Argentine Hake Merluccius Hubbsi Research Articles

Prey contribution to the diet of pink cusk-eel Genypterus blacodes (Forster, 1801) revealed by stomach content and stable isotopic analyses in the southwestern Atlantic

This paper studied the diet of the pink cusk-eel Genypterus blacodes, using a combination of stable isotope (δ13C and δ15N) and stomach content analyses, from specimens captured during eight scientific trawl surveys carried out from 37°S to 53.3°S, and from 65 to 390 m depth. A total of 1615 specimens were analyzed, from which 795 (49.22 %) that ranged from 15 to 114 cm in total length (TL), contained prey. The pink cusk-eel fed mainly on fish and crustaceans. Among fishes, the most important were the notothenioid Patagonotothen ramsayi and the Argentine hake Merluccius hubbsi. The most important crustaceans consumed were the lobster krill Munida gregaria, isopods (Cirolana spp., Serolidae), stomatopods (Pterygosquilla armata) and gammarid amphipods. Ontogenetic diet shifts were detected with the TL, with an increase consumption of fish and a decrease consumption of crustaceans. Moreover, there were changes in the diet associated with depth and region. The isotopic structure of the food chain showed the classic enrichment with trophic level increase. While the stomach contents analysis in a subregion indicated that crustaceans were the predominant prey, followed by cephalopods and fish, Bayesian mixing models showed differential assimilation to pink cusk-eel muscle, with fish as the main assimilated prey and a relatively minimal inputs of crustaceans and cephalopods. Clear distinctions between the pelagic and benthic baselines were detected, with pink cusk-eel participating in both benthic and pelagic pathways. The pink cusk-eel occupied the role of top predator in the Southwestern Atlantic ecosystem (trophic level ∼4) and the δ15N did not exhibit changes with respect to an analyzed specimen of the year 1962.

Contrasting distributional patterns of two co-occurring ctenophores in relation to ichthyoplankton and environmental features in the Southwestern Atlantic Ocean

Assessing the ecological role of ctenophores is crucial to understanding ecosystem functioning, including the recruitment of fish stocks. During austral summer in the North Patagonia Ecosystem (NPE) (41-48°S), the ctenophores Mnemiopsis leidyi and Pleurobrachia pileus co-occur with the peak of ichthyoplankton abundance of 2 important fishing resources: the Argentine anchovy Engraulis anchoita and the Argentine hake Merluccius hubbsi, in association with a highly productive tidal front system. We analyzed 367 plankton samples collected in the NPE over 13 yr (2005-2018) to determine the abundance and spatial distribution of M. leidyi and P. pileus, their spatial overlap with ichthyoplankton (eggs and larvae of hake and anchovy), and their relationship with environmental features. Both ctenophore species displayed contrasting distributional patterns, associated with different physical environments, particularly temperature. M. leidyi showed a higher spatial overlap with ichthyoplankton compared to P. pileus. In addition, we found a significant negative correlation between the biomass of M. leidyi and the abundance of both fish larvae, suggesting a potential negative impact (via predation and competition) on the survival and recruitment of these 2 fisheries resources.

The effect of physical and biological variables upon condition of Merluccius hubbsi (age-0+) of the northern stock (argentine shelf, SW Atlantic Ocean)

Argentine hake Merluccius hubbsi is one of the most important fishery resources in the Argentinean Continental Shelf (ACS; SW Atlantic Ocean). In the last decades, the Northern stock (34°30′-41°S) has supported a drastic biomass decreasing due to overexploitation. Since the strength of a year class is highly influenced by the survival of age-0+ individuals, studies on their nutritional condition are essential. Age-0+ northern hake nurse in a highly complex oceanographic and ecological system, where environmentally-driven changes upon their physiological status are expected. Hence, several condition (relative condition factor, hepatosomatic index, liver lipid content) and feeding (prey intake) indices were combined with physical (temperature, salinity) and biological (chlorophyll- a concentration, prey abundance) variables to determine spatial variations in age-0+ hake nutritional status. Better conditioned individuals inhabited areas of the study region where chlorophyll- a concentration and zooplanktonic prey abundance exhibited their maximum. A bottom-up control of age-0+ hake physiological status is suggested, mediated by the consumption of the herbivorous euphausiid Euphausia lucens , which was the preferred prey. These lipid-rich prey would be beneficial with respect to other available options in the environment, such as hyperid amphipods. Results complement previous observations upon individuals of the Patagonian stock, and provide a thorough insight into age-0+ Northern hake nutritional status, significantly contributing to M. hubbsi recruitment studies and management in the ACS. • Nutritional condition of age-0+ Merluccius hubbsi was studied between 34°-41°S. • Morphometric and liver-based indices were determined. • Spatial differences in condition were related to physical and biological variables. • Condition was bottom-up mediated by the consumption of herbivorous prey. • Data are relevant in the context of hake recruitment studies.

Digestive proteinases from the marine fish processing wastes of the South-West Atlantic Ocean: Their partial characterization and comparison.

Fish processing generates plenty of waste that is directly discarded in open-air dumps and water sources, or treated in the same way as urban solid waste, causing serious pollution problems. The waste represents a significant source of high-value bioproducts with potential applications in different industrial processes such as the production of feed, fertilizers, biodiesel and biogas, detergent additives and cosmetics. The objective of this study was to characterize and compare specific activities under different pH values and temperature conditions of acid and alkaline proteinases and viscera yield from the following fish species: Argentine hake Merluccius hubbsi, Brazilian flathead Percophis brasiliensis, Brazilian codling Urophycis brasiliensis and Stripped weakfish Cynoscion guatucupa. Individuals were fished off the coast of Mar del Plata (Argentina) by a commercial fleet and the viscera were immediately extracted and kept on ice until use. Stomach proteinases from four species had the highest activity at pH2, with stability in the range of pH 2-4. The optimum pH was 11.5 from intestinal enzymes of C. guatucupa, M. hubbsi and P. brasiliensis and 9.5 from intestinal enzymes of U. brasiliensis. Alkaline proteinases from all species were highly stable in the range of 7-11.5. The optimum temperature of stomach proteinases from the four species studied were 30 and 50°C, with stability at 10 and 30°C during 150 min. The optimum temperature of intestinal enzymes from the tested species were 50°C with high stability at 10 and 30°C during 150 min. Alkaline proteinase from all species and acid proteinases from C. guatucupa were inactive at 70°C after 150 min, while there was a residual activity lower than 5% at 80°C on pre-incubated stomach enzymes of M.hubbsi, P. brasiliensis and U. brasiliensis after 5, 10 and 20 min, respectively. Digestive proteinases recovered in this study could be appropriate for technological usage, reducing manufacturing costs, obtaining revenue from fishery wastes, and contributing to the reduction of environmental pollution.

Marine fish imported from Argentina as source of human diphyllobothriosis in Europe? Ecological evidence from dolphins.

Diphyllobothriosis caused by the Pacific broad tapeworm Adenocephalus pacificus (syn. Diphyllobothrium pacificum) is an emerging parasitic disease reported also from non-endemic areas, including Europe (Spain). The origin of these human cases is unknown but should be related to fresh marine fish imported from endemic areas. In this study, we molecularly confirmed common dolphins Delphinus delphis off Argentina as euparatenic transit hosts of A. pacificus. Preliminary analysis of their stomach content, together with data from previous studies from the Southwest Atlantic, showed that common dolphins feed almost exclusively on schooling Argentine hake Merluccius hubbsi and Argentine anchovy Engraulis anchoita. Therefore, we suggest that Argentine hake and Argentine anchovy may represent the intermediate hosts of A. pacificus in the Southwest Atlantic, but also in Europe to where M. hubbsi is imported on ice (unfrozen).

First data on the age and growth of Brazilian flathead Percophis brasiliensis (Pisces: Perciformes) in San Matías Gulf, northern Patagonia (Argentina)

Brazilian flathead Percophis brasiliensis is a commercially important perciform fish caught as bycatch by trawlers throughout its latitudinal distribution range (from 23° S in Brazil to 47° S in Argentina). It is associated with the catches of Argentine hake Merluccius hubbsi and Patagonian red shrimp Pleocticus muelleri in San Matías Gulf (SMG). The main objective of this study was to describe the first data on the growth of this species in SMG and to compare the results with available information for other areas of the Argentine Continental Shelf (ACS). The study was carried out using 294 specimens (196 females, 97 males and one of indeterminate sex) collected over four non-consecutive years from commercial/recreational fishing and during research cruises. The age of individuals was determined by reading and counting opaque-hyaline rings on the sagittae otoliths. The maximum ages observed were 14 years for females and 12 years for males. Growth parameters were estimated using the von Bertalanffy mode. Significant differences in L∞ parameter between sexes were found (L∞ males = 54.58 cm; L∞ females = 78.31 cm, p < 0.05). Growth parameters were different from those determined in previous studies for the ACS.

Morphological and biochemical approaches to assess the nutritional condition of the Argentine hake Merluccius hubbsi larvae from two different nursery areas.

The Argentine hake, Merluccius hubbsi, is one of the most important fishing species in the Argentine Sea due to its great abundance and high-quality meat. The study of the nutritional condition is widely used to determine the physiological state of the fish larvae and to estimate their survival possibilities. The larval nutritional condition reflects the environmental conditions to which they have been exposed and represents a useful instrument to determine favourable nursery areas. It also provides tools for the comprehensive management of a population subjected to fishing exploitation. This study aimed to determine potential differences in the nutritional condition of M. hubbsi larvae from the two fishing stocks (Northern and Southern) of the species. The authors assessed the nutritional condition of larvae captured during the 2012 main reproductive peak in the nursery areas of each population. Two different methodologies were applied: a morphometrical approach, by recording five morphometric variables, and a biochemical technique, employing the RNA/DNA index (RDs ) and its derived index of growth performance. The morphometrical indexes did not show differences in the larval condition between both stocks. Nonetheless, the RDs index did detect differences in the nutritional condition of larvae from different stocks. The RDs index of larvae in pre-flexion and flexion stages showed significant differences between stocks, indicating that these stages are more susceptible to starvation. The results suggest that the biochemical indexes prove to be more sensitive than the morphometric indexes to detect slight differences in hake larvae nutritional condition. The scope and limitations of these techniques for the analysis of the nutritional condition of larvae are discussed.

Seasonal and spatial variability in condition of age‐0+ Argentine hake Merluccius hubbsi Marini, 1933, in the San Jorge Gulf (Argentina): A bottom‐up perspective

AbstractIn the north Patagonian region of the Argentinean Continental Shelf, the San Jorge Gulf (SJG; 45°‐47°S, 65°30ʹ‐67°30ʹW) is the main nursery ground of age‐0+ Argentine hake Merluccius hubbsi Marini, 1933, one of the most important fishery resources in Argentina. The gulf exhibits strong seasonal and spatial fluctuations in environmental features, which might affect survival of age‐0+ individuals and recruitment to the adult population. Our main goal was to evaluate the seasonal and spatial dynamics of their nutritional status within the SJG in winter 2016, spring 2016 and summer 2017. Condition indices (relative condition factor Kn, hepatosomatic index HSI and liver lipid content %L) and diet information (feeding incidence and relative importance of prey) were combined with physical (temperature and salinity) and biological (satellite chlorophyll‐a concentration; chl‐a) data. Age‐0+ condition indices and prey intake showed significant seasonal variations, with minimum values in winter, intermediate in summer and maximum in spring, strongly coupled to the mean chl‐a concentration in each season. Herbivorous euphausiids Euphausia spp. were the preferred prey along the study period. A bottom‐up effect on condition of age‐0+ hake is suggested, manifested as lower condition values in winter, the less productive season. Spatially, better conditioned individuals matched sectors of the gulf where chl‐a concentrations were higher, coupled to the presence of frontal systems. Monitoring age‐0+ hake nutritional status is relevant in the current global change scenario, which might modify phytoplankton biomass and composition and, consequently, the herbivorous zooplankton abundances.

Predicting habitat use by the Argentine hake Merluccius hubbsi in a warmer world: inferences from the Middle Holocene.

Fish skeletal remains recovered from two archaeological sites dated in the Middle Holocene of Tierra del Fuego (Argentina) were analysed to describe habitat use patterns by hake in the past and predict changes in a warmer world. Mitochondrial DNA was successfully extracted and amplified from 42 out of 45 first vertebra from ancient hake and phylogenetic analysis assigned all haplotypes to Argentine hake (Merluccius hubbsi). According to osteometry, the Argentine hake recovered from the archaeological site were likely adults ranging 37.2-58.1cm in standard length. C and N stable isotope analysis showed that currently Argentine hake use foraging grounds deeper than those of Patagonian blenny and pink cusk-eel. Argentine hake, however, had a much broader isotopic niche during the Middle Holocene, when a large part of the population foraged much shallower than contemporary pink cusk-eel. The overall evidence suggests the presence of large numbers of Argentine hake onshore Tierra del Fuego during the Middle Holocene, which allowed exploitation by hunter-gatherer-fisher groups devoid of fishing technology. Interestingly, average SST off Tierra del Fuego during the Middle Holocene was higher than currently (11°C vs 7°C) and matched SST in the current southernmost onshore spawning aggregations, at latitude 47°S. This indicates that increasing SST resulting from global warming will likely result into an increased abundance of adult Argentine hake onshore Tierra del Fuego, as during the Middle Holocene. Furthermore, stable isotope ratios from mollusc shells confirmed a much higher marine primary productivity during the Middle Holocene off Tierra del Fuego.

Development of the digestive system of Argentine hake, Merluccius hubbsi, larvae.

The Argentine hake Merluccius hubbsi is an important fishery resource of the Southwestern Atlantic Ocean and it is also a potential species for cultivation. In this work, the digestive system development in field-caught hake larvae was studied using histological and histochemical approaches. The digestive tract of larvae was divided into: oropharyngeal cavity (OPC), esophagus, stomach (that develops in the preflexion stage), and intestine. The annexed digestive glands consisted of the liver and the exocrine pancreas. At the beginning of the preflexion stage, teeth were developed in the OPC. There were mucous cells in the esophagus secreting different glycoconjugates from hatching. The enterocytes in the posterior intestine exhibited supranuclear vesicles associated with protein absorption. Mucous cells were observed in the posterior intestine in the preflexion stage and, in the anterior region, ending the flexion stage. Each type of glycoconjugates has a specific role. Acidic mucins lubricate and protect from mechanical damage, sialomucines protect from bacterial infections and neutral mucins regulate the acidity of mucus secretion, protect against abrasion and participate in the formation of the chyme, indicating a pregastric digestion. The liver was present since hatching with pancreatic tissue inside and increased in size acquiring the typical structure with hepatocyte cords, sinusoids, vacuoles, and hepatic duct. The hepatocytes vacuolization increased with larval development. The pancreas became extra-hepatic, with basophilic acinar cells and acidophilic zymogen granules. Throughout the ontogeny, the increased structural and functional complexity of the digestive system reflected the transition to exogenous feeding and nutritional increasing needs.

Trophic niche changes during settlement in the Argentine hake Merluccius hubbsi reveal the importance of pelagic food post metamorphosis

Trophic niche changes during settlement in the Argentine hake Merluccius hubbsi reveal the importance of pelagic food post metamorphosis

Are hakes truly opportunistic feeders? A case of prey selection by the Argentine hake Merluccius hubbsi off southwestern Atlantic

Prey selection and feeding strategy of the Argentine hake Merluccius hubbsi were investigated by analyzing the diet and prey availability in the main nursery area of the Patagonian stock (42.4°–46.4 °S, 70–102 m depth). Stomach contents from fish captured using a bottom trawl net, and zooplankton samples collected with a Bongo net, were analyzed. Acoustic data were examined to identify pelagic aggregations and quantify relative prey abundance. The Argentine hake M. hubbsi fed mainly on crustaceans (92.7%IRI), followed by fish (7.1%IRI) and cephalopods (0.2%IRI). Among crustaceans, the diet was dominated by euphausiids (Euphausia spp.), the lobster krill Munida gregaria, and the hyperiid amphipod Themisto gaudichaudii. The most consumed fish was other hake by cannibalism. Prey availability was also numerically dominated by the euphausiids (Euphausia spp.), followed by the hyperiid amphipod T. gaudichaudii and the lobster krill M. gregaria. Ontogenetic dietary changes were detected: consumption of euphausiids and amphipods decreased with predator´s total length, and the consumption of the lobster krill M. gregaria was higher in adult specimens. The Argentine hake M. hubbsi showed positive prey selection for lobster krill M. gregaria. The consumption of Euphausiids decreased with the increasing acoustic abundance of the lobster krill M. gregaria. The cannibalism was denso-independent. The Argentine hake appeared to be opportunistic when the proportion of prey eaten to the proportion present in the environment was compared, but deeper analyses confirmed that zooplankter with increased abundances and higher energy density was the preferred prey.

The opportunistic sense: The diet of Argentine hake Merluccius hubbsi reflects changes in prey availability

Changes in the abundance of some species in the San Matías Gulf (north Patagonia, Argentina) have been observed in recent years; in particular increases in crustaceans populations that could be influencing the trophic relationships and food web structure. The Argentine hake Merluccius hubbsi has been the main demersal resource that supports a fishery since 1971. Given that M. hubbsi is a generalist and opportunistic predator, its diet from the perspective of specific composition and feeding strategy was evaluated. Fourteen species were identified belonging to four zoological groups (3 fishes, 4 molluscs, 6 crustaceans and 1 bryozoan). The most commonly consumed prey was the lobster krill Munida gregaria (index of relative importance -%IRI- 72.19%) followed by the white shrimp Peisos petrunkevitchi (%IRI 19.04%) and M. hubbsi (%IRI 7.95%). Most prey were infrequently consumed and at low abundances, which it is common for a generalist-opportunistic predator. Substantial changes in the diet composition were detected when compared to a previous study, showing a large increase in crustacean occurrence in concordance with the abundance changes observed in the environment. The results from this study highlighted the importance to consider information about population trends and trophic relationships to better understand the dynamics of marine communities under exploitation.

Effect of nursery ground variability on condition of age 0+ year Merluccius hubbsi

This study examined the southern or Patagonian (41°-55° S) stock of Argentine hake Merluccius hubbsi, the more abundant of the two stocks on the Argentinean continental shelf. Pre-recruits (age 0+ year individuals) of this stock settle and grow in the San Jorge Gulf (45°-47° S, 65° 30' W), a complex habitat with large spatial variability in environmental features. Relative condition factor, hepatosomatic index, lipid content and fatty-acid composition of muscle and liver, and diet information were combined with physical and biological data to evaluate: how nutritional status of age 0+ year hake varies spatially within the nursery ground; whether changes in condition are related to environmental factors and feeding; whether the indices are interchangeable metrics of condition. Both morphometric and biochemical indices showed dissimilar spatial trends; enhanced liver-based condition coincided with low salinity nutrient rich waters, higher chlorophyll-a values and abundances of Euphausia spp., the preferred prey at most stations, suggesting a bottom-up effect on age 0+ year hake condition. Diminished condition at stations where Thermisto gaudichaudii was the main prey could derive from lower prey quality in terms of energy density and essential fatty acids content. Coastal waters of the gulf would be essential habitats for M. hubbsi pre-recruits. Future monitoring of condition with liver-based indices is encouraged in the gulf, where interannual increasing trends of satellite-derived chlorophyll-a values have been observed, which could have implications for recruitment of the species.

Influence of environmental conditions on the reproductive success and recruitment of the Argentine hake Merluccius hubbsi (southwestern Atlantic Ocean)

AbstractThe Argentine hake Merluccius hubbsi represents the dominant demersal fish and one of the main fisheries in the Argentine Sea. We analyzed over 17 years (September 1997–February 2015) of satellite surface chlorophyll concentration (CHL) and sea surface temperature anomaly (SSTA) data in the main spawning (SUB) and nursery (SJG) areas of the Patagonian stock of M. hubbsi. The variability observed in these environmental conditions was related to interannual differences in the reproductive success of hake. CHL values were maximum during austral spring (October–November) and minimum during winter (June–August). Blooms started in late September and lasted on average 128 and 110 days at SUB and SJG, respectively. At SUB, average CHL at the time of reproduction, the day of occurrence of the maximum chlorophyll concentration, and fall SST anomalies were significantly related to recruitment (RVPA) a year later and to two Larval Survival Indices (LSISSB and LSITEP) considered. At SJG, RVPA, LSISSB, and LSITEP showed negative correlations with fall (March–May) SSTA. Total egg production was not related to fall SSTA or spring phytoplankton dynamics at SUB or SJG. Significant positive trends were observed in the time series of CHL and SSTA in the study area. The trends observed in CHL represent average increases of 40.7% and 35.7% since 1997 at SUB and SJG, respectively. The potential implications of long‐term changes in environmental conditions for hake reproductive success are discussed.

Age estimation, growth and maturity of the Argentine hake (Merluccius hubbsi Marini, 1933) along the northernmost limit of its distribution in the south-western Atlantic

ABSTRACTAge, growth and length-at-maturity of the Argentine hake (Merluccius hubbsi) were studied in the northernmost limit of the species distribution in the south-western Atlantic. A total of 351 otoliths and information from 1610 specimens sampled from the industrial double-rig trawl landings between May 2013 and April 2014 were used. Age and growth were estimated by counting and measuring increments in sectioned sagittae otoliths, and length at maturity was estimated based on macroscopic gonadal analysis. For both sexes, hepatosomatic index and condition index increased mainly during spring, reaching a maximum at the end of summer before the subsequent spawning season began. Gonadosomatic index was highest in April, believed to correspond with peak spawning. The annual periodicity of alternate opaque and translucent zones was validated by marginal increment analysis. Growth curves were fitted to back-calculated size at age by fitting the three-parameters von Bertalanffy growth function. The maximum age was 5 years in fish of either sex. Females attained larger sizes than males. The parameters of the von Bertalanffy growth equations were: L∞ = 533 mm, k = 0.231 year−1 and t0 = −0.935 year for females; L∞ = 394 mm, k = 0.405 year−1 and t0 = −0.463 year for males. The mean length and age at first maturity was 273 mm at 1.9 years for males and 274 mm at 2.0 years for females.

Morphological and molecular characterisation of Aporocotyle margolisi Smith, 1967 (Digenea: Aporocotylidae) from the North Pacific hake Merluccius productus (Ayres) (Gadiformes: Merlucciidae) off Oregon, USA.

Aporocotylid blood flukes conspecific with Aporocotyle margolisi Smith, 1967 were collected from the bulbus arteriosus of the North Pacific hake Merluccius productus (Ayres). This study revisits the morphology of A. margolisi, including drawings, measurements and scanning electron microscopy images, and provides for the first time molecular data for the large subunit of the ribosomal RNA (28S rDNA) and the mitochondrial cytochrome c oxidase subunit 1 (cox1) genes for this species. A 28S rDNA phylogenetic study of A. margolisi, and all available Aporocotyle spp., was also performed. The distribution range of A. margolisi is extended to the Pacific coast of the USA. We provide a morphological comparison of Aporocotyle spp. from the Pacific coast in North America as well as other Aporocotyle spp. infecting hake. Comparisons with the original description revealed that the new specimens of A. margolisi were considerably larger with respect to all morphological features, except for shorter spines. Molecular results showed a close relationship between A. margolisi and A. argentinensis Smith, 1969 from the Argentine hake Merluccius hubbsi Marini. The phylogenetic relationships of Aporocotyle spp. point to a possible co-speciation of hakes species and these blood fluke parasites.

Trends and variability in extended ocean color time series in the main reproductive area of the Argentine hake, Merluccius hubbsi (Southwestern Atlantic Ocean)

Fil: Marrari, Marina. Consejo Nacional de Investigaciones Cientificas y Tecnicas; Argentina. Universidad de Buenos Aires; Argentina. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografia Naval; Argentina

Trophic ecology of yellownose skate Zearaja chilensis, a top predator in the south-western Atlantic Ocean.

The diet and trophic level (TL ) of the yellownose skate Zearaja chilensis in the south-western Atlantic Ocean (35°-54° S), and how these varied in relation to body size, sex, maturity stage, depth and region were determined by analysis of stomach contents. From 776 specimens analysed, 671 (86·5%) ranging from 180 to 1190 mm total length (LT ) had prey in their stomachs. The diet was dominated by fishes, mainly the notothenioid Patagonotothen ramsayi and the Argentine hake Merluccius hubbsi. The consumption of fishes and crabs increased with increasing predator size, and these preys were more important in the north than in the south. Isopods and other crustaceans were consumed more in the south and their consumption decreased as the size of Z. chilensis increased. The TL of Z. chilensis increased with LT from 4·29 to 4·59 (mean 4·53), confirming their ecological role as a top predator. The small and large size classes exhibited a low diet overlap and the highest spatial segregation, whereas medium and large specimens had higher co-occurrence and dietary overlap indices. A clear distinction in tooth shape was noted between sexes in adult specimens, with males having longer cusps. This sexual heterodonty may be related to reproductive behaviour, increasing the grasping ability of males during courtship, because there were no differences in diet between the sexes.

Assessing the effects of demersal fishing and conservation strategies of marine mammals over a Patagonian food web

The San Matías Gulf (SMG) is a semi-enclosed ecosystem where the Argentine hake Merluccius hubbsi (AH) has been the main fishery resource since 1971. During the 20th century the South American sea lion Otaria flavescens (SASL) population was severely reduced in this ecosystem due an intense hunting, but in the 1970's conservation was promoted and hunting was banned. As a consequence SASL have been slowly recovering, until the 1990's when rapidly rebuilt their populations. Recent studies indicate that they feed mostly over commercially profitable medium-sized AH. Also, medium-sized and large hake are well-known cannibals that feed heavily over smaller AH. Fishing trawlers affect juvenile and medium-sized AH and artisanal long-liners capture exclusively large AH. The objective of this study was to evaluate the effect of a growing SASL population over the AH in the SMG, considering the changes in the fishing activity as well as the size-structured cannibalism within the AH population. The evaluations were based on time series of hake and SASL biomass using the “Ecopath with Ecosim” dynamic modelling approach. The analyses show that over 4 decades the increase in Sea Lions biomass has not generated a significant increase in the predation mortality over AH. On the other hand, an increase and subsequent variations in the fishing mortality seems to be related with long-term variations in large AH abundance, and a decrease in medium-sized AH abundance, constraining the cannibalism mortality. This led to a positive effect over juvenile AH abundance due to a released cannibalism pressure, even considering that the less abundant larger AH are also the main spawners of the population. In this scenario, where it seems that trawlers and long-liners have replaced several predators over the SMG food web, SLAS population is still growing but they may not reach the pristine abundance levels of the time before hunting.