Potential management measures for rays in Welsh inshore waters

This is a draft, working document relating to management and conservation issues for skates and rays. It relates only to advice on possible management strategies within the inshore waters of Wales, and does not necessarily apply to elasmobranch management issues at a national or international level.

1 Introduction

1.1 Classification

Skates and rays (Family Rajidae) are relatively large-bodied elasmobranch fishes, of which 15 species have been recorded from UK waters. Of these, only about 7 or 8 species are commonly encountered in the coastal waters of England and Wales. Historically, all these skate and ray species were contained in a single genus (Raja), although a recent taxonomic revision of the Family Rajidae has resulted in the creation of several genera. Their classification and maximum lengths (for UK waters) are given below, with the five species that occur most regularly in Welsh waters given in bold.

Common name	Scientific name	Maximum length (cm)
UK ray species that have been recorded from Welsh waters
Common skate	Dipturus batis	250
Blonde ray	*Raja brachyura*	120
Shagreen ray	Leucoraja fullonica	100
Thornback ray (roker)	*Raja clavata*	99
Smalleyed ray	*Raja microocellata*	80
Spotted ray	*Raja montagui*	80
Cuckoo ray	*Leucoraja naevus*	70
UK ray species occurring outside Welsh waters
Norwegian skate	Dipturus nidarosiensis	200
White skate	Rostroraja alba	200
Long-nosed skate	Dipturus oxyrhinchus	150
Sandy ray	Leucoraja circularis	120
Undulate ray	Raja undulata	100
Arctic skate	Amblyraja hyperborea	85
Thorny ray	Amblyraja radiata	60
Round ray	Rajella fyllae	55

Within the United Kingdom, species with an extended rostral cartilage (i.e. long-snouted species) have typically been termed skates and species with shorter snouts termed rays. Elsewhere in the world, the term skate is typically used for all members of the family Rajidae, whereas the term ray is used for, for example, manta rays and stingrays. For the purpose of this report, we use the term ray, as it is the more frequently used term for UK skates and rays.

1.2 Exploitation

Historically, the common skate was relatively abundant in the Irish Sea and elsewhere in UK coastal waters. By the 1960s, however, this large-bodied species was more or less extirpated from the Irish Sea, and is now caught mainly off the Shetland Islands and western shelf edge of Ireland and Scotland. This decline was attributed to exploitation. Subsequently, the populations of other rays have been reported as declining in UK coastal waters, including around the Welsh coasts, and improved management of their fisheries is considered to be a priority by conservation bodies and fisheries biologists.

There are several reasons why ray populations are susceptible to over-fishing: they are slow growing, late-maturing fishes with a low fecundity. Protective egg cases are laid on the seabed, and the developing embryos hatch as smaller versions of the adults after 6–9 months, depending on the water temperature. The young are relatively large (e.g. thornback rays hatch at a length of ca. 10 cm), and are thus prone to capture in towed gears from an early age. The low fecundity of rays (ranging from 40-150 eggs per year, depending on the species) also means that recruitment is dependent on the stock size of reproductively active females, in contrast to most teleost species, which spawn thousands of eggs, and where environmental conditions play an important role in recruitment processes. Hence, the life-history characteristics of rays make them potentially sensitive to over-exploitation.

Although rays are not usually the targeted species, over recent decades, they have been an important constituent of mixed demersal fisheries, where the primary species are flatfish (e.g. plaice and sole), gadoids (e.g. cod) and anglerfish. Because these fisheries have been managed to conserve the target species, there has been a lack of management measures directed specifically at ray stocks.

2 Management options

There are several potential methods of protecting ray stocks from excessive exploitation and these are discussed in this document. Any management plan needs to balance the benefits, or potential benefits, of introducing measures to arrest declines in ray populations, with any consequent costs to the fishing industry. Rays, however, are an important resource for both commercial and recreational fishermen, and well-managed populations should have benefits to all user groups in the medium and long term.

Potential methods for the improved management of skates and rays include the following:

(a) Marine Protected Areas or No Take Zones

(b) Gear restrictions in certain areas and/or at certain times of the year

(d) Restricted landing of females

(e) Technical measures (e.g. mesh sizes)

(f) Quotas – catch or fishing effort

(g) Licenses

(a) Areas in which no fishing takes place

Marine Protected Areas (MPAs) or No Take Zones (NTZs) have been suggested as one of the better ways of protecting elasmobranch fish, particularly those which are usually taken as a by-catch species. For an MPA to be effective in protecting rays, it is necessary to identify those areas that are important for certain life-history stages and to determine what the optimal size for an MPA would be. Most tagging studies on rays have indicated that juveniles’ movements tend to be relatively localised, whereas adults may range over wider areas. Hence, protecting important inshore nursery areas throughout the year and/or spawning areas during the peak spawning season would have perceivable benefits for reproductive success. It would be important to gauge how the establishment of any such area(s) would effect the fishing industry, particularly inshore fishermen, and what would be the effect of displacing fishing effort. Furthermore, any designated MPA is unlikely to benefit all species of ray to the same extent, and it would be important that an MPA was primarily designed to benefit those species that were either the most sensitive and/or have declined the most. Additionally, there is a need to decide whether fishing gears which do not catch rays (e.g. surface gill nets, pots) could be allowed in any MPA, see below.

(b) Gear restrictions in certain areas and/or at certain times of the year

Most rays are taken as an important by-catch in mixed demersal beam and otter trawl fisheries. They are also taken in set nets (e.g. gill and tangle nets), where they may either be targeted or taken a by-catch in nets set for anglerfish and turbot. Controls on the use of such gears in certain areas, throughout the year or during those parts of the year when breeding females or juveniles are most vulnerable, may help to reduce mortality of rays. Other fishing interests (e.g. potting and recreational angling) may continue unhindered, and such restrictions may not be as negatively impacting to local fishing communities as an MPA.

(c) Size restrictions (i.e. minimum and/or maximum landing sizes)

Some Sea Fisheries Committees have by-laws that stipulate a minimum landing size (MLS) for rays within the 6-mile zone in the waters of the British Isles. There is no national or European MLS for rays. An MLS would increase the chances of survival of juvenile rays, if it can be enforced and providing that the mortality rate of discarded fish is low. Whilst tagging studies suggest that rays are no more likely to die after being caught and released than are plaice, for example, preliminary studies by Kaiser and Spencer (1995) indicated that, although 100% of cuckoo rays caught in a beam trawl were initially alive, only 59% survived over the next 5 days. Further work on the survivorship of juvenile rays (representing those sized fish that would potentially be discarded) is required.

There are, however, several problems regarding the establishment of minimum landing sizes for rays. First, rays are ‘winged’ at sea (i.e. the pectoral fins are removed and the backs discarded) in many areas, and separate minimum landing sizes would be required for fish landed whole (referring to total length and/or disc width) and for processed fish (referring to ‘wing’ length or width).

Second, should an MLS be allotted on a multi-species basis, or species by species? In the case of the former, an MLS designed to protect the juvenile stocks of the most vulnerable species, which are likely to be the larger-bodied species, may result in fishermen having to discard unacceptably large numbers of marketable fish of the smaller species. It may also, theoretically, promote the landing of larger individuals, including the larger and more sensitive species, and females, which attain larger sizes, and may inadvertently benefit the smaller, faster-growing species more than the larger, slower-growing species, to the ecological detriment of the larger and more vulnerable species.

A multi-species MLS would also require an improved knowledge of the species composition of rays from different regions at different times of the year, which would require increased market sampling.

A separate MLS for each of the commonly occurring species (5 in Welsh waters), may be less easy to enforce and fishermen found with undersize fish may claim ignorance regarding species that they view as morphologically similar. Rays are generally landed and recorded as mixed species, and the market is more focused on grading by size than species. An EU-wide decision to record landings at a species level would make stock assessments more accurate and management decisions more effective.

Finally, any MLS brought in as an SFC byelaw only affects the inshore fishermen and not affecting larger operations further offshore: such measures can be unpopular with some segments of the fishing industry.

Maximum landing sizes have been used in some fisheries, for example to protect the larger and more fecund females in a stock, or because of the bioaccumulation of pollutants such as mercury in older and larger fish. A maximum landing size would have the benefit of protecting the ray species that are considered to be the most vulnerable to exploitation, and may also indirectly favour females, which attain a larger body size, thus potentially enhancing the reproductive output of the stock. Such a measure might be used at certain times of the year (e.g. the spawning season), or be only applicable to female fish (see below). In the latter scenario, this would require that fish are only gutted, and not winged, at sea. Males and female rays can have some differences in the fins (e.g. presence of malar and alar thorns in mature males), but this could be contentious if only wings are landed. A maximum landing size (and/or other measures to protect females) used in conjunction with a less draconian MLS (and other measures to protect juveniles) may be a more fishermen-friendly measure than a relatively large minimum landing size.

(d) Restricted landing of females

As the fecundity of rays is low, recruitment is dependent on the status of the mature female stock. Hence, a healthy population of mature females is essential to sustain stocks and fisheries. Measures to protect mature females, particularly during the breeding season, could be easy to enforce, as rays are easily sexed externally and often segregate sexually and by size. Experienced fishermen may know which sites are favoured by large female rays and, if such fish were protected, then they may be encouraged to avoid such locations, depending on the distribution and abundance of other fish.

(e) Technical measures (e.g. mesh sizes)

Rays are large, broad fish that are vulnerable to most methods of fishing with nets. As rays tend to be a by-catch in trawl fisheries, mesh size regulations tend not to be of much use for ray conservation. Any trawl mesh size designed to promote the non-retention of immature rays would severely affect the catch rates of the targeted species such as plaice and sole. Tangle nets, on the other hand, are often used to target rays, and there is some potential for introducing mesh size controls to help protect small rays.

(f) Quotas

Quota management attempts to limit the level of fishing mortality on target species, and controls on catches (actually landings) or fishing effort are determined on the basis of stock status and forecasts of future impacts on stocks due to various levels of exploitation. This information is not currently available for rays, but assessment methodologies for elasmobranchs are being developed under a three-year EU-funded programme across Europe. To help this, we need to collect accurate data on the species composition of catches from the various fisheries that take rays.

(g) Licences

Licensing has been implemented as one of the management tools in elasmobranch fisheries in the USA: for example, there is limited access to the Atlantic shark fisheries. Although it may be useful to restrict the number of fishermen who target rays (e.g. set nets and demersal long-lines), such gears are not the main cause of fishing mortality of rays and trawl fisheries are already subject to restrictive licensing.

Summary

It is unlikely that any single management measure will protect ray populations around Wales, and a suite of measures would be more effective. Below we offer a range of measures that could be implemented singly or together on a regional scale for Wales, by the Sea Fisheries Committees, for consideration:

1. Protect certain inshore nursery areas, with the aim of reducing mortality on juvenile fish. These areas are known for small-eyed and thornback rays, and juvenile spotted rays often occur with the latter. Juvenile cuckoo rays tend to occur further offshore, and closed areas are probably not a viable option. Little is known about the distribution of juvenile blonde rays. Discrete, inshore nursery areas could be protected through the restriction of gears that can be used (e.g. no trawling and, depending on the mesh size, set nets), which would allow inshore fishermen to set pots for crustaceans and molluscs and recreational angling rather than having a NTZ.

2. Set a minimum landing size to protect juvenile rays. As rays tend to be relatively site-specific, juveniles should gain protection from gear restrictions in nursery areas (see above). Juveniles can, however, also be taken outside such areas and a MLS would be a useful management measure if it can be shown that discarded fish have a good chance of surviving. Ideally, such an MLS should match the size of rays being protected by trawl bans in nursery areas.

3. A maximum landing size, or prohibition of landing mature females, during the spawning season (e.g. May–August) which would serve to protect the spawning-stocks of the more vulnerable species (e.g. blonde and thornback rays). This would be easy to enforce if fish are landed whole, although it would be problematic if rays are winged at sea, and may need to be accompanied by a requirement for fish to be landed whole. Larger sized fish have a higher market value and so may encourage c

4. In addition, the landing of sensitive species (e.g. common skate) could be banned. This would be of negligible or no impact to the revenues of Welsh fishermen, but would be good PR. Fishermen should also be encouraged to report any unusual skate species landed.

Data requirements

Once it is established whether or not there is strong evidence of declines in ray stocks, it could be decided which of the above measures might be implemented in Wales. Additional data would be required to justify the use of measures:

1. Protection of inshore nursery areas

Where are these areas? Catches by commercial vessels or scientific surveys showing fish of each species under a particular size (to be agreed), locality and time of year. Also knowledge of which fisheries occur there, which of these catch small rays, and whether there are other places for fishermen to fish if a particular area were to be closed.

2. Minimum landing size

Growth rates and size at maturity information (already available for some species), plus knowledge of the size at which juveniles disperse from nursery areas. Information on survival rates of discarded fish (tagging?).

3. Maximum landing size

As above, but identifying average size at which females of each species become mature, and their spawning season. In which fisheries are rays landed whole, or winged at sea, and how would a requirement for fish to be landed whole be received?

4. Ban on landing of sensitive species

Identification of which species this may be applied to, and how to monitor catches of these and unusual ray species. A Welsh/English ray identification key is required.