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This paper not to be cited without prior reference to the authors. International Council for Exploration of the Sea

ICES C.M. 1981/G:66

Stomach Contents Studies in Relation to Multispecies Fisheries Analysis and Modeling for the Northwest Atlantic" E. Cohen, M. Grosslein, M. Sissenwine, F. Serchuk, and R. Bowman National Oceanic and Atmospheric Administration National Marine Fisheries Service Northeast Fisheries Center Woods Hole Laboratory Woods Hole, Massachusetts 02543 USA

• Abstract



The need for and usefulness of food habits data in multispecies fishery models are reviewed with particular focus on experience in the northwest Atlantic. V~rious methods are compared for obtaining quantitative estimates of food consumption by fishes in the natural environment, and for evaluating the importance of predatorprey interactions in multispecies fish communities." Sampling problems relative to critical parameters (e.g., estimates of daily rations partitioned by size and prey category, selectivity functions) are discussed, and analytical approaches are suggested for testing some key assumptions such as constancy of selectivity coefficients in relation to changes in prey abundance. Finally, the feasibility and benefits are considered of applying current data on predator-prey interactions to multispecies VPA models.

Le besoin et l'utilite de donnees de regime alimentaire dans modeles de peche multi-especes sont revues avec concentration particuliere d'experience dans l'Atlantic nord-est~ Divers methodes sont comparees pour obtenir des devis quantitatifs de consommation alimentaire par poissons dans le milieu naturel et pour evaluer l'importance d'actions reciproques de ravageur-proie dans les communautees multi-especes de poissons. Problemes d'echantillonage ayant rapport aux parametres exigeants (e.g., evaluations de ration quotidienne partitione par taille et categorie de proie ~ fonctions de selectivite) sont discutes, et des approches analytique sont suggeres pour 1 I examen d'assomptions tels que la constance de coefficients de selectivite par rapport aux changements d'abondance de proie. En fin, la practicabilite et benefices de l'application de donnees courants d'actions reciproques de ravageur-proie aux modeles VPA multi-especes sont consideres.

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Introduction Historically, single species fishing assessment models have been widely utilized to eva1uate the population dynamics of Northwest At1antic marine fishery stocks. In almost all of these cases; these models have concomitant1y served as bio1ogica1 bases for resource management activities. The conceptual and analytical constraints of the single species approach have long been recognized (Dickie, 1973, 1979; Gulland, 1974, 1978; Larkin, 1977; Hongskul, 1979; Steele, 1979; May'et al., 1979); indeed, more often than not, fishery assessment scientistshave tempered their scientific advice to management agencies by either explicit or' implicit consideration of the robustness of their models in realistically characterizing'population parameters and expected exploitation impacts. Nonetheless, analytical treatment of fish stocks as equilibrium~ situated, independent, non-interactive entities inhabiting a constant environment is unrealistic. Unfortunately, the transition from single species to multispecies assessment and management is not facile. Progress towards this end in Northwest Atlantic Fisheries was initiated in the mid-1970's when it was demonstrated, through application of a multispecies surplus production'model (Brown et al., 1976), that total equilibrium yield for the finfish community from the Gulf of Maine-to Cape Hatteras was lower than the sum of equilibrium yields from individual single species assessments. The implication from this analysis and related studies (Larkin, 1956, 1963, 1966; Pope, 1976; Silliman, 1975; Hon~ood, 1976; Clark and Brown, 1977) was that species interactions (i.e., predation and competition) could substantially influence both the structure and energy flow within fishery systems .As a consequence, the International Commission for Northwest Atlantic Fisheries (ICNAF) implimented a de facto multispecies management approach in 1974 \vhen a two-tier quota system was adopted which limited the total catch of all finfish and squid,(i.e., second tier) to less than the sum of individual species catch limits (Hennemuth, 1977; Doubleday, 1979). Coupled with reductions in fishing effort predicated on achieving a rate of fishing mortality corresponding to FO 1 (Gulland and Boerema, 1973), the ICNAF management regimen in thelate 1970's promoted the recovery of fishery stocks which had declined in abundance during 1963-1974 (Clark and Brown, 1979; Doubleday, 1979). • Although the multispecies scientific advice provided to ICNAF proved helpful in rebuilding the fish biomass, the nature and magnitude of the presumed species interactions have not been rigorously evaluated, particularly predator-prey interactions. Comprehensive investigations of food habits of major species were begun in 1963 by the Northeast Fisheries Center (NEFC) of the National Marine'Fisheries Service (NMFS). These studies revea1ed that predation between pre-recruits and older fish may be a very significant if not the dominant linkage affecting fish production. However, on1y recently have attempts been made to evaluate the complex predator-prey interactions involved (Edwards and Bowman, 1979; Grosslein et al., 1979, 1980; Cohen et al., 1981). Quantitative analysis of these multispecies interactions called.for both---more comprehensive models and for more detailed and quantitative data on food consumption.

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A number of multispecies Virtual Population oAnalysis (VPA) models and other multispecies models (Andersen and Ursin, 1977; Pope, 1979; Helgason and Gislason, 1979; Sparre, 1980; Majkowski, 1981) havebeen developed recently for evaluating the potential importance of interspecific predation inregulating biomass and species composition in multispecies fishery systems. Aspects of these analytical approaches are compared in Table lofor VPA models. Given quantitative estimates of food consumption by major fish predators (in terms of size and species composition of fish prey), these models can provide useful insight into the role of predator-prey interactions in controlling populations (Ursin, 1979; Sparre, 1980). The similarities and the differences among these models were reviewed by the ICES Working Group on Multispecies Assessmentomodels with particular reference to the ways in which predator-prey interactions are calculated, and the critical inputs from food habits data (ICES, Anon., 1980). Our studies have paralleled the approaches described in the ICES working group report exceptoothat we are a bit further ahead in estimating food consumption, but not as far along in model description. Since our model is patterned largely after that of Andersen and Ursin (1977) we have not discussed it here. Rather, we have focused on a cr.itique of the principal food consumption data needs and the problems of obtaining accurateoestimates of key parameters, using our current data base onofood consumption for illustration. °

Multispecies Fisheries Research Needs Multispecies modeling approaches treat natural mortality as a function of predation. This is a significant departure from single species approaches where natural mortality is usually assumed to be time invariant. Multispecies models partition natural mortality into predation mortality and another component of natural mortality due to other causes, e.g., disease. The former component is adynamie function of the predator field experienced by the prey. The latter ois usually treated as a constant and considered to be much smaller than predation mortality. °

TIle estimation of predation mortal i tyo by species and age or size category is the essence of multispecies fisheries modeling and research needs. The predation mortality rate suffered by a group of prey (of a specific species and age or size) depends on the(l) total consumption by predators, (2) the predators preference for a specific prey, (3) the abundance of the prey, (4) the abundance of predators.

The consumption by a predator is a function of the abundance of su itable prey. When there is very little to eat, consumption is necessarily small. As prey abundance i ncreases, consumpti on i ncreases. Even tually, prey abundance becomes hi gh enough so that predators are satiated. At still higher prey abundance, consumption is relatively constant (independent ofosuitable prey abundance). Several functions describing a non-linear relationship beu~een consumption rate and prey abundance have been proposed (e.g., Ivlev, 1961; Holling, 1959). For very small prey and predators, laboratory experiments could be implemented in order to test feeding functions and estimate parameters. However, laboratory experiments are not usually feasible for fishery problems due to the size of predators and complexities and scale of natural predator-prey fields. II

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Thus, aseries of field estimates of predator consumption and associated suitable prey abundance arenecessary in order to determine feeding functions empirically. Lacking a time series of field measurements of consumption rate and prey abundance, Andersen and Ursin (1977) simulated these variables and fit parameters of the feeding function by tuning their model. In spite of the variability in suitable prey abundance typical of marine fishery systems, the growth rate of most,exploited fish populations is remarkably constant (Grosslein et al., 1980). This observation mightindieate that fish typieally f~ed to satiatio~ thus eonsumption rate is relatively constant. The assumption that eonsumption rate is independent of prey abundance distinguishes the'multispecies VPA's from the more complex Andersen'and Ursin model. • For multispecies VPA1s, consumption rate may be calculated based on the energy requirements of the predator, i.e., assimilated eonsumption equals metabolism plus growth plus reproductive eosts; or it may be estimated from stomaeh contents. Grossleinet al. (1980) applied theformer approach to Georges Bank finfish. Cohen and Grosslein-Y1981) have applied the latter approach to some of the same populations. The results are compared later in this paper. In order to estimate consumption rate based on stomach eontents data, it is also neeessary to estimate digestion rate. Digestion rate experiments in the laboratory are feasible but difficult. Numerous factors which effect digestion rate must be considered. The energy balance approach to estimating consumption rate does not require stornach content data or an estimate of digestion rate, but other physiologieal parameters are necessary. For example, theassimilation rate and metabolie rate of a feeding fish must be estimated. Electivity (i.e., preference) must be know in order'to determine the amount of suitable prey for each predator and proportion of its diet from each prey type. Electivity can be used on the species and size composition of stomaeh contents. Unfortunately, such data is difficult to interpret beeause of the differential digestion rate of various types of stomachcontents. A description.of electivity also requires knowledge of prey abundance (which is discussed below). Andersen and Ursin (1977) suggest that electivity is primarily a function of the (predator weight)/(prey weight) ratio. The species of the prey is of secondary importance and generally ignored in their model. Stomach contents data describing the size,of prey items is obviously critieal to examining this hypothesis. Hahm and Langton (1980) have provided a preliminary examination of, (predator weight)/ . . (prey weight) ratios for predators on Georges Bank. We have emphasized the need and use of stomach contents data as a basis for multispecies analysis and modeling. Nevertheless, the ongoing need for more and better data describing fish abundance (of all sizes, species and life stages) cannot be ignored.



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The variance of estimates of fish population.size is probably one of the principal sourees of errors in the analysis of,multispeeies fisheries. The problem of estimating population size is most severe for fish at the extremes of the size range. We have little basis for estimating predation:mortality on large adult . fish (e.g., eod, haddock), sinee the abundance of apex predators (e.g., pelagic sharks, marine mammals) is seldom known ..



Our lack of estimates of the abundance of very small fish is of even greater cancern •. Young-of-the-year (YOY) of many species are important prey of larger fish. Grasslein.et~. (1980) notedthatasingle species on Georges Bank, silver hake, consumes more 'fish than·the production of all fish age 1 and older, indicating that silver hake consumption of YOY is substantial. Without knowing the abundance of these small fish, the predation mortality they suffer cannot be estimated and the effeet of predation on future recruitment is unclear although potentially very significant. Although young-of-the-year fish are not necessarily accounted for explicitly in multispecies VPA, assumptions coneerning their abundance'are critical. If the abundance of YOY is overestimated, then predation mortality on'older fish will be underestimated since an unrealistically high proportion of the predators' diet will by of YOY. The converse occurs if abundance of YOY is underestimated. Thus, stomach contents data is critically needed as a basis of multispecies fisheries, analysis and modeling. Other data and laboratary experiments are also essential to future progress in this areaof research. Overview of NEFC Food Habits Research The NEFC has been studying the food habits of Northwest Atlantic fish since 1963. The procedure for collecting fish stomachs has changed several times leading to several distinct data sets (Langton et al., 1980). ,During the period 1963-1966 fish were selected from the catch at randoITland their stomach contents recorded at sea, thus providing a qualitative data set for 65 species of fish. Starting in 1969 and continuing until 1972, fish were randomly sampled but the stomachs were preserved in batches in formalin without,corresponding predator lengths; 'these stomachs were processed in the laboratory where ,the prey was identified to the,lowest taxon possible and its wet weight determined. Quantitative estimates of gut contents for average sized predators were obtained in this way'for 80 speeies (Bowman, Maurer, and Murphy, 1976; Grosslein et ~., 1980). Beginning in 1973 and continuing until 1980. individual stomaehs and predator, lengths were colleeted from selected fish preserved at sea and analyzed ashore. These data provide quantitative as well as qualitative food habits data for 45 species of fish and squid (Grosslein et al., 1980). All of these stomach sampling programs were eonducted concurrently wit~bottom trawl surveys which covered wide areas of the shelf (Cape Hatteras to Western Nova Scotia since 1967), and at least two seasqns (spring and autumn) each year. Stomaeh sampling had to be done as time and manpower allowed, and therefore, sampling for any one species in any one area was sparse'; sample sizes for a given species and area comparable to Georges Bank

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usually did not exceed 50 fish per cruise. Thus, although the data base at NEFC is probably one of the largest and most complete'collections of food habits data available, the quantitative data for any one species and size category is quite limited on aper cruise basis. A new sampling protocol has been instituted this year similar to that recommended by the lCES Working Group (lCES, Anon., 1980), and foeusing on key speeies including major fish predators in the Georges Bank-Nantucket Shoals region. These species are eod. silver hake, yellowtail flounder, spiny dogfish and haddock, with quarterly sampling by size eategory (0-10, 11-20, 21-35, 36-50, 51-75, ~ 76 em) and stomaehs preserved for laboratory analysis. During the first trial of this new protocol onthe spring 1981 bottom trawl survey, a total of 745 stomachs (for all • 5 species) was eollected in the Georges.Bank region (about 20,000 square miles). In addition to the quantitative samples. qualitative samples were also collected at sea in the Georges Bank area for the three piseivorous speeies (eod, silver hake and spiny dogfish) to help identify their fish prey thraugh first-hand observations of gut contents: Aeeurate and eomplete identifieation of fish prey is diffieult to obtain on preserved samples because the samples are processed on contract by persons not skilled in identifying fish remains. Qualitative sampling only was done in other parts of the survey area to monitor ehanges in prey composition for dominant finfish species (particularly fish eaters) and ~quids. Although there are limitations and sourees 'of error inherent in our existing food habits data, we have begun to examine several of the key proeesses relating to predator-prey interaetions in multispeeies cornmunities. These are: 1) seleetion orelectivity of prey by predators, 2) consumption rates in relation to growth and food supply of predators, and 3) predation on pre-reeruits. Grosslein et al. (1980) have shown that in spite of the large deeline in finfish biomass on Georgesl3ank fram the middle 1960's to the mid 1970 1 s, there were no gross ehanges in prey composition in terms of frequeney of oeeurrence by major taxafor • five principal demersal speeies (Figure 1). However, it was observed that of the two fish eating species, eod and silver hake. eod showed a modest decline in frequeney . of fish prey (after accounting for a negative bias on the order of 5% inpereent oeeurrenees of fish in the 1963-66 stomaeh data series as described in Grosslein et al .• 1980) reflecting mostly a drop in frequeney of gadoid prey but very little change in herring, a preferred fish prey of eod. About the same level of deeline in frequency of oecurrenee offish prey in cod was noted for the Gulf of Maine. On the other hand, silver hake showed essentially no change in the percent oecurrence of fish prey on Georges Bank (after adjusting for the bias noted above) even though the biomass of virtually all finfish species declined substantially on Georges Bank including silver hake and other gadoids which make up the bulk of the silver hake diet (Figure 1). Similarly, white hake showed essentially no change in the proportion of fish consumed in the Gulf of Maine (Figure 1).

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The apparent ineansisteney between ead and silver hake in ehanges af the frequeney of occurrenee of fish prey from the high biomass to the low biomass period on Georges Bank could reflect sampling errors (the numbers of stomaehs are small considering the time spans involved). Also, it is quite likely that a total biomass index, even on an individual speciesbasis, may not be closely eorrelated withstomach contents since it is the pre-recruit stages which make up the bulk of the fish prey. Thus, the fact that percent occurrence of herring remained stable in Georges Bank eod, despite a major decline in herring biomass, may be related to the appearanee of the strang 1970 year c1ass whieh cou1d have made a large contributionto the eod diet before the herring stoek'as measured by VPA co11apsed on Georges Bank. Increases in the amount of sand lanee in stomachs of si1ver hake (Bowman, 1980) and cod (personal communication, Char1es Byrne) during the 1970·s are consistent with the known large increase in the sand 1ance population. Clear1y what is needed is intensive samp1ing of fish. predator stomachs and independent estimates of prey abundance (especially pre-recruits) during the periods of major fluctuations in order to eva1uate the basic re1ationships governing predation rates and prey preference. . The data on whether growth and consumption have changed.since the stocks declined is variable. Haddock have shown adefinite increase in growth and there is same evidence of a decrease in age of maturity (Gross1ein et a1., 1980). The data are .not so c1ear-cut for other species such as herring, co~ yellowtai1 andsilver hake (Grosslein et a1., 1980). More detailed comparisons are needed on an annual basis, of growth-andlfood consumption in relation to prey abundance. This past year we have started an evaluation of the sources and magnitudes of error in estimates of daily ration and annual consumption for various species of fish (Durbin et a1., 1980; Pennington,' 1981; Cohen and Grosslein, 1981). Using an exponentia1 moder-of digestion coup1ed with feeding (E1liott and Persson, 1978; Eggers, 1977; Pennington, 1981), and the size-specific 1973-1976 food habits data, we have ca1cu1ated .the foodconsumption ofhaddock and silver hake and compared the values with those derived from metabolie considerations by Gross1ein et~. (1980). The age~specific consumption to biomass ratios based on .theoretica1 energy requirements for these two species (see Tab1e 21, Gross1ein et a1., 1980) were applied to the recent VPA biomass-at-age estimates for the periodl1973-1976, in order to construct an estimate of theoretica1 consumption which wou1d be comparab1e (i.e., same biomass at age) to the consumption estimate derived from stomach content data. Haddockand silver hake were chosen because they represent the most reliable VPA data of the 5 speeies examined. The stomach-content based consumption estimate for silver hake was 1ess than the theoretica1 eonsumption (65% of theoretica1) whereas for haddock, the stomaeh-content estimate was nearly 2~ times the theoretica1 estimate (Tab1e 2), In order to account for these discrepaneies entirely with errors in the digestion rate a, we wou1d have to assume the same proportional differences in a, i.e., a = 1.0 vs .• 395 for haddock, and a = .036 vs •. 005 for silver hake. Attributing the differenee for silver hake to a differenee in a does not seem unreasonable, but the difference for haddock seems too large espeeial1y since there are some reasonable digestion rate data on haddock.

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Nevertheless, digestion rate can vary significantly·with predator species and ·with "temperature, type of prey and mean size for a particular predator (Fänge and Grove, 1979; Durbin et al., 1980). Digestion rate might also depend on size of predator for given prey-and meal size (Daan, 1973). It is easy enough to correct for temperature hut the other factors are difficult to measure and it·;s clear that more laboratory studies on digestion are necessary for key species. There are, of course, other sources of error likely to be involved. For example, there might be significant errors in the metabolic cooefficients and the derived agespecific consumption/biomass ratios used in the theoretical consumption estimate. Also, large sampling errors and bias could occur in both VPA and mean gut content estimates. Pennington (1981) has shown that.in order to. reduce possible bias in the • estimator of mean stomach contents due to strong periodic.feeding patterns, and uneven sampling with time of day, the catch/tow should be broken·down by hour of the day. Typically in our data base for a single cruise, there are a number of hours for which there are no or very few stomachs sampled. Another large source of error in food habits data lies in the extreme variability of stomach content samples taken at the same station. Pennington et al. (1980) have shown that the variability of the total weight of stomach contentsfor cod within a tow is greater than the variability due to area and time of day. seasons, and years, and they estimate that 780 fish should be sampled in order to determine a + 10% change in the mean weight of stomach contents with 95% certainty. Large temporal and spatial variability in prey composition also is possible. as is evident in the observations of Vinogradov (1977) on Georges Bank. With regard to the level of predation mortality on pre-recruits. we have concluded that it is probably very high in the Georges Bank area. As noted earlier. total consumption (mostly fish on a weight basis) of silver hake alone was estimated to be more than twice as great as the total production (exclusive of O-group) by all fish species combined (Table 22, Grosslein et al., 1980), thus implying that much of the balance of silver hake consumption must-Consist of O-group fish. Cohen and Grosslein (1981) have shown that silver hake have the capacity, based on daily ration ~ estimates and average prey size, to consume up to b~o orders of magnitude more youngof-the-year fish than were back calculated from VPA and other population data using current estimates of M (0.4 for silver hake and 0.2 for cod, haddock. pol lock and yellowtail flounder). These species are thought to represent the major part of the fish diet of silver hake (Grosslein et al., 1980). The natural mortality in the postlarval stage appears to be very high-at-reast for silver hake and haddock with M = 20 yr- 1 (Cohen and Grosslein. 1981). This high natural mortality is probably· predation mortality and is sufficiently large to cause significant recruitment fluctuations. .

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Concluding Remarks Our recent work-has demonstrated that predation by fish on pre-recruits (particularly YOY) is potentially an important factor controlling recruitment fluctuations in a multispecies finfish community. The research and data needed in order to further investigate the recruitment problem relative to fish predation were outlined in a previous·section (i.e., abundance of fish predation andefish prey by size or a~e including YOY, consumption rate of predators, and prey preferences of preda tors) . . All this information will be required concurrently for a series.of years during which'major fluctuations in abundance of pre-recruits for key species occur. As noted by ICES (Anon., 1980) the sampling need not be in consecutive years. However, there are definite advantages to having an unbroken time series.at least until the most important species have exhibited substantial recruitment fluctuations, since it is not possible to predict these fluctuations in advance and it is difficult to start up large scale sampling programs on short notice. Sampling errors associated with the above estimates are not well documented but generally can be expected to be large. Also some of the estimates are extremely difficult to make, notably pre-recruit abundance andthe associated prey suitability coefficients and predation mortalities. For this reason it is not likely that it will be possible to test defintively all the important assumptions and hypotheses of interest with empirical data. Therefore, conclusions about long-term management strategies will have to be based partlyon model simulations. We feel that a major focus of research in the next few years should be on estimating the magnitude of sampling errors for the above items and we have highlighted some major errors in need of study, particularly those associated with food consumption and predation morta 1i ty.



Accurate population size and age structure estimates of the major stocks are essential for definitive calculations. One source of error in such estimates results from inadequate measures of discards. lt is difficult to estimate the precision of population size estimates, but at least some first approximations should be made so that their importance can be assessed relative to the other sources of error. Estimates of absolute abundance of pre-recruitS are perhaps the most difficult of all but they are crucial to valid estimates of predation mortality and predator-prey II suitabilityll or selectivity coefficients. Surveysof late larval or post-larval stages should prove helpful in conjunction with sampling of the stomach contents of fi sh preda tors. Sampling of stomach contents will have to be intensive in both-time and space and a number of possible biases as well as II random ll sampling errors investigated. Regurgitation and IIsecondaryll feeding in the cod end of the tra\'-Il are potentially serious problems, and steps can and should be taken to measure or ameliorate them (Daan, 1973; ICES, Anon., 1980). In addition, large sampling errors can occur as a result of: 1) migrations and contagious joint density distributions of predators and prey. 2) unusual or aperiodic environmental factors (cloudy vs. clear weather,

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temperature, oxygen depletion, oceurrenee of atypieal prey), 3) eorrelation between catchability and diel feeding patterns,and 4) physiological state of fish (spawning.which alters feeding activity. The species identification of fish prey and determination of their size (age) composition in the live undigested state also pose significant problems and the associated errors should be estimated. Two methods to improve this are to examine otoliths or scales for ages of prey, and to use as a guide, observations on the sizes of corresponding prey organisms caught in the trawl (including those inside stomachs) or other samplers. Additional laboratory work is needed on digestion rates particularly in relation to prey type, meal size and.predator size. With respect to prey preference coefficients, we may get some insight into their constancy by comparing diet of a given predator in areas with different prey eompositions. Also comparisons can be made of consumption by fish predators over time, in relation to inferred, fluctuations of pre-reeruit stages of key species based on VPA results; analyses of this type can be made on the NEFC archive of stomach content datafor the Georges Bank region. Finally, the food habits data base at NEFC is·suitable for estimating selectivity of predators by the method of Sparre (1980) or Andersen and Ursin(1977).· . Specific studies of growth rates of selected species in relation to food consumption and biomass of predators and (fish) prey are needed as a basis for evaluating our ideas about the importance of fish relative to other prey, and the possibility of competition. Useful insights might be gained by comparing relative constancy of growth rates beu'Ieen fish consumers and "other food" consumers over a period of·years and between geographie areas. At the NEFC we are concentrating our initial modeling efforts on predatoryjprey interactions for the Georges Bank area because we have the best overall data base including other trophic levels as well as fish for this region. We are also intereste~ in adjaeent waters from Cape Hatteras to the Gulf of Maine but it is presently not ... possible to adequately sample the entire region for quantitative eonsumption data. Even on Georges Bank, we have not been able to sample all the potential fish predators (e.g., maekerel) adequately because we also need to monitor trends in selected benthos feeders (notably haddock and yeliowtail flounder) as one means of evaluating "health" of the benthic community which may be affected by oil production activities. International cooperation in food habits studies probably will be a necessity in the Northwest Atlantic for the same reasons it is needed in the North Sea.

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References Andersen, K. P. and Ursin, E. 1977. A multispecies extension to the Beverton and Holt theory of fishing with accounts of phosphorus circulation and primary produetion. Medd. Dan. Fisk. Havunders. N.S. 7: 319-435. Anonymous. 1980. Report of the ad hoc working group on multispecies assessment model testing. ICES C.M. 1980/G:2. Bowman, R. E. 1980. Silver hake's (Merluccius bilinearis) regulatory influence on the fishes of the Northwest Atlantie. U.S. Oept. of Com., NOAA, NMFS, NEFC, Woods Hole Lab. Ref. Ooe. No. 80-05. 10 pp. Bowman, R. E., Maurer, R. 0., and Murphy, J. B. 1976. Stornach eontents of 29 fish species from five regions.inthe Northwest Atlantie data report. U.S. Oept. of Com., NOAA, NMFS, NEFC, Woods Hole Lab. Ref. Ooe. No. 76-10. 37 pp. Brown, B. E., Brennan, J. A., Grosslein, M. 0., Heyerdahl, E. G., and Hennemuth, R. C. 1976. The effeets of fishing on the marine fish biomass in the Northwest Atlantie from the Gulf of Maine to Cape Hatteras. Int. Comm. Northw. Atlant. Res. Bull. 12: 49-68. Clark, S. H. and Brown, B. E. 1977. Changes in biomass of finfishes and squids from the Gulf of Maine to Cape Hatteras, 1963-74, as determined from research vessel survey data. Fish. Bull., U.S. 75(l): 1-21. Clark, S. H. and Brown, B. E. 1979. Trends in biomass of finfishes and squids in ICNAF subarea 5 and statistical area 6, 1964-1977, as determined from research vessel survey data. Investigation Pesquera 43(1): 107-122. •

Gohen, E. and Grosslein, M.· 1981. Food consumption in five speeies of fish on Georges Bank. ICES G.M. 1981/G:68. Gohen, E., Grosslein, M., Sissenwine, M., Steimle, F., and Wright. W. 1981. An energy budget of Georges Bank. In M. C. Mercer (ed.), Multi-Species Approaehes to Fisheries Management advice. Can. Spec. Publ. Fish. Aquat. Sei. 58. Oaan, N. 1973. A quantitative analysis of the food intake of North Sea eod, Gadus morhua. Neth. J. Sea Res. 6(4): 479-517. Diekie, L. M. 1973. Managementof fisheries ecologieal subsystems. Fish. Soe. 102(2): 470-480.

Trans. Amer.

Oiekie, L. M. 1979. Perspeetives on fisheries biology and implications for management. J. Fish. Res. Board Can. 36: 838-844.

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Doubleday, W. G. 1979. A brief review of. the evaluation of resource management advice in the ICNAF area 1965-78, p. 59-66. ~ Interim Report of the ACMRR Working Party on the Scientific Basis of Determining Management Measures. FAD Fisheries Circular No. 718, FIR/C 718, 112 p. Durbin, E., Durbin, A., Langton, R., Bowman, R., and Grosslein, M. 1980. Analysis of stomach contents of Atlantic cod,(Gadus morhua) and silver hake (Merluccius bilinearis) for the estimation of daily rations. ICES C.M. 1980/L:60. Edwards, R. L. and Bowman, R., E. '1979. Food consumed by continental shelf fishes, p. 387-406. 1n Predator-prey systems in fish communities and their role in fisheries management. Sport Fishing Institute, Washington, D.C.

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Eggers, D. M. 1977. Factors in interpreting data obtained by diel sampling of fish stomachs. J. Fish. Res. Bd. Can. 34: 290-294 . . Elliott, J. M. and Perssan, L. 1978. The estimation of daily rates of food consumption for fish. J. Anim. Ecol. 47: 977-991. Fänge, R. and Grove, D. 1979. Digestion. In' W. S. Hoar, D. J. Randall, and J. R. Brett (eds.), Fish Physiology, Val. VITr, Bioenergetics and Growth. pp. 162260. Academic Press, N.Y. Grosslein, M. 0., Brown, B. E., and Hennemuth, R. C. 1979. Researchassessment and management of marine ecosystem in the NorthwestAtlantic - A case study. pp. 289-357. In J. Cairns,Jr., G. P. Patil, and W. E. Waters (eds.), Environmental Biomonitoring, Assessment, Prediction, and Management - Certain Case Studies and Related Quantitative Issues. Statistical Ecology, Val. 11, International Cooperative Publishing House. Fairland, Maryland. • Grosslein, M. 0., Langton, R. W., and Sissenwine, M. P. 1980. Recent fluctuations in pelagic fish stocks of the Northwest Atlantic-Georges Bank region, in relation to species interactions. Rapp. P.-v. Reun. Cons. int. Explor. Mer 177: 374-404. Gulland, J. A. 1974. Fishery science and the problems of management, pp. 413-429. In F. R. Harden Jones (ed.), Sea Fisheries Research, Elek Science, Landon. Gulland, J. A. 1978. Fishery management: Amer. Fish. Soc. 107(1): 1-11.

New strategies for new conditions.

Gulland, J. A. and Boerema, L. K. 1973. Scientific advice on catch levels. Bull., U.S. 71(2): 325-335.

Trans. Fish.

Hahm, W. and Langton, R. 1980. Prey selection based on predator/prey weight ratios for some Northwest Atlantic fish. ICES C.M. 1980/L:62. Helgason, T. and Gislason,H. 1979. VPA-analysis with species interaction due to predation. Int. Council Explor. Sea, Demersal Fish Committee, C.M. 1977/G:52.

-13-

Hennemuth, R. C. 1977. Some biological aspects of optimum yield, p. 17-27. In H. Clepper (ed.), Marine Recreational Fisheries 2, Sport Fishery Institute, Washington, D.C. Holling, C. S. 1959. Some characteristics of simple types of predation and parasitism. Can. Entomol. 91: 385-398. Hongskul, V. 1979. Report on the studies of multispecies systems in fisheries. p. 73-84. In Interim Report of the ACMRR Working Party on the Scientific Basis of Determining Management Measures. FAO Fisheries Circular No. 718, FIR/C 718, 112 pp.

4It

Horwood, J. W. 1976. Interactive fisheries: A two species Schaefer model. Comm. Northw. Atlant. Fish., Sel. Pap. 1: 151-155.

Inter.

Ivlev, V. S. 1961. Experimental ecology of the feeding of fishes. Translated from Russian by D. Scott. Yale Univ. Press, New York, Conn. 302 pp. Langton, R., North, B., Hayden, B., and Bowman, R. 1980. Fish food habits studies sampling procedures and data processing methods utilized by the Northeast Fisheries Center, Woods Hole Laboratory, U.S.A. ICES C.M. 1980/L:61. Larkin, P. A. 1956. Interspecific competition and population control in freshwater fish. J. Fish. Res. Board Can. 13: 327-342. Larkin, .P. A. 1963. lnterspecific competition and exploitation. Board Can. 20: 647-678.



J. Fish. Res.

Larkin, P. A. 1966. Exploitation in a type of predator-prey relationship. Fish. Res. Board Can. 23: 349-356 •

J.

Larkin, P. A. 1977. An epitaph for the concept of maximum sustainable yield. Trans. Amer. Fish. Soc. 106(10): 1-11. Majkowski, J. 1981. Application of a multispecies approach for assessing the population abundance and the age-structure of fish stocks. Can. J. Fish. Aquat. Sei. 38: 424-431. May, R. M., Beddington, J. R., Clark, C. W., Holt, S. J., and Laws, R. M. 1979. Management of multispecies fisheries. Science 205(4403): 267-277. Pennington, M. 1981. Estimating the average food consumption by fish in the field. ICES C.M. 1981/G:69. Pennington, M., Bowman, R., and Langton, R. 1980. Variability of the weight of stomach contents of fish and its implications for food studies. ICES C.M. 1980/L:63. Pope, J. G. 1976 .. The effect of biological interaction on the theory of mixed fisheries. Int. Comm. Northw. Atlant. Fish., Sel. Pap. 1: 157-162.

~

-14-

Pope, J. G. 1979. A modified cohort analysis in which constant natural mortality is replaced by estimates of predation levels. Int. Council Explor. Sea, Pelagic Fish Committee, C. M. 1979/H:16. 7 p. Sill iman, R. P. 1975. Experimental exploitation of competing fish population. Fish. Bull., U.S. 73(4): 872-888. Sparre, P. 1980. A goal function of fisheries (Legion Analysis). Int. Council Exp1or. Sea, Demersal Fish Committee, C. M. 1980/G:40. 81 p. Steele, J. H. 1979. Some problems in the management of marine resources, p. 103140. ~ T. H. Coaker (ed.), Applied 8io10gy, V01. IV, Academic Press, New York. Ursin, E. 1979. On mu1tispecies fish stock and yie1d assessment in leES. Paper de1ivered at workshop on Mu1tispecies Approaches to Fisheries Management Advice, St. John~s Newfoundland, November 1979. Vinogradov, V. I. 1977. Dai1y feeding rhythms and food rations of the si1ver hake, Merluccius bilinearis, and the red hake, Urophycis chuss,in the Northwest Atlantic. J. of Icthyology 17(4): 605-609.



Table 1.



Data requirements. for various mu14ll pecies Virtual Population Analysis ~) assessment models. VPA Model Majkowski 1981

Pope 1977

1. Catch (#I S ) at age for predator-

Yes

Yes

Yes

Yes

2. Fishery mortality (F) by age

Yes

Yes

Yes

Yes

3. Fishery mortality (F) for the

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

5. Non-predation induced instan-

Yes

Yes

Yes

Yes

6. Annual total food biomass con-

Yes

Yes

Yes

prey fish species for each calendar year group, for each predator-prey fish species for the most recent calendar year for which catch at age data are available

oldest age group in the catch for each predator-prey fish sr.ecies in each calendar year ( 'Termi nal F") 4. Mean weight at age for all

predator-prey fish species for each calendar year for which catch data are available taneous natural mortality (i.e. MI), by age group, for each predator-prey fish species for each calendar year

sumption, by age group, for each predator-prey fish species for each calendar year (i .e. "annual ration" )

Helgason and Gislason 1979

Sparre 1980

Data Requirements

Calculated from (4), (1O) and (11)

Table 1.

(Continued)

Data Requirements

Pope 1979

VPA Model Sparre Helgason and Gislason 1980 1979

7. Food preference for each age group of fish predator species for each age group of fish prey species (i.e. 11 food suitabil ity")

Empirical

Functional relationship

Functional re1ati onshi p

Empi ri cal

8. Total biomass of the ecosystem at

No

Calculated from (9) and computed total fish biomass in model

Yes (but assumed constant in all years)

No

Yes (but assumed constant in a11 yea rs )

Calculated by subtracting computed fish biomass from (8)

No

the beginning of each calendar year

9. Total biomass of food species not No considered in the model (i.e. o ther food"), by catch at age data, for all calendar years. lI

Majkowski 1981

10. Annual species specific total biomass consumption rate (constant for all years) for each predatorprey species in model

No

Yes

No

Yes, if (6) not available

11. Species-specific power function (constant) relating speciesspecific annual food consumption rate (constant) to fish body weight for all predator-prey species in model

No

Yes

No

Yes, if (6) not available

12. Fraction of the total annual fish consumption for each age group of predator fish species, of prey species (constant) in model

Yes

No

No

No

13. Fraction of average stomach contents, for each age group of predator fish species, of each age group of prey, i ncl udi ng other food" for each calendar year

No

No

Yes, if (7) not provided (assumed constant over all years)

No

lI

Table 2.

Camparisan of food consumption derived fra m age-specific consumption/biomass ratios in Grosslein et al. (1980), (Column A) with consumption based on stomac~contents data (Column B), Cohen and Grosslein (1981). Values in kg wet wgt/km 2. Biomass data for period 1973-1976.

Haddock Silver Hake

A

B

B/A

2,461

6,058

2.46

24,076

15,675

.65

, \

--=---~~--

o

GEORGES BANK

63-66

[[]] 73-76

%

-r---.J.-----'------'-----'------'-----,

1--------100

Crustacea

75 50

25 1-----

O-+---L-_...l...l..1..U.---'-_....L.J-.J.-LJL...-J_--LJ-I..1.-'--"---L-l.-L-J.....L-..1--.L...L-l.-'-'--i

Pisces

25 O+-L_.LLl-LL-L_.LLl...u..--==:t:::I;:;:r::L.-c==:u..J...J...L_ _-==::o..--1

1--

Polychaeta

50

25 1----

0-+---L-_...l...l..1..U.

Echinodermata

.-JL---.L..I....L.l--'--"-....Ll.-L-J.....L-..1--.L..........U--i

25

1-------- 0 -J--t==D:IDMol/usca

..l--l..!..Ll..l-===::t.......:=::I-_--j

25 0-L-L_.LU..lL_ _-==.-l-_.LU..Ll.-.t:=:1:Cl:D.._ _.c=::::::L-.l_...l

l....-

GULF OF

D

MAINE

ITlJ]

63-66



73-16

% -y--_--.1. 1 - - - - - - - 75 Crustacea

L -_ _...L...-_ _-I...._ _--'-_ _- - ' - _ - - ,

50

25 1--

O-4-...1---L.J..U...L..L._I...l,..;,.l.J-L_...L.J,..;...l...I-L--~.l..J..1...J._--'-~L..===