DFR Project Review 1994 Final R&D Project Report

DFR Project Review 1994 Final R&D project report

1. Project No: MF0108

2. Title: Migratory Behaviour and Physiology

3. Commenced: 1989/90

4. STA Planned Completion Date: March 1993

5.

6. Scientific objectives

To describe the migratory behaviour of plaice and cod in order to identify the mechanisms underlying the regular seasonal changes in stock distribution and to develop a predictive model of fish migration on the European continental shelf.

7. Results

(a) Seasonal migrations: Fish tracking and midwater trawling experiments have shown that plaice and cod both use the tidal streams to migrate in the southern North Sea and that large numbers of plaice move through the Dover Strait on their way to spawn in the eastern English Channel. Maturing fish move south on south-going tides in October, November and December and spent fish migrate back into the North Sea on north-going tides in January, February and March. Males spend much longer on the spawning ground than females.

(b) Swimming speed, depth and orientation: Ground tracks suggest that plaice moving by selective tidal stream transport orientate down tide and swim at a speed of 0.5-1 body length per second, thus saving energy and increasing their rate of migration. Plaice (which have no swimbladder) frequently swim within 4 m of the surface, but cod (which have a closed gas-filled swimbladder) swim lower in the water column and maintain neutral buoyancy at a particular depth. As a result, plaice have complete freedom of vertical movement but cod are constrained and are unable to swim much above their selected depth of neutral buoyancy.

(c) Patterns of vertical movement in the sea: Fish migrating by selective tidal stream transport leave the bottom at the slackwater preceding the appropriate transporting tide and spend about six hours in midwater before returning to the bottom for the duration of the opposing tide. They are rapidly transported considerable distances because their vertical movements are synchronised with those of the tidal streams. At other times of the year, plaice appear to adopt a different pattern of behaviour, moving off the bottom and into midwater at approximately 24 h as opposed to 12 h intervals. Plaice on their summer feeding grounds south of the Dogger Bank behave in this way and move into midwater for a few hours each night; plaice on their winter spawning grounds in the Southern Bight may do the same. Fish which adopt this pattern of diel vertical migration make only very local movements because their vertical movements are not synchronised with the tidal streams.

(d) Activity patterns of plaice in the laboratory: Both patterns of vertical movement have been observed in tidal stream tanks but tidally synchronised behaviour has been shown by only a few fish and selective tidal stream transport has not been maintained in the tank for more than 4 or 5 days. Most experimental fish have shown a diel pattern of activity, remaining on the bottom during the day and swimming in midwater during the night and the time spent in midwater has varied seasonally with the length of the night. The most recent experiments indicate that both patterns of activity may be regulated by "biological clocks".

(e) Migration model: The prototype tidal stream migration model has been transferred to the VAX computer and improved algorithms implemented as planned. The model is operational and has been extended to allow the use of real time data from fish tracking experiments and data storage tags. Validation has proceeded to plan, user manuals and reports are being prepared and a public demonstration was given in Conwy in July at the Fisheries Society of the British Isles conference "Factors influencing the distribution of fish". Plans to incorporate tidal stream data from the Bidston hydrographic model have been deferred because of lack of support from AEP3 (allocated staff absent on foreign exchange). Otherwise this task will be completed by the end of the project and will be available for the next phase of the research programme (see below).

(f) Improved fish tracking techniques Several important technical advances have been made during the project. DFR's engineers have developed a pressure-sensitive electronic tag that allows the depth of the fish to be measured with much greater precision than previously and have installed a new battery pack in the basic transponding acoustic tag. Used in conjunction with a new tag mount, which keeps the transducer clear of sand when the fish is resting on the seabed, tag life has been increased to at least 6 - and possibly as much as 10 - days. The acquisition in 1992 of an Acoustic Doppler Profiler (ADCP) for RV Corystes now allows direct measurements of the speed and direction of the water at the depth at which the fish is swimming. Previously this information could only be obtained by extrapolation from recording current meters which might be moored several miles away. These new techniques allow us to estimate the swimming speed and orientation of migrating fish, both of which are important factors in modelling rates of migration and resulting seasonal changes in distribution.

8. Overall conclusions

Along with most other commercially exploited demersal fish, plaice and cod make regular seasonal migrations between summer feeding grounds and winter spawning grounds and some of these migrations are extensive. For example, many fish which feed in the central North Sea, spawn in the Southern Bight and eastern English Channel. Plaice and cod migrate by selective tidal stream transport and there is evidence to suggest that in plaice the vertical movements of migrating fish are synchronised with the tidal streams by a "biological clock". A clock probably also controls the nocturnal vertical movements of the same fish during the seasons of the year when they are not migrating. There is also evidence that migrating fish orientate and swim downtide during tidal stream transport. Swimming speeds are such that this behaviour must be taken into account when modelling migration and trying to predict the resulting seasonal changes in stock distribution. Existing data have proved to be of sufficient quality to validate the tidal stream migration model completed during this project and demonstrate its potential, but more data are needed before it will be possible to provide the indices of fish movement that are required for spatial management models which take account of seasonal changes in fish distribution.

9. Targets & Outputs:

With the exception of the incorporation of tidal stream predictions from the Bidston hydrographic model (section 7(e)) and completion of the user manuals for the tidal stream simulation model, all of the original targets have been met.

Additionally, we have undertaken the production of a series of laboratory data reports covering all fish tracking data collected to date. The task is proceeding well, one report has been published and another is well advanced; the rest will follow as time allows. The need for these reports arose from difficulties experienced in preparing succinct papers for scientific journals without losing important and original data.

We have also organised and contributed to a CFRD Working Group on fish migration, which was initiated after the start of the project. The group has met three times and is making good progress with its tasks of reviewing the state of knowledge of fish migration on the European continental shelf, assessing the importance of migration in relation to customer needs and identifying future research objectives. The task should be completed by the end of FY 1994/95.

Internationally, we have organised a Mini-Symposium on fish migration to be held during the ICES Statutory Meeting in St John’s, Newfoundland in September 1994 and have obtained financial backing from the European Commission for a workshop on Electronic Tags in Fisheries to be held in Lowestoft in November 1994. The ICES mini-symposium will consider the role of migration in the distribution and abundance of marine fish and the implications for management. The tag workshop, which it is hoped will involve about 25 scientists from Europe and North America and last for 3-4 days, will evaluate the contribution of electronic tags to fisheries research and management, identify constraints to further progress and define new research objectives.

Publication of scientific papers is proceeding broadly to plan (see attached reference list) and most of the intended papers have been completed, although that describing the results of the plaice midwater trawling experiments in the Dover Strait is still only in draft. Data on the vertical distribution of spawning plaice, which have been analysed as planned, will be published in due course in a laboratory technical report, rather than a refereed journal.

10. Uptake and implementation:

The migration model has been used to provide predictions of tidal stream speed and direction for DFR's North Sea groundfish survey and is now available for predictive modelling of migrations and seasonal changes of distribution of demersal fish anywhere on the continental shelf. This work will start shortly and will form a major part of the next (proposed) phase of the research programme. Papers derived from the model are expected to make an important contribution to the mini-symposium on fish migration to be convened at the ICES Statutory Meeting in 1994 and to provide an input to work now being initiated by the ICES Long Term Management Measures Working Group. The model will also be an essential tool to DFR in interpreting information recovered from data storage tags and has already proved its worth in analysing data from the nine tags returned so far from the first releases of these new tags (see MF0109) in December 1993 (50 fish) and March 1994 (40 fish). The tidal stream tank work has laid the foundations of a new programme to investigate the physiological mechanisms controlling activity patterns in migratory fish. This is being undertaken by a PhD student, who is using both the large tidal stream tank and the smaller 'mini' annular tanks developed during the course of this project to permit rapid replication of experiments.

11. Further work:

Recent developments within ICES and the EC have emphasised the need for a much better understanding of fish migration in order to develop improved methods of fish management in the medium to long term. Because of its special research capabilities (which are not available to other European marine institutes), DFR is particularly well placed to respond to these needs and a substantial new programme of research is therefore proposed. This aims to improve our understanding of fish migration to the level at which it is possible to model seasonal changes of distribution and produce indices of movement which can be used in improved stock management models and in assessing proposed technical conservation measures.

12. Publications:

Arnold, G. P.& Metcalfe, J. D. (1989). Acoustic telemetry: progress and potential in understanding fish behaviour. Proc. Inst. Fisheries Acoustics, 11: 96-103.

Arnold G. P. & Metcalfe, J. D. (1989) Fish migration: orientation and navigation or environmental transport? J. Nav., 42: 367-374.

Arnold, G. P., Greer Walker, M. & Holford, B. H. (1990). Fish behaviour: achievements and potential of high-resolution sector scanning sonar. Rapp. P.-v. Réun. Cons. int. Explor. Mer, 189: 112-122.

Greer Walker, M. & Emerson, L. S. (1990). The seasonal migration of sole (Solea solea) through the Dover Strait. Neth. J. Sea Res., 25: 417-422.

Metcalfe, J. D. & Arnold, G. P. (1990). Time and tide wait for no plaice. New Scientist, (1698), 52-55.

Metcalfe, J. D. & Arnold, G. P. (1990). Fish movements in the open sea. Fish. Spotlight, 1989-90, 11-12.

Metcalfe, J. D., Arnold, G. P. & Webb, P. W. (1990). The energetics of migration by selective tidal stream transport: an analysis for plaice tracked in the southern North Sea. J. mar. biol. Ass. U.K., 79: 149-162.

Arnold, G. P. & Greer Walker, M. (1992). Vertical movements of cod (Gadus morhua L) in the open sea and the hydrostatic function of the swimbladder. ICES J. Mar. Sci., 49: 357-372.

Metcalfe, J. D., Fulcher, M. F. & Storeton West, T. J. (1992). Progress and developments in telemetry for monitoring the migratory behaviour of plaice in the North Sea. Wildlife telemetry remote monitoring and tracking of animals. I. G. Priede & S. M. Swift (eds.) pp 359-366.

Metcalfe, J. D., Holford, B. H. & Arnold, G. P. (1993). Orientation of plaice (Pleuronectes platessa) in the open sea: evidence for the use of external directional clues. Mar. Biol. 117: 559-566.

Arnold, G. P., Greer Walker, M., Emerson, L. S., & Holford, B. H. (1994). Movements of cod (Gadus morhua L.) in relation to the tidal streams in the southern North Sea. ICES J Mar. Sci., 51: 207-232 pp.

Buckley, A. A. (1994). Open sea fish tracks: plaice fitted with compass tags. Data Rep., MAFF Direct. Fish. Res., Lowestoft, (35), 60 pp.

Arnold, G. P. & J. D. Metcalfe (in draft). Seasonal migrations of plaice (Pleuronectes platessa L.) through the Dover Strait. Marine Biology (?).