SAMPLING NORTH ESK JUVENILE SALMON POPULATIONS BY MEANS OF ROTARY SCREW TRAPS (RSTS): 7. CRUICK, SPRING 2007.

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1 Not to be quoted without prior reference to the authors Crown copyright 2009 Marine Scotland Science Internal Report No: 09/09 SAMPLING NORTH ESK JUVENILE SALMON POPULATIONS BY MEANS OF ROTARY SCREW TRAPS (RSTS): 7. CRUICK, SPRING F MacKay and G Smith May 2009 Marine Scotland Science Freshwater Laboratory Montrose Field Station Inchbraoch House South Quay Ferryden Montrose DD10 9SL

2 SAMPLING NORTH ESK JUVENILE SALMON POPULATIONS BY MEANS OF ROTARY SCREW TRAPS (RSTs): 7. CRUICK, SPRING 2007 F MacKay and G Smith Fisheries Research Services, Freshwater Laboratory, Montrose Field Station, Inchbraoch House, South Quay, Ferryden, Montrose INTRODUCTION The monitoring programme on the North Esk is central to FRS s stock assessment strategy for Atlantic salmon (Salmo salar, L.). Indices of abundance are routinely estimated for North Esk salmon at a range of life history stages and the data used to infer stock status throughout the country where, for example, only catch or ad hoc juvenile survey data may be available. Data from the North Esk also play an important role in international salmon management. The North Esk is one of only 15 index sites in countries bordering the North East Atlantic where stock and recruitment data are available to assess the status of salmon populations. An important aspect of the North Esk monitoring programme is the assessment of salmon populations at the sub-catchment scale. Since 2002, rotary screw traps (RSTs) have been used to sample the juvenile populations within the North Esk catchment. As part of this long term programme, an RST was deployed in the Cruick, a lowland tributary of the North Esk, in the Spring of 2007 and the results are summarised here. This report is one of a series describing the juvenile sampling work on the North Esk. The format is common throughout the series, providing a brief summary of the key results. More detailed analyses drawing on the results from a number of exercises will be published from time to time. OBJECTIVES 1. Record biological characteristics, behaviour and run timing of salmon smolts emigrating from the Cruick in Record presence of other species. Site Tagging and sampling site - the RST was sited approximately 300m upstream of the Cruick s confluence with the North Esk (Fig. 1). Main stem recapture site Kinnaber Mill trap (KMT), a fixed smolt trap situated in a lade in the lower reaches of the main stem of the North Esk (Fig. 1). Equipment Trap - four foot diameter, aluminium rotary screw trap (Fig. 2). Further information on RSTs is available in the FRS leaflet Rotary screw traps in Scotland (FW 27/06/06) 1

3 Tags Glass encapsulated passive integrated transponder (PIT) tags. For more information regarding PIT tags and RFID (radio frequency identification), please refer to When possible, the RST was operational for four days during each week of the study, or until 100 fish were sampled for the week, from 21st March until the 25th May 2007 (Fig. 3). A sample of the fish taken by the RST were weighed, their fork lengths measured and were tagged using PIT tags before being released. Smolts were released approximately 10m downstream of the trap to minimise the incidence of recapture. Since the RST requires a pressure of water to turn the funnel and allow it to fish, the low flow conditions throughout much of the 2007 sampling programme (particularly during May) prevented fishing for much of the smolt run (Fig. 3). RESULTS AND COMMENTARY RST Operation and Daily Catches The daily catch of salmon smolts varied from 0 to 418 (Fig. 3). A total of 672 smolts were caught of which 225 were measured for length and 170 were weighed. A small sample of scales was also taken from each of the 225 measured fish and from these it was possible to determine the age of 192 fish. In addition to salmon smolts, salmon parr, large numbers of brown trout, large numbers of sea trout smolts, minnows, an eel, a lamprey, a stoneloach and a toad were also captured. There was some damage observed on the salmon smolts which were examined, with ten (4.4%) showing minor damage, the majority of which (seven) were typical of bird marks (3%). In addition to the damaged fish, two sea trout smolts and two salmon smolts were dead when removed from the trap, and one salmon smolt died during handling. Age composition Three age groups of salmon smolts were caught (Fig. 4), the majority of which were two year olds (82.8%), followed by one year olds (16.7%) and then three year olds (0.5%). No four year old smolts were caught. Size of smolts The size of fish caught ranged from under 9cm to over 15cm with little difference in size between older and younger fish (Table 1 and Fig. 5). Recaptures within the Cruick Of the 226 salmon smolts tagged at the Cruick, a total of 8 tagged fish (3.5%) were recaptured at the tagging site: five were caught one day after tagging, two were caught 19 days after tagging and one was caught 26 days after tagging. While it is not unusual to recapture fish at their original tagging site, the time between tagging and recapture for three of the fish was far longer than anything encountered during other RST sampling exercises. Previously, the longest interval between tagging and recapture was in 2004, also at the Cruick, when a fish was recaptured nine days after release (see Report Number 3 this series). 2

4 Recaptures at KMT Of the 226 fish tagged at the Cruick in 2007, a total of 20 smolts (9%) tagged at the Cruick in 2007 were recaptured at KMT. The time taken for the fish to travel the 12.5km between the Cruick trap and KMT ranged from 1 to 28 days (median 6.5 days). The speed at which the smolts travelled between the two sites ranged from 0.45 and 12.5km/day (median 1.92km/day). ACKNOWLEDGEMENTS We thank Marine Scotland personnel (colleagues at Montrose Bryce Whyte, Ian Simpson, Jackie Anderson and Julian MacLean - and Support Services in Aberdeen) whose tireless efforts made this project possible. Thanks are also extended to the Esk District Salmon Fishery Board and the fishery and landowner, Mr Campbell Adamson, for their permission and support during this project. 3

5 TABLE 1 The size of fish caught emigrating from the Cruick showing the minimum, mean and maximum values for length and weight in each age class (actual values for the one three year old caught). Length (mm) Weight (g) Smolt age (years) Min Mean Max Min Mean Max

6 FIGURE 1 The River North Esk catchment, showing the Cruick tributary (highlighted in white), the tagging and sampling site (RST) and the recapture site (KMT).

7 The rotary screw trap at the Cruick. FIGURE 2

8 FIGURE 3 The numbers of salmon smolts caught emigrating from the Cruick per day during the 2007 smolt run Daily catch of smolts /03/07 # * * * * * * * * * * * * * **** 29/03/07 05/04/07 12/04/07 19/04/07 26/04/07 03/05/07 10/05/07 17/05/07 24/05/07 # Funnel jammed Date * Trap not fishing due to low water

9 FIGURE 4 The percentage of smolts in each age class caught emigrating from the Cruick in % Age (Years)

10 FIGURE 5 Box and whisker plot of the length of fish caught emigrating from the Cruick in each age class during Box shows interquartile range, whiskers show non-outlier maximum and minimum values, dark circles show median values and open circles show outliers.