Lise Langård

Recent changes in distribution and relative abundance of cetaceans in the Norwegian Sea and their relationship with potential prey

This study aimed to assess possible shifts in distributional patterns of cetaceans residing in the Norwegian Sea, and if possible relate the distribution to their feeding ecology during the summer seasons of 2009, 2010 and 2012. During this same period, historically large abundances in the order of 15 million tonnes pelagic planktivorous fish such as Norwegian spring-spawning herring (Clupea harengus), northeast Atlantic mackerel (Scomber scombrus) and blue whiting (Micromesistius poutassou), have been reported feeding in the Norwegian Sea during the summer. There is also observed elevated average surface temperatures and a reduction in zooplankton biomasses. Such changes might influence species composition, distribution patterns and feeding preferences of cetaceans residing the region. Our results show higher densities of toothed whales, killer whales (Orcinus orca) and pilot whales (Globicephala melas), than the previous norm for these waters. Baleen whales, such as minke whales (Balaenoptera acutorostrata) and fin whales (Balaenoptera physalus), which is often associated with zooplankton, displayed a distribution overlap with pelagic fish abundances. Humpback whales (Megaptera novaeangliae) were observed in low numbers, indicating shift in habitat preference, compared to sighting data collected only few years earlier. Our study illustrate that both small and large cetaceans that reside in the Norwegian Sea have the capability to rapidly perform shifts in distribution and abundance patterns dependent of the access to different types and behaviour of prey species.

The Dynamics of a Metapopulation: Changes in Life-History Traits in Resident Herring that Co-Occur with Oceanic Herring during Spawning

Different populations of Atlantic herring are regarded as forming a metapopulation, but we know little about the dynamics of the connectivity and degree of interbreeding between the populations. Based on data from three periods between 1962 and 2011, we identified the presence of two components of herring in a small semi-enclosed coastal marine ecosystem based on different somatic growth patterns and mean vertebrae sum (VS). The two components were interpreted as belonging to a resident herring population and the migratory, oceanic Norwegian spring spawning (NSS) herring population, and they co-occurred during spawning. In the 1960s, resident herring characterized by slow growth and low VS co-occurred with rapid growth, high VS oceanic NSS herring. Similar slow-growing resident and rapid-growing NSS herring were found in the 1970–80s, but both populations now had low VS suggesting similar origins. Finally, in the 2000s both populations showed rapid growth. The changes coincided with the NSS herring going from a state of high abundance and oceanic distribution to a collapse in the late 1960s that resulted in a coastal distribution closer to resident herring populations, before full recovery and resumption of the migratory, oceanic pattern in the 1990s. During all three periods, NSS herring were only present in the local system up to an age of about five years, but the synchronous spawning of the populations supports mixed spawning and interbreeding. During the investigation period both longevity, length at age (growth) and length-at-first maturity increased markedly for the resident herring, which then became more similar to the NSS herring. Genetic and/or cultural factors are believed to be the main causes of the observed changes in life history traits, although some effect of changes in environmental factors cannot be excluded. Our study suggests that relationships among populations in a metapopulation can be highly dynamic.

SOUND PRODUCTION IN PRE-SPAWNING HERRING, COD AND HADDOCK IN A NATURALLY ENCLOSED ECOSYSTEM

Scholz, K., & Ladich, F. (2006). Sound production, hearing and possible interception under ambient noise conditions in the topmouth minnow Pseudorasbora parva. J. Fish Bioi. 69, 892-906. Vasconcelos, R. 0., Amorim, M. C. P., & Ladich, F. (2007). Effects of ship noise on the detectability of communication signals in the Lusitanian toadfish. J. Exp. Bioi. 201, 2104-2112. Wysocki, L.E., Amoser, S., & Ladich, F. (2007). Diversity in ambient noise in European freshwater habitats: noise levels, spectral profiles and impact on fishes. J. Acoust. Soc. Am. 121, 2559-2566.

Performance of the Nordmøre Grid in Shrimp Trawling and Potential Effects of Guiding Funnel Length and Light Stimulation

AbstractThe introduction of the Nordmore grid to shrimp trawls has reduced the issue of bycatch to that of small-sized species and juveniles that are able to pass through the grid and enter the small-meshed cod end together with the targeted shrimp. This study estimated the size- and species-selective performance of the Nordmore grid in the configuration most often applied by fishermen and made a preliminary exploration of the effects of reducing the length of the guiding funnel in front of the grid and mounting light-emitting diodes (LEDs) around the escape exit. Experimental fishing trials were conducted in the Barents Sea to assess the size-selective properties of a 19-mm bar spacing Nordmore grid, mandatory in this Norwegian trawl fishery targeting deepwater shrimp Pandalus borealis (also known as northern shrimp), and its potential improvement. Results were obtained for the target species and four bycatch species: redfish Sebastes spp., Haddock Melanogrammus aeglefinus, Atlantic Cod Gadus morhua, and...

Thermal stratification influences maturation and timing of spawning in a local Clupea harengus population

Maturation and timing of spawning in relation to temperature were studied in a local Atlantic herring Clupea harengus population inhabiting a small semi-enclosed ecosystem (7 km(2)) separated from the larger outer fjord system by narrow sills on the west coast of Norway. Ambient temperatures varied annually up to 4° C during both the pre-spawning and spawning periods from February to April, but without affecting the spawning time. Instead, the timing of spawning was found to be related to thermal stratification in response to spring warming, which occurred about the same time every year regardless of initial temperatures.

Acoustic Tagging: A Suitable Method for the Study of Natural Herring Behavior Around Spawning?

Herring schools can be studied by standard acoustic methods, but to understand the relationship between the individual and school levels as well as the interactions between subpopulations of herring, it is essential to learn more about individual herring behavior. Acoustic tagging has successfully been used to track individual fish of various species, but herring are highly sensitive to being handled and are therefore not easy to tag. In this study, we tagged herring with acoustic transmitters to track prespawning and spawning individuals. The conditions for a tagging experiment were ideal because the herring remained in a single school (>100,000 fish) for more than 1 mo within an area of ∼200 m2 in the sheltered semienclosed Lindaspollene basins (Johannessen et al. 2009). This is a small (7-km2) well-defined ecosystem in western Norway, which comprises 3 distinct 60- to 90-m-deep basins containing numerous islets along with several sheltered sites. Here we evaluate whether acoustic tagging is a suitable method for the study of the natural behavior of herring around spawning.

New approach for modelling size selectivity in shrimp trawl fisheries

New approach for modelling size selectivity in shrimp trawl fisheries Roger B. Larsen*, Bent Herrmann, Manu Sistiaga, Jesse Brinkhof, Ivan Tatone, and Lise Langård The Arctic University of Norway UIT, Hansine Hansens veg 18, 9019 Tromsø, Norway SINTEF Fisheries and Aquaculture, Brattørkaia 17C, N-7010 Trondheim, Norway Norwegian Directorate of Fisheries, Postbox 185 Sentrum, 5804 Bergen, Norway *Corresponding author: tel: þ4777644536; fax: þ4777646020; e-mail: roger.larsen@uit.no These authors equally contributed to this study.