Reproductive Ecology of European Hake (Merluccius Merluccius) and Its Relation with The

VERTIMAR-2005
Symposium on Marine Accidental Oil Spills

Reproductive ecology of European hake (Merluccius merluccius) and its relation with the Prestige oil spill

RosarioDOMINGUEZand FranSABORIDO-REY

Instituto de Investigaciones Marinas (CSIC), Eduardo Cabello 6, 36208 Vigo, Spain

ABSTRACTEuropean hake (Merluccius merluccius) ovaries have been sampled regularly since 1999 until 2004. Since December 2002 with the Prestige oil spill weekly samples were collected in order to asses the potential impact of the fuel. Maturation process, fecundity, energetic reserves dynamic and atresia have been analyzed in females. Changes in the different reproductive parameters have been observed, especially regarding atresia rate. However, it is discussed to what extend they are the consequence of natural fluctuations or due to important alterations in the ecosystem, i.e. basically severe shifts in food availability or energetic unbalance, both due to the oil spill.

1. INTRODUCTION

One of the most important of the fuel and its components spill of fisheries resources is the reduction of the reproductive potential at both the individual and population level (National Research Council, 2002). At individual level it has been observed alterations in the hormone levels, inhibition of the gonad development, fecundity reduction and lower egg and larval viability (Idler et al., 1995; Johnson et al., 1995; Thomas & Budiantara, 1995; Truscott et al., 1992). The reproductive potential will also depend on the energetic storage. All this bioenergetic processes are the consequences of the energy assimilation rate (feeding), growth rate and condition factor which will determine through allocation rules the energy towards maturation and annual gametes development, especially oocytes (Saborido-Rey & Kjesbu, 2005). The energetic balance may be altered in different manner by the presence of pollutants in the environment.

2. RESULTS AND DISCUSSION

Two periods have been analyzed, from January 1999 to July 2000, i.e. before the Prestige oil spill, and from January 2003 to July 2004, i.e. right after the oil spill. The most important reproductive feature analyzed that yielded differences among both periods was the presence of high rate of atresia. While during the period before the oil spill the proportion of females with high level of atresia was low at all analyzed months (Figure 1). In the period after the oil spill the proportion of females with high levels of atresia was very high, especially during the autumn, one year after the oil spill (Figure 2).

Atresia is a normal feature occurring in all fish species during oocyte development. Usually, at individual level, atresia is observed at very low rate, but occasionally atresia rate is high enough to consider such female as being in reproductive failure or as skip spawning. This situation is normal, being the consequence of a bad female condition which cannot afford the reproductive event. The reasons behind the failure are diverse, but normally due to a lack of energy available for reproduction. However, massive presence of females on reproductive failure indicates the presence of important environmental stress. Nevertheless, high rates of atresia are always observed at the end of the spawning season as part of the residual oocyte resorption. In species with low population spawning synchronicity, as hake, the key question is how to distinguish massive atresia of post spawning females from females in reproductive failure. This issue is further discussed.

Figure 1. - Proportion of atresia by month from January 1999 to July 2000. Shaded bars indicate normal atresia. White bars indicate abnormal high rate of atresia.

Figure 2. - Proportion of atresia by month from January 2003 to July 2004. Shaded bars indicate normal atresia. White bars indicate abnormal high rate of atresia.

REFERENCES

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