DEEP WATER DEMERSAL FISHERIES

John D.M. Gordon
Senior Research Fellow
Scottish Association for Marine Science
Oban
PA34 1QA
UK
Introduction
 
Although the fishes that live in the deep oceans are frequently described as deep-sea fishes it has become customary to refer to those that are exploited in the fisheries as deep-water fishes. This avoids confusion with the term deep-sea fishery meaning a fishery that takes place in distant waters. It is becoming accepted that a deep-water fish is one that lives, at least for most of its life cycle, at depths greater than 400 metres. The exploited fishes of the continental shelf are generally divided into two categories, pelagic and demersal. In the deep sea the pelagic extends from the surface to abyssal depths and it is usual to divide it into three zones. The epipelagic zone includes all those fish living in the upper photic layer of the ocean, such as the tuna fishes. The mesopelagic zone spans the depth range from below the photic zone down to about 1000 metres and supports an abundant and diverse fish fauna. Some mesopelagic lanternfishes (family Myctophidae) that form dense aggregations are, or have been, exploited in areas such as the Arabian Sea and the Southern Oceans. Although there is no exploitation of mesopelagic fishes in the North Atlantic it is important to recognise that many are diel vertical migrators. They migrate to the surface at night and return to the depths during the day and, in doing so, form an important link in the deep-water food-chain. The bathypelagic fishes occur from about 1000 metres down to abyssal depths and are generally highly adapted, often in bizarre ways, to life in a dark, food-poor environment. They are in low abundance and biomass and are of no commercial value.
 
The deep-water demersal fishes are generally divided into two categories, benthic and benthopelagic. The benthic fishes are those that have a close association with the seabed and include species such as skates and flatfishes. Benthopelagic fishes are those that swim freely and habitually near the ocean floor and, in the areas where deep-water fisheries are commercially viable, they comprise most of the exploited biomass.
 
The general concept of the deep sea is of a dark, cold, food scarce environment where biomass decreases exponentially with depth. How then do the continental slopes, underwater rises and seamounts in some areas of the world support deep-water fisheries? The demersal fish populations of the slopes of the Rockall Trough have been the subject of intensive study by the Scottish Association for Marine Science (SAMS) since the mid 1970s and these studies have contributed to an explanation of this phenomenon. By using fine mesh bottom trawls capable of catching almost all sizes of fish it has been shown that there is a diverse demersal fish fauna of in excess of 130 species between about 400 metres and abyssal depths. At any given depth down to about 1500 metres a research trawl will yield between about 40 and 50 different species of fish. Below this depth the number of species present rapidly declines. The estimation of total fish biomass is complicated by the selectivity of the different trawls types. For example, the larger more mobile fishes will avoid the small bottom trawls used by oceanographic research vessels. However, by combining data from different trawls it has been shown that there is usually a peak of demersal fish biomass on the slope at depths of about 1000 metres. The food supply required to support this peak of biomass is the key to this paradox. Studies by SAMS of the diets of over 70 different fish species have shown that relatively little use is made of benthic invertebrates. Epibenthic, hyperbenthic, benthopelagic and pelagic organisms, especially crustaceans, are the main food items of the dominant benthopelagic component of the demersal fish populations.
 
The ultimate source of almost all energy for the deep sea is the production of phytoplankton in the euphotic zone, which in turn is consumed by the herbivores, which are then preyed on by the carnivores. A certain amount of the energy from this food chain reaches the deep sea as a continuous rain of dead organisms or their products. Recently, it has been shown that there is a rapid seasonal input of organic material directly associated with dead phytoplankton to the sediments of the deep sea. The quantities of these materials reaching the sea bed declines with increasing depth and the resulting production of benthic invertebrates, which are very largely dependent on such energy input, could never support the observed demersal fish populations. The rapid sinking of large, dead organisms to the sea bed can provide a valuable food source for some scavenging fish species. However, there is little doubt that the success of the benthopelagic fishes of the slopes results from the transfer of the energy of surface production downwards, via the mesopelagic fauna of both fishes and invertebrates. One pathway is via the overlapping food chains of organisms that occupy specific depth ranges. Many mesopelagic organisms also carry out daily vertical migrations feeding near the surface at night and returning to depths of about 1000 metres during the day where they form a deep-scattering layer. Where this downward vertical migration impinges onto the slope or the sides of seamounts it provides a source of food for the demersal fishes. The horizontal impingement of the scattering layer onto the slope or the horizontal movements of the demersal fishes into the scattering layer will also increase feeding opportunities. It is therefore reasonable to assume that the abundance, diversity and peak biomass at mid-slope depths is a consequence the efficient transfer of surface production into deep water via overlapping mesopelagic food chains and the daily or seasonal transfer by vertical migration.
Although on a world-wide scale there are probably many areas of slope that have not been explored, the general picture that emerges is that deep-water fisheries mostly occur at depths between about 400 and 1500 metres and tend to be associated with areas where there is high surface productivity. These are generally at higher latitudes or in upwelling areas. Similar explanations could account for the aggregation of exploitable fishes around oceanic islands and seamounts. However, additional factors such as enhanced productivity around seamounts, resulting from topographical modifications to the hydrography and circulation, may also be important.
 
The deep-water fisheries
The exploited deep-water demersal fishes can somewhat arbitrarily be divided into three main groups.
(1) On the upper continental slope there are many species that extend from the outer continental shelf into deeper water. In the northeastern Atlantic examples of such species are the anglerfishes (Lophius spp.), ling (Molva molva), tusk (Brosme brosme) and hake (Merluccius merluccius). These may even be encountered in coastal waters and may have rather shallow nursery areas.
 
(2) Also on the upper continental slope are species that are closely related to shelf species but spend almost their whole adult life in deep water. Examples of such fishes are blue ling (Molva dypterygia), blue whiting (Micromesistius poutassou), greater forkbeard (Phycis blennoides) and deep-water redfish (Sebastes mentella).
 
(3) Many of the recently developed deep-water fisheries are for species whose distribution extends from the upper slope to abyssal depths and are characterised by species such as the roundnose grenadier (Coryphaenoides rupestris), black scabbardfish (Aphanopus carbo) and the orange roughy (Hoplostethus atlanticus). These demersal fishes have probably evolved mainly in the shallower waters and have secondarily invaded the deep sea but on many separate occasions. Although well-adapted for life at depth, their special morphological features are usually less well-developed than those found in the meso- and bathypelagic fishes that have undergone much of their evolution in deep water.
 
It is the fishes of group 3 and some of group 2 that comprise the 'new' deep-water fisheries that are the subject of this report. The fisheries for the pelagic or semi-pelagic species, such as blue whiting and redfishes, are well documented and are beyond the scope of this paper.

Some deep-water fisheries in the northeastern Atlantic are quite long-established, especially around oceanic island groups where the opportunities for shallow-water bottom fishing are limited. The longline fishery for black scabbardfish at Madeira has been in existence since the 17th Century and for most of this time it was an artisanal fishery. This has begun to change in recent years with the introduction of larger vessels and the increasing mechanisation of the fishing technique. The present level of landings is most probably being maintained by the exploitation of new grounds farther from the islands. A similar situation exists around the Azores, where there has been a major decline in the fishery for some species such as the kitefin shark (Dalatias licha) and there are concerns about the sustainability of the fishery for the red seabream (Pagellus bogaraveo). Many of the fisheries of the continental slopes of the Iberian peninsula are also artisanal and seasonal. At certain times of the year vessels will change from fishing on the shelf and target deep-water species such as red seabream, greater forkbeard and deep-water sharks. The fishery for red seabream in northern Spain has virtually collapsed while another near the Straits of Gibralter is strictly regulated.. There has also been an all-year-round longline fishery for black scabbardfish off mainland Portugal since 1983 and at the present time it does not appear to be over-exploited. The bottom trawl fishery off Portugal which targets Norway lobster (Nephrops norvegicus) in deep-water and has the rose shrimp (Parapenaeus longirostris) and numerous finfish as a bycatch developed in the late 1970s. The Norway lobster is currently considered to be overexploited and the fishery now concentrates on the red shrimps (Aristeus antennatus and Aristeomorpha foliacea) of the outer shelf and upper slope.
 
Further north in the Atlantic, one of the earliest deep-water bottom trawl fisheries was for the roundnose grenadier. The fishery, which was prosecuted mainly by the former Soviet Union and other eastern European countries, began in the late 1960s and rapidly increased reaching peak levels in the 1970s. Much of the fishery was in what were international waters before the introduction of 200 mile fishery limits. The decline in the fishery was partly the result of extending national fisheries limits to exclude or regulate the activities of foreign vessels in areas such as the continental slope off Iceland, the Icelandic sector of the Reykjanes Ridge and the UK sector of the Rockall and Hatton Banks. The break up of the Soviet Union also contributed to the decline. This fishery continues, but on a much smaller scale, on the Mid-Atlantic Ridge and Hatton Bank. There remain doubts about whether the reported landings reflect the true scale of the fishery both historically and at the present time. It is almost certain that the two species of grenadier, roundnose and roughhead (Macrourus berglax) were not always separated in the landings from the more northerly areas. It is also important to recognise that the bycatch of many deep-water species from these fisheries may not have been adequately reported. There was also another important fishery for alfonsino (Beryx splendens) on the more southerly parts of the Mid-Atlantic Ridge but again the reported landings may not reflect the true scale of the fishery.

The extension of national fishery limits and the consequent closure of traditional fishing grounds for shelf species to foreign vessels led some countries to search for new resources. In the 1970s both the United Kingdom and Germany carried out extensive bottom trawl surveys of the deep water to the west of Scotland and Ireland. Despite the discovery of potentially exploitable resources of species, such as roundnose grenadier, black scabbardfish and blue ling, there was little interest from the markets. The only fishery that developed from these surveys was a directed German trawl fishery on spawning aggregations of blue ling in the northern parts of the Rockall Trough in the mid 1970s, but this had all but ceased by the early 1980s. France also entered the fishery in the late 1970s not only targeting the spawning aggregations but also beginning a more general all-year-round bottom trawl fishery along the continental slope. It was the development of markets, mostly in France, for the bycatch of roundnose grenadier, black scabbardfish and sharks that led to the present fishery for 'new' deep-water species. Although the main fishery is by France there have also been landings of deep-water species by the UK and Ireland. The UK landings have been mainly the bycatch of Scottish trawlers targeting monkfish (Lophius piscatorius) in deep water. The landings of orange roughy (Hoplostethus atlanticus) which began in 1992 are almost all from the larger French trawlers fishing in deeper waters than those exploited by the mixed deep-water fishery.
 
Before 1997 most of the slopes of the Rockall Plateau and a large part of the Hatton Bank were within the UK 200 mile Fishery Limit. In that year the UK conformed with the United Nations Convention on the Law of the Sea and no longer claimed a 200 mile fishery limit around Rockall, an uninhabited rock about 19 m high and with a base of about 25 metres. The controversy over the exploitation of the previously controlled haddock fishery on the Rockall Bank, now largely in international waters, has largely overshadowed the developments that are taking place in the deeper waters around the slopes of the Rockall Plateau and on the Hatton Bank. Although previously there was no effective regulation on the quantity of deep-water fishes that could be taken in these areas, there were restrictions on who could fish in the area and data were available on landings. Now an international fleet is exploring and exploiting the area and there are concerns that not all landings are being adequately reported. A wide range of seamounts and underwater ridges in the international waters of the northeast Atlantic are also being exploited for species such as orange roughy, alfonsino and deep-water cardinal fish (Epigonus telescopus).

In addition to the deep-water bottom trawl fishery there is also a static gear fishery. Norwegian longliners have for many years fished along the edge of the continental slope for ling, blue ling and tusk, although blue ling is a relatively small component of the catch. There is also a UK and Spanish longline fishery, the former landing mostly in Spain, for hake with a bycatch of other deep-water species, such as sharks. If the market price is favourable, these fleets may change to target deep-water sharks. Deep-water longline fisheries also take place on the Hatton Bank and there are reports of significant catches of Greenland halibut. Deep-water gillnet fisheries target anglerfish and sharks, with a bycatch of the deep-water red crab (Chaceon affinis).
All these fisheries occur to the south of the Wyville-Thomson Ridge which extends between Shetland and the Faroe Islands at a depth of about 500 metres. This Ridge causes a physical separation of the relatively warmer deep Atlantic waters from the much colder deep Norwegian Sea waters and results in a major faunal discontinuity. Although there is some similarity between the fish assemblages at or above sill depth, there is little or no similarity at greater depths. The deep-water fish fauna of the Faroe-Shetland Channel and the Norwegian Sea is less diverse than that of the warmer Atlantic. Fish abundance and biomass decrease rapidly below about 500 metres until by 1000 metres, where the water temperature is < 0°C, the biomass is about 1% of that on the upper slope. The deep-water fisheries of this area are mainly on the upper slope and into the transition zone between the warmer Atlantic and the colder Norwegian Sea waters. The important species are Greenland halibut, and redfishes in cold waters, and ling, tusk and blue ling in relatively warm waters. There are also occasional landings of the less marketable roughhead grenadier.
There are semi-pelagic trawl fisheries that have a wide distribution along the oceanic margin of the eastern North Atlantic and which occur on either side of the Wyville-Thomson Ridge. The blue whiting is the most important, but there is also a well established but much smaller fishery for the greater silver smelt or argentine (Argentina silus) in the Rockall Trough and off Norway. Blue whiting is an important food source for deep-water demersal fish, but there are concerns for the future of the stock because, for political reasons, the annual landings are presently more than twice the recommended TAC of 620000 tonnes for the International Council for the Exploration of the Sea (ICES) area. In recent years a fishery for greater silver smelt has developed in Icelandic waters.
 
Deep-water fishes and their life history strategies
Deep-water fisheries are very long lived and slow growing, have a high age/size at first maturity and a low fecundity. This sentence, or a variant of it, is frequently used in the context of deep-water fisheries. Almost inevitably, this statement is coupled with the orange roughy. The question that is seldom addressed is how valid is this generalisation?
 
For a biologist, deep-water fishes are difficult to work with because they can seldom be obtained as living specimens. Although our knowledge of their biology is steadily improving, parameters such as metabolism and age validation, which usually require living fish, are difficult and expensive to investigate. One review of the metabolism of the whole spectrum of deep-water fishes suggests that 'seamount associated', aggregating fishes, such as orange roughy and the deep-water oreos, have a higher metabolism than the dispersed deep-water benthopelagic species, such as roundnose grenadier and other macrourid fishes. The high metabolism of the seamount associated species is thought to be related to the energy that has to be expended in maintaining position around seamounts. Nonetheless the orange roughy and oreos share many characteristics, such as great longevity, high age at first maturity and low fecundity all of which make them vulnerable to over-exploitation. Also, the low water content and high protein and lipid content of the flesh, compared with dispersed deep-water species, means that they have a high commercial value.
Since the exploited fishes of the Rockall Trough and adjacent areas represent a wide range of different species and because they have been the subject of research for many years it is appropriate to use them to illustrate the diversity of life history strategies of deep-water exploited fishes.
 
The Gadiformes (cod-like fishes) are represented by four families. The family Gadidae, which on the shelf is represented by species such as cod, ling, haddock and whiting is represented in the deep water by blue whiting, blue ling and the greater forkbeard. The blue whiting, which only occasionally intrudes on to the continental shelf, has the typical life cycle of a shallow-water gadoid fish. The blue ling, although only seldom caught on the shelf, is closely related to the ling and shares many of its life history characteristics. The larval stages are pelagic, but little is known of the distribution of the juvenile stages. Earlier studies have reported unvalidated ages of up to about 15 years but a recent, Nordic study concluded that age could not be reliably estimated. The blue ling has a well-defined spawning season and appears to have a preference for spawning around offshore banks in the northern areas of the Rockall Trough. It is these spawning aggregations that have been important for the fishery. Although nothing is known of the stock structure of blue ling, the observation that some of these spawning aggregations do not appear to recover after several years of intensive fishing might be evidence in support of discrete spawning stocks. The blue ling has a high fecundity typical of many gadoid species. The greater forkbeard is an upper slope species with a relatively unimportant bycatch in the Rockall Trough,. Further south off the Iberian peninsula, around the Azores and in the Mediterranean there are significant landings of this species whose maximum age has been estimated at 12 years.
 
The hake (Family Merluccidae) is primarily a species of the outer continental shelf, although the upper slope component of its population has been exploited for many years and is particularly important in more southern areas and the Mediterranean. Its life history is typical of the shelf gadiforms.
 
The 'true' deep-water gadiforms belong to the families Moridae and Macrouridae. Only two morids of the North Atlantic are of sufficient body size to be of commercial interest. Mora (Mora moro) is landed in small amounts from the Rockall Trough fishery, often combined with the greater forkbeard. There is the potential for a long line fishery for mora around the Canary Islands. Nothing is known about the age and growth of this species. The other large morid is the blue hake (Antimora rostrata) which is most abundant at about 2000 m in the Rockall Trough and, as such, is unlikely to be commercially exploited. However, off Canada and Greenland it has a shallower distribution and there have been experimental landings. The two species of grenadier, roundnose grenadier and the roughhead grenadier have, at least in the North East Atlantic, quite separate distributions. The roundnose grenadier is found in the relatively warmer waters of the Atlantic margins. Although the age of roundnose grenadier has only been validated up to about 6 years there is general agreement on the interpretation of growth zones in the otoliths. Ages of up to about 70 years have been estimated, but these are exceptional and the ages of fish landed from the Rockall Trough tend to be less than 30 years. The estimated age at first maturity is about 8 to 10 years. There have been several studies on the reproduction of this species and the results tend to be contradictory, ranging from all-year-round, through an extended spawning period to a discrete spawning period. This may indicate separate spawning stocks, but the evidence for or against separate stocks at the present time is tenuous. The roundnose grenadier has a relatively low fecundity (10000 to 60000 eggs) but the eggs are much larger than those of shelf gadoid fishes. The eggs are pelagic and from the results of investigations in the Skagerrak they are to be found deep in the water column. In the Atlantic the eggs have never been reported and larval stages are rare. The Skagerrak investigations suggest that the juveniles adopt the demersal habit after spending about 8-10 months in the pelagic zone, feeeding mainly on copepods. The roughhead grenadier tends to occupy the colder waters mainly under the influence of Norwegian Sea water. This species, although it has similar eating qualities to the roundnose grenadier, has a very rough scaly skin that makes it difficult to fillet. It is therefore frequently discarded. Its life history characteristics are similar to those of the roundnose grenadier.
 
The black scabbardfish has sometimes been referred to as a pseudoceanic species in the sense that it has pelagic affinities but is generally found over continental slopes and around islands and seamounts. The eggs and larval stages of the black scabbardfish are unknown and juvenile fish are seldom caught. The largest mature and spawning fish are found in the southern areas of its distribution and mature fish have been reported from the Mid Atlantic Ridge. However, with very few exceptions, the fish found along the continental slopes of Northern Europe are immature sub-adults. One hypothesis to explain this distribution is to consider that there is a single northeastern Atlantic stock with separate spawning and juvenile feeding grounds but attempts to test this hypothesis have so far been inconclusive. There have been some recent studies on age estimation, and although the results have not been validated, there appears to be general agreement that this is not a long-lived species. Ages of 12 to 15 years were estimated for the mature fish caught around Madeira.
 
There are numerous species of deep-water sharks or dogfish mostly belonging to two families. The catsharks (Scyliorhinidae) are of little commercial interest except in southern Europe and the Mediterranean countries, where the deep-water blackmouth dogfish (Galeus melastomus) is landed. In common with other scyliorhinids it lays relatively small numbers of large eggs. Sharks, because they lack calcified hard parts are more difficult to age than bony fishes, and although some progress has been made in defining growth bands in the vertebrae it has not been possible to validate them as annual rings and therefore the longevity of these sharks is unknown. The squalid sharks (Squalidae) produce live young and as a family are characterised by having a spine in front of each of the two dorsal fins. Only two of the several species that are caught in the bottom trawl fisheries to the west of the British Isles are landed. These are the leaf scale gulper shark (Centrophorus squamosus) and the Portuguese dogfish (Centroscymnus coelolepis). They have overlapping depth distributions, although the latter tends to be the deeper living species. The discards of the birdbeak dogfish (Deania calceus) are high because it is difficult to skin. Markets are being developed for a few other species. Leaf scale gulper shark and Portuguese dogfish are also landed by longliners either as a directed fishery or as a bycatch. The directed fisheries, which are mostly on the slopes off northern Spain and Portugal, are mainly for leaf scale gulper shark or the closely related gulper shark (C. granulosus). Portuguese dogfish is an important bycatch of the longline fisheries for black scabbardfish. The dorsal spines of some shallow-water squalid sharks are useful structures for age estimation and some recent studies on leaf scale gulper shark have yielded unvalidated estimated ages of 21 to 70 years. Portuguese dogfish generally produce about 14 young at parturition. There is no obvious seasonal cycle of reproduction and there are reports that the gestation period for an individual may be as long as 3 years. The gravid females of leaf scale gulper shark have not been observed, but ovarian egg counts suggest that the litter size is about 10. The deep-water sharks are often segregated by sex and size and sometimes, apparently, also by size and depth. Besides the sharks, there are other species of elasmobranch fishes, rays and chimaerids, that are landed in small amounts but they are not identified to species and little is known of their biology. Markets are developing for some of the chimaerid fishes.
 
The orange roughy is probably the most frequently cited example of a deep-water exploited fish. Although it has a dispersed phase, it also aggregates along steep continental margins and around seamounts or underwater ridges and it is the exploitation of these aggregations that comprises the bulk of the fishery. It has been noted above that the orange roughy may belong to a group of seamount-associated fish, with a somewhat different metabolism to other deep-water fishes such as the dispersed grenadiers. This metabolism results in a high quality and valued flesh. The orange roughy fishery has been established around New Zealand since 1979 and, because of its value to the New Zealand economy, it has been the subject of considerable research. Undoubtedly, the single and most controversial factor is the estimation of age. The otolith, the calcareous ear bone frequently used for ageing bony fishes, has a complex shape in this species which makes it difficult to interpret and count growth zones. The first few years of growth have been validated but after that age has been estimated using radiometric techniques which have yielded ages in excess of 100 years. Some argue that the radiometric method is seriously flawed and that the fish are younger. The orange roughy also reaches reproductive maturity at a large size/high age and up to 50% of adult females may not spawn in every year. In New Zealand waters the age at first maturity is estimated at >20 years.
 
The argentine fishery exploits seasonal aggregations of spawning fish along the shelf edge. Age estimates suggest that fish can be up to 40 years old. The spawning period can be prolonged and the fecundity is relatively low.
 
The above account of the biological characteristics of many of the exploited deep-water fish species of the Rockall Trough reveals a wide range of life history strategies many of which have there counterparts in the shelf fisheries. The shallow-water fisheries of the North Sea are becoming more and more dependent on the recruiting year class and selection is resulting in younger ages at first maturity. Could the age structure of fishes of the North Sea at the end of the 19th Century have been comparable with many of the present stocks of deep-water species? Whatever the answer, there is little doubt that the frequently cited orange roughy is at one extreme of a wide range of life history strategies. Depletions, similar to the collapse of the orange roughy in the northern Rockall Trough, have occurred for shelf species such as the Atlantic halibut and skates in the North and Irish Seas. The Northeast Atlantic Fisheries Commission (NEAFC) have recognised that deep-water species have a diverse range of life histories and have requested ICES to rank species in terms of vulnerability to fishing as determined from available information on life history strategies.
 
Catch versus landings - the discard problem
At any given depth on the upper to mid continental slope of the Rockall Trough a series of bottom trawls might yield about 40 to 50 different fish species but relatively few of these, including many of the exploited species described above, will account for most of the biomass. Other prominent species are the smoothheads, (Alepocephalus bairdii and A. rostratus), some of the discarded sharks and chimaerids. The smoothheads have a very watery flesh and attempts to market them have generally been unsuccessful, although in recent years Spain has been reporting significant landings from the Hatton Bank. In some deeper hauls in the Rockall Trough they can comprise up to about 50% or more of the total catch. In southern areas the deeper living A. bairdii can comprise 75% of the catch and the mid-slope A. rostratus can also be a significant discard.
 
The remainder of the deep-water catch comprises fishes belonging to several families representing a wide variety of life history characteristics. Many have body shapes that cause them to be caught at a smaller size by trawls with the mesh sizes commonly used in shallow-water fisheries. They frequently lack mucus, have large deciduous scales and this, together with the effects of depth-related pressure and temperature change, means that virtually all fishes retained by a trawl and brought to the surface will be dead. Thus after the fishes to be landed have been selected the remainder of the catch will be discarded as dead fish. The proportion of discards to landings is dependent on depth but in the mixed fishery it can amount to at least 50% of the total catch.
 
Fishes entering a trawl and subsequently escaping through the meshes are also likely to sustain considerable external damage and as a consequence suffer a high mortality. These have sometimes been referred to as 'no-catch discards' and although they may comprise a smaller proportion of the total biomass, numerically they could represent a significant part of the juvenile stock of exploited species and an important component of the food chain. The fragility of the skin probably means that selectivity devices such as square mesh panels and sorting grids may be of little value for the conservation of deep-water fishes. It has been suggested that longlining might be a more selective method of exploiting deep-water fishes, but many of the target species such as roundnose grenadier and orange roughy do not take baited hooks. Sharks comprise a high proportion of deep-water longline catches and many are species that are currently discarded.
 
Ecosystem effects of fishing activity
The ICES Working Group on the Ecosystem Effects of Fishing Activities (WGECO) has commented that the effects of fishing gears on habitats are generally the most long-lasting and irreversible of all effects of fishing on ecosystems. They recognise the emphasis given by ICES Study Group on the Biology and Assessment of Deep-sea Fishery Resources (SGDEEP) to the importance of understanding the life history characteristics of many deep-water species, which indicate that those species can sustain only very low exploitation rates. However, WGECO also stressed its concern about the effect of fishing on the physical and biogenic features of the deep-water habitats. Although the current effort by bottom trawls in deep water is less than on the shelf the scale of the impact is likely to be greater because the fishing activity is constrained by relatively narrow continental margins with the added dimension of a wide depth range. It is also likely that the deep-water habitats will be more vulnerable to the effects of disturbance. WGECO concludes by urging "ICES to attach priority in its advice, and management agencies in their regulations, to ensuring that these new and expanding fisheries are kept sustainable both with regard to the mortalities inflicted on all species (target and non-target) and effects on habitats".
 
In recent years there has been an increasing awareness of the effects of deep-water fishing on habitats and this is particularly true of habitats where the damage to hard bottom fauna, including corals, is readily observable. Some countries such as Australia, New Zealand and Norway, who have exclusive control of their EEZ have taken action to protect such sensitive areas such as seamounts and coral reefs. There are plans to protect sensitive areas in European Union waters, such as the Darwin Mounds close to the Wyville Thomson Ridge. There is currently no legal framework for creating Marine Protected Areas or similar regulated areas in international waters.
 
Most deep-water bottom trawling and a considerable proportion of static gear fishing occurs in areas of soft bottom sediments. The effect of fishing activity on these areas has been largely ignored although photographic evidence at depths between 700 and 1300 m in the Rockall Trough shows the presence of trawl marks on the seabed in 2 to 12% of all photographs. All the SAMS time-series of bottom trawls in the Rockall Trough were carried out in an area known as the Hebridean Terrace that has been subjected to heavy fishing effort in recent years. This is an area of soft sediments at depths greater than 600 m and while fishing between 1975 and 1992 no research trawls were damaged by seabed obstructions. On returning to the area in 1999 and using the same trawl that was used throughout the 1980s, a small shrimp trawl with no rock-hopper gear, the nets were severely damaged by large boulders. These boulders had little or no encrusting organisms and were most probably glacial erratics, long buried in the sediment and now brought to the surface by the rock-hopper footropes of commercial bottom trawls. This is a clear indication of the disturbance caused to soft sediments by trawling. Apart from the physical impact there is also a need to consider the effect of the high level of discards into the ecosystem. In a study in Australian waters an increase in the crab population following exploitation was attributed to the input of discards.
 
The status of the stocks
Although some of the deep-water fisheries in the North East Atlantic had been established for many decades, it was the French bottom-trawl fishery in the Rockall Trough that first attracted the attention of other nations and the European Commission (EC). In 1993 the EC convened a meeting of experts to advise the Council of Fisheries Ministers "--on the state of knowledge on these fisheries, particularly aimed at the possibility of implementing a management system ---". At the same time ICES asked two of its Working Groups to comment on the status of these fisheries and in 1994 convened the SGDEEP which has met in plenary every second year. Also in 1994 an Advanced Research Workshop sponsored by NATO and the European Commission examined the status of Atlantic deep-water fisheries and produced a series of recommendations which were, in part, based on experiences in other areas. All of these studies and reports highlighted the special features that were considered to make these fisheries highly susceptible to over-exploitation. They highlighted the problems of assessing the state of the stocks in a situation where there was limited data on landings at the species level and where biological information was sparse. The advice in these early years was always that a cautious approach should be adopted to the exploitation and that fishing effort should be kept at a low level until sufficient information was gathered from existing fisheries to enable scientifically-based management decisions.
 
In 1995 the UK House of Lords Select Committee on Fish Stock Conservation and Management collected evidence and gave opinions on deep-water fishing. One of the conclusions of their report was that "Ideally we would recommend an interim suspension of all deep-sea fishing, but we recognise that it could not be enforced at present. We accordingly recommend that research should be carried out as a matter of urgency into the likely sustainable catch levels, technical measures to minimise damage to non-target and juvenile deep-water fish and the importance of deep-water fish in the food chains to other marine organisms. International collaboration should be sought on research (which is highly expensive in deep-water fisheries), suitable management strategies, including the possibility of licensing schemes, and enforcement". Later that year the EC funded a major multinational shared cost, research project entitled "Developing deep-water fisheries: data for their assessment and for understanding their interaction with and impact on a fragile environment (EC FAIR 65/655), which was co-ordinated by SAMS. Although the study area extended from Iceland to Greece a significant part of the work was carried out in the Rockall Trough. Scotland and France monitored and sampled the landings and sent observers on commercial vessels to estimate discarding. Germany analysed and archived the historical survey data that pre-dates the fishery. All partners were involved in biological studies with particular emphasis on age estimation and reproduction. At the same time the Nordic countries were supporting a joint Norwegian, Faroese and Icelandic study on blue ling, ling and tusk. Following the completion of these projects there has been a decline in research and monitoring of deep-water fisheries. Another source of funding for monitoring and research was the EC Study Contracts in support of the Common Fisheries Policy. These have supported the working up of historical data, preliminary studies on assessment and multinational studies on species such as black scabbardfish and deep-water sharks. The management of most of these funds by the EC was phased out in 2001 and they were transferred to national governments who are required to collect and manage data needed to conduct the Common Fisheres Policy. Research on deep-water fisheries, that requires multinational collaboration, is unlikely to be high on the priority lists of national governments. Thus, the research that has made such a significant contribution to the work of the ICES SGDEEP (see below) is not being maintained.
 
ICES routinely uses age-based methods to assess the status of the fish stocks in its area. Such data are almost entirely lacking for the deep-water species. At the start of the fishery the reported landings were unreliable and were often in grouped categories. The effort data were also unreliable because the technology of deep-water fishing was steadily improving and the most productive grounds were being discovered and exploited. It was not until 1998 that SGDEEP made the first assessments, based mainly on a time series of catch per unit of effort (CPUE) of a part of the French bottom trawling fleet that had not changed much since the start of the fishery. It was acknowledged that there were many assumptions, such as arbitrary definitions of stock boundaries, lack of information on discarding and under-reporting of landings from international waters. However, these assessments, taken together with the obvious downward trend in CPUE, led SGDEEP to conclude that the stocks were outside safe biological limits. The report was evaluated by the ICES Advisory Committee on Fisheries Management (ACFM) in May 1998 and the advice given was as follows. "Most deep-water species are, at present, considered to be harvested outside safe biological limits as embodied in the precautionary approach. ICES recommends immediate reduction in fisheries that cannot be shown to be sustainable. All remaining fishing activity should be conducted in the context of effective management which emphasizes documentation of fishing activity, and which can react appropriately to biological characteristics of the populations.Deep-water species are inherently vulnerable. Localized populations can be quickly depleted by fisheries, even within a single season. Some populations (e.g. red sea bream, blue ling and orange roughy) are known to have collapsed in some areas, and there is insufficient data on other stocks to determine what level of fishing is sustainable."

NEAFC were sufficiently concerned about the status of the stocks that in June 1999 the European Commission, on their behalf, hosted and chaired an Open Hearing on Deep-Sea Species. After hearing reports on the status of the stocks and discussing some of the monitoring issues, the group noted that "given the ICES advice on the urgent need to reduce fishing mortality on most stocks, time does not appear to favour delaying management action". After considering the applicability of various possible management options it was concluded that probably a combination of effort limitation and total allowable catches (TACs) would be the most effective management tools.
 
At the 18th Annual Meeting of NEAFC in November 1999 the EC made a proposal concerning deep-water species. This noted the ICES advice on the poor state of the stocks and drew attention to the fact that the NEAFC control and enforcement scheme contained provisions to authorise vessels to fish, record catches and report these catches to NEAFC. They recommended that contracting parties should review their existing management and take action to ensure that there was no increase in fishing effort. They also recommended that information on catches and other relevant data be communicated to ICES. Deep-water species were defined as blue ling, ling, tusk, roundnose grenadier, black scabbardfish and argentine. However, it appears that because this proposal was not circulated in advance, no final decision was made at the NEAFC meeting. In the press release following the meeting it was noted that several proposals for management had been discussed and that these would be given priority during the next working year of NEAFC.
 
The SGDEEP met again in February 2000 and updated the assessments based on the CPUE time-series and came to similar conclusions as in 1998, namely that the stocks were outside safe biological limits in relation to the proposed reference points. At their May 2000 meeting the ACFM gave an overall precautionary advice and for the first time made specific recommendations for selected species. For blue ling they recommended "that there be no directed fisheries for this stock and measures be implemented to reduce/minimise catches of this stock in mixed fisheries". The directed fisheries for blue ling are on spawning aggregations. For roundnose grenadier ICES recognised that the stocks were reaching a critical state and recommended an immediate reduction in fishing effort by 50% for ICES Sub-areas VI and VII and Division Vb combined. A similar recommendation was made for black scabbardfish. For the other deep-water fish species they recommended that fisheries be permitted only when they expand very slowly, and are accompanied by programs to collect data that allow evaluation of stock status. ACFM also had to address two requests for advice, one from NEAFC and the other from the EC.
 
The requests to ICES from NEAFC were (1) what further information is needed to provide a basis for comprehensive management measures for appropriate stock units (which might include conventional catch, effort and gear restrictions) to conserve deep water species? and (2) what interim management measures could be introduced based on existing biological information? In answer to request 1, ACFM highlighted the concerns that the true scale of the fishery in international waters was not being reported and that some of the time-series of CPUE were not being updated. They also drew attention to probable ecosystem effects resulting from the high levels of discards and the mortality of escapees. They recognised that there was an urgent need for research on stock discrimination. (It is opportune at this point to mention that another ICES Working Group on the Application of Genetics on Fisheries and Aquaculture recommended that high priority be given to research on deep-water fish species.) In their answer to request 2, ACFM considered that a "stringent reduction of fishing effort" might be a possible interim measure. Since many of the fisheries are mixed fisheries, they considered that a TAC regulation was "not very likely to be effective". They discounted a change to more selective longlining and were doubtful of the efficacy of closed areas both for biological and enforcement reasons. In 1993 the EC had considered licensing as a possible conservation measure and this was again considered by ACFM who phrased it as follows. "An immediate step towards effectively controlling the fishery could be the strict regulation of the numbers of boats, trawl-hours or numbers of hooks per day etc. Because, there is virtually no overlap with conventional shelf species there would be no conflict with any existing management measures. However, this can hardly be seen as an interim measure but rather as a medium term-measure."
 
The EC requested ICES to provide advice on possible management measures to be applied to deep-water species as indicated in the Memorandum of Understanding. In particular, ICES was requested to indicate the probable utility of application of (1) TACs, (2) geographical and/or temporal closures, (3) other technical measures including appropriate mesh size, hook size and gear structure and (4) effort limitation. In addition, ICES was requested to comment on environmental impacts created as a result of fishing for deep-water species and to advise on possibilities for reducing or eliminating such effects. At their May 2000 meeting, ACFM decided to set an ad hoc group from among their number to consider these requests and in particular how deep-water fisheries were managed on a global scale. The advice to the EC was formulated at the November meeting of ACFM and consists of a series of 13 points, many of which are further elaborated on in an annex. In the background to the reply they highlight the fact that there have been numerous warnings and recommendations to adopt the precautionary approach and that these have gone unheeded. As a result most of the stocks are already over-exploited and that it is too late to adopt the precautionary approach. Finally ACFM concludes that "the immediate threat is that stocks may be fished down before the status of the stocks can be assessed. Compared to the economic damage of fishing down resources, a zero TAC for a few years might be a tolerable measure to prevent damage to the most sensitive habitats." ACFM recognises that it is the deep-sea ecosystem including the fish stocks that is sensitive and requires protection. They considered that no single management measure was likely to be effective. Closed areas were considered only to be a long-term measure and much more research was necessary to assess the necessary parameters. Gear limitation and especially a trawl ban for selected species/areas was considered to be a useful measure. It could also be used as a measure to prevent the fishery moving into new areas. ACFM recognise that drastic reductions in catches are unavoidable and suggest setting TACs on the basis of 1-2 % of virgin biomass per year. However, they recognise that some species may be less vulnerable and could withstand a higher rate of exploitation. Many of Europe's deep-water fisheries are mixed fisheries and it was recognised that using TACs as the primary management tool would be difficult. The low levels of TAC required could render the fishery unviable for fleets solely dependent on the deep-water resource and varying quotas for different species could lead to more incentive to discard, high-grade or misreport. They conclude that "implementation of TACs for deep-water stocks, not accompanied by other measures, probably would not prevent deep-sea ecosystems suffering adverse impacts." ACFM states that a general licensing system should be implemented by the EC. This should be combined with TACs, seasonal and area closures and possibly with gear limitation. The remaining points are all concerned with the need for strict and effective enforcement, comprehensive data collection, surveys and research, support for studies on ecosystem effects and maintaining a dialogue between managers, the industry and scientists.
 
At the 19th Annual meeting of NEAFC in 2000 it was reported that ICES did not consider the establishment of TACs, area closures and gear restrictions as effective management measures. Experience from other areas had shown that no management measure implemented alone could provide an effective protection of deep-sea stocks. The EU suggested that it was important that NEAFC should take responsibility and that it should open up a discussion on different regulatory measures. The problem of reporting catches was raised and it was pointed out that all contracting parties to NEAFC had an obligation to report all catches to the secretariat on a monthly basis. In the press release following the meeting it was stated that NEAFC had agreed to improve its reporting procedures for better monitoring of deep-water species.
 
Prior to the 19th annual meeting of NEAFC a group of non-governmental organisations (NGOs) led by Seas-at-Risk wrote to NEAFC urging them to apply the precautionary principle and take measures to reduce effort and regulate deep-water fisheries. Although the letter was circulated to the heads of delegations it was not tabled as it was not submitted by a contracting party.
 
In July 2000 the EC issued a press release expressing concern about the state of deep-water fish stocks and stating that there was a to act quickly to protect fragile deep-water fish species before irreversible damage is caused by unregulated fisheries. The EC stated that it was considering proposals to set TACs with effect from 2001, in the context of the Common Fisheries Policy. They stated that "the need for equitable allocations of resources between Member States would guide the setting of quotas." The EC also recognised that many of these stocks extended beyond Community waters and that cooperation with other parties would be necessary. This press release came after the ICES ACFM advice to NEAFC that questioned the value of TACs for regulating the mixed deep-water fisheries was in the public domain. Seas-at-Risk then began to question the EC on their reasons for proposing management by TAC alone, apparently in contradiction to the ACFM advice to NEAFC. The EC gave various reasons for its stance, not least that it was awaiting the reply from ACFM to its own request for advice. On 13th November Seas-at-Risk wrote to the EC welcoming the fact that management measures were being considered and asking why the other ICES ACFM recommendations were not being implemented. In reply the EC agreed that it was not implying that TACs should be or would necessarily be the primary management instrument but were definitely a step in the right direction. To implement measures other than TACs would be unrealistic within the available timescale because of the "institutional requirements to be observed".
 
On 1 December 2000 the EC published its proposals for the regulation of fisheries for 2001 which included for the first time TACs for black scabbardfish, greater silver smelt, roundnose grenadier, orange roughy, blue ling and a few other species. The proposed quotas were apparently to effect a 20% reduction in landings.
In proposing quotas for deep-water species applicable to EU member countries, it was implicit that they applied to all ICES Sub-areas irrespective of whether the catch was taken in EU or international waters. For example, for roundnose grenadier the applicable zone was "Community waters and waters not under the sovereignty or jurisdiction of third countries in ICES Sub-areas I through XIV." Therefore, all EU member states would be limited to their allocated quota irrespective of where it was caught within the ICES area. Non EU countries however would be free of any controls over their deep-water fishing in international waters. It is this situation that is causing the present controversy over the haddock on the Rockall plateau, a large part of which is now in international waters. Fishing for haddock by EU countries is still controlled under existing quotas for ICES Sub-area VI but some non- EU vessels can fish unhindered in the international parts of Sub-area VI. A failure to agree on international quotas is also threatening blue whiting stocks in the ICES area.
 
For all these species except for the greater silver smelt, France was allocated a significant part of the proposed quota that reflected this country's dominance in deep-water fishing. During the week before the December 2000 meeting of the Fisheries Ministers it was evident from reports in both the fishing press and national press that the UK and Ireland were going to oppose the introduction of TACs which would only allocate them a very small quota within their territorial areas. At the meeting the Fisheries Ministers deferred the setting of TACs for one year. The need to take measures "to protect these vulnerable stocks" was recognised but the postponement was decided upon "so as to have more time to collect more information and scientific advice. However, in order to prevent the risk of encouraging a rush to fish these stocks to set historical track records, the Council decided that this year's and next years catches would not be taken into account for the setting of such TACs."
 
At the 19th Annual Meeting of NEAFC the EC noted that two statements on scientific advice from ACFM on some of deep-water species were inconsistent and contradictory.

These were "ICES recommends immediate reduction in these fisheries unless they can be shown to be sustainable" and "consistent with a precautionary approach fishing should not be allowed to expand faster than the acquisition of information necessary to provide a basis for sustainable exploitation". This latter point and others were elaborated in an Annex to the NEAFC request for advice from ICES in 2001. The request to ICES included the following (b) clarify the statements on advice for stocks where there is little biological information. In reply to (b) ICES ACFM explained that the first statement applied to those fisheries that are already considered to be harvested outside safe biological limits (Category 2). The second statement referred to new fisheries that may develop on virgin stocks or where only a limited part of the stock has been exploited (Category 1). Where the state of a stock is unknown, such as in the case of the deep-water sharks, then Category 1 advice applied.
 
At the time of writing (October 2001) the EC are reviewing the current situation with a view to making new management proposals to place before the Fisheries Ministers in December. It is clear that TACs together with other measures are likely to be a key part of their strategy.
 
Despite the statement by the EC that any fishing in 2000 or 2001 will not count towards any future TAC based on track record, it is clear that the deep-water stocks have come under even greater pressure both in the EU sector and in international waters. Ireland is undergoing a major fleet renewal programme and many of the vessels, both trawlers and longliners, have been fishing in deep-water. Although the Scottish industry has indicated that there will be no new entrants into the fishery it appears that effort has increased. Clearly there are political initiatives to gain a better deal for the UK and Irish industry. This prompted the Scottish Executive to issue a press release following the December 2000 meeting of European Fisheries Ministers which stated that "the executive achieved most of its main negotiating priorities in the key stocks for the Scottish fishing industry, including:
 
  • Secured a deferral of proposals to set TACs for deep-water species for the first time"

The press release ends with the sentence "Generally speaking we have secured the best deal for the industry in the light of very negative scientific advice and having regard to the sustainability of the stocks".
 
If there is a very real concern for the sustainability of the resource, and the council of fisheries ministers could not agree a modest first step towards a management of the resource then the precautionary approach should have been adopted and the fishery should have been closed. Even if the EC had succeeding in initiating control measures their value would have been diminished by a lack of action on the part of NEAFC in controlling the fishery in international waters. It is perhaps not much of a consolation, but at least in the Rockall Trough we know a lot about the ecosystem that is being destroyed. From the small amount of available knowledge, the Hatton Bank is a different ecosystem and we will never know what we are in the process of destroying. On a global scale most deep-water fisheries appear to be over-exploited and new fisheries very soon reach this state.
 
TACs and the accompanying technical measures that have so obviously failed to conserve the mixed trawl fisheries of the shelf are likely to be even more inappropriate in deep-water. Most new deep-water fisheries start off with high catch rates but as the accumulated biomass of older fish is removed catch rates decrease. To compensate for this the effort increases and the fragile deep-water ecosystem, confined as it is to relatively small areas, is put under even greater stress. If these fish are to be exploited, and some would argue that they should not be exploited, then only the sort of strict control that would come from a licensing system, as first suggested by the EC in 1993, would seem to be appropriate. The fleet would be relatively small and, if there was a will, regulations such as those relating to gear type, fishing days, areas or seasonal closures etc. could all be tailored to the changing circumstances of the fishery and effectively enforced. To solve the problem of data collection and monitoring the carrying of a scientific observer could be a condition of the license. This would help to overcome the very serious decline in monitoring and research that has occurred in recent years. There is general agreement amongst scientists, the fishing industry and the politicians that the deep-water stocks are seriously overexploited but political imperatives dictate that uncertainties and inconsistencies in the scientific assessment and advice are used to postpone the urgent action that is required.