Survival rates and physiological recovery responses in the lesser-spotted catshark (Scyliorhinus canicula) after bottom-trawling.

In 2019, Europe will adopt a no-discards policy in fisheries. This entails the landing of captured species unless strong evidence is provided supporting their survival and recovery after fishing. Thus, research on this topic is gaining momentum. Bottom-trawling, as a non-selective fishing method, is characterized by a high proportion of discards including vulnerable key species, such as demersal sharks. Their survival may also depend on capture depth. By paralleling onboard and laboratory experiments with the small-spotted catshark, Scyliorhinus canicula, we offer a robust experimental design to assess the survival of discarded sharks. Catsharks were captured by bottom-trawling at two depths (shallow ~89 m and deep ~479 m). Blood samples were collected following trawl capture and analyzed for stress biomarkers (lactate, osmolality, phosphate, urea). During recovery in onboard tanks, behavior was video-recorded and fish were re-sampled after 24 h. A second experiment was conducted in laboratory facilities to simulate air-exposure after trawling and to analyze the physiological recovery. Our results showed that 95.7% of the animals survived 24 h after trawling. We confirmed that trawling elicited acute stress responses in catshark but that they managed to recover. This was demonstrated by lactate concentrations that were 2.6 mM upon capture, but recovered to assumed baselines after 24 h (0.2 mM). Non-invasive video monitoring revealed behavioral differences with depth, whereby those captured at 89 m depth required longer to recover than those captured at 479 m depth. Implementation of standardized survival studies by fishery managers can benefit from holistic physiological approaches, such as the one proposed here.

Initial effects of the toxic waste spill (Aznalcóllar mine accident) on the aquatic macrofauna of the Guadalquivir Estuary.

The initial effects of the toxic waste spill in April 1998 at the Aznalcóllar mine (SW Spain) on the nektonic community of the Guadalquivir Estuary were examined at three sampling sites using univariate and multivariate techniques. Since studied communities showed a considerable seasonal trend, only seasonally homogenous periods were compared to analyse effects of the spill: May-August 1997 (before spill) and May-August 1998 (after spill). Results of both techniques (two-way nested ANOVA and ANOSIM tests, P > 0.05) indicated that there was no significant difference between the nektonic community of the estuary before and after the spill (monthly number of species, abundance, biomass and similarity among samples). Conversely, an unusually high density was observed at the outer sampling site immediately after the spill for species typical of more stagnant estuarine habitats. This feature seems to indicate that the fauna in the estuarine area through which the untreated water penetrated into the main course may have been disturbed. Results also suggest that this initial sudden input of fresh water to the estuary could have enhanced the effects of an increased river flow (a drop in the salinity). Nevertheless, longer temporal series of data, especially for permanent estuarine inhabitants, are recommended before conclusions can be drawn on the effects of the toxic waste spill on estuarine communities.

Quantification of the age-pigment lipofuscin in brains of known-age, pond-reared prawns Penaeus japonicus (Crustacea, decapoda).

A quantitative study of the lipofuscin content was carried out by image analysis in brains of known-age, pond-reared Penaeus japonicus (Crustacea, Decapoda) with the aim of assessing the applicability of the lipofuscin technique as an estimator of the physiological age in penaeids. With this purpose, three distinct measurements of lipofuscin levels (% area fraction, granule density and mean granule size) were recorded in ten sections of the olfactory lobe cell mass (OLCM) per animal. The image analysis was based on the autofluorescence emitted by the pigment, which accentuates the contrast between the lipofuscin granules and the background tissue. The concentration of lipofuscin increased significantly with age and was independent of sex. The relationship between age and lipofuscin concentration (area fraction and granule density) was best described by a seasonalized von Bertalanffy function, since the accumulation rate of the pigment dramatically slowed down in fall-winter, probably as a result of reduced seasonal metabolism. The present results confirm the potential of the lipofuscin method in the estimation of physiological age in penaeids and suggest that the application of this methodology can be useful in studies of age structure in wild populations and in the assessment of natural resources. J. Exp. Zool. 286:120-130, 2000.