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A new study examines Cod Survivability in the Irish Fly-shoot Seine fishery
Highlights
- Study on post-capture cod survival in the Irish fly-shoot seine fishery successfully completed.
- Cod survival was poor mainly due to barotrauma.
- Survivorship pop-up satellite archival tags were effective in assessing cod survival and elucidating mortality causes.
- sPATs have major potential to assess survival in other species.
The study conducted a pilot-scale assessment of cod (Gadus morhua) survival in the fly-shoot seine fishery using survivorship pop-up satellite archival tags (sPATs). The study was carried out onboard the MFV Róise Catriona, a 24metre steel fly-shoot seine (SSC) vessel during commercial fishing operations off Irelands south-west coast in ICES divisions 7.j.g between 20 – 23 July 2022.
Fly-shoot seining for demersal species is a commercially important fishery for Irish vessels operating in the Celtic Sea. Poor stock status has led to parts of the Celtic Sea having no directed fishery permitted for Atlantic cod where the quota is exclusively for bycatches in fisheries for other species (EU, 2020).
Irish fishermen need to reduce cod catches to help improve stock sustainability and avoid early cessation of fishing operations under the European Union (EU) landing obligation.
Bottom-trawlers can use raised fishing line gear or change fishing grounds to avoid cod in the Celtic Sea. SSCs do not have this gear option, and limited grounds suitable for seining are available outside the Celtic Sea which restricts their movements.
Irish fishers reported that seine-caught cod are in excellent condition and requested an assessment of post-capture survival towards application for an exemption under the EU landing obligation (LO).
Figure 1.
Supporting information on fish condition including vitality on a modified four-point scale – excellent, good, poor and moribund – was collected for all cod caught during the trial.
Ten cod of suitable size for tagging (≥ 55 cm) in excellent and good vitality were tagged and released.
Cod in poor and moribund vitality were assumed to have died. A Kaplan-Meier estimator was used to assess cod survival. Of 96 cod caught during the trial, 53 (55%) were ≥ 55 cm with 18 (34%) of these found to be in excellent or good vitality.
Tagged fish were representative of the latter component of the catch. All 10 tags reported data with tag deployment period ranging from 2 to 21 days and a mean survival of 10 days. Assuming a 34% survival probability at time zero, survivability gradually decreased to zero at day 20 when all fish were assumed to have died. Barotrauma was likely the main cause of poor survival in this study.
Alterations to fishing operations to reduce barotrauma are technically feasible but unlikely to be commercially viable. The sPATs and tagging procedures used in this study generally worked well in estimating cod survival rates, elucidating mortality causes and have potential applications for other species.
The MFV Róise Catriona targeted mixed demersal fish using a fly-shoot seine constructed from polyethylene twine with rope ground gear and a 100 mm T90 cod end. This fishing operation encircles fish by deploying port seine ropes which are attached to flotation buoys and payed out until the seine net is set. The starboard seine ropes are then payed out until the port rope is picked up and hauling can commence. Once hauling commences, the seine ropes gradually come together as the vessel moves slowly forward into the tide. Data were recorded on operational parameters that could affect survivability such as depth, haul duration and total catch weight for each haul.
