Academic journal article Estonian Journal of Ecology

Individual Fecundity of the Autumn Spawning Baltic Herring Clupea Harengus Membras L/Sugiskuderaime (Clupea Harengus Membras L.) Individuaalne Viljakus

Academic journal article Estonian Journal of Ecology

Individual Fecundity of the Autumn Spawning Baltic Herring Clupea Harengus Membras L/Sugiskuderaime (Clupea Harengus Membras L.) Individuaalne Viljakus

Article excerpt

INTRODUCTION

Advanced understanding in the dynamics of fish fecundity is of fundamental importance in fish and fisheries ecology and also has strong practical significance. It has been empirically shown that individual fecundity of fish is directly related to fish stock recruitment variation, suggesting thereby that fecundity is an important component of fish stock dynamics (Rickmann et al., 2000). More specifically, fecundity of individual fish is required for the assessment of the reproduction potential of fish stocks (Bleil & Oeberst, 2005). Stock reproductive potential is, in turn, subject to interannual fluctuations due to environmental changes influencing maturation, growth, and condition of fish (e.g., Morgan & Rideout, 2008). As a response to the changing environment, different sub-species of fish have evolved with intriguing reproductive strategies that reflect spatially small-scale adaptation to surrounding environmental conditions and ecological niches (Murua & Saborido-Rey, 2003).

Herring, unlike most other clupeoids, are total spawners with a group-synchronous ovarian organization (Murua & Saborido-Rey, 2003). However, at a population level, they may be considered serial spawners, similar to most other Clupeiformes. They accomplish this by spawning in waves over a protracted spawning season, the older herring usually spawning first, with the younger herring and recruits spawning in subsequent weeks (Ware & Tanasichuk, 1989). Thus multiple intra-annual spawning (in this case wave spawning) can be considered as 'intraseasonal iteroparity' (Jennings & Beverton, 1991).

Several life history parameters of fish related to reproductive biology may change over time and space. Amongst others, these include: reproductive rate (size-specific fecundity), age or size at maturation, quality or size of gametes, timing of maturation and spawning (Bailey & Almatar, 1989). Specifically, fecundity-at-length variability in autumn spawning herring in the Gulf of Maine (Kelly & Stevenson, 1985), spring and autumn spawning herring in the Gulf of St Lawrence (Lambert, 1987), the Clyde spring spawning herring (Bailey & Almatar, 1989), but also in a range of other fish species (Bagenal, 1973) has been suggested and has been related to density dependent effects. In addition, interannual differences in length-specific fecundity of the Norwegian spring spawning herring were explained by variation in weight-at-length, that is higher fecundity of spawners in better condition (Oskarsson et al., 2002).

Baltic Sea fish populations have fluctuated over time, and an increasing amount of historical evidence is becoming available for several commercial fish species on the magnitude and direction of these fluctuations, together with identification of the drivers responsible (e.g., Eero et al., 2011). Studies on Baltic herring started already in the late 19th century, when on the basis of morphometric and meristic characters, two races--spring and autumn spawners--were distinguished (Heincke, 1898). While spring spawning herring generally constitute most of the herring landings in the Baltic Sea, the importance of the autumn spawners has varied over time. For instance, about a century ago autumn spawners constituted the main part of the herring catches in the Baltic Sea, which was often based on a few strong year-classes (Hessle, 1931, and references therein). Unfortunately, information on the Baltic autumn spawning herring is relatively fragmental and almost lacking during the past decades.

In the northern Baltic Sea, at the border of its distribution area, autumn herring finds favourable conditions only during the periods of relatively warm winters and high salinity with abundant year-classes being formed only after mild winters (Ojaveer, 2003). Autumn spawning herring made a substantial contribution of herring landings in the Gulf of Riga until the mid-1970s accounting for up to 47% in some years, but the fish fell into deep depression since then and has not recovered yet (Ojaveer, 2003). …

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