Pablo Arechavala-Lopez

Coastal fish farms are settlement sites for juvenile fish.

Two south-west Mediterranean fish farms were monitored over a period of 22 months to test if sea-cage fish farms act as settlement habitats for juvenile fish. Twenty juvenile fish species were found to settle at farms throughout the year. Fish assemblage composition varied markedly over time and was dependent on the spawning period for each species. The most abundant species were Obladamelanura, Atherina sp., Diplodussargus, Boopsboops and Lizaaurata. Up to 3783+/-1730 individuals/cage were found closely associated with the cages. Highest densities were observed during the warmer summer and autumn months. Zooplankton sampling and stomach content analyses of the most abundant species were done to assess prey availability, selectivity and diet overlap among species. Copepods were the main prey item for all juvenile fish species, irrespective of fish size. Ivlevs Index indicated that food was not a limiting factor for juvenile fish at farms. Furthermore, food pellets from the farm affected the food chain by modifying the fatty acid profiles of farm-associated zooplankton and juveniles of L. aurata and O. melanura. These results show that aquaculture can directly influence the body composition of juvenile fish that recruit to sea-cage fish farms.

Morphological differences between wild and farmed Mediterranean fish

Gilthead seabream (Sparus aurata L.) and European seabass (Dicentrarchus labrax L.) are important commercial marine fish species both for aquaculture and fisheries in the Mediterranean. It is known that farmed individuals escape from farm facilities, but the extent of escape events is not easy to report and estimate because of the difficulty to distinguish between wild and farmed individuals. In this study, significant differences provided through morphometry evidence that the cranial and body regions of seabream and seabass are different regarding their farm or wild origin at different scales. Morphological variations have been shown to be a valuable tool for describing changes in shape features. Therefore, the biomass contribution of escapees to local habitats could be determined by identifying escaped individuals from fisheries landings as a first step to assess the potential negative effects of fish farm escapees on the environment, and their influence on wild stocks and local fisheries.

Discriminating farmed gilthead sea bream Sparus aurata and European sea bass Dicentrarchus labrax from wild stocks through scales and otoliths.

The study of mass and standard length (L(S) ) relationships showed that farmed individuals had higher values than wild fishes for both gilthead sea bream Sparus aurata and European sea bass Dicentrarchus labrax. Such differences were more pronounced in larger individuals than smaller ones and were more noticeable in S. aurata than in D. labrax. Additionally, differences in external characteristics of scales were detected between origins. A high proportion of farmed S. aurata had a regenerated nucleus (98%) and scale malformations (73%), and there were no annual rings in the farmed D. labrax (100%). Variation in otolith morphology was examined through shape descriptors such as area, perimeter, circularity, roundness, mass, height and length relationship and elliptic Fourier descriptors (EFDs). Important differences were found within geographical origins according to each shape descriptor separately, but no clear patterns distinguished wild and farmed fish. Discriminant analysis with either all shape descriptors together or EFDs was able to classify with high accuracy both S. aurata (89·5-95·7%) and D. labrax (93·2-95·2%) according to their origin. Hence, this study suggests the use of scale characteristics as the easiest and quickest way to distinguish farmed or escaped fishes, and secondly, the usefulness of EFDs or shape descriptors to improve such separation.

Aggregations of bluefish Pomatomus saltatrix (L.) at Mediterranean coastal fish farms: seasonal presence, daily patterns and influence of farming activity

Bluefish, Pomatomus saltatrix (Linnaeus, 1766), is commonly observed close to Mediterranean open-sea fish farms. It usually preys on wild fish that are attracted to farms, but also on farmed fish by biting holes in sea cages net walls. In the current telemetry study, we found that the tagged bluefish stayed close to fish farms during spring and early summer. However, most of the tagged fish disappeared from the farms during autumn, when the sea water temperature dropped. When aggregating at farms, bluefish were present at deeper waters during day time, but moved closer to the surface during night time. In addition, periods when there was operational activity at the farms might influence on daily swimming depth of bluefish. Therefore, bluefish individuals seem to find an optimal foraging habitat around Mediterranean fish farms.

Assessing the Influence of Salmon Farming through Total Lipids, Fatty Acids, and Trace Elements in the Liver and Muscle of Wild Saithe Pollachius virens

Abstract Saithe Pollachius virens are attracted to uneaten salmon feed underneath cages at open-cage salmon farms in Norway. The aggregated Saithe have modified their feeding habits as they have switched from wild prey to uneaten food pellets, which could lead to physiological and biochemical changes in the Saithe. Variations in profiles of total lipids, fatty acids, and trace elements in Saithe liver and muscle were measured to evaluate the influence of fish feed from salmon farms on wild Saithe populations. Farm-aggregated Saithe had higher fat content in liver tissues than did individuals captured more than 25 km away from farms, but no clear differences were found in muscle tissues. High proportions of fatty acids of terrestrial origin, such as oleic, linoleic, and linolenic acids, in liver and muscle tissues of farm-aggregated Saithe reflected the presence of wild Saithe at farms. Accordingly, low proportions of arachidonic, eicosapentaenoic, and docosahexaenoic acids in Saithe tissues mirrored the feeding activity at farms. Variations in specific trace element signatures among fish groups also revealed the farming influence on wild Saithe. High levels of Fe, As, Se, Zn, and B in liver, but also As, B, Li, Hg, and Sr in muscle of Saithe captured away from farms indicated the absence of feeding at farms.

Large-scale use of fish traps for monitoring sea trout (Salmo trutta) smolts and sea lice (Lepeophtheirus salmonis) infestations: efficiency and reliability

ABSTRACT Lice-infected sea trout populations were monitored using fish traps in the Romsdalsfjord (Norway). The reliability and efficiency of this capture technique, which allows estimation of lice infestation rates without killing the fish, was evaluated through a mark–recapture study. A total of 2447 sea trout smolts were captured, tagged and released over a three-year period. There was a considerable variation in capture rates (range: 0.4–17.7 fish per day) and sea lice numbers (number of lice per fish: 2.8–30.3; number of lice per gram body weight: 0.02–0.69) among localities, sampling times and years. Recapture rates of tagged fish with traps, which were low (2% or 0.11 fish per day), showed that the risk for pseudoreplication was minor, in terms of counting lice on the same fish several times. Most of the tagged sea trout (90%) were recaptured within the first two months after release, and no significant variations in lice numbers were found between tagging and recapture. The lack of differences in lice levels between tagging and recapture during the first week after tagging indicated that the method most likely would not significantly underestimate the lice infestations due to loss of lice during handling. Therefore, our results confirm that the use of fish traps is a suitable method for estimation of lice numbers on wild salmonids.

Implications of Sea Bream and Sea Bass Escapes for Sustainable Aquaculture Management: A Review of Interactions, Risks and Consequences

ABSTRACT Gilthead sea bream and European sea bass aquaculture is widely established in the Mediterranean and North-eastern Atlantic regions, and rearing is mainly in coastal net-pen facilities. The rapid growth of the fish farming industry increases the potential number of farmed fish in the wild. Escape-related issues are likely to increase unless escape-management policies are included into the aquaculture legislation in the near future. This review summarizes the potential direct interactions among escaped fish and nearby farmed fish stocks, wild conspecifics, and coastal fish populations, since these interactions could compromise sustainability in coastal areas. Socioeconomic implications are also addressed, given that escape events can also lead to economic losses for farmers and may alter local fishery landings. Fish markets and consumers might be also affected. This review compiles the current knowledge on the potential effects of escapees in coastal areas, and contributes to the existing risks analyses regarding sea bream and sea bass escapes. Eventually, the need to design management policies to prevent or minimize escape events and to mitigate further impacts, applicable to Mediterranean countries and of special interest in areas where these species are locally absent, is discussed in the context of sustainable fin-fish aquaculture.

Variations in coastal fish species composition captured by traps in Romsdalsfjord, Western Norway

Fish traps are widely used in Norwegian fjords, especially those designed for monitoring salmonid populations in the marine environment, although many other marine fish species are also captured. The composition and spatio-temporal variations of fish species captured by fish traps were monitored in five different coastal locations throughout the Romsdalsfjord region, Western Norway, from May to August during the three consecutive years (2011–2013). Twenty-three fish species were captured by traps in coastal waters, both resident and migratory fishes. The most common fish and with greater catchability were saithe (Pollachis virens) and sea trout (Salmo trutta), followed by cod (Gadus morhua), pollack (P. pollachius), herring (Clupea harengus) and mackerels (Trachurus trachurus and Scomber scombrus). However, the captured assemblage presented great spatial and seasonal variations, in terms of mean daily catch, probably associated with hydrographical conditions and migrational patterns. Information obtained in this study will help us to better understand the compositions and dynamic of coastal fish populations inhabiting Norwegian coastal waters. In addition, traps are highly recommended as a management tool for fish research (e.g. fish-tagging experiments, mark and recapture) and conservation purposes (coastal use and fisheries studies).

Depth matters for bivalve culture in integrated multitrophic aquaculture (IMTA) and other polyculture strategies under non-eutrophic conditions

Bivalve cultivation, in single cultivation or in polyculture (including integrated multitrophic aquaculture; IMTA), is generally limited to eutrophic waters. We carried out a modeling study to test if, under meso- and oligotrophic conditions, depth could be a key factor for bivalve productivity associated to IMTA and other polyculture strategies. We applied the model Farm Aquaculture Resource Management (FARM) at three strata of the water column in two coastal fish farm areas in the Mediterranean Sea, using water column variables sampled seasonally to estimate the potential mussel production. According to FARM, mussel production was high in both areas and, in some cases, almost doubled when mussels were cultured below 25-m depth compared to shallower levels. Phytoplankton abundance is expected to notably influence mussel production compared to particulate organic matter. Thus, in meso- and oligotrophic stratified waters, where chlorophyll maximum is relatively deep, depth can be a key factor for the productivity of mussel cultivation. The obtained results could help to maximize the production of suspension-feeding bivalve cultivation and, therefore, the expansion and development of sustainable aquaculture in non-eutrophic marine waters.

Efectos del piojo del salmón Lepeophtheirus salmonis (Copepoda: Caligidae) en las poblaciones de truchas (Salmo trutta) de la costa NE Atlántica

Los piojos del salmon son parasitos externos de salmonidos en ambientes marinos. En los ultimos anos, la abundancia de este parasito ha aumentado debido a la presencia de cultivos de salmones en jaulas de engorde en mar abierto. Entre los salmonidos, la trucha es especialmente vulnerable a las infecciones por el piojo ya que permanece en aguas costeras durante su periodo marino, donde se situan las instalaciones acuicolas de cultivo del salmon. En el presente trabajo se recopila la informacion existente sobre los efectos del piojo del salmon en las poblaciones de truchas silvestres que habitan las costas del NE Atlantico, y evaluar posteriormente el estado actual de dicha problematica. La acuicultura de salmon aumenta la abundancia de piojos, los cuales impactan negativamente sobre las poblaciones de truchas, aumentando la mortalidad, cambiando las pautas migratorias y disminuyendo el crecimiento. Estas conclusiones se basan en estudios cientificos que abarcan desde experimentos en el laboratorio o en el campo de los efectos del piojo en las truchas a nivel individual, hasta estudios poblacionales de dichos impactos. En resumen, el conocimiento adquirido en esta revision evidencia la existencia de un efecto general y persuasivo de los piojos en las poblaciones de truchas, especialmente en areas de cultivo intensivo. Los efectos derivados de altos niveles de infestacion implican inevitablemente una reduccion en la abundancia y el tamano corporal de las truchas que vuelven a agua dulce a reproducirse, afectando a la dinamica poblacional a nivel local, asi como a pescadores deportivos y comerciales.