Human impacts on the world's oceans have been substantial, leading to concerns about the extinction of marine taxa. We have compiled 133 local, regional and global extinctions of marine populations. There is typically a 53-year lag between the last sighting of an organism and the reported date of the extinction at whatever scale this has occurred. Most disappearances (80%) were detected using indirect historical comparative methods, which suggests that marine extinctions may have been underestimated because of low-detection power. Exploitation caused most marine losses at various scales (55%), followed closely by habitat loss (37%), while the remainder were linked to invasive species, climate change, pollution and disease. Several perceptions concerning the vulnerability of marine organisms appear to be too general and insufficiently conservative. Marine species cannot be considered less vulnerable on the basis of biological attributes such as high fecundity or large-scale dispersal characteristics. For commercially exploited species, it is often argued that economic extinction of exploited populations will occur before biological extinction, but this is not the case for non-target species caught in multispecies fisheries or species with high commercial value, especially if this value increases as species become rare. The perceived high potential for recovery, high variability and low extinction vulnerability of fish populations have been invoked to avoid listing commercial species of fishes under international threat criteria. However, we need to learn more about recovery, which may be hampered by negative population growth at small population sizes (Allee effect or depensation) or ecosystem shifts, as well as about spatial dynamics and connectivity of subpopulations before we can truly understand the nature of responses to severe depletions. The evidence suggests that fish populations do not fluctuate more than those of mammals, birds and butterflies, and that fishes may exhibit vulnerability similar to mammals, birds and butterflies. There is an urgent need for improved methods of detecting marine extinctions at various spatial scales, and for predicting the vulnerability of species.

Extinction vulnerability in marine populations

The Ecology of Fishes on Coral Reefs

Reef fish spawning aggregations are attractive and often lucrative to fish but particularly vulnerable to fishing, with many cases of declines or extirpations. While awareness of the risks of aggregation exploitation has grown substantially in the tropical western Atlantic in the last decade, the phenomenon of aggregation-spawning is little known in the vast Indo-Pacific region where few aggregations are managed or monitored, and are rarely considered in marine-protected area designations. Even in the tropical western Atlantic and Caribbean, marine-protected area planning, until recently, did not typically consider spawning aggregations. Available data and analyses of aggregation-fisheries and aggregating species strongly suggest that: (1) the majority of known aggregations that are exploited are yielding declining landings; (2) aggregating species show greatest overall declines in local fisheries when their aggregations are also exploited; (3) from an economic perspective, aggregation fishing may yield lower prices for fish, or aggregations may be more valuable unexploited, as a source of fish for local fisheries or as tourist attractions; (4) hyperstability can mask declines in aggregation-fisheries, based on fishery-dependent data; (5) monitoring of aggregation catches by either fishery-dependent or fishery-independent means is deceptively challenging. There are also possible ecosystem-level consequences of reducing or eliminating spawning aggregations. We conclude that aggregation-fisheries are likely to be sustainable only for limited subsistence-level use, that the precautionary principle should be more widely applied in aggregation-fisheries and that, despite growing interest in aggregations over the last decade, few of the key biological questions necessary for effective management have been, or are being, addressed.

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Are aggregation-fisheries sustainable? Reef fish fisheries as a case study

A major objective of the use of marine reserves in management of coral reef fisheries is protection of a critical spawning stock biomass to ensure recruitment supply to fished areas via larval dispersal. However, very little empirical evidence exists on the rates and patterns of increase of density and biomass of target species following the closure of a coral reef or part of a reef, nor on how quickly any gains potentially useful to fisheries can be lost if reserves are subsequently opened to fishing. This paper presents empirical evidence derived from the visual monitoring of density and biomass of large predatory coral reef fish (Serranidae (Epinephelinae), Lutjanidae, Lethrinidae and Carangidae as a group) in two small marine reserves and at two control sites in the Philippines from 1983 to 1993. At one reserve (Sumilon) a complex history of management allowed seven mea- surements of density and biomass at durations of reserve protection ranging from -2 (i.e., fished for 2 yr) to 9 yr. At the second reserve (Apo), seven measurements were taken at durations of reserve protection ranging from 1 to 11 yr. Density of large predators provided an excellent indicator of the effects of marine reserve protection and fishing. Density decreased significantly twice when the Sumilon reserve was opened to fishing (1985, 1993), and increased significantly three times following durations of marine reserve protection of 5 yr (Sumilon reserve and nonreserve sites, 1987-1991) and >6 yr (Apo reserve beyond 1988). Density of large predators at the Apo nonreserve site (open to fishing) did not change significantly, remaining low throughout the study. Significant positive linear correlations of mean density of large predators with years of reserve protection were observed at both reserves. The rates of increase were 1.15 and 0.72 fish-1000 m-2.yr-' at Sumilon and Apo reserves, respectively, with mean density ranges of -4-17 fish/1000 m2 (-2 to 9 yr of protection) at Sumilon and 0.5-9.5 fish/1000 m2 (1-11 yr of protection) at Apo. The pattern of increase of mean biomass with years of reserve protection was more curvilinear than that of mean density, particularly at Sumilon, where a slow increase was observed in the first 3-5 yr (reflecting delayed recruitment and a natural delay to the period of maximum individual mass growth), followed by an increasing rate over the next 4 yr. Mean biomass ranges were -1.5-18 kg/1000 m2 (-2 to 9 yr of protection) at Sumilon and 1-10.5 kg/ 1000 m2 (1-11 yr of protection) at Apo. At Sumilon reserve, 2 and 1.5 yr of unregulated fishing, respectively, eliminated density and biomass gains accumulated over 5 and 9 yr of marine reserve protection.

Marine Reserves: Rates and Patterns of Recovery and Decline of Large Predatory Fish

Coastal fisheries in the South Pacific are reviewed, including descriptions of fisheries, catch composition, catch rates and fisheries biology studies conducted on target stocks. The most widely targeted coastal fish stocks are reef fishes and coastal pelagic fishes. Small pelagic species are important for subsistence and small-scale commercial fisheries. Previously, small pelagic resources were important as a source of live bait for pole-and-line tuna fishing, but this method is declining and only one large bait fishery is left in the region in the Solomon Islands. The pole-and-line bait fisheries represent the only large-scale industrial fisheries to have operated in the coral reef lagoons of the Pacific. Estuarine resources are of major importance only in the large islands of Melanesia but are the staple diet of a relatively large proportion of the total South Pacific population. Deep slope fish stocks form the basis of only two commercial fisheries in the region and expansion of deep slope fishing comparable with the 1970s and 1980s is unlikely to occur again. Commercial fisheries development is currently orientated towards small- and medium-scale long-line fisheries for offshore pelagic resources, where high value tunas and billfishes are caught for export markets. The total coastal fisheries production from the region amounts to just over 100000 tyr -l , worth a nominal US$262 000 000. About 80% of this production is from subsistence fishing. Just under half the total annual commercial catch comes from fishing on coral reefs, which includes a small tonnage of deep slope species. Invertebrates are the most valuable inshore fisheries resources and these include sea-cucumbers, trochus and pearl oyster. Lobsters and mangrove crabs form the basis of small-scale commercial fisheries, as also do penaeid shrimps, except in PNG where they are caught in large quantities through trawling. Mariculture of shrimps is becoming increasingly popular in the region and is a major industry in New Caledonia. The greatest influence on coastal fisheries in the Pacific through the next decade is likely to come from southeast and east Asia, where the demand for high value coastal fishes and invertebrates has led to large scale depletions and has motivated entrepreneurs to seek stocks in the neighbouring Pacific islands.

Coastal fisheries in the pacific islands

Using otolith weight–age relationships to predict age-based metrics of coral reef fish populations at different spatial scales

From 1990 to 1993, samples of coral trout, Plectropomus leopardus, were collected at two coral reefs closed to fishing since 1987 in the central Great Barrier Reef (GBR). The age structure was dominated by a strong cohort which settled in early 1984 and which accounted for 54%, 45%, 42% and 36% of the experimental hook-and-line catches at Glow and Yankee reefs. Catch rates (fish person-1 hour-1) per age class per reef per year provide the first reliable estimates of the exponential rate of mortality of coral trout in zones of the GBR Marine Park closed to fishing. The annual mortality rate between the ages of 6 and 9 years was 0.115 (s.e. 0.040) at Glow reef and 0.189 (s.e. 0.100) at Yankee reef. The annual mortality rate between ages 6 and 9 years was 0.147 (s.e. 0.028) at the two reefs combined. Age-specific estimates of annual mortality ranged from 0.024 (age 7–8 at Glow) to 0.442 (age 6–7 at Yankee) but were unreliable because of small sample sizes. This is one of the first estimates of mortality rate of an exploited species in an area closed to fishing in the tropics.

Mortality rate of a cohort of the coral trout, Plectropomus leopardus, in zones of the Great Barrier Reef Marine Park closed to fishing

Nous avons etudie une forte classe d'âge dans la population de merou etoiles bleues (Plectropomus leopardus) du centre du recif de la Grande Barriere, en Australie. De 1990 a 1993, nous avons preleve des echantillons de ce merou sur deux recifs de coraux fermes a la peche depuis 1987, et sur deux recifs ou la peche etait ouverte. Sur les recifs fermes, la structure d'âge etait dominee par une forte cohorte qui s'est etablie au debut de 1984 et qui a represente 54, 45, 42 et 36% des captures experimentales effectuees a l'hamecon de 1990 a 1993, respectivement. La presence d'une cohorte aussi forte n'est pas apparue sur les recifs voisins ou la peche etait ouverte, ce qui peut etre du a la faible taille des echantillons. C'est la premiere fois qu'on peut suivre chez des poissons des coraux une classe d'âge dominante au fil du temps en examinant les structures d'âge. Les resultats demontrent que de fortes fluctuations interannuelles du recrutement peuvent avoir un effet notable sur l'abondance locale des populations de merou etoiles bleues, et que les episodes de recrutement importants peuvent rester presents dans la structure d'âge des populations de cette espece. En outre, etant donne que l'âge du recrutement a la peche est de 3 ans environ, les resultats indiquent que des recensements annuels des poissons juveniles pourraient permettre de predire jusqu'a 3 ans d'avance l'effectif du recrutement.

Temporal tracking of a strong cohort in the population of a coral reef fish, the coral trout, (Plectropomus leopardus) Serranidae: Epinephelinae, in the central Great Barrier Reef, Australia

Age and growth of longtail tuna (Thunnus tonggol) were assessed by examination of annual growth increments in sectioned sagittal otoliths from 461 fish (238–1250 mm fork length, LF) sampled from tropical and temperate waters in the central Indo-Pacific between February 2003 and April 2005. Edge and microincrement analyses (presumed daily increments) suggest that longtail tuna deposit a single annual growth increment mainly between August and October. Age was, therefore, estimated for all fish by counting assumed annual growth increments. Ages ranged from 154 d to 18.7 years, with most fish being 3–9 years. Five growth models were fitted to length-at-age data, all of which indicated that the species is relatively slow-growing and long-lived. Recaptures of two tagged fish at liberty for 6.2 and 10.5 years support this notion. A bias-corrected form of Akaike's Information Criterion determined that the Schnute–Richards model provided the best fit to length-at-age data, with model parameter estimates (sexes combined) of L{infty} = 135.4 cm LF, K = 22.3 year–1, t0 = 0.120 years, {delta} = 150.0, v = 0.019, and {gamma} = 2.7 x 10–8. There was no significant difference in growth between sexes. The results suggest that longtail tuna grow more slowly and live longer than other tuna species of similar size. Coupled with their restricted neritic distribution, longtail tuna may be vulnerable to overexploitation by fisheries, and caution needs to be exercised in managing the species until more reliable biological and catch data are collected to assess the status of the population.

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Age and growth of longtail tuna (Thunnus tonggol) in tropical and temperate waters of the central Indo-Pacific

The otoliths of the scarid Scarus schlegeli (Bleeker) from the Lizard Island on the northern Great Barrier Reef showed a series of clear periodic bands. The rate at which bands are deposited on the otoliths was distinguished by mark-recapture experiments using tetracycline and marginal increment analysis. Mark-recapture experiments were carried out both in the field and in a large aquarium system. One otolith band was deposited during the liberty periods of July 1990 to April and September 1991 while two similar bands were formed from November 1989 to February 1991. The marginal increment analysis indicated that annual bands were formed around the austral summer. Scales also displayed regular period check marks. These provided relatively reliable aging estimates for the younger fishes up to 5 years.

Dong C. Lou

Papers

Using otolith weight–age relationships to predict age-based metrics of coral reef fish populations at different spatial scales

Mortality rate of a cohort of the coral trout, Plectropomus leopardus, in zones of the Great Barrier Reef Marine Park closed to fishing

Temporal tracking of a strong cohort in the population of a coral reef fish, the coral trout, (Plectropomus leopardus) Serranidae: Epinephelinae, in the central Great Barrier Reef, Australia

Age and growth of longtail tuna (Thunnus tonggol) in tropical and temperate waters of the central Indo-Pacific

Validation of annual growth bands in the otolith of tropical parrotfishes (Scarus schlegeli Bleeker)