Degeneration of postovulatory follicles in the Iberian sardine Sardina pilchardus: structural changes and factors affecting resorption

Inaccuracy in the aging of postovulatory follicles (POFs) and in estimating the effect of temperature on the resorption rate of POFs may introduce bias in the determination of the daily spawning age classes with the daily egg production method (DEPM). To explore the above two bias problems with f ield-collected European pilchard (Sardina pilchardus, known regionally as the Iberian sardine), a method was developed in which the time elapsed from spawning (POF age) was estimated from the size of POFs (i.e., from the cross-sectional area in histological sections). The potential effect of the preservative type and embedding material on POF size and the effect of ambient water temperature on POF resorption rate are taken into account with this method. A highly significant loglinear relationship was found between POF area and age; POF area shrank by approximately 50% per day. POFs were also shown to shrink faster at higher temperatures (approximately 3% per degree), but this temperature effect is unlikely to be an important source of bias in the assignment of females to daily spawning classes. The embedding material was also shown to influence the size of POFs, the latter being significantly larger in resin than in paraffin sections. In conclusion, the size of POFs provides an indirect, reliable estimation of the time elapsed from spawning and may thus be used to test both the validity of POF staging criteria for identifying daily classes of spawners and the effect of other factors (such as temperature and laboratory processing) in applications of the DEPM to S. pilchardus and other fish species

Sound production during competitive feeding in the grey gurnard

The acoustic repertoire of captive grey gurnard Eutrigla gurnardus during competitive feeding consisted of three types of sound: knocks, grunts and growls. Knocks were audible as a single sound, whereas grunts and growls were perceived as longer, pulsed sounds to the human ear. Typically, knocks were composed of 1–2 pulses, grunts of 4–8 pulses and growls >10 pulses. Growls were longer and had shorter pulse periods than grunts. All sound types had peak frequencies of c. 500 Hz. The sequences of behaviours observed during feeding interactions suggest that grey gurnard obtain food both by scramble and contest tactics. Competing fish emitted knocks mainly while grasping a food item and also during other non-agonistic behaviour, suggesting that knock production may reflect a state of feeding arousal but could also serve as a warning of the forager’s presence to nearby competitors. Grunts were mainly emitted during frontal displays, which were the most frequent behavioural act preceding grasps, suggesting that they may play a role in deterring other fish from gaining access to disputed food items

Differences in sounds made by courting males of three closely related Lake Malawi cichlid species

Courtship sounds made by three sympatric cichlid species, Pseudotropheus zebra, P. callainos and an undescribed species known as P. ‘zebra gold’ were recorded and compared to investigate the potential role of acoustic signals in mate choice. Sounds were emitted during ‘quiver’ and ‘circle’ components of the male courtship display and consisted of rapidly repeated pulse units. Some sound variables differed significantly among species with P. callainos generally being separated from the other two species. This species produced sounds with higher peak frequency (for a given length) and lower number of pulses than P. ‘zebra gold’ and higher pulse durations than P. zebra. In addition, standard length was inversely related to peak frequency in both P. ‘zebra gold’ and P. callainos (this relation was not tested in P. zebra due to the small sample size). These differences might indicate different regimes of intraspecific sexual selection among the three species

Discarding practices for commercial gadoids in the North Sea

Understanding fishers' discarding behaviour, and anticipating their reactions to changes in the biological or regulatory characteristics of a fishery, are important for dealing with the problem of discarding. In this paper, we investigate the discarding of haddock (Melanogrammus aeglefinus), whiting (Merlangius merlangus), and Atlantic cod (Gadus morhua) in the North Sea, using data collected by scientific observers onboard Scottish demersal vessels. We describe discarding on each trip by species-specific discard curves and explore how these curves depend on biological and regulatory variables. There are large differences in the size of discarded fish between inshore and offshore areas, with offshore-operating vessels discarding larger fish (high-grading). Increases in legal landing size correspond to immediate increases in the size of discarded fish, particularly for haddock and cod in inshore areas. In general, discarding practices for haddock and cod are similar over time and consistent across gears, whereas decisions for the lesser valued whiting are more variable and can be affected by the catch composition

Distribución y abundancia de trompetero (Macroramphosus spp.) en aguas portuguesas (1998-2003)

Data from 10 acoustic surveys targeting sardine (spring and autumn), 3 acoustic surveys targeting blue whiting (spring) and 9 groundfish surveys (summer and autumn) were used to describe the distribution and relative abundance of snipefish (Macroramphosus spp.) off Portugal and the Gulf of Cadiz in recent years (1998-2003). Snipefish (8-17 cm) were regularly found off Portugal, occasionally in large concentrations, but were absent from the Gulf of Cadiz. Off northern Portugal, snipefish were distributed along the outer shelf and upper slope, clearly separated from sardine (the most abundant species in the inner shelf) and partially overlapping with blue whiting (Micromesistius poutassou), the most abundant species in the upper slope. Snipefish were most abundant in the outer shelf of south-western Portugal, preferentially distributed in large aggregations around the Canyon of Setubal and partially overlapping with the distribution of boarfish (Capros aper) and blue whiting (both abundant in the upper slope of south-western Portugal). Off southern Portugal snipefish were almost exclusively distributed in the outer shelf and were significantly smaller than in south-western (intermediate) and northern Portugal (large). Acoustic estimates of total snipefish biomass ranged between 176 – 504 thousand tonnes within the study period, with more than half off south-western Portugal. Within the period 1998-2003, and despite the lack of directed fishing activity, a marked decline in abundance and a small but significant increase in mean length were observed, particularly off south-western Portugal.Datos de 10 cruceros acústicos dirigidos a la sardina (Sardina pilchardus) (primavera y otoño), 3 cruceros acústicos dirigidos a la bacaladilla (Micromesistius poutassou) y 9 cruceros demersales (verano y otoño) fueron utilizados para describir la distribución y abundancia relativa del trompetero (Macroramphosus spp.) en la costa portuguesa y Golfo de Cádiz en los últimos años (1998-2003). El trompetero (con tallas comprendidas entre 8 y 17 cm) estuvo presente frecuentemente en aguas portuguesas, en ocasiones en elevadas concentraciones y ha estado ausente del Golfo de Cádiz. En las aguas del Norte de Portugal, el trompetero estuvo presente sobre el exterior de la plataforma continental y la parte superior del talud, claramente separado de la sardina (la especie más abundante de la plataforma interior) y sobrepuesto parcialmente a la bacaladilla, la especie más abundante del talud superior. El trompetero fue más abundante en el exterior de la plataforma continental del Sudoeste de Portugal, encontrándose preferencialmente en elevadas densidades alrededor del cañón de Setúbal, solapándose parcialmente al ochavo (Capros aper) y a la bacaladilla, ambos abundantes en el talud superior del sudoeste de Portugal. Al sur de Portugal, el trompetero se encontró casi exclusivamente en la plataforma exterior, siendo los individuos significativamente más pequeños que en el sudoeste (medianos) y en el norte (mayores). La estimación acústica de la biomasa del trompetero osciló entre 176000-504000 toneladas en el periodo estudiado, con más de mitad en la zona sudoeste de Portugal. En el periodo de 1998-2003, se verificó un descenso acentuado en la abundancia y un ligero aumento del tamaño medio de los individuos, especialmente en el sudoeste de Portugal

Differences in life history features of long rough dab Hippoglossoides platessoides within Scottish waters

Recent studies have shown differences in life history features of long rough dab Hippoglossoides platessoides among populations of the North Atlantic. Here, length frequency distributions from commercial catches and age information from otolith readings are used to compare long rough dab from the North Sea and the West of Scotland. Catch data from the Scottish demersal fisheries show differences in the length distribution of long rough dab between the 2 areas, with large fish (>20 cm) more prevalent in the North Sea. The maximum length of long rough dab observed in commercial catches is 8 cm greater in the North Sea, where otolith readings indicate that the species has a greater longevity. Growth models suggest that long rough dab of age 3+ are significantly smaller in the West of Scotland. Potential explanations for the observed contrasts in hie history features include spatial differences in temperature-related metabolic costs, food availability, sex ratios (males tend to be smaller), or age-specific loss rates (emigration or mortality). Of these, we conclude that the hypothesis involving temperature-dependent metabolic costs is the least likely explanation