Growth Of Fish Populations Research Articles

The potential trade‐off between artisanal fisheries production and hydroelectricity generation on the Kafue River, Zambia

Summary1. Freshwater resource managers are increasingly obligated to consider the impacts of large river engineering projects on ecosystem services. We evaluated the effect of altered water regime from the operation of a large dam on the production of the downstream tropical floodplain fishery of the Kafue River, Zambia. We compared the benefits of increased hydropower relative to potentially lost fishery production.2. We compiled a long‐term data set consisting of experimental gillnet catches, artisanal harvesting effort and monthly river flows for 25 years prior to and 29 years after the 1977 completion of the upstream Itezhi‐Tezhi Dam. As a metric of the flood regime, we calculated a canonical correlation score for each hydrological year before and after dam closure. For the period following dam construction, we used the Muskingum method of flood routing to estimate ‘no‐dam’ flows through the fishery area and downstream hydroelectric turbines at the Kafue Gorge Dam.3. We compared 16 alternative models of catch per unit effort (CPUE) with and without an effect of water regime on fish population growth rate. Using the two best fitting models, we estimated the total observed fishery harvest and simulated ‘no‐dam’ fisheries harvest and found no significant effect of altered water regime on fishery production.4. We estimate that the large upstream dam increases downstream hydropower production by about $18 million USD per annum. The reduction in fishery production caused by the altered water regime is not significantly different than zero, although the average reduction amounts to about $2.3 million annually. The total estimated value of harvest ranges from $1.3 million to $56 million annually.5. Large observed declines in fish abundance over the 54‐year study period are attributed primarily with similarly large increases in total fishing effort in this mostly open‐access artisanal fishery.6. These results contrast with other examples of the effects of flow alteration on fish, probably because levels of fisheries exploitation on the Kafue River are very high relative to better studied regions on other continents; our focus on the whole fish community; and the unprecedented length of the time series we considered. If the goal is to sustain fishery production, investments in altering flow regime are likely to be less effective than investments to decrease fishing effort.

How long can fisheries management delay action in response to ecosystem and climate change?

Sustainable management of fisheries is often compromised by management delaying implementation of regulations that reduce harvest, in order to maintain higher catches in the short-term. Decreases or increases in fish population growth rate driven by environmental change, including ecosystem and climate change, affect the harvest that can be taken sustainably. If not acted on rapidly, environmental change could result in unsustainable fishing or missed opportunity for higher catches. Using simulation models of harvested fish populations influenced by environmental change, we explore how long fisheries managers can afford to wait before changing harvest regulations in response to changes in population growth. If environmental change causes population declines, delays greater than five years increase the probability of population collapse. Species with fast and highly variable population growth rates are more susceptible to collapse under delays and should be a priority for revised management where delays occur. Generally, the long-term cost of delay, in terms of lost fishing opportunity, exceeds the short-term benefits of overfishing. Lowering harvest limits and monitoring for environmental change can alleviate the impact of delays; however, these measures may be more costly than reducing delays. We recommend that management systems that allow rapid responses to population growth changes be enacted for fisheries management to adapt to ecosystem and climate change.

Ontogenetic allometry of the bluemouth, Helicolenus dactylopterus dactylopterus (Teleostei: Scorpaenidae), in the Northeast Atlantic and Mediterranean based on geometric morphometrics

The bluemouth, Helicolenus dactylopterus, is a deep-sea scorpionfish widely distributed in the Atlantic Ocean and the Mediterranean. It is a common by-catch associated to many demersal fisheries. However, there is little information about the stock structure, stock dynamics and life history parameters of the bluemouth. From the perspective of stock identification, it is important to study growth in fish populations to better understand the possible morphological differences among populations and when and why do they arise. Thus, the aim of this study was to determine the growth (allometric) trajectories of shape for several bluemouth populations in Northeast Atlantic and Mediterranean using landmark-based geometric morphometric techniques. In this study, ontogenetic allometry was present in all of the bluemouth samples. Ontogenetic shape changes were most evident in the head and pectoral area, affecting the position of the snout, preopercular spines and pectoral fins, but changes in body depth and length were also important. However, the degree to which these ontogenetic shape changes were present in bluemouth from each of the studied areas was different, indicating that their growth trajectories are not homogeneous. The importance of this finding for size-correction of the shape variables in morphometric studies for stock identification is also discussed.

The effect of Danish seine selectivity and retention on growth estimates of tiger flathead Platycephalus richardsoni

This work demonstrates the correction of gear-selectivity and retention effects in estimation of growth in fish populations. The selectivity bias can be removed from length-at-age and length increment data. To correct for bias, a maximum-likelihood estimator that incorporates gear selectivity, a size-dependent retention function and several stochastic growth models are provided. The estimator allows the use of joint samples collected by fishing gears with different selectivity, which increases sample size and data representativeness, and thus improves accuracy of population parameter estimates. Data collected from retained tiger flathead caught by Danish seine gear were used for numerical analysis of the selectivity bias. Stock assessment implications of bias in growth estimation are discussed.

CONSISTENT EXPECTATIONS EQUILIBRIA AND COMPLEX DYNAMICS IN RENEWABLE RESOURCE MARKETS

Price fluctuations under adaptive learning in renewable resource markets such as fisheries are examined. Optimal fishery management with logistic fish population growth implies a backward-bending, discounted supply curve for bioeconomic equilibrium sustained yield. Higher discount rates bend supply backward more to generate multiple steady-state rational expectations equilibria. Under bounded rationality, adaptive learning of a linear forecasting rule generates steady-state, two-cycle as well as chaotic consistent expectations equilibria, which are self-fulfilling in sample average and autocorrelations. The possibility of “learning to believe in chaos” is robust and even enhanced by dynamic noise.

A mathematical model of a shallow and Eutrophic Lake (The Keszthely Basin, Lake Balaton) and simulation of restorative manipulations

Concern about the overall management of lakes has been growing, and a lake ecological model provides the guidelines necessary for such management. In this study, an ecological model describing the ecosystem of the Keszthely Basin, Lake Balaton, Hungary, one of the typical shallow and eutrophic lakes, was proposed. This model includes three types of zooplankton and two types of fish as well as two types of algae and nutrients. Parameters concerning the algae and fish were estimated based on observations in the basin between 1991 and 1995. The other parameters and the structure of the model were determined by our previous study. The parameters of the model were calibrated with the Monte Carlo technique, and its predictability was confirmed. The effects on the basin's ecosystem of three restorative manipulations, namely a biomanipulation, reduction of loading phosphorus, and dredging the sediment, were assessed by simulation studies using the proposed model. The simulation results indicated that a biomanipulation that removed 90% of the bream should suppress the growth of algae temporarily through bottom–up regulation; however, this effect seemed to not be perpetuated in this basin. The reduction of loading phosphorus seemed to be the most effective means to suppress algal growth, while dredging of sediment seemed to be the most desirable restoration method from the standpoint of the overall management of the lake, because it was expected to accelerate the growth of fish population as well as to suppress algal growth. Furthermore, the algal growth suppresion mechanism of the dredging was disccused on the basis of the model calculations.

Biological reasons for the unsuitability of growth parameters and indices for comparing fish growth

Parameters k and L∞ in the Von Bertalanffy equation and their derivatives ω=kL∞, φ = logk + 2logL∞; as well as slopes bL/t of the regression L=atb (t, years), relative increments (CI=[L2–L1]/L1), specific growth rates (Cv=InL2–InL1), growth characteristics (Clh = CvxL1) and growth constants (Clt=Cvx[t2 + t1]/2) were analyzed. A total of 121 bream Abramis brama stocks in the first 10 years of life were studied. At the same real growth rate (the average absolute linear annual increments, mm year–1) the values of k, L∞, ω, φ, bL/t, CI, Cv and Clt in different stocks vary within almost the whole range. The main reason is the natural process of growth self-regulation: the relation between the average body lengths in the first year (L1) and the relative growth rates (slopes bL/t) is negative (bL/t = exp[0.1183–0.0053L1], r=0.76). The above relation defines 4 principal types of the Ford-Walford lines. Thirty four percent of the stocks have rather steep slopes of the lines and even parallel the absolute slope of 45°, so the L∞ values of these stocks have no biological significance. The authors recommend a simple and more precise, from a biological point of view, approach for comparing fish population growth rates.

Fed up with parasites? A method for estimating asymptotic growth in fish populations

The accumulation of parasites in a fish host is modelled as a function of the total amount of prey consumed. The accumulated parasite load is then expressed as a function of fish length so that the asymptotic growth, L∞, of any population of commonly infected fish can be estimated. Estimates of L∞ are obtained for orange roughy (Hoplostethus atlanticus), albacore tuna (Thunnus alalunga) and the New Zealand southern arrow squid (Nototodarus sloanii).

Stocking effects on a fish population growth with time lag regulation.

The simple logistic model with time lag control is employed to consider the constant rate stocking effects. Stocking increases the equilibrium level of the population. The stability of the equilibrium depends on all parameters employed in the model. The equilibrium becomes unstable and the limit cycle arises under the sufficient level of stocking although the product of the increasing rate and time lag is less than π/2. Stocking produces the increase of the amplitude and the decrease of the period of the population's fluctuation. Careful stocking is desired in controlling natural populations.

A control theoretic model of multispecies fish harvesting

A mathematical model of the growth of mass of a multispecies fish community is constructed taking into account natural growth, mortality and breeding. The Sterile Male Technique (STM) propounded Taylor and Costello (1973) is applied with a view to controlling ecological resources which are essential for the growth of fish populations. The optimal harvest policy is studied by invoking Pontryagin's Maximal Principle. Dynamical behaviour of the system is discussed at length.

An Evaluation of RNA–DNA Ratio as a Measure of Long-Term Growth in Fish Populations

The value of RNA–DNA ratio as a measure of long-term growth of fish populations under semi-natural conditions and when subjected to environmental manipulations was determined. Populations of carp and smallmouth bass of known age distribution were established in artificial ponds maintained at two fertility levels. After 15 months, population growth rates (as percent increase in weight) and RNA–DNA ratios of muscle tissue from selected fish were measured. Each species exhibited a range of population growth rates. The relation between population growth rate and individual fish RNA–DNA ratio for each species was significant. When reproduction occurred, the relation was not significant unless young-of-the-year fish were excluded from population growth rate calculations. Age of fish was also found to have an important effect on RNA–DNA ratio, with the ratio being higher in younger fish.RNA–DNA ratio can be a reliable indicator of long-term population growth in fish when population age structure is known and recruitment is controlled. The method has potential for use in detecting response to environmental changes before growth rate changes become severe.