Daniel Pauly* and Rainer Froese t *Fisheries Centre, University of British Columbia, and t International Centerfor Living Aquatic ResourcesManagement, Manila
I. Major Adaptations of Fishes fish spawning usually suffer tremendousand largely II. Respiratory Constraints to Growth and Related unpredictable mortalities, thus uncoupling spawn- Processes ing from recruitment. III. Distribution of Exploited Fish Stocks trophic level A number indicating the position of a IV. Ecosystem Impacts of Fisheries specieswithin an ecosystemthough the number of V. Managing Fish Biodiversity Information stepslinking it to the plants. By definition, plants VI. Preserving Fish Biodiversity are TL = 1, herbivoresare TL = 2, and so on. Note that trophic levelsdo not needto be whole numbers; intermediate values occur among omnivorous con- GLOSSARY sumers. biomass Collective weight or massof all the members of a given population or stock at a given time, or, on the average,over a certain time period. FISH STOCKSARE POPULATIONS OF "FISH," THAT bioquads Occurrencerecord of organisms,serving as IS, VERTEBRATESWITH GILLS AND FINS, SUB- key units for biodiversity researchand consistingof jECTED TO EXPLOITATIONBY HUMANS. Popula- four elements(species names, location,. time, and tions are componentsof species,inhabiting part of their source). overall range,and usuallyhaving little geneticexchange catches The fish (or otheraquatic organisms)ora given with adjacentpopulations. The major adaptations de- stock killed during a certainperiod by the operation termining the spatial distribution of fish stock biomass of fishing gear(s). This definition implies that fish pertainto the anatomy,reproductive biology, and respi- not landed, that is, discardedat sea,or killed by lost ratory physiology of the speciesto which the stocks gear ("ghost fishing"), should be counted as pan of belong.Also, fishing hasbecome increasingly important the catch of.a fishery. to the biodiversity of fish, either through its direct im- ecosystem Area where a setof speciesinteract in char- pacts (changes of stock size and age structure, and acteristic fashion,and generateamong thembiomass overallbiomass reductions, down to extirpation of pop- flows that are stronger than those linking that area ulations), or by modifying the ecosystemsin which to adjacentones. they are embedded. Researchdevoted to monitoring recruitment Entry of juvenile fish into the (adult) the biodiversity of fish (or other organisms) must be stock. Recruitmentis distinguished from reproduc- able to handle large amountsof suitably formatted dis- tion, becausethe eggsand larvae that result from tributional information, here defined as consisting of
Encyclopedia of Biodiversity, Volume 2 Copyright @ 2001 by Academic Press. All rights of reproduction in any form reserved. 801 802 FISH STOCKS
"bioquads." Managementregimes aiming at preserving breathers,to perceivethe constraintsunder which fish, fish biodiversity will haveto include much stricter regu- as water breathers,were forced to evolve. lation of fishing and the establishmentof no-takeareas. Water is an extremely dense medium, 775 times heavierand 55 times more viscous than air. Also, water contains30 times less oxygenthan air, and this oxygen I. MAjOR ADAPTATIONSOF FISHES diffuses 300,000 times more slowly than in air. These physical constraints,which shapedall early life-forms, A. Anatomyand Physiology including the jawlesspredecessors of the fish, the agna- thans,are bestvisualized by describingthe major evolu- With about 25,000 recognized species in over 500 fami- tionary trends leading from agnathansto modem fish lies, fish are the most diverse vertebrate group. How- (Fig. lA). ever, their watery habitat, while failing to protect them The first of these trends was the evolution of jaws from modem fishing gear, makes it difficult to fully from the first upper and lower gill archesof agnathans. appreciate this diversity, and the extent to which it is This built on the intimate connection,in the mostprim- now threatened. It is even more difficult for us, as air itive vertebrates,between the feeding apparatus (i.e.,
Thunnus obesus, A = 7.5
Leiognathus dussumieri
t Pterolepis nitidus (15 cm) Cyprinus carpio, A = 2.2 Gazzaminuta
Pomatochistus minutus, A = 0.6
Secutor ruconius
Cyprinus carpio (1m) Cetorhinus maximus (15m)
FIGURE1 Major evolutionary trends from agnathansto extant fishes. (Note that no direct ancestor-descendantrelationships are implied among the groups depicted.) (A) Trends toward larger gills; (B) trends toward efficient jaws; (C) trends toward effective paired and unpaired fins. [Note the aspectratio of the caudal fin, defined by A = h2/s,where h is the height and s the surface (in black) of the caudal fin, and of which high values define fast, large-gilled continuous swimmers, and converselyfor low values.)
. FISH STOCKS 803
the mouth) and the respiratoryapparatus (i.e., the gills adjacentto slits on both sides of the anterior part of the alimentary canal). Water-breathing invertebrates lack this close connectionbetween feeding and breath- ing, one reasonwhy eventhe largestamong them (giant squids) cannot reach the mass of the largest fish (20 metric tons, for the whale shark Rhincodontypus). The reorganizationof the head of early fish allowed larger gills to evolve, which allowed the higher meta- bolic ratesrequired for swimming in openwaters. This transition was assistedby the gradualloss of the heavy armor protecting the slow, bottom-slurping agnathans. The fine "teeth" covering the bodies of sharksare ves- tiges of this armor. Fast swimming in open water required better fins, both for propulsion and for steering.Propulsion is pro- vided in most fish by oscillationsof a caudalfin whose aspectratio (Fig. lC) graduallyincreased toward tunas and other derived, fast-swimming groups with very large gills. Steering,on the other hand, is provided by dorsal, pectoral, and anal fins. These fins are stiffened FIGURE2 Schematicrepresentation of how changes in water level for preciseaction by hard, bony rays in the mostderived canmultiply, by creatingisolated subpopulations, the numberof species fish, the teleosts,whose evolutionary successwas fur- occurring in a givenarea. Such a mechanism,driven by repeatedclimatic ther enhancedby a complexly built protrusile mouth changes,is thought to explain the large number of fish speciesin SoutheastAsian marine waters and in the Great Lakes of Africa. that enables capture of a wide range of food items (Fig. 1B). Subtle anatomical changesin fish can thus create more niches for increasingthe numbers of specialists, larvae encounter, even during spawning seasonsat- which then occupy increasing numbers of closely tuned with zooplankton production cycles,are usually packedniches. Ecosystemsin which thesechanges have far too low to allow survival of fish larvae, and the run for long periods,undisturbed by physical changes, overwhelming majority of such larvae perish. Those therefore contain very large numbers of fish species. that tend to survive usually happenedto have hatched Their numbersare evenlarger in areassuch as the Great within plankton-rich water layers.These layers are usu- Lakes of Africa and the tropical Indo-Pacific, where ally a few centimetersthick and last for only a few days changesof water levelshave repeatedlyisolated basins of calm, betweenwind-driven or other mixing events, and subpopulations,thereby accelerating species differ- suchas storms or upwelling pulses,that enrich surface entiation (Fig. 2). waters with nutrients from deeperwaters. This implies that large biomassesof fish can build up only when and where the local oceanographicconditions take the form of "triads" defined by (1) nutrient enrichment, B. Reproduction and Recruitment such as generated by wind-driven mixing, (2) high Though many ancient fishes such as sharks and rays plankton concentration, such as generatedby various or the coelacanth Latimeria chalumnaepractice internal mechanismsincluding fronts, and (3) retention of lar- fertilization and produce few large eggs or live offspring, vae, required to prevent these weak swimmers from most recently evolved fishes produce numerous small drifting away from suitable habitat. In pelagic fishes eggs that are fertilized externally and develop as part that build high biomass, for example, the anchovies of the plankton, without parental care. The larvae that andsardines in coastalupwelling systemsoff northwest- emerge from those eggs, after less than one day in warm em and southwesternAfrica, Peru,and California,these tropical waters and up to two weeks (and more for larger triads occur only when the coastalwinds rangefrom 4 to eggs) in cold temperate waters, are usually elongated, as 6 m per second.Weaker winds do not generateenough befit small, finless zooplankton feeders. enrichment,and strongerwinds dispersethe larvae off- The average zooplankton concentrations that these shore. 804 FISH STOCKS
Fish have developed several strategies to deal with declines with size, becausethe two-dimensional gill the uncertain recruitment that results from the triad area cannot keep up with the three-dimensionalin- requirements. One is being small, shott-lived, and capa- creaseof body mass.Hence larger fish disposeof rela- ble of quickly building up large biomass under favorable tively less oxygen to supply their metabolism,the rea- environmental conditions. The other is being large, son why they ultimately stop growing. Also, long-lived, and capable of weathering long series of environmental factors that tend to increasemetabolic recruitment failures through repeated spawning by old, rate-especially elevatedtemperatures, but alsoinclud- large, and highly fecund adults. An example of the ing other form of stress-have the effect of reducing former strategy is provided by the Peruvian anchovy the maximum size that the fish of a given population Engraulis ringens,whereas the northern cod, Gadus mor- can reach (Figs. 3A and 3B). This is why tropical fish hua, provides an example of the latter. Yet another tend to be smaller than their respectivecold-water rela- strategy is to reduce the dependence on environmental tives. A similar mechanismexplains the nearly constant conditions by various forms of parental care, such as relationship in fish betweensize at first maturity and nesting and guarding (e.g., in catfishes, family Clarii- maximum size (Figs. 3C and 3D). dae), mouth-brooding (e.g., in cardinal fishes, family Apogonidae), and live-bearing (e.g., in ocean perches, genus Sebastes). B. Adaptation to Respiratory Constraints Another imponant feature of fish stocks is that, con- trary to earlier assumptions of homogeneity, most ap- Fish have~volved various strategiesand tacticsto over- pear to consist of well-differentiated individuals, each come respiratory constraints. One strategy,illustrated aiming to reproduce at the very place where it was in Fig. IB, is to evolve large gills, a route taken by hatched. Or, put differently: most migratory fish tend numerous open-water ("pelagic") species,culminating to "home." This behavior, well documented only in in tunas (Fig. 4). Pacific and Atlantic salmon (Oncorhynchus and Salmo, Another strategy is the evolution of life cycles in respectively), implies that individual fish, when repro- which the juveniles migrate to deeper,cooler waters as ducing, do not seek "optimal" sites, but rather spawn they grow and then, upon maturing, produce eggsthat as close as possible to the site at which they hatched, quickly float up to the warmer surface layers, out of and to which they are imprinted. This tendency to either reach of the often cannibalistic adults. Such typical stay in or return to a certain area makes it difficult for cycles are completed by an onshore drift of the larvae fish stocks to rebuild once they have been decimated to coastal areas,and productive shallow nurseries for by local overfishing or pollution. the early,voracious juveniles, which againmigrate into deeperwaters as they grow. A tactic to accommodatemetabolic stress,which is particularly useful in areaswith strong seasonaltemper- II. RESPIRATORYCONSTRAINTS TO ature oscillations, is for the feeding adults to store fat GROWTHAND RELATEDPROCESSES during the warmer part of the season(late summer to early fall). Fat requires far less oxygen for maintenance A. BasicGeometrical Constraints than protein of muscle and other tissues.As tempera- ture declines, the accumulated fat is converted into Fish growth, as in other animals,requires both food other tissues,notably gonads,whose contentsare shed and oxygen,the latter being required to synthesizethe in spring, thus reducing body masswhen temperatures substance(adenosine triphosphate or ATP) that serves again start to increase.These cycles, which use fat as as fuel to all organisms.For oxygento be metabolically protection againstrespiratory stress, are the reasonwhy available,it must be inside the fish body, that is, it must temperatefish tend to containmore muscleand visceral havepassed though its gills. Thus,since oxyg~ncannot fat than tropical species,where temperatures,although be stored inside the fish body (contrary to food, which high, do not fluctuate much in the course of a year. can be stored as gut contentsand as fat), the metabolic Another tactic that delaysrespiratory stress is associ- and growth rate of fish are largely proportional to the ated with ontogenetic shifts in diet composition. Here, surface area of their gills. So fish that quickly reach the young fish feed on a diffuse,small prey (e.g.,inverte- large sizes have gills with large surface areas (as in brate zooplankton), while the adults, via their sheer tunas), and conversely in slow-growing fishes (like size, can capture energy-rich prey such as other fish, groupers). Moreover, gill area per unit of body mass which are acquired at lessercost by the predator. FISH STOCKS 805
A B
.:E 0> "CD" ~ >- "U 0 .e I:: 0 "-E:. E :J 0 I:: 8 Wmax Wmax2 Wmaxl ~I:: ~ 0 c D '0 .:E 0>
"~ >- "U 0 ';ij ~ tU a Q
Q
Wm1 Wmax1 Wm1 Wmax2
Body weight
Maintenance metabolism
FIGURE3 Schematicrepresentation of the relationshipslinking, in fish, respiratoryarea (and hencemetabolic rate), maximum body size, and size at first marurity. (A) As body size increases,gill area per body weight decreases,down to a level when it suffices only for maintenancemetabolism. This defines the maximum size that can be reached. (B) Any environmental factor increasingoxygen demand for maintenance(such as elevatedtemperarure) reduces the maximum size that fish can reach. (C) The relative metabolic rate at first marurity (Qm)is necessarilyhigher than that associatedwith maximum size (Q-). (D) An evolved, near constancyof the ratio Q../Q- (about 1.4 from guppy to luna) ensuresthat fish destined to remain small (as in caseB) also spawn at smallersizes.
C. Relationshipsbetween Growth bility to various predators, mainly by their ability and Mortality to grow quickly through "small-size" stagesin which mortality is highest. Fish capableof reaching large size Whichever strategy and tactic fish use to grow, more and that have a high longevity also have low rates time will be neededin large speciesthan in small fish of natural mortality (Fig. 5). Hence fishing tends to for the size at first reproduction to be reached.Large have a stronger impact on species with low natural sizes thus imply, other things being equal more time mortality, such as sharks or rockfishes. Becausethese during which the growing fish may becomethe prey are often the top predators, their reduction tends of some predator. Hence the evolution of large fish to disrupt the food webs in which they are em- was coupled with a reduction of their relative vulnera- bedded. 806 FISH STOCKS
6
5 ';: ~ 0 N. 4 ';: .-0 .E! 3 ...c m E 0 0 2 c{ Z 0
0 0 1 2 3 4 5 6 7 8
Aspect ratio of caudal fin FIGURE4 Relationshipbetween DNA contents of body cells (a measureof cell size) versus caudal fin aspectin fish. Note triangular patterns, indicating that active fish with high aspect ratios are limited to small cells (which are metabolicallymore active than large cells), whereas more sluggish fish may have either small or large cells. Basedon records in FishBase98.
III. DISTRIBUTIONOF EXPLOITED river loaches,Balitoridae) to the mouths of temperate FISHSTOCKS and tropical rivers (e.g.,many gray mullets, Mugilidae). In the marine realm, fish range from the intertidal to A. Overall Distribution Ranges the ocean'sabyss, both as predators in their desert-like expanses(e.g., skipjack tuna, Katsuwonuspelamis) or Although mostly confined to water, fish occur in a as componentsof the rich, newly discovereddeep-sea wider range of habitats than any other vertebrate or vent ecosystems(e.g., some live-bearing brotulas, By- invertebrate group. Thus, fish range from the upper thitidae). Environmentaladaptations include the ability reaches of streams in high mountain ranges (e.g., many to deal with an enormous range of pressures (from FISH STOCKS 807
about one to hundreds of atmospheres),temperatures are extracted.Shelves may have rocky or soft (sandy (from -1.8°C in polar waters to about 40°C in hot or muddy) substrates,and usually support two weakly springs,tolerated by some tilapias),and salinities (from connectedfish communities,one species-richand con- close to distilled water preferred by the discus fish, sisting of bottom or "demersal" fishes,the other con- Symphysodondiscus, of Amazonia to about 10%, e.g., sistingof fewerspecies of open-wateror "pelagic"fishes. in West African hypersaline coastallagoons inhabited The fish of demersalcommunities are those exhibiting by the blackchin tilapia, Sarotherodonmelanotheron), the specializedfins and mouths mentioned earlier, en- to list only three environmentalfactors. No single fish abling utilization of distinctive food sources,particu- speciesor family, however,spans more than small frac- larly on reefs in both temperateand tropical regions. tions of theseranges. Rather, these various adaptations On coral reefs, this fine partitioning of resources are exhibited by a bewildering variety of fonns, ranging culminates in hundreds of fish speciessharing a single from minute gobies that are fully grown at close to 1 reef, with dozens of specialists for each of its food cm (e.g., Mystichthys luzonensis)to the 15 m reached resourcetypes, from the filamentousalgae consumed, by whale sharks (Rhincodontypus). Thesetwo species, for example,by damselfishes(Pomacentridae), the en- incidentally, are exploited for food in the Philippines. crusting algae consumed by parrot fishes (Scaridae), The fonner, despite its turnover rate, is in dangerof the coral themselves,consumed by butterfly fishes extinction in the smalllake where it is endemicbecause (Chaetodontidae),to the small invertebratesconsumed of overfishing and pollution. The latter will be extir- by, for example,wrasses (labridae). A vast array of pated if the new directed, export-oriented fishery for predators such as groupers (Serranidae)and sharks this slow-growing fish continues. (Carcharhinidae)regulate the number of these smaller fishes. Hard-bottom shelvesand, in tropical areas,the coral reefs that occur down to 30 m are also exploited B. Adaptations to Open-OceanHabitats wherever they occur. The fishing gearused over hard Fish have different strategiesto deal with the low pro- bottomsare mainly traps and handlines(the latter both duction of the oceans.Tuna haveadopted a high-energy sport and commercial),which are rather selectivegears strategy,wherein their tightly packed schools quickly that would have relatively minor impacts were it not move from one food patch to the other, essentially for their excessivenumbers. hopping from one "oasis" to the next and minimizing the time spent in the intervening desert-like expanses. 2. DemersalFish Stocks Others,notably the lantern fishes (Myctophidae),occur The demersalfish living in, on, or just aboveshelf soft in scattered populations that, at dawn, migrate from bottoms consist of specializedflatfishes and rays and 1000 m down to the surfacewaters, and back again at numerousgeneralized teleosts feeding on bottom inver- dusk. These different strategies imply very different tebrates(the zoobenthos)and smallerfishes. The com- biomasses:tens of millions of metric tons for the major plex communities thus formed can reach very high tuna species(prior to their recent depletion by various biomass,at shallow depth in the tropics (20-50 m) and longline, purse seine, and other fisheries) against an deeper in colder waters. In the warm waters of the estimatedglobal biomassof one billion metric tons for tropics,bacteria induce a quick remineralizationof the the lantern fish and associatedcommunities. The latter deadorganic matter (detritus) falling out of the lighted number is often viewed as a promising figure, from part of the water column. This allows very little detritus which various estimatesof potential yields have been to becomeavailable for consumption by the zooben- derived. Most of theseestimates, however, do not con- thos. In cold water, on the other hand, the short but sider the extremelydilute nature of this biomass(usu- intensive burst of algal production occurring in the ally less than 1 g per metric ton of water). spring is consumed only partly by the zooplankton of the upper water layers. Most of the remainder is consumedas detritus after falling down to the seabot- C. ShelfCommunities tom as "marine snow." Thus, cold-water soft-bottom. communities can occur in very deep waters, down to 1. Definition of Neritic Stocks the shelf slopes(200-300 m) and well beyond. Indeed, Most fish stocks are neritic, that is, occur above the the latesttrend in fisheries"development" is the exploi- continental shelves, the productive areas of shallow tation of deep-seastocks of cod-like fish (order Gadi- waters (down to 200 m) around the continents, from formes), orange roughy (Hoplostethusatlanticus), and which about 90% of the world marine fisheriescatches other fish, down to depthsof 1000 m or more, through 808 I FISH STOCKS ventures that evenin principle could neverbe managed events,and their subsequentrebuilding, mainly from so as to achievesustainability. recruits produced off northern Chile. Wherever they occur, soft-bottomshelves are nowa- Pelagic fish tend to form tightly structured, dense days invariably subjected to bottom trawling, a very schools,which protects them from predatorsand facili- unselective fishing method that is environmentally tates detection and herding of scatteredfood patches. damaging.This involves dragginga heavy,chain-stud- The fisheries rely on this behavior when deploying ded net over the sea bottom and "catching," that is, purse seines, which can surround and catch such removing all that it encounters.Not surprisingly, this schoolsin one go, often with associatedpredators such procedure hasoften beencompared to harvestingcrops as dolphins. Large pelagics such as billfish (Xiphiidae with a bulldozer. Trawler catchesthus consist of tar- and Istiophoridae)are caughtby arraysof longlines, set geted species(usually shrimps in the tropics and sub- by the thousandsalong shelf edges,which also capture, tropics) plus a vast number of nontarget species,often besidesthe target species,large amounts of by-catch the juveniles of demersalswith large adult siZes, and (notably sharks). These sharkswere previously left on literally parts of the habitat of bottom-fishes,notably the spot, but are now finned before the carcassesare sessile invertebrates and chunks of reefs lifted from discarded.Longlines are indeed as unselective as the the seabottom. Nontargetspecies and debris are then now banned giant driftnets that, in the 1980s,erected discarded,and it is therefore trawlers that contribute "walls of death" that were hundredsof kilometers long most to the globaldiscarding problem. Presently,about acrossthe migratory routes of fish in the North Pacific 30 million metric tons of various fish speciesare dis- and the Atlantic. carded; this is a very high discardrate when compared to the 90 million metric tons that appear in global 4. Overall Status of Neritic Stocks landing statistics. When combined, the demersaland pelagic fisheries of The contribution of trawlers to habitat destruction, shelvesand adjacentwaters representmajor threats to including conversionof richly structured bottom habi- fish biodiversity. Particularly endangeredare groupers tatsinto featurelessexpanses of mud, is well recognized, and other slow-growing bottomfish, and pelagics such and can only be comparedin termsof scalewith global asbluefin tuna and variousspecies of sharksand billfish. deforestationand the ensuingtrend toward desertifica- Besidesthe fisheries,one factor contributing to this tion. Only recently has the impact on biodiversity of endangermentis the traditional separationof research this mode of fishing begunto be evaluatedin systematic devotedto fisheriesmanagement ("stock assessments") fashion. The information so far availableindicates high from that devoted to conservationand to ecosystem impacts and a tendencyfor small generaliZedfish and research.Both lines of researchare separatedinstitu- invertebratesto replace larger specializedfish, a trend tionally, in termsof their methodsand publication out- that amplifies the food web effectsto be describedlater. lets, and in terms of what they perceiveas their man- dates. Overcoming this separation is crucial if fish 3. Pelagic Fish Stocks biodiversity is to be maintained in the face of the on- The pelagic communities over most shelf areas pre- slaught by fisheries. Key needsare the developmentof viously consistedof both major and minor stocksand tools and conceptsfor integrating information on fish stocklets of herrings, sardines (Clupeidae), anchovies biodiversity and ecosystemfunction with the knowl- (Engraulidae),and their relatives,and of their preda- edgegained through a centuryof applied,single-species tors, notably mackerelsand tunas (Scombridae)and fisheries research.Before considering these, however, various jacks (Carangidae).In many parts of the world, evidencefor fisheriesimpacts on ecosystemswill be pre- pelagic fisherieshave eliminated the minor stocksand sented. stocklets, and now depend wholly on annual recruit- ment to the remaining major stocks. The overfishing of old, highly fecund adults in theseremaining stocks IV. ECOSYSTEMIMPACTS explains much of their volatility. Indeed, the present OF FISHERIES emphasisof much fisheries researchon "variability" is thus devoted largely to a secondaryphenomenon cre- A. HistoricalTrends ated by the fisheryitself. It is true, however,that pelagic stocks, feeding lower in the food web, often closely The earliestfishing gear so far identified by archeolo- track environmental changes,such as the decline of gistsare bone harpoonsthat were recovered,along with the Peruviananchovy Engraulis ringens during EI Nino other evidenceof systematicfishing, from a site 90,000 FISH STOCKS 809
years old, in the present~dayDemocratic Republic of notion of sustainable fishing to establish itself. This Congo (formerly Zaire). Tellingly, the mainspecies that notion implies that some appropriate level of fishing was targetedappears to have been a now extinct, very effort (number of vessels or gear, mesh size) exists large freshwatercatfish. such that catches (or "yield") can be maintained at high This pattern of fisheries exterminating the stocks levels-hence the concept of "maximum sustainable upon which they ori~nally relied, then moving on to yield" or MSY. This led to the emergence of "fish popula- other species,is now understood to be common. This tion dynamics" and "stock assessments,"wherein math- contradicts earlier perceptionsof the ocean'squasi-in- ematical models of single-species fish stocks and of their exhaustible resources,as expressedamong others by response to targeted fishing became the mainstay of such Victorian grandeesas the geologistCharles Lyell fisheries research. R. J. Beverton, S. J. Holt, and J. A. and the zoologist Thomas Huxley. They were misled Gulland in England, W. E. Ricker in Canada, and by the then prevailing abundanceof various stocksof W. E. Schaefer in the United States proposed most of coastal fish (notably herring, Clupea harengus),and these still-used models during an extremely creative by what may be called "Lamarck'sFallacy": the notion period lasting from the early 1950s to the mid-1970s. that "animals living in the waters, especially in sea- Yet in spite of these advances, the fisheries never water. ..are protected from the destruction of their became sustainable. One obvious reason was that, given speciesby Man. Their multiplication is so rapid and a resource to which access was essentially open, the their meansof evadingpursuit or traps are so great that fisheries never could limit their collective effort at the there is no likelihood of his being able to destroy the level supposed to generate MSY. Rather, effort levels entire speciesin any of theseanimals." increased well beyond that, permitting some fleet own- The industrializationof the fisheries,first in Northern ers to increase their stakes even as the aggregate "rent" Europeand then in North America at the end of the nine- from the fisheries declined. Recent trends toward subsi- teenth century, quickly showedthese predictions to be dization of offshore and distant water fleets, driven by wrong. Most coastalstocklets of herring and other small international competition, have aggravated these eco- pela~cs were extirpated,and fadedeven from memory, nomic issues, enabling commercial profits to be gained therein soon followed, after the introduction of bottom even from strongly overexploited stocks. These devel- trawling, by coastalstocks of demersalfishes. opments are so widespread that they have rendered The practical responseto this was the introduction obvious the impacts which fisheries have on eco- of bigger boats with bigger engines,fishing farther off- systems. shore. Another responsewas the creation of research bodies (suchas the International Council for the Explo- ration of the Sea,founded in 1902) to assessthe reason C. Fishing Down MarineFood Webs why the resourceswere declining. Also, severalcoun- The ecosystem impacts of fisheries are due mainly to tries (notably Norway and the United States)initiated the fact that the targeted fish function as part of food costly programs wherein juvenile cod and other fish webs, both as consumers and as prey. Within food webs, were raised in hatcheriesand then thrown into the sea, the fish of different species occupy distinct trophic lev- in the vain hope that they would replenish the stocks els (TL), each defining a step away from plants, which rather than be eaten by happy predators (which they have a definitional TL of 1. Thus, fish feeding on plank- were). tonic algae have TL ~ 2, fish feeding on herbivorous zooplankton have TL ~ 3, and so on. It is important B. Emergenceof the here to Tecognize that most fish tend to have intermedi- ate TL values (2. 7,3.5,4.1, etc.), reflecting the catholic SustainabilityConcept nature of their diet. The First World War put an end to the stocking pro- Fisheries, by removing biomass from one of several grams. It also established that a strong reduction of fish stocks, necessarily modify food webs, thus forcing fishing effort, as causedby the drafting of fishers and predators of the targeted species to shift toward avail- vesselsinto the war effort, and the spiking of major able alternative prey, if any. Such adjustments were fishing grounds by underwatermines (thus creatingthe previously not distinguishable from natural fluctua- first marine protected areas),would lead to a recovery tions. They have gradually become highly visible, how- of depleted fish stocks. Yet the SecondWorld War, and ever, because they change the mean trophic level of the another demonstrationof stocksrebuilding themselves landings extracted from different stocks. Moreover, the when subjected to less fishing, was required for the changes induced by fishing are not of a random nature, 810 I FISH STOCKS
with decreasesin one area matched by increasesin is true for objective reasons(ecosystems are complex, another. Rather, they are directed, with a clear down- and their behavior under exploitation, due to the large ward trend (Fig. 6A), due to the link betweengrowth number of stocks to be considered,is difficult to simu- and natural mortality mentioned in Section II. Thus, late) and for subjective reasons(notably a perceived in large fish, evena low levelof fishing monality gener- lack of suitable field data on these many stocks). ated by a well-managedfishery will quickly exceedthe The recentdevelopment of robust ecosystemsimula- low level of total mortality (ie., natural + fishing mor- tion tools should allow the first of these issues to be tality) that canbe accommodatedby the stock. By-catch addressed.Overcoming the second not only involves speciesare evenmore endangeredbecause the fishing pointing out the existenceof suitable data, often lost will not stop as their numbers dwindle until they are in the "gray literature," but in making such data avail- eradicated,as has happenedwith rays in the Irish Sea. able in suitable format to all who are awareof the need The trend of mean trophic level resulting from this for a transition from single-speciesto ecosystem-based (see Fig. 6A), reflecting a phenomenon now known fisheriesassessments. This brings us to the issuesrelated as "fishing down marine food webs," provides a clear to the standardization,dissemination, and usesof bio- indication that, globally, fisheriesgenerate levels of ef- diversity information. fort well pastthose required for sustainability,however defined. Indeed, other indices can be used to indicate that global changeshave occurred in the composition V. MANAGINGFISH of global fisherieslandings, and in the structure of the ecosystemsfrom which these landings are extracted BIODIVERSITYINFORMATION (Fig.6B). A. Biodiversityas a ConceptualChallenge Fisheries-inducedmodification of the structure of marine and freshwaterecosystems has strong indirect Thereis a widespreadperception that the main obstacle impacts on fish biodiversity, in addition to the direct to the conservationof fish stocksand of fish biodiversity impactsof reducingthe biomassof the targetand associ- is "lack of data," a notion strengthenedby public state- ated stocks by a factor of 10 or more, as is usually the ments of biologists worried about the lack of funding case. Incorporating these indirect effects in fisheries for relevantresearch. However, simple lack of data can- stock assessmentshas proven to be difficult so far. This not be the problem, not after the 250 years since Lin-
3.81
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....~ I FISH STOCKS 811
naeuscreated the taxonomicstandards required for bio- richness (number of speciesencountered) is derived diversity research, 100 years of applied fisheries directly from the bioquads from a given area. Distinc- research,and at least50 yearsof advancesin ecosystem tiveness(how much the speciesencountered differ from research.Rather, the problem here is the fragmentation each other) is derived from the classificationof these of the databasecollected so far. Indeed, many studies speciesinto higher taxa such as families, orders, and conductedin recentyears on the statusof various stocks classes.Representativeness (how closely an arearepre- fail to consider previous knowledge on their relative sentsa predefined ecosystemtype) is derived by com- abundance and distribution, and thus contribute to paring observedspecies composition with the typical shifting baselines,wherein only the most recent and composition of the ecosystemtype under study. The usually low estimatesare used as reference for conserva- utility of speciesto humanscan be derived from pub- tion or rebuilding efforts. lished, or local knowledge,or from catchesin the case One reasonfor this reluctanceof biologiststo consol- of fish. Statusof threat can be derived from trends in idate existing datainto comprehensive,global databases the distribution area defined by bioquads. Rarity can may be due in part to the perception that biological be estimatedfrom the number of bioquadsavailable for dataare too difficult to standardize,or are uselessonce a species in a given area, standardized by sampling standardized.Addressing these issues will be a key task effort. of biodiversity research,and we now presenta few ideas Taxonomistshave made a consciouseffort to system- related to this. atically compile dataof this sort in specimencollections, There is consensusthat the objects of biodiversity and to publish them in original species descriptions researchare genes,populations, species,and ecosys- and revisions.As a result, bioquad-typedata are readily tems. However, there is little consensusas to what available in enormous numbers (about 10 million for distinguishesbiodiversity from the existing disciplines fish alone) in museum collections,survey reports,his- of fisheriesbiology, ecology,biogeography, population torical photos and films, and other forms (criterion 3). genetics, or taxonomy. As a result, the array of data While museumcollections go back over 200 years,some being claimed to be essentialfor biodiversity studies literature containsverifiable records that date back to readslike a compositelist of the data traditionally used antiquity (criterion 4). Also, archeologicaldata reach in the older disciplines,with few attemptsat integration back to the dawn of modem humanity (see the earlier or prioritization. Suchintegration and prioritization are record pertaining to giant catfish). possible,however, by giving emphasis,in biodiversity Numerous scientific surveysand projects also con- studies,to data that are: (1) relevantto current research tinuously collect contemporary bioquads. Other issues(e.g., richness, rarity, distinctiveness,representa- sourcesare the commercialfisheries and the many lay- tiveness, threat, function, and utility of species); (2) personswhose hobby is to observeand sometimesto part of the data traditionally collected in taxonomy, collect fish and other wildlife. Theseactivities are most biogeography, population genetics, and ecology; (3) likely to continue in the foreseeablefuture (criterion widely available,in sufficient quantity; (4) pertinent to 5). An increasingnumber of the precedingdata sources past, present,and most likely future trends; (5) easyto are available in computer-readableform (criteria 3, 5, collect; (6) easyto standardize; (7) easyto verify; and and 6). (8) suggestiveof new lines of research. Efforts do exist to standardizethe elementsof the bioquad (criterion 6). For example,the Species2000 Initiative hasembarked on the task of providing a stan- B. Bioquadsas Key Biodiversity dard referencelist of the valid namesof the known 1.75 Data Sets million speciessharing Earth with humans (see the website www.sp2000.org). Geographicalcoordinates A minimum core of biodiversity information that fulfills and the international date and time format are obvious these eight criteria is provided by "bioquads" (from standardsfor items (2) and (3), although there remains "quads," short for quadriads), consisting of: (a) the a need for a global gazetteerto deal efficiently with scientific name of a taxon, usually a biological species localities reported without coordinates,and there is a or other evolutionarily significant unit; (b) the locality need for standardsto deal with date and time ranges. where a specimenof this taxon has beenencountered; On the other hand, standards exist for sources such (c) the date (time) of the encounter;and (d) the author- as printed publications, databases,photos, films, and ity or source reporting (a)-(c). personalcommunications. Many of thesewere consid- Of the researchitems mentioned under criterion (1), ered when developing FishBase,a computerizeddata- 812 .' I FISH STOCKS baseon the biology ,ecology,and usesof fish containing a vast number of bioquads (see the following). The necessaryverification (criterion 7) of millions of datapoints can only be done automatically.Basically, a computer canverify a scientific name againsta stan- dard list, comparethe indicated locality and date against the establishedrange of a species,and judge the reliabil- ity of a source,for example,by the number of outliers it has reported prevIously. Procedureswill have to be established,however, on how to deal with the different types of outliers, some of which may representvalid new information. An important considerationis how fast a research agendabased on bioquads will be exhausted(criterion 8). Important here is the ability of well-structured rela- tional databasesto interlink independentlydeveloped datasets. Thus, the scientific name links to all available information on a species,including taxonomy,system- FIGURE 7 Interrelationships of the elements of biodiversity, articu- atics, genetics,biology, ecology,and human uses.The lated through the four elements of bioquads (species, location, times, locality connectsto all available information on sur- and source). rounding environments,including province, country, continent, habitat, ecosystem,and tectonic plate. The combination of species,locality, and date points to a population or stock. Date and time in connection with the locality canbe usedto infer a wide rangeof environ- bioquads as defined previously. Important here is that mental conditions, from local temperaturesto current a new original of this graph is generated on the fly, from fisheries legislation. The source relates to the human currently available bioquads, every time the relevant dimension, such as personsand institutions working routine of FishBase is evoked, and that each of its "dots" on certainspecies groups or in a certainarea, represent- can be clicked to verify the four elements of the underly- ing the scientific interface between humans and the ing bioquad. other species(Fig. 7).
C. Databasesas Tools for Managementof VI. PRESERVINGFISH BIODIVERSITY Biodiversity Information A. Traditional Approachesto Two major initiatives presently exist to assembleand Stock Management make widely available,for researchon fish biodiversity, the information presendyheld by various institutions None of the foregoing considerationswill help, how- (notably museums). One is NEODAT, which makes ever, if fisheriesare allowed to continue undermining accessibleon the Internet about 400,000 bioquad rec- their resourcebase, which they will if fisheries manage- ords pertaining to freshwater fish of the Neouopics ment continues to rely on the panoply of approaches (NEODAT; www.fowler.acnatsciorg). The other is so far deployed.These traditional approachesinclude, FishBase,an ongoing international collaborativeproject among other things: (1) meshsize restriction; (2) re- dedicated to assemblingthe estimated 10 million ex- striction on the amount and/or speciesof fish that may isting fish bioquadsand to combining them with other, be legally landed; (3) effort limitation, for example, standardizedbiological information on fish. The inten- through caps on the vesseltonnage that may deployed; tion here is to provide a global relational database, and (4) seasonalclosures. addressinghead-on the data fragmentationissue men- Besidesbeing extremely hard to enforce, these ap- tioned earlier (seewww.fishbase.org). proaches-which are invariably conceived in the con- Figure 8 shows the geographicdistribution of Nile text of single-speciesassessments-fail to addressthe tilapia, Oreochromisniloticus, through dotsrepresenting ecosystemeffects mentioned earlier. Thus, mesh sizes FISH STOCKS 813
FIGURE8 Distribution of Nile tilapia (OreochromisnilotiC1tS) based on 425 bioquadscontributed by the MuseeRoyal de l'Mrique Centrale, Tervuren, Belgium, and other sources. In the computerizedversion of this graph, each dot can be "clicked" to reveal the four elementsof the underlying bioquad, thus allowing identification of outliers, temporal trends, etc.
above a certain limit, meant to protect the young of a B. ~arine Protectedi\reas given species,do not prevent associatedspecies form being caught. Indeed,when combinedwith restrictions There is an emerging consensus among fisheries scien- on total allowable catch (TAC), and on the landing of tists and conservationists that the only fisheries man- bycatch (as is often the case), mesh size restrictions agement tool that will allow the recovery of damaged becomethe very reasonfor discarding both the young stock and ecosystems is the establishment of Marine of targetedspecies and the nontargetspecies. Limits on Protected Areas (MP As), including permanent N 0-Take nominal fishing effort are subverted by technological zones as their core. Such core zones are easy to en- developments,such as improved gearsand navigation force-at least relative to the task of enforcing mesh instruments (e.g., GPS), which increasethe catching sizes or TACs. Also, technology-driven increases of power of fishing vessels.Thus, government-runvessel fishing effort can be ignored, and there is assurance retirement schemesoften end up subsidizing the mod- that the long-lived organisms of seafloors and their ernization of fishing fleets. Finally, seasonalclosure of associated fish communities can gradually return to a various areasusually has negligible ecologicalimpacts, semblance of their original configurations. However, becausethe fishing effort expendedduring the open much research will have to be devoted to identifying seasonis sufficient for the seabottom to be scrapedup the optimal size and location of MP As, particularly for numeroustimes by trawlers,and for the stocksof long- migratory stocks. lived fishes to be severelyimpacted. Still, traditional fisheries management, aimed at lim-
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iting effective fu;hing effort, will have to continue around MPAs, lest they becomemarine larders or fu;h- Bibliography attracting rather than fu;h-producingzones from which Froese, R., and D. Pauly (eds.). (1998). FishBase 98: Concepts, Design resources are drained by fu;heries operating at their and Data Sources. ICLARM, Manila. [Distributed with two CD- ROMs; also see the website www.fishbase.org.] very periphery. Hawksworth, D. L, P. M. Kirk, and S. D. Clarke (eds.). (1997). Finally, the social context of fu;herieswill have to Biodiversity Information: Needs and Options. CAB International, change:fu;heries do not harvestcrops they have sown. Wallingford, United Kingdom. Rather,they exploit the natural productivity of wildlife; Miller, R I. (ed.). (1994). Mapping the Diversity of Nature. Chapman &: thus there are inherent limits to global fu;h catches,and Hall, London. future fu;herieswill not meet the demand of an ever- Mooney, P. (ed.). (1998). Ecosystem management for sustainable fisheries. Ecol. Appl., Supplement to 8(1). increasinghuman population. Indeed,the massiveeco- National Research Council. (1999). Sustaining Marine Fisheries. Na- system changesalready describedindicate that these tional Academy Press, Washington, D.C. limits have been reached in most parts of the world, Nelson, J. (1994). Fishes of the World, 3rd ed. John Wiley &: Sons, and that sustainable fisheries must be embedded in New York. some form of ecosystemmanagement. Pauly, D. (1994). On the Sex of Fishes and the Gt:nd£Tof Scientists: Essays in Fisheries Science. Chapman &: Hall, London. Paxton, J. R., and W. N. Eschmeyer (eds.). (1998). Encyclopedia of SeeAlso the FollowingArticles Fishes. Academic Press, San Diego. Reaka-Kudla, M. L., D. E. Wilson, and E. O. Wilson (eds.). Biodiversity ADAPTATION. FISH, BIODIVERSITYOF. FISH II. Understanding and Protecting our Biological Resources.Joseph CONSERVATION. MARINE ECOSYSTEMS Henry Press, Washington, D.C.