4. MANAGEMENT POLICIES AND THE POLICY SETTING PROCESS
4.1 Identification and evaluation of policies
The policy options appropriate to the management of elasmobranch fisheries in the Northeast Atlantic are built on the premise of open access and include the various licensing and gear restrictions implemented to help regulate the exploitation of teleost species subject to catch controls. There has been no cost-benefit analyses of these policy options with respect to their implications for elasmobranch fisheries.
4.2 Policies adopted
Elasmobranch fisheries are virtually unregulated in Europe, and there has been little or no attempt to manage them at either national or regional levels. As a consequence, there have been very few constraints on shark fishing effort in the Northeast Atlantic (ICES 1989). TACs are the standard tool used to manage exploitation rates of the main commercial stocks in the ICES area, and these have been applied to approximately 15% of the fish caught or landed from EU waters (Anon 1994). There has never been a TAC or catch quota established for any elasmobranch species or stock to limit fishing by EU member states (see 3.2.5). As a rule, however, TACs which have been agreed for teleost stocks in FAO Area 27 have exceeded ICES' recommendations, and actual catches have often exceeded the agreed limits. This type of regulation may therefore have imposed little constraint on the activity of these fisheries, or on the mortality of the stocks, especially in sea areas where non-TAC species make up a high proportion of the catch (Anon 1994). Within the EU, every country has an agreed maximum fishing capacity under the Multi Annual Guidance Programme (MAGP), within which maximum fishing capacities are set for different fisheries. There are no technical conservation measures laid down in EU legislation specific to any elasmobranch fishery.
4.3 Resource access
The fisheries in the waters of the Northeast Atlantic are controlled within a 200 mile radius of the coastline. For countries which are part of the EU, the Common Fisheries Policy (CFP) sets out the rules applicable to all fisheries within Community waters. Other non-EU countries which have traditional fisheries in Community waters negotiate quota allocations with the EU, both to obtain access to EU waters and to provide access to EU vessels wishing to fish in their national waters. Agreement was reached in 1978 on catch regulations between the EU and Norway and the Faeroe Islands following the imposition of 200 miles fishery limits in the 1970s. Such arrangements allow Norway and Faeroe Islands vessels to have access to certain fisheries resources in Community waters in exchange for equivalent opportunities in their waters. In December each year, the EU and these countries agree on the following year's TACs and national shares of the joint stocks, and also an exchange of quotas for other stocks. The original agreements entered into force in 1981 were renewed in 1991 and ran until June 1997. This agreement entitles Norway to take basking sharks in ICES sub-areas IV, VI and VII (North Sea and west of the British Isles) and, with the Faeroes, porbeagles from all EU waters.
Plans to apply TACs to all North Sea species from 1 January 1998 failed to be approved at the Council of Ministers in December 1997. This will considered again at the meeting in March 1998 and is expected to include spurdog and a number of ray species, but at present there are no EU catch quotas for any elasmobranch species.
The CFP recognises that coastal states have exclusive access and authority to manage fisheries within their territorial waters, out to 12 nautical miles from baselines, subject to EU regulations. For example, Norwegian vessels may not fish for Basking Sharks or other species within the UK. 12 miles belt. Within the outer half of the territorial waters (6–12 miles), other EU member States may have historic rights entitling them to limited access to certain fisheries (Grey 1995). Access to elasmobranch fisheries is therefore available to any country which has an historic right to fish those grounds. Responsibility for enforcing the regulations of the CFP rests with the fisheries officers in EU member states, and access to any fishery within a country's 200 mile exclusive economic zone (EEZ), or out to the median line between coastal states, is monitored and controlled by the fishery officers of that country.
In Europe, it is a requirement that commercial fishing vessels are licensed. Licences are issued by the country in which a vessel is registered at the discretion of the minister or appropriate authority, and the licence conditions are the responsibility of each country. There are different licence categories in the UK, which can be specific and relate to vessel, gear, target species and ICES sub-divisions or, if non-pressure stocks (no TAC) are the intended quarry, which confer few restrictions on the vessel's activity. In practice, this means that provided a licence can be obtained for a vessel, it can commence commercial fishing for elasmobranchs in the Northeast Atlantic.
In the UK, there is no charge for issuing a licence (at the present time) though, once licences have been issued by the Fisheries Minister, they can be bought and sold between fishermen or through licence brokers. The cost varies enormously depending on the category and type of licence, and ‘pressure stock’ licences, which carry a quota entitlement, are the most expensive.
There are no property rights associated with fisheries in the Northeast Atlantic, other than for extremely localised fisheries for bivalve molluscs along the coasts of the UK and France.
4.4 Gear restrictions
Not having the status of TAC species, fisheries for elasmobranchs have had no specific gear restrictions, though gear limitations are applied to fisheries that take elasmobranchs as bycatch. An example of this is the 2.5km maximum permitted length of drift net used to target albacore tuna in the Northeast Atlantic, which will restrict the numbers of pelagic sharks taken in this fishery. In effect, this imposes a limit on the fishing effort directed at sharks and other elasmobranchs, but has little if any restraint on the species caught or their size. Individual countries may have national or localised restrictions applied to the licences issued, but this information is not readily available. However, a regulation in the Azores restricts the length of net per boat that may be used in the directed fishery for kitefin shark (ICES 1989).
An EU regulation (No. 3094/86) has been amended from 31 December 1997 to regulate for the first time the mesh sizes used in set gill nets, entangling nets and trammel nets. These gears tend to be size-selective for round fish, since there is a close relationship between the circumference of a mesh and the girth of any fish which it retains. Rays and skates tend to become entangled in several meshes, and their selectivity by size is less clear cut. Each of the most important commercial species has been assigned to one of six mesh size ranges, with the lowest specified mesh size in each range intended to avoid the capture of undersized or juvenile fish. Essentially, the catch retained on board, expressed in live weight, must be made up of no less than 70% of one or any combination of species listed against the corresponding mesh size range. Spurdog is included in the target species for the 120–219 mm mesh size ranges, whilst other sharks and skates and rays may be taken with nets having a mesh larger than 220mm (though they can be included in the 30% bycatch by weight in nets with smaller meshes). This regulation should not unduly restrict the choice of mesh size for fishermen who are currently using enmeshing nets to take good quality fish, since it is based largely on current fishing practices in North-west European waters.
4.5 Vessel regulations
Within the EU, every country has an agreed maximum fishing capacity, which is reviewed by scientists and Commission staff every 4 or 5 years. Those currently implemented are detailed under MAGP IV, within which maximum fishing capacity in Gross Tonnage and Engine Power (kW) are set for different stocks, segments (catching gears) and fisheries. Effort control in the EU is constantly under review and may in the furture include limits on boat-days fished as well as changes in fleet structure.
National fishery legislation may also contain separate gear and or fishing ground regulations. To date, no such controls apply to vessels landing elasmobranchs, other than those attending other species caught in the fishery in which elasmobranchs are taken as bycatch, and there has been no assessment of their impact on elasmobranch landings or stocks.
4.6 Biological regulations
Only Norway on a national level, and the UK at local level, have introduced any form of technical constraints on elasmobranch fisheries based on biological considerations. In the early 1960s there were fears of imminent over-exploitation of the spurdog stock following record landings by Norway, and the Norwegian authorities introduced a minimum legal catch size of 70cm in March 1964. This applied only to Norwegian vessels fishing and landing in Norway's territorial waters. It was possible for the Norwegian fishery to target such large specimens because mature female dogfish occurred most abundantly on rough, stony grounds which represented no problem to the Norwegian longliners (Holden 1977). No other country has implemented an MLS for spurdog, but, because the market tends to require large fish, it is unlikely that such a regulation will have much conservation benefit.
At a local level, where elasmobranchs are important commercially, or for sport fishing, attempts have been made to control the mortality of juveniles of some species. In England and Wales, local bylaws can be proposed by a District Sea Fisheries Committee and forwarded to the Ministry of Agriculture, Fisheries and Food for confirmation, provided they satisfy the case made out for fisheries conservation. Sea Fisheries Committees in three districts in England (Southern; Kent and Essex; and Cumbria) currently have regional bylaws setting minimum landing sizes for skates and rays caught within six miles of baselines. In at least one of these, the original concern regarding the decline in large rays was expressed by sport fishermen. In each case, these sizes were set to protect immature rays and are given both for the complete fish, with the measurement taken from wing tip to wing tip (disc width), and for a single wing width, if the wings have been removed from the body prior to landing (as they usually are). Owing to the imprecise selectivity characteristics of most gears used to catch rays, it is likely that such regulations may result in considerable numbers of small fish being discarded at sea, though the level of survival of these fish is not known.
A similar, though voluntary, measure exists in two sport fisheries targeting blue shark. Since the early 1990s, anglers participating in the recreational fishery off the Cornish coast have attempted to only land sharks weighing in excess of 34 kg, all others caught are released. The Irish sport fishery, which tends to catch larger specimens, is also believed to be self-regulated with anglers only landing sharks greater than 45kg (Vas 1995).
In the Irish Sea, a local statute has given full protection to the basking shark within a three-mile zone around the Isle of Man since 1989, though the numbers previously killed in this area must represent a negligible proportion of the population. A similar statute protects basking shark around the island of Guernsey in the English Channel.
4.7 Catch/quota allocation
Member states of the EU have individual shares in the various TACs agreed at the Council of Ministers in Brussels every December. The national allocations (agreed and fixed on the basis of ‘relative stability’) are based on the catch of each TAC species taken by that country during an historic reference period and are managed variously at fleet, producer organisation or single vessel level according to the management arrangements applying in each member state. There are no such TACs for elasmobranch species. Under the agreement between the EU, Norway and the Faeroe islands, however, annual quotas were established in 1982 to enable Norway to take 800t of basking shark livers and 500t of porbeagle sharks in EU waters. These quotas were reduced in 1985 to 400t of basking shark livers, which is equivalent to approximately 800–1000 animals (S. Pollard, in litt. 1996), and 200t of porbeagle. Currently, the porbeagle quota remains at 200t, while the annual quota of basking shark livers was reduced from 400 to 100t in 1994. Actual catches are much less than this. Under the agreement with the EU, vessels registered in the Faeroe Islands are also entitled to take porbeagle from EU waters (Gauld 1989). An initial quota of 300t was agreed in 1982, which was reduced to 150t in 1984 and further reduced to 125t in 1985, the level at which it remains today (Fleming and Papageorgiou 1997). There is no catch limit on either species for EU members, despite the concern about declining stocks (Munzol-Chapuli et al. 1993).
4.8 Discussion
Elasmobranch fisheries per se are essentially unregulated and unmanaged within the Northeast Atlantic. To date, EU fisheries regulations have been directed at selected fin fish and shellfish through TACs and some technical measures (mesh sizes, fish landing sizes and seasonally restricted areas). There has been much criticism of the ineffectual attempts to manage fish stocks in the ICES area and, in particular, the lack of enforcement of fishery regulations. A major difficulty in managing fishery resources is the diversity of species taken in a particular fishery and, in many situations, it is impossible to introduce a management measure targeting one species, or group of species, without affecting the exploitation of other species inhabiting the same grounds. This problem is particularly acute in bottom trawl fisheries and has implications for the sustainability of skate and ray stocks. An illustration of this has been the dwindling numbers of the larger species of rays in comparison to the smaller varieties in the North Sea and Irish Sea (Brander 1981; Walker and Heessen 1996).
The main weakness of the present management regime in the Northeast Atlantic is not that advice is lacking on the biological sustainability of commercial stocks, but that there are no explicit objectives with which to guide and test the management process. The CFP was originally conceived to sustain the fisheries of Europe by providing access to other States' waters and maintaining employment and markets, and the sustainability of particular resources was only considered where this was a contributary factor. Elasmobranch fisheries, because they were either extremely widespread, or relatively localised and generally did not contribute greatly to the earnings of the main fleets, were left out of the equation. Now, it appears that it is the threat which fisheries pose to many of these species' populations from an ‘environmental’ viewpoint which is stimulating initiatives and campaigns for their conservation by better fisheries management.
5. THE MANAGEMENT PLANNING PROCESS
5.1 Provision of resource management advice
Currently, three ICES Study Groups deal with the assessment and/or collection of biological data and information on elasmobranch species. At the Statutory Meeting of ICES in 1988, the Demersal and Pelagic committees recommended the establishment of a Study Group on Elasmobranch Fishes (SGEF). The first meeting of SGEF took place in Dublin in 1988 and subsequently it has met in August 1995 and again in May 1997 to collate appropriate data on a limited number of commercial species. Each meeting was attended by scientific representatives of a number of countries with interests in elasmobranch fisheries, both within and outside the EU. At none of these meetings were sufficient data available to carry out assessments of any elasmobranch stock, and advice on the state of the stocks was neither given nor called for.
Whilst the SGEF is responsible for the compilation of biological information and assessment of shelf and pelagic elasmobranch species, the ICES Study Group on Deep-water Species has a similar responsibility for the deep-water sharks. Both these Study Groups are integrated with the Study Group on the Assessment of Other Species and Shellfish, which is responsible for exploring and extending the methodological framework, and identifying the appropriate data requirements, for stocks of species currently not subject to the ICES assessment procedure.
Were any of the study groups in a position to give advice on exploitation levels or safe biological limits for elasmobranch stocks, the relevant information and assessment results would be submitted to the ICES Advisory Committee for Fisheries Management (ACFM). This committee meets twice a year and in November issues its report on the state of stocks, advice on management and relevant factors to be considered by managers when agreeing TACs for the forthcoming year. This takes place at the Council of Ministers in Brussels in December when fisheries ministers from EU member states negotiate with the Commission to achieve national quotas for stocks which will satisfy their constituent fishing industries. This is set against the advice given by ACFM and the implications for the future state of the stocks given different levels of exploitation (see 2.3). Once the TACs have been agreed, and a further round of negotiations carried out between the Commission and third countries (e.g. Norway), national quotas are allocated according to the shares agreed under the policy of ‘relative stability’.
Development of technical measure regulations (e.g. mesh sizes, closed areas) usually arise from proposals of the EU's Scientific, Technical and Economic Committee on Fisheries (sometimes using reports prepared by specific ICES Study Groups), and take the form of a ‘non-paper’ which is disseminated to member states for consideration and consultation with their respective industries. The responses are collated by the Commission, and the proposal is redrafted until the Internal Fisheries Group - in which scientific experts may play a part - is satisfied that it has progressed as far as is possible in achieving its objective. Although there is considerable scope for informed input to this process, from fishermen and scientists, the final article often lacks the ability to achieve the level of conservation originally intended.
5.2 Fishery statistics
5.2.1 Introduction
European fish landing statistics are compiled from data whose quality varies from country to country. In some cases, landings and fishing effort figures are reported for the country as a whole, while other countries report them for separate regions. In the UK, for example, statistics are collected separately for fisheries districts in England, Wales, Scotland and Northern Ireland and compiled by the Ministry of Agriculture, Fisheries and Food (MAFF) in London. In all countries, however, these data are ultimately compiled into national statistics which are then forwarded to FAO where they are collated and recorded along with the statistics submitted by other countries around the world.
Countries bordering the Northeast Atlantic provide similar data to ICES, which has recorded landing data for sharks since 1903. The categories for recording elasmobranchs have changed over time, but the ICES database currently includes the following categories: porbeagle, basking shark, Greenland shark, blue shark, shortfin mako, spurdog, common skate, long-nosed skate, thornback ray, spotted ray, shagreen ray, cuckoo ray, “catsharks (Scyliorhinidae)”, “dogfishes and hounds”, “dogfish sharks nei” (nei=not elsewhere indicated), “various sharks nei”, “cartilaginous fishes nei” and “skates nei.” However, not all countries specify their data to this level and some countries tend to be rather recalcitrant in providing data at all. The ICES species coding for sharks, skates and rays has recently been re-evaluated with the intention of improving information at the species level, and identification sheets for the most important species of deep-water sharks, and skates and rays, including ‘skate wings’ have been prepared.
Landings of these species reported to ICES are logged into the database at the species level, but, when publishing its Fisheries Statistics, ICES groups the porbeagle, basking, Greenland, blue and shortfin mako sharks, catsharks and “various sharks nei” into one category: “cartilaginous fishes nei”. Data on skates and rays are likewise grouped under a single category.
5.2.2 Methods used for collection of catch and effort data
Within the EU, operators of fishing vessels of 10m and greater in length are required to complete a logbook of catches and submit landing declarations for TAC species. It is not mandatory to distinguish other species of fish and at the present time elasmobranch species are often recorded together. For vessels under 10m, the regulations require submission of a sales note by the first seller or buyer. Fishing effort is recorded in a unit appropriate to the gear used, but a common measure of fishing activity is the days spent at sea on each trip. This can be matched with the corresponding fishing capacity unit (see Section 3.2.3) to provide an estimate of effective effort. Countries outside the EU, such as Norway, operate a similar recording scheme. When the market staff or vessel's crew sort and weigh the catches prior to sale, they may separate species and sizes of fish. This more detailed information is recorded together with their respective weights and, later, the sale values. In most countries, there is an established system to make these market data available to officials who collate them with the respective catch and fishing effort data entered in fishermen's logbooks. These are then compiled into national statistics.
5.2.3 Evaluation of the data collection process
In the case of elasmobranchs, except spurdog, sorting on the market is seldom at the species level, and consequently any resulting statistics cannot be used for assessment purposes. This problem is exacerbated for rays, which are often landed as wings and for which there have been no readily available identification charts. Similarly, the larger shark species are often processed at sea and the vessel may only land a small proportion of the whole fish. This not only makes identification difficult or impossible, it also seriously effects the accuracy of estimates of the total weight caught.
EU regulations require vessels of 10 m or greater to submit a landing declaration detailing quantities of each species after each trip and within 48 hours of landing. For vessels under 10m, the submission of a sales note is required within 48 hours of sale. Similar regulations cover landings made outside the country of registry of the vessel. However, transmission of the resulting statistics to international bodies (e.g. ICES or FAO), may occur only once each year and often with a delay of several years.
The provision of correct and timely landings figures is dependent in the first instance on enforcement (and penalties for non-complience, which seem to be lacking) and, in the case of elasmobranchs, on there being an internationally acceptable species sorting and identification protocol. EU Council Regulation (COM(95)322 final) establishes a list of species to be systematically recorded in fisheries logbooks and landing declarations. This includes those species subject to TAC and quota, those subject to technical conservation measures in EEC Regulations, those subject to international measures for the conservation and protection of living marine resources and species of particular scientific or commercial interest. If implemented, this would include highly migratory species in EU waters; basking, mako and porbeagle sharks, and also spurdog, catsharks and smoothhounds. No skates or rays are listed in the proposal. Another major improvement in the quality of landing statistics would be the requirement to land all the catch and preferably as whole fish.
The need for greatly improved recording and reporting of elasmobranchs and their products at species level in landings, markets and trade is widely acknowledged. Several organisations have recognised that there are considerable problems with undertaking these activities because of the inadequate nature of keys for the identification of elasmobranch species, particularly after initial processing of the catch has taken place. As a result, ICES and the Ocean Wildlife Campaign (a consortium of US non-governmental organisations with an interest in marine environmental issues) are producing new keys and guides.
The International Commission for the Conservation of Atlantic Tunas (ICCAT) established a Shark Working Group in 1995 with a primary objective to improve the identification of shark species caught as bycatch in fisheries targeting tunas and tuna-like species. ICCAT has produced and distributed a shark data collection form to all of its contracting parties, in order to improve data collection, and has collaborated closely with ICES by exchanging observers at ICES study group and ICCAT workshop meetings.
The major impediment to any of these solutions is the reluctance of fishermen to adopt new practices for which they cannot perceive a benefit. This suggests that in addition to providing identification keys to assist species sorting and requiring more detailed reporting of elasmobranch catches in logbooks and on markets, there needs to be an emphasis on educating people in the utility of this information in helping to sustain their fisheries.
5.2.4 Data processing, storage and accessibility
Data on catches and fishing effort from vessels and fleets exploiting marine fish resources around Europe are now chiefly stored on dedicated databases which reside either within national fishery administrations or at fisheries research institutes. Staff based at ports collect information from the landings of commercial fishing vessels. Data recorded include: quantity and value of each species landed; fishing ground or area of capture; the amount of time spent fishing (effort) by larger vessels; and the gear used. The sources of this information include EU logbooks and landings declarations, sales notes, and interviews with the skipper or owner of the vessel. Each country has its own system for storing and manipulating such data, but in all cases, the data pertaining to an individual vessel are confidential to the originator and the database operator, and only when statistics have been aggregated to the fleet or national level are they provided to international organisations such as ICES or FAO.
In England and Wales, historic data have until recently been stored off-line on magnetic tape, with each tape storing one year's records. Information retrievals were therefore relatively slow, since each tape had to be loaded before a processing job could be started on a particular year. It follows that across-year comparisons are not straightforward and, because all jobs must be set up and run by trained staff, users have no direct access to the data, and output is restricted to printed tables or limited file formats. This system has now been replaced by an on-line database, which gives users remote access to information and allows more flexible retrievals, including across-year tabulations. In future, all major database developments will have a similar user interface, be accessible via PC and, ultimately, across the Internet. Considerations of data security and confidentiality will obviously restrict access to such databases linked in this way.
In addition to landings data, port staff also collect information on the length distributions of the commercially-important fish species in landings. The England and Wales biological sampling database has been developed so that all length and age sampling data are available on-line on magnetic disk. Summaries by species, month, fishing area, port, or gear, or combinations of these can be extracted. This system is designed so that users can quickly extract information from the database and use it directly in other packages such as spreadsheets and Geographical Information Systems. Fishery institutes from several countries are presently involved in EU-funded projects to improve and standardise the collection of biological sampling data, and to develop international databases into which national data sets can easily be imported and which ICES, for example, can use directly for stock assessments purposes.
ICES has a well-established system for co-ordinating the provision and storage of data arising from fishing surveys on research or commercial vessels. Along with fishing position and gear details, all fish caught are identified to species, where possible, otherwise to family, and the measurements of all fish identified are recorded on paper forms or input directly to the database using electronic data capture systems. National data are compiled in a standard format and collated by ICES on the International Bottom Trawl Survey (IBTS) or International Beam-trawl Survey databases. The data held by ICES in this way are available to be used for research and assessments by all participating national scientific institutes.
5.3 Stock assessment
5.3.1 Assessment practices
No elasmobranch species in the Northeast Atlantic has been subject to the regular stock assessments carried out by ICES for many teleost species. Initiatives taken by the ICES SGEF to attempt stock assessments of elasmobranchs have been hindered by lack of basic biological knowledge and data on changes in relative abundance. Although collected by many institutes, such data are not readily available, and data collation and analysis for elasmobranchs is not well coordinated on a European basis, having a low priority in relation to data on the commercially important teleost species. The SGEF aims to find out what type of data have been collected and where and, more importantly, to develop an understanding of the population dynamics of the species and the changes in life history parameters in response to exploitation as a basis for providing management advice.
Of the Northeast Atlantic elasmobranch fisheries, only that for spurdog has been subject to attempts at assessment, usually by applying production models. One characteristic of elasmobranchs that makes the application of this methodology more suited than to teleosts, is that the number of young that can be produced depends closely on the number of mature females in the population. This deterministic stock/recruitment relationship enables compensatory changes in life-history parameters in response to exploitation to be incorporated into production models. A major limitation is that time-series of catch and effort data which cover a range of stock abundance are required for the results of the model to be reliable. These are rare, and the application of such models is further put in doubt if fishermen direct their effort towards high density areas (‘hot spot’ fisheries), which may apply especially to spurdog.
On the basis that there is a single NE Atlantic stock, Gauld (unpublished data) has estimated the total mortality rate (Z) on males to be 0.3–0.47 over the period 1980–1984, which falls within the range given by Holden for the early 1960s. Holden and Meadows (1964) provided a method of estimating the level of Z that can be withstood by an elasmobranch population at constant recruitment, as a function of the mean number of female young produced per year, the age at which half the females attained maturity, and natural mortality. Even at a Z of 0.3, and with 50% female maturity at 82 cm, the replacement rate of 0.7 (at the upper 95% confidence limit) would mean that the stock could not maintain itself at the prevailing rate of fishing because the female part of the stock could not produce enough young to maintain recruitment.
A life-history type of model, incorporating density-dependent sub-models for growth, fecundity and recruitment, was developed to simulate changes in the reproductive dynamics of the NW Atlantic stock of spurdog (Silva 1993a, 1993b). It suggested that the increase in abundance observed during the 1980s and early-1990s is, at least partially, explained by changes in juvenile growth observed during the 1970s, which subsequently resulted in an increase in the mean size at maturity and in fecundity. This compensation mechanism may also explain why the decline of the Northeast Atlantic population appeared to be arrested, and even reversed, in the 1970s.
A further development of the life-history model by Rago et al. (1994), combined with a Y/R sub-model, gave an estimated fishing mortality (F) of 0.26 on fully recruited females in 1993. At a minimum length at entry into the fishery of 84cm, the maximum F that would ensure replacement recruitment was about 0.25. Yield per recruit decreases with increasing minimum size, owing to the slow growth of spurdog at these sizes and, since reproduction in females occurs primarily in animals above 80cm, and a substantial amount of fishing occurs on fish as small as 50cm, F in excess of 0.1 would probably result in negative female pup replacement, i.e. the population would decline.
It is probable that these models would be equally applicable to all live-bearing shark species, and possibly to oviparous skates and rays, provided information was available on their life history parameters and population dynamics of the species in response to exploitation. Although blue sharks are a key species in the oceanic ecosystem, nothing is known of their stock structure or population size in the Northeast Atlantic and a lack of biological knowledge has prevented any assessment of the impacts of fishing mortality on their population (Bonfil 1994).
There are no known surveys directed at elasmobranchs in the Northeast Atlantic, though rays and dogfish are captured in some routine groundfish surveys. Samples are generally identified to species, sexed, weighed and measured. On some surveys, additional biological information on, e.g. reproductive state and stomach contents, is also collected. Exploratory voyages to investigate the potential for deep-water fisheries were carried out by a number of countries in the early 1970s, and data on the identity and relative abundance of deep-water sharks are available from the relevant reports (e.g. Bridger 1978). Similar surveys continue to be made, though these are mainly aimed at evaluating commercial opportunities and cannot necessarily be considered to furnish time series from which indices of abundance can be derived.
5.3.2 Measures of stock abundance
Landings of elasmobranchs in European countries are generally not sorted by species and, as a consequence, commercial catch-per-unit of effort (CPUE) data are usually not accurate enough for analysis of species abundance trends. There are, however, a few exceptions to this, particularly in trawl or seine fisheries, where it is known that landings data refer to a single species and where the fishing effort recorded might be regarded as representing a true estimate of sampling activity. Elasmobranchs cannot be aged easily and, therefore, weight at age or growth data are generally not available. Data collected in the North Sea by the ICES IBTS has provided useful indices of abundance for some species of ray (Walker 1995). Similar data sets are probably available from other surveys carried out in other areas on the continental shelf of the Northeast Atlantic (see 4.2.3).
An examination of the fishery trends presented in Section 1.2.2 indicates that spurdog catches in the North Sea have fallen since the mid-late 1970s. Catches increased in the late 1970s in the Irish Sea, Celtic Sea and English Channel, following a period in which little was caught, but declined after reaching a peak between 1980 and 1988, depending on area. CPUE data for spurdog are available either from commercial fisheries or research vessel surveys for most sea areas around the British Isles. The longest time series are for Scottish seine netters and trawlers fishing in the North Sea and to the west of Scotland. These suggest that the population in the North Sea increased in abundance between 1967 and 1977, when it is thought that there was a change in the pattern of migration, and then returned to the level observed in the early 1960s. This high abundance period corresponds with a much more marked peak on the west coast, where there was also a second peak in 1985–88 which was not seen in the North Sea data. Commercial CPUE data for English and Welsh Vessels in the Irish Sea indicate a peak in abundance between 1982 and 1985. It must be borne in mind, however, that the apparent decline of spurdog in all areas since the late 1980's may be partly due to the fact that this is not a TAC species in the Northeast Atlantic, and reporting of dogfish catches is not mandatory. Spain, for example, is understood to have taken catches of several thousand tonnes of spurdog which do not appear in ICES Fisheries Statistics.
The IBTS and English groundfish survey in the North Sea show peaks in the relative abundance of spurdog, but not in corresponding years. In the former survey, the highest abundance index occurred in 1976, after which few of the species were caught. The maximum peak in the UK survey was seen in 1986, corresponding to a peak in the Kattegat/Skagerak IBTS series. CPUE from the English Celtic Sea survey (1982–95) show wide fluctuations with no discernible trends. These discrepancies are probably due to variations in catchability of the species since spurdog are known to be fast swimmers, moving around in large packs, and the half-hour hauls used in research surveys are unlikely to take a representative sample of the stock.
It appears, therefore, that wide fluctuations in the abundance of spurdog (and other highly migratory shark species) in a particular sea area might not reflect the overall stock trends and that short time series (i.e. less than 15–20 years) for limited sea areas do not necessarily indicate the historic status of the stock. Local abundance increases may be the result of an influx of maturing fish to a particular area, which are soon depleted as fisheries develop. However, the general conclusion is that spurdog populations in the Northeast Atlantic appear to have been depleted by directed fishing since World War II. In the 1970's, scientists in the UK and Norway considered that this stock was overexploited and urged for restrictions since when most indices of abundance have shown a marked decline. Except for minimum landing size regulations in some countries (primarily for commercial reasons), nothing has been imposed.
Though the data exist for several catshark and ray species, there has been no comparable analysis of survey data for distribution, CPUE or length composition changes. This is a task which ICES will have to deal with in preparing to give advice on biological safe limits over the next few years.
5.3.3 Biological advice review process
The procedure used by ICES to provide the European Commission and national administrators with scientific advice on the exploitation/management of marine fish stocks is described in Section 4.1. This advice is based on stock assessments carried out by working groups made up of scientists from each of the countries which have fisheries for a particular group of stocks, normally arranged by sea area. There is no external review at this time, though retrospective analyses are carried out for all stocks and information is provided on the quality and consistency of successive annual assessments. The results of this work, which is subject to peer scrutiny within these working groups, are then submitted to ACFM (which comprises delegates from all countries affiliated to ICES) for review, further scrutiny and re-analysis if required. The assessment working group reports, and the report of ACFM which contains the subsequent management advice, are published by ICES. Many countries arrange for their scientists to present these results to representatives of the fishing industry prior to TAC negotiations in Brussels. In this way, the advice given by ICES on the biological basis for management of fish stocks is subject to quality control and a wide spectrum of independent expert opinion.
5.3.4 Biological management reference points
Because elasmobranch species are not covered by TACs and their response to exploitation cannot be elucidated by the conventional assessment procedures used by ICES, no advice has been given on the status of the stocks. This is reflected in the low priority given to these species by national institutes. In the light of recent international initiatives (e.g. the Intermediate Meeting of Ministers in Bergen, March 1997) and in view of the adoption of the Precautionary Principle, however, there is now a need for appropriate advice. The population dynamics of these species are easier to predict than those of most teleosts due to the deterministic relationship between stock and recruitment and the relatively uniform survival rate of juveniles and adults and it may be relatively easy to determine limit reference points (defined as replacement mortalities) using basic information on age at maturity, fecundity and rate of change in population size at different mortalities (see Section 4.3). By providing threshold values, rather than catch options, ACFM should be in a good position to give advice on elasmobranch stocks, though ICES has yet to agree what the biological management reference points should be for any stock. It is most likely, however, that values of fishing mortality and spawning stock biomass will be chosen which give a high probability that the stock will be able to sustain itself through recruitment.
5.4 Sustainability of the resource
The question of sustainability of elasmobranch fisheries was raised - though not answered - by Holden in 1974 and, more than two decades later, there is no doubt that in all the well established elasmobranch fisheries in the Northeast Atlantic, landings have declined or even ceased. This reduction is not always obvious if one examines only the total amount landed from the entire FAO Area 27. There are numerous examples where, following a number of years of good fishing in a particular locality, the targeted species disappeared or was reduced to the extent that the fishery was no longer worthwhile. One recent example is the spurdog fishery in the Irish Sea, where they were initially landed as bycatch by trawlers targeting other species, but which expanded due to the development of a fleet of longline vessels based at Holyhead. In 1981, 920t were landed by English and Welsh vessels and, by 1984, this had increased to 2500t and landings eventually peaked at 3940t in 1987. The landings in 1996 amounted to 1133t. The Norwegian basking shark and porbeagle fisheries are other examples of this phenomenon.
The report of the 1995 meeting of the ICES SGEF states that the catches of all elasmobranch species have declined in the North Sea since the 1970s (ICES 1996). The abundance of the spurdog has fluctuated widely in a particular sea area irrespective of overall stock trends and this is seen as an indication that short time series (i.e. less than 15–20 years) are of little use for stock assessment purposes. A further complication in the assessment of highly mobile and widely distributed elasmobranch species is defining ‘the stock’, i.e. that part of a species' population which is exploited and requires management as a unit (Pawson and Jennings 1996).
Research directed at the skate and ray fisheries of the North Sea has shown that the larger species of the Rajidae have been severely depleted. In parallel with reductions in the common skate and thornback ray populations, there has been an increase in abundance and distribution of the starry ray. Similar scenarios have been witnessed in western areas, where larger species of Raja have declined in abundance or even disappeared from an area (i.e. common skate in the Irish Sea and Bay of Biscay). The situation for the large sharks is similar to that of the spurdog in that they are highly mobile with a poorly known stock structure and distribution. In particular, their biology and life history needs further investigation. Little is known about the recently exploited deep-water sharks, but, as with the deep-water teleosts, it is likely that their populations consist mainly of old, slow-growing fish with a low capacity for production and are particularly vulnerable to exploitation.
Whilst there is some evidence that compensatory mechanisms can change the stock-recruitment relationship in some elasmobranch species (Holden 1977; Gauld 1979), Holden considered that any increase in fecundity is likely to be small, being limited by the maximum size of the adult female for placentally and aplacentally viviparous sharks (e.g. blue shark and spurdog, respectively). For the oviparous species such as rays, fecundity will be limited by the rate of egg laying and the available food supply. What is irrefutable, however, is that the total declared landings of elasmobranchs from the Northeast Atlantic have declined since 1970. During the interim there have been temporary reverses when a localised fishery has developed, but overall there has been a decline in the landings from the majority of grounds.
5.5 Discussion
5.5.1 The manager's perspective
Since there is no attempt to manage elasmobranch fisheries in the Northeast Atlantic, and no relevant advice is required or provided currently by ICES, it is not possible to state with any certainty what information or outcome is desired by managers. The deficiencies and intended developments have been outlined in Sections 4.1 to 4.3.3, but it is not possible at this time to provide a ‘manager's perspective’ on the process. However, it may be said that for those marine teleosts which are managed by TAC and technical conservation measures within the EU CFP, ‘political’ considerations seldom, if ever, affect the provision of biological advice, though consideration of its likely impact on national fisheries certainly affects the outcome of TAC negotiations (often to increase TACs above those considered ‘safe’) and the strength of technical regulations. It is at these negotiations that any conflicting requirements by stakeholders (for example, national quotas which add up to more than the maximum catch advised by ICES, or mesh size increases which a particular fleet cannot comply with for economic reasons) are reconciled. It is seldom the case that the biological advice offered is completely unacceptable, though the extent to which administrators will ignore the advice to reach a management decision depends on their own national policy as regards the balance between biological, social and economic needs. The major factor involved in decisions on possible management actions is the need to arrive at a consensus, within the EU and with third parties such as Norway, and the scientific case for conservation can act as common ground on which to find a solution.
Until recently, ICES has provided managers with a practical and deterministic form of advice which unambiguously linked future catches and fishing rates to changes in stock status, especially spawning stock biomass. ICES is now, however, beginning to express uncertainty in the biological advice by giving probabilities of stock changes consequent on particular future levels of fishing (though inclusion of uncertainty in the historic assessments of stock status and response to exploitation is rare). It is doubtful whether this form of advice is sufficiently understood by managers for them to be able to judge whether they need further assistance in handling advice which expresses options and forecasts in probability terms.
5.5.2 The user's perspective
For the reasons given above, it has not been thought useful to seek the views of fishermen or their representatives on a non-existent management process with respect to elasmobranch fisheries. Judging from our experience with feedback from fishermen prosecuting the TAC species, they already feel that their views are not considered sufficiently in the process of stock assessment and provision of management advice. Nevertheless, they do have a considerable input to decisions affecting management.
6. FISHERY MANAGEMENT REGULATIONS
6.1 The regulations
In Section 3.2 of this report, it is made clear that there is negligible regulation of elasmobranch fisheries in the Northeast Atlantic. The biological and ecological characteristics common to most elasmobranchs are a major problem for managing their fisheries, as is the low priority given to these species compared with those teleosts subject to TACs. Regulatory mechanisms usually employ one or two general options: indirect or direct catch or effort controls. In the waters administered by the EU Commission, the majority of fisheries have direct regulations that aim to control output by setting a maximum catch quota or TAC. To date there are no TACs for elasmobranchs, apart from those mentioned previously relating to basking shark and porbeagle, though it is intended that TACs will be set for spurdog and (mixed) skates and rays in the North Sea within the next year.
6.2 Regulations and the communication process
Regulations implemented under the EU's CFP are binding on all vessels of member states and those others fishing in Community waters, from baselines out to the 200-mile limit. These regulations, along with any national rules, are enforced by agencies of each member state within its respective jurisdiction, out to the 200-mile limit or median line with another country. The cost of this enforcement is borne by the state, and we are not aware of any cost-benefit analysis of its implications. In general, it is assumed that the regulations are ineffective in achieving the level of restraint on fishing mortality or improvement in exploitation pattern intended when they were conceived, but the fact that the vast majority of ‘regulated’ fisheries in the Northeast Atlantic continue suggests that the CFP is having some conservation benefit.
At a local level, in fisheries that are the sole responsibility of one country or region and which rely on resources not exploited elsewhere, regulations are developed as much with the interests of the exploiters in mind as with conservation of the biological resource. As a consequence, disputes over access or technical measures are usually resolved before the regulations are adopted or confirmed, which in England and Wales is by ministerial discretion. It is unlikely, however, that elasmobranch fisheries could be adequately controlled by anything other than regulations which are internationally agreed.
7. THE LAW AND ENFORCEMENT
7.1 Legal status
The legal status of the elasmobranch fisheries prosecuted within EU waters of the Northeast Atlantic is that they are a common property to which vessels with the appropriate licence have open access. There are no property rights to sharks taken in international waters outside the 200-mile limit. The legal powers with which these fisheries could be ‘managed’ are, presumably, those attending to any fishery in which elasmobranchs are taken as bycatch. Only for basking sharks and porbeagles are there any specific controls, and these are essentially arrangements to allow non-EU and EU vessels to pursue historical fisheries in other countries' waters.
7.2 Enforcement problems
There are no seasonal closures of elasmobranch fisheries and hence the question of enforcement of fishing out of season, or in closed areas, does not arise. Whilst there are size limits for some species, such as spurdog in Norwegian waters and rays within the 6-mile zone in some fishery districts around England and Wales, there are no available data on the catches of undersized fish and the attendant discard rates. Neither have we any data on the quantities of undersized fish at markets, since elasmobranchs tend not to be covered by most countries' market sampling schemes. Hence, it is not possible to assess the scale of mortality of undersized individuals, nor the requirement for enforcement of these regulations.
7.3 Surveillance
Surveillance of fishery regulations in the Northeast Atlantic is conducted at sea by naval patrol vessels and/or those operated by enforcement or fishery protection agencies and, in some countries, from the air. In most cases, this involves observations of fishing positions and, from vessel boardings, checks on mesh sizes and the design of catching gear, and ensuring that the catch is legal both for size and species (for TAC stocks) and conforms with the details written in the vessel's logbook. Since there are virtually no regulations to enforce with respect to elasmobranchs, very little of the cost of this exercise could be offset against the value of their fisheries. If elasmobranchs are to be afforded more protection in future, the main problems will relate to species identification and, for the widely distributed species, co-ordination of surveillance between nations and outside national limits.
7.4 The legal process
A description of the legal basis for enforcement of fishing regulations in the Northeast Atlantic is outside the authors' competence, though in the UK we know that it is left to the courts to determines culpability on the basis of evidence supplied by the enforcement agencies and fisheries departments. A convicted offender's vessel and gear may be impounded and catch confiscated, subject to the agreed monetary fine being paid.
8. MANAGEMENT SUCCESS
8.1 Profitability of the fishery
It is quite likely that the various fisheries for elasmobranchs in the Northeast Atlantic do create wealth, given that fishermen are prepared to process and market their shark, dogfish and ray catches, the prices for which generally compare favourably with those for species such as cod. However, those economic evaluations of fisheries in the region which have been published (there are none for elasmobranchs) suggest that very few of them actually make an economic profit per se. There have been no studies on the division of the income of the fishery between the harvesting, wholesale, processing and retail sectors of which we are aware.
8.2 Issues of equity and efficiency
As there are no management objectives or policies set for elasmobranch fisheries in the Northeast Atlantic, it is not possible to say what the implications are for social welfare, or how stakeholders are involved in discussion of these considerations.
9. MANAGEMENT COSTS
Similarly, there are no specific management costs, though several countries, in contributing research and commercial data and scientists time to ICES' attempts to develop stock assessments for some elasmobranch species, incur costs which might be set against the value of the fishery.
10. ACKNOWLEDGMENTS
This report has been prepared mainly by reference to existing publications, and is particularly dependent on those which have recently reviewed the fisheries and trade for sharks and other elasmobranchs in the Northeast Atlantic. These are indicated in the reference list, but we would especially like to acknowledge the TRAFFIC report (Fleming et al. 1997) and the reports of the ICES fisheries in the UK.
11. BIBLIOGRAPHY
Reports used most extensively in this study
Anon. 1997. Discussion paper, Pursuant to CITES resolution Conf. 9.17. An overview of the impacts on the biological status of sharks. Tenth meeting of the conference of the parties, 9–20 June 1997, Harare, Zimbabwe.
Fleming, E.H. and Papageorgiou, P.A. 1997. Shark fisheries and trade in Europe, TRAFFIC Europe, 78 pp.
ICES 1995. Report of the Study Group on Elasmobranch Fishes. ICES CM 1995/G:3, 88 pp.
ICES 1997b. Report of the Study Group on Elasmobranch Fishes. ICES CM 1997/G:2, 121 pp.
References
Aasen, O. 1961. Pigghaundersokelsene. Fiskets Gang, Arg. 47: 36–44.
Aasen, O. 1962. Norske pigghamerkninger 1958–61. Fisk. og Hav., (3): 1–5.
Aasen, O. 1963. Norske pigghamerkninger 1962. Fisk. og Hav., (2): 10–15.
Aasen, O. 1964. The Exploitation of the Spiny Dogfish (Squalus acanthias L.) in European Waters. Fisk. Dir. Skr. ser. Havunders, 13 (7): 5–16.
Anon. 1991. Species Profile: Dogfish. Report No. 2003. Market Development Department, Sea Fish Industry Authority, Edinburgh.
Anon. 1994. The New Common Fisheries Policy. European Commission, Directorate General for Fisheries, Brussels.
Anon. 1995. Yearbook of Fisheries Statistics: Production 1995. FAO, Rome.
Anon. 1996a. FISHSTAT PC. Fishery Information, Data and Statistics Unit, FAO Fisheries Department, Rome.
Anon. 1996b. Statlant 27A, Cartilaginous Fishes in ICES Fishing Areas. ICES, Copenhagen.
Berrow, S.D. 1994. Incidental capture of elasmobranchs in the bottom-set gill-net fishery off the south coast of Ireland. J. Mar. Biol. Ass. UK, 74 (4): 837–847.
Bonfil, R. 1994. Overview of wold elasmobranch fisheries. FAO Fisheries Technical Paper, No. 341. FAO, Rome, 119 pp.
Brander, K. 1981. Disappearance of Common Skate Raja batis from the Irish Sea. Nature, 290: 48– 49.
Bridger 1978. New deep-water trawling grounds to the west of Britain. Laboratory Leaflet No. 41, Lowestoft: MAFF, Direct Fish. Res., 40 pp.
Casey 1985. Transatlantic migrations of the blue shark: a case history of co-operative shark tagging. pp. 253–268, in R.H. Strond (ed.), World Angling Resources and Challenges; Proceedings of the First World Angling Conference. Cape d'Agde, France, Sept. 1984. Florida Int. Game Fish Ass.
Clarke, E. 1987. Fisheries and use of deep-sea shark (synopsis). In Sharks: an inquiry into biology, behaviour, fisheries and use. S.F. Cook (ed.). Oregon Sea Grant Comm. Pub. EM8330: 221– 225.
Compagno, L.J.V. 1984. FAO species catalogue. Vol. 4. Sharks of the world. An annotated and illustrated catalogue of shark species known to date. Part I. Hexanchiforms to Lamniformes. FAO Fish. Synop., 125: 1–249.
Dulvy, N.K. 1995. Preliminary report on the status of the skate and ray fishery in the Irish Sea (unpublished paper), University of East Anglia, Norwich.
Fergusson, I.K. 1994. Notes on the shark fauna of the Sicilian Channel, with reference to future insitu studies by means of tagging. pp.22–25 in R.C. Earll and S.L. Fowler (eds)., Proceedings of the second European Shark and Ray Workshop, 15–16 February 1994: Tag and release schemes and shark and ray management plans. Unpublished report..
Gauld, J.A. 1982. The dogfish - an ocean rover. Scottish Fish. Bull., 47: 13–16.
Gauld, J.A. 1989. Recordings of porbeagles landed in Scotland, with observations on the biology, distribution and exploitation of the species. Scottish Fisheries Research Report No. 45. DAFS, Edinburgh: 1–13.
Gauld, J.A. and McDonald, W.S. 1982. The results of tagging experiments on spurdogs (Squalus acanthias L.) around Scotland. ICES CM 1982/H:51.
Grey, M.J. 1995. The coastal fisheries of England and Wales, Part III: A review of their status 1992– 1994. MAFF Fisheries Research Report No. 100, DFR, Lowestoft. 99 pp.
Hjertenes, P.O. 1980. The spurdogs in the North Sea area: the Norwegian fishery and observations on the changes in the migration patterns. ICES CM 1980/H:60.
Holden, M.J. 1965. The stocks of spurdogs (Squalus acanthias L.) in British waters and their migrations. Fisheries Investigations, Series II, Volume XXIV, No. 4, MAFF, London.
Holden, M.J. 1974. Problems in the rational exploitation of elasmobranch populations and some suggested solution'. pp 117–37 in Harden-Jones, F.R. (ed), Sea Fisheries Research, John Wiley and Sons, New York.
Holden, M.J. 1977. Elasmobranchs. pp 187–215 in Gulland, J.R. (ed.). Fish Population Dynamics, John Wiley and Sons, New York.
Holden, M.J. and Meadows, P.S. 1964. The fecundity of the spurdog (Squalus acanthias L.). J. Cons. Perm. Int. Explor. Mer. 28: 418–424.
ICES 1989. Report of the Study Group on Elasmobranch Fishes. ICES CM 1989/G:54.
ICES 1997a. Advance Release of Tables 1–6 of ICES Fisheries Statistics (formerly Bulletin Statistique), Vol 81 1996. ICES C.M.1997/Gen: 5.
Kunzlik, P.A. 1988. The Basking Shark. Scottish Fisheries Information Pamphlet No. 14 DAFS, Aberdeen, 21 pp.
Last, P.R. and Stevens, J.D. 1994. Sharks and rays of Australia. CSIRO Division of Fisheries, 513 pp.
Mejuto, J. 1985. Associated catches of sharks, Prionace glauca, Isurus oxyrinchus and Lamna nasus, with NW and N Spanish swordfish fishery in 1984. ICES C.M. 1985/H: 42: 16pp.
Munoz-Chapuli, R. 1984. Ethologie de la reproduction chez quelques requins de l'Atantique Nord-Est. Cybium, 8(3): 1–14.
Munoz-Chapuli, R., Notarbartolo di Sciara, G., Séret, B. and Stehmann, M. 1993. The Status of the Elasmobranch Fisheries in Europe. Report of the Northeast Atlantic Subgroup of the IUCN Shark Specialist Group. Unpublished.
Myklevoll, S. 1968. Basking shark fishery. Commercial Fisheries Review 30: 59–63.
Myklevoll, S. 1989. Basking shark: off-season observations and catches in Norway and a case of albinoism. Paper to the ICES SGEF, April 1989, Dublin.
Pawson, M.G. and Jennings, S. 1996. Mini review: “A critique of methods for stock identification in marine capture fisheries.” Fisheries Research, 25: 203–217.
Pawson, M. and Nichols, V. 1994. Recapture patterns of rays tagged in the Bristol Channel and Irish Sea. Unpublished report, pp. 10–13 in R.C. Earll and S.L. Fowler, eds, Proceedings of the second European Shark and Ray Workshop, February 1994.
Rago, P.J., Sosebee, J.K.T., Brodziak, S.A., Murawski, S.A. and Anderson, E.D. 1994. Distribution and dynamics of Northwest Atlantic spiny dogfish (Squalus acanthias). NOAA Northeast Fish. Sci. Center Ref. Doc. 94–19, 29 pp. plus tables and figures.
Rose, D.A. 1996. An Overview of World Trade in Sharks and Other Cartilaginous Fishes. TRAFFIC International. 106 pp.
Sainsbury, J.C. 1997. Commercial fishing methods, and introduction the vessels and gear. Fishing News Books, 352 pp.
Shafer, T.C. 1970. Migration and distribution of the spiny dogfish (Squalus acanthias L.) in the western North Atlantic. Master's thesis. University of Rhode Island, Kingston, RI, USA.
Silva, H.M. 1993a. The causes of variability in the stock-recruitment relationship in the spiny dogfish, Squalus acanthias, in the NW Atlantic. ICES CM 1993/G:52, 17 pp.
Silva, H.M. 1993b. A density-dependent Leslie matrix-based population model of spiny dogfish, Squalus acanthias, in the NW Atlantic. ICES CM 1993/G:54, 17 pp.
Stamatopoulos, C. (1993). Trends in Catches and Landings; Atlantic Fisheries: 1970–1991. FAO Fisheries Circular No. 855.1. FAO, Rome.
Stevens, G.A. 1936. Migrations and growth of the thornback ray (Raia clavata L.). J. mar. biol. Ass. U.K., 20: 605–614
Stevens, J.D. 1990. Further results from a tagging study of pelagic sharks in the north-east Atlantic. J. mar. biol. Ass. UK, 70: 707–720.
Stott, F.C. 1982. A note on the catches of basking sharks, Cetorhinus maximus (Gunnerus), off Norway and thier relation to possible migration paths. J. Fish Biol. 21: 227–230.
Sutcliffe, R. 1994. Twenty years of tagging common skate and tope off the west coast of Scotland. pp 14–16 in R.C. Earll and S.L. Fowler (eds). Proceedings of the second European Shark and Ray Workshop, February 1994: Tag and release schemes and shark and ray management plans. Unpublished report.
Templeman 1944. The life history of the spiny dogfish (Squalus acanthias) and the vitamin A values of dogfish liver oil. Res. Bull. Div. Fish Resour. Newfoundland. (15), 102 pp.
Vas, P. 1995. The status and conservation of sharks in Britain. Aquatic Conservation: Marine and Freshwater Ecosystems, 5: 67–79.
Vas, P., Granger, K.A. and Thorpe, T. 1996. The status of the Blue Shark (Prionace glauca, Linnaeus 1758) and its fisheries in the Northeast Atlantic. Paper presented to the Third European Shark and Ray Workshop, October 1996, Birmingham.
Vince, M.R. 1991. Stock identity in spurdog (Squalus acanthias L.) around the British Isles. Fish. Research, 12: 341–354.
Walker, P.A. 1994. Tagging experiments on Rajids in the North Sea and English Channel. pp 7–9. in R.C. Earll and S.L. Fowler (eds), Proceedings of the second European Shark and Ray Workshop, February 1994: Tag and release schemes and shark and ray management plans. Unpublished report.
Walker, P.A. 1995. Sensitive skates or resilient rays? A North Sea Perspective. Shark News, No. 5. IUCN/SSC Shark Specialist Group.
Walker, P.A., and Heessen, H.J.L. 1996. Long-term changes in ray populations in the North Sea, ICES J. Mar. Science, 53: 1085–1093.
Walker, P.A., Howlett, G., and Millner, R.S. 1997. Distribution, movement and stock structure of three ray species in the North Sea and eastern English Channel.- ICES J. Mar. Science, 54: 797–808.
Wheeler, A. 1969. The Fishes of the British Isles and North-West Europe. Macmillian and Co. Ltd.
