Bernard A. Megrey

End-To-End Models for the Analysis of Marine Ecosystems: Challenges, Issues, and Next Steps

Abstract There is growing interest in models of marine ecosystems that deal with the effects of climate change through the higher trophic levels. Such end-to-end models combine physicochemical oceanographic descriptors and organisms ranging from microbes to higher-trophic-level (HTL) organisms, including humans, in a single modeling framework. The demand for such approaches arises from the need for quantitative tools for ecosystem-based management, particularly models that can deal with bottom-up and top-down controls that operate simultaneously and vary in time and space and that are capable of handling the multiple impacts expected under climate change. End-to-end models are now feasible because of improvements in the component submodels and the availability of sufficient computing power. We discuss nine issues related to the development of end-to-end models. These issues relate to formulation of the zooplankton submodel, melding of multiple temporal and spatial scales, acclimation and adaptation, behavioral movement, software and technology, model coupling, skill assessment, and interdisciplinary challenges. We urge restraint in using end-to-end models in a true forecasting mode until we know more about their performance. End-to-end models will challenge the available data and our ability to analyze and interpret complicated models that generate complex behavior. End-to-end modeling is in its early developmental stages and thus presents an opportunity to establish an open-access, community-based approach supported by a suite of true interdisciplinary efforts.

Fish reproductive biology : implications for assessment and management

Contributors vii Preface ix Acronyms x Introduction 1 Tore Jakobsen, Michael J. Fogarty, Bernard A. Megrey and Erlend Moksness Part I Biology, Population Dynamics, and Recruitment Chapter 1 Recruitment in Marine Fish Populations 11 Michael J. Fogarty and Loretta O Brien Chapter 2 Reproductive Dynamics 50 Dimitri A. Pavlov and Natal ya G. Emel yanova Chapter 3 Recruitment Variability 98 Edward D. Houde Chapter 4 Effects of Fishing on the Population 188 Marie-Joelle Rochet and Lise Marty Part II Information Critical to Successful Assessment and Management Chapter 5 Egg, Larval, and Juvenile Surveys 229 Nancy C.H. Lo, Paul E. Smith, and Motomitsu Takahashi Chapter 6 Stock Identification 252 Gavin A. Begg and Steven X. Cadrin Chapter 7 Stock Assessment Models and Predictions of Catch and Biomass 279 John G. Pope Chapter 8 Applied Fisheries Reproductive Biology: Contribution of Individual Reproductive Potential to Recruitment and Fisheries Management 321 Olav S. Kjesbu Part III Incorporation of Reproductive Biology and Recruitment Considerations into Management Advice and Strategies Chapter 9 Current Paradigms and Forms of Advice 369 Kevern L. Cochrane Chapter 10 Management: New Approaches to Old Problems 395 Carl M. O Brien Chapter 11 Implementing Information on Stock Reproductive Potential in Fisheries Management: The Motivation, Challenges and Opportunities 438 C. Tara Marshall Species Index 465 Subject Index 468 A colour plate section falls between pages 292 and 293

Computers in Fisheries Research

This is the second edition of a book that reviews current and future computer trends in fisheries science applications. The first edition was published 10 years ago. Individuals have been quick to realize the potential of computers in fisheries and scientists continue to take advantage of the rapidly advancing tools and technology. This book provides a valuable sampling of contemporary applications and in some cases compares recent developments to the status of the situation 10 years ago. In many cases perspectives are presented by the same authors that contributed to the first edition. Scientists will have an opportunity to evaluate the suitability of different computer technology applications to their particular research situation thereby taking advantage of the experience of others.

A Revised Alverson and Carney Model for Estimating the Instantaneous Rate of Natural Mortality

Abstract The Alverson and Carney (AC) model for estimating the instantaneous rate of natural mortality (M) was reformulated to include β and t 0 parameters. The revised Zhang and Megrey (ZM) model could be used for the estimation of M instead of the AC model since von Bertalanffy and allometric growth parameters are readily available for most exploited fish stocks. It was determined from the new formulation that the ratios of the age at maximum biomass (t mb) to the maximum age (t max) for pelagic and demersal species were significantly different from 0.38, the value originally proposed by Alverson and Carney. The ratios for these two ecological groups were 0.302 and 0.440, respectively, and were significantly different. We examined the sensitivity and bias in M from the new formulation relative to those from the AC model, which assumed that β = 3.0 and t 0 = 0. Estimates of M from the AC model are most sensitive to the assumption that growth starts at t 0 = 0 when growth rates are high as well as to the ...

Climate Regime Effects on Pacific Herring Growth Using Coupled Nutrient-Phytoplankton-Zooplankton and Bioenergetics Models

Abstract We used a nutrient-phytoplankton-zooplankton (NPZ) model coupled to a fish bioenergetics model to simulate the weight-at-age responses of Pacific herring Clupea pallasii to climate regimes. The NPZ model represents the daily dynamics of the lower trophic levels by simulating the uptake and recycling dynamics of nitrogen and silicon and the photosynthesis and grazing interactions of multiple functional groups of phytoplankton and zooplankton. The bioenergetics model simulates the number and mean weight of Pacific herring for each of 10 age-classes. Three zooplankton groups simulated in the NPZ model provide estimates of the prey used to determine the consumption component of the herring bioenergetics model. We used a spawner-recruit relationship to estimate the number of new age-1 individuals joining the herring population every year. The coupled models were applied to the coastal upwelling area off the west coast of Vancouver Island. Model simulations were performed to isolate the effects of each...

Application of a bioenergetics growth model for European anchovy (Engraulis encrasicolus) linked with a lower trophic level ecosystem model

A bioenergetics model is implemented for European anchovy (Engraulis encrasicolus) and applied to the north-eastern Aegean Sea (eastern Mediterranean Sea). The model reproduces the growth of anchovy in a one-way linked configuration with a lower trophic level (LTL) ecosystem model. The LTL model provides densities for three zooplankton functional groups (heterotrophic flagellates, microzooplankton and mesozooplankton) which serve as available energy via consumption for the anchovy model. Our model follows the basic structure of NEMURO.FISH type models (North Pacific Ecosystem Model for Understanding Regional Oceanography for Including Saury and Herring). Several model parameters were specific for the Mediterranean or the Black Sea anchovy and some others were adopted from related species and NEMURO.FISH due to lack of biological information on E. encrasicolus. Simulation results showed that the fastest growth rate occurs during spring and the slowest growth rate from August to December. Zooplankton abundance during autumn was low implying that decreased prey density lead to a reduction in anchovy weight, especially for the age-3 class. Feeding parameters were adjusted to adequately fit the model growth estimates to available weight-at-age data. A detailed sensitivity analyses is conducted to evaluate the importance of the biological processes (consumption, respiration, egestion, specific dynamic action, excretion and egg production) and their parameters to fish growth. The most sensitive parameters were the intercept and exponent slope of the weight-dependent consumption and respiration process equations. Fish weight was fairly sensitive to temperature-dependent parameters.

Comparative analysis of marine ecosystems: international production modelling workshop

Understanding the drivers that dictate the productivity of marine ecosystems continues to be a globally important issue. A vast literature identifies three main processes that regulate the production dynamics of such ecosystems: biophysical, exploitative and trophodynamic. Exploring the prominence among this ‘triad’ of drivers, through a synthetic analysis, is critical for understanding how marine ecosystems function and subsequently produce fisheries resources of interest to humans. To explore this topic further, an international workshop was held on 10–14 May 2010, at the National Academy of Sciences Jonsson Center in Woods Hole, MA, USA. The workshop compiled the data required to develop production models at different hierarchical levels (e.g. species, guild, ecosystem) for many of the major Northern Hemisphere marine ecosystems that have supported notable fisheries. Analyses focused on comparable total system biomass production, functionally equivalent species production, or simulation studies for 11 different marine fishery ecosystems. Workshop activities also led to new analytical tools. Preliminary results suggested common patterns driving overall fisheries production in these ecosystems, but also highlighted variation in the relative importance of each among ecosystems.

Alaskan Groundfish Resources: 10 Years of Management under the Magnuson Fishery Conservation and Management Act

Abstract In this paper, we examine management under the 1976 Magnuson Fishery Conservation and Management Act (MFCMA) and its effect on Alaskan groundfish resources. The history of the groundfish fisheries in the northeast Pacific are traced, and the statuses of several important exploited species groups are compared between pre- and post-MFCMA periods. Generally, the stocks managed in the Exclusive Economic Zone off Alaska have benefited from management measures. Inadequate monitoring of the increasing domestic fishery threatened to nullify gains that had been made in the ability to assess the condition of the stocks, but a domestic observer program was implemented in 1990.

A Review of Biological Assumptions Underlying Fishery Assessment Models

This paper presents a review of fishery assessment models commonly used in the management of marine fisheries. In our review particular attention is paid to underlying biological and technical assumptions, both implicit and explicit. We also discuss the development of important fishery assessment models and their various levels of complexity from a historical perspective. The models reviewed include production models, dynamic pool models, sequential population assessment models (VPA and/or cohort analysis), spawner-recruit models, and simulation models. Each model is described in terms of management objectives, information needs, mathematical formulation, assumptions, advantages and disadvantages. The practical utility of a model from a stock assessment and/or management perspective is also discussed.

Changes in the abundance and distribution of walleye pollock (Theragra chalcogramma) in the western Gulf of Alaska (1961–1984)

Abstract Changes in the abundance and recruitment of western Gulf of Alaska walleye pollock ( Theragra chalcogramma ) during 1961–1984 were examined. Bottom trawl survey CPUE estimates increased between the early 1960s and early 1970s. Independent biomass estimates from acoustic surveys and catch-at-age analyses of foreign and joint venture fisheries indicate that another increase in abundance occurred during 1978–1981, but that stock size has declined since 1981 or 1982. Biomass was estimated at 950 000 metric tons (t) in 1973–1974, 2.3–3.8 million t in 1981 and 1.8 million t in 1984. The fluctuations in stock size reflect substantial changes in year-class strength. These include the occurrence of strong year classes in 1967, 1970, 1972 and 1975–1979. Weak year classes apparently occurred in 1980–1982. Based on spawner-recruit estimates since 1976, pollock recruitment may be strongly density dependent. It is believed that there has been a shift, since 1977, in the abundance of pollock from the Kodiak-Chirikof area, westward towards the Shumagin Islands.