Effects of experimental harvest on red sea urchins (Strongylocentrotus franciscanus) in northern Washington

Commercial harvest of red sea urchins began in Washington state in 1971. Harvests peaked in the late 1980s and have since declined substantially in Washington and other areas of the U.S. west coast. We studied effects of experimental harvest on red sea urchins in San Juan Channel (SJC), a marine reserve in northern Washing-ton. We recorded changes in density and size distribution of sea urchin populations resulting from three levels of experimental harvest: 1) annual size-selective harvest (simulating cur-rent commercial urchin harvest regulations), 2) monthly complete (non–size selective) harvest, and 3) no harvest (control) sites. We also examined re-colonization rates of harvested sites. The red sea urchin population in SJC is composed of an accumulation of large, old individuals. Juvenile urchins represent less than 1% of the population. Lower and upper size limits for commercial harvest protect 5% and 45% of the population, respectively. Complete harvest reduced sea urchin densities by 95%. Annual size-selective harvest significantly decreased sea urchin densities by 67% in the first year and by 47% in the second year. Two years of size-selective harvest significantly altered the size distribution of urchins, decreasing the density of legal-size urchins. Recolonization of harvested sites varied seasonally and occurred primarily through immigration of adults. Selective harvest sites were recolonized to 51% and 38% of original densities, respectively, six months after the first and second annual harvests. Yields declined substantially in the second year of size-selective harvest because of the fishing down of the population and because of low recolonization rates of harvested sites. We recommend that managers consider the potential efficacy of marine harvest refuges and reevaluate the existing upper and lower size limits for commercial harvest to improve long-term management of the sea urchin fishery in Washington.

Impact of plankton structure on primary productivity in two beels of West Bengal, India

Planktonic community in floodplain wetlands embodies the energy transfer through this phase and indicates trophic status of lake. Originally rich bottom coupled with a conducive physicochemical environment encourages fast colonization of the plankton population. Present investigation was carried out in two floodplain wetlands having characteristics of open (Amda beel) and closed (Suguna beel) system. The physicochemical parameters of water and soil of the investigated heels were by and large conducive for planktonic growth. The density of plankton population varied between 1,346 and 2,170 u/l in Suguna bed whereas in Amda beel it ranged from 1,030 to 1,802 u/l. Seasonal fluctuations in water column were conspicuous and mostly dependent on the replenished resources and volume, A mixed and balanced population of diversified fauna constituted the plankton population of the investigated ecosystems. Mostly the diversity was observed to be maximum during winter seasons with coincidence of favorable temperature, dissolved oxygen and other physico-chemical parameters of water besides optimum solar penetration. Richness of planktonic structure in closed system (Suguna) resulted in higher fish production (1,570,05 kg/ha/yr) than that of open system (Amda) (384.4 kg/ha/yr).

Influence of a fish bacterium Lactobacillus sp. on the production of swordtail xiphophorus helleri (Heckel 1848)

The influence of a fish gut bacterium Lactobacillus sp on the production of swordtail Xiphophorus helleri was studied for a period of one year. The Lactobacillus sp P21 produced bacteriocin-like inhibitory substance and exhibited wide spectrum of action against Aeromonas hydrophila, Bacillus spp, Pseudomonas spp and Citrobacter freundi in vitro. The growth performance of X. helleri reared in the presence of Lactobacillus P21 at 106/ml rearing water was better than the control. The total plate counts, total MRS agar counts and the counts of motile aeromonads, presumptive pseudomonads, lactose fermenters and lactose non-fermenters in the gut of probiotic group were comparatively low than the control. On day 60 the count of Lactobacillus sp P21 was observed to be log 5.28/g in the gut of X. helleri indicating colonization of this bacterium in the gastrointestinal tract. The fecundity of X. helleri was in the range of 9-134. On average, it produced from 39.42±18.72 fry/female in control group to 53.00±23.57 fry/female in probiotic group. The increase in average fecundity in probiotic group over the control group was about 25%. There existed significant difference between probiotic group and control in respect of average fecundity/female (p<0.02), average number of fry survived /female (p<0.006) and average number of fry dead/female (p<0.029). The results of the present study demonstrated that the rearing of X. helleri in probiotic-enriched water have growth inducing ability and favourably influenced the reproductive performance in terms of high fecundity, high fry survival, reduced fry mortality and reduced fry deformity.