Fish population dynamics and management Post-Chernobyl radiocaesium in fish from two Cumbrian lakes The Chernobyl reactor accident occurred ') 3000 , Devoke Water howeswater on the 26 April 1986 and the plume kg passed over England during 2-3 May (Bg • 1986. Much of the remaining activity 2000 - • • continued northwards over Scotland. but ; • .9 some moved westwards and then • • • *so• • returned to traverse Wales and northern 1000 .1.2, . • England during 7-8 May. Limited • :I 1114:1 radioactivity •S •• 1••:. • • •• • deposition occurred throughout the UK • •• and the highest values were recorded in -••' ••••••p I Cumbria. North Wales and pails of r, n Scotland. Early monitoring of fish showed Muscle 1986 1987 1988 1986 1987 1988 that, whilst the radiological significance of Months the fallout on marine fish was negligible. radionuclide accumulation by freshwater fish was significant, especially in high deposition areas such as the Cumbrian Lake District. It was soon found that there FIgure 19 Muscle rachocaectum values (Fig kg we/ ought) 1o3incinndua tic 0171De yoke were wide variations between lakes, fish Voter (-11= I ibb eind Lowesponier (n = 145) species and individuals of the same species in the same lake The objective of Overall geometric means for Radiocaesium content increased with fish the present investigation was to evaluate radiocaesium in brown trout (540 Bq kg) weight for wild trout from both lakes, sources of variation in rachocaesium in and perch (1192 Bq ka ) m Devoke Water perch from Devoke Water but not perch fish from two lakes. Devoke Water and were significantly higher than those in or pike from Loweswater Values for Loweswater. This work was performed in Loweswater (trout 404. perch 989 Bg kg -). perch were generally higher than those conjunction with staff from the Ministry of and mean values for perch were for trout in Devoke Water (Figure 18). and Agriculture. Fisheries and Food (MAFF) significantly higher than means for trout in the power-function relationship between and was supported financially by NERC both lakes. Mean values for pike (568 Bq radiocaesium content and fish weight and the Commission of the European kg ) in Loweswater lay between the invalidates the use of uncorrected means Communities. values for trout and perch. for temporal comparisons. Radiocaesium 3000- values in pre-Chernobyl trout and stocked trout were markedly lower than those in post-Chernobyl wild trout (Figure 113)This discrepancy between wild and 1000 • recently stocked trout provides strong 5 evidence that the food chain rather than kg • the water is the main route of SOO radiocaesium transfer to the fish. Bq (R The stomach contents of [rout and perch from Devoke water indicated a diverse 00 diet from zooplankton to sticklebacks. Both the trout and perch were in good 100 condition according to their length-weight • relationships and there was no indication radioactivity that diet differences had any significant Stocked trout 50 effect on the radiocaesium content of individual fish. Muscle • • There was a large variation in radiocaesium values between individual • Pre-Chernobyl fish, as data for trout from both lakes 10 1 1 1 1 1 , 1 i 1 LDS_ ' clearly show (Figure 19). When these 10 50 100 500 1000 Wet weight (Wg) values were scaled to a standard weight Figure 18 Relationship between muscle rad:cacti1/2W (R Bq kg.) and Net weight bilSci) for individual of trout to remove the marked effect of fish h1=:7:,: LIsig and r., , ,i from awoke Water regression lines are btted for both specles bui values for size, monthly geometric means for 18 stocked gout and 2 pre-Chernobyl gout were omitted from analysis (points enclosed by broken radiocaesium increased from April/May line). 1986 to a maximum in October 1986 in 13 Devokc Water and February 1987 in relative value of planting out unfed salmon Loweswater, then decreased parr or of feeding the parr in the hatchery exponentially at a slow rate in Devoke for rive weeks before planting. Studies Water and a fast rate in Loweswater, and made by MAFF in natural streams and finally increased slightly in Loweswater rivers have the Advantage of dealing with only (Figure 20). Geometric means for the "real world" but suffer some perch and pike followed a pattern sinElat problems in interpretation of the results to that for trout, except that maxima because of difficulties of control and occurred in Februaiy/March 1987 for replication. The studies by IFE have used perch,in both lakes and in lune 1987 for the Grasshohne channels (Figure 21) as pike in Toweswater "streams" to be stocked. The four chamiels can be set up as replicates in Although this work has evaluated some le= of Row and bed material and the sources of vanation in fddlocaesirun numbers of fish leaving the channels and content in fish, especially the effects of fish dying in the channels can be accurately size and diet, it has also shown that there determined The four channels provide ale many unsolved problems. Differences two replicates of each of the two between species may be due to different neatments (stocking with unfed parr and metabolic rates (for example, different stocking with 5 weeks fed pan-) (Figure rates of gastric evacuation), and 22) The results from these small artificial differences between takes may be due to streams and those obtained from real variations in their limnology and the streams are complementaiy to one nature of their catchments. These and another and will be published jointly related problems are now being licr 21 G—me. )1 Grasknolme investigated. Preliminary data analyses suggest that 10 chant r m Thrly dna' Isi weeks after the commencement ot tyttie. Studies on strategies for the feeding, the fish stocked as unfed parr have a higher mean weight than the Esh planting of young, hatchery stocked as fed parr, but only about half Assessment of stress in wild reared salmon the population density Similar populations of fish As pan of a wider contract for MAFF, experiments are now in progress with Exposure of fish to environmental stress short-term studies have been made in trout. induces a complex series of physiological recent years in an attempt to Assess the changes. collectively Diown as the stress response A key element of the response 1000 Devoke Water is activation of the hypothalamio-pitunary- • interrenal axis, resulting in elevation of the • • hormone conisol. Atthough In the short- term. the stress response is believed to be of adaptive value to the fish, in the longer term, unalleviated, or chronic. stress can be very damaging Cortisol 500 itself has been implicated as a causal ') • kg Bq (GM 1000 Loweswater radioactivity PILTI. 2.2A r dilli on (So'ne ['an- Muscle 500 • 0 1111 1986 1987 1988 Months Figure 20 Relationship between geometric mean (GM) rachoactithly in hi OlVn trout (GM Sri kg I time 0 months from May 19862 for Dedoke Water and &ayes-water (bmken /mos simply snow /roods, solid lines are exponential curves) 14 factor in stress-induced reduction of growth, disruption of the reproductive ml system, arid immunosuppression. ml Furthermore, the fact that cortisol elevation is a consistent feature of the (ng stress response has led to its use as a 160 (pg 16 reliable index of stress, Although most of our work, and that of others, has concentrated on the study of the effects of steroids environmental stress on fish within the steroids controlled conditions provided by the aquacultural environment, the 120 12 measurement of plasma cortisol levels provides a potentially useful diagnostic tool for assessing the likely effects of environmental stress on natural conjugated populations of fish. However, despite the 80 8 fact that plasma conisol levels are a good immunoreactive indicator of stress, their very lability under conditions of stress is a problem. A clear free demonstration of this is provided by removing fish individually from a single 40 4 holding tank. After a few minutes, plasma conisol levels in consecutive fish show a biliary stepwise increment, due to the immunoreactive disturbance associated with the removal and of previous fish (Figure 23). Under 0 0 controlled experimental conditions, this Con Ac Chr Con Ac Chr Biliary Con Ac Chr problem can be overcome, but, when sampling from wild populations, Plasma Plasma Bihary free Biliary prolonged disturbance of the fish is often cortisol steroids conjugated unavoidable, particularly if trapping or steroids netting is necessary to remove individuals. We have therefore been looking for an alternative to plasma Figure 24 The levels of cortisol In the blood, and free and conjugated corlicostemids in the bile for rainbow trout al rest (Con), following one hour of acute stress (AO and following twenty-four bows ol cortisol levels to indicate the "stress chromc stress (Chi). each value Is die mean for 10 fish ± SE status" of fish; an indicator of stress that is stable during short-term disturbance, such as that needed to sample the fish. When fish secrete large amounts of a levels in fish subjected to no stress at all. hormone into the bloodstream, as is the Both acute and chronic stress significantly 90 case with cortisol during stress, rather elevated blood conisol levels when ') ml than being allowed to accumulate in the compared to those of the unstressed fish blood, the hormone is removed. or (Figure 24). However, acute stress had no (ng - cleared". Clearance of cortisol occurs effect on the levels of unconjugated and 50 via two routes, the kidney (in the urine). conjugated derivatives of cortisol in the cornsol and the liver (in the bile), In addition, to bile. The levels of these compounds only aid clearance, the hormone is usually become elevated after exposure to metabolised to an inactive derivative, and prolonged stress.