Francisco Sardà

Climate influence on deep sea populations.

Dynamics of biological processes on the deep-sea floor are traditionally thought to be controlled by vertical sinking of particles from the euphotic zone at a seasonal scale. However, little is known about the influence of lateral particle transport from continental margins to deep-sea ecosystems. To address this question, we report here how the formation of dense shelf waters and their subsequent downslope cascade, a climate induced phenomenon, affects the population of the deep-sea shrimp Aristeus antennatus. We found evidence that strong currents associated with intense cascading events correlates with the disappearance of this species from its fishing grounds, producing a temporary fishery collapse. Despite this initial negative effect, landings increase between 3 and 5 years after these major events, preceded by an increase of juveniles. The transport of particulate organic matter associated with cascading appears to enhance the recruitment of this deep-sea living resource, apparently mitigating the general trend of overexploitation. Because cascade of dense water from continental shelves is a global phenomenon, we anticipate that its influence on deep-sea ecosystems and fisheries worldwide should be larger than previously thought.

Spatio-temporal variations in megabenthos abundance in three different habitats of the Catalan deep-sea (Western Mediterranean)

The spatio-temporal variations in the megafauna (fishes, crustaceans, and other invertebrates) in three different habitats on the slope in the Western Mediterranean (Catalan coast off Barcelona) have been investigated. Samples were collected at two fixed stations during 1991 and 1992, one inside and one outside a submarine canyon (at depths between 450 and 600 m) and additional samples were collected at another station on the lower slope (at a depth of 1200 m) in each season of the year. Three replicates of each sample were taken at each station. Differences observed between habitats, seasons, and zoological groupings were verified statistically by factorial ANOVA. The habitat appeared to be the main factor responsible for the differences observed in biomass and abundance values for the zoological groupings considered. Decapod crustacean biomass was higher in the submarine canyon than in neighbouring zones, and smaller species and juveniles were more abundant inside the canyon in the case of both fishes and crustaceans. Fish biomass was most abundant in the lower slope. Seasonality was also a factor, although to a lesser extent. Seasonal variations in biomass, especially fish biomass, were recorded in the deepest zone (1200 m). Crustaceans displayed lower sensitivity to seasonal factors, whereas other invertebrates did not, on the whole, exhibit seasonal variations.

Gastric evacuation of different foods byNephrops norvegicus (Crustacea: Decapoda) and estimation of soft tissue ingested, maximum food intake and cannibalism in captivity

Gastric evacuation, maximum food intake and mortality during starvation were studied inNephrops norvegicus (L.) by means of simple laboratory experiments. Lobsters were collected by trawling off Barcelona (northwest Spain) at 400 m depth in winter 1986, and were held individually or in groups and fed different types of food:Nereis spp. (soft tissue, muscle), some species of Crangonidae (mostly hard tissue, carapace) andEngraulis encrassicolus (soft and hard tissues, combined muscles and bones). The digested matter was subsequently examined and analyzed from the stomach contents. Laboratory results were compared with the stomach contents of individuals collected from the field. Gastric evaluation was calculated as weight of stomach contents at Timet = stomach-content weight × 100:weight of food ration — residual weight of food, and the characteristic appearance of identifiable food items at different digestion times (0.5, 1, 2, 3, and 5 h) was recorded and illustrated, providing a basis for establishing the time of ingestion of the last meal and the underestimation of soft, compared to hard tissues. Underestimation of soft tissues may yield errors which constitute up to 10% of the soft food actually ingested. Maximum food intake was estimated at 0.25 g g−1 body wt d−1, and feeding did not recommence until 24 h after a previous meal. Finally, we present data on mortality resulting from cannibalism which occurred in conjunction with starvation: this ranged from 0% in isolated individuals to 36.6% in individuals held in groups.

A history of recent advancements on Nephrops norvegicus behavioral and physiological rhythms

Biological rhythms are a widespread feature of living organisms, being expressed at any level of their organization. Behavioral and physiological rhythms can affect the results on species stock assessment when the timing of sampling is not taken into account. That timing is of importance since animals may be present or not in a certain area of sampling depending on their activity cycle. As an example of this, the rhythmic behavior and physiology of one of the most commercially important European decapods, the Norway lobster (Nephrops norvegicus) was studied. These rhythms affect its commercial catchability at a diel and at a seasonal scale. Nephrops inhabits muddy bottoms where animals dig burrows that save them from the trawl tow capture when occupied. Catch patterns have been widely used as proxy of activity rhythms of populations of different depths. Catches show a modulation upon the day-night cycle since animals emerge under optimum environmental illumination in order to feed. Emergence is also affected in a not fully clarified manner by other variables of environmental and demographic nature (e.g. food presence, hunger state, sex, size, reproductive stage, territorialism and mating). All these features make Nephrops a good model of reference for studies on biological rhythms of other commercially important deep water decapods in relation to their ecological context. In this review, we summarize the actual knowledge on Nephrops behavioral and physiological rhythms. We will compare data obtained from laboratory tests on single individuals with data obtained from trawling of populations of different depths. We will also describe some new hypotheses on the rhythmic regulation of the species behaviour, as well as potential scenarios for future research.

Assessing perceptions: Do Catalan fishermen catch more shrimp on Fridays?

The information amassed through the lifetime of individual fishermen by natural observation is of a scale and quality not normally accessible to scientific surveys. Obtaining such information and rendering it scientifically useful is one step in gaining new insights in the functioning of marine ecosystems and fisheries. In this paper, we illustrate this idea by analysing the rose shrimp (Aristeus antennatus) fishery in the Catalan Sea (NW Mediterranean). Catalan fishermen assert that the catch of rose shrimp in the area is higher on Fridays than on other days of the week. We tested the validity of this assertion by analysing a 2-year data set on landings and sale prices for rose shrimp at the port of Barcelona (Spain). We established three hypotheses to account for the fact that rose shrimp catch is highest on Fridays. The first hypothesis assumes that as trawling proceeds during the week, sediment resuspension is increased over the fishing grounds and food opportunities for the rose shrimp are enhanced and reach its maximum on the last day of the working week (Fridays). The second hypothesis states that competitors (mainly demersal fish) are removed from the fishing grounds at a higher rate than shrimp, thus fish catch would decrease towards the end of the week, while shrimp catch would increase. The third hypothesis is based on the assumption that market dynamics determine the higher shrimp catch on Fridays by the higher prices fetched by this species at the auction, thus driving fishermen to concentrate on rose shrimp towards the end of the week. Analysis of the data in the light of the three hypotheses indicates that only hypothesis two and three could have a real influence. We establish the working mechanisms to account for this result: the ability of fishermen to remove competitors at a differentially higher rate and the better location of rose shrimp shoals in the course of the week, leads to a higher catch of rose shrimp in the study area towards the end of the week. The subconscious factors at work during the fishing process coupled with the ecological behaviour of the species targeted result in the small-scale temporal variability in shrimp catch observed by Catalan fishermen.

Enzymatic and morphometric analyses in mediterranean populations of the rose shrimp, Aristeus antennatus (Risso, 1816)

Eleven samples of rose shrimp (Aristeus antennatus) from different areas of the Mediterranean Sea and adjacent Atlantic waters were subjected to morphometric and electrophoretic analyses. The object was to characterize possible population differences that would account for previously reported differences in behavioural patterns observed in commercial fishing activity. Genetic analysis of 27 enzyme systems yielded only fifteen useful loci of which fibre had allele variants, but only two of them were polymorphic within 95%. Morphometric analysis of nine body and appendage measurements revealed significant differences between sampling sites in scaphocerite length, uropodal length, and the length of the articles on the third walking leg. The samples analysed genetically could not be differentiated, but morphological differences were compared between different hydrographic regions of the Mediterranean Basin.

Age and growth of Nephrops norvegicus in the Catalan Sea, using length-frequency analysis

Abstract Length-based methods were used to study age and growth of Nephrops norvegicus in the Catalan Sea. The width of the class interval was examined and 1 mm was found most appropriate for the carapace length-based analysis. Two direct methods, Bhattacharyas and Cassies, and one indirect, ELEFAN I, were used for age determination. Cassies method was found very subjective and inadequate, while Bhattacharyas and ELEFAN I more effective, easy to apply and more objective. The results of Bhattacharyas method showed the best agreement with those derived from captivity studies; seven age groups were well defined for males and four for females. Mature female age groups were difficult to detect by any method, indicating the effect of reproduction on female growth. Growth parameters of the Von Bertalanffy model and of the seasonally oscillating Von Bertalanffy formula, estimated by FISHPARM and ELEFAN I, were quite close to those derived from captivity studies. ELEFAN I seemed to produce the best results and the Von Bertalanffy model was not found to be superior to its seasonal counterpart, a fact that gives reason for futher studies. Paulys empirical formula for fish, used for the estimation of instantaneous natural mortality of this species gave reasonable values. The similarity between the results of the present work and those derived from captivity studies, gives support to the potential use of length-based analysis for the estimation of N. norvegicus biological parameters; however, many factors should be taken into account in order to achieve representative samples suitable for length-based analysis.

CIRCADIAN OXYGEN CONSUMPTION PATTERNS IN CONTINENTAL SLOPE NEPHROPS NORVEGICUS (DECAPODA: NEPHROPIDAE) IN THE WESTERN MEDITERRANEAN

Abstract The oxygen consumption of Nephrops norvegicus animals collected from the upper continental slope (400 m depth) in the northwestern Mediterranean was monitored under constant conditions of darkness and temperature. Two experiments were performed starting at the beginning of the expected day and at the beginning of the expected night phases, respectively. Mean oxygen consumption values recorded during the expected night were significantly higher than those recorded during the expected day. The slopes of the time series of oxygen consumption data of the two experiments were recalculated in consecutive 1-h intervals, being then averaged for corresponding 1-h time intervals. The plotting over a 24-h cycle of these mean hourly-values revealed a global nocturnal increase in the oxygen consumption in the laboratory. This result is discussed and compared with previously reported catch patterns accounting for emergence from burrows in the field, and locomotor and cardiac activity rhythms recorded in constant conditions in the laboratory in animals from the same depth.

Annual and diel light cycle as a predictive factor in deep-water fisheries for the prawn Aristeus antennatus Risso, 1816

Abstract Using daily catch data on the rose prawn (Aristeus antennatus) an attempt was made to construct a model relating catch per unit effort (CPUE) and a luminosity factor proportional to luminosity levels at the bottom on the prawn fishing grounds. A close relationship between this luminosity factor (defined in the text) and catchability was observed. Daily catch rates were highest during the 2 h immediately after sunrise, associated with a certain optimum light threshold. Within this pattern catch rates varied with longitude according to season and trawling depth. Based on these findings, novel alternatives for the future management of this resource are presented.

Relationship between size and depth in decapod crustacean populations on the deep slope in the Western Mediterranean

Abstract The size distribution of decapod crustaceans in relation to depth between 900 and 2200 m on the slope in the Catalan Sea (Western Mediterranean) was analysed in a series of four surveys carried out in 1988–1989. Regression analysis and multivariate cluster analysis were applied to data matrices relating size frequency to depth for each species. The results indicated a tendency for size to decrease significantly with depth in the most abundant species in the decapod communities studied ( Aristeus antennatus, Acanthephyra eximia, Pontophilus norvegicus and Polycheles typhlops ). Mean weight calculated for all the species combined also decreased significantly with depth. In addition, major changes in size frequency structure were observed at around 1400 and 2000 m for certain species, coinciding with the results for community structure in the same zone. Trophic aspects would appear to be an important cause of these phenomena for deep-water decapods in the Mediterranean.