Evaluating modifications to fishing gear in trammel net fisheries targeting Cuttlefish, Soles, and Rays.
MINOUW partner & Lead scientist:
CCMAR (Centro de Ciências do Mar do Algarve) , Karim Erzini
Fishing method and species:
Monofilament trammel nets with 110 mm stretched mesh inner panel (0.30 mm diameter monofilament), 40 meshes high, and 60 cm stretched mesh outer panels (0.60 mm diameter monofilament), 3 meshes high. Species targeted are Cuttlefish (Sepia officinalis), Soles (Solea spp.), Rays (Raja spp.).
What is the discards problem?
Trammel nets have low species selectivity, catching a large number of target and non-target species. Previous studies in the Algarve reported high discard rates, mainly of small pelagic fishes (mackerel and sardine) and non-commercial invertebrates such as sea urchins.
What activities did the MINOUW project carry out?
- Testing of a modified trammel net with "greca" (selvedge, or guarding net).
- Estimating handling and sorting costs.
- Comparison of commercial catches of standard and modified trammel nets.
- Evaluation pros and cons of the use of modified trammel nets (i.e. is it economically worthwhile?).
What outcomes were expected?
- Establish whether it is possible to reduce the by-catch of unwanted invertebrates by using a single panel of large mesh netting (3 meshes high) attached to the footrope below and to the trammel net above.
- Evaluate the effect of the use of the by-catch reducing device (BRD) on the commercial catch (i.e. the economic yield). The benefits of the BRD in terms of handing time will also be evaluated. This will allow a final evaluation of the likelihood of the modified gear being voluntarily used by the fishermen, given the additional cost of the gear associated with the modification.
- Understand what factors lead to discarding practices and how new technologies (modifications to nets; use of lights) can mitigate the problem of discards in bottom trawl fisheries.
- Foster fishers’ involvement in the process of finding solutions to mitigate the impact of the Landings Obligation in their activity. Encourage fishing practices and technologies that minimize fishing impact on ecosystems.
Significant reduction in by-catch and discards of finfish and invertebrates as well as decreases in handling time and net damage associated with removal of discards, was recorded. Modifying trammel nets by incorporating a guarding net between the footrope and the trammel net can significantly reduce by-catch, discards, handling time and net damage. However, in some fisheries targeting bottom associated species such as soles, modified nets will result in a loss of income due to reduced catch rates of target species such as soles.