Wild sea trout (Salmo trutta L.) smolts, tagged with miniature acoustic transmitters, were tracked in the River Conwy, North Wales, to describe the freshwater and estuarine patterns ofmigration. Migration in freshwater was predominantly noctumal, although there were changes in this pattern in the lower reaches <>fthe estuary with fish moving during both the day and night. The noctumal pattern ofmigration in freshwater would appear to be the result ofa rhythm ofswimming activity which results in the smolts moving up into the water column after dusk and migrating seawards. Smolts tagged earlier in the study spent significantly longer in the river before migrating into coastal waters than fish tagged later in the study. The movement of smolts through the estuary was indicative ofa selective ebb tide transport pattern of migration. All the smolts migrated seawards on an ebb tide elose to the surface and within the fastest moving section ofthe water column. Smolt migration in the lower portion ofthe estuary was indicative ofactive directed swimming and there was no apparent period ofaccIimation required when moving from fresh to saltwater. The behaviour ofthe smolts is discussed in relation to the possible environniental and physiological cues controlling estuarine migration.

This chapter contains sections titled: Introduction Salmon management Salmon reference points for England and Wales Sea trout management Alternative BRPs for sea trout Management of the Salmo trutta complex Conclusions Acknowledgements

Most exploitation of Atlantic salmon (Salmo salar) is restricted to "homewater fisheries". which operate close to or within the rivers of origin of the stocks, but two "distant-water fisheries" are permitted to operate off the west coast of Greenland and in the Norwegian Sea, and take salmon from a large number of rivers over a wide geographical area. Providing robust quantitative catch advice for these mixed-stock fisheries depends upon the ability to forecast stock abundance for about 2000 salmon river-stocks around the North Atlantic, more than 1500 of which are in Europe. A "run-reconstruction" model is presented for estimating the historic pre-fishery abundance (PFA) of salmon for countries or regions around the Northeast Atlantic, based upon catch data and estimates of non-reporting rates and exploitation rates. These estimates are then used to develop predictive models of PFA on the basis of estimates of the egg deposition, derived from the run-reconstruction model and various environmental data. Although the selected environmental indices correlated with the PFA of both southern and northern European stock complexes, the main statistical significance in the forecast models was provided by temporal trends in the PFA. Clearly. such a model is only tenable in the short term. and will be poor at predicting a major change in stock status. Alternative approaches, based upon juvenile production indices and including Bayesian techniques, are therefore being considered. Crown Copyright (C) 2004 Published by Elsevier Ltd on behalf of International Council for the Exploration of the Sea. All rights reserved.

Most exploitation of Atlantic salmon (Salmo salar) is restricted to "homewater fisheries". which operate close to or within the rivers of origin of the stocks, but two "distant-water fisheries" are permitted to operate off the west coast of Greenland and in the Norwegian Sea, and take salmon from a large number of rivers over a wide geographical area. Providing robust quantitative catch advice for these mixed-stock fisheries depends upon the ability to forecast stock abundance for about 2000 salmon river-stocks around the North Atlantic, more than 1500 of which are in Europe. A "run-reconstruction" model is presented for estimating the historic pre-fishery abundance (PFA) of salmon for countries or regions around the Northeast Atlantic, based upon catch data and estimates of non-reporting rates and exploitation rates. These estimates are then used to develop predictive models of PFA on the basis of estimates of the egg deposition, derived from the run-reconstruction model and various environmental data. Although the selected environmental indices correlated with the PFA of both southern and northern European stock complexes, the main statistical significance in the forecast models was provided by temporal trends in the PFA. Clearly. such a model is only tenable in the short term. and will be poor at predicting a major change in stock status. Alternative approaches, based upon juvenile production indices and including Bayesian techniques, are therefore being considered. Crown Copyright (C) 2004 Published by Elsevier Ltd on behalf of International Council for the Exploration of the Sea. All rights reserved.

Atlantic salmon, as a result of their population structure and behaviour, are potentially subject to a complex array of fisheries, ranging from those within rivers harvesting single stocks, to distant-water mixed stock fisheries that harvest fish from different countries, stock complexes, and continents. In addition, estuarine and in-river fisheries may catch fish from more than one stock or stock component, where these are present. One of the main challenges in managing salmon across this range of fisheries is to account for the differing status of stocks with respect to safe biological limits, noting that stocks of differing productivity may require different harvest strategies. Also, the existence of sequential harvest in different fisheries provides unique challenges, because decisions in an individual fishery cannot be made in isolation of the impacts of other fisheries on those stocks. We illustrate the uncertainties and complexities involved in managing mixed stocks of salmon, whether in homewaters or in distant-water fisheries, and examples are given to illustrate how science and management are, or should be, developing to face these challenges. (C) 2004 International Council for the Exploration of the Sea. Published by Elsevier Ltd. All rights reserved.

Ireland has one of the last remaining commercial salmon driftnet fisheries in the North Atlantic, with recent catches averaging 162000 salmon (1997-2003), approximately 20% of the total landings of salmon in the entire North Atlantic. Since 2001, the Irish commercial salmon fishery has been managed on the basis of Total Allowable Catch (TAC) in each of 17 salmon fishing districts. This has been made possible by applying a number of new and innovative techniques to the estimation of conservation limits (CLs) and prefishery abundance (PFA) for combined stocks in each district. Stock and recruitment parameters from well-monitored European rivers were "transported" to all Irish rivers using a Bayesian hierarchical stock and recruitment (BHSRA) model. This provided the posterior probability distributions of the model parameters and related reference points, including individual river CLs. District PEA and the number of spawners were estimated for a baseline period of 1997-2003, using district catch data, estimates of unreported catch, and exploitation rate. Harvest guidelines were established on the basis of surplus of spawning fish over the CL for the baseline period. In line with scientific advice, the commercial fishery has been reduced from 212 000 fish in 2002 to 182 000 in 2003. In 2004, a total catch (including the rod catch) of approximately 160 000 wild salmon was advised. (C) 2004 International Council for the Exploration of the Sea. Published by Elsevier Ltd. All rights reserved.

The European eel, Anguilla anguilla (L.), has a complex life history and many aspects of the biology and population dynamics of this species remain unknown or, at best, poorly understood. Relatively little is also known about the status of the stocks and fisheries, but available data suggest that recruitment of glass eels has been falling for the last 20 years and is at historically low levels. Yellow and silver eel catches have also been falling in many parts of the species range over a similar time-scale. Re-examination of the principles applied to fisheries management over recent years has resulted in the adoption of a 'precautionary approach' to the conservation, management and exploitation of fish stocks, and in an explicit need to take account of uncertainties in management to reduce risks to stocks and their environment. Such an approach is highly relevant to the management of the European eel and requires that urgent consideration is given to harvest strategies and decision structures for the national and international management of stocks and fisheries. Provisional biological reference levels should be established to provide an equable assessment of the status of stocks in all parts of Europe and to evaluate the need for management measures in all fisheries. These will need to be reviewed as further information comes available. Monitoring and research on eel stocks should therefore be enhanced and co-ordinated to improve our understanding of the status of stocks throughout Europe and the biology of the species.

The control of exploitation in fisheries for Atlantic salmon (Salmo salar L.) and trout (S. trutta L.) has both biological and socio-economic objectives, the former relating to the protection of the productive capacity and diversity of the resource and the latter to issues such as the allocation of any harvestable surplus to different user groups. In fulfilling the biological aims, managers can restrict catches or fishing effort to ensure that sufficient fish from each population are permitted to spawn; they may also consider options for increasing the production of the stock, such as habitat improvement or stocking. Biological reference points (e.g. limits and targets) are increasingly being used to provide an objective measure of the status of stocks and determine the possible need for management actions, although a range of other stock indicators may be required to fully protect the diversity of our stocks. This is consistent with the application of a precautionary approach to salmon fishery management as adopted by the North Atlantic Salmon Conservation Organisation (NASCO). NASCO has agreed that a limit reference point (or conservation limit) for Atlantic salmon should be set at the spawning stock size that will give maximum sustainable yield (SMSY). Fisheries should therefore be managed to ensure that there is a high probability that these limits are exceeded, and actual escapement should usually be higher than these thresholds. NASCO has proposed that stocks should be maintained above their conservation limits by setting higher, and thus more precautionary, management targets, although alternative approaches are possible. ICES and NASCO have favoured a fixed escapement strategy for the management of salmon fisheries, although in practice, this strategy is being implemented in a variety of ways. In many fisheries, approaches more akin to ‘floor policies’ or ‘proportional threshold harvesting’ are being employed although the merits of different strategies for the management of commercial and recreational salmon fisheries have yet to be fully explored. Scientists still have some way to go in fully incorporating uncertainty into their management advice, but the objective must be to utilise the best information available to them, regardless of its imperfections, in developing management options and to account explicitly in their advice for the various sources of uncertainty both in the current state of scientific knowledge and in our ability to control fisheries. These management approaches have mainly been developed for the management of Atlantic salmon, but there would clearly be merits in developing similar approaches to protect production of both migratory and non-migratory trout stocks.

The migratory behaviour of wild Atlantic salmon Sa/rna salar (L.) sma Its during their emigration from fresh water to the marine environment has been studied in 4 river systems in England and Wales using acoustic telemetry. Smolts trapped in freshwater and implanted with miniature acoustic transmitters were monitored during their subsequent migrations through the river estuaries and into coastal waters. Migration in freshwater was predominantly nocturnal, although there was a seasonal change in this pattern with later run fish moving during both the day and night. Sma Its tagged earlier in the studies spent significantly longer in the rivers before migrating into coastal waters than fish tagged later in the studies. The movement of smalts through the estuaries was indicative of a nocturnal selective ebb tide transport pattern of migration. All the smolts migrated seawards on an ebb tide close to the surface and within the fastest moving section of the water column. Smolt migration in the lower portion of the estuaries was indicative of active directed swimming and there. was no apparent period of acclimation required when moving from fresh to saltwater. Migration within coastal waters was again rapid within the upper water column and movement occurred during both day and night. There was a strong tidal component to the speed and direction of movement.

The document reports on the major findings from a definition study to appraise the options to develop fish tracking equipment, in particular tags and data logging systems, in order to improve the effeciency of the Agency tracking studies and to obtain a greater understanding of fish biology. The definition study was in two parts. The first, Phase 1, collated and evaluated all the known tracking systems that may be suitable for studies of fish which are either produced commercially or have been constructed for specific in-house studies. Phase 2 was an evaluation of all the tracking equipment considered to merit further investigation in Phase 1. The deficiencies between existing and required technologies to improve the efficiency of Agency's tracking studies and to obtain a greater understanding of fish biology are also identified.

Thirty-two wild Atlantic salmon (Salmo salar) smolts, tagged with miniature acoustic transmitters, were tracked in the River Conwy, North Wales, to describe the freshwater and estuarine patterns of migration. Migration in fresh water was predominantly nocturnal, although there was a seasonal change in this pattern with later run fish moving during both the day and night. Smolts tagged earlier in the study spent significantly longer in the river (mean 456 ± 43 h) before migrating into coastal waters than fish tagged later in the study (mean 201 ± 30 h). The movement of smolts through the estuary was indicative of a nocturnal selective ebb tide transport pattern of migration. All of the smolts migrated seawards on an ebb tide close to the surface and within the fastest moving section of the water column. The nocturnal pattern of migration would appear to be the result of an endogenous rhythm of swimming activity that results in the smolts moving up into the water column after dusk and migrating seawards. Smolt migration in the lower portion of the estuary was indicative of active directed swimming and there was no apparent period of acclimation required when moving from fresh to salt water.

Abstract The movement of sea trout. Salmo trutta L., smolts through the estuary of the River Avon, southern England was studied using miniature 300 kHz acoustic transmitters and an array of strategically placed acoustic sonar buoys. Sea trout smolts were trapped 3.25 km above the head of tide as they moved downstream and the transmitters were surgically implanted into the peritoneal cavity of the fish. Subsequent movement of the smolts through the estuary was predominantly nocturnal and occurred mainly during an ebb tide or the period of slack water between two high waters. During the hours of darkness the ground speed of the smolts through the estuary was similar to that of passively drifting objects. However, where movement did occur during daylight hours ground speeds of smolts were significantly slower. Vertical salinity profile measurements of the estuary indicated that individual smolts may have experienced salinities ranging from fresh to 100% sea water during their migration. The behaviour of the smolts is discussed in relation to the possible environmental and physiological cues controlling the estuarine migration.

Hatchery-reared Atlantic salmon, Salmo salar L., parr and wild smolts which were microtagged and released into rivers in north-east England were recaptured by the fisheries at West Greenland, Faroes and on the Irish west coast, by the homewater net fisheries and by rod fisheries in rivers in north-east England. No significant differences were observed in the patterns of exploitation of hatchery-reared and wild fish in the distant water fisheries. The distribution of tag recoveries in coastal waters was strongly influenced by the pattern of fishing effort which was concentrated in the middle of the fishery area, but recaptures tended to be biased towards the river of release. There were significant differences in the distribution of recaptures of fish released in different rivers and between hatchery-reared and wild fish from the River Wear. There were also differences in the timing of recaptures of hatchery and wild fish from this river in the coastal net fishery. Very few fish were recaptured in rivers other than the one in which they were released, and there was no significant difference between straying rates for hatchery and wild fish. The relative numbers of recaptures in the coastal fishery and in the home river was the same for translocated hatchery fish and wild fish, thus refuting the suggestion that hatchery-reared fish have a reduced ability to home. The distribution of recaptures within fresh water provides clear evidence of tributary-specific homing of hatchery-reared fish.

The behavioural and physiological effects of surgical implantation of dummy miniature acoustic transmitters into the peritonealcavities ofjuvenile Atlantic salmon, Salmo salar L., were assessed. lntraperitoneal implantations had no significant effect on growth, feeding or swimming behaviour in either parr or smolts. Recovery from the surgical implantation was both rapid and total; infection was absent; and physiological processes such as smoltification and maturation of testes in precocious parr were unaffected. Expulsion of the transmitter through the body wall, not through the implantation wound, occurred in a number of fish but without adversely affecting the animals. The intraperitoneal implantation technique is discussed in relation to its use during biotelemetry studies.

Aquaculture ResearchVolume 21, Issue 3 p. 369-372 Preliminary results from the use of a new technique for tracking the estuarine movements of Atlantic salmon, Salmo salar L., smolts A. MOORE, Corresponding Author A. MOORE Ministry of Agriculture, Fisheries and Food, Fisheries Laboratory, Lowestoft, Suffolk, EnglandDr Andrew Moore, Ministry of Agriculture, Fisheries and Food, Fisheries Laboratory, Lowestoft, Suffolk NR33 OHT, England.Search for more papers by this authorI. C. RUSSELL, I. C. RUSSELL Ministry of Agriculture, Fisheries and Food, Fisheries Laboratory, Lowestoft, Suffolk, EnglandSearch for more papers by this authorE. C. E POTTER, E. C. E POTTER Ministry of Agriculture, Fisheries and Food, Fisheries Laboratory, Lowestoft, Suffolk, EnglandSearch for more papers by this author A. MOORE, Corresponding Author A. MOORE Ministry of Agriculture, Fisheries and Food, Fisheries Laboratory, Lowestoft, Suffolk, EnglandDr Andrew Moore, Ministry of Agriculture, Fisheries and Food, Fisheries Laboratory, Lowestoft, Suffolk NR33 OHT, England.Search for more papers by this authorI. C. RUSSELL, I. C. RUSSELL Ministry of Agriculture, Fisheries and Food, Fisheries Laboratory, Lowestoft, Suffolk, EnglandSearch for more papers by this authorE. C. E POTTER, E. C. E POTTER Ministry of Agriculture, Fisheries and Food, Fisheries Laboratory, Lowestoft, Suffolk, EnglandSearch for more papers by this author First published: July 1990 https://doi.org/10.1111/j.1365-2109.1990.tb00474.xCitations: 6AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume21, Issue3July 1990Pages 369-372 RelatedInformation

In the years 1985–1987, salmon were tracked in the estuary of the River Fowey, Cornwall using the ‘sonar buoy’ system developed at the M.A.F.F. Fisheries laboratory and described by Solomon & Potter (1988). Sixty‐one salmon were caught and tagged in the estuary, 25 with radio and 36 with combined radio and acoustic transmitters. About half these fish were not recorded entering the freshwater reaches of the R. Fowey, and from tag recoveries it seems likely that about 27% were returning to other rivers. For fish returning to the R. Fowey the time between tagging and entry into fresh water varied between 9 h and 130 days. In the estuary the fish largely moved in the same direction as the tidal currents, although movements over the ground against the current were more common in the bottom 2 km and the top 2 km. During periods of low river‐flow in summer all salmon tracked in the estuary dropped back out to sea where they stayed for varying periods: some of these made several sorties past the estuary mouth and on occasions well up the estuary before finally entering fresh water. During periods of higher river discharge, in both the summer and the autumn, some fish remained in the estuary for longer periods, sometimes holding position in deep, sheltered water. Most fish entered fresh water at night during periods of increased freshwater discharge, although at very high flows fish also entered in daylight.

A ‘sonar buoy’ tracking system has been developed at the MAFF Fisheries Laboratory based upon acoustic transmitting tags and relay units which retransmit the pulsed acoustic signal as a radio signal. The output from several such ‘sonar buoys’ is monitored by a single automatic recording station on the shore. The system has been used on salmon in the estuary of the River Fowey in Cornwall, providing useful data on the behaviour of returning adults before they enter the river. The tags also transmit a radio frequency signal to allow tracking in the river itself. Of fourteen fish tagged in 1985, six were recorded entering the river between 12 h and 41 days after being released. Another fish was recaptured in a coastal net 160 km to the east. These few preliminary results indicated two distinct patterns of behaviour: one fish remained in deep water in the lower estuary for several days, often lying near moored ships or jetties; at other times fish made extensive excursions up the estuary with the tide, usually returning with the ebb.