Case Study 3 Report – Black scabbardfish in ixa

Executive Summary

This case-study deals with the southern component of the Portuguese fishery for black scabbardfish in ICES subarea IXa.

The insufficient knowledge on the stock structure of this resource leads to admit a single stock along the NE Atlantic. For management purposes and due to the different nature of fisheries in the northern and southern areas, the stock is divided into: i) Southern component (the present Case Study): that uses longline as fishing gear; and ii) Northern component. The CPUE at the southern component (ICES subarea IXa) has been relatively stable during the last decade and at the northern component CPUE data indicate a decline in abundance since 1990.

The major gaps in knowledge of this species in NE Atlantic refer to stock structure and its dynamics. Several studies to test the hypothesis of one stock along the NE Atlantic have already been undertaken but the results were inconclusive. The stock dynamics, specifically the spatial and temporal distribution of the different life stages, is also deficiently perceived. The most recent hypothesis is that the dispersion of the different life stages of black scabbardfish is associated with vertical and horizontal migrations dependent on feeding and reproduction along the NE Atlantic (Anon., 2000): eggs hatch around Macaronesia area at great depths; during the first years of life, juveniles migrate in search of food to more northern waters (W British Isles), where they live at depths of 300-400 m, moving to greater depths to feed; after a period of growth in that area, they move south (Mainland Portugal) and sink to the deep water column layers, where they reach the adult phase; later, adults move away to Macaronesia waters to spawn. Moreover, there is poor knowledge regarding the natural mortality, growth and recruitment.

The main gaps with fishery data deals with: effort, log book and VMS data not only for the Portuguese fishery for black scabbardfish in ICES subarea IXa (present case study) but for all the fisheries exploiting the stock. For the case study under analysis there are data from landings since 1988 but the obligation to fill logbooks was only established long after the start of the fishery. Vessel Monitoring System (VMS) data from the Portuguese surveillance (period: 2000–2004) and data from the monitoring system that records the activity of fishing vessels (MONICAP) were analysed and were considered adequate for assessing the distribution of the fishing grounds and fishing time. However the recent EU adoption of 2 h time interval to transmit position proved to be inadequate for estimating fishing effort especially in static gears as the longlines. An important example of good practice is the active collaboration between IPIMAR and stakeholders from this fishery to update historical data, as well as, initiate self-sampling programs.

For the black scabbardfish stock there is no fisheries independent data, despite efforts done by the Planning Group on Northeast Atlantic Continental Slope Survey to propose an international coordinated survey on slope and deep-water areas of the NE Atlantic.

Under the DEEPFISHMAN it has been proposed to assess the exploitation status of the Mainland Portugal component of the stock in face of the available knowledge and data. However it is recognized that this must be extended to the whole stock area. Hence an essential starting point to be undertaken under DEEPFISHMAN is to develop an operating model that represents the fisheries and fish stock dynamics by describing a particular “scenario”. Some input parameters could be estimated using the assessment method developed for this case study. Furthermore a set of plausible OMs based on realistic input parameters could be tested, as well as, the performance evaluation of the different Harvest Control Rules.

The main management issues currently facing black scabbardfish stock are: i) the evaluation of the actual exploitation level of the stock in relation to MSY; ii) the proposal of management measures other than TACs for mixed fisheries; iii) the coordination of management measures with other areas of the stock besides ICES; and iv) the evaluation of different management scenarios, namely the possibility to define spatial and temporal closures to protected life stages (e.g. juveniles and spawners). For all these issues and bearing in mind that the present case study deals only with a fraction of the overall stock, a concerted action plan particular with the main players investing or exploiting the resource is required.