Biology, Fishery, Conservation and Management of Indian Ocean Tuna Fisheries

The focus of the study is to explore the recent trend of the world tuna fishery with special reference to the Indian Ocean tuna fisheries and its conservation and sustainable management. In the Indian Ocean, tuna catches have increased rapidly from about 179959 t in 1980 to about 832246 t in 1995. They have continued to increase up to 2005; the catch that year was 1201465 t, forming about 26% of the world catch. Since 2006 onwards there has been a decline in the volume of catches and in 2008 the catch was only 913625 t. The Principal species caught in the Indian Ocean are skipjack and yellowfin. Western Indian Ocean contributed 78.2% and eastern Indian Ocean 21.8% of the total tuna production from the Indian Ocean. The Indian Ocean stock is currently overfished and IOTC has made some recommendations for management regulations aimed at sustaining the tuna stock. Fishing operations can cause ecological impacts of different types: by catches, damage of the habitat, mortalities caused by lost or discarded gear, pollution, generation of marine debris, etc. Periodic reassessment of the tuna potential is also required with adequate inputs from exploratory surveys as well as commercial landings and this may prevent any unsustainable trends in the development of the tuna fishing industry in the Indian Ocean

Population dynamics and life histories of foliaceeous corals

The population dynamics of five species of foliaceous corals (Agaricia agaricites forma purpurea, A. lamarcki, Leptoseris cucullata, Montastrea annularis, and Porites astreoides) was followed on Jamaican reefs using annual photographic censuses. Overall, population cover, size frequencies, and number of colonies were stable over the monitored period from 1977 to 1980. However, individual colonies were in turmoil: of the original 883 colonies, 315 were killed outright and 499 suffered partial colony mortality (injury) at least once during the 3 yr. Partial mortality generated an additional 189 colonies by fission, while larval recruitment added another 201, and fusion subtracted 40 colonies. The net result was a decrease of < 10% in number of colonies. There was considerable variation among years and sites in measured life history parameters, as well as striking differences between species. The most stable populations were M. annularis and A. lamarcki, followed by P. astreoides, A. agaricites, and L. cucullata. Rates of partial- and whole-colony mortality were strongly dependent on colony size for all species. Typically, small colonies either were unharmed, or were killed outright, while most large colonies survived but were injured each year, often by extensive amounts. The amount of tissue lost from a population through injuries was usually much greater than through the death of whole colonies, even in a year which included a major winter storm. Frequently, large corals were split asunder by partial mortality to produce several daughter colonies, which presumably were of identical genotype. Therefore counts of physically separate colonies exceeded the number of genetically distinct individuals (genets), by at least 20%. Individual genets, measured as the lateral extent of known daughter colonies, were frequently up to 5 m across, and for M. annularis and A. lamarcki were certainly several centuries old. Colony extension rates measured in situ were very weakly dependent on depth from - 10 to -55 m, and were independent of colony size. Small colonies showed much faster relative changes in area, although even the largest corals continued to grow if they avoided major injuries. Within a size-class, the fates of colonies were diverse because of differential rates of growth and shrinkage, so that size was a very poor indicator of age. Differences in the life history and "mobility" between species are reflected in the taxonomic and morphological composition of coral communities over the reef. Shallow-water assemblages of foliaceous corals are composed of more dynamic, delicately built species, while many deeper water communities are dominated by slower growing, robust species. Ironically, disturbance on coral reefs often seems to favor the organisms most vulnerable to damage

Mass mortality of the echinoid Diadema antillarum Philippi in Jamaica

[Extract] During the summer of 1983 Jamaican populations of the ubiquitous spiny sea urchin, Diadema antillarum Philippi, suffered mass mortalities. The die-off spread around most of the ocastline of Jamaica wihtin about 8 weeks, causing local mortality rates close to 100%. Diadema antillarum is a major herbivore (Randall et al., 1964; Ogden et al., 1973; Sammarco et al., 1974; Carpenter, 1981), whose feeding activities cause considerable amounts of bioerosion (Steam and Scoffin, 1977) and affect coral settlement (Sommarco, 1980; 1982). Therefore, the drastic decline of Diadema populations could result in far reaching changes in overall reef community structure and dynamics. Here we describe the outbreak and course of the urchin die-off along part of the north coast of Jamaica, and give a brief outline of its effect on the reef ecology so far

Climate-mediated mechanical changes to post-disturbance coral assemblages

Increasingly severe storms and weaker carbonate materials associated with more acidic oceans will increase the vulnerability of reef corals to mechanical damage. Mechanistic predictions based on measurements of colony mechanical vulnerability and future climate scenarios demonstrate dramatic shifts in assemblage structure following hydrodynamic disturbances, including switches in species' dominance on the reef and thus potential for post-disturbance recovery. Larger colonies are more resistant to factors such as disease and competition for space, and complex morphologies support more associated reef species. Future reefs are thus expected to have lower colony abundances and be dominated by small and morphologically simple, yet mechanically robust species, which will in turn support lower levels of whole-reef biodiversity than do present-day reefs

Temperature-mediated transitions between isometry and allometry in a colonial, modular invertebrate

The evolutionary success of animal design is strongly affected by scaling and virtually all metazoans are constrained by allometry. One body plan that appears to relax these constraints is a colonial modular (CM) design, in which modular iteration is hypothesized to support isometry and indeterminate colony size. In this study, growth rates of juvenile scleractinians (less than 40 mm diameter) with a CM design were used to test this assertion using colony diameters recorded annually for a decade and scaling exponents (b) for growth calculated from double logarithmic plots of final versus initial diameters. For all juvenile corals, b differed significantly among years, with isometry (b=1) in 4 years, but positive allometry (b>1) in 5 years. The study years were characterized by differences in seawater temperature that were associated significantly with b for growth, with isometry in warm years but positive allometry in cool years. These results illustrate variable growth scaling in a CM taxon and suggest that the switch between scaling modes is mediated by temperature. For the corals studied, growth was not constrained by size, but this outcome was achieved through both isometry and positive allometry. Under cooler conditions, positive allometry may be beneficial as it represents a growth advantage that increases with size