Unexploited Species Research Articles

Exploitation, secondary extinction and the altered trophic structure of Jamaican coral reefs

AbstractCoral reef communities of the Greater Antilles in the Caribbean have a long history of anthropogenic disturbance, driven by the exploitation for food of both vertebrate and invertebrate species. Exploitation, coupled with region wide declines of coral environments has resulted in local and regional vertebrate extinctions. The impact of those extinctions on reef communities, however, remains largely unexplored. Here we show, using a highly resolved model coral reef-seagrass food web, that at least 40 of 188 expected vertebrate species are absent from Jamaican coral reefs. Twenty one of the absent species are of high trophic level and are exploited by humans. The remainder of the absent species are unexploited, and comprises a significantly high proportion of specialized reef foragers. Many of those species are also more trophically specialized than their closest trophic competitors. We conclude that the absence of unexploited species from Jamaica is caused by the overexploitation of high trophic level species, and consequent trophic cascades and secondary extinction among their prey in an increasingly degraded reef environment. The result is a reef community depauperate of both exploited high trophic level predators, and unexploited, specialized lower trophic level reef foragers.

EXPLOITED SPECIES IMPACTS ON TROPHIC LINKAGES ALONG REEF–SEAGRASS INTERFACES IN THE FLORIDA KEYS

The removal of fish biomass by extensive commercial and recreational fishing has been hypothesized to drastically alter the strength of trophic linkages among adjacent habitats. We evaluated the effects of removing predatory fishes on trophic transfers between coral reefs and adjacent seagrass meadows by comparing fish community structure, grazing intensity, and invertebrate predation potential in predator-rich no-take sites and nearby predator-poor fished sites in the Florida Keys (USA). Exploited fishes were more abundant at the no-take sites than at the fished sites. Most of the exploited fishes were either omnivores or invertivores. More piscivores were recorded at no-take sites, but most (approximately 95%) were moderately fished and unexploited species (barracuda and bar jacks, respectively). Impacts of these consumers on lower trophic levels were modest. Herbivorous and smaller prey fish (< 10 cm total length) densities and seagrass grazing diminished with distance from reefs and were not negatively impacted by the elevated densities of exploited fishes at no-take sites. Predation by reef fishes on most tethered invertebrates was high, but exploited species impacts varied with prey type. The results of the study show that, even though abundances of reef-associated fishes have been reduced at fished sites, there is little evidence that this has produced cascading trophic effects or interrupted cross-habitat energy exchanges between coral reefs and seagrasses.

Spatial analysis shows that fishing enhances the climatic sensitivity of marine fishes

We compare the changes in geographic distribution of exploited fish species versus unexploited ones living in the same environment. For this comparative study, we use the 50-year larval fish time series from the California Cooperative Oceanic Fisheries Investigations, which allows us to view fishing as a treatment effect in a long-term ecological experiment. Our results indicate that exploited species show a clearer distributional shift in response to environmental change than unexploited species, even after accounting for life history and ecological traits and phylogeny. The enhanced response (improved signal–noise ratio) to environmental change in exploited species may be a consequence of reduced spatial heterogeneity caused by fishery-induced age (size) truncation and the constriction of geographic distribution that accompanies fishing pressure. We suggest that reduced spatial heterogeneity can cause exploited populations to be more vulnerable to climate variability, an effect that could have considerable importance in the management of fish stocks. This is the first study to compare the geographic distributions of a large suite of exploited and unexploited fish species from the northeastern Pacific in response to climate variability.

Fishing elevates variability in the abundance of exploited species

The separation of the effects of environmental variability from the impacts of fishing has been elusive, but is essential for sound fisheries management. We distinguish environmental effects from fishing effects by comparing the temporal variability of exploited versus unexploited fish stocks living in the same environments. Using the unique suite of 50-year-long larval fish surveys from the California Cooperative Oceanic Fisheries Investigations we analyse fishing as a treatment effect in a long-term ecological experiment. Here we present evidence from the marine environment that exploited species exhibit higher temporal variability in abundance than unexploited species. This remains true after accounting for life-history effects, abundance, ecological traits and phylogeny. The increased variability of exploited populations is probably caused by fishery-induced truncation of the age structure, which reduces the capacity of populations to buffer environmental events. Therefore, to avoid collapse, fisheries must be managed not only to sustain the total viable biomass but also to prevent the significant truncation of age structure. The double jeopardy of fishing to potentially deplete stock sizes and, more immediately, to amplify the peaks and valleys of population variability, calls for a precautionary management approach.

A comparison of long-term trends and variability in populations of larvae of exploited and unexploited fishes in the Southern California region: A community approach

We have constructed an “expert-knowledge classification system” to categorize 309 fish taxa in the California Cooperative Oceanic Fisheries Investigations ichthyoplankton database into primary (coastal, coastal-oceanic, and oceanic) assemblages based on their principal ecological domains and subsequently, secondary assemblages according to the habitat affinities of adults. We examined effects of fishing, climate, adult habitat, and age-at-maturation on long-term variation of fish populations. We tested the hypothesis that populations of unexploited taxa track climatic trends more closely than those of exploited taxa insofar as climatic signals may be confounded by fishing effects. Most oceanic taxa (23/34) showed a significant relationship with environmental variables and followed the trend of the Pacific Decadal Oscillation. Very few coastal (3/10) and coastal-oceanic (3/23) taxa exhibited a significant relationship with environmental signals; however, several fluctuated coherently, and age-at-maturation is an important factor. The lack of close correlation between fish populations and environmental signals in the coastal and coastal-oceanic assemblages indicates that these species might show nonlinear biological responses to external forcing rather than a simple linear tracking of environmental variables. We did not find a systematic pattern indicating that fishing influenced population fluctuation of exploited species. Constrained comparisons of exploited to unexploited species living in the same habitat and reaching maturity at the same age revealed evidence of overexploitation for some species but not for all. Our results suggest that considering life history and ecological characteristics of fish species and applying a community approach are important in understanding fishing effects on fish populations in the context of a changing environment.

Settlement and recruitment of coral reef fishes in moderately exploited and overexploited Caribbean ecosystems: implications for marine protected areas

In order to evaluate the impact of heavy exploitation on settlement and recruitment rates of coral reef fishes, the abundances of pre-settlement and pre-recruitment fishes were monitored at Discovery Bay, Jamaica, where fish stocks are heavily exploited and at several sites around the British Virgin Islands (BVI) where exploitation is moderate. Light traps set concurrently at Discovery Bay and at three fringing reefs in BVI caught many species of pre-settlement reef fishes, except grunts and parrotfish, and one BVI site (Hans Creek) may be an area of particularly high settlement. In contrast, heavily exploited fish stocks at Discovery Bay had greatly reduced settlement rates compared with all three sites in BVI. Settlement rates of unexploited species were more similar in Discovery Bay and BVI. Abundances of juvenile fish caught in wire-mesh traps were monitored over several years in Discovery Bay and at three sites in BVI. Consistently low numbers of exploited species were taken at Discovery Bay compared to the BVI sites, indicating that settlement and recruitment rates have been low in recent years. Exploited fish populations in the small marine protected area (MPA) at Discovery Bay are expected to increase very slowly as a result of settlement and recruitment limitation.

Stationarity and rate of dampening of modeled indices of fish abundance in relation to their exploitation status in the Northwest Atlantic Ocean

Time series modeling of indices of fish abundance provided support for Ricker’s theoretical concept of the effects of fishing on cycling and population behavior. Modeled damped oscillations of indices of fish abundance through time reflected a reduction of effect of density-dependent compensatory mechanisms with increased fishing pressure. ARIMA models tended to explain less variability for exploited than for unexploited species. Therefore, the utility of these models is limited for exploited species.

In vitro shoot culture of wild Oryzae and other grass species

A method was developed for the in vitro clonal propagation of shoots from a range of wild rice and other grass species that have important genetic traits such as drought resistance and salinity tolerance. The axenic multiple shoot cultures, which were suitable for DNA and protein extraction or direct protoplast isolation, could be maintained without subculture for between 2 and 3 months or rapidly multiplied for the subsequent production of mature plants and seeds. Basal sections of the micropropagated shoots also provided novel explants for the production of highly embryogenic callus, from some species, that could be regenerated into green plants. It is envisaged that this clonal propagation technique could aid the genetic manipulation of cultivated rice by providing a means to vegetatively conserve valuable genetic resources, a technique to rapidly multiply novel hybrid material and a source of embryogenic callus that will allow the application of biotechnological techniques, such as somatic hybridization and genetic transformation, to previously unexploited species.

Nahal Hadera V : An open-air site on the Israeli Littoral.

A stratified open-air site near Hadera, Israel, was excavated in the spring of 1973, yielding a vast quantity of Kebaran stone tools and abundant faunal remains. The site stood in the centre of the broad coastal plain which existed during the period of lower sea levels 15 000 years ago. The fauna recovered includes both unexploited species indicating the local environment and the remains of ungulate herd animals which formed the basis of the epi-palaeolithic economy. The second section of the article examines the lithic technology of the site's inhabitants.