Margarida Castro

Discards of the Algarve (southern Portugal) crustacean trawl fishery

The crustacean trawl fishery off the Algarve coast (southern Portugal) takes place on the lower continental shelf and upper continental slope at depths between 150 and 600 m. This is a multi-species fishery targeting the shrimps Parapenaeus longirostris and Aristeus antennatus and the Norway lobster Nephrops norvegicus, with the latter two species the most important in the landings. The fishery is characterised by significant by-catch and discarding of a large number of species. As part of a study on the fate of trawl fishery discards, this component of the study focused on the quantification of the by-catch and discards of crustacean trawlers. Sampling took place on board seven commercial trawlers from June 1998 to October 1999. Data was collected from 48 tows in 22 fishing trips. The observers collected all of the catch that was discarded by the crew during the sorting operation and samples were taken to the laboratory for identification, weighing and measuring. The quantities of target species were recorded along with the presence of retained by-catch. Commercially valuable species that were retained included Plesiopenaeus edwardsianus, Aristeomorpha foliacea, Plesionika sp., and the fishes Lophius piscatorius and Merluccius merluccius. However, most of the species had no or little commercial value and were almost always discarded to the sea (90%). A total of 91 species were identified, 47 vertebrates and 44 invertebrates corresponding to 65 families. The Teleostei (78% and 68%) were the dominant group, both in number and weight. The species Micromesistius poutassou (34%), Gadiculus argenteus (10%) and Hoplostethus mediterraneus (8%) were the most important in weight. Ten species represented more than 82% of all discards in weight. Gadiculus argenteus (29%), Hoplostethus mediterraneus (21%) and Nezumia sclerorhynchus (10%) accounted for 60% of all discards in numbers. Data on the landed species composition is also presented.

Spawning of Hexaplex (Trunculariopsis) trunculus (Gastropoda: Muricidae) in the laboratory: description of spawning behaviour, egg masses, embryonic development, hatchling and juvenile growth rates

Summary Some authors have studied and described different aspects of the reproductive cycle of Hexaplex (Trunculariopsis) trunculus, but most data are quite ancient and fragmented, lacking information in important respects on the reproductive cycle of this species. Based on several individual and collective spawns deposited in laboratory aquaria, this study provides additional and more detailed information on the spawning behaviour and egg-laying pattern, description of the general morphology and dimensions of the spawns, egg capsules, eggs, embryos and early post-metamorphic juveniles, as well as the first data available on the growth rate of T. trunculus hatchlings and juveniles (until 4 months old). Females deposited an average of 118 ± 89 tongue-shaped egg capsules per individual spawn, measuring on average 5.5 mm length x 4.7 mm width x 2.6 mm thickness. These egg capsules contained 723 ± 66 eggs with an average diameter of 240 ± 8 μm. T. trunculus is a direct developer species (metamorphosed hatchlings) with an incubation period of approximately 1 month. At hatching, individuals measured 1.64 ± 0.22 mm shell length and presented a growth rate of 2.5 mm/month at the end of 4 months. The breeding habits, embryonic development, hatchling and juvenile growth rates are discussed in terms of their implications for the management of the artisanal fishery for T. trunculus in the Ria Formosa lagoon and the assessment of the potential of this muricid species for molluscan aquaculture.

Comparison of indices for the assessment of reproductive activity in Hexaplex trunculus (Gastropoda: Muricidae)

Abstract The present study compares the ability of conventional condition indices (based on weight of the whole organism, weight of its flesh, and/or its shell weight) and visual quantitative indices (based on measures of the digestive gland, gonad, and capsule gland on digitized images of sections of these organs) for the assessment of reproductive activity in Hexaplex trunculus. To estimate conventional indices, a total of 120 standard-sized specimens (50 males and 70 females) in the 60–70 mm shell length interval were analysed. To estimate visual quantitative indices, a total of 903 specimens (501 males and 402 females) were analysed for the gonadosomatic index (GSI); females were also analysed for the capsule gland index (CGI). Compared to conventional indices, the visual quantitative indices (GSI and CGI) followed seasonal variations of the species reproductive cycle and identified broad changes in reproductive development (being highly accurate in detecting the main period of gonad maturation and spawning that occurred between May and June). Results indicate that both GSI and CGI constitute simple, practical and efficient indices for the routine assessment of reproductive activity in H. trunculus, providing a useful and reliable alternative to conventional condition indices and to histological analyses. Results of this study encourage the use of similar sampling procedures and analytical techniques, and analogous visual quantitative indices, to assess reproductive activity in other gastropod species.

Gametogenic cycle of Hexaplex (Trunculariopsis) trunculus (Gastropoda: Muricidae) in the Ria Formosa lagoon (Algarve coast, southern Portugal)

The gametogenic cycle of the banded murex, Hexaplex (Trunculariopsis) trunculus, from the Ria Formosa lagoon (Algarve coast, southern Portugal) was studied through macro- and microscopic analyses of the gonads during a i -year study period (March 2003 -February 2004). The overall samples presented a balanced sex ratio, with males dominating among smaller individuals and females predominating in larger size-classes. The gametogenic cycle of T. trunculus in the Ria Formosa lagoon comprised an extensive period of gonadal activity, with the simultaneous occurrence of distinct developmental stages of gametogenesis in both sexes almost year-round, and with males invariably presenting gonads in more developed stages of gametogenesis than females. Spawning occurred mainly from May to June 2003, apparently triggered by the rising seawater temperature during spring. Due to the extensive period of gonadal activity, T. trunculus exhibited a short resting phase that occurred simultaneously in both sexes between June and August 2003 and coincided with the period of warmest seawater temperatures. Considering these findings, a closed season in the fishing activity should be implemented during the main spawning period of T. trunculus (May and June), in order to protect the female broodstock and collective spawns.

Fate of discards from deep water crustacean trawl fishery off the south coast of Portugal

Abstract Trawling for crustaceans takes place on the south coast of Portugal at depths between 200 and 800 m. Large amounts of discards are released back to sea, reaching the bottom in the general area where trawling occurs. The objective of this work was to study the time taken for decomposition of the discards, to identify the most important scavenging species involved, and to evaluate the impact on the species targeted by the fishery. We conducted a series of 22 trials, using traps baited with samples of the discards. The time of immersion varied between 1 and 40 h. The amount of tissue removed from the discards was evaluated on a qualitative scale of 1–3, and quantitatively. The species caught in the traps were identified. Considerable consumption of the bait had occurred after 5 h of immersion. After 24 h of immersion only fish bones were left; past 40 h, consumption was complete. The conger eel (Conger conger) was the most common fish species present in the traps. Two species, the amphipod Scopelocheirus hopei and the isopod Natatolana (Cirolana) borealis, were identified as most important for the recycling of organic matter in the system. The stomach contents of a sample of species caught in trawls were analysed for the presence of small scavengers. Preliminary results show that S. hopei and N. (C.) borealis are part of the diet of some of the target species of this fishery, such as the Norway lobster, Nephrops norvegicus and the rose shrimp Parapenaeus longirostris.

Occurrence of Panulirus argus (Latreille, 1804) (Decapoda, Palinuridae) in the northwest islands of the Cape Verde Archipelago (Central-East Atlantic)

[Panulirus argus is herein reported from the Cape Verde Islands for the first time. In May 2002 and February 2005, local lobster fishermen captured two specimens at depths of 20-40 m. Other occurrences of this species during the last 15-20 years suggest that a permanent population of P. argus is established in the Cape Verde Archipelago. Two invasion theories (ship ballast mediation and dispersal during the larval phase) and two possible source populations (Brazil and the Caribbean) are proposed, and discussed in view of oceanic currents. A presenca de Panulirus argus nas ilhas de Cabo Verde e referida pela primeira vez. Em Maio de 2002 e Fevereiro de 2005, dois exemplares foram capturados por pescadores locais, a profundidades de 20-40 metros. A ocorrencia desta especie nos ultimos 15 a 20 anos sugere a existencia de uma populacao permanente de P. argus no Arquipelago de Cabo Verde. Sao propostas duas teorias para explicar a ocorrencia desta populacao (transporte de larvas na agua de lastro dos navios e por correntes oceânicas), e sugeridas duas possiveis populacoes de origem (Brasil e Caraibas)., Panulirus argus is herein reported from the Cape Verde Islands for the first time. In May 2002 and February 2005, local lobster fishermen captured two specimens at depths of 20-40 m. Other occurrences of this species during the last 15-20 years suggest that a permanent population of P. argus is established in the Cape Verde Archipelago. Two invasion theories (ship ballast mediation and dispersal during the larval phase) and two possible source populations (Brazil and the Caribbean) are proposed, and discussed in view of oceanic currents. A presenca de Panulirus argus nas ilhas de Cabo Verde e referida pela primeira vez. Em Maio de 2002 e Fevereiro de 2005, dois exemplares foram capturados por pescadores locais, a profundidades de 20-40 metros. A ocorrencia desta especie nos ultimos 15 a 20 anos sugere a existencia de uma populacao permanente de P. argus no Arquipelago de Cabo Verde. Sao propostas duas teorias para explicar a ocorrencia desta populacao (transporte de larvas na agua de lastro dos navios e por correntes oceânicas), e sugeridas duas possiveis populacoes de origem (Brasil e Caraibas).]

Comparing Trawl and Creel Fishing for Norway Lobster (Nephrops norvegicus): Biological and Economic Considerations

This study compares the fishing activity and landings of the trawl and creel fisheries for Norway lobster (Nephrops norvegicus (L.)) off the Portuguese coast, and evaluates the financial viability of two vessels typical of each fleet. Crustacean trawlers are part of an industrial fleet that, besides Nephrops, targets deep water shrimps. Creels are used by a multi-gear, multi-target artisanal fleet, fishing only in areas unavailable to trawlers and, when catching Nephrops, set specifically to target this species. Trawlers have in recent years contributed with 85% of the landings in weight, but only 74% in value (2005–2009 average). Despite smaller landings, the Nephrops creel fishery provides individuals of larger size and in better condition, thereby obtaining higher unit prices. Economic viability was also higher for the creel vessel, with trawling being only viable if major costs (such as labor and fuel) are covered by the revenue from other target species (e.g., the rose shrimp). At present, Nephrops populations on the South and SW coast are subject to intense fishing and to a recovery plan. The possibility of reallocation of some of the fishing effort directed at Nephrops from trawlers to creels is discussed in terms of the conservation of the resource and economic return.

The effect of dietary antioxidants on lipofuscin accumulation in the crustacean brain

Abstract Lipofuscin accumulation is associated with ageing at the subcellular level. A strong correlation between lipofuscin and age has been found in crustaceans using histological techniques. This association has been proposed as the basis for a methodology to age crustaceans and in some cases lipofuscin levels were found to be better correlated with age than size. The experiment presented here was designed to test the potential effect of diet, in particular dietary antioxidants, on lipofuscin accumulation and age estimation. The shrimp, Penaeus japonicus , was reared in an aquaculture facility and fed commercial pellets with modified vitamins C and E contents. One group was fed with levels of vitamins C and E of 1000 and 150 mg/kg, respectively, and another group with 2500 and 5000 mg/kg, respectively. The experiment started when the shrimp were 19 weeks old. Samples were obtained at this point and at ages 33 and 43 weeks. Lipofuscin was measured in the nerve cords (antennal neuropils and oesophageal connectives) in an area adjacent to the brain. Dietary antioxidants significantly affected lipofuscin levels. High vitamin content in the diet resulted in lower percentage of the observed area covered with lipofuscin, lower lipofuscin granule density and lower average granule size. Gender had no effect on any of these variables and granule size did not significantly change within each treatment. Lipofuscin area and granule density increased with age in both vitamin treatments. These results suggest that age estimation using lipofuscin indices may be biased when: (1) wild populations are dispersed over diverse environments; (2) the age estimation of wild individuals is based on the results obtained using laboratory-reared individuals.

Field estimation of daily ration of Norway lobster (Nephrops norvegicus) in the south of Portugal

Abstract Daily ration estimates of Norway lobster (Nephrops norvegicus) from field samplings over a 24‐h cycle were obtained. Four tows were conducted in the middle continental slope, off the south coast of Portugal. The results from Eggers (1977, 1979) and Elliot & Persson (1978) daily ration models were compared, by the Worobec 8‐method (1984), showing no significant differences among them. The estimates of food consumption obtained varied from 1.098 to 1.170 g dry food per 100 g body wet weight in males and 1.642 to 1.755 g dry food per 100 g body wet weight in females. Our results were compared with daily rations reported for other crustaceans. Daily ration values were compared and tested by a two‐way ANOVA, with interaction, showing significant differences between sexes. This has been registered for other decapods and may be explained by a period of active growth in females, on the onset of vitellogenesis, increasing their nutritional/ feeding needs.

Influence of growth and reproductive cycle on the meat yield and proximate composition of Hexaplex trunculus (Gastropoda: Muricidae)

This study aimed to assess the influence of growth and reproductive cycle on the meat yield and proximate composition of the banded murex (Hexaplex trunculus) from the Ria Formosa lagoon (Algarve coast, southern Portugal). Samples of the edible portion (all soft-body tissues) were analysed monthly during one year. The average meat yield was 37 . 9 ± 4 .6%, with females containing more edible content (39.1 + 4.7%) than males (36.8 ± 4.2%). The proximate composition comprised 70.7 ± 1.4% moisture, 20.1 ± 1.2% protein, 1.6 ± 0.3% fat, 3.0 ± 0.3% ash, and 4.6 :t 1.2% carbohydrate, corresponding to an energetic value of 119.2 ± 7.5 kcal/100 g wet weight. The meat yield was influenced by specimen size, increasing significantly during growth. Both meat yield and proximate composition presented seasonal fluctuations related to the reproductive cycle, which coincided mainly with the periods of maturation and spawning of this species in the Ria Formosa. Finally, H. trunculus meat yield and proximate composition were compared with similar information available for other marine gastropods.