A new study correlates smaller sized fish to bottom trawling in heavily trawled areas. Scientists have previously presumed that fish that who escaped and did not get caught in the trawler became skinny due to hunger, this new study indicates that this is not the case instead the study points towards altered food sources to be the cause.
A research group from the Bangor University in the UK investigated the effect of bottom trawling on two commercially important flatfish species, plaice (Pleuronectes platessa) and dab (Limanda limanda), in a heavily trawled area of the Irish Sea found. Their findings indicates a correlation between smaller sized fish and heavy bottom trawling.
In their study the researchers compared preferred prey, range of prey, and overall stomach energy contents and fullness of plaice and dab. The overall body condition was found to decrease in plaice while no change was observed in dab. The results are contrary to what previously have been assumed, that decreased fish size is a result of heavy trawling and reduced prey availability, the researchers found that plaice left behind where found with full stomachs hence no sing of hunger, and argue that even though trawling frequency increases, the ratio between predator and prey remains unchanged . The decrease in body size/condition of plaice is argued to be due to shifting to energy-poor prey items coupled with having to search longer for prey ie using more energy. Thus “fish living in highly trawled areas are still able to maintain food intake when the consumption and quantity of food is changed as a result of chronic bottom trawling”. No significant changes where seen for dab, this is thought to be due to dab being a generalist feeder and thus able to more switch prey more easily than plaice.
The findings from the study are indeed noteworthy results which may have implications for fishery management and as the authors point out “understanding the relationship between trawling, benthic impacts, fish foraging and resultant body condition is an important step in designing successful mitigation measures for future management strategies in bottom trawl fisheries”. The findings from this study makes one contemplate about the correlation between the skinny cod and trawling in the Baltic Sea.