Review and Conclusions D. Roberts Queen’s University, Belfast

 Since the appearance of humans Strangford Lough has been exploited by them – first, in prehistoric periods, by hunter-gatherers then by farmers  Because population density was low, early exploitation was probably sustainable although the landscape started to change as a result of agriculture  In Medieval times exploitation increased and this continued into post-medieval and recent times with increasing exploitation for food, minerals, recreation and waste disposal and agricultural intensification

 The most recent changes i.e. changes in benthic and intertidal communities, as we have heard, led to the present study which was charged with trying to identify probable causes  A number of changes have been documented over the last years and their causes and consequences suggested The presentation is in two parts:  review longer historical perspective  review of present study [SLECI]

PERIOD Molluscs oysters, limpets, cockles, winkles, whelks CRUSTACEA crabs, lobster, prawns Finfish Herring, salmon, whitefish Seaweed Dulse, Laminaria, fucoids Habitat/ species changes Prehistoric 10,000-1,600 BP Mediaeval 1, BP Post- medieval 17 th C 18 th C 19 th C Fish traps ND Fish traps ND oyster fishery ND oyster fishery ND herring seaweed industry seaweed grids oysters decline ND herring decline seaweed collapse minimal Middens ND Historical Perspective ( McErlean et al., 2002) ND ND = no data

PERIODMolluscsCRUSTACEAFinfishSeaweed Habitat/ species changes 20 th C s s 1970s-1980s 1990s-2000 ND Collapse of oysters ND Herring decline ND Herring collapse ND Spartina introduced Oyster aquaculture; scallop fishing Potting: Cancer, Homarus, Nephrops ND Modiolus damage (Brown ’89); Skate absent Historical Perspective Oyster restoration aquaculture: Pecten; Mytilus Potting: portunids ND experimental seaweed aquaculture Modiolus damage confirmed; Sargassum ND = no data

Subtidally the major documented changes between the earlier studies and the present study have been in biogenic reefs of Modiolus: Habitat/species changes confirmed/recorded by SLECI by SLECI  Large-scale reductions in the extent, reported by recent surveys were confirmed by both direct observation and broadscale mapping  Densites have declined and community structure has changed

 Other subtidal communities were largely unchanged in both species composition and abundance when compared with earlier studies  Indeed all major habitat types/ biotope complexes reported by Ulster Museum sub-littoral surveys in the 1970s and 1980s are still present  However, population structure at the remaining intact sites studied is comparable to earlier studies and there is evidence of recruitment Habitat/species changes confirmed/recorded by SLECI by SLECI

Intertidally: Zostera and Ostrea have declined and increased within the last 100 years, Ascophyllum has declined over recent years and the local distributions of Gibbula umbilicalis and Osilinus lineatus have changed Zostera and Ostrea have declined and increased within the last 100 years, Ascophyllum has declined over recent years and the local distributions of Gibbula umbilicalis and Osilinus lineatus have changed Habitat/species changes confirmed/recorded by SLECI by SLECI

There has been:  a general decline in commercial fishing  a steady but regulated expansion in aquaculture  no major changes in pollutant loadings apart from tin and chromium levels which have both declined  blooms of some algal species We have witnessed a number of introductions of non- native and non-local species, both deliberate: Spartina, Crassostrea gigas, Ostrea edulis and Pecten maximus and Accidental: Sargassum Other Changes

 In the 1970s & 80s Modiolus beds were known to be extensive in Strangford Lough (Seed & Brown, 1977; Erwin, 1978, Erwin et al, 1990).  In the early 1990s certain areas, particularly those occupied by the M. modiolus/ Chlamys varia community, were impacted by mobile fishing gear (Service & Magorrian, 1997).  Brown (1989) published report suggesting trawling has damaged M modiolus communities in Strangford Lough  Trawling and dredging are known to damage biogenic reefs and seabed communities (Watling & Norse, 1998; Cranfield et al. 2003).

 As a result of recommendations by DARD (formerly DANI a number of legislative measures were introduced in 1993 to manage fishing activity.  Judging by fishing returns for species such as scallops (Pecten & Aequipecten), fishing using mobile bottom gear peaked between the late ‘80s and early ’90s  In their 1997 paper Service and Magorrian suggested that reduction in fishing activity would afford the opportunity to follow recovery  SLECI found no evidence of recovery of Modiolus reefs in impacted areas

 Communities damaged by bottom gear and discards attract predators and may be subject to heavy predation  Evidence for this is provided by increasing starfish abundance in visual fast counts of benthic video surveys between 1993 and 2002 and the observation of large starfish in the SLECI diving survey  Damage to the reef structure and its epifauna, especially sponges, increases its vulnerability to predation (see Bloom, 1975, Pitcher & Bingham, 2002)  In impacted areas we have heard that K-selected (long-lived) species are generally decreasing and r- selected (short-lived) species are increasing in both Modiolus and infaunal communities

Experience Elsewhere Studies by Cranfield at al & 2003 in the Foveaux Strait, New Zealand, where o yster dredging has occurred over 130 years, contribute to our understanding of interactions between fishing and biogenic reefs :  As well as removing the reefs and oysters, dredging resulted in the release of large volumes ofbiogenic sediments which were deposited elsewhere and the seafloor reverted to underlying pebble gravel so that the substrates underlying biogenic reefs were exposed  As well as removing the reefs and oysters, dredging resulted in the release of large volumes of biogenic sediments which were deposited elsewhere and the seafloor reverted to underlying pebble gravel so that the substrates underlying biogenic reefs were exposed  Before dredging, bryozoan reefs and associated oysters (Ostrea [Tisostrea] chilensis) were tidally oriented in areas of strong current

 Other sites showed the development of biogenic reefs of Modiolus areolatus which were also tidally oriented  They concluded that attempts to rebuild a fishery may be more successful if combined with habitat restoration  The Foveaux Straitexperiences strong tidal currents which accelerate this process  The Foveaux Strait experiences strong tidal currents which accelerate this process  Surveys in 1998 revealed that some sites which had been unfished for 49 years showed no regeneration of biogenic reefs

Relevance to the present study Although the Foveaux Strait is in a near open ocean situation and Strangford Lough is enclosed, there are parallels in that both experience strong tidal flows In Strangford Lough, strong tidal flows surge through the Narrows and through the central channels becoming dissipated in the upper reaches of the Lough It is possible that any impact on Modiolus reefs will be accelerated by tidal currents and the release of sediment

 Ascophyllum may have declined as a result of a combination of increased grazing by limpets and changes in wind patterns INTERTIDAL CHANGES  Zostera densities declined as a result of disease and may be expanding now in response to improved water clarity  Recent increases in Ostrea are probably a result of restoration and over-summering commercial stocks but this may have occurred fortuitously at the time when Modiolus densities were declining so that oysters can capitalise on primary production no longer being used by Modiolus

 Strangford Lough is a complex system  It has been used by humans since prehistoric times with changes in resource exploitation in response to changes in demands and different levels of impact from relatively benign to localised extinction of species  The most recent impact has been the severe decline in Modiolus biogenic reefs and changes in their associated communities SUMMARY and CONCLUSIONS

 Other recent changes include increases in Zostera and Ostrea ; decreases in Ascophyllum and distributional changes in Gibbula umbilicalis and Osilinus lineatus  Although apparently well studied our understanding of the Lough is incomplete  Long-term data are fragmentary and monitoring has been inadequately coordinated - i.e. fisheries and environmental data, environmental/habitat monitoring

Acknowledgements Principal Investigators Bernard Picton, UM; Matthew Service, DARD Investigators Carys Ann Davies; Annika Mitchell; James Strong; Heather Moore; Samantha Vize;Alex Portig; Jane Preston; David Smyth