UNITED UTILITIES _________________________ MANCHESTER SHIP CANAL STRATEGIC REVIEW OF FISH POPULATIONS _________________________ FINAL REPORT September 2007 APEM REF: 410039 CLIENT: United Utilities ADDRESS: Haweswater House, Lingley Mere Business Park, Lingley Green Avenue, Great Sankey, Warrington, WA5 3LP PROJECT No: 410039 DATE OF ISSUE: September 2007 PROJECT DIRECTOR: Dr. Keith Hendry PROJECT MANAGER: David Campbell, M.Sc. SENIOR SCIENTIST: Adrian Pinder Dr. Keith Hendry Riverview, Embankment Business Park, Heaton Mersey, Stockport, SK4 3GN Tel: 0161 442 8938 Fax: 0161 432 6083 Website: www.apemltd.co.uk Registered in England No. 2530851 APEM Scientific Report - 410039 EXECUTIVE SUMMARY Since the onset of the industrial revolution, the River Mersey has been subject to intense ecological stress from a number of sources. Hence, until the mid 1980s the Mersey and its estuary were infamous as being one of the most grossly polluted waterways in Europe. With the primary pollutants being derived from domestic and industrial effluents, the physical alteration to the natural hydraulics of the system imposed when building the Manchester Ship Canal have also been responsible for amplifying the issues associated with poor water quality. Over the last 20 years, enormous improvements in water quality have been achieved throughout the basin, which has driven a concomitant increase in general ecological health and the partial recovery of fish populations. Although these improvements are very much tangible, the future recovery and long-term development of fish populations is still heavily constrained by ongoing water quality issues and a legacy of historical pollution and physical engineering. Since its opening in 1894, the Manchester Ship Canal (MSC) has played a central role in governing the ecological functioning of the Mersey Basin and due to the morphological characteristics of this water-body, will continue to impact on the recovery of fish populations for the foreseeable future. Water quality in many of the peripheral rivers flowing into the Canal now meets the standards set out by the EC Freshwater Fish Directive, to support either a cyprinid or salmonid fishery. Despite a general improving trend, the MSC and the lower reaches of the Rivers Irwell and Mersey, continue to fail to meet the required criteria to support cyprinid fisheries. This is largely due to the deep slow flowing nature of these water-bodies exacerbating the effect of consented sewage effluent and storm sewage discharges. Such conditions are responsible for promoting the accumulation of organically enriched sediments, stratification, hypoxia and high ammonia concentrations. The observed recovery of fish populations has been affected through a combination of artificial stocking programmes and natural recolonisation. The artificial stocking of coarse fish has been extensive, with over half a million fish being stocked throughout the catchment within the last two decades. Analysis of these records in conjunction with fisheries surveys, suggest that such operations are limited in their success, with frequent observations of little or no natural recruitment evident from the initial input. Poor recruitment of rheophilic species (gravel spawners) such as dace and barbel is particularly evident. Investigation into the factors (i.e. water quality or habitat degradation) limiting the success of fishes within this ecological guild will require further investigation. Although diverse habitats exist within the peripheral rivers of the catchment, access to these habitats is often denied by impassable in-stream structures, such as weirs. Spawning substrates such as gravel and macrophytes (water plants) are absent from the upper MSC and therefore the presence of fish in these areas is likely to either originate from artificial stocking or from an influx of in-drifting larvae from immediate upstream habitats. Should such habitats be made available or simulated i Final Report – September 2007 APEM Scientific Report - 410039 where currently unavailable, notwithstanding water quality, fish production is likely to be enhanced. The return of Atlantic salmon after a 200-year absence is an excellent biological indication of the improvements in water quality over recent years. The subsequent discovery of their successful reproduction in the River Goyt in 2005 provides the first evidence that under certain environmental conditions, successful navigation of the MSC is possible for the adults of this species. Further investigation into the timing of migrations, spawning success and the survival of parr and smolts will be required in order to assess the long-term viability of a self-sustaining population of salmon in the Mersey Basin. Growth appears to be excellent for most species of coarse fish, many exceeding the expected national growth averages. Condition factors are also favourable, further indicating that food supply and the habitat requirements of the adult life stages of many species are at least adequate throughout the catchment. Conversely, the ecological requirements of dace do not appear to be fully accommodated under current environmental conditions. Despite extensive stocking efforts throughout the catchment, dace have shown little evidence of successful reproduction, with growth rates also falling below the expected national average. Sex reversal has been highlighted as a factor with potential for impacting on the health of fish populations nationally. Very high frequency of feminisation was evident in roach and perch from the upper MSC. At present these data are limited to a series of primary observations. Greater attention will need to be dedicated towards these mechanisms in order to understand the ecological significance of the process of feminisation. In general there is currently a paucity of data regarding the spawning success and recruitment of coarse fish. This is a key area for investigation, which would provide the essential data required for the effective future management of fish populations in the Mersey. The early life history of fish is a particularly vulnerable period for all species. Eggs and larval fish have greatly reduced tolerance to unfavourable environmental conditions, such as sewage fungus and low levels of dissolved oxygen. Water quality, appropriate habitat and food availability also have critical implications for the production future generations. Comprehensive surveys of spawning sites, larval fish and their diets are therefore essential, in order to identify habitat and water quality bottlenecks. Although historically abundant, the eel Anguilla anguilla and migratory (sea and river) lamprey species have failed to capitalise on the improvements in water quality and remain absent from the upper catchment. The presence of high densities of eels in the Rivers Weaver and Gowy confirm that the Mersey Estuary receives a healthy influx of elvers. Despite this, it would appear that the MSC is currently acting as a barrier to migration. Physical, physiochemical and ecological factors may all play a role in preventing recolonisation but suggest excellent potential for the experimental reintroduction of these species to the upper catchment. ii Final Report – September 2007 APEM Scientific Report - 410039 Episodic events of poor water quality have been identified as a cause and continual threat of fish kills. Storm Sewage Overflows pose a significant risk throughout the catchment, but can be particularly problematic in the lower River Irwell and MSC, where river discharge is rarely sufficient to dilute such inputs. Although stratification and hypoxic conditions prevail throughout the MSC, the largely lacustrine nature of this nutrient-rich channel also promotes the generation of algal blooms. Although not directly toxic to fish, the chemical processes driven by such blooms include extreme diel ranges in dissolved oxygen, increased alkalinity and increased toxicity of ammonia. Such conditions are believed to exist periodically during favourable conditions throughout the canal, with strong evidence of occasional fish kills. In the presence of almost limitless nutrient supplies, algal growth in the MSC can only be expected to get worse. Over 500 physical barriers, such as weirs, have been identified throughout the Mersey catchment. Not only do these restrict, or in many cases deny the passage of migratory species to spawning and rearing habitats, they also prevent the genetic mixing of coarse fish stocks and have serious implications for natural recolonisation, following localised fish kills. Weirs and lock gates have also been identified as effectively trapping fish within confined pounds of the MSC, which can have catastrophic consequences to fish, should water quality suddenly deteriorate. Recent examples of this occurred in 2006, and would be anticipated to be repeated regularly during still, hot conditions or following storm sewage discharges. In summary, despite the considerable improvements to water quality in the Mersey Basin over the past 20 years, the Manchester Ship Canal presents a major strategic barrier to the recovery and further development of coarse and salmonid fish populations within the catchment. Periodic deteriorations in water quality can be expected to cause regular fish kills, particularly with improving water clarity, as algal blooms become more frequent. These conditions, together with the physical barriers to movement and migration will also significantly constrain the development of fish populations throughout catchment and