This section considers the fish stocks that are not comprised of highly migratory species and occur exclusively in the high seas, i.e. in waters beyond the areas of national jurisdiction, as referred to as high seas fish stocks in section 2.1. Most of the currently known high seas stocks are comprised of deep-water species, but several others may exist for pelagic species. Most of the information from this section has been adapted from relevant chapters in FAO (2005a), and advice and information from the Advisory Committee on Fisheries Management of the International Council for the Exploration of the Sea, and other Regional Fisheries Organizations. Most fisheries for these deep-water species are relatively recent and the development of a majority of them has outpaced the ability to provide scientific information and to implement effective management. There is no rigorous definition of a deep-water fishery, but in general, they occur in depths of at least 500 m, and they are commonly thought of as occurring at depths of 1 000 m or more. Current technology allows fishing to depths of somewhat deeper than 2 000 m. Also, relatively little is known about many of the species and most of the fisheries.
Deep-water species live at depths where there is virtually no light or primary productivity. Most nutrients and production is retained in surface waters above the permanent thermocline. Although many species migrate vertically to feed at night, those that do not, depend (directly or indirectly) on a rain of dead plants and animals from surface waters for food. Some species only inhabit deep waters in their adult stage, and may be exploited during both their shallow and deep-water phases, complicating the interpretation of whether such catches should be defined as deep water or not. Deep-water species have diverse life history strategies, although little is known about their stock structure, migrations, and general biology and ecology. Since they live in low productivity environments, they are expected to be slow growing and mature late in life, which has been confirmed for some important species (e.g. orange roughy which do not mature until age 20 or older, and can live to more than 100 years old).
In general, deep-water species are believed to be particularly vulnerable to overexploitation and depletion (at least localized) because of their slow growth and late maturity. Some species form dense aggregations which are accessible to fisheries which have developed the capability to fish in deep water over the last few decades. Deepwater fisheries often exploit aggregations associated with topographic features like seamounts, ocean ridges and canyons. However, fisheries associated with particular topographic features usually do not persist, presumably because of localized depletion of the fishery resource.
While most fish families of deep-water species occur worldwide, the existence of deep-water basins bounded by the continents and oceanic ridges has resulted in regional differences. Another important feature of deep-water fishes is that new discoveries continue, e.g. the relatively recent discovery of a 4.5-m, 750-kg megamouth shark (Megachasma pelagios) in Hawaii in 1976 (Taylor, Compagno and Struhsaker, 1983) and a six-gilled stingray (Hexatrygon bickelli) discovered in Port Elizabeth (Heemstra and Smith, 1980), both representing new taxonomic families. Some of the species that are now fished in deep water were taken at shallower depths in the past, but fishing has extended into deeper waters as deep-water fishing technology has improved and stocks in shallower areas have been fished down.
Important species that form deep-water aggregations include orange roughy (Hoplostethus atlanticus) and the oreos (Allocyttus spp., Neocyttus spp. Pseudocyttus spp., etc), which are often fished together, alfonsinos (Beryx spp.), Patagonian toothfish (Dissostichus eleginoides) in Southern Ocean fisheries, armourhead (Pseudopentaceros spp.) and various species of Scorpaenidae found on both coasts of North America.
Major fisheries for deep-water species (particularly orange roughy) first developed off New Zealand and Australia in the late-1970s and 1980s, and they have developed rapidly elsewhere since 1990. The development of deep-water fisheries has been prompted by three related factors: (1) depletion of species and stocks in shallower water (and associated regulations that restrict fishing in shallower water); (2) the high value of some deep-water species, and (3) advances in technology that make fishing in deep water possible and commercially viable. On the high seas, management of deep-water fisheries has lagged behind the development of the fisheries, even where there are Regional Fishery Bodies with a purview over the species. As noted above, the International Council for the Exploration of the Sea (ICES, 2005) has recently (October 2005) provided advice for the management of deep-water fisheries under purview of the Northeast Atlantic Fisheries Commission. The ICES evaluation is probably broadly applicable; therefore it is reproduced below (adapted for a more general context):
"Most exploited deep-water species are considered to be harvested unsustainably; however, it is currently not possible to provide advice for specific fisheries for deep-sea species. Consistent with a precautionary approach, [...] immediate reduction in established deepsea fisheries [should occur] unless they can be shown to be sustainable. Measures should also be implemented to reduce exploitation of deep-sea species by fisheries primarily targeting shelf species (hake, anglerfish, and megrim). New deep-sea fisheries or expansion of existing fisheries into new fishing areas should not be permitted unless the expansion is very cautious, and is accompanied by programmes to collect data which allow evaluation of stock status as the basis for determining sustainable exploitation levels.
[...]
For several species there is a concern that catch rates can only be maintained by sequential depletion of relatively isolated concentrations/sub-units of a stock. The smallest unit for which data are reported at present [...] may not be appropriate for monitoring or managing this type of fishing activity. The depth range within an area may be very wide, and the sizes of the areas are very different."
The orange roughy (Hoplostethus atlanticus) (Figure 48), a member of the Trachichthyidae family, is found in the North and South Atlantic, in the Southern Indian Ocean, the Tasman Sea, around New Zealand, and in the South Pacific. They are found within EEZs, some are straddling stocks, while others are entirely on the high seas. The species is mainly caught at depths over 800 m by fisheries on fish aggregations associated with seamounts. The proportion of the resource outside of the fished area is not known. Fisheries appear to have sequentially depleted fish aggregations that may or may not correspond to distinct stock units. Recruitment appears to be irregular and the time lag between spawning and recruitment to the spawning aggregations that are the targets of most fisheries is so long (about 20 years), that even in the presence of long time series of data it will be very difficult to assess the influence of fisheries on recruitment. The theory upon which the concept of a sustainable yield is based implies that there should be a compensatory response in recruitment as a result of fishing, but there is no evidence so far that this is the case for orange roughy. Sustainable exploitation rates are thus bound to be very low, and may be in the order of 5 percent of biomass.
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FIGURE 48
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The orange roughy fishery developed mostly in the Pacific Ocean (Figure 49) with smaller catches in the Atlantic and Indian Oceans. Catches peaked in the early-1990s at 90 000 tonnes, but they have declined since in all oceans to less than 26 000 tonnes in 2004.
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FIGURE 49
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The oreo dories (Allocyttus spp., Neocyttus spp. and Pseudocyttus spp.), members of the Oreostomadidae family occur close to the sea bed in deep waters. They form large aggregations over rough grounds near seamounts and canyons in the Antarctic, Atlantic, Indian and Pacific Oceans and world catches are reported primarily off South Africa, New Zealand and southern Australia. As for orange roughy, the proportion of the resource outside of the fished area is not known and fisheries appear to have sequentially depleted fish aggregations that may or may not correspond to distinct stock units. Recruitment appears at best irregular, and like orange roughy, there is no evidence of a compensatory response in recruitment. Estimates from New Zealand indicates Maximum Sustainable Yield (MSY) to be of the order of 1.6 percent of initial biomass if the population is not to be reduced by more than 80 percent with a 20 percent probability (FAO, 2005a). Some oreo dories fisheries have been managed on the basis of management units combining species, which means that species are not individually protected.
Catches of oreo dories are overwhelmingly from the Pacific Ocean with comparatively minuscule catches reported from the Atlantic and Indian Oceans in recent years (Figure 50). Catches have been relatively stable around 20 000 tonnes since the mid-1980s, but after declining to around 15 000 tonnes in 2003 they increased again to 20 000 tonnes in 2004.
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FIGURE 50
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Alfonsino (Beryx splendens), belong to the Bericidae family and are found in the Atlantic, Indian, western and central Pacific Oceans though they are generally not present in the Northeast Pacific. They inhabit the outer shelf (180 m) and slope to at least 1 300 m depth, and they may make vertical migrations at night. Beryx splendens are caught in mid-water trawls over shallower seamounts, underwater ridges and on the slope edges between 300 and 500 m. Genetic studies suggests that alfonsinos may have an ocean-wide population structure, but the relationship between the various fish aggregations is not known. If the hypothesis of an oceanwide population structure proves true, it could be that individual aggregations cannot be exploited sustainably if most recruitment originates irregularly from one or a few areas (which can differ from year to year). Furthermore, if fishing depletes an aggregation that was destined to supply recruits over a large geo-graphic area, the adverse affect on the broader population may be much greater than a localized depletion. Some aggregations may occur in areas that are rarely suitable for recruits to settle; thus fishing on these aggregations will not be sustainable. Thus, it is important to better understand stock structure and geographic pattern of successful spawning and settlement of recruits. Indeed, such information is generally needed for deep-water species that are fished in seemingly isolated aggregations. However, unlike many deep-water species, alfonsinos growth and mortality rates are relatively high (natural mortality is estimated to be around 0.23), which means that the species should be better able to sustain a fishery than other less productive deep-water species.
Catches of alfonsino have occurred in the Atlantic, Indian and Pacific Oceans since the late-1970s. Catches in the Pacific Ocean have increased steeply from 1999 to 2003. Overall, catches remained less than 4 000 tonnes until 1995, but have increased to 15 000 tonnes in 2003 before declining to 7 000 tonnes in 2004 (Figure 51).
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FIGURE 51
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Toothfishes (Dissostichus spp.), belong to the Notothenidae family and have a circumpolar distribution within Antarctic and Southern Ocean waters. Patagonian toothfish (D. eleginoides) (Figure 52) are found asymmetrically around southern South America and Antarctic toothfish (D. mawsoni) occurs in high latitudes, in the Pacific region. The two species overlap between 60 °S and 65 °S and both occur to depths of 3 000 m. The northern limit for most populations of Patagonian toothfish is 45 °S, except along the Chilean and Argentinian coasts where they may extend north in deeper cold water. Significant populations of Patagonian toothfish exist in the waters of, and adjacent to, the various sub-Antarctic islands and in the waters of Chile, Argentina, Uruguay and Peru.
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FIGURE 52
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The problem of illegal, unreported and unregulated fishing (IUU), while considerably reduced during the 2003 - 2004 season (6 342 tonnes estimated to have been caught in FAO statistical area 41 - Southwest Atlantic - and 3 701 tonnes in area 87 - Southeast Pacific), remains a major concern. Further, catches of toothfish reported as taken in the Indian Ocean in particular, i.e. outside of the CCAMLR management area, are believed to have been harvested from stocks within the management area. Past declines in toothfish stocks targeted by IUU fishing fleets have been fast and significant. For example, resources of toothfish in Prince Edward Islands (South Africa) have been reduced to only a few percent of the pre-exploitation biomass.
Catches of toothfishes increased steeply from less than 2 000 tonnes in 1983 to 40 000 tonnes in 1992, and catches have been fluctuating around that value since (Figure 53), but declining to 27 000 tonnes in 2004. Toothfishes are caught in the Atlantic, Indian, Pacific and Southern Oceans, with the Atlantic and Southern Oceans making the largest contributions.
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FIGURE 53
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Armourheads (Pseudopentaceros spp.) belong to the Pentacerotidae family. There are at least three known species all associated with seamounts: the pelagic armourhead (P. richardsoni) in the Southeast Atlantic, western Indian Ocean and South Pacific; and the slender armourhead (P. wheeleri) and the longfin armourhead (P. pectoralis) in the North Pacific, (P. pectoralis was commonly misidentified as P. richardsoni in the North Pacific). The fishery for armourhead in the North Pacific illustrates the potential evolution of seamount fisheries. Japanese and former USSR vessels began trawling in the Emperor Seamount chain and the northern Hawaiian Ridge areas in 1969. The total catch for the former USSR vessels is not known but is estimated at over 133 400 tonnes in the period 1969 - 1977. Between 1969 and 1977, the Japanese fleet sent two to five trawlers a year to this area and averaged catches of 22 800 - 35 100 tonnes a year. Between 1977 and 1982 catches fell to 5 800 - 9 900 tonnes. Ninety percent of the catch was described as being pelagic armourhead (P. richardsoni), but was most likely longfin armourhead (P. pectoralis). This once dominant armourhead have later been replaced by alfonsino (Beryx splendens), although the alfonsinos have never been as abundant as armourhead was. There is no evidence that either of the fish stocks will recover enough to allow commercially viable fisheries in the near future.
The above catches of armourheads in the 1960 - 1970s in the North Pacific do not appear to have been reported to FAO as the maximum reported is 435 tonnes in 1993.
Hoki (Macruronus novaezelandiae) is a benthopelagic Merlucciidae, that usually lives near the bottom in the Southwest Pacific Ocean, but the species also form mid-water aggregations for spawning. Large adult fish generally occur deeper than 400 m, while juveniles may be found in shallower water. Mid-water trawl fisheries target aggregations near canyons that are often close to the coast in areas of narrow continental shelves. While fisheries for hoki are generally considered deep-water fisheries, most of the catch is from EEZs. The significance of hoki as a high seas fish stock is probably minor.
The stock structure is uncertain and it is not always clear that TACs set for specific geographic areas correspond to distinct biological units. Management experience in at least some jurisdictions indicates that fisheries exploiting hoki can be sustainably managed.
The hoki fishery occurs almost entirely in the Pacific Ocean with small catches reported from the Indian Ocean (Figure 54). Catches have increased steeply from around 50 000 tonnes in 1985 to 230 000 tonnes in 1988. Catches have been fluctuating in excess of 200 000 tonnes since, except in 2004 when they declined to 160 000 tonnes.
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FIGURE 54
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In addition to the species described above, a number of deep-water species have been treated under section 4.2.2 on straddling stocks in the Northeast Atlantic. Some of them potentially make up also high seas fish stocks.
A further suite of deep water, or at least slope species, have been the target of fisheries in many tropical regions. These can be targeted by small-scale deep-water fisheries usually along the shelf break and shelf slope wherever the continental shelf is relatively narrow and the fishing grounds are accessible to fishermen using small fishing boats. The principle species consist of members of the Lutjanidae (snappers), Serranidae (seabasses; groupers and fairy basslets), and Carangidae (jacks and pompanos) families and most importantly include the eteline snappers (e.g. Etelis coruscans and E. carbunculus) and the jobfishes (e.g. Pristomopoides filamemtosus, P. typus and P. multidens). These fisheries are particularly important to small island States that often have few other demersal fish resources though they are also widely found along the continental margins in tropical and sub-tropical areas. However, they are probably not significant as high seas fish stocks.
Knowledge of the biology, life cycle, population dynamics, and stock structure of high seas stocks remains limited. However, based on available information on slow growth rates, sporadic recruitment, and the rapid depletion of fish aggregations, orange roughy and oreo dories should be regarded as overexploited or depleted in all areas where fishing has developed. Alfonsinos may be able to sustain slightly higher exploitation rates but lack of knowledge on other parameters and biological characteristics calls for caution and exploited stocks should be considered fully if not overexploited. The toothfishes and hoki are fully exploited or overexploited.
