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High seas resources

High seas resources are those resources which exist beyond national jurisdiction. They include species which are distributed essentially beyond 200 miles although these species may spend part of their life cycle in the coastal areas for reproduction or feeding. They also include portions of EEZ stocks which extend beyond 200 miles (referred to as straddling stocks) and species which undertake extensive migrations between the EEZs and high seas, across oceans and/or across many EEZs. The extension of their distribution and the mobility of the fleets exploiting them have a direct bearing on the type of management arrangement which will be adequate to ensure sustainability (e.g., local, regional, ocean-wide or even global).

In biological terms and depending on the closeness of their relationships with the bottom, high seas resources can be neritic or oceanic with a range of intermediate categories (Figs. 1 and 2). High seas neritic resources have their life cycle and distribution largely confined to the continental shelf and upper slope despite the fact that they extend to and may be caught in the high seas. Neritic high seas resources will be found where a 200-mile zone has not yet been claimed (e.g., off China or in the Mediterranean Sea) or where continental shelves extend beyond 200 miles (as on the North Pacific shelf or on the Flemish Cap in the Northwest Atlantic). Neritic resources can be demersal (i.e., having strong relations with and dependence on the bottom) or pelagic (i.e., living in the upper layers of the ocean and having little contact with the bottom). Demersal high seas resources include mostly straddling stocks and a few strictly high seas stocks on seamounts.

Figure 1

Figure 1 Illustration of the terminology used in the text

Figure 2

Figure 2 Types of high seas resources (from a biological point of view)

High seas oceanic resources are distributed and caught mainly beyond the outer shelf and/or migrate extensively across the open ocean even though they may pass a key stage of their life cycle close inshore and yield large catches inside the EEZs. These resources are essentially pelagic for most of their life cycle but some demersal resources exist on seamounts. A glance at the FAO SPECIESDAB (Global Species Database for Fishery Purposes) indicates that close to 400 species can be considered purely or significantly oceanic (Garcia and Majkowski, 1992). There are about 50 species of cephalopods, 40 species of sharks, 60 species of marine mammals and 230 fish species. The biological information available on these species and their present potential and status is generally poor, except perhaps for some whales and large tunas and their management and conservation are a matter of concern. Most oceanic high seas resources are dispersed, difficult to harvest economically and extremely difficult to study with the required accuracy. They are usually exploited by long-range fleets operating in areas where target species concentrate for feeding or reproduction. Average densities available in the high seas are much lower than in upwelling areas and coastal zones. Biomass of plankton, mesopelagic fish, krill and small prey fish species are accumulated in hydrographic structures and critical areas where predators (oceanic jacks, some gadoids, squid, tunas, seals, whales, dolphins, sharks, etc.) are economically available. The increasing scarcity of coastal resources due to overfishing in EEZs is an incentive to increase pressure on these areas and on the often fragile species which inhabit them.

Highly migratory species

Highly migratory species are referred to in Article 64 of the 1982 Convention which provides for the rights and obligations of coastal and other States whose nationals fish for these species. A list of species considered highly migratory at the time of elaboration of the Convention was attached to the agreement (see Annex 1). No operational definition of “highly migratory” has been given (see also Fig. 2).

Article 64 reflects the view that the management of highly migratory species requires cooperation between the coastal State and other States fishing for the resource. A trend is developing in which fishing agreements are signed between coastal and distant-water fishing nations (DWFNs) through which the DWFNs accept to pay for the access to tunas in the EEZs and where the coastal State unilaterally fixes (or negotiates) the quotas or the number of licences (e.g., in the South Pacific area, Seychelles, Mauritius, Morocco, Senegal, etc.). This trend has sometimes been taken as implying de facto a privileged right for the coastal State (Munro, 1993). The list of highly migratory species given in the Convention includes species with wide geographic distribution, both inside and outside the 200-mile zone and within which they undertake migrations of variable distances. They are pelagic species, and often have neritic and oceanic phases in their life cycle. The list includes 11 tuna, 12 billfish species, pomfrets, 4 species of sauries, dolphinfish (Coryphaena spp.), oceanic sharks and cetaceans (both small and large). Mammals are treated separately (Article 65) and will not be considered further here. It is important to note that there are species undertaking large-scale migrations which have not been included in this list.

For example, Euthynnus lineatus, that is probably more oceanic than the other two Euthynnus species, is not included. Other three tuna-like species (Acanthocybium solandri, Allothunnus fallai, and Gasterochisma melampus) classified as oceanic in the FAO SPECIESDAB are not included in the list. Many other tuna-like species migrate long distances while remaining close to the continent, and may be considered as highly migratory or straddling. In addition, some scientific names have changed in the meantime and the list, as it presently stands, is not satisfactory from a scientific point of view.

The total catches identified and reported to FAO on species and groups of species listed in the Annex I of the 1982 Convention have increased from 1.7 million t in 1970 to 4.3 million t in 1991 (Figure 3 and Table 2).

Figure 3

Figure 3: Catches of Highly Migratory Species and Straddling Stocks (source: FIDI, FAO)

Table 2
Catches of Highly Migratory Species
Species1991 Catches in t
Albacore168 797
Northern bluefin tuna30 182
Bigeye tuna238 353
Skipjack tuna1 556 732
Yellowfin tuna1 011 764
Blackfin tuna2 107
Atlantic black skipjack20 787
Kawakawa156 312
Southern bluefin tuna12 398
Frigate and bullet tunas206 099
Pomfrets168 853
Marlins48 228
Sailfishes7 364
Swordfish67 142
Other billfish57 777
Sauries402 210
Dolphinfish37 062
Oceanic sharks62 386
Total4 254 553

Straddling stocks

The 1982 Convention does not use the term “straddling” stocks, instead it refers in Article 63.2 to a “stock or stocks of associated species occurring both within the exclusive economic zone and in an area beyond and adjacent to the zone”. A case not foreseen explicitly by the Convention, however, is that of a stock occurring within the EEZs of two or more coastal States and the adjacent high seas3. As the straddling nature of a stock is a local (geographic) peculiarity related mostly to the shelf width, straddling stocks must be referred to not only by their species name (like the highly migratory species) but also by their specific location (e.g., Grand Banks cod). In most cases the limit of this jurisdiction is 200 miles but there are still areas where EEZ claims have not yet been made (e.g., in the Mediterranean). The degree to which a stock “straddles” usually depends on the extension of the shelf beyond the limit of the national jurisdiction and its seasonal availability thereof. Straddling stocks can be demersal or pelagic and, depending on the shelf width, they can be neritic or oceanic.

3 In this paper both types of stocks are considered as straddling

The usual understanding seems to be that straddling stocks are mainly EEZ “residents” (i.e., their overall biomass is largely in the EEZ) which straddle “out” in the high seas a few miles and perhaps only seasonally (Fig. 2). The “adjacency” required implies probably that there should be some geographic continuity between the EEZ and straddling portions of the stock. It is important to understand that when a shelf extends beyond 200 miles, it is the whole species assemblage which is straddling and not merely the target species.

In addition, some stocks could be mainly “high seas residents” (i.e., their overall biomass is largely outside the EEZs) which straddle “in” the EEZs (Fig. 2). Most of the species occurring in the high seas are found inside and outside the 200-mile limit, either at the same time or sequentially (e.g., during the various phases of their life cycle) and could be considered “straddling”, at least from a purely biological point of view. This is particularly important for small island countries which have a tiny piece of shelf (the reef and lagoon) in the middle of an immense oceanic ecosystem. Their reef resources are purely national but their oceanic resources, which represent a very large proportion of the marine resources available to them for development, are straddling or highly migratory. This particular situation renders the small island resources very vulnerable to high seas fishing and probably underlies the particularly deep concern of these countries towards uncontrolled high seas fishing. Whether or not their oceanic resources can be called straddling in legal terms, they are straddling in biological terms and merit the same type of coordinated management.

The biological distinction between the straddling and highly migratory species is not always straightforward. The Chilean horse mackerel, for instance, which straddles about 1 500 miles off the EEZs of Chile and Peru is a particular case of straddling stock which might, from the biological standpoint, be as “highly migratory” as some of the smaller tunas mentioned in the 1982 Convention. It has already been mentioned that some of these small tropical tuna species have limited migrations outside the EEZs, particularly when their lifespan is significantly reduced by fishing.

The number of straddling stocks is largely underestimated by the following factors:

4 Article 63.2 refers to “stocks of associated species”

The management issues related to straddling stocks depend on their biological characteristics and, in particular, on the degree of mixing between the EEZ and high seas compartments of the stock (Fig. 4). In instances where mixing is considerable (probably in most cases) because of random dispersion, ontogenic or seasonal migrations, the stock should be managed as one single unit, and management measures must be harmonized over the entire range of distribution of the stock.

Sedentary stocks with no movement and no mixing

Resource may be fixed [coral] or buried [clams]. Each compartment may be managed separately but depletion of spawners in one compartment may affect the other.

Low diffusion stock, little movement and little mixing

Stock compartments could be managed separately with little error. Depletion of spawning stock in one compartment may affect reproduction in the other.

High diffusion stock. Extensive random Movements and important mixing

Stocks should be managed as one unit. Management needs to be identical on both sides. Mismanagement of one of the compartments will directly affect the other

Inshore-offshore ontogenic migrations

The stock should be managed as one single unit. Specific measures [quotas, mesh size, effort controls] may be area-specific. Age-specific fisheries should be managed as sequential fisheries.

Sequential fisheries

Seasonally migrating stock

The stock should be managed as a single unit. Seasonal patters need to be taken into account.

Figure 4

Figure 4: Different types of straddling stocks

It is extremely difficult, considering the deficiency in the data related to straddling stocks, to assess the real economic dimension of the straddling stock problem (at least in terms of reported landings). In order to provide a very crude order of magnitude, and following the analysis given below area by area, the reported landings of the species known as “straddling” or “likely to straddle” have been calculated. The figures (Tables 3 and 4) should be regarded with extreme caution. There is no reliable information in this respect and there will not be any until such time that a proper reporting/collecting system is set in place. The total catches (in EEZs and adjacent high seas) have evolved from 5.8 million t in 1970 to 12.4 million t in 1991, after a peak of 13.7 million t in 1988–89 (Fig. 3). In 1991, the total catches were about 11.4 million t of demersal fish and squids and 1 million t of tuna and tuna-like species including highly migratory species (Table 3).

Table 3
Catches in 1991 of straddling or potentially straddling stocks by region
(Catches in '000 t)
Statistical Division (Ocean region)Tuna-like speciesOther speciesTotal
21 (N.W. Atlantic)0.9739.1740.0
27 (N.E. Atlantic)0.3437.0437.3
31 (W.C. Atlantic)30.6030.6
34 (E.C. Atlantic)7.207.2
37 (Mediterranean)97.558.4155.9
41 (S.W. Atlantic)3.0782.5785.5
47 (S.E. Atlantic)0.500.5
51 (W. Indian)86.7086.7
57 (E. Indian)44.2044.2
61 (N.W. Pacific)281.03 905.64 186.6
67 (N.E. Pacific)01 372.21 372.2
71 (W.C. Pacific)239.40239.4
77 (E.C. Pacific)246.25.8252.0
81 (S.W. Pacific)
87 (S.E. Pacific)26.94 017.64 044.5
Total1 065.611 408.312 473.9

It appears from these figures that the Northwest and Southeast Pacific areas are the most important sources of straddling stocks (mainly demersal) followed by the Northeast Pacific and the Southwest Atlantic.

Table 4
Catches in 1991 of straddling or potentially straddling stocks by species
SpeciesTuna-likeOther species
American plaice (Long rough dab) 51 342
Atlantic bonito85 
Atlantic cod 422 625
Atlantic halibut 3 544
Atlantic Spanish mackerel538 
Greenland halibut 69 181
Illex illecebrosus 15 743
King mackerel328 
Longfin squid 19 564
Silver hake 105 973 + 23 000
Witch flounder 15 152
Yellowtail flounder 20 250
TOTAL N.W. ATLANTIC (Area 21)951746 374
Atlantic bonito305 
Blue whiting (= Poutassou) 433 745
Illex illecebrosus 3 226
TOTAL N.E. ATLANTIC (Area 27)305436 971
Atlantic bonito2 399 
Atlantic Spanish mackerel19 359 
Flyingfishes nei1 568 
Illex illecebrosus 4
King mackerel5 565 
Seerfishes nei726 
TOTAL W.C. ATLANTIC (Area 31)30 6224
Atlantic bonito1 918 
Flyingfishes nei457 
Plain bonito399 
West African Spanish mackerel3 795 
TOTAL C.E. ATLANTIC (Area 34)7 2140
Atlantic bonito25 997 
Atlantic horse mackerel10 083 
Atlantic mackerel7 220 
Blue whiting (=Poutassou) 11 626
European hake 39 047
Jack and horse mackerels nei22 114 
Mediterranean horse mackerel32 081 
Plain bonito9 
Todarodes sagittatus sagittatus 7 775
TOTAL MEDITERRANEAN (Area 37)97 50458 448
Salilota australis 57
Antarctic rockcods, noties nei 3
Argentine hake 521 312
Atlantic bonito1 887 
Atlantic Spanish mackerel26 
Blue jack mackerel316 
Flyingfishes nei664 
Grenadiers 14 858
Illex argentinus 77 428
King mackerel67 
Patagonian grenadier 9 686
Patagonian hake 1 944
Patagonian toothfish 2 232
Sevenstar flying squid 3
Southern blue whiting 154 941
TOTAL S.W. ATLANTIC (Area 41)2 960782 464
Atlantic bonito473 
West African Spanish mackerel  
TOTAL S.E. ATLANTIC (Area 47)4850
Flyingfishes nei90 
Indo-Pacific king mackerel9 483 
Lanternfishes2 210 
Longtail tuna29 414 
Narrow-barred Spanish mackerel32 447 
Seerfishes nei12 673 
Streaked seerfish372 
TOTAL W. INDIAN (Area 51)86 6900
Flyingfishes nei2 039 
Indo-Pacific king mackerel14 360 
Longtail tuna1 080 
Narrow-barred Spanish mackerel13 697 
Seerfishes nei12 181 
Streaked seerfish850 
TOTAL E. INDIAN (Area 57)44 2070
Alaska (Walleye) pollock 3 521 306
Flyingfishes nei620 
Indo-Pacific king mackerel627 
Japanese flyingfish6 328 
Japanese Spanish mackerel247 855 
Longtail tuna17 370 
Seerfishes nei8 212 
Todarodes pacificus 384 310
TOTAL N.W. PACIFIC (Area 61)281 0123 905 616
Alaska (Walleye) pollock 1 372 187
TOTAL N.E. PACIFIC (Area 67) 1 372 187
Flyingfishes nei32 432 
Indo-Pacific king mackerel7 950 
Japanese Spanish mackerel1 427 
Longtail tuna115 293 
Narrow-barred Spanish mackerel60 385 
Seerfishes nei21 399 
TOTAL W.C. PACIFIC (Area 71)239 4230
Eastern Pacific bonito1 315 
Flyingfishes nei44 
Jumbo flying squid 5 846
Pacific sierra5 404 
Seerfishes nei2 
TOTAL E.C. PACIFIC (Area 77)246 1885 846
Longtail tuna  
Narrow-barred Spanish mackerel20 
Orange roughy 69 440
Oreo dories 20 646
Seerfishes nei1 137 
TOTAL S.W. PACIFIC (Area 81)1 15790 086
Chilean jack mackerel 3 852 928
Eastern Pacific bonito25 357 
Flyingfishes nei85 
Pacific sierra1 473 
Patagonian grenadier 164 679
TOTAL S.E. PACIFIC (Area 87)26 9154 017 607
WORLD TOTAL1 065 63611 415 600

The next two sections cover respectively highly migratory species and straddling stocks. The section on highly migratory species discusses not only the species listed in the 1982 Convention (such as tunas, billfish, marlins, oceanic sharks, marine turtles, pomfrets, dolphinfish and sauries) but other species of actual or potential importance to high seas fisheries with similar biological characteristics (such as tuna-like species, squids, oceanic horse mackerel, etc., of which very little is known). For each of these groups, whenever possible, the resources, the fisheries and the present status of stocks will be described. The following high seas resources are not reviewed here:

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