Internal injuries in whiting (Merlangius merlangus) caught by tickler-chain and pulse-trawl gears

Electrical pulse fishing has been widely adopted by Dutch fishers as an economically viable alternative to tickler-chain trawling for common sole (Solea solea) in the North Sea. Concerns exist, however, that the use of electrical pulses may cause spinal injuries and haemorrhages, as previously shown for Atlantic cod (Gadus morhua). To find out whether other gadoids are similarly affected, we studied injury occurrences in whiting (Merlangius merlangus) catches on commercial vessels. To distinguish mechanically and electrically-induced injuries, we compared (1) injuries for pulse gears with electrical pulses either turned on or off and (2) injuries from pulse-trawl catches with those in tickler-chain trawling. Spinal injuries were visualised with X-radiography and internal haemorrhages with subsequent dissection. Injuries were categorised on a severity scale and their location was quantified along the anteroposterior fish axis. Major spinal injury occurrence in (1) pulses-on and pulses-off samples were lower than 1% and not significantly different between catch methods. Major spinal injury occurrence was slightly higher in (2) tickler-chain catches (2.4%) than in pulses-on samples (1.1%). Major haemorrhage occurrences were also low. The slightly higher occurrences of these haemorrhages in pulses-on samples (1.8%) compared to fish caught with tickler chains (0.3%) and their locations suggest that they may be partly related to electrical-pulse exposure. Overall, our results indicate that injuries in whiting are rare and primarily due to mechanical impact. These findings suggest that pulse trawling is unlikely to impose increased mortality on whiting populations compared to the tickler-chain technique.