The Fish Populations of the Lower Forth Estuary, including the Environmental Impact of Cooling Water Extraction. M.F.D. Greenwood Department of Biological Sciences University of Stirling A thesis presented for the Degree of Doctor of Philosophy October 2001 IMAGING SERVICES NORTH Boston Spa, Wetherby West Yorkshire, LS23 7BQ www.bl.uk THESIS CONTAINS VIDEO CD DVD TAPE CASSETTE Declaration The work presented in this thesis is the result of my own investigations. It has not been nor will be submitted in candidature for any degree, in this or any other university. M.F.D. Greenwood 2 Abstract The present study investigated the fish populations of the lower Forth Estuary, east Scotland. Cooling water extraction by the 2400 MW Longannet Power Station (LPS) inevitably removes a certain quantity of fish from the estuary, all of which experience mortality. The present study employed a sampling regime of greater intensity than previous studies to investigate the extent of mortalities from January 1999 - December 2000. Collections of fish impinged on intake screens were made eight times monthly, at L W or HW of spring or neap tides during the day or by night. Marine species dominated the assemblage of fish collected, with sprat, herring, and whiting contributing> 80% of total abundance. Sprat was twice as abundant as herring in 1999, while the proportions were very similar in 2000. Total abundance of all species 7 7 collected in 1999 was estimated at 1. 09 x 10 , while the value of 3.29 x 10 in 2000 was three times larger. These figures were the largest recorded among British estuarine and marine power stations, but were precisely the correct order based on an exponential relationship between total impingement and water abstraction rate established from data from other locations. Validation of the estimated total biomass of fish removed was given by comparison with the known total mass of all materials disposed to landfill. Statistical analysis of impingement data showed that tidal range and season were the most important environmental variables influencing the rate of removal of fish from the estuary. That light was not significant for most species is attributed to high levels of turbidity and the resulting low visibility by day and night. Demersal and benthic fish abundances collected from 1982 - 2000 in 30 annual trawls at three sites in the mid-lower Forth Estuary were analysed. Species tended to be present in greatest abundance at the most seaward of the sites. Patterns of seasonal abundance reflected those observed in the impingement study at LPS, and catches tended to be greatest at L W. Total species richness showed no significant trend over time, whilst total annual abundance of fish captured in trawls showed a significant negative trend. This was largely due to significant declines in the two most abundant species, namely whiting and eel pout, attributable in the latter case to increasing temperatures. Changes in the ichthyofaunal composition were largely driven by whiting, eel pout, cod and plaice. Eight of ten common species showed no significant trend in abundance over the length of the time series, suggesting them to perhaps be at equilibrium densities. Quantities of commercially fished species above minimum landing size limits that were removed by LPS were very low, and restricted to herring and occasional whiting. The quantity of juveniles that could have recruited into the fished populations was expressed as equivalent adults. The values were larger than any previously reported in the UK, primarily due to the quantities of juvenile fish impinged being greater than at any other British power station, and the importance of the Forth as a nursery area for marine species. It was concluded that LPS is the dominant UK power station in terms of magnitude of impingement losses. It may be prudent to consider a precautionary approach to mitigate losses, and to this end options for reduction of the magnitude of impingement are discussed. 3 Contents Declaration .................................................................. " ..................................... " ......... 2 Abstract. ........................................................................................................................ 3 Contents ........................................................................................................................ 4 Acknowledgements ..................................................................................................... l 0 Dedication ............. '" ........... " ................................................... '" ................................ 12 Glossary of Abbreviations ........................................................................................... 13 Chapter 1: Introduction ................................................................................................ 15 1.1. Overview ......................................................................................................... 15 1.2. The study area: the Forth Estuary ..................................................................... 17 1.3. The ichthyofauna of estuaries ........................................................................... 22 1.3.1. Categories of estuarine fish ....................................................................... 22 1.3.2. Characteristics of estuarine fish ................................................................. 23 1.4. Thermal power generation and the aquatic environment.. ................................. 27 1.5. Aims of the present study ................................................................................. 31 Chapter 2. Fish extraction by Longannet Power Station, 1999 & 2000: extent of impingement and influences on impingement rate ....................................................... 33 2.1. Introduction ...................................................................................................... 3 3 4 2.2. Materials and methods ................................................................................. 37 2.2.1. Study site ............................................................................................. 37 2.2.2. Sampling protocol ................................................................................ 38 2.2.3. Potential errors associated with the sampling method ........................... 39 2.2.3.1. Number of samples taken during each sampling session ............... 39 2.2.3.2. Sampling duration ........................................................................ 40 2.2.3.3. Residence time within system and sampling efficiency ................. 42 2.2.4. Calculation of total annual impinged fish abundance and biomass ........ 44 2.2.5. Examination of potential predictors of impingement rate ...................... 45 2.3. Results ......................................................................................................... 48 2.3.1 Water quality parameters near the LPS water intake ............................. 48 2.3.2 Composition ofLPS impingement samples, 1999 - 2000 ..................... 51 2.3.3 Abundance and mass estimates of fish impingement at LPS, 1999 - 2000 ............................................................................................................. 54 2.3.4 Predictors offish impingement rate at LPS ........................................... 62 2.4 Discussion ................................................................................................... 70 2.4.1. Species composition of impinged LPS ichthyofauna ................................. 70 2.4.2. Extent ofLPS impingement ...................................................................... 73 2.4.2.1. Abundance and biomass estimates ofLPS impingement, 1999 - 200073 2.4.2.2. Comparison of estimated LPS impingement with predictions based on water extraction rate ......................................................................................... 75 2.4.2.3. Comparision of estimated fish biomass impinged with known values of all materials disposed to landfill ....................................................................... 78 2.4.3. Assessment of significant predictors of impingement rate at LPS .............. 80 2.4.3.1. Water quality parameters as predictors ofLPS impingement .............. 80 5 2.4.3.2. Environmental and operational predictors ofLPS impingement .... 87 2.5. Conclusions ..................................................................................................... 96 Chapter 3. Fish populations in the mid- and lower Forth Estuary: temporal, tidal and spatial variations in fish abundance as assessed by demersal and pelagic trawling ....... 97 3.1. Introduction ................................................................................................. 97 3.2. Materials and methods ............................................................................... 101 3.2.1. Agassiz trawl study ................................................................................. 101 3.2.1.1. Field study .................................................................................. 101 3.2.1.2. Generalised Linear Modelling of Agassiz data ............................ 101 3.2.1.3. Non-parametric exploratory analysis of Agassiz trawl data ......... 102 3.2.1.3. Investigation of population size variability in relation to species latitudinal range ............................................................................................. 103 3.2.1.4. Preliminary