Egg Production

GANIAS, K.; MURUA, H.; CLARAMUNT, G.; DOMINGUEZ-PETIT, R.; GONCALVES, P.; JUANES, F.; KENEDDY, J.; KLIBANSKY, N.; KORTA, M.; KURITA, Y.; LOWERRE-BARBIERI, S.; MACCHI, G. J.; MATSUYAMA, M.; MEDINA, A.; NUNES, C.; PLAZA, G.; RIDEOUT, R.; SOMARAKIS, S.; THORSEN, A.; URIARTE, A.; YONEDA, M.

Handbook of Applied Fisheries Reproductive Biology for Stock Assessment and Management

CSIC

Año: 2013;

Understanding the reproductive biology of any species becomes of crucial importance as it determines the productivity, the resilience of the species to exploitation and its capability of recovery. In this context, the stock-recruitment relationship is considered a cornerstone in fisheries management as the biomass reference points are usually dependent on stock-recruitment models. Traditional recruitment models assume that the reproductive potential of a population is proportional to its spawning stock biomass; this, then, is commonly used to set biological reference points. However, standard spawner recruits models originally used the term, but subsequently used the term SSB as a proxy for fecundity. In such cases, it is assumed that a given weight of adult biomass has the same probability of generating the same level of recruitment. This implies that the survival rates of offspring are independent of parental age, body size or condition and that total relative fecundity and annual egg production, by length and between years, is invariable. However, there is increasing evidence indicating that a direct proportionality between spawning stock biomass and egg production may not exist. In particular, the reproductive potential is affected by several factors, such as adult age structure and diversity, proportion of first-time and repeat spawners and nutritional condition; that are poorly reflected when limiting the representation of reproductive potential by spawning stock biomass. This limitation could even be more pronounced in the case of indeterminate fecundity species, where the production of eggs per unit SSB may vary substantially among years depending upon environmental conditions (temperature, food availability, etc.) during the spawning season. In these species, feeding conditions will greatly influence spawning activity and the rate of recruitment of previtellogenic oocytes into the stock of yolked oocytes. Additionally, it has been documented that fecundity within a stock varies annually and can undergo long-term changes. In light of these issues, there is a clear necessity for comprehensively examining the interannual variation of fecundity and adult egg production; which, in turn, will permit an understanding of the underlying mechanisms regulating annual variability in egg production. This component represents the production processes that yield the number of potential zygotes, a quantity that becomes modified by mortality processes during the dynamics of early life stages, to arrive ultimately at the number of recruits. Moreover, adult egg production information, in combination with concurrent estimates of egg production at sea (from ichthyoplankton surveys) would enable the estimation of spawning stock biomass, independently of commercial fishery data. This approach would increase the knowledge with regard to the state of the population and improving the standard assessment of any commercially valuable fish species. In this chapter, techniques for estimating fecundity and egg production of fishes with different reproductive strategies are described, both classical techniques as well as most recently developed techniques based on digital image analysis and modern stereology. Additionally, this chapter includes description of methods use to study egg production regulation processes, specifically those used to estimate atresia, to determine reproductive cycle duration and to analyze its alterations. Thus, methods to estimate the egg production, annually and/or on a daily basis will be determined, to allow the application of egg production methods. Another section will be devoted to standardize and harmonize the methods used for different laboratories in order to allow standardized comparison between studies and data. Finally, suitability of each method depending on reproductive strategy and tactic of each species and/or stock are considered