"Marine Protected Areas and SPECIES"
Marine Protected Areas and Common skate (Dipturus intermedia) Position paper Summary 1. Common skate (Dipturus intermedia) are included on the MPA search feature list for Scottish territorial waters (Marine Scotland, 2011a). Around the UK, the common skate is found almost exclusively in Scottish waters. Currently there are no existing protected area measures that help to safeguard common skate and they have been identified as a search feature priority in the West MPA region (which lies within OSPAR Region III, Celtic Seas). The species is widely spread across the region, but appears to be concentrated in certain deep sea lochs and inshore deep channel areas. 2. On the basis of the available evidence, it is recommended that two previously identified search locations are subject to a more detailed assessment against the MPA Selection Guidelines for common skate. These are Loch Sunart, and Loch Sween and the Sound of Jura (mapped on Figure 1 overleaf). Replication in the MPA network for common skate may be attained if both search locations are progressed as MPAs. 3. Common skate is key to a third party MPA proposal by the Scottish Sea Angling Conservation Network (SSACN). Encompassing both MPA search locations, their proposal also covers the Firth of Lorn and Sound of Mull. There is evidence for resident mature common skate in both of these other areas which could serve to provide connectivity between the recommended search locations (see Figure 1). The merits of progressing these additional areas should be discussed at workshop 4. 4. Loch Sunart and the Loch Sween and the Sound of Jura search locations both encompass multiple MPA search feature priorities but are considered here primarily in relation to their potential to contribute to the protection of common skate. The reason these locations are important for common skate is that the evidence suggests; significant aggregations of large reproductively mature individuals high site-fidelity (residency) of individuals to these locations 5. The evidence used to support Loch Sunart and the Loch Sween and the Sound of Jura search locations for common skate is: records of concentrations of large mature common skate as indicated by recreational angling and trawl surveys high site-fidelity as indicated by tag-recapture data and an acoustic tracking study 6. Significant concentrations of common skate are also presently found in other areas, notably a large offshore area to the west of Hebrides, an inshore area on the west side of the Isle of Harris and the inshore waters of Orkney. However, there are currently insufficient data to determine whether skate in these areas are transient or residential or if these areas are especially important for a particular life-history stage, such as egg case deposition. 1 Figure 1 Map showing the two MPA search locations on the west coast of Scotland (within the Celtic Seas OSPAR Region III) that are relevant to common skate, as well as the two additional areas for common skate covered by the SSACN third party MPA proposal 2 Purpose of document 7. This position paper has been produced to support identification of MPA search locations suitable for conserving common skate. 8. Common skate are a search feature priority in territorial waters of the OSPAR Celtic Seas Region (fully encompasses the West and South-west MPA regions). Recently it has been demonstrated that there are two species of what used to be classed ‘common skate’ or Dipturus batis; namely D. intermedia and D. flossada (Inglesias et al., 2010). In the west of Scotland, the vast majority of individuals are D. intermedia (Griffiths et al. 2010). The species is listed as ‘critically endangered’ and based on evidence for site fidelity is considered to be a priority within the following MPA search locations; 1) Loch Sween and the Sound of Jura, and 2) Loch Sunart. In addition, this species is key to a third party MPA proposal by the Scottish Sea Angling Conservation Network (SSACN) for five discrete areas that also include the Firth of Lorn and Sound of Mull for common skate. 9. Although not currently considered as MPA search locations, Orkney waters and West Loch Tarbert on the Isle of Harris, also appear to hold important concentrations of common skate. The species is also present in the following previously identified search locations: Windsock; Geike Slide and Hebridean Slope; Skye to Mull; North-west sea lochs and Summer Isles; Gairloch, Loch Torridon and Northern Inner Sound; Loch Carron and Loch Kishorn; and, the Small Isles. However, no information is available on site fidelity for these locations. 10. Marine Scotland’s Marine Nature Conservation Strategy (Marine Scotland, 2011b) advocates a three pillar approach to conservation in the marine environment; with the three pillars representing species-specific measures, site protection and a wider seas policy approach. There are fisheries restrictions on skate with a zero TAC and mandatory release since 2009. It is important to emphasise that for the widely distributed common skate, wider conservation measures (in addition to site protection) will be required. Distribution in Scottish waters 11. A large amount of data are available on the distribution of common skate from research vessel surveys, tagging studies and catch records. Since the 1920s common skate have been caught in Marine Scotland Science trawl surveys of the North Sea and west coast of Scotland. In recent years an average of less than 1 individual is caught per hour of trawling, although in the distant past at some locations large catches (up-to 150 fish per hour) were recorded. These data concur with Walker and Hislop (1998) that the species was once common in the North Sea, but since the 1970s has become very rare there. Across the West MPA region it is still widespread, albeit at relatively low density. Consequently, it is practical to focus attention on the west region for this species. Tag-recapture data from recreational sea anglers and recent research projects suggests there are certain sea lochs and inshore deep channels where large mature individuals are resident in relatively high numbers. There is also some evidence that shallow reef areas are used by common skate for laying their egg-cases, however, there is no evidence to point toward specific sites as nursery grounds for this species (Ellis et al., 2011). In combination these data sources (Figure 2) have been used to assess the distribution, abundance and degree of residency of common skate in the West MPA region. 3 Figure 2 Map showing spatial extent of all sources of data used to assess distribution and abundance of common skate in Scottish waters. Each dot represents a survey station or observation record. Also shown are the previously identified MPA search locations (see legend for details) Perceived role of MPAs for common skate 12. The common skate (D. intermedia) is a large (up-to 285 cm long and over 100 kg), long-lived (in excess of 50 years), late-maturing species (> 11 years at first maturity) with low fecundity. Around the UK it is found almost exclusively in Scottish waters (Griffiths et al., 2010) and although once widespread across the northern North Sea is now largely confined to the West MPA region. It is vulnerable to trawl and long-line fisheries and has shown a marked decline and significant range contraction over the past century, largely as a consequence of removal by fisheries (Walker and Hislop, 1998). Protection from fisheries is therefore a key means of conserving this species and closing areas may confer significant benefits. The degree of protection arising from closing an area, however, will depend on the level of site fidelity of fish throughout the period they are vulnerable to fishing gears (Polunin, 2002). As common skate are vulnerable to fishing gears from the time they hatch out of their egg case this means that protection of the entire life cycle may be needed. There are no directed fisheries for common skate. Landings data since 2008 suggest minor by-catch (a total of 18 tonnes between 2008-2011) of common skate, mainly from the sea area to the north and west of the Hebrides and Orkney which is not within any of the search locations. 13. An extensive tag-recapture programme first established by Glasgow Museum in the 1970s and more recent electronic tagging programmes (Wearmouth and Sims, 2009) provides considerable evidence for high site fidelity of mature common skate in certain sea lochs, inner firths and sounds. As such, area protection may be expected to reduce fishing mortality on these mature individuals that may compromise a highly significant component of the breeding biomass (OSPAR, 2010). Importantly there is also evidence for occasional straying between areas suggesting that there is the 4 potential for the species to re-colonise its former range. For a widespread species such as common skate that is distributed far beyond all of the search locations, an effective conservation programme should also include other fisheries management measures. Evidence base 14. MSS trawl survey data for the west coast is available from 1925 (a total of 1,580 hauls recorded common skate). However the frequency, time of year and the types of survey gears and methods were variable over this period until 1986. It is nevertheless useful for establishing the distribution of the species and for giving a general insight into the range contraction of the species over the past century (Figure 3). Figure 3 Maps of the distribution and abundance (not standardised) of common skate based on research vessel surveys for each decade over the past 90 years. Green areas are the previously identified MPA search locations 15. Since 1986, when the International Bottom Trawl Survey quality standard was introduced for the west coast area, consistent data have been collected for the first and last quarter of each year. These data allow for better definition of presence and abundance and more reliable estimates of abundance and density (Figure 4). 16. Other sources of recent data include a series of inshore trawl surveys undertaken between 2003-2005 and an ad-hoc survey in the Firth of Lorn area undertaken in 2010 by SAMS (Figure 5). These provide important information in those inshore areas (including sea lochs) not covered by the IBTS surveys. 5 Figure 4 Map showing the presence and absence of common skate on the west coast of Scotland based on data from the International Bottom Trawl Survey during the period 1986-2008. Yellow points = presence, green points = absence. Previously identified MPA search locations also indicated Figure 5 Map showing presence and absence of skate based on data collected in ad-hoc surveys of the inshore areas of the west region in the 2000’s (green points = absence, yellow points = presence) 6 17. Over 2000 presence records are available from a variety of sources amalgamated by SNH (Figure 6). A further key source of information is the extensive tag-recapture programme (~2000 individuals tagged and released) that the recreational sea angling community have practised since the 1970s (Figure 7). Figure 6 Map showing extent of records of skate gathered by SNH (presence only) Figure 7 Map showing main area of tag-recapture data collected by Glasgow Museum and SSACN. Green points are release sites, yellow points recaptures. See legend for MPA search location symbology 7 18. This data derives mainly from the area that includes the Sound of Mull, Loch Sunart, the Firth of Lorn and the Sound of Jura. The tag-recapture data provides strong evidence for a high degree of residency with very occasional exchange between areas. Only recently (since 2008) have landings been reported to the species level for skates and rays and so catch statistics of common skate are limited to the past 3 years (Figure 8). Figure 8 Map showing proportional size of landings of common skate per ICES rectangle for the period 2008-2011 (total landings were 18 tonnes) 19. Table 1 summarises the evidence base for each of the types of areas that could be used to help contribute to the protection of common skate and recommends which should be considered further in terms of supporting identification of MPA search locations for common skate. Table 1 Summary of the evidence base for the types of areas that could be used to help contribute to the protection of common skate in Scottish waters Type of area Evidence base Recommendation Concentrations of mature Tag-recapture from anglers OSPAR recommends protection of the residential individuals and telemetry data shows reproductive component of stock; long term site fidelity reducing mortality on large mature females may be the most effective way of achieving this Areas where egg cases Observational records from Protection of egg cases from physical are found in high density divers disturbance may increase survival to (equivalent of spawning hatching (vulnerable life-history stage) grounds) Areas of high density Trawl survey data indicates Until further information is available on some areas of higher than site fidelity, need to rely on wider average density conservation measures 8 Type of area Evidence base Recommendation Areas of high juvenile Trawl survey data do not Not considered further density (nursery grounds) indicate that there are geographically discrete nursery grounds for common skate (< 50 cm long) MPA search location proposals 20. The following search locations all fall within the distribution of common skate based on survey data: Windsock; Geike Slide and Hebridean Slope; Skye to Mull; North-west sea lochs and Summer Isles; Gairloch, Loch Torridon and Northern Inner Sound; Loch Carron and Loch Kishorn; Small Isles; Loch Sunart; and, Loch Sween and Sound of Jura. Table 2 summarises each area. Of these locations, Loch Sunart and the Sound of Jura appear to be key sites for residential groups of mature common skate. The tag- recapture data provides the strongest evidence for this. In the Loch Sunart / Sound of Mull area, out of over 500 skate tagged and released, 38 % were recaptured. Of the recaptures 90 % were from the release area, with the remaining 10 % recaptured from the neighbouring Firth of Lorn. In the Sound of Jura, out of 170 individuals tagged and released, 10 % have been recaptured, all of which were tagged and released in this area. Some individuals have been recaptured multiple times over many years providing strong evidence for very limited home ranges in mature individuals. 21. In October 2011, 20 large common skate were fitted with acoustic transmitters in the Sound of Jura. A series of receivers were placed throughout the Loch Crinan area and Sound of Jura. The first data were recovered in February 2012 from 2 of the receivers in the area. Between these 2 receivers all 20 skate were detected in the first month after release and approximately half of those were still being detected in February. This indicates that those individuals have largely stayed within 2 kilometres of where they were released. Further data will be needed to be recovered to confirm how far afield the remainder of the tagged individuals had moved. 22. The same tag-recapture programme provides similar strong evidence for residential groups of common skate in the Firth of Lorn (an area covered by the SSACN third party MPA proposal). It is possible that the Sound of Mull and Firth of Lorn are part of the same population unit. The MSS inshore trawl survey data independently confirmed the presence of common skate in Loch Sunart. It should, however, also be noted that this survey sampled a number of other sea lochs including Loch Hourn where the presence of common skate could not be confirmed. This suggests these large mature skate are quite specific to particular areas rather than being generally associated with deep sea lochs. For the remaining search locations, while there is evidence for the presence of common skate, including large mature individuals, there is no information on whether they are resident. It is possible that some groups of common skate are vagrant and migratory while others are and residential and site-specific. Evidence from Data from the Orkney Skate Trust suggests the Hoy MPA search location should also be reconsidered for common skate. 23. Common skate are found in association with ‘shelf deeps’ habitat, e.g. Sound of Jura. They may also use shallow reef habitat for laying their egg-cases as is reported by the Orkney Skate Trust and SNH. However, there is little further evidence for functional relationships with other priority feature habitats or species. 9 Table 2 Summary of MPA search locations and third party MPA proposals within which the status of common skate was assessed; rows in bold text are those proposed search locations for common skate, rows in plain text are areas not recommended for progression on the basis of common skate alone Location Other mobile species Comments/evidence MPA search features Loch Sunart n/a Strong evidence for resident mature individuals Loch Sween and Sound of n/a Strong evidence for resident Jura mature individuals Firth of Lorn and Sound of n/a Evidence for resident mature Mull (third party proposal) individuals Windsock n/a Presence of mature individuals Geike Slide and Hebridean Basking shark Presence of mature individuals Slope Skye to Mull Basking shark and minke Presence of mature individuals whale North-west sea lochs and n/a Presence of mature individuals Summer Isles Gairloch, Loch Torridon and n/a Presence of mature individuals Northern Inner Sound Loch Carron and Loch Kishorn n/a Presence of mature individuals Small Isles n/a Presence of mature individuals Hoy n/a Presence of mature individuals Issues and opportunities 24. Two further areas, the waters around Orkney and West Loch Tarbert on the Isle of Harris have been suggested by recreational anglers and conservation organisations as areas of particular significance for common skate. 25. Replication in the network for common skate may be attained if both Loch Sween and Sound of Jura, and Loch Sunart MPA search locations are progressed. The third party proposal for the larger area that also encompasses Firth of Lorn and the Sound of Mull could provide linkage between these site locations. A greater degree of replication around Scotland would be achieved if the Orkney and West Loch Tarbert sites turn out to contain critical habitat for common skate or contain mature resident groups of fish and are therefore progressed in the future. Next steps 26. The concurrent acoustic tracking and data storage tag project is monitoring the movements of 20 common skate in the Loch Crinan / Sound of Jura area. This will give better definition of the degree of residency and individual home ranges of the common skate found in this area. Preliminary results have been obtained but full results will not be available until October 2012. Further electronic tagging using data storage tags will be undertaken in other areas, e.g. Loch Sunart, Isle of Harris, Orkney and more offshore areas over the coming year. An extensive analysis of the SSACN tag- recapture database is currently being undertaken to elucidate individual movement patterns, whether dispersal is sex biased and to assess factors such as growth rates 10 and survival. Further analysis is needed of the survey data so that area-weighted densities can be computed and spatial and temporal trends in abundance mapped. Data from other EC member states research vessel surveys (via ICES DATRAS database) will be collated to further add to the distribution database. Information on estimation of discards of common skate will also be extracted from the MSS observer programme database. References Ellis, J.R, Milligan, S.P., Readdy, L., Taylor, N. and Brown M.J. (2011). Spawning and nursery grounds of selected fish species in UK waters. CEFAS Science Series Technical Report no. 147, CEFAS, Lowestoft. pp. 1-53. Griffiths, A.M., Sims, D.W., Cotterell, S.J., El Nagar, A., Ellis, J.R., Lynghammar, A., McHugh, M., Neat, F.C., Pade, N.G., Queiroz, N., Serra-Pereira, B., Rapp, T., Wearmouth, V.J., Genner, M.J. (2010). Molecular markers reveal spatially-segregated cryptic species in a critically endangered fish, the common skate Dipturus batis. Proceedings of the Royal Society B, 277, 1497-1503. Iglésias, S.P., Toulhoat, L. and Sellos, D.Y. (2010). Taxonomic confusion and market mislabelling of threatened skates: important consequences for their conservation status. Aquatic Conservation: Marine and Freshwater Ecosystems, 20: 319-333. OSPAR (2010). Background document for common skate, Dipturus batis. OSPAR, London. pp. 1-18. Polunin, N.V.C. (2002). Marine protected areas, fish and fisheries. In: Hart, PJB; Reynolds, JD, ed. Handbook of Fish and Fisheries. Oxford: Blackwell, pp. 293-318. Walker, P.A. and Hislop, J.R.G. (1998). Sensitive skates or resilient rays? Spatial and temporal shifts in ray species composition in the central north-western North Sea between 1930 and the present day. ICES Journal of Marine Science, 55, 392-402. Wearmouth, V.J. and Sims, D.W. (2009). Movements and behaviour patterns of critically endangered common skate Dipturus batis revealed by electronic tagging. Journal of Experimental Marine Biology and Ecology, 380, 77-87. 11