Impact of pulsed direct current on embryos, larvae, and young juveniles of Atlantic cod and its implications for electrotrawling of brown shrimp

The application of electrical pulses in fishing gear is considered a promising option to increase the sustainability of demersal trawl fisheries. In the electrotrawl fishery for brown shrimp Crangon crangon, an electrical field selectively induces a startle response in the shrimp. Other benthic organisms remain mainly on the seafloor and escape underneath a hovering trawl. Previous experiments have indicated that this pulse has no short-term major harmful effects on adult fish and invertebrates. However, the impact on young marine life stages is still unknown. Because brown shrimp are caught in shallow coastal zones and estuaries, which serve as important nurseries or spawning areas for a wide range of marine species, electrotrawling on these grounds could harm embryos, larvae, and juveniles. We carried out experiments with different developmental stages of Atlantic Cod Gadus morhua, which are considered vulnerable to electrical pulses. Three embryonic stages, four larval stages, and one juvenile stage of Atlantic Cod were exposed to a homogeneous electrical field of 150 V-peak/m for 5 s, mimicking a worst-case scenario. We detected no significant differences in embryo mortality rate between control and exposed groups. However, for the embryonic stage exposed at 18 d postfertilization, the initial hatching rate was lower. Larvae that were exposed at 2 and 26 d posthatch exhibited higher mortality rates than the corresponding nonexposed control groups. In the other larval and juvenile stages, no short-term impact of exposure on survival was observed. Morphometric analysis of larvae and juveniles revealed no differences in measurements or deformations of the yolk, notochord, eye, or head. Although exposure to a worst-case electrical field did not impact survival or development for six of the eight young life stages of Atlantic Cod, the observed delayed hatching rate and decreased survival for larvae might indicate an impact of electric pulses and warrant further research

The swimming kinematics of larval Atlantic cod, Gadus morhua L., are resilient to elevated seawater pCO2

Kinematics of swimming behavior of larval Atlantic cod, aged 12 and 27 days post-hatch (dph) and cultured under three pCO2 conditions (control-370, medium-1800, and high-4200 μatm) from March to May 2010, were extracted from swim path recordings obtained using silhouette video photography. The swim paths were analyzed for swim duration, distance and speed, stop duration, and horizontal and vertical turn angles to determine whether elevated seawater pCO2—at beyond near-future ocean acidification levels—affects the swimming kinematics of Atlantic cod larvae. There were no significant differences in most of the variables tested: the swimming kinematics of Atlantic cod larvae at 12 and 27 dph were highly resilient to extremely elevated pCO2 levels. Nonetheless, cod larvae cultured at the highest pCO2 concentration displayed vertical turn angles that were more restricted (median turn angle, 15°) than larvae in the control (19°) and medium (19°) treatments at 12 dph (but not at 27 dph). Significant reduction in the stop duration of cod larvae from the high treatment (median stop duration, 0.28 s) was also observed compared to the larvae from the control group (0.32 s) at 27 dph (but not at 12 dph). The functional and ecological significance of these subtle differences are unclear and, therefore, require further investigation in order to determine whether they are ecologically relevant or spurious

Staff training to improve participant recruitment into surgical randomised controlled trials : a feasibility Study Within A Trial (SWAT) across four host randomised controlled trials simultaneously

Objective To test the feasibility of undertaking a simultaneous Study Within A Trial (SWAT) to train staff who recruit participants into surgical randomised controlled trials (RCTs), by assessing key uncertainties around recruitment, randomisation, intervention delivery and data collection. Study design and setting Twelve surgical RCTs were eligible. Interested sites (clusters) were randomised 1:1, with recruiting staff (surgeons and nurses) offered training or no training. The primary outcome was the feasibility of recruiting sites across multiple surgical trials simultaneously. Secondary outcomes included numbers/types of staff enrolled, attendance at training, training acceptability, confidence in recruiting and participant recruitment rates six months later. Results Four RCTs (33%) comprising 91 sites participated. Of these, 29 sites agreed to participate (32%) and were randomised to intervention (15 sites, 29 staff) or control (14 sites, 29 staff). Research nurses attended and found the training to be acceptable; no surgeons attended. In the intervention group, there was evidence of increased confidence when pre and post training scores were compared (mean difference in change 1.42; 95% CI 0.56, 2.27; p = 0.002) – there was no effect on recruitment rate. Conclusion It was feasible to randomise sites across four surgical RCTs in a simultaneous SWAT design. However, as small numbers of trials and sites participated, and no surgeons attended training, strategies to improve these aspects are needed for future evaluations. Trial registration ISRCTN registry: DISC (ISRCTN18254597), registered on 4th April 2017; PROFHER 2 (ISRCTN76296703), registered on 5th April 2018; IntAct (ISRCTN13334746), registered on 10th April 2017; and START:REACTS (ISRCTN17825590), registered on 5th March 2018. The training SWAT has been submitted to the MRC SWAT repository (SWAT111) Keywords: Randomised controlled trial (RCT), Study Within A Trial (SWAT), recruitment, staff training, professional education, feasibility study, surgical trial