Elina Halttunen

Survival, Migration Speed and Swimming Depth of Atlantic Salmon Kelts During Sea Entry and Fjord Migration

In contrast to most species of Pacific salmon (Oncorhynchus spp.), Atlantic salmon (Salmo salar L.) is an iteroparous species such that it may survive and return to spawn repeatedly. Little information exists on these survivors (kelts) even though they might contribute significantly to salmon production when returning as repeat spawners. In order to estimate survival, timing of migration, swimming progression and swimming depth of Atlantic salmon kelts during sea entry and fjord migration, 60 individuals were captured, tagged with acoustic transmitters (of which 20 with depth sensors) and released in the River Alta, Northern Norway. In addition, 172 kelts were also tagged with external Carlin tags to obtain reliable recapture rates in the fisheries. Nearly all (95%) kelts tagged with acoustic transmitters were recorded during their outward migration at four transects of acoustic receivers deployed across the river mouth and Alta Fjord. Most of the kelts migrated through the 30 km long fjord in only 1–2 days (mean time 33 h, range 7–138 h) and generally stayed close to the surface during the fjord migration (individual mean depth of 2 m, range of individual means 0–15 m). Ninety-two percent (55/60) were recorded at the outermost transect 30 km from the river mouth, indicating a high minimum survival rate. The high survival rate and fast progression of kelts throughout the fjord indicate that sea-entry and early sea migration is not a critical phase for Atlantic salmon kelts, despite their weakened condition after spawning and overwintering in the river. Even though kelt migration overlapped partly with the fishing season both in the river and the fjord, and the kelts migrated in shallow waters exposed to several types of fishing gear, reported recapture rates were small (3%, 6 of all 232 tagged kelts).

Salmon lice infestations on sea trout predicts infestations on migrating salmon post-smolts

Salmon lice infestations on sea trout predicts infestations on migrating salmon post-smolts Knut Wiik Vollset,* Elina Halttunen, Bengt Finstad, Ørjan Karlsen, Pål Arne Bjørn and Ian Dohoo Uni Research, LFI Freshwater Biology, Nygårdsporten 112, 5006 Bergen, Norway Institute of Marine Research, PO Box 6404, NO-9294 Tromsø, Norway Norwegian Institute for Nature Research, PO Box 5685 Sluppen, N-7485 Trondheim, Norway University of Prince Edward Island, Charlottetown, Canada *Corresponding author: tel: þ4755584723; e-mail: knut.vollset@uni.no.

The gill maggot Salmincola salmoneus as an indicator of repeat spawning in Atlantic salmon Salmo salar

The potential of the gill maggot Salmincola salmoneus for use as an indicator of repeat spawning in Atlantic salmon Salmo salar was studied in adult fish captured during their return migration to the River Alta (n = 659) and River Namsen (n = 540) in Norway. Eighty-eight and 49% of previous spawners identified by scale readings were infected with S. salmoneus in the two rivers, respectively. Salmincola salmoneus can be used as a reliable, rapid and objective field indicator of repeat spawning in S. salar as nearly all infected fish (99·4%) were identified as repeat spawners, although it is important to have appropriate background information on S. salmoneus prevalence on the postspawning individuals within the same population.

Salmon lice evasion, susceptibility, retention, and development differ amongst host salmonid species.

Salmon lice evasion, susceptibility, retention, and development differ amongst host salmonid species Samantha Bui*, Elina Halttunen, Agnes M. Mohn, Tone Vågseth, and Frode Oppedal Institute of Marine Research, Matredal 5984, Norway Sustainable Aquaculture Laboratory – Temperate and Tropical (SALTT), School of BioSciences, University of Melbourne, Victoria 3010, Australia Institute of Marine Research, Tromsø 6404, Norway Department of Biology, University of Bergen, Bergen 7800, Norway *Corresponding author: tel: þ47 456 37 697; e-mail: samantha.bui@hi.no

Modelled salmon lice dispersion and infestation patterns in a sub-arctic fjord

Salmon lice infestation is a major challenge for the aquaculture industry in Norway, threatening wild salmonid populations and causing welfare problems for farmed salmon. Lice dispersion and infestation patterns are simulated by combining a high-resolution hydrodynamic model for the Norwegian coast and fjords with an individual-based model for salmon lice. We here present results from Altafjorden, a sub-arctic fjord with large stocks of wild salmonids, where the inner part is protected as a National Salmon Fjord. The outer part of the fjord hosts several fish farms, and our simulations demonstrate how ocean currents can disperse lice between farms as well as into the protected part of the fjord. The relative contributions from the farms in the different parts of the fjord depends on their locations relative to the currents and circulation patterns in the fjord. Knowledge of how the highly variable water currents disperse salmon lice within fjord systems is necessary for managing farm locations and production quotas, if the goal is to minimize infestation pressure on wild salmonids and between fish farms.

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.