Movement of sea lamprey through a vertical-slot fishway (built at the Coimbra dam, in central Portugal) was continuously monitored between 2013 and 2016 by a video recording system. Visual count data were used to quantify the overall successful movements and identify seasonal and circadian patterns of fishway use. Explicative models (Boosted Regression Trees) were used to study the relationship between frequency of successful movements during the species migration peak and environmental variables. The aim of the study was to identify predictors that may be related with successful sea lamprey upstream migration through the fishway. Collected information was used to support further management recommendations for optimizing the fishway performance. During the 4-year study, near 50,000 lampreys successfully negotiated the Coimbra dam fishway reaching the upper stretch of river Mondego.Migratory peak occurred between April and May with an increase in passages during the night period (between 11 p.m. and 6 a.m.). It was observed an increase in use frequency that was related with the combined effect of flow and temperature. Higher passages were achieved when Coimbra dam discharge flows are lower than 100 m 3 /s and temperature between 15 and 19°C. Flow discharges higher than 150 m 3 /s seemed to inhibit successful sea lamprey passage. In dry years, when flows are almost constantly lower than 50 m 3 /s, temperature was the most important factor influencing fishway use.
We analysed the ovarian dynamics of the anadromous semelparous allis shad Alosa alosa for which our working hypothesis was that mature pre-spawning females would have very low or even exhausted primary growth (PG) oocyte reserves; semelparity has been linked with the depletion of the pool of PG oocytes. To test this hypothesis, the PG oocytes were enumerated, their recruitment pattern to the secondary growth (SG) phase was analysed and their potential replenishment from the pool of oogonia was examined in females caught very close to the Mondego River mouth, in central Portugal and along the river. The development of the SG oocytes was also analysed, the fecundity (batch, total and annual) values were estimated and the intensity of atresia was quantified. Ovarian samples and histological sections were investigated in parallel. A dynamic recruitment pattern of PG oocytes to the SG phase was revealed, where all PG oocytes were recruited and were not replenished by oogonia. Annual fecundity was subject to down-regulation due to atresia prior to spawning and its size was multiple times higher than the size of batch fecundity. Lack of population synchronicity in ovarian development and spawning migration was also observed.This multifaceted analysis of the ovarian dynamics of this species will contribute to management efforts for this critically endangered and economically important fish throughout its geographical distribution. The results reported in this study will also assist in unravelling the complexity of the early processes of oogenesis in fish.
K E Y W O R D Salosines, anadromy, fecundity, oocyte recruitment, oogonia, semelparity
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