Fish Reproductive Biology

Implications for Assessment and Management

Tore Jakobsen, Michael J. Fogarty, Bernard A. Megrey, Erlend Moksness, Tore Jakobsen, Michael J. Fogarty, Bernard A. Megrey, Erlend Moksness

• Publisher: Wiley-Blackwell
• Year: 2016
• ISBN:
  9781118752708
• Edition: 2
• Topic: Tecnología e ingeniería
• Subtopic: Pesca y acuicultura

Fish recruitment is a key process for maintaining sustainable fish populations. In the marine environment, fish recruitment is carried out in many different ways, all of which have different life history strategies. The objective of this book is to argue for greater linkages between basic and applied research on fisheries recruitment, and assessment and management of exploited fish stocks.

Following an introductory chapter, this second edition of Fish Reproductive Biology is organized into 3 main sections:

• Biology, Population Dynamics and Recruitment
• Information Critical to Successful Assessment and Management
• Incorporation of Reproductive Biology and Recruitment Considerations into Management Advice and Strategies

The authors collectively bring a wide range of diverse experience in areas of reproductive biology, fisheries oceanography, stock assessment, and management.

Fully updated throughout, the book will be of great interest to a wide audience. It is useful as a textbook in graduate and undergraduate courses in fisheries biology, fisheries science, and fisheries resource management and will provide vital information for fish biologists, fisheries scientists and managers.

Part I
Biology, Population Dynamics, and Recruitment

CHAPTER 1
Recruitment in Marine Fish Populations

Michael J. FogartyLoretta O'Brien

1.1 Introduction

The production of viable eggs by a population provides the raw material for recruitment (the number of young ultimately surviving to a specified age or life stage). Recruitment processes in the sea reflect the interplay of external forcing mechanisms such as physical drivers in the environment that affect demographic rates, and stabilizing mechanisms exhibited by the population. Many marine populations fluctuate widely in space and time (Fogarty et al. 1991). These dramatic changes are attributable to fluctuations in biotic and abiotic factors affecting growth and/or mortality rates during the early life history (Fogarty 1993a). Potentially countering these sources of variability are internal regulatory mechanisms that can compensate for population changes. Considerable attention has been devoted to the development of recruitment models embodying different types of compensatory processes operating during the pre-recruit phase of the life history (see Rothschild 1986, Hilborn & Walters 1992, Quinn & Deriso 1999 and Walters & Martell 2004 for reviews). In contrast, the issue of compensatory changes in factors such as fecundity, adult growth, and maturation affecting reproductive output has received less attention in modeling recruitment dynamics (but see Ware 1980, Jones 1989, Rothschild & Fogarty 1989, 1998). We argue that a complete model of population regulation of marine fishes must allow for the possibility of compensatory processes operating during both the early life history and the adult stages, and that a refined understanding of reproductive processes as described in the contributions to this book is essential in the quest to understand recruitment of marine fishes. In particular, integrating our emerging understanding of maternal effects on reproductive success of fish, as documented in this volume, into management models is essential.

In this chapter, we attempt to set the stage for several themes found throughout this volume—factors controlling the effective reproductive output of the population, the fate of fertilized eggs and larvae, and the implications for assessment and management of exploited marine species. In subsequent chapters these issues are explored in greater individual detail. An understanding of recruitment processes is essential if we are to predict the probable response of a population to exploitation and to proposed management actions. These predictions require an analytical framework. Here, we trace the theoretical developments relating recruitment to the adult population to provide such a framework. Our interest centers on exploring the consequences of different recruitment mechanisms, demonstrating how these processes can be modeled, and illustrating their importance for stability and resilience of the population. In a variable environment, sustainable exploitation is possible only if the population exhibits some form of compensation in response to variation in population size at some stage in the life history. The general issue of the role of compensation in population dynamics is therefore of both theoretical and practical importance. Correctly accounting for the effective reproductive output of the population, including the consideration of factors such as maternal effects on egg and larval viability, the age composition of the adult population, female condition, and how these are affected by population density or abundance, is critical in understanding the form of the relationship between recruitment and egg production and how the population will respond to exploitation.

An illustration of the magnitude of change in these population components is provided by trajectories of recruitment and adult biomass over the past five decades for Icelandic cod, an economically and ecologically important fish population (Figure 1.1a,b). Attempts have now been made to refine estimates of reproductive output by reconstructing the total egg production by the female population (Figure 1.1c) and to understand how factors such as the age diversity of the spawning stock (Figure 1.1d) affect recruitment success. Estimates of each of these quantities are becoming increasingly available for more marine fish populations (e.g. Marteinsdottir & Thorarinsson 1998, Trippel 1999, Marteinsdottir & Begg 2002, Marshall et al. 1998, 2003, Morgan et al. 2011, Cervino et al. 2013, Macchi et al. 2013). We will return to the relationship between recruitment and spawning stock biomass (SSB) or total egg production for Icelandic cod in Section 1.2.4 to further explore these issues, and in Section 1.8.1 we address the issue of whether consideration of the age diversity of the adult population improves the predictability of recruitment for this population (Marteinsdottir & Thorarinsson 1998).

Figure 1.1 Time series of estimates of (a) recruitment (millions of 3-year-old fish), (b) spawning stock biomass (thousand Mt), (c) total viable egg production (trillions), and (d) age diversity of spawners (Shannon–Weiner index) for Icelandic cod. Based on assessment data from ICES (2014) and fecundity relationships from Martinsdottir & Begg (2002).

In the following, we describe several models incorporating factors affecting survivorship from the egg stage to recruitment. These include competition for limiting resources, cannibalism, and the interaction of compensatory growth and size-dependent mortality. Our initial treatment will focus on deterministic processes for a single pre-recruit stage. We then broaden our development to encompass consideration of compensatory processes operating during the post-recruit phase of the life history, the stability properties of these models, multistage life history patterns, the implications of maternal effects, and the effects of environmental and demographic stochasticity. Throughout, the implications of these factors for management of exploited populations is of primary interest.

1.2 Recruitment theory

Consider the life cycle diagram depicted in Figure 1.2. For the population to persist, a sufficient number of progeny must, on average, survive to replace the parental stock. For the purposes of illustration, we show several stanzas including egg, larval, juvenile and adult stages. The eggs produced by the different adult stages can, in principle, exhibit different viabilities and have different probabilities of successful transition to the larval stage. For the purposes of this simple illustration we do not trace the effect of the size or age of the adult females beyond the egg stage, but we extend this treatment to later stages as well in a subsequent section. The transitions between stages represent the probability of surviving and growing into the next stage during a specified time interval. Note that the population becomes vulnerable to exploitation following the first juvenile stage in this example. In the following, we use the size or age at first harvest as the demarcation point for recruitment. The life cycle is completed with the production of eggs by the adult component of the population. The fishery reduces the pro...