUnrestrictedFaculty of Health SciencesSDG-03:Good heatlh and well-bein
Fine-scale 3-dimensional movement behaviour of silky sharks Carcharhinus falciformis associated with fish aggregating devices (FADs)
No full textThe silky shark Carcharhinus falciformis is the primary elasmobranch bycatch in the global tuna purse seine fishery using fish aggregating devices (FADs). Information on the associative behaviour of this species with floating objects remains limited. Here the use of various electronic tags provided important new insight into this behaviour. Thirty-eight juvenile silky sharks (69 to 116 cm total length; TL) were tagged with acoustic tags at 9 drifting FADs equipped with satellite-linked acoustic receivers in the western Indian Ocean (total monitoring = 154 d). Presence/absence and swimming depth data were transmitted from the receivers. A subset of 17 individuals was also fitted with pop-up satellite archival tags (PSATs; n = 13), or internal archival tags (n = 4). Behavioural data were successfully collected from 20 of the tagged sharks, covering a total of 300 d. Fine-scale movements of one individual were observed by active tracking, lasting 2 h 46 min. Sharks remained associated with the FAD where they were tagged for extended periods (2.84 to 30.60 d, mean = 15.69 d). Strong diel changes were observed in both FAD association and swimming depth. Typically, individuals moved away from FADs after sunset and returned later that night, then remained closely associated until the following evening. Vertical behaviour also changed around sunset, with sharks using fairly constant depths, > 25 m, during the day and switching to rapid vertical movements during the night, with descents > 250 m recorded. The actively tracked individual returned to a FAD from >1.2 km away. Long residence times and close association highlight the vulnerability of silky sharks to incidental capture in FAD fisheries
First descriptions of the behavior of silky sharks, Carcharhinus falciformis, around drifting fish aggregating devices in the Indian Ocean
No full textSilky sharks, Carcharhinus falciformis (Muller and Henle, 1839), are the primary elasmobranch bycatch species in tuna purse seine fisheries throughout the world's major oceans. Juveniles of this species commonly associate with drifting fish aggregating devices (FADs) deployed to enhance tuna catches in these fisheries. Here we present results from the first investigation into the behavior of juvenile silky sharks associated with drifting FADs in the western Indian Ocean. A total of 10 silky sharks were tagged with coded acoustic transmitters around drifting FADs equipped with acoustic receivers. Following release, all sharks undertook an excursion away from the FAD with which they were associated. Two individuals were subsequently never detected, while the initial absence period of the eight detected sharks ranged between 0.1 and 3.5 d. After returning, total association times averaged 5.19 d (SD = 3.15 d) and related horizontal movement rates ranged from 8 to 50 km d(-1). Short excursions away from the FAD were undertaken by some individuals, all of which lasted a few hours and were made at night. During periods of association, silky sharks typically occupied the upper 35 m of the water column for the majority of the observation period. These results provide new insights into our understanding of associative behaviors. Further studies are needed to improve assessment of the impacts of FADs on the ecology of this species, a major concern considering the large number of FADs deployed
Are drifting FADs essential for testing the ecological trap hypothesis ?
No full textBecause tropical tunas are known to aggregate around floating objects, it has been suggested that the large number of drifting fish aggregating devices (FADS) built and deployed by purse seiners could act as an 'ecological trap'. This hypothesis states that these networks of drifting FADS could take fish to areas where they would not normally go or retain them in places that they would otherwise leave. Because the ecological trap hypothesis was first advanced for drifting FADs, some have argued that only studies using drifting FADs can test this hypothesis. However, because working with drifting FADs is difficult, accepting this precept would preclude the scientific community from providing urgently needed information to organizations charged with management of fisheries that exploit drifting FADs. We argue that because both anchored and drifting FADs alter the natural environment, the more easily accessible anchored FADs can be used to test the ecological trap hypothesis. Also, based on a comparative scientific approach, we argue that understanding the behaviour of tunas around anchored FADs can improve our general understanding of tunas around all types of floating objects and help design new, well focused studies for drifting FADs. As anchored FADs are easier to access and offer a greater potential for research, we encourage scientists to design and conduct studies (in particular on the behaviour of fish at FADS) around the moored structures
Mortality rate of silky sharks ( Carcharhinus falciformis) caught in the tropical tuna purse seine fishery in the Indian Ocean
No full textScientists aboard French purse seine vessels recorded the number and condition of silky sharks (Carcharhinus falciformis) caught during three fishing cruises in the Indian Ocean. A sample of 31 individuals that showed signs of life were tagged with satellite tags to investigate their postrelease mortality. The majority of individuals (95%) were brought on board using the brailer. Combining the proportion of sharks that were dead (72%) and the mortality rate of those released (48%), the overall mortality rate of brailed individuals was 85%. Few individuals (5%) were not brailed as they were entangled and landed during the hauling process. The survival rate of these individuals was high, with an overall mortality rate of meshed individuals of 18%. The combination of these two categories led to an overall mortality rate of 81%. This high value reflects the harsh conditions encountered by sharks during the purse seine fishing process. Consequently, methods that prevent sharks being brought on board are a priority for future investigations, but good handling practices should also be promoted as they could reduce mortality by at least 19%.Des scientifiques embarqués sur des thoniers senneurs français ont enregistré le nombre ainsi que la condition des requins soyeux (Carcharhinus falciformis) capturés pendant trois campagnes de pêche dans l’océan Indien. Un échantillon de 31 individus, présentant des signes apparents de vie, ont été marqués avec des marques satellites pour estimer leur mortalité après leur remise à l’eau. La majorité des individus (95 %) a été embarquée à bord à l’aide d‘une salabarde. En utilisant la proportion des requins morts (72 %) et le taux de mortalité des individus remis à l’eau (48 %), le taux de mortalité global d’individus a été estimé à 85 %. Quelques individus (5 %) n’ont pas été embarqués au moyen de la salabarde car emmaillés et remontés avec le filet lors du virage. Le taux de survie de ces individus était élevé, ainsi le taux de mortalité global n’était que de 18 %. Pour les deux catégories confondues, le taux de mortalité global s’élève à 81 %. Cette valeur élevée reflète la dureté des conditions rencontrées par les requins pendant le processus de pêche. Par conséquent, les méthodes empêchant la mise à bord des requins devraient constituées la priorité des recherches futures. Cependant la mise en œuvre de bonnes pratiques de manipulations devrait aussi être encouragée car elles permettraient de réduire la mortalité d’au moins 19 %
Drifting along in the open-ocean : the associative behaviour of oceanic triggerfish and rainbow runner with floating objects
No full textMultispecies aggregations at floating objects are a common feature throughout the world's tropical and subtropical oceans. The evolutionary benefits driving this associative behaviour of pelagic fish remains unclear and information on the associative behaviour of non-tuna species remains scarce. This study investigated the associative behaviour of oceanic triggerfish (Canthidermis maculata) and rainbow runner (Elagatis bipinnulata), two major bycatch species in the tropical tuna purse seine fishery, at floating objects in the western Indian Ocean. A total of 24 rainbow runner and 46 oceanic triggerfish were tagged with acoustic transmitters at nine drifting FADs equipped with satellite linked receivers. Both species remained associated with the same floating object for extended periods; Kaplan-Meier survival estimates (considering the censored residence time due to equipment failure and fishing) suggested that mean residence time by rainbow runner and oceanic triggerfish was of 94 and 65 days, respectively. During daytime, the two species increased their home range as they typically performed short excursions (<2 h) away from the floating objects. Rainbow runner performed more excursions per unit time than oceanic triggerfish; the mean excursion index was 0.86 (+/- 0.8 SD) for oceanic triggerfish and 1.31 (+/- 1.1 SD) for rainbow runner. Ambient light intensity appears to be the stimulus triggering the onset and end of the associative modes. The observed prolonged residency of these two major bycatch species suggests that they are more vulnerable to the tropical tuna purse seine gear than the targeted tuna species
Behaviour and vulnerability of target and non-target species at drifting fish aggregating devices (FADs) in the tropical tuna purse seine fishery determined by acoustic telemetry
No full textCharacterizing the vulnerability of both target and non-target (bycatch) species to a fishing gear is a key step towards an ecosystem-based fisheries management approach. This study addresses this issue for the tropical tuna purse seine fishery that uses fish aggregating devices (FADs). We used passive acoustic telemetry to characterize, on a 24 h scale, the associative patterns and the vertical distribution of skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares), and bigeye tuna (Thunnus obesus) (target species), as well as silky shark (Carcharhinus falciformis), oceanic triggerfish (Canthidermis maculata), and rainbow runner (Elagatis bipinnulata) (major non-target species). Distinct diel associative patterns were observed; the tunas and the silky sharks were more closely associated with FADs during daytime, while the rainbow runner and the oceanic triggerfish were more closely associated during the night. Minor changes in bycatch to catch ratio of rainbow runner and oceanic triggerfish could possibly be achieved by fishing at FADs after sunrise. However, as silky sharks display a similar associative pattern as tunas, no specific change in fishing time could mitigate the vulnerability of this more sensitive species. For the vertical distribution, there was no particular time of the day when any species occurred beyond the depth of a typical purse seine net. While this study does not provide an immediate solution to reduce the bycatch to catch ratios of the FAD-based fishery in the western Indian Ocean, the method described here could be applied to other regions where similar fisheries exist so as to evaluate potential solutions to reducing fishing mortality of non-target species
Banning is not enough : the complexities of oceanic shark management by tuna regional fisheries management organizations
No full textAbstractRecently, declining populations of several pelagic shark species have led to global conservation concerns surrounding this group. As a result, a series of species-specific banning measures have been implemented by Regional Fishery Management Organizations (RFMOs) in charge of tuna fisheries, which include retention bans, finning bans and trading bans. There are both positive and negative aspects to most management measures, but generally, the positive aspects outweigh the negatives, ensuring the measure is beneficial to the resource and its users in the long term. Banning measures are a good first step towards the conservation of pelagic shark species, especially since they improve conservation awareness among fishers, managers and the public. Measures that impose total bans, however, can lead to negative impacts that may jeopardize the populations they were intended to protect. The majority of pelagic shark catches are incidental and most sharks die before they reach the vessel or after they are released. The legislation set out by RFMOs only prevents retention but not the actual capture or the mortality that may occur as a result. Managers should be fully aware that the development and implementation of mitigation measures are critical for a more effective conservation strategy
