1992. Biomass spectra of aquatic ecosystems in relation to fisheries yield Can. j. Fish. Aquat. Sci. 49: 1528-1 538.The biomass density of aquatic ecosystems can be expressed as an allsmetric function of organism body sine. The log-log plot of this relation, termed the biomass spectrum, is used to cornpare aquatic ecosystems in various parts of the world. We develop a standardized presentation for several example environments where detailed data on biomass density by body size in the trophic positions, phytoplankton, zooplankton, benthos, and fish, make it possible to establish overall or primary spectral slopes. The basic methodology is adapted for application to other ecosystems where less detailed data are available, Spectra from all the different environments exhibit a unifc~rrn low slope, but with different intercepts that appear to reflect ecosystem differences in nutrient circulation and availability. Detail on the secondary structuring at various positions in the trophic system appears to provide information useful for distinguishing between long-term changes in productivity and short-term perturbations in biomass or abundance.La densite de la biomasse presente dans un 6cosystGme aquatique peut &re exprimee ssus forme de fonction allom6trique de la taille des srganisrnes. On utilise le graphe log-log de cette relation, appelee spectre de biomasse, pour cornparer les 6cosystemes aquatiques de diverses parties du globe. On dabore aussi une presentation normalisee de plusieurs types d'ersvironnernents pour lesqslels des donnees detaillkes sur la densit6 de la biomasse en fonction de la taille des srganisrnes au niveau trophique, nooplancton, phytoplancton, benthos et pisson, permettent d'etablir la pente globaleou primaire du spectre. On adapte les methodes fondamentales pour qu'elles s'appliquent A d'aartres 6cosyst&rnes pour lesquels des dsnnees dktaill6es ne sont pas disponibles. Les spectres obtenus de tous les differents environnernents rnontrent une faible pente uniforrne, mais les differents interceptes semblent r6fl6ter des difgrences dans le cycle et la disponibilit6 des aliments au rsiveau des 6cosyst6mes. Bes details sur la structure secondaire 2 diverses positions du systerne trophique semblent fournir de B'informatisn utile dans la separation des variations 21 long terme de la prsductivit6 et des perturbations 3 court terme de la biomasse ou de t'absndance.(xuesa redicting biological production in communities from energy flux through its trophic components has been a prime focus of ecology. Attempts to use Lindeman's (1942) original fornulation, specifying predator-prey trophic linkages between species grouped into "levels, ' have demonstrated the difficulties of arriving at models that are both sufficiently realistic and sufficiently general (Lane and Collins 1985). The practical failure of the trophic level calculations (Mmn et al. 1989) in the past is due partly to the complexity of the systems modelled and partly to continued uncertainty about the time and space scales on which it is possibl...

The structure of animal communities and the energy flux through them may be characterized by biomass ratios, ecological efficiencies, and production efficiencies of the component organisms. Here, we interpret these ratios in terms of the elementary processes of food intake, specific production rate, and gross growth efficiency that underlie them. Recent information confirms that the magnitude of all these processes is related to the average body mass of the organisms involved. However, our analysis shows that this well—known dependence reflects the influence of two different basic biological properties. One of these is the metabolism—body—size relation of individual that is familiar from physiology. The other less well—recognized property appears as an ecological population factor reflected in the distribution of particle sizes within animal groups in the community and is probably related to the relative sizes and distributions of predators and their prey. It appears that both the physiological and ecological size relationships have to be recognized as scaling factors in order to transform measures of biological production of various parts of communities into common terms for comparison. Current data on the generality and stability of community structure and production suggest that by using this twofold size scaling, trophic energy flow within the community can be determined from the distribution of body sizes without the necessity of specifying trophic levels of the organisms involved. The ecological size scaling can be seen as an index of the system nature of ecosystems.

In an earlier paper we described the growth of fishes, ΔW/Δt, in relation to the experimentally measurable variables, body weight (W), food intake (R), and total metabolism (T). Here we review experimental evidence of the nature of the relation between T and W, and its dependence on R and temperature. Making use of the basic energy equation, pR = T + ΔW/Δt, where p is the term for correction from injested to utilizable energy, we calculate T as the difference between the energy equivalents of R and ΔW/Δt, for comparison with results of oxygen consumption studies. Application to a number of published experimental results suggests that with constant food availability, this index of total metabolism, T, derived from feeding experiments, shows the same rate of change with body weight, W, as has been found by oxygen consumption studies under standard conditions. That is, the two sources of data provide estimates of a common γ in the relation[Formula: see text]where α and γ are the fitted parameters for the curve.When fish are fed on a "maintenance" diet, the value of α calculated from the food-growth difference (the growth change is rarely nil in a given experimental observation period), appears to correspond with that characterizing the "routine" metabolic level in oxygen consumption studies. Higher α levels result from higher levels of food availability, and at ad libitum feeding α appears to approach the levels known in oxygen consumption studies as "active" metabolic levels. Temperature effects in the experiments were estimated from multiple regression analyses and showed an elevation of α with increasing temperature. The long-term effect of temperature on α was comparable with that predicted by the Krogh correction at ad libitum feeding, but was significantly lower when food was limited, as at "maintenance" feeding.From a survey of effects of different designs of feeding experiments on these metabolic parameters, it appeared that apparently aberrant values of the weight exponent γ may instead be mistaken interpretations of changes in the level of metabolism α. That is, within the limiting conditions of standard or active metabolism, changes in temperature during experiments or manipulations of the availability of food by the experimenter, sometimes unintentionally, elicit adaptative responses in the level of metabolism, α. These show up in the results as effects on γ when the changes in conditions are gradual, hence confounded with body-size changes during growth.The ability to make distinctions between effects of various factors on these two metabolic parameters appears to depend upon a distinction between experiments conducted with a view to learning what fish do under particular circumstances, and experiments designed to explore what fish are capable of doing. The former type reveal a remarkable conservatism in the basic relation between metabolism and body size, γ. Results from the latter reflect possibilities of metabolic adaptation to environmental circumstances. The apparent predictability of the response of the total metabolism to various conditions of food energy supply and dissipation suggests that the remainder of the energy system, represented by the growth, may be similarly predictable. If this is true outside the laboratory, measurements of the metabolic parameters, α and γ, already familiar in physiological and behavioural research, could be directly used as indices of the (relative) positions of various sizes and species of fish in natural production systems.

Reexamination of published data on growth and feeding of fishes shows that when fish are fed on one type of food, the logarithm of the gross growth efficiency (log K) decreases with increase in rations. For a number of species and experimental situations this relation is adequately described by the linear equation[Formula: see text]whence[Formula: see text]where ΔW is the growth, R the rations intake during the period of time Δt, and a and b are the parameters fitted to the linear form of the equation. With a single food-supply level, rations are highly correlated with body weight so that either one may be used to predict the growth efficiency. However, comparison with experimental situations which induce changes in rations intake at given body size, suggests that body size is not the determining factor as long as environmental conditions are within the normal biokinetic range. That is, the basic pattern of distribution within the animals of the energy intake is described by a knowledge of the rate of intake and two parameters.The action of various environmental factors appears to be reflected in this equation in different ways. In the experiments examined changes in temperature, which are known to affect the level of total metabolism, affected the value of R but the parameters a and b remained unchanged. That is, temperature changes appeared to affect only the energy turnover rate, not the distribution of energy in the fish. By contrast, changes in factors such as salinity and metabolic wastes, which are known to affect the metabolic load, affected the values of a and b, and showed interaction with body-size as well. The factor having the most important influence on the parameters seemed to be the type of food, especially with respect to particle-size. We infer that this simple effect on the linear equation is a characteristic expression of the complex integration of expenditures during searching and grazing with the success of this activity.These observations imply that the growth efficiency equation, or what we term K-line, provides a useful index of the costs of particular behaviour patterns in particular ecological situations. Together with observations on metabolic rates it may also be used to describe the growth of fishes in relation to their food supplies. It is thus a potential indicator of the relative positions of life-history phases of various species in the production system represented by a natural community.

Fluctuations in total landings and in catch per boat have characterized the Digby scallop fishery since it began in 1920. An analysis of records of the fishery indicates that, although changes in fishing methods have been partly responsible for early changes in catch, their influence in recent years has been small and changes in abundance have been primarily responsible for fluctuations in the fishery since it reached its full development in the mid-thirties.Changes in abundance are assessed from analyses of catch records, special "census-fishing" techniques, submarine photography and marking experiments. Estimates from the different methods correspond.Scallops are recruited into the catchable population as six-year-old year-classes. Abundance is high when these recruited year-classes are strong, but is low when they are weak. Abundance in any year is correlated with water temperature six years previously. Both abundance and the strength of individual year-classes are correlated with water temperatures which prevailed at the time the scallops were present as pelagic larvae.It is concluded that changes in the abundance of the catchable scallop stocks result from the combined action of temperature and circulation on the pelagic larvae. Low temperatures retard larval development, and are indicative of great exchange of the water in the Bay of Fundy with outside water masses. This apparently leads to heavy losses of the larvae from the Bay, poor sets on the parent beds, weak year-classes and low abundance of the catchable stocks of six years later. High temperatures speed larval development and are indicative of a closed Fundy circulation which holds the larvae in the vicinity of the parent beds. This leads to good sets, strong year-classes and high abundance of the catchable stocks six years later.