Stellan F. Hamrin

Biomanipulation as an Application of Food-Chain Theory: Constraints, Synthesis, and Recommendations for Temperate Lakes

ABSTRACT The aim of this review is to identify problems, find general patterns, and extract recommendations for successful biomanipulation. An important conclusion is that the pelagic food chain from fish to algae may not be the only process affected by a biomanipulation. Instead, this process should be viewed as the “trigger” for secondary processes, such as establishment of submerged macrophytes, reduced internal loading of nutrients, and reduced resuspension of particles from the sediment. However, fish reduction also leads to a high recruitment of young-of-the-year (YOY) fish, which feed extensively on zooplankton. This expansion of YOY the first years after fish reduction is probably a major reason for less successful biomanipulations. Recent, large-scale biomanipulations have made it possible to update earlier recommendations regarding when, where, and how biomanipulation should be performed. More applicable recommendations include (1) the reduction in the biomass of planktivorous fish should be 75% or more; (2) the fish reduction should be performed efficiently and rapidly (within 1–3 years); (3) efforts should be made to reduce the number of benthic feeding fish; (4) the recruitment of YOY fish should be reduced; (5) the conditions for establishment of submerged macrophytes should be improved; and (6) the external input of nutrients (phosphorus and nitrogen) should be reduced as much as possible before the biomanipulation. Recent biomanipulations have shown that, correctly performed, the method also achieves results in large, relatively deep and eutrophic lakes, at least in a 5-year perspective. Although repeated measures may be necessary, the general conclusion is that biomanipulation is not only possible, but also a relatively inexpensive and attractive method for management of eutrophic lakes, and in particular as a follow-up measure to reduced nutrient load.

Electrofishing — Theory and practice with special emphasis on salmonids

This report attempts to establish guide-lines for electrofishing in population studies and is the result of literature studies and experience from electrofishing in Denmark, Finland, Norway and Sweden. Equipment, safety and training, sampling design and precision requirements for various types of investigations, population estimation and fishing practice are discussed. The results are put forward in the form of recommendations. Special attention is paid to the sampling design of surveys in streams of different types and for different purposes. Examples of the computation procedures are also included.

Predator Regulation and Primary Production Along the Productivity Gradient of Temperate Lake Ecosystems

More than any other ecological discipline, limnology has claimed to be an ecosystem oriented and holistic science (Rodhe 1979; Wetzel 1983). In other ecological disciplines, an intense debate has taken place recently concerning whether or not the ecosystem is a meaningful ecological unit (e.g., Simberloff 1980 vs Levins and Lewontin 1980), but this has not been the case in limnology. We will argue that, although the ecosystem orientation in limnology is not the same as that represented by systems ecology today (Patten and Odum 1981; Odum and Biever 1984), both have a common historical root. Consideration of this historical circumstance is essential for understanding why the importance of complex intertrophic interactions has largely been neglected in limnology. The development of limnology has been treated by Elster (1974) and Rigler (1975), among others. We take a somewhat different approach by focusing mainly on what has constrained the development of limnology. In doing so we consider two factors which have had major impacts on the discipline: (1) lake typology, and (2) the multidisciplinary nature of limnology. A third factor, the integration between theory and application, has strongly influenced the development of the discipline but will not be treated in this context.

Predatory efficiency and prey selection: interactions between pike Esox lucius, perch Perca fluviatilis and rudd Scardinus erythrophthalmus

PREDATORY EFFICIENCY AND PREY SELECTION - INTERACTIONS BETWEEN PIKE ESOX-LUCIUS, LUCIUS, PERCH PERCA-FLUVIATILIS AND RUDD SCARDINUS-ERYTHROPHTHALMUS

Fat content as a factor inducing migratory behaviour in the eel (Anguilla anguilla L.) to the Sargasso Sea

Fat content as a factor inducing migratory behaviour in the eel (Anguilla anguilla L.) to the Sargasso Sea

Factors determining the uptake of persistent pollutants in an eel population (Anguila anguilla L.).

The distribution of persistent pollutants in an eel population from a eutrophic lake of southern Scandinavia was examined. The origin of PCBs, DDT, DDE and lindane found in the fish was most likely the atmosphere. The most important factors for uptake of the chlorinated hydrocarbons was age (exposure time), growth rate and fat content. The life cycle of the eel is unique with a stage in freshwater when energy reserves (fat stored in muscular tissue) and lipophilic pollutants are accumulated. This stage is followed by a long migration to the spawning areas in the Sargasso Sea when pollutants are released from the fat deposits. These two stages followed by a once-in-a-lifetime spawning behaviour, makes the eel especially vulnerable to persistent pollutants. The effects of persistent pollutants combined with the eels unusual life cycle may explain the decline in the eel population in northern Europe in recent decades.

Density dependent interactions in lake ecosystems : whole lake perturbation experiments

Density dependent interactions between higher and lower trophic levels were studied in two consecutive whole lake experiments in a highly productive lake. In the first experiment, the zooplanktivor ...

Pike as a selective predator. Effects of prey size, availability, cover and pike jaw dimensions

An experiment was performed to study the influence of prey size, availability, the presence or absence of cover and pike jaw dimensions on prey consumption by pike. Rudd in schools of 10 were offered to pike in outdoor pools. Pike weighed between 66.4 and 182.1 g. Schools of 10 rudd contained two, five or eight fish with mean sizes between 5.6 and 6.8 g, the remaining fish weighing between means of 12.4 and 14.1 g. Cover was provided by a 1 m2 mat of plastic netting supporting simulated plant stems spaced at 5 cm intervals. Pike chose mostly from the small size category and the presence of cover did not significantly influence the choice made. Increased availability of the chosen prey size increased food intake. Pike never completely dropped the large prey from the diet despite its low availability; a case of partial preference. The jaw dimensions of the pike were most closely correlated with the body dimensions of the small rudd. It is suggested that the prey size eaten was determined by an interaction between pike jaw morphology and the relative swimming speeds of pike and rudd, rather than by a behavioural choice.

Synthesis of theoretical and empirical experiences from nutrient and cyprinid reductions in Lake Ringsjön

The reduction in external phosphorus load to Lake Ringsjön during the 1980s, did not result in improved water transparency during the following ten-year period. Furthermore, a fish-kill in the Eastern Basin of the lake, in addition to a cyprinid reduction programme (biomanipulation; 1988–1992), in contrast to theory, did not lead to any increase in zooplankton biomass or size. This absence of response in the pelagic food chain may have been attributed to the increase in abundance of YOY (0+) fish, following the fish reduction programme. Despite the lack of effect on zooplankton, there was a decrease in phytoplankton biomass, a change in species composition and an increase in water transparency following biomanipulation. In 1989, one year after the fish-kill in Eastern Basin, the Secchi depth (summer mean) increased from 60 cm to 110 cm. In the following years, water transparency increased further, despite an increase in phosphorus loading. An unexpected effect of the biomanipulation was an increase in benthic invertebrate and staging waterfowl abundances, which occurred 2–4 years after fish reduction. Hence, the response in the benthic community following biomanipulation was considerably stronger than in the pelagic community. A likely explanation is that reduction in abundance of the benthic feeding fish species bream (Abramis brama), strongly affected the benthic invertebrate fauna. In this paper, we present what we believe happened in Lake Ringsjön, and which processes are likely to have been important at various stages of the restoration process.

The Role of Behaviour and Morphology in the Selection of Prey by Pike

Explaining and predicting prey selection has been one of the major tasks of optimal foraging models (Hart, 1986; Stephens & Krebs, 1986). Most models assume that optimal choice is brought about by some behavioural process. For example the basic prey model as used by Werner and Hall (1974), assumes that animals are able to rank prey by their profitabilities and to make decisions about which prey type to include in the diet. There is no implication from the models that an animal must be able to calculate complex optimisation relations but in so far as the forager uses a rule of thumb to make a foraging decision, behaviour is the main process involved (Stephens & Krebs, 1986).