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- Reducción de la captura secundaria y los descartes en la pesquería costera de pequeña escala del Algarve utilizando una red de trasmallo de monofilamento equipada con una red de protecciónPublication . Szynaka, Monika; Bentes, Luis; Monteiro, Pedro; Rangel, Mafalda; Erzini, KarimExperimental fishing was conducted off the port of Quarteira (southern Portugal) from October 2016 to February 2017 using standard trammel nets and modified nets rigged with a guarding net. The commercial catches of trammel nets rigged with a guarding net were 46.1% and 38.0% less than those of the standard net in numbers and economic value. However, there were significantly fewer commercial discards in biomass in the modified trammel nets (68.2%) and by-catch abundance and biomass were also lower in the modified nets (41.8% and 17.3% less, respectively). For the two main fish by-catch species, the modified net caught 62.2% fewer longfin gurnards (C. obscurus) and 33.1% fewer greater weever (T. draco) than the standard nets. Timing the removal from the nets of the main by-catch and discards species revealed savings in time associated with the use of modified nets. However, net damage occurred twice as much as in the modified net, probably contributing to the reduced commercial catches. The results indicate that trammel nets with the guarding net reduce by-catch and discards and save time, but are unlikely to be adopted by fishers targeting soles due to the higher costs of the modified nets and losses in commercial catches and earnings.
- Reduction of by-catch and discards in the Algarve small-scale coastal fishery using a modified monofilament trammel netPublication . Szynaka, Mj; Erzini, KarimThe purpose of this project is to reduce bycatch by modifying a monofilament trammel net commonly used in small scale fisheries along the southern European and Mediterranean coasts. The standard trammel net consists of three layers of netting: a small mesh inner panel and two large mesh outer panels. The modified net has a single layer of netting 3 meshes high between the trammel net and the footrope termed “greca”, also known as a selvedge net. The main goal was to provide enough evidence of benefits that the modification poses, such as reduction in environmental deterioration, decrease in bycatch removal, and preventing a fisheries collapse, to local fishermen to convince them switch to the “greca” net. Fishing was conducted off the coast of Algarve with the boat departing from Quarteria from October 2016 to February 2017 with a total of 20 trips. Each fish and invertebrate was identified and measured, and recorded in which net type it was caught after a 24 hour soak time period. The time that it took to remove bycatch species was later analyzed using videos recorded onboard using GoPros and net damage assessment was conducted after the sampling period. Analysis using PRIMER and PERMANOVA showed that the factors depth and target catch affected commercial catch among the net types. This was also true for the combined catch data. Bycatch was also affected by the factor seasonality, however the separation between the two seasons was moderately distinct. When observing commercial catch, the greca net caught 53.9% of that of the standard trammel net regarding abundance and 64.3% of that of the standard trammel net in biomass. The economic value of the greca net catches was 61.8% of that of the standard net. The most significant decrease in commercial catch was seen among the sole species (or demersal commercial catch). Regarding discards, the greca trammel net caught 45.3% of that in the standard trammel net in commercial discards abundance and 57.7% of that in the standard net in bycatch abundance. The greca trammel net commercial discard biomass was 31.8% of that of the standard trammel net and 80.4% of the standard net bycatch biomass. For the three main bycatch species greca net catches for Longfin gurnards (Chelidonichthys obscurus) were 37.8% of those of the standard net caught, 128.4% of the standard net for Atlantic chub mackerel (Scomber colias) and 66.9% of those of the standard net for the Greater weever (Trachinus draco). The time it took to remove an individual from the net was timed and the six most abundant bycatch species’ exhibited the importance of reducing bycatch. Some species will eventually take away many hours over the course of a year that could be spent on removing commercial catch or reducing labor in general. Less bycatch also reduces the damage that occurs in the net, relieving fishermen of additional costs in repairs. This also prevents loss in commercial catch, such as the observed decrease in catch rate of sole species in the modified trammel net. The results suggest that the greca modification, or selvedge net, did reduce bycatch abundance but, also reduced abundance and earnings in commercial catches. It is concluded that further research needs to be conducted on ways toreduce bycatch using trammel nets while maintaining similar if not increasing earnings.