Not to be quoted without permission of the authors
Fisheries Research Services Report No 4/95
HABITAT ASSESSMENT AND SURVEY OF
LAMPREY POPULATIONS OCCURRING IN
AREAS OF CONSERVATION INTEREST
Report to Scottish Natural Heritage
Contract Number: SNH/080/95AEB
R Gardiner, R Taylor and J Armstrong
April 1995
The Scottish Office Agriculture and Fisheries Department
Freshwater Fisheries Laboratory
Faskally
Pitlochry
Perthshire
PH16 5LB
HABITAT ASSESSMENT AND SURVEY OF LAMPREY
POPULATIONS OCCURRING IN AREAS OF
CONSERVATION INTEREST
R Gardiner, R Taylor and J Armstrong
SOAFD Freshwater Fisheries Laboratory
Pitlochry
PROJECT OBJECTIVES
Three objectives were agreed with Scottish Natural Heritage (SNH).
1.
To assess the availability of substrate that is suitable for providing
nursery grounds for sea, river and brook lamprey ammocoetes on the
stretches of river identified by SNH.
2.
To survey the nursery grounds by electrofishing to quantify the
populations of sea lamprey and river/brook lamprey ammocoetes.
(Because it is not possible to distinguish the ammocoete larvae of
river and brook lamprey until the later stages of metamorphosis, our
commitment was only to differentiate the ammocoete larvae of the
sea lampreys from those of the other species).
3.
To produce material that will aid SNH in developing a strategy for the
conservation and monitoring of lamprey populations. This would
include assessing what data could be collected on adult lampreys on
the river systems if there is a continuation of the programme in 1995.
THE STUDY RIVERS
The following stretches of river (see Figs 1-5) were identified by SNH for
study:
Sea Lamprey Petromyzon marinus L.
River Leven/Loch Lomond
River Spey (Grantown to the estuary; also a supplementary request to include
a site between Newtonmore and Kingussie where FFL staff had observed sea
lampreys spawning in 1984)
River Teith/River Forth (Doune to River Forth Estuary)
River Lamprey Lampetra fluviatilis (L.)
River Endrick/Loch Lomond (Gartness down to Loch Lomond)
River Teith/River Forth (Doune to River Forth Estuary)
Brook Lamprey Lampetra planeri (Bloch)
1
River Endrick/Loch Lomond (Gartness down to Loch Lomond)
River Teith/River Forth (Doune downstream to Stirling)
BIOLOGICAL BACKGROUND
Sea Lamprey
The sea lamprey Petromyzon marinus L. is a large anadromous species of
lamprey. As with other anadromous lampreys, the adults at sea feed
parasitically on fish. Attacks by young adults on fish in fresh water prior to
movement out to sea also occur (Hardisty, 1986a). The species is widely
distributed on both sides of the North Atlantic, with the range on the European
side extending into the Mediterranean and Baltic. At sea, it may be found far
from land, and there are records of specimens being taken at depths of up to
4,000 m (Hardisty, 1986a). The returning adults, which reach 60-90 cm in
length, enter a number of medium to large Scottish rivers. Spawning occurs
in warm conditions (commonly July) in shallow runs, often at the tail end of
pools, in moderate to fast current speeds of up to 1-2 m.s-1, and where the
substrate is of pebbles and small cobbles ranging from 1-5 cm in diameter
(Hardisty, 1986a). Both the spawning activity and the large spawning pits
which are excavated can often be seen clearly from the river bank.
River and Brook Lampreys
The river lamprey Lampetra fluviatilis (L.) is a smaller species than the sea
lamprey, commonly growing to 25-35 cm in length, and occurs in rivers of the
North Sea, Baltic and eastern North Atlantic, and locally in the Mediterranean
(Hardisty, 1986b). It is found in a number of Scottish rivers, particularly in
their lower reaches. It is generally anadromous, often using estuaries as
feeding areas. However, occasional land-locked populations occur, as in
Loch Lomond in Scotland and Lake Ladoga in Russia, where the adult
feeding stage is in freshwater lakes. The Loch Lomond population is
apparently the only land-locked population in the British Isles. Spawning of
river lampreys occurs in spring, commonly in April, but is less likely to be
noticed by casual observers on the river bank than the spawning of sea
lampreys.
The brook lamprey Lampetra planeri (Bloch) spends its entire life in
fresh water and has a similar general distribution to the river lamprey
(Hardisty, 1986c), but can be found in stretches of streams above waterfalls
which would not be accessible to river lampreys. It is widespread in Scottish
rivers and streams. Adults of this species do not feed and are generally
smaller than those of the other two species, commonly 12-15 cm, and
occasionally exceeding 17 cm, in length. Brook lampreys often spawn at the
same time of year as river lampreys.
The brook lamprey and river lamprey have closely similar
morphological characteristics. They are currently considered to be a pair of
separate species with the river lamprey being the ancestral type from which
2
the brook lamprey has evolved. The existence of other similar pairs of closely
related parasitic and non-parasitic species which are found in the same
geographical region occurs frequently over the global range of lampreys
(Potter, 1986). There is no paired non-parasitic species to the sea lamprey.
The spawning nests of brook and river lampreys are constructed in
gravel and sand beds where current speeds are moderate; river lampreys
often prefer somewhat faster currents than brook lampreys (Hardisty,
1986b,c). As with sea lampreys, the tail ends of pools, just before the river
breaks into a riffle, are favoured spawning areas. Frequently, spawning of
brook and river lampreys may occur at the same time in the same areas.
However, the size difference may preclude successful mating in the wild
(Huggins and Thompson, 1970), as this involves the male attaching to the
anterior end of the female and bringing the urinogenital papilla close to the
cloaca of the female. Hybridisation of the two species can readily be
achieved by artificial fertilisation (Hardisty, 1986b,c).
The Biology of Ammocoete Larvae
Within a few weeks of hatching, the ammocoete larvae of all three species of
lamprey disperse downstream from the spawning areas to nursery areas
where they live in burrows and feed on fine particulate material, including
algae, diatoms and detritus. At this stage, although sea lampreys can be
identified as such, there is no reliable definitive method for distinguishing river
and brook lampreys. Ammocoete larvae spend several years in the nursery
areas which have a soft substrate (mud, silt or sand), such as occurs in
backwaters or in slack water at the edge of streams. Stability of the river bed
is important and unstable sandy substrates are avoided by ammocoetes
(Morman, Cuddy and Rugen, 1980). Ammocoetes have only a limited ability
to tolerate hypertonic sea water dilutions (Hardisty, 1986a, 1986b, 1986c).
The densities of ammocoetes in the nursery areas will be influenced
by such factors as the numbers of spawning adults; the extent and suitability
of spawning areas; the survival of eggs and early larvae in the spawning
areas and during dispersal to the nursery areas; the proximity of the nursery
areas to the spawning areas; and the extent and suitability of the nursery
areas. At high ammocoete densities, inter- and intraspecific competition for
space would seem likely to occur. There is little background information
available on the typical densities of ammocoetes, although in southern
Sweden densities of Lampetra ammocoetes ranging from 10-113 m-2 have
been recorded in favourable habitats (Malmqvist, 1980).
Within the nursery areas, it is likely that the growth rates of the
ammocoetes will be influenced by such factors as the amount and quality of
suitable food material and the water temperature. In North America the
growth rates of sea lamprey ammocoetes have been shown to be density
dependent and this results in relatively early transformation to the adult stage
where densities are low (Potter, 1980). There is no information on whether
the capacity for growth may also differ from stock to stock.
3
Until recently, information on the growth rates and ages of ammocoete
larvae was based mainly on length-frequency analysis. However, a
technique which gives a direct age determination has recently been
developed in North America. This is based on the examination of structures
known as statoliths, which are analogous to teleost otoliths and are found in
the otic capsules of lampreys (Volk, 1986; Beamish and Medland, 1988;
Medland and Beamish, 1991).
Transformation into the Adult Form
The ammocoete larvae transform into the adult form with the development of
a full sucker and rasping teeth, silvering of the skin and the appearance of
well-formed eyes. It is believed that this occurs at a particular size, rather
than at some fixed age (Hardisty, 1986d). Much of the change during
transformation takes place over a few weeks in late summer or early autumn.
Prior to transformation, at least in the case of sea lampreys, an arrested
growth phase may occur during which length does not change appreciably
but the weight increases as a result of the deposition of lipid (Lowe et al.,
1973; O'Boyle and Beamish, 1977). During transformation, and for a period
prior to migration to the adult feeding grounds which may last several months,
the lampreys cease feeding and both length and weight decrease. At this
stage they may be found in open water or places where water currents are
swifter and the substrate is made up of larger particles than are favoured by
ammocoetes. This may be because of increased oxygen requirements (see
Hardisty, 1986d). In all three species, a capacity for marine osmoregulation,
which is only partial in the case of the brook lamprey, develops during
transformation (Hardisty, 1986a, 1986b, 1986c).
Transformation of river lampreys commonly takes place at a length of
9-12 cm (Hardisty, 1986b; Maitland and Campbell, 1992). Compared with
river lampreys, transformation of brook lampreys generally occurs at a larger
size (often 13-15 cm, or more, in length) and greater age (Hardisty, 1986c),
although there are populations where transformation takes place at shorter
length (Maitland and Campbell, 1992). As has already been mentioned, the
ammocoete larvae of brook lampreys and river lampreys cannot be
distinguished with certainty, although large larvae are likely to be brook
lampreys. Differences in the morphology develop during transformation and
by the completion of transformation the river lamprey may be distinguished
from the corresponding stage of the brook lamprey by the relatively longer
snout region, relatively larger disc and eye, slender body form, less rounded
trunk and more intense silvering of the skin.
In addition, during
transformation, attrition of oocytes occurs in female brook lampreys which
appears to be associated with the smaller size at spawning, and in river
lampreys a complete lumen in the newly developed foregut develops,
whereas in brook lampreys the intestine atrophies (Hardisty, 1986b,c).
The little information available suggests that British sea lampreys
probably transform at a length of 12.5-15 cm, like those from North America
(Potter and Osborne, 1975).
Factors Expected to Influence the Population Size of Lampreys
4
The factors which would be expected to influence population size of
populations of river and sea lampreys would include satisfactory access to
spawning grounds, the existence of sufficient spawning and nursery areas,
and satisfactory habitat for the growing adults (with a sufficiently large
population of prey fish). In the case of brook lamprey populations, the
presence of satisfactory spawning and nursery areas will be of key
importance.
Even as early as the 1800's, the construction of dams was blamed for
the decline of sea lampreys on the east coast of the USA (Goode, 1884, cited
by Morman et al., 1980), and more recently the same problem has been
shown to be responsible for the decline in the commercial river lamprey
fisheries in Finland (Tuunainen et al., 1980). Lampreys do not jump over
barriers on their upstream migration and cannot swim as rapidly as many
teleosts (Wardle, 1975). Therefore, facilities which are adequate to permit
the passage of salmonid fishes may be inadequate to allow migration of
lampreys.
EXISTING INFORMATION ON THE LAMPREY POPULATIONS
OF THE STUDY RIVERS
River Leven
Maitland et al. (1994) mention reports of adult sea lampreys spawning at a
site in the River Leven, between the barrage and the footbridge at Balloch,
which they describe as the only known spawning site in the Lomond
catchment.
They also reported finding sea lamprey ammocoetes
infrequently. Brook lampreys were also mentioned as being present from the
loch outflow to the tidal limit.
River Spey
On 12 July 1983, several pairs of sea lampreys were observed spawning at
NN 751993 (between Newtonmore and Kingussie) (R Gardiner, personal
observation).
River Forth/River Teith
Maitland et al. (1984b) cite early references to the river lamprey as being
frequent in the rivers of the Forth area. Their own studies on large samples
of river lampreys collected over the period 1979-1981 from the intake screens
of Kincardine and Longannet Power Stations confirmed that it was a
common species in the upper estuary. They showed that these lampreys
spent approximately 1.3 years in estuarine or marine environments, where
they fed mainly on clupeids (either sprat Sprattus sprattus (L.) or herring
Clupea harengus L., both of which were abundant in the estuary). In 1984,
spawning of river lampreys in the River Forth occurred on 25 April at a water
temperature of 11.9°C (Maitland et al., 1994).
5
The brook lamprey is described by Maitland et al. (1984b) as being
very common in many streams in the Forth area. However, they suggest that
the sea lamprey is uncommon in the area.
River Endrick
The landlocked population of river lampreys in Loch Lomond has already
been mentioned in this report. In this population the mature adults reach a
size of only 17-25 cm and differ substantially from normal river lampreys by
being markedly darker in colour, and having a very large sucking disc,
prebranchial area and eye (Maitland, 1980; Maitland et al., 1994; see Plate
accompanying Maitland et al., 1984a). The population in Loch Lomond
spends only one summer feeding in the loch and Maitland (1980) found from
samples collected between 1951 and 1979 that powan Coregonus lavaretus
(L.) was the main prey species, with the incidence of powan bearing lamprey
scars ranging from 26-50% between years. Fresh scars only occurred in
summer - especially July and August. From the number of lamprey-marked
powan present in Loch Lomond, it was considered that there was a large
population of river lampreys in Loch Lomond. Brown (1895) also considered
them to be abundant in the loch.
The River Endrick is the largest feeder stream of Loch Lomond and a
major study of its lamprey populations was carried out by Maitland and his coworkers, mainly over the period 1983-1985 (Maitland et al., 1994). They
found, by trapping at Drymen Bridge in 1983-84 and 1984-85, that adult river
lampreys started to appear in the River Endrick in late September, with the
main runs occurring in October to December. Adult river lampreys were
described as being common in the lower River Endrick between October and
March.
Spawning took place in late March and early April, probably at water
temperatures of between 5.1 and 9.2°C, which is earlier, and at a lower
temperature than is typical elsewhere in Great Britain. In addition to the
many dwarf river lampreys taken in the River Endrick, three larger river
lampreys of 28.9-33.3 cm were also captured. It was suggested that these
were likely to have been anadromous lampreys from the Clyde estuary, since
they were of normal river lamprey appearance. Maitland's group suggests
that the River Endrick may be the only stream used by spawning river
lampreys from Loch Lomond, although Lamond (1931) also recorded having
seen them spawn in the Luss Water earlier this century.
Maitland's group found that adult brook lampreys were much more
abundant than river lampreys in the River Endrick. The spawning of brook
lampreys took place in April and May, after the river lampreys had spawned;
this may prevent hybridisation between individuals which are more similar in
this river in size than is typical elsewhere (see Section II of the present
report).
Prior to the construction of the Leven barrage, adult sea lampreys
were occasionally reported in the loch (Lamond, 1931). More recently,
Maitland et al. (1994) reported that a feeding sea lamprey of 20 cm length
6
had been retrieved by an angler from a salmon Salmo salar L. caught in the
loch, but this lamprey could have been carried upstream by the salmon. They
found no larval sea lampreys in their study on the River Endrick.
SURVEY WORK
Site Visits
Five sites were visited on each of the following stretches of river. At each site
the availability of substrate that was suitable to provide nursery grounds for
ammocoetes was assessed, and surveys by electrofishing were conducted
to confirm and quantify the populations of ammocoetes.
River Leven
(Sites L1-L5)
River Spey (Grantown to estuary)
(Sites S1-S5)
River Teith/River Forth (Doune to Stirling)
(Sites T1-T5)
River Endrick (Gartness down to Loch Lomond)
(Sites E1-E5)
There were also two supplementary sites - one just above Lanrick
weir, about 2.5 km above Doune on the River Teith (Site T6), and one on the
River Spey between Newtonmore and Kingussie (Site S6), the latter at the
request of SNH. On each stretch of river the sites are numbered in order
from furthest downstream to furthest upstream. The locations of the sites
visited are given in Table I and mapped in Figures 1-5.
The visits were carried out during periods of low water conditions
between 16 August-16 September. While making the arrangements to visit
sites, background information was sought concerning local records of
lampreys spawning, and of weirs and waterfalls which might be obstructions
to migration.
At each site, details were recorded of the extent of habitat which
looked likely to provide suitable nursery area for ammocoetes, and one or
more small areas, often of 2.3 m2 (1.53 m square), were marked out with fibre
glass poles and intensively electrofished using unpulsed DC.
In addition to the sampling of favourable habitat, a total of four areas
with beds of cobbles and boulders, which were considered less likely to
provide suitable habitat for ammocoetes, were fished at Sites L3 and S2 on
the Leven and Spey.
The use of a voltage of about 400 V, which is higher than those levels
routinely used in electrofishing surveys, increased the efficiency with which
ammocoetes were drawn from the bed and prevented many from attempting
to escape. The fishing electrode was kept away from the edges of each
sample area (other than against banks) to avoid drawing in ammocoetes from
outside the area boundaries. Generally fishing was continued until few (if
7
any) ammocoetes were still being caught. However, in some areas with high
densities of ammocoetes, fishing was discontinued before this point.
Because of the time it took to draw ammocoetes out of the bed, and the
problem of having to wait for suspended silt disturbed by the fishing to clear,
each sample could take over 30 minutes to collect. Densities were estimated
simply from the total numbers caught in each sample area.
We had initially intended to carry out successive fishings of the areas
to allow an estimate of total numbers to be made. However trials showed that
after a single intensive fishing few additional ammocoetes were caught in a
second fishing. Timed fishings were also found to be less useful than the
method adopted as the speed with which ammocoetes were collected
depended at least as much on physical factors as on their densities. The
adopted sampling protocol met with SNH approval.
In each sample area, details were recorded of the type and character
of bed, presence of detritus and aquatic vegetation, depths and current speed
(if any), and a comprehensive set of photographs were taken. At a selection
of sites, water samples were taken and subsequently analysed for a range of
determinands. The catches of ammocoetes were taken back to the
Laboratory for detailed examination.
Examination of the Lampreys
At the Laboratory, all ammocoetes were anaesthetized using MS222,
measured and examined live using a low/medium power binocular
microscope. Ammocoetes were readily identified to river/brook lamprey or
sea lamprey on the basis of head and tail pigmentation patterns and tail
shape (Potter and Osborne, 1975). For many of the ammocoetes, counts of
the number of trunk myomeres were made to provide absolute confirmation of
the identification (Potter and Osborne, 1975). Even the smallest ammocoetes
caught, which were little more than 1 cm in length, could readily be identified
under the binocular microscope. Where transformation had clearly started,
the stage of transformation was noted.
Length-frequency histograms for river/brook lamprey ammocoetes and
sea lamprey ammocoetes were prepared for each site. Separate
length-frequency histograms were prepared for transforming ammocoetes.
A number of ammocoetes are being kept deep-frozen for future
statolith examination. The remainder of the ammocoetes were preserved in
neutral 4% formaldehyde in case further examination would be useful.
8
RESULTS OF THE SURVEY WORK
Access for Migratory Lampreys and General Features of the Study
Rivers
River Leven
There are no obstructions downstream of the barrage into Loch Lomond at
the head of the River Leven. The river discharges into the Firth of Clyde
which provides a variety of estuarine habitats.
River Spey
There are no major obstructions to the upstream movement of lampreys. The
river discharges direct into Spey Bay, there being no proper estuary.
River Teith/River Forth
Lanrick weir (NN 705205) is a possible obstruction to upstream movement of
lampreys. There is a substantial area of estuary available with habitat
ranging from physically protected inner estuary to open firth.
River Endrick
This is the main inflow to Loch Leven and anadromous lampreys would have
to reach it via the River Leven and Loch Lomond. The barrage at Balloch
may hinder movement of lampreys into Loch Lomond, as they would have to
find and successfully use the fish pass. (Although we did not visit this pass
we were advised by the former head bailiff for the Loch Lomond Angling
Improvement Association, N Gillies, that it is small and with a limited flow,
and that the salmon and sea trout it is intended for mainly ascended by
leaping the barrage rather than using the pass). However, as already
mentioned, the early information of Lamond (1931) suggests that
anadromous lampreys have never been common in the loch.
On the River Endrick itself, the Pots of Gartness at the head of the
study stretch would prevent any further upstream movement of lampreys,
unless they were carried upstream while attached to the migratory salmonids
which can ascend this fall.
The role of Loch Lomond in providing feeding areas for landlocked
adult river lampreys has already been mentioned.
Availability of Spawning and Nursery Habitat
River Leven
Areas of pebble and cobble which would be suitable as spawning areas for
sea lampreys occurred downstream of Balloch and at Bonhill.
9
Over much of the river, because of the fairly steep gradient, areas of
favourable nursery habitat for ammocoetes were restricted to infrequent slack
areas in backwaters and at bends. Areas of good nursery habitat were more
extensive in the upper tidal reaches than further up the river. There is little
saline intrusion into the upper tidal reaches above the weir at Dumbarton.
River Spey
Areas of pebble and cobble which would be suitable as spawning sites for
sea lampreys occurred regularly at the tails of pools in both study stretches.
Much of the main stretch identified for study (Grantown to the estuary)
is of fairly steep gradient, and backwaters or other areas which provide
favourable nursery habitat only occurred infrequently, or were very limited in
extent. On the supplementary stretch identified for study (Newtonmore to
Kingussie) the gradient was relatively gentle and many extensive nursery
areas were available for ammocoetes.
River Teith/River Forth
Suitable areas for lampreys to spawn in were available in many places along
this stretch of river. From Lanrick Weir downstream to about Steeds there
were only moderate amounts of nursery area available for ammocoetes.
From Steeds down, and particularly in the upper tidal reaches, suitable
nursery areas were more numerous and more extensive. There is little saline
intrusion into the upper tidal reaches above Stirling.
River Endrick
We considered that suitable spawning areas were mainly limited to the
reaches from Drymen upstream. Over the whole study stretch extensive
nursery areas were available.
Information Collected on Adult Lampreys in the Current Survey
The local reports that were readily available referred mainly to sea lampreys.
Even dense populations of river/brook lampreys frequently seem to go
unnoticed.
River Leven
N Gillies and P Holmes reported that sea lampreys had regularly spawned in
recent years in an area just downstream of the barrage at Balloch
(NS 393894), and that spawning had also taken place in an area at the head
of a riffle a little above the footbridge at Bonhill (NS 394793).
10
River Spey
There were many reports (J Gray, S Milne, B Milne, I Tennant, R Laughton)
of sea lampreys spawning regularly in the stretch of river identified for study
between Grantown and the estuary. One report (R Laughton) mentioned a
large number of spawning sea lampreys (at Boat o' Brig NJ 329518, mid-July
1989). On Knockando Beat, S Milne felt that sea lampreys were more
common in recent years than they had been in the 1950s. We also received
occasional reports of brook lampreys spawning.
On the stretch of river between Newtonmore and Kingussie, several
pairs of sea lampreys were observed spawning at NN 751993 on 12 July
1983 (R Gardiner, personal observation). However, sightings of sea
lampreys appear less common on these upper reaches than below Grantown
(J Dallas).
River Teith/River Forth
We obtained reports of sea lampreys spawning in recent years on the River
Teith about 2 km above Doune at NN 705025 (I Baird) and on the River
Forth at NS 777955 just below the M9 Motorway Bridge (T McKenzie). There
were also sightings of sea lampreys on the River Teith, mainly from Lanrick
Weir (NN 703027) downstream (Mr Thomson), but with one about 8 km
further upstream near Cambusmore (T McKenzie).
River Endrick
We obtained no reports of sea lampreys. We did get reports of lampreys
spawning in the River Endrick from Drymen upstream, and from the
descriptions of the sizes of the lampreys it seems likely that some referred to
brook lampreys and some to the small river lampreys.
Populations of Ammocoetes
The characteristics of the areas sampled, and the numbers of ammocoetes
caught at each site are given in Tables II and III; plots of the length-frequency
distributions are given in Figures 6-9. These are mainly based on exhaustive
fishing of the sample areas. However, at Sites S6 and T4, fishing was
stopped at an earlier stage.
River/Brook Lamprey
Lampetra ammocoetes were found at all 22 sites. Their local population
densities were generally high, and averaged 22.6 m-2 in the nursery areas.
Very few ammocoetes were found at Site L4, probably as a result of a local
water quality problem which may have affected the area fished. (We
understand that this problem has now received attention). At Sites E1 and E2
the densities were also low, which may be a result of a lack of suitable
spawning areas nearby.
11
Relatively few transforming Lampetra ammocoetes were caught.
However, from these few lampreys it is possible from their lengths (and,
where transformation was well advanced, appearance) to draw some
conclusions about the likely river lamprey/brook lamprey composition at the
sites (see the present report, Section II). The lengths of those caught at the
sites on the Rivers Forth and Teith ranged from 8.8-11.6 cm, and this,
together with their appearance, indicated that they were mainly transforming
river (rather than brook) lampreys. The lengths and appearance of the
transforming Lampetra from the sites on the Rivers Endrick and Spey
indicated that they may have been mainly transforming brook lampreys One
particularly large transforming lamprey of 18.7 cm was caught in the Endrick.
The transformers from the River Leven were at a relatively early stage, but
their lengths would be consistent with there being a mix of both river and
brook lampreys.
Some differences in appearance were noted between Lampetra
ammocoetes from the various rivers. For example, in the River Endrick, the
larger ammocoetes were frequently mottled with large pale patches. There
were also occasional examples of this on the River Teith. It is not clear the
extent to which these apparent differences might reflect different strains of
lamprey or differences in rearing conditions. At one site on the River Spey
(Site S1) a "golden" ammocoete which lacked melanophores was caught.
Sea Lamprey
Sea lamprey ammocoetes were found at one of the five Leven sites, four of
the six Spey sites and four of the six Forth/Teith sites. The densities were
much lower than the densities of river/brook lamprey ammocoetes, as has
been reported elsewhere in mixed populations of Lampetra and sea lamprey
ammocoetes (Hardisty, 1986a). The highest proportion of sea lamprey
ammocoetes occurred in the stretch of the River Spey between Grantown
and the estuary (Sites S1-S5). Overall the average density of sea lamprey
ammocoetes in the nursery areas at the sites where they were found was
0.54 m-2. No transforming sea lamprey ammocoetes were caught.
Growth Rates
The modes in the length-frequency plots representing ammocoetes of age
0+ and age 1+ were generally distinct in the length-frequency plots for the
Lampetra ammocoetes (Figs 1-4). The modal lengths of age 0+ and age 1+
ammocoetes are given in Table IV. The later modes are less distinct which
suggests that there may be several overlapping age classes. It is clear that
at least in the first two years of life there are differences in growth rates in
different rivers with those of the River Endrick growing particularly quickly.
Age 0+ sea lamprey ammocoetes were caught in September in the
River Teith, but not at the sites on the other rivers which contained sea
lampreys, which may reflect the earlier sampling dates on these rivers. The
average length on the River Teith (Sites T2-T5) of age 0+ sea lamprey
ammocoetes (13.12 ± σ1.36 cm (8)) was significantly less (z = 12.78,
12
p<0.0001) than that of age 0+ Lampetra ammocoetes (19.63 ± σ2.97 cm
(342)), presumably as a result of the much later spawning in sea lampreys.
In all three study rivers in which sea lampreys were caught, the lengthfrequency distributions suggest that this size difference between sea lamprey
and Lampetra ammocoetes is carried through at least to age 1+ (Table IV).
We are hoping that examination of statoliths will allow these conclusions to be
tested (although this is not part of the present contract).
Controls
No ammocoetes were caught in the four areas with substrate dominated by
cobbles and boulders which were fished as controls at Sites L3 and S2.
GENERAL CONCLUSIONS FROM THE SURVEY WORK
Sea Lamprey
The survey work and other information collected has confirmed that the
Leven, Spey and Forth/Teith all have populations of sea lamprey. Both the
survey work and the other available information suggest sea lampreys are
more abundant in the Rivers Spey and Forth/Teith than in the Leven.
River/Brook Lamprey
The survey work has confirmed that all four rivers have large populations of
river and/or brook lamprey. The results indicate that the population on the
River Teith is mainly of river lamprey. The survey did not produce information
on the status of the River Endrick as a spawning area for the very interesting
land-locked population of river lampreys which occurs in the loch.
CONSERVATION REQUIREMENTS
The major requirements for the conservation of lampreys are the
maintenance of access to spawning grounds, preservation of sufficient
spawning and nursery areas, and the maintenance of satisfactory habitat for
the adults. A key feature of the adult habitat will be the availability of a
sufficiently large population of prey fish. It is not known to what extent
lamprey populations home to their natal areas and are dependent on the
maintenance of particular spawning sites. Often there is insufficient
information to determine which of the various possible factors are limiting
population size. The collection of such information would be very useful in
the development of conservation management strategies.
13
River Leven - Sea Lamprey
Our results, and the other information, indicate that this is a small population.
As such, it would be vulnerable to disturbance of the adults and any damage
to the spawning areas presently used. While in the past, poor water quality in
the lower river and adjacent estuary may have been a constraint on
population size, this should no longer be the case since the water quality is
considered to be fair (Class B) to good (Class A) in the latest overview of
Scottish rivers (The Scottish Office Environment Department, 1992).
River Spey - Sea Lamprey
A likely constraint on the population size of sea lampreys in the River Spey is
the availability of suitable nursery areas on the reaches of the river which sea
lampreys regularly use. We suggest that it is important to ensure awareness
of the need to limit damage to these areas during river maintenance
operations, and possibly to carry out any new maintenance in such a way as
to encourage the creation of new areas.
River Teith - Sea Lamprey and River/Brook Lampreys
There are good populations of anadromous lampreys in the River Teith
despite the poor quality (Class C) of water in the upper estuary (The Scottish
Office Environment Department, 1992). Again, one likely constraint on
population size is the availability of suitable nursery areas on some reaches
of the river and we again suggest that it is important that such areas be
protected from damage during river maintenance operations.
River Endrick and Loch Lomond - River/Brook Lampreys
The uniqueness in the British Isles of the river lamprey population of Loch
Lomond makes it of particular conservation interest. Its very uniqueness
suggests that an unusual set of circumstances may have been required for it
to have evolved.
As has already been mentioned, the main prey fish for lampreys in
Loch Lomond is the powan. The high proportion of powan which had marks
from previously attached lampreys (Maitland, 1980) suggests that the number
of available prey fish may be a constraint on population size as has been
shown to be the case with the landlocked sea lampreys of the North
American Great Lakes.
A major concern is the recent introduction of a number of introduced
species. Gudgeon, Cottus gobio L., dace, Leuciscus leuciscus (L.) and ruffe,
Gymnocephalus cernuus (L.) have already established large populations in
the catchment, and there is a risk that increased mortality from ruffe predation
of powan ova may seriously impact on the powan population (Adams, 1994).
Because of the rarity of powan (it is found naturally in only one other Scottish
loch), and the potential vulnerability of the Loch Lomond population, attempts
are being made to safeguard Scottish powan by establishing other
populations at two nearby lochs. (Maitland and Lyle, 1990). Consideration is
14
also being given to attempting to establish another stock of river lampreys at
one of these sites, or at a separate new site (Lyle and Maitland, 1994).
It is possible that the population of river lampreys depends largely on
the short length of river from Drymen to the Pots of Gartness to provide
suitable spawning areas and that the extent and placement of suitable
spawning areas rather than the extent of suitable rearing areas may be a
constraint on population size. Therefore measures to ensure the protection of
these areas from damage, and disturbance at spawning time, should be
considered.
NEED FOR FURTHER WORK
A priority for work is further study of the population of landlocked river
lampreys of Loch Lomond. We feel this because of the conservation
importance of this unique population in the British Isles, the recent changes
which could affect the population and the lack of up-to-date information in this
changing situation. The survey last year did not provide information on the
present strength of the population as it was not possible to identify any of the
ammocoetes positively as river rather than brook lampreys. We feel that
there may be a case for updating some of the earlier work of Maitland on the
adult lampreys. This should include observations at spawning time which
would confirm the spawning areas. It may be possible to quantify the adult
population by a mark-recapture study over the winter. It would also be
valuable to know the extent to which the population is dependent solely on
the River Endrick, rather than using any of the other inflows.
We would also suggest that some genetic work on river/brook
lampreys would be useful. Although currently classed as a separate species
it is not known how often brook lamprey populations may have originated
from river lampreys in different areas. Morris (1989), using univariate and
multivariate statistics, has shown that the Loch Lomond river lamprey is in
some ways intermediate between the normal forms of river and brook
lampreys and suggested that it represents an intermediate stage between
these two species. Both river lamprey and brook lamprey are reported to
have identical karyotypes (Hardisty, 1986b,c), and it would be informative to
know the extent to which river and brook lampreys from the same area are
similar genetically and differ from river and brook lampreys from elsewhere.
We are not aware of work where the progeny of river lamprey x river lamprey
crosses and brook lamprey × brook lamprey crosses from streams where
both species occur, have been reared through to metamorphosis to establish
that only river lampreys or brook lampreys result.
Although we know of no other examples of land-locked populations of
river lampreys in the British Isles, there may be scope for articles in the
angling press which could seek evidence of lamprey predation in other fresh
waters.
ACKNOWLEDGEMENTS
15
Many people have been helpful to us in providing information and allowing
ready access for sampling. We would also like to thank Mike Robb for
assistance in the field. Special thanks are due to SNH's Nominated Officer,
Willie Duncan, who provided enthusiastic and helpful support. Also of SNH,
Lyndsey Kinnes made many of the arrangements for the sites we visited on
the River Endrick, and Kristin Scott ensured co-ordination between our
sampling and a river corridor survey on the River Spey which was happening
at the same time. Thanks are also due to Martin Hardisty, for his interest in
this study and for the advice so willingly given. The Forth, Clyde and NorthEast River Purification Boards helped with advice on river heights and
provided useful background information.
REFERENCES
Adams, C.E. (1994). The fish community of Loch Lomond, Scotland: its
history and rapidly changing status. Hydrobiologia, 290, 91-102.
Beamish, F.W.H and Medland, T.E. (1988). Age determination for
lampreys. Transactions of the American Fisheries Society, 117, 6371.
Brown, A. (1895). Reptiles and fishes. In: A Guide to the Natural History of
Loch Lomond and Neighbourhood. (Lumsden, J.) Glasgow: David
Bryce and Son. (Cited by Lamond, 1931).
Hardisty, M.W. (1986a). Petromyzon marinus Linnaeus, 1758. In: The
Freshwater Fishes of Europe. Vol. 1, Part I. Petromyzontiformes.
(Hol_ík, J. ed.), pp94-116. Wiesbaden:Aula-Verlag.
Hardisty, M.W. (1986b). Lampetra fluviatilis (Linnaeus, 1758). In: The
Freshwater Fishes of Europe. Vol. 1, Part I. Petromyzontiformes.
(Hol_ík, J. ed.). pp249-278. Wiesbaden:Aula-Verlag.
Hardisty, M.W. (1986c). Lampetra planeri (Bloch, 1784). In: The Freshwater
Fishes of Europe. Vol. 1, Part I. Petromyzontiformes. (Hol_ík, J. ed.).
pp279-304. Wiesbaden:Aula-Verlag.
Hardisty, M.W. (1986d). General introduction to lampreys. In: The
Freshwater Fishes of Europe. Vol. 1, Part I. Petromyzontiformes.
(Hol_ík, J. ed.). pp19-83. Wiesbaden:Aula-Verlag.
Huggins, R.J. and Thompson, A. (1970). Communal spawning of brook
and river lampreys, Lampetra planeri Bloch and Lampetra fluviatilis L.
Journal of Fish Biology, 2, 53-54.
Lamond, H. (1931). Loch Lomond: A Study in Angling Conditions. Glasgow:
Jackson, Wylie and Co.
16
Lowe, D.R, Beamish, F.W.H. and Potter, I.C. (1973). Changes in the
proximate composition of Petromyzon marinus (L.) during larval life
and metamorphosis. Journal of Fish Biology, 5, 673-682.
Lyle, A.A and Maitland, P.S. (1994). The importance of the Loch Lomond
National Nature Reserve for fish. Hydrobiologia, 290, 103-104.
Maitland, P.S. (1980). Scarring of whitefish (Coregonus lavaretus) by
European river lamprey (Lampetra fluviatilis) in Loch Lomond,
Scotland. Canadian Journal of Fisheries and Aquatic Sciences, 37,
1981-1988.
Maitland, P.S. and Campbell, R.N. (1992). Freshwater Fishes of the British
Isles. London: HarperCollins.
Maitland, P.S., East, K. and Morris, K.H. (1984a). Lamprey populations in
the catchments of the Forth and Clyde estuaries. Institute of
Terrestrial Ecology Annual Report 1983, 17-18.
Maitland, P.S. and Lyle, A.A. (1990). Practical conservation of British
fishes: current action on six declining species. Journal of Fish
Biology, 37, 255-256.
Maitland, P.S., Morris, K.H. and East, K. (1994). The ecology of lampreys
(Petromyzonidae) in the Loch Lomond area. Hydrobiologia, 290, 105120.
Maitland, P.S., Morris, K.H., East, K., Schoonoord, M.P., Van der Waal,
B. and Potter, I.C. (1984b). The estuarine biology of the river
lamprey, Lampetra fluviatilis, in the Firth of Forth, Scotland, with
particular reference to size composition and feeding. Journal of
Zoology, London, 203, 211-225.
Malmqvist, B. (1980). Habitat selection of larval brook lampreys (Lampetra
planeri, Bloch) in a south Sweden stream. Oecologia, 45. 35-38.
Medland, T.E and Beamish, F.W.H. (1991). Lamprey statolith banding
patterns in response to temperature, photoperiod and ontogeny.
Transactions of the American Fisheries Society 120, 255-260.
Morman, R.H, Cuddy, D.W. and Rugen P.C. (1980). Factors influencing
the distribution of sea lamprey (Petromyzon marinus) in the Great
Lakes. Canadian Journal of Fisheries and Aquatic Sciences, 37,
1811-1826.
Morris, K.H. (1989). A multivariate morphometric and meristic description of
a population of freshwater feeding river lampreys, Lampetra fluviatilis
(L.), from Loch Lomond, Scotland. Zoological Journal of the Linnaean
Society, 96, 357-371.
17
O'Boyle, R.N. and Beamish, F.W.H. (1977). Growth and intermediary
metabolism of larval and metamorphosing stages of the landlocked
sea lamprey, Petromyzon marinus L. Environmental Biology of
Fishes, 2, 103-120.
Potter, I.C. (1980). Ecology of larval and metamorphosing lampreys.
Canadian Journal of Fisheries and Aquatic Sciences, 37, 1641-1657.
Potter, I.C. (1986). The Petromyzoniformes with particular reference to
paired species. Canadian Journal of Fisheries and Aquatic Sciences,
37, 1595-1615.
Potter, I.C. and Osborne, T.S. (1975). The systematics of British larval
lampreys. Journal of Zoology, London 176, 311-329.
The Scottish Office Environment Department. (1992). Water Quality
Survey of Scotland.
Tuunainen, P., Ikonen, E. and Auvinen, H. (1980). Lampreys and lamprey
fisheries in Finland. Canadian Journal of Fisheries and Aquatic
Sciences, 37, 1953-1959.
Volk, E.C. (1986). Use of otic elements (statoliths) to determine age of sea
lamprey ammocoetes (Petromyzon marinus). Canadian Journal of
Fisheries and Aquatic Sciences, 43, 718-722.
Wardle, C.S. (1975). Limit of fish swimming speed. Nature, 255, 725-727.
GENERAL BIBLIOGRAPHY
In addition to the specific references given above, the following books,
articles and symposium proceedings provided much useful information on
lampreys and their biology.
Hardisty, M.W. and Potter, I.C. (eds). (1971, 1972, 1981, 1982, 1982). The
Biology of Lampreys. Volumes 1, 2, 3, 4A, 4B. London: Academic
Press.
Hol_ík, J. (ed). (1986). The Freshwater Fishes of Europe. Vol. 1, Part I.
Petromyzonti-formes. Wiesbaden: Aula-Verlag.
Larsen, L.O. and Dufour, S. (1993). Growth, reproduction and death in
lampreys and eels. In: Fish Ecophysiology. (Rankin, J.C. and Jensen, F.B.
eds). London: Chapman and Hall.
Proceedings of the 1979 Sea Lamprey International Symposium (SLIS).
Canadian Journal of Fisheries and Aquatic Sciences 37, No 11
(1980). pp 1585-2214.
18
TABLE I
Sites visited
Site
River
Location
Bank
Grid
Reference
Date of Visit
L5
Leven
Balloch
Left
NS 395813 16 August
L4
Leven
Alexandria
Right
NS 394803 24 August
L3
Leven
Bonhill
Right
NS 393793 16 August
L2
Leven
Dalquhurn
Right
NS 394784 24 August
L1
Leven
Upper tidal stretch
Right
NS 395777 24 August
S6
Spey
Above Kingussie
Left
NN 752992 19 August
S5
Spey
Tulchan Beat B
Left
NJ 117335 30 August
S4
Spey
Tulchan Beat D
Left
NJ 141355 30 August
S3
Spey
Knockando
Left
NJ 201412 25 August
S2
Spey
Orton
Left
NJ 318525 18 August
S1
Spey
Brae
Left
NJ 332556 25 August
T6
Teith
Just above Lanrick
Weir
Right
NN 703027 22 August
T5
Teith
Inverardoch
Left
NN 731006 1 September
T4
Teith
Keir
Left
NS 758977 5 September
T3
Teith
Between
Greenocks and
Steeds
Left
NS 762971 5 September
T2
Teith
Between
Greenocks and
Steeds
Left
NS 760969 5 September
T1
Forth
Upper tidal stretch
Left
NS 780960 22 August
E5
Endrick Fords Bridge
Right
NS 504859 6 September
E4
Endrick Gaidrew
Right
NS 484865 16
September
E3
Endrick Drymen
Right
NS 472873 6 September
E2
Endrick Kilmaronock
Left
NS 453882 16
September
E1
Endrick Wardshill
Left
NS 448885 6 September
TABLE II
Characteristics of sample sites
Extent of
favourable
habitat for
ammocoetes
Areas
sampled
L5
Isolated areas of
favourable habitat
along left bank.
Right hand bank
had few suitable
areas
Over a 16 m
stretch of suitable
habitat along edge
of bank above foot
bridge
Mud, sand and silt
and including a
few scattered
boulders
0.5 m
Almost
slack
water
Algae and
detritus
present
Reports of sea
lampreys
spawning about
100 m above site.
L4
Very few areas
which looked
suitable in this
stretch of river
A narrow strip
against bank and
an area of about
30 m below an
outfall
Sand, silt and mud
0.5 m
Slack
None
It appeared that
area was affected
by sewage. Silt
smelly when
disturbed.
L3
More extensive
areas of suitable
habitat along both
banks
Over a 20 m
stretch of suitable
habitat along edge
of bank.
Soft sand and silt
with top sample
area being of
slightly coarser
substrate
0.4 m
Slow
Detritus
present and
some pond
weed
L2
Mainly stony with
few areas of
suitable bed.
Isolated area
along bank edge
below right hand
bend in river
Sandy with some
boulders and
woody debris
0.5 m
Gentle
Algae and
detritus
present
L1
Extensive
suitable habitat
along bankside
and into deeper
water
Area along bank
edge and into
deeper water just
before left hand
bend in river
Soft mud and silt
with scattered
boulders.
Slow would also
depend on
state of
tide.
Algae, detritus
and various
macrophytes
present
S6
Very extensive
A shallow shaded
Mixture of soft
Slack
Lot of detritus
Site
CHARACTERISTICS OF AREAS SAMPLED
Bed composition
Typical
maximum
depth
Very much
dependent
on tide
0.15 m
Typical
current
speed
Aquatic
vegetation
and detritus
Other information
Water Chemistry
pH
Alk
µeq/l
Cond
µS/cm
NO3
µeq/l
PO4-P
µg/l
Abs-250
6.88
241
71
9
2
0.105
7.09
255
78
11
0
0.111
230
57
7.58
Reports of sea
lampreys
spawning about 80
m from top sample
area.
Sea lampreys
Site
Extent of
favourable
habitat for
ammocoetes
areas of suitable
habitat
Areas
sampled
CHARACTERISTICS OF AREAS SAMPLED
Bed composition
Typical
maximum
depth
Typical
current
speed
area along edge of clay, mud and silt
bank
S5
Restricted areas Over a 15 m
of suitable habitat stretch below
island in river
S4
Suitable localised
areas with some
favourable
looking oxbows
and backwaters.
S3
Restricted areas Sample areas
of suitable habitat spread over a
along both banks 75 m stretch at tail
of pool including a
small backwater
section
S2
Few favourable
areas along this
stretch of main
stem except a
backwater
channel
S1
T6
Aquatic
vegetation
and detritus
pH
Alk
µeq/l
Cond
µS/cm
NO3
µeq/l
PO4-P
µg/l
Abs-250
spawned about
100 m above site
in 1983.
present
(1983 data)
Sand and silt
0.75 m
Gentle
Detritus
present
Ranged from quite
a firm silty, sandy
bed at bottom end
of backwater to
softer sand
towards top end
0.5 m
Slack
Lots of
detritus
present
Varied from silty
sections among
lots of twigs to soft
sandy areas
0.35 m
Slack/
Gentle
Lots of
detritus
present
Backwater, with
sample areas
spread over a
25 m length
Varied from coarse
sand at top of
backwater to
cobbles and
scattered pebbles
and boulders
towards bottom
0.25 m
Slack
Algae and
detritus
present
Excellent long
backwater but
few suitable
areas along main
stem
Backwater, with
sample areas
about half way
down
Sand with some
gravel
0.2 m
Slack
water
Lots of algae
and detritus
present
Restricted areas
suitable
Area in front of
lade intake, along
bank edge just
above this and in a
Varied from silty to
muddy with a high
organic content,
leaves and woody
0.3 m
Ranged
from slack
to gentle
Detritus
present
Backwater
between oxbow
and main stem.
Samples spread
over about 10m
Other information
Water Chemistry
6.96
216
53
9
-
0.200
Reports of sea
lampreys
spawning at top
end of this pool
7.74
492
101
21
0
0.076
Area where Lord
Percy obtained
samples
7.04
178
55
7
0
0.100
Site
Extent of
favourable
habitat for
ammocoetes
Areas
sampled
CHARACTERISTICS OF AREAS SAMPLED
Bed composition
small backwater.
debris covering
part of the bed
Typical
maximum
depth
Typical
current
speed
Aquatic
vegetation
and detritus
Other information
Water Chemistry
pH
Alk
µeq/l
Cond
µS/cm
NO3
µeq/l
PO4-P
µg/l
Abs-250
T5
Localised
favourable areas
along edge of
bank
Area of suitable
habitat below
mouth of Ardoch
Burn
Sand, silt and
gravel
0.6 m
Gentle
Detritus
present
7.29
475
81
23
-
0.205
T4
Scattered
favourable areas
along both banks
.
Section along
bank edge beside
overhanging
grassy bank
Soft sand and silt
0.6 m
Slack
Detritus
present
7.06
256
57
14
-
0.162
T3
Small backwater in Gravel and sand
Scattered
with a layer of thick
favourable habitat exposed
along both banks gravel/pebble bank silt
0.35 m
Slack
Detritus
present
T2
Very extensive
areas along both
banks
Area of suitable
habitat next to
steep sided bank
and extending into
deeper water
Sand, silt and
some woody
debris
0.65 m
Slack
water
Detritus
present
T1
Extensive
favourable areas
on right hand
bank, more
restricted areas
on left bank.
Area of favourable
habitat along bank
edge
Mud, clay and
sand with some
boulders and rocks
0.5 m
Slack
water
Detritus
present
7.30
287
72
13
4
0.108
E5
Extensive
suitable areas
along both banks
Small isolated
pocket above
footbridge
Deep mud and silt
0.3 m
Slack
water
Algae and
detritus
present
7.65
955
150
33
-
0.345
E4
Shallow favourable Fine deep silt
Extensive
area next to bank
suitable areas
along both banks.
0.3 m
Almost
slack
water
A little aquatic
vegetation
and detritus
Report of sea
lampreys
spawning a little
above this site
Site
Extent of
favourable
habitat for
ammocoetes
Areas
sampled
CHARACTERISTICS OF AREAS SAMPLED
Bed composition
Typical
maximum
depth
Typical
current
speed
Aquatic
vegetation
and detritus
Other information
Water Chemistry
pH
Alk
µeq/l
Cond
µS/cm
NO3
µeq/l
PO4-P
µg/l
Abs-250
present
E3
Abundant
suitable areas
along both banks
Tail end of
exposed sand bar
Silt and fine sand
E2
Widespread
areas of suitable
habitat.
Spread over a 160 Ranged from
m stretch following muddy, silty to
an ' S ' bend in the sandy
river
E1
Scattered
suitable areas
along banks
Narrow marginal
zone dropping
quickly into deep
water
Deep fine mud
with emergent
grasses, some
decomposing
organic material,
gassing when
disturbed
0.45 m
Slack
water
Some detritus
present
7.51
1005
157
42
-
0.474
0.3 m
Almost
slack
Detritus
present
7.36
1090
170
37
25
0.356
0.6 m
Slack
water
Some aquatic
vegetation
present
7.21
956
153
39
-
0.509
Livestock drinking
site
TABLE III
Numbers of ammocoetes caught at each site
Site
Approx
area
fished
(m2)
Total
ammocoetes
River/brook lamprey ammocoetes
Transforming
Others
Total
Total
per m2
Sea lamprey
ammocoetes
Total
Total
per m2
L5
6.9
98
0
98
98
14.2
0
0
L4
10
2
0
2
2
0.2
0
0
L3
9.2
129
2
125
127
14.0
2
0.2
L2
9.2
138
19
119
138
15
0
0
L1
23
131
11
120
131
5.7
0
0
S6
2.8*
386
2
384
386
138
0
0
S5
4.6
186
0
186
186
40.4
0
0
S4
9.2
319
0
313
313
34
6
0.7
S3
4.6
298
7
288
295
64
3
0.7
S2
16.0
100
6
88
94
5.9
6
0.4
S1
4.6
96
2
93
95
20.6
1
0.2
T6
11.5
88
0
88
88
7.7
0
0
T5
4.6
378
1
376
377
82
1
0.2
T4
2.3*
459
0
450
450
195.7
9
3.9
T3
2.8
109
0
109
109
38.9
0
0
T2
3.4
240
6
231
237
69.7
3
0.9
T1
5.1
141
3
137
140
27.5
1
0.2
E5
2.5
67
6
61
67
26.8
0
0
E4
2.3
228
3
225
228
99.1
0
0
E3
9.2
160
2
158
160
17.4
0
0
E2
18.4
36
0
36
36
2.0
0
0
E1
4.6
6
2
4
6
1.3
0
0
All
sites
166.8
3795
72
3691
3763
22.6
32
*Fishing not exhaustive
TABLE IV
Approximate modal lengths of age 0+ and age 1+ ammocoetes
River
River/brook lamprey
length (mm)
Sea lamprey
length (mm)
0+
1+
0+
1+
Forth/Teith
20
42
13
30
Leven
17
42*
-
30
Spey (S2-S5)
25
50
-
40
Endrick
31
72
-
-
*Tentative estimate