Environmental Biology of Fishes55: 339–341, 1999.© 1999Kluwer Academic Publishers. Printed in the Netherlands.

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Susan M. SogardAlaska Fisheries Science Center, National Marine Fisheries Service, Hatfield Marine Science Center, Newport,OR 97365, U.S.A. (e-mail: susan.sogard@hmsc.orst.edu)

Chambers, R.C. & E.A. Trippel (ed.) 1997. Early life history and recruitment in fish populations. Chapman andHall, London. 596 pp.

Variability in the abundance of fish populations hasintrigued and plagued fisheries researchers since theirscience began. Our current paradigm suggests that thisvariability arises during the early life stages, when mor-tality rates are high and only slight changes in survivalcan dramatically affect the abundance of fish attain-ing a recruitment interval (Houde 1987). An impor-tant consequence of this variability in early mortalityis that adult abundance is often a poor predictor of thenext generation. Favorable conditions during the earlystages result in strong cohorts or year classes, whereaspoor conditions lead to year class failure. For commer-cial species, the temporal pattern of occurrence of theseconditions is crucial; a single strong year class can dom-inate and sustain the fishery for many years, dependingon the species’ life span. In contrast, a string of pooryear classes may have devastating economic effects.Our ability to identify such favorable and unfavorableconditions would obviously have scientific value inunderstanding population regulation, as well as greatpractical value in allowing us to predict the future avail-ability of fish for commercial harvest. This well definedgoal has, however, remained frustratingly elusive asresearchers unravel the underlying complexities of thelinkage between early life stages and recruitment.

This book attempts to summarize the current stateof knowledge in this rapidly growing field and assessthe success of research efforts directed at understand-ing recruitment variability as it is generated duringearly life stages. The foundation of the book is a seriesof symposia papers presented at the 1994 meeting ofthe Early Life History Section of the American Fish-eries Society. This meeting was a particularly stimu-lating and exciting one due in no small part to theefforts of Chris Chambers and Ed Trippel, symposiaorganizers and this book’s editors. Their selection of

speakers/authors and research topics resulted in broadyet coordinated coverage of the many issues involved inthe study of recruitment variability. The various authorsfor the most part make good use of related chapters,giving the book a far more cohesive structure than sim-ilar volumes that compile the contributions of multipleauthors. This is not a haphazard collection of indepen-dent papers, but an integrated, collaborative effort witha clear underlying framework.

Michael Sinclair nicely sets the stage in chapter 1,with a historical perspective on the contributions ofJohann Hjort and his colleagues (circa 1902–1914) toearly life history studies. This is a fascinating accountof what Sinclair convincingly deems a paradigm shift inthe underlying theory of fishery science, as the Scandi-navian scientists began to recognize the importance ofindividual year classes and early life history processesin abundance fluctuations, rejecting the prior paradigmof changes in migration patterns as the cause of inter-annual variability. This paradigm shift was potentiallymotivated by newly developed aging techniques andthe serendipitous occurrence of the unusually strong1904 year class of herring, which clearly dominated thefishery in subsequent years and reinforced the percep-tion of interannual variability in recruitment success.Hjort’s two major hypotheses of mechanisms regulat-ing year class strength, variation in the timing of foodavailability during a critical period of development oflarvae and variation in transport processes advectinglarvae to or from appropriate nursery locations, con-tinue to drive much of the research attempting to resolvethe recruitment problem.

Subsequent chapters are divided into 3 sections. Thefirst deals with the initial environment encountered bynewly spawned eggs and the role of parental life his-tory in setting the scene for the potential success of

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their progeny. The second tackles the various selectivemechanisms that can determine the winners and losersof the survival game during the early life intervals. Thethird section attempts to incorporate information onthese processes to evaluate how they regulate subse-quent recruitment.

The various chapters form a balanced mix of theoret-ical development, reviews of empirical data, and mod-elling approaches. Modelling techniques are receivingincreased emphasis as it becomes clear that recruit-ment variability is unlikely to be determined by sim-ple relationships with environmental variables, and theinherent complexity of potential controlling mecha-nisms requires simultaneous analysis of multiple inter-acting factors. Unfortunately, several of the modellingintensive chapters spend too much time describing thedetails of the models rather than discussing the resultsof their simulations and the implications for under-standing recruitment variability.

One prevalent theme throughout the book is theimportance of relative size among individuals in acohort in determining the likelihood of survival atsucceeding stages. The ‘bigger is better’ hypothesishas received extensive attention in recent years (e.g.,Miller et al. 1988, Paradis et al. 1996, Sogard 1997) asresearchers attempt to discern the characteristics thatallow an individual to beat the odds and survive the haz-ardous early life stages. Size relationships clearly areconsidered to play a vital role in selecting the survivorswithin a cohort and determining the relative successof separate cohorts, but potential trade-offs with otherecological and physiological requirements moderate orsuppress size-dependent processes. Eight chapters ofthe book address some aspect of this hypothesis, withmost progressing beyond simplistic, static studies ofpredator size vs. prey size to a more realistic, dynamicapproach that better evaluates the context, timing, andpotential trade-offs involved in size-selective mortal-ity. For example, using a combination of empiricalexperiments and modeling methods, Rice et al. aptlydescribe the importance of timing to the benefits ofrapid growth for larvae interacting with predators thatare also growing. They provide an excellent graphicdepiction of Pope’s (1994) surfing analogy of wavesin the size spectra of predators and prey, suggestingthat slow growth can be advantageous if it keeps preywell behind the vulnerability range for the wave ofgrowing predators. Conover & Schultz’s chapter alsodemonstrates the importance of context to size advan-tages. They suggest that local adaptation has resulted

in genetically based differences in growth rate ofAtlantic silversides along a geographic gradient, withselection processes supporting the bigger-is-betterhypothesis in northern populations but not in south-ern populations. For the latter, they propose theintriguing hypothesis that physiological trade-offs inenergetic demands can counteract the advantages ofrapid growth, despite advantages of larger body size.Although the various chapters addressing size-basedrelationships reveal much about the mechanisms ofselective mortality, they often neglect to emphasize theimportance of variability in these processes in gener-ating recruitment variability. Factors that may stronglyinfluence mortality in one year may not do so underdifferent environmental conditions. For example, size-selective mortality appears to be more intense in yearswhen overall survival is low (Sogard 1997). Unfor-tunately, evidence for a direct link between fluctua-tions in these processes and actual fluctuations in earlymortality is limited.

The evolution of reproductive modes and their con-sequences for eggs, embryos and larvae forms anotherimportant theme. The chapter by Trippel et al. outlinesa particularly timely hypothesis: reproductive charac-teristics vary among different ages of mature adults,and removal of larger/older adults by fisheries can haveserious consequences for the resilience of a populationto environmental variability. A restricted age structuremay restrict the range of reproductive traits on whichthe environment operates. If age-dependent changes inreproductive patterns, such as the timing of spawning,represent a form of bet-hedging (the match/mismatchhypothesis extended across a lifetime), age truncationin many of the world’s fisheries may have serious con-sequences at the population level, especially for long-lived species, in which longevity may have evolved inresponse to extended periods of unfavorable environ-mental conditions. Two stocks with similar biomassbut one with a broad age structure and one comprisedprimarily of young fish may differ greatly in theirreproductive success. Consideration of the relevance ofage diversity in a local population is directly related tocurrent debates over the use of reserves in fisheriesmanagement.

There are several notable strengths to the book. Onementioned above is that the various contributions relatewell to each other while at the same time cover a broadrange of topics. Most of the contributions are conceptu-ally based, with considerable emphasis on underlyinghypotheses, evidence that either supports or refutes the

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theory, and critical analysis of the various techniquesused to explore recruitment variability. Unlike manyedited volumes, none of the chapters here would bemore appropriate as a stand alone journal article. Onlya few authors diverge from the main theme, present-ing topics that are still interesting even if unrelatedto understanding recruitment variability. Chapters thatare primarily reviews are thorough and insightful; theyshould provide readers with a solid background inthe issues and controversies in this field. Many ofthe chapters include a section recommending futureresearch directions, with valuable ideas on potentiallyinformative studies. For the most part the book has beencarefully edited, with few typographical errors or othermistakes, although the graphs for figures 17.6 and 17.7are switched.

One glaring omission in the book is the absence ofcontributions analyzing Hjort’s other hypothesis, thatpopulation regulation during the early life stages canhave a primarily physical source via transport pro-cesses affecting the spatial distribution of larvae. Like-wise, the effects of physical processes such as stormactivity, mixing properties, temperature patterns, etc.on survival of larvae, have been given short shrift.A primary focus on physical factors is evident onlyin Frank’s chapter, which provides an enlighteningaccount of how variation in drift of larvae of twoadjacent stocks can lead to misidentification of stockmembership in surveys of larvae, in turn masking realenvironmental influences on year class strength. Cowen& Sponaugle’s chapter on coral reef fishes reflectsthe greater emphasis on physical transport processesin tropical systems compared to temperate systems.In general, however, the book leaves one with theimpression that all the important influences on mor-tality of larvae are biologically based, and our researchattention should be focused on biological processes,such as the size-based predator/prey interactions preva-lent in the book. This is misleading and neglects themany contributions emphasizing the role of physicalfactors in recruitment variability (see, for example,results of the Fisheries Oceanography CoordinatedInvestigations program in vol. 5, suppl. 1 ofFisheriesOceanography).

One historical tidbit in Sinclair’s chapter that I foundparticularly surprising was that Hjort himself did notadvocate a research focus on mechanisms of recruit-ment variation. Apparently he felt that the problemwas too complex and not tractable, and effort would bemore productive if concentrated on assessing the sizeand age composition of stocks to allow identification ofyear class strength, clearly the direction taken by fish-ery science in the following decades. Today we mightask if Hjort was correct, and despite our technologicaltools, the recruitment problem remains intractable andwe should direct our research resources elsewhere. Oursuccesses in identifying the causes of recruitment fluc-tuations and predicting year class strength from abun-dances of early life stages are still minimal at best. Thepessimistic view is that Hjort was right, and we willnever be able to provide solid predictions of year classstrength. I prefer the optimistic view, that with suchvastly improved technologies as detailed otolith micro-chemistry, genetic identification of local populations,satellite imagery of physical oceanographic processes,and rearing of early life stages for experimental analy-sis, we are on the verge of a new era of clearly identify-ing the causes of recruitment variation. This book willaid many researchers in designing the future studiesthat will take us to this next level of understanding.

References cited

Houde, E.D. 1987. Fish early life dynamics and recruitment vari-ability. Amer. Fish. Soc. Symp. 2: 17–29.

Miller, T.J., L.B. Crowder, J.A. Rice & E.A. Marschall. 1988. Lar-val size and recruitment mechanisms in fishes: toward a con-ceptual framework. Can. J. Fish. Aquat. Sci. 45: 1657–1670.

Paradis, A.R., P. Pepin & J.A. Brown. 1996. Vulnerability of fisheggs and larvae to predation: review of the influence of therelative size of prey and predator. Can. J. Fish. Aquat. Sci. 53:1226–1235.

Pope, J.G., J.G. Shepherd & J. Webb. 1994. Successful surf-ridingon size spectra: the secret of survival in the sea. Phil. Trans. R.Soc. Lond. B 343: 41–49.

Sogard, S.M. 1997. Size-selective mortality in the juvenile stageof teleost fishes: a review. Bull. Mar. Sci. 60: 1129–1157.