Benthic Habitats and the Effects of Fishing

Symposium Abstract: Fish Landings, Discards, and Benthic Material from Otter Trawling in the Western English Channel

S. P. Cotterell

doi: https://doi.org/10.47886/9781888569605.ch54

A fleet-stratified sampling design was employed between 1998 and 2000 to study fish discards and landing and to quantify the other incidentally caught material. The studied techniques were <12m single boat otter trawling, <12m paired demersal trawling and >12m single boat otter trawling. Trips for <12m ranged from one to three days while those for >12m boats were one to six days. These boats operated out of the four principle English ports of ICES area VIIe, western English Channel. On board the boats and prior to any sorting by the crew a sample (~40kg) of the catch was taken and all fish were identified and measured, and their fate (whether to be landed or discarded) was noted. All non-fish material was stored in the fish hold for later detailed analysis. The non-fish material was categorised as benthos, or biogenic, inorganic, or anthropogenic material. The benthos was classified, weighed and measured. Also, a system to assess its degree of damage was developed, allowing length-weight regressions to be generated for the more common invertebrate species. On average 60% (by weight) of the haul was landed, 10% was bait fish, 20% was discarded and 10% was non-fish material. Landing samples were compared to confidential catch composition figures of trip landings. British Geological Survey data was used to assess the substrate over which the trawl had passed and benthos composition was compared to historical data sets. From this study it would appear that economic overfishing would occur before irreparable benthic disturbance for these techniques.