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Final Report to EMFF/MMO Project ROPE (ENG3420) Response of predators to Protection and Enhancement Funded by European Maritime and Fisheries Fund Project ROPE (ENG3420) Response of predators to Protection and Enhancement


Abstract and Figures

Project ROPE (Response of predators to Protection and Enhancement), funded by the European Maritime & Fisheries Fund (EMFF) and implemented by University of Plymouth aims to improve understanding of the movements of commercially and recreationally important fish and crustaceans in the Lyme Bay region of South Devon and Dorset. Project ROPE applies innovative acoustic tracking technology to: (1) Understand how the UK’s largest offshore rope-cultured mussel farm influences the movement behaviour of brown crab [Cancer pagurus], lobster [Homarus gammarus] and seabass [Dicentrarchus labrax]; and (2) Determine if the increase in economically valuable fisheries species observed at the offshore mussel farm will ‘spill over’ into adjacent fishing grounds.
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Final Report to EMFF/MMO
Project ROPE (ENG3420)
Response of predators to Protection and Enhancement
Funded by European Maritime and Fisheries Fund
Simon J Pittman, Emma V Sheehan, Thomas Stamp, Luke A Holmes and Adam Rees
School of Biological and Marine Sciences
University of Plymouth
In collaboration with Offshore Shellfish Ltd
December 2020
Project ROPE (ENG3420)
Response of predators to Protection and Enhancement
Recommended citation: Pittman SJ, Sheehan EV, Stamp T, Holmes LA, Rees A (2020). Project ROPE (ENG3420).
Response of predators to Protection and Enhancement. Final Report. December 2020. University of Plymouth.
1. Introduction
Project ROPE (Response of predators to Protection and Enhancement), funded by the
European Maritime & Fisheries Fund (EMFF) aims to improve understanding of the
movements of commercially and recreationally important fish and crustaceans in the Lyme
Bay region of South Devon and Dorset. Within this broad goal, ROPE applies innovative
acoustic tracking technology to:
(1) Understand how the UK’s largest offshore rope-cultured mussel farm influences the
movement behaviour of brown crab [Cancer pagurus], lobster [Homarus gammarus]
and seabass [Dicentrarchus labrax]; and
(2) Determine if the increase in economically valuable fisheries species observed at the
offshore mussel farm will spill over into adjacent fishing grounds.
This project builds on the University of Plymouth’s long-term monitoring program (including
Project RETURN ENG1388 & Recover Reef ENG4234) which has been tracking conditions in
Lyme Bay for over a decade and has been monitoring the ecological effects of an offshore
mussel farm since the beginning of its development in 2013. The mussel farm, operated by
Offshore Shellfish Ltd and located between three and six miles offshore in Lyme Bay is
expected to become the largest of its type in European waters covering a total area of 15.4
square km and capable of producing up to 10,000 tonnes of native blue mussels per year.
Our underwater monitoring surveys have
shown that the farm which exists as a living
floating reef structure has increased the
local abundance of marine predator
species including brown crab, lobster and
seabass; important species to the inshore
fishers of Dorset and Devon (Rees et al.
2018). The vertically hanging ropes
(“droppers”) that are home to millions of
blue mussels, Mytilus edulis, also attract
fish and many other plant and animals that
settle on the mussels forming a novel
foodweb (Figure 1). For pelagic fish, the farm structure acts as an aggregation device with
large shoals of Atlantic horse mackerel (Trachurus trachurus), or scad, frequently seen
swimming and feeding amongst the
droppers where sea bass have been
observed feeding on the scad.
Underneath the ropes, crabs and lobsters
feed on the mussels that fall to the seabed
(Figure 2). Although we know that crabs,
lobsters and predatory fish utilise the site
for food and shelter, due to the habitat
enhancement that the ropes, moorings
and fallen mussels provide, we know very
little about the movements of these key
predators around the farm, or how long
Figure 1. Rope-grown blue mussels in Lyme Bay.
Figure 2. Fallen mussels and foraging brown
crab under the mussel farm in Lyme Bay.
they remain resident, or if there is movement between the farms and the surrounding fishing
To investigate animal movements in and around the mussel farm, this project has tagged and
acoustically tracked multiple species including bass, brown crab, spider crab and lobsters. The
tags emit a unique coded acoustic ping which is recorded and monitored by underwater
hydrophones (acoustic receivers) placed inside the farm and in nearby estuaries.
Understanding the way that marine animals respond to the mussel farm is an important in
understanding the ecological effects of offshore aquaculture. This information is critical to
the evaluation of the environmental footprint of offshore aquaculture in the region for the
industry, consumers and decision making in spatial planning. There is growing interest in
offshore shellfish aquaculture in the UK and significant scope for expansion of sustainable
aquaculture in the south west UK (Kershaw et al. 2020). Furthermore, with the expansion of
marine protected areas (MPAs) globally, ecological surveillance and monitoring will
increasingly play a key role in the development of effective evidence-based policy for
mariculture development in and around MPAs (Brown et al. 2020).
Understanding the broader ecological effects of the mussel farm beyond its operating space
is critical to inform the Dorset and East Devon strategy for aquaculture, Dorset Coast Strategy,
Fisheries Local Action Groups, IFCAs and the Marine Management Organisation marine
This first-of-its-kind research project in the UK that is tracking animal movements at an
offshore farm has been co-designed in close collaboration with the farmers at Offshore
Shellfish and in consultation with the local fishing industry through the Lyme Bay Fisheries
and Conservation Reserve. From its inception, the project has received strong support from
the seafood industry (Shellfish Association of Great Britain, Morrisons Supermarket, The
Fishmongers Company), marine conservation groups (Blue Marine Foundation & Marine
Conservation Society) and government agencies with responsibility for effective marine
planning and licencing (Natural England, Marine Management Organisation, Defra & the
Devon & Severn Inshore Fisheries and Conservation Authority). Representatives from all
sectors supporting the view that robust scientific evidence is vital to underpin policies and
strategic decisions for sustainable and responsible use of our oceans.
Our primary research question is: How do commercially important fish and crustaceans use
the space within and around the mussel farm (human-modified structure) including
connectivity with estuaries?
To address this question Project ROPE uses the latest advances in acoustic telemetry to track
the fine-scale daily movements of individual animals at the mussel farm and the broader-scale
movements in the Lyme Bay region. The ROPE acoustic array (incorporating Project
SPILLOVER [ENG4341]) extends the geographical extent of detection provided by the
previously funded Project I-BASS (Immature Bass Acoustic Stock Surveillance) (ENG1389)
adding value to previous EMFF investments and making these projects, when combined,
among the biggest acoustic marine animal tracking projects in the UK.
1.1 Summary of achievements
In the first year of this 18 month project, the project team purchased the acoustic tracking
equipment, constructed moorings and made modifications to the design of the acoustic
retrieval canister (ARC) to reduce biofouling and entanglement with fishing gear. In addition,
we designed an animation to communicate the purpose and methods of the project and
conducted local consultations and delivered presentations on the project to the Lyme Bay
fishing community (Lyme Bay Fisheries and Conservation Reserve Consultative Committee)
where study site selection was discussed.
In the second year of the project, we conducted a range test at the mussel farm to inform the
design of the passive acoustic array and deployed receivers to construct a positioning system
to track fine-scale animal movements at the farm. With the help of local fishermen, we then
caught, tagged and released 73 crustaceans at the mussel farm and 62 seabass from estuaries
closest to the mussel farm to examine movements at the farm and to detect any inshore-
offshore connectivity patterns (see Section 3). To determine the importance of the mussel
farm as a food source for crab and lobster we also collected crustacean tissue samples for
stable isotope and lipid biomarker analysis (Sardenne et al. 2019). Comparision of results from
tissue analysis for crustaceans at the farm (41 animals) and inside the MPA (23 animals) will
determine how important the rope-grown blue mussels are as a food source compared with
food from areas distant from the farm.
2. Materials and Methods
2.1 Study site characteristics
Project ROPE is implemented in the offshore waters of Lyme Bay, south west England (South
Devon and Dorset) (Figure 3). The seabed under the mussel farm acoustic array is relatively
flat with depths varying between 22-24 m (mean = 23.07 m ±0.36 SD). According to the Devon
Biodiversity Records Centre marine substrates map, the dominant substrate is mud and sand
and the biotope is Cerianthus lloydii and other burrowing anemones in circalittoral muddy
mixed sediment (SS.SMx.CMx.ClloMx). This biotope type has been modified by the presence
of the mussel farm particularly by fallen mussels that increase the topographic complexity
and biological material on the seabed. The nearest highly structured benthic habitat is located
inside the Lyme Bay and Torbay Special Area of Conservation (SAC) (Natural England 2010)
and the Statutory Instrument (an MPA), approximately 2 km east of the mussel farm, where
the exclusion of bottom-towed gear has supported the recovery of a diverse reef biotope and
sediments comprised of mosaics of mixed faunal turf communities and pink sea fans on rock
and mixed sediments (Sheehan et al. 2013). The region supports diverse and recreational and
commercial marine uses (Rees et al. 2010) and has been identified as a region for the growth
of aquaculture. Shellfish aquaculture production in the region already accounts for a
significant proportion of English mussel production (D&S IFCA 2020). The single largest
producer of blue mussels in the south west region is Offshore Shellfish Ltd with two active
sites in Lyme Bay (Figure 4).
Figure 3. The location of one of the operational areas for Offshore Shellfish (mussel
farm site 2) in Lyme Bay, South Devon, UK.
Figure 4. The mussel farm (Offshore Shellfish) in Lyme Bay, South Devon, UK.
Image source: CGTN
2.2 Acoustic fine-scale positioning system
To investigate the fine-scale movements of tagged animals at the mussel farm, Project ROPE
implemented the VEMCO ultrasonic aquatic fine-scale positioning system (VPS). In order for
VPS to calculate a position for a transmitter, a single transmission must be detected by at
least 3 time-synchronized receivers at known locations. VPS operates in three dimensions
taking the parameters of 3D positions for the detecting receivers, range differences, and the
estimated depth of the transmitter to calculate intersection points. VPS uses hyperbolic
positioning, also known as time difference of arrival (TDOA), which is a technique based on
measuring differences in transmission detection times at pairs of time-synchronized receivers
and converting these to distance differences using the signal propagation speed. These
transmissions are also used for calibrating the locations of receiver stations and measuring
the effects of positioning error (see Smith et al. 2013 for more detail). To investigate
movements outside of the array we have conducted active acoustic surveys by manually
towing a transponding hydrophone from a small vessel.
2.3 Acoustic receivers and moorings
The acoustic telemetry equipment purchased, constructed and modified for Project ROPE
comprises a canister to hold the retrieval line, floats, receivers (hydrophones), mooring
equipment and acoustic transmitters. VR2AR receivers are equipped with a transmitter to
allow communication with other receivers while deployed and they have a simple motorised
quick release mechanism to enable the receiver to be retrieved at the surface. The upper
plate of the canister attaches to the VR2AR mooring brackets and holds three 11” 8.4 kg
buoyancy trawl floats (Figure 5). This section ascends to the surface when the VR2AR acoustic
release is activated by the user resulting in the lug at the base of the receiver unwinding and
detaching the buoyant top plate. Each canister holds 45 m of 8 mm polysteel rope that is
shackled to the chain anchor. This is the retrieval line. One end of the rope (coiled inside the
rope canister) is also attached to the upper plate and spools out as the top plate ascends.
The rope canister remains attached to the release lug at the base of the VR2AR and is held in
place on the seabed by the chain anchor. After the top plate has been retrieved at the surface
the canister and anchor can then be lifted to the surface using the retrieval line. Where it was
possible to attach receivers directly to the mussel farm headlines, a purpose-built weighted
mooring, a dropper, (Figure 6) was designed and constructed to hold the acoustic receivers
in a downward facing position. In addition to fixed position receivers (ARCs and droppers), a
boat-towed omni-directional hydrophone was used for manual tracking (Figure 8).
Figure 6. Design of farm-attached
receiver moorings
Prusik knot
51 mm PVC
flat hose
covering 1.5
m x 7mm
long link
steel chain
Tape to aid removal of fouling
during maintenance
Figure 7. Haulage of anchor chain at
Dart Harbour
45 m of 8 mm
retrieval line
70 kg anchor
1 m x 24 mm strop
line, thimbles/shackles
Copper tape on
canister to
reduce biofouling
Wire rope to
with fishing gear
VEMCO Acoustic Release
(VR2AR) receiver with
copper sleeve to reduce
Heavy acetal top
plate to hold
receiver and floats
Canister to
3 x floats lift top
plate and receiver
to the surface
45 m
retrieval line
Figure 5. Design of seabed moorings using acoustic retrieval canisters (ARCs)
2.4 Acoustic transmitters (tags)
Project ROPE uses Vemco acoustic coded tags (V9-1L) for
crustaceans and V9P-2L (pressure sensor) coded tags for seabass.
The V9-1L is 24 mm in length and 9mm in diameter, weighing 2.1g in
water. The V9P-2L is 31 mm in length and 9 mm in diameter,
weighing 2.8g in water. Coded tags, using a pulse-position
modulating coding scheme, send out acoustic transmissions at 69
kHz. Project ROPE tags were programmed to send transmissions
randomly either side of an average delay of 180 seconds to reduce
the likelihood of data collisions from multiple simultaneous
transmissions. Tag transmissions include an ID number which identifies a specific tag and for
V9P tags also transmits pressure sensor data. The pressure sensor transmitters were
programmed to record pressure in water depths up to 68 m. For applications such as site
residency studies coded transmissions are desirable because of significantly increased battery
life and the large number of unique IDs available on a single frequency. From activation the
V9-1L tags used for crustaceans are expected to last for approximately 450 days (1 year & 3
months) and the V9P tags for seabass for 170 days (5.6 months) after accounting for some
battery power loss during storage.
Figure 8. Hydrophones used by Project ROPE to track animals carrying tags in Lyme Bay.
2.5 Range testing to determine the optimal acoustic array configuration
A range test was conducted to determine the effective distances required between acoustic
receivers to achieve sufficient detection efficiency i.e. the proportion of coded transmissions
from a coded transmitter detected by a receiver. The receiver spacing is crucial in the spatial
design of acoustic arrays because complete overlap of detection ranges is required to
maximise positional accuracy. The detection range, i.e. the area surrounding the receiver in
which tag transmissions can be detected, varies over space and time due to dynamic
environmental condition (Kessel et al. 2014, Brownscombe et al. 2019, Reubens et al. 2019).
In offshore marine environments wind speed has been identified as an important influence
on receiver tilt and the scattering of sound waves that reduced sound propagation through
water and the detection probability (Reubens et al. 2019). The speed of transmission is vital
for the accuracy of triangulation within the VPS. VR2Tx receivers have a built-in transmitter
that allows communications with other receivers as well as from a hydrophone deployed at
the surface and can be used as a synchronising tag for improved position estimates.
Five VEMCO VR2Tx acoustic receivers were deployed at different horizontal distances to one
another on lines in the north-west sector of the mussel farm to test the effect of distance (43
- 412 m) and offshore environmental conditions (i.e. wind speed, wave action, tides) on
detectability (Figure 9). The location was chosen to place the receivers among heavily mussel
laden ropes. VR2Tx receivers were programmed to record tilt angle of the receiver every hour.
All receivers were placed at similar depth. The range test was conducted for 1 month to
adequately sample varying ocean conditions including frequent seasonal storms that serve to
represent the worst conditions for detectability. VEMCO range test software was used to
analyse the data.
Inter-receiver distances (Euclidean) metres
Figure 9. Position and distance between the acoustic receivers for range testing at
mussel farm Site 2.
2.5.1 Results from the range test
Comparing the results from receivers placed at different distances from internal transmitters
revealed that the greatest spacing that also achieved very good detection efficiency was 165.5
m. Detection efficiency began to diminish beyond 200 m (Figure 10A). Detection efficiency
was similar during day and night. Rough sea conditions during storms was the most important
factor in diminishing detection efficiency as evidenced by receiver tilt angle (Figure 10C). At
distances less than 200 m, performance was sufficient with a large proportion of detections
recorded throughout the test duration, although the impact of storms was clear (Figure 10B).
Analysis of wave height data with detection efficiency suggested that reduced detection
efficiency is observable where wave height exceeds 2 m (Figure 10B). Historical daily wave
height data (Figure 11) from a Lyme Bay monitoring station (West Bay) from April 2016 to
March 2020 suggests that the months of April to August provide the calmest conditions of the
Figure 10. A. Detection probability at 165.5 m distance between receiver and
transmitter. B. Detection probability and wave height during range testing.
Figure 10 C. The tilting of the receiver (tilt angle) during storms combined with
acoustic scattering of the transmission coincides with loss of detections.
Figure 11. Historical (2016-2020) wave height in Lyme Bay (West Bay) showing the 2-
metre acoustic signal-disruption threshold (red line). Source: Channel Coastal
Observatory (
2.6 Design of the acoustic array for fine-scale positioning of tagged animals
The four main design factors that influence positional error in a VPS array are: 1.) array
geometry or configuration (optimal receiver spacing and uniformly spaced across the array),
the accuracy of receiver time synchronisation, 3.) the positional accuracy (geographical
coordinates of receivers), and 4.) the estimated velocity of sound. VPS provides a relative,
unitless estimate of how sensitive a calculated position is to errors in its inputs; this is referred
to as horizontal position error (HPE). Analysing the relationship between HPE and the
calculated positions for transmitters with known locations allows us to characterise HPE in
terms of distance. The precision outside of the receiver array declines markedly with distance
from receivers. The model of positional errors for a 4-receiver array below shows low HPE
(higher positional accuracy) is greater for transmitters inside the array (green = HPE<20) than
those outside (red = HPE>20).
To construct a fine-scale positioning system at the offshore mussel farm, Project ROPE
deployed 31 acoustic receivers on the headlines of the mussel farm structure and 7 acoustic
receivers anchored on the seabed outside of the main mussel-bearing farm structure (Figure
13). The geometry of the array provides more than 100% overlapping detection using a four-
receiver configuration. The approximate array area is 1 km2 with the mean distance between
nearest receivers being 141.7 metres 11.3 SD). To correct for any drifting in the receiver
clocks a reference tag called a synchronisation tag (synctag) was placed within the array
(between four receivers) (Figure 13) to transmit a signal from a known location on a random
time delay.
Figure 12. VEMCO acoustic receiver array distance calculator showing spatial pattern of
positional errors with an overlapping 4-receiver configuration.
2.7 Placement of additional receivers in Lyme Bay and South Devon estuaries
To extend the geographical scope of detection beyond the existing array established through
EMFF-funded Project I-BASS (Immature Bass Acoustic Stock Surveillance), 16 receivers were
deployed in estuaries closest to the mussel farm in west Lyme Bay and two were placed on
the seabed at 30 m depth close to an offshore shipwreck (SS Radaas torpedoed and sunk by
UB-40 in 1917) (Figure 14). Eight receivers were deployed at Exmouth by Exeter Port Authority
and seven at Teignmouth with help from Teignmouth Harbour Commission. This
complements existing receivers in the River Dart and Salcombe. Receivers are also being
placed in the River Axe in Lyme Bay and the Rivers Yealm (Figure 15), Erme and Avon in West
Devon to increase the geographical coverage of detectability for fish tagged by Project ROPE.
Bird’s eye view of double
Figure 13. Project ROPE VPS acoustic array configuration positioned in a central location
within mussel farm Site 2.
2.8 Tagging crustaceans and fish
2.8.1 Crabs and lobsters. Project ROPE researchers worked with local fishermen to set and
pull strings of lobster pots (max 10 pots per string) over a three-week period in August 2020.
Pots were baited with either scad, or pout and mackerel. All animals caught within traps were
removed, recorded and returned to the ocean. Commercial species of fish and crustacean
were counted and measured. Brown crab (Cancer pagurus), lobster (Homarus gammarus) and
common spider crab (Maja brachydactyla) were measured (carapace length for lobster and
width for crabs), sexed and then tagged with V9-1L transmitters using a clear marine epoxy
resin to completely cover the transmitter and the Project ROPE contact information for
reporting of re-caught animals (Figure 16).
Figure 14. Sonagram of the shipwreck SS
Radaas showing one of the acoustic
retrieval canisters (ARC) descending to the
sandy bottom between wreck structures.
Figure 15. Project ROPE scientist attaching
a VEMCO VR2Tx receiver to a pontoon
ladder in the Yealm estuary, South Devon.
Figure 16. A female lobster carrying
Tag no. 17044 and named Mandy
Wolfe (of Blue Marine Foundation). As
well as being given a unique numerical
code, many animals were named after
local people associated with the
research project including local
The intention was that tagged animals caught by fishermen outside of the farm would be
reported to the project (see section 5) thus providing direct evidence of connectivity
(potential spill-over) from the mussel farm to the local fisheries. Tagged animals were
released at the farm site (Figure 18 & 19) and GPS coordinates of the release location were
recorded and mapped (Figure 20). The average carapace width for the brown crabs was 136.9
mm (± 28.5 SD) and average carapace length for the 49 lobsters was 113.8 mm (± 30.5 SD)
(Figure 17). Although the timing of moulting is not known for our tagged individuals, however,
Two tagged male spider crabs
(149 & 106 mm)
Figure 17. Summary statistics for the size of tagged male and female crustaceans.
the size range of tagged animals (adults) coincides with a reduced frequency of moulting and
therefore the potential for a greater tag carrying duration. Research shows that the
probability of moulting declines as carapace length (width for brown crabs) and age increases
(Öndes et al. 2017, Coleman et al. 2020).
Figure 18. A lobster equipped with a V9 transmitter being released into the
acoustic array at the offshore mussel farm in Lyme Bay.
Figure 19. Underwater video of a tagged lobster and crab being released from
the fishing vessel Golden Scallops at the offshore mussel farm in Lyme Bay.
2.8.2 European seabass (Dicentrarchus labrax). 50 fish at the mouth of the River Exe and 12
fish at the mouth of the River Teign were caught with rod and line by local fishermen and
delivered to submerged keep nets placed near the location at which the surgical procedure
took place. The following day, fish were carefully transferred in aerated containers from the
keep nets to an aerated holding tank in the ROPE mobile surgical unit (Figure 21).
Figure 20. Map of the crustacean capture and release sites in and around the mussel
farm in Lyme Bay.
Figure 21. The keep net (left) and (right) the Project ROPE mobile surgical unit.
Fish were weighed (kgs) and placed in a water bath with anaesthetic until sedated (avg. 6
mins 36s). Transmitters were surgically implanted into the peritoneal cavity (avg. time of
surgery 2 mins 50s) (See Stamp et al. 2021 for details). Scales were extracted for age
determination and body length (fork length in centimetres) was measured before placing fish
into a shaded aerated container where recovery was monitored. Water quality (temperature,
salinity and dissolved oxygen) in all containers was measured periodically throughout the
surgical operations. Fish were released after at least an hour of post-operative observation
had been completed (Figure 23). Procedures strictly adhered to UK Home Office accredited
training and licensing.
Fish tagged at Exmouth were slightly larger than those at Teignmouth. At Exmouth, the largest
(Rex of the Exe) was 59.5 cm FL (2.45 kg) and the smallest (Little Jack) was 28 cm (0.26
kg). At Teignmouth, the largest (Sam Simmonds) was 56 cm FL (1.2 kg) and the smallest
(Teigny) was 33 cm (0.46 kg) (Figure 22). Based on length-weight relationships these fish
are likely to be less than 7 years old.
Exmouth (n = 50 fish)
Teignmouth (n = 12 fish)
Figure 22. Length and weight frequency distributions for tagged seabass from the
River Exe and River Teign. The mean value is indicated with a vertical dashed line.
2.9 Tissue collection for chemical analyses
Tissue samples from brown crabs (39% female and 61% male) and European lobster (64%
female and 36% male) were collected from pots set inside the MPA and inside the mussel
farm (Figure 24). The carapace width for brown crabs ranged from 8.2 cm to 16.3 cm (average
11.1 cm) at the mussel farm and from 11.2 cm to 19.9 cm (average 15.2 cm) inside the MPA.
The carapace length for lobster ranged from 6.6 cm to 16.3 cm (average 10.4 cm) at the
mussel farm and from 9 cm to 10.2 cm (average 9.6 cm) inside the MPA. Crab muscle tissue
was collected by removing the rear right swimming leg and for lobster by removing the
endopod of the 4th swimming leg. Blue mussel tissue was collected from ropes at the farm.
Tissue samples were wrapped in foil, labelled and placed immediately in a liquid nitrogen
Dewar (shipper) on board the fishing vessel. All samples were then stored in a freezer (-80oC)
at the University of Plymouth for later analyses.
Figure 23. Short video clip (19s) of the release of two tagged seabass at Exmouth Marina.
3. Preliminary findings
Project ROPE acoustic tracking will continue until early summer 2021 when a full data
download and detailed analyses will take place with results interpreted for peer-reviewed
scientific publications. Here, we highlight some preliminary findings from detections during
(1) towed hydrophone surveys in and around the mussel farm; (2) lobsters recaptured during
tagging; (3) detections during and after the acoustic range test at the mussel farm; and (4)
detections from existing receivers (Project I-BASS) retrieved from the River Dart and
Salcombe. To date, no tagged crabs or lobster have been caught and reported by fishers.
3.1 Towed hydrophone survey
Five individual lobsters were detected in the region of the mussel farm (Site 2) using a boat-
towed omni-directional transponding hydrophone deployed to the study site two to three
weeks after tag and release. 25 days after release Angus Walker (9.1 cm carapace length)
was detected approximately 360 m SE of his release location. Angry Bertha (14.5 cm) was
detected 475 m SE from release location after 18 days; Dr Alun Morgan (7.1 cm) at 860 m
NNW from the release location after 20 days; Andrew Spiller (7.9 cm) 790 m N of release
location after 22 days; and Jean Claw van Damme (13.7 cm) at 780 m WSW of release location
after 26 days.
Figure 24. Map of the locations inside the mussel farm and inside the MPA where crabs,
lobster and blue mussel were captured for tissue sampling.
3.2 Crustaceans recaptured during tagging
Two lobster were recaught during subsequent potting for Project ROPE. A male lobster
(Gavin Zieman) was recaptured 10 days after tagging at a location approximately 400 m
(straight line distance) NNW of his initial tag and release location. A female lobster
(Pandora) was recaptured 18 days after tagging approximately 600 m (straight line distance)
north of her initial tag and release location (orange points on Figure 25).
3.3 Connectivity between estuaries and offshore mussel farm
We have detected two-way movements of European seabass confirming ecological
connectivity between South Devon’s estuaries and the offshore mussel farm in Lyme Bay. Two
fish that visited the mussel farm returned to the estuary where they were first tagged by our
research team. Catie (35.3 cm FL when tagged) left Salcombe Harbour on Feb 3rd 2020 and
was detected at the mussel farm in early June 2020 before being re-detected back in
Salcombe on 25th July 2020. This is a minimum travel distance of approximately 80-90 km if
Catie were to have made a directional swim following the coastline between Salcombe and
the mussel farm although it is highly likely that the route taken was more circuitous. Three
other fish (Mairi, Travis and Loki) that were tagged and released in the River Dart had also
visited the mussel farm in the period April to June 2020. Loki (26.8 cm FL when tagged) left
the River Dart in September 2019 and was detected at the mussel farm in April 2020 and then
re-detected in the River Dart in May 2020. Mairi (28.4 cm FL when tagged) and Travis (29.8
Figure 25. Map showing the short-term movements detected by recaptures and towed
hydrophone surveys within a month of initial release.
cm FL when tagged) were last detected in the River Dart in June and May 2019 and then
detected visiting the mussel farm in spring of 2020, but at the time of writing neither fish have
since been detected.
3.4 Other broad scale inter-estuary movements
One fish (Keats at 42.5 cm FL weighing in at 0.855 kg) tagged and released at Polly Steps,
Teignmouth on the afternoon of 16th October 2020 was detected at Salcombe Harbour four
days later on the evening of 20th October. Keats was also detected in the River Dart estuary
on route to Salcombe. An additional 36 seabass tagged by Projects ROPE and I-BASS have
been detected moving between the River Dart and Salcombe (a route of at least 30 km if
following the shallow coastal waters) (Figure 26). The inter-estuary movements detected in
Project ROPE concur with the extensive new evidence from Project I-BASS that have revealed
in detail these behavioural patterns. Results from I-BASS will also be forthcoming in peer-
reviewed publications in 2021.
Figure 26. European seabass movements connect estuaries and the offshore mussel
farm in Lyme Bay. The dashed lines are not actual movement pathways and serve
only to illustrate the directions of broad-scale connectivity patterns based on pairs
of locations with confirmed presence of an individual fish.
4. Communication products
i.) Webpage. A project webpage was written and published
ii.) News item. A news release was written to promote the project.
iii.) Animation. An animated 1-minute explainer video (see screenshot) for
projects ROPE and SPILLOVER was created and shared via open access platform
YouTube (Figure 27) through the University of Plymouth and with project
funders, stakeholders and the broader public through social media (Twitter)
(Figure 28).
Figure 27. Online explainer animation for Project ROPE
Figure 28. One of many Twitter posts for Project ROPE
iv.) Presentations. Presentations featuring the project were delivered at the
following venues:
1st March 2019 - Verbal presentation to Lyme Bay Fisheries & Conservation
Consultative Committee
28th June 2019 - Poster presentation to 5th International Conference on Fish
Telemetry (not funded by ROPE)
1st Oct 2019 - Verbal presentation to Lyme Bay Fisheries & Conservation
Consultative Committee
29th Oct 2019 - Verbal presentation to Marine & Coastal Policy Research Group,
University of Plymouth
31st Oct 2019 - Verbal presentation to Association for Scottish Shellfish Growers,
Oban (not funded by ROPE)
17th November 2020 Verbal online project update to Lyme Bay Fisheries &
Conservation Consultative Committee
v.) Other communications:
To include the local fishing community in the project and raise awareness on the
project goals, we designed and distributed postcards (Figure 29) and posters to
communicate the tagging component of the project to the fishing communities and the
broader public. The printed posters were pinned on noticeboards in harbours at Beer,
Axmouth, Lyme Regis, Charmouth and Brixham and handed to fishermen and to
harbour masters (Appendix A). The postcards were handed out at the Lyme Bay
Fisheries & Conservation Consultative Committee meetings. For project enquiries and
for reporting tag sightings we set up a dedicated response line and email, and a QR
code with a link to the project website. To encourage tag reporting we offered a prize.
The initiative followed institutional GDPR procedures for processing and storing
personal data.
Back of postcard
Front of postcard
Figure 29. Postcards designed to communicate Project ROPE to fishers and the
broader public and to encourage the return of information on tagged crabs and
vi.) Public consultation on site selection for the proposed MPA acoustic array
vi.) Publications
The integrated objectives of Projects ROPE & SPILLOVER were highlighted in our article
(Sheehan et al. 2019) published in the Food Science & Technology Journal in 2019
Cited as:
Sheehan EV, Bridger D, Mascorda Cabre L, Cartwright A, Cox D, Rees S, Holmes L, Simon
P (2019) Bivalves boost biodiversity. Food Science & Technology 33(2): 18-21.
An interim project report and this final report were submitted to EMFF.
5. Project challenges
In addition to delays in field work related to Covid-19, our greatest challenge was in reaching
agreement with the local fishing community on an acoustic tracking site within the MPA.
After receiving a lot of interest in the project when initially introduced to the fishers at the
Lyme Bay Consultative meeting we then experienced opposition from a small group of
fishermen at the following Lyme Bay Consultative Committee meeting where a site was
proposed and discussed. In response, we designed and conducted a consultation process
involving detail discussions and an open evening for knowledge exchange. This led to further
consultation that included several alternative sites of which all received opposition due to the
concern over lost fishing grounds and potential entanglement with nets. At the time of writing
we have not yet re-scheduled discussions for a new proposed site in the MPA.
In addition, we had originally planned to tag seabass caught at the mussel farm and other
offshore locations, however, bass caught offshore did not survive the barotrauma of being
raised to the surface from depth (20-30 m). Instead, seabass caught in the nearby shallow
estuaries were successfully caught and tagged with a 100% survival rate.
Due to delays to fieldwork our project deadline was extended through a request to MMO to
May 2021.
6. Next steps
The data collection from our tagged animals has commenced and will continue for several
months into 2021 in order to build up a picture of nocturnal and diurnal movement patterns,
site fidelity and longer-term space use patterns.
We will continue to promote the project and encourage fishers to report information
on tags found to establish broader scale movements.
Continue maintenance of acoustic equipment and conduct occasional manual towed
hydrophone surveys.
Analyse data as it becomes available and interpret the results with regard to
environmental variables.
The results from project ROPE will be made available to funders, project partners, all
stakeholders and the broader public through the project webpage, future presentations,
scientific publications and via the final project report.
Cited references
Brown AR, Daniels C, Jeffery K, Tyler CR (2020). Developing general rules to facilitate evidence-
based policy for mariculture development in and around Marine Protected Areas (MPAs) in
England. Report to Research England (Strategic Priorities Fund), 30pp.
Brownscombe JW, Griffin LP, Chapman JM, Morley D, Acosta A, Crossin GT, Iverson SJ, Adams
AJ, Cooke SJ, Danylchuk AJ (2020). A practical method to account for variation in detection
range in acoustic telemetry arrays to accurately quantify the spatial ecology of aquatic
animals. Methods in Ecology and Evolution 11(1):82-94.
Coleman MT, Agnalt AL, Emmerson J, Laurens M, Porter JS, Bell MC (2020) From the Adriatic
to Northern Norwaygeographic differences in moult increment and moult probability of the
European lobster (Homarus gammarus), across the natural range. ICES Journal of Marine
D&S IFCA (2020) Devon and Severn IFCA Mariculture Strategy 2020.
Kershaw S, Beraud C, Heal R, Posen P, Tew I, Jeffery K (2020). Mapping of Areas of Potential
Aquaculture within the Dorset and East Devon Fisheries Local Action Group (FLAG) area. Cefas
Contract C7731, European Maritime and Fisheries Fund (EMFF) grant number ENG3016, pp.
Kessel ST, Cooke SJ, Heupel MR, Hussey NE, Simpfendorfer CA, Vagle S, Fisk AT (2014) A
review of detection range testing in aquatic passive acoustic telemetry studies. Reviews in
Fish Biology and Fisheries 24(1):199121.
Natural England (2010) Inshore Special Area of Conservation (SAC): Lyme Bay and Torbay
SAC Selection Assessment Document Version 2.5.
Öndes F, Kaiser MJ, Murray LG (2017) Relative growth and size at onset of sexual maturity of
the brown crab, Cancer pagurus in the Isle of Man, Irish Sea. Marine Biology Research
Rees SE, Attrill MJ, Austen MC, Mangi SC, Richards JP, Rodwell LD (2010) Is there a winwin
scenario for marine nature conservation? A case study of Lyme Bay, England. Ocean & Coastal
Management 53(3):135-145.
Rees A, Sheehan EV, Attrill MJ (2018) The Lyme Bay experimental potting study: A
collaborative programme to assess the ecological effects of increasing potting density in the
Lyme Bay Marine Protected Area. A report to the Blue Marine Foundation and Defra, by the
Marine Institute at the University of Plymouth.
Reubens J, Verhelst P, van der Knaap I, Deneudt K, Moens T and Hernandez F (2019)
Environmental factors influence the detection probability in acoustic telemetry in a marine
environment: results from a new setup. Hydrobiologia 845(1):81-94.
Sardenne F, Forget N, McKindsey CW (2019) Contribution of mussel fall-off from aquaculture
to wild lobster Homarus americanus diets. Marine Environmental Research 149:126-136.
Sheehan EV, Stevens TF, Gall SC, Cousens SL, Attrill MJ, Fulton CJ (2013) Recovery of a
temperate reef assemblage in a marine protected area following the exclusion of towed
Demersal fishing. PLoS One 8: e83883.
Smith F (2013) Understanding HPE in the VEMCO positioning system (VPS). V1.0. VEMCO.
Document # DOC-005457-01.
Appendix A Examples of poster/postcard distributions sites (Beer, Lyme Regis, Axmouth)
For more information contact:
Dr Emma Sheehan, School of Biological & Marine Sciences
University of Plymouth
ResearchGate has not been able to resolve any citations for this publication.
Technical Report
Full-text available
In July 2008, the UK Government (Defra) implemented a Statutory Instrument (SI) (The Lyme Bay Designated Area (Fishing Restrictions) Order 2008) which closed a 60nm area of Lyme Bay to bottom towed fishing gear. The objective was to protect and recover the sensitive reef habitats that were being damaged by bottom towed fishing activities, predominantly scallop dredging. A comprehensive study (MB0101 Marine Biodiversity R&D Programme) by the University of Plymouth, the Marine Biological Association (MBA) and Plymouth Marine Laboratories (PML) was undertaken in order to assess the ecological and socio-economic impacts of the SI (Attrill et al. 2011; Mangi et al. 2011). However, static gear fishing (mainly potting), commercial scallop diving, recreational fishing and recreational diving activities have been permitted to continue inside the protected area. Concerns were soon raised by local fishermen over significant increases in the level of commercial potting activity within the designated area. The environmental impacts of potting on both the seabed epibiota, reef associated species and on local fisheries are not understood. In partnership with the Blue Marine Foundation, the University of Plymouth developed an experimental 4 year project to assess the impacts associated with increasing potting activity for the first time, in partnership with local Lyme Bay fishermen. The project started in 2013 and was extended by 1 year.
Full-text available
Anthropogenic subsidies to natural systems can influence the diet of mobile omnivore species and co-occurring species. This study assessed if fall-off from mussel aquaculture subsidized wild populations of mobile scavengers and predators, such as the commercially important lobster Homarus americanus. A Bayesian stable isotope-mixing model with parameters determined from the literature and from a 105 days laboratory feeding experiment was applied to wild lobsters to determine how important the various food sources were in these lobsters, especially mussel fall-off. Isotopic values were mainly affected by lobster size with model outputs indicating that large lobsters (> 80 mm cephalothorax) fed mainly on mussels from the mussel farm (46% of the diet) while small ones fed mostly on the rock crab Cancer irroratus (99%). The contribution of mussel subsidies to the lobster's diet was thus size-specific and direct (i.e. through mussel fall-off and not through co-occurring species such as rock crab). The absence of a link between food sources and lipid energy content in lobsters suggested that the reduction of rock crab consumption would have to be more drastic to affect the general health of large lobsters in the short term.
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Acoustic telemetry is a commonly applied method to investigate the ecology of marine animals and provides a scientific basis for management and conservation. Crucial insight in animal behaviour and ecosystem functioning and dynamics is gained through acoustic receiver networks that are established in many different environments around the globe. The main limitation to this technique is the ability of the receivers to detect the signals from tagged animals present in the nearby area. To interpret acoustic data correctly, understanding influencing factors on the detection probability is critical. Therefore, range test studies are an essential part of acoustic telemetry research. Here, we investigated whether specific environmental factors (i.e. wind, currents, waves, background noise, receiver tilt and azimuth) influence the receiver detection probability for a permanent acoustic receiver network in Belgium. Noise and wind speed in relation to distance, the interaction of receiver tilt and azimuth and current speed were the most influential variables affecting the detection probability in this environment. The study indicated that there is high detection probability up to a distance of circa 200 m. A new setup, making use of features that render valuable information for data analysis and interpretation, was tested and revealed general applicability.
Full-text available
In this study, the relative growth, size–weight relationships and size at onset of maturity of the brown crab Cancer pagurus were investigated in the Isle of Man. For the analyses of relative growth and size at onset of maturity, the samples were collected seasonally between autumn 2012 and spring 2013 using several methods: pot surveys, dredge and trawl surveys, market surveys and shore surveys. Results showed that allometric growth occurred in the chelipeds of males (n = 87) and in the abdomen of females (n = 222). Four different measures of maturity (behavioural, functional, morphometric and physiological) were examined. With respect to the behavioural maturity, the smallest female crab found with a sperm plug measured 110 mm CW, whereas in terms of functional maturity the smallest ovigerous female had a CW of 134 mm. Based on direct observations of gonad maturity, 50% of females were mature at 108 mm CW, whereas 50% of males were mature at 89 mm CW. The size at the onset of maturity measurements of female and male C. pagurus based on gonad development is smaller than the current minimum landing size (130 mm), and therefore this suggests that the current minimum landing size is an adequate management measure.
Full-text available
Marine Protected Areas MPA have been widely used over the last 2 decades to address human impacts on marine habitats within an ecosystem management context. Few studies have quantified recovery of temperate rocky reef communities following the cessation of scallop dredging or demersal trawling. This is critical information for the future management of these habitats to contribute towards conservation and fisheries targets. The Lyme Bay MPA, in south west UK, has excluded towed demersal fishing gear from 206 km2 of sensitive reef habitat using a Statutory Instrument since July 2008. To assess benthic recovery in this MPA we used a flying video array to survey macro epi-benthos annually from 2008 to 2011. 4 treatments (the New Closure, previously voluntarily Closed Controls and Near or Far Open to fishing Controls) were sampled to test a recovery hypothesis that was defined as ‘the New Closure becoming more similar to the Closed Controls and less similar to the Open Controls’. Following the cessation of towed demersal fishing, within three years positive responses were observed for species richness, total abundance, assemblage composition and seven of 13 indicator taxa. Definitive evidence of recovery was noted for species richness and three of the indicator taxa (Pentapora fascialis, Phallusia mammillata and Pecten maximus). While it is hoped that MPAs, which exclude anthropogenic disturbance, will allow functional restoration of goods and services provided by benthic communities, it is an unknown for temperate reef systems. Establishing the likely timescales for restoration is key to future marine management. We demonstrate the early stages of successful recruitment and link these to the potential wider ecosystem benefits including those to commercial fisheries.
Full-text available
Passive acoustic telemetry provides an important tool to study the spatial ecology and behaviour of organisms in marine and freshwater systems, but understanding the detection range of acoustic receivers is critical for interpreting acoustic data and establishing receiver spacing to maximize study efficiency. This study presents a comprehensive review of how acoustic detection range has been considered and assessed to date, summarizes important variables to monitor when determining the detection range of a receiver array, and provides recommendations to account for detection range during experimental design, analysis and data interpretation. A total of 378 passive acoustic telemetry studies (1986–2012) were scored against a set of pre-defined criteria to provide a standardized assessment of how well detection range was accounted for, from a maximum possible score of 45. Scores ranged from 0 to 39 (11.1 ± 0.4; mean ± 1 SE). Over the past decade mean scores have been consistently between 6.7 and 12.9 which indicates that detection range has not been adequately considered in most contemporary acoustic telemetry studies. Given the highly variable nature of detection range over space and time, it is necessary to create a culture of detection range testing among the scientific community. For robust telemetry studies it is recommended that consideration of detection range should be given a greater focus within study design, execution and data analysis. To aid array design in new systems, short-term detection range tests should be conducted in the most representative area of the study system prior to deployment. As well, fixed distance sentinel tags should ideally be deployed at a representative receiver site within the array to provide a continuous assessment of detection range and influential environmental parameters should be monitored to facilitate modeling of detection range variability over time. When warranted, data analysis should incorporate modeled variation in detection ranges.
This study collated existing data on lobster moult increment from studies across the range of Homarus gammarus, together with new tagging data from Orkney, United Kingdom. Generalized additive models were used to investigate geographical differences in absolute moult increment and moult probability. Absolute moult increment was seen to differ significantly between regions and between sexes and showed a non-linear relationship with pre-moult size. Smaller absolute moult increments were observed at southern and northern latitudes with larger increments observed in the centre of the species range. Temperature was identified as a significant factor explaining differences in absolute moult increment between regions, consistent with there being a thermal optimum for growth for in H. gammarus. Moult and double moult probabilities decline with pre-moult size, with greatest probability of moulting occurring around day 250. Probability of double moulting increased with mean annual sea surface temperature. Regionally variable growth patterns, and localized adaptation to abiotic variables such as temperature, should therefore be taken into account when defining lobster stock assessment and fishery management areas.
Acoustic telemetry is a popular tool for long‐term tracking of aquatic animals to describe and quantify patterns of movement, space use, and diverse ecological interactions. Acoustic receivers are imperfect sampling instruments, and their detection range (DR; the area surrounding the receiver in which tag transmissions can be detected) often varies dramatically over space and time due to dynamic environmental conditions. Therefore, it is prudent to quantify and account for variation in DR to prevent telemetry system performance from confounding the understanding of real patterns in animal space use. However, acoustic receiver DR consists of a complex, dynamic, 3‐dimensional area that is challenging to quantify. Although quantifying the absolute DR of all receivers is infeasible in the context of most acoustic telemetry studies, we outline a practical approach to quantify relative variation among receiver DR over space and time. This approach involves selecting a set of sentinel receivers to monitor drivers of variation in detection range. Each sentinel receiver is subject to a range testing procedure to estimate detection efficiency (DE; the proportion of total transmissions detected by the receiver), at a range of distances from the receiver, to derive the maximum range (MR; distance from the receiver where DE is 5%) and Midpoint (distance from the receiver where DE is 50%). A reference transmitter is then placed at the Midpoint, providing a standardized measure of long‐term variation in DE, with each station having similar freedom of variance. Variation in reference tag DE is then combined with MR to calculate a DR correction factor (DRc). A modelling approach is then used to estimate DRc for all receivers in the array at spatial and temporal scales of ecological interest, which can be used to correct animal detection data in various ways. We demonstrate this method with a hypothetical dataset, as well as empirical data from an acoustic telemetry array to delineate spatiotemporal patterns of fish habitat use. This is a flexible and practical approach to account for variation in acoustic receiver performance, allowing accurate spatial and temporal patterns in aquatic animal spatial ecology to be revealed.
A statutory two hundred and six square kilometre ‘closed area’ in Lyme Bay, South West England entered into force on the 11 July 2008 to protect the reef substrate and the associated biodiversity from the impacts of trawling and dredging with heavy demersal fishing gear. This case study provides an example of how the ecosystem approach has been incorporated into decision making for marine nature conservation and shows that despite sound ecological knowledge of a marine area, the current reliance on traditional neo-classical economic valuations for marine spatial planning can obscure other issues pertinent to the ecosystem approach. With the Government seeking win–win scenarios for stakeholders in the designation of Marine Conservation Zones under the Marine and Coastal Access Act, experience of marine spatial planning in Lyme Bay has revealed that a win–win must be a long-term goal based on a thorough evaluation of the environmental, social and economic values of marine biodiversity.