Exploitation dynamics of fish stocks

I address the question of the fluctuations in fishery landings. Using the fishery statistics time-series collected by the Food and Agriculture Organization of the United Nations since the early 1950s, I here analyze fishing activities and find two scaling features of capture fisheries production: (i) the standard deviation of growth rate of the domestically landed catches decays as a power-law function of country landings with an exponent of value 0.15; (ii) the average number of fishers in a country scales to the 0.7 power of country landings. I show how these socio-ecological patterns may be related, yielding a scaling relation between these exponents. The predicted scaling relation implies that the width of the annual per capita growth-rate distribution scales to the 0.2 power of country landings, i.e. annual fluctuations in per capita landed catches increase with increased per capita catches in highly producing countries. Beside the scaling behavior, I report that fluctuations in the annual domestic landings have increased in the last 30 years, while the mean of the annual growth rate declined significantly after 1972.Comment: 27 pages, 19 figure

Implications of fisheries during the spawning season for the sustainable management and recovery of depleted fish stocks: a conceptual framework

Fishing during the spawning season may negatively affects the reproductive potential and reproductive dynamics of exploited fish stocks due to a variety of mechanisms such as the disturbance of the natural spawning behaviour, effects on the age, size and sex composition of the spawning population and effects on the population genetics. The effect may differ between species in relation to the spawning strategy and population dynamic characteristics. Based on first principles of reproductive biology, population biology and fishing methods, a theoretical framework is developed on the effects of fishing during the spawning period. This framework is used to structure a review of the available scientific evidence. Implications of the findings on the recovery of depleted fish stocks and the sustainability of exploitation will be discussed and illustrated for a selection of North Sea fish stocks (flatfish, roundfish and pelagic)

Status and scope of research on pelagic fisheries of India

Extensive and indiscriminate exploitation of marine natural resources, during the last three decades is leading to a situation where no more commercial fish stocks may be left in the sea by year 2050 unless ecosystems are protected and the biodiversity is revived, warns a new study cataloging the global collapse of marine ecosystems (Worm et al., 2006). The task of understanding the dynamics of large marine ecosystems to offer effective and relevant scientific advice to develop management interventions is a difficult, complex, expensive and lengthy process. This is especially true in the Indian context where the country has an EEZ of 2.02 million km2, which contributes nearly 40% of the total fish production from the Indian Ocean. Fishes have been mentioned in the ancient literature of India including the epics such as Ramayana and Mahabaratha. Excavations from Mohenjodaro and Harappa indicate that fishing with hooks and nets was common as back as 3000 B.C. and over the years fishing and fisheries in India have evolved at a rapid pace (Ayyappan et al., 2004). Marine fisheries is basically harnessing a natural resource and therefore its management must anchor on knowledge- based interventions generated through close monitoring of their distribution, abundance, exploitation, population dynamics and fluctuations of fish stocks in relation to natural factors and anthropogenic interventions. Against a scenario of an ever-increasing population and stagnant marine fish production in recent years, per capita seafood availability is a serious concern. The countr

Fishing and the impact of marine reserves in a variable environment

We use discrete-time models to investigate the impact of marine reserve establishment on fishery catch and biomass levels in open-access and quota-regulated fisheries under conditions of recruitment variability and natural mortality events. We find that under the conditions of variability tested, reserves can increase the probability of achieving target levels of biomass (60%, 35%, and 5% of carrying capacity) and can reduce catch variability in neighbouring fisheries, making future planning in the fishery more efficient. The size of the reserve required to meet each objective will depend on the initial condition of the stock and the exploitation rate in the fishery. Reserve coverage of between 20% and 40% prevent stock collapse in most cases. In heavily exploited fisheries, reserves are also likely to enhance mean catches, particularly in highly variable systems. If the stock has previously been heavily exploited, large reserves (greater than or equal to60%) may be required to significantly increase the probability of achieving target biomass levels. However, once stocks have recovered, reserve coverage may be reduced without a reduction in this probability of success

Stock assessment of protogynous fish: evaluating measures of spawning biomass used to estimate biological reference points

In stock assessments, recruitment is typically modeled as a function of females only. For protogynous stocks, however, disproportionate fishing on males increases the possibility of reduced fertilization rates. To incorporate the importance of males in protogynous stocks, assessment models have been used to predict recruitment not just from female spawning biomass (Sf), but also from that of males (Sm) or both sexes (Sb). We conducted a simulation study to evaluate the ability of these three measures to estimate biological reference points used in fishery management. Of the three, Sf provides best estimates if the potential for decreased fertilization is weak, whereas Sm is best only if the potential is very strong. In general, Sb estimates the true reference points most closely, which indicates that if the potential for decreased fertilization is moderate or unknown, Sb should be used in assessments of protogynous stocks. Moreover, for a broad range of scenarios, relative errors from Sf and Sb occur in opposite directions, indicating that estimates from these measures could be used to bound uncertainty