Life history strategies and spatial dynamics of the Barents Sea capelin (Mallotus villosus)

Dr. Scient. Thesis. / Department of Fisheries and Marine Biology. University of Bergen. NorwayThis thesis consists of four papers on the life history strategy and spatial distribution of the Barents Sea capelin (Mallotus villosus). In the first two papers, sex specific aspects of capelin life history are investigated from a combination of field sampling and modelling. Paper III deals with the development of a concept for modelling spatial distribution of fish, and in Paper IV the concept is applied for the Barents Sea capelin. Female capelin were found to invest much more energy into reproductive tissue than males. Capelin fecundity was found to depend upon body weight, and inter annual variation in fecundity is related to variation in body weight. A life history model (Paper II) predicts that males have a higher fitness associated with semelparity than females since males may fertilise many females, whereas female fitness is limited by her number of eggs. Given a high or variable adult mortality risk, it may be more profitable for males to be semelparous than iteroparous. Capelin is therefore predicted to have sex specific life history strategies with semelparous males and iteroparous females. This prediction is supported by literature on capelin ecology. In Paper III a concept for modelling spatial distribution of fish is developed. The background for applying a new approach to studying fish distribution, is the lack of approaches for solving specific problems related to capelin ecology. The model is individual based and behaviour is calculated using an artificial neural network where weights are evolved using a genetic algorithm. Through simulating evolution by natural selection in a seasonal spatial model with life cycle, physiology, mortality, and reproduction, the individuals with the best "genetic weights" become increasingly more common in the population. Eventually the population consists of well-adapted individuals, which migrate back to spawning areas in winter, and grow and avoid being eaten throughout the rest of the year. The importance of separating between reactive and predictive behaviour in controlling local search and long distance migration respectively, is discussed. In Paper IV this model is elaborated to include: explicit representation of each stage in the life cycle of the Barents Sea capelin, larval drift, and evolution of spawning areas and timing of reproduction. Furthermore the model includes life history traits such as size at maturity, allocation of energy, and number of reproductive events. Larval drift was associated with a warm water area, and the evolved spawning ground was situated upstream from this, in the outskirts of the range for capelin spawning. The migration pattern follows the same general pattern as that of the Barents Sea capelin. In a simulation with stochastic mortality rates, sex specific life history strategies with semelparous males and iteroparous females were evolved, which supports the predictions from Paper II. The major achievement of this study is the development of an evolutionary system for fish migration, and the way this is applied to provide predictions about the life history and spatial dynamics of the Barents Sea capelin. Another important finding is the recognition that some aspects of capelin life history strategy are sex specific, with female iteroparity and male semelparity

Horizontal distribution and overlap of planktivorous fish stocks in the Norwegian Sea during summers 1995–2006

The Norwegian Sea harbours several large pelagic fish stocks, which use the area for feeding during the summer. The period 1995–2006 had some of the highest biomass of pelagic fish feeding in the Norwegian Sea on record. Here we address the horizontal distribution and overlap between herring, blue whiting and mackerel in this period during the summers using a combination of acoustic, trawl and LIDAR data. A newly developed temperature atlas for the Norwegian Sea is used to present the horizontal fish distributions in relation to temperature. The centre of gravity of the herring distribution changed markedly several times during the investigated period. Blue whiting feeding habitat expanded in a northwestern direction until 2003, corresponding with an increase in abundance. Strong year classes of mackerel in 2001 and 2002 and increasing temperatures throughout the period resulted in an increased amount of mackerel in the Norwegian Sea. Mackerel was generally found in waters warmer than 8°C, while herring and blue whiting were mainly found in water masses between 2 and 8°C. The horizontal overlap between herring and mackerel was low, while blue whiting had a large horizontal overlap with both herring and mackerel. The changes in horizontal distribution and overlap between the species are explained by increasing stock sizes, increasing water temperature and spatially changing zooplankton densities in the Norwegian Sea

Modelling secondary production in the Norwegian Sea with a fully coupled physical/primary production/individual-based Calanus finmarchicus model system

The copepod Calanus finmarchicus is the dominant species of the meso-zooplankton in the Norwegian Sea, and constitutes an important link between the phytoplankton and the higher trophic levels in the Norwegian Sea food chain. An individual-based model for C. finmarchicus, based on super-individuals and evolving traits for behaviour, stages, etc., is two-way coupled to the NORWegian ECOlogical Model system (NORWECOM). One year of modelled C. finmarchicus spatial distribution, production and biomass are found to represent observations reasonably well. High C. finmarchicus abundance is found along the Norwegian shelf-break in the early summer, while the overwintering population is found along the slope and in the deeper Norwegian Sea basins. The timing of the spring bloom is generally later than in the observations. Annual Norwegian Sea production is found to be 29 million tonnes of carbon and a production to biomass (P/B) ratio of 4.3 emerges. Sensitivity tests show that the modelling system is robust to initial values of behavioural traits and with regards to the number of super-individuals simulated given that this is above about 50,000 individuals. Experiments with the model system indicate that it provides a valuable tool for studies of ecosystem responses to causative forces such as prey density or overwintering population size. For example, introducing C. finmarchicus food limitations reduces the stock dramatically, but on the other hand, a reduced stock may rebuild in one year under normal conditions

Numerical domination and herring migrations

There is accumulating evidence in favour of the hypothesis that herring migrations are influenced by social learning. The “adopted-migrant hypothesis” postulates that recruit spawning herring learn migration patterns by schooling with older individuals. However, this learning can be interrupted if the stock is unstable or if there are lack of overlap between recruits and the adult stock. There have been five reported changes in the location of the wintering area of Norwegian spring spawning (NSS) herring during the last 50 years. These changes co-occur with the recruitment of relatively strong year classes to the spawning stock. Simulations of schools containing naïve and experienced fish have shown that when abundant enough, naïve individuals repel guidance from a minority of experienced individuals. This process is referred to as numerical domination. We argue that numerical domination obstruct social learning from adults to recruits and plays a key role in establishing new wintering areas in NSS herring

Opportunities for advancing ecosystem-based management in a rapidly changing, high latitude ecosystem

Unprecedented and rapid changes are ongoing in northern high latitude, marine ecosystems, due to climate warming. Species distributions and abundances are changing, altering both ecosystem structure and dynamics. At the same time, human impacts are increasing. Less sea ice opens for the opportunity of more petroleum-related activities, shipping and tourism. Fisheries are moving into previously unfished habitats, targeting more species across more trophic levels. There is a need for ecosystem-based fisheries management (EBFM) and ecosystem-based management (EBM) to take the rapid, climate driven changes into account. Recently, there has been much development in qualitative, semi-quantitative, and quantitative scientific approaches to support EBFM and EBM. Here, we present some of these approaches, and discuss how they provide opportunities for advancing EBFM and EBM in one high-latitude system, namely the Barents Sea. We propose that advancing EBFM and EBM is more about adding tools to the toolbox than replacing tools, and to use the tools in coordinated efforts to tackle the increasing complexities in scientific support to management. Collaborative and participatory processes among stakeholders and scientists are pivotal for both scoping and prioritizing, and for efficient knowledge exchange. Finally, we argue that increasing uncertainty with increasing complexity is fundamental to decision making in EBFM and EBM and needs to be handled, rather than being a reason for inaction or irrelevance.publishedVersio

Bioenergetics modeling of the annual consumption of zooplankton by pelagic fish feeding in the Northeast Atlantic

The present study uses bioenergetics modeling to estimate the annual consumption of the main zooplankton groups by some of the most commercially important planktivorous fish stocks in the Northeast Atlantic, namely Norwegian spring-spawning (NSS) herring (Clupea harengus), blue whiting (Micromesistius poutassou) and NEA mackerel (Scomber scombrus). The data was obtained from scientific surveys in the main feeding area (Norwegian Sea) in the period 2005–2010. By incorporating novel information about ambient temperature, seasonal growth and changes in the diet from stomach content analyses, annual consumption of the different zooplankton groups by pelagic fish is estimated. The present study estimates higher consumption estimates than previous studies for the three species and suggests that fish might have a greater impact on the zooplankton community as foragers. This way, NEA mackerel, showing the highest daily consumption rates, and NSS herring, annually consume around 10 times their total biomass, whereas blue whiting consume about 6 times their biomass in zooplankton. The three species were estimated to consume an average of 135 million (M) tonnes of zooplankton each year, consisting of 53–85 M tonnes of copepods, 20–32 M tonnes of krill, 8–42 M tonnes of appendicularians and 0.2–1.2 M tonnes of fish, depending on the year. For NSS herring and NEA mackerel the main prey groups are calanoids and appendicularians, showing a peak in consumption during June and June–July, respectively, and suggesting high potential for inter-specific feeding competition between these species. In contrast, blue whiting maintain a low consumption rate from April to September, consuming mainly larger euphausiids. Our results suggest that the three species can coexist regardless of their high abundance, zooplankton consumption rates and overlapping diet. Accordingly, the species might have niche segregation, as they are species specific, showing annual and inter-annual variability in total consumption of the different prey species. These estimates and their inter-annual and inter-specific variation are fundamental for understanding fundamental pelagic predator-prey interactions as well as to inform advanced multispecies ecosystem models.publishedVersio

Havforskningsinstituttets infrastrukturbehov for innhenting av marine data i perioden 2021-2030

Forskningsfartøyer vil fortsatt være våre viktigste plattformer for havovervåkning og -forskning for Havforskningsinstituttet den kommende 15-årsperioden. Samtidig pågår det en rivende utvikling innen havobservasjonsteknologi som sammen med bruk av innleide fartøyer og nyutviklede biofysiske modeller vil kunne dekke deler av det økte overvåkningsbehovet langs kysten, både på kort og lengre sikt. Vi ønsker en gradvis oppbygging av kapasitet i ubemannede farkoster de kommende årene både for å øke effektivitet og kvalitet i toktgjennomføring og for å erstatte noe av fartøykapasiteten.publishedVersio

Commitments to sustainable fisheries: Empty words or reality?

The Our Ocean conferences focus on voluntary commitments by different pledgers in support of actions towards a clean, healthy and productive ocean. We analysed the content and summarised the progress of implementation of the commitments related to sustainable fisheries at the Our Ocean conferences during 2014–2018. A total of 77 different entities provided commitments. Governments was the largest group (34) followed by NGOs (23). The majority (58%) of commitments were related to enforcement, transparency and cooperation. In particular, combating illegal, unreported and unregulated fisheries and support for the port state measures process were the focus of many of the commitments. To increase transparency and effectiveness of commitments, we suggest that more emphasis should be put on documenting and evaluating the impact of commitments. There is good progress in the implementation, and the commitments are largely reality and not empty words. We consider that the commitments have been successful in terms of generating attention and providing funding of projects that are supportive of sustainable fisheries. The diversity of pledgers is large, and an objective gap analysis on requirements for achieving sustainable fisheries regionally could provide pledgers with common ground and further increase the impact of the Our Ocean conferences.publishedVersio

Assessment of commitments on sustainable fisheries to the Our Ocean conferences : Where are we now?

Many ocean commitments have been made at the five Our Ocean conferences since 2014 under six different areas of action. The Institute of Marine Research was given the task of evaluating the 182 commitments made to the action area “Sustainable fisheries”. We analysed the content, summarised the progress of implementation and evaluated the impact of the commitments. A total of 77 entities provided commitments. Governments made up the largest group and accounted for 65% of the commitments. NGOs were the second largest group of pledgers and accounted for 20% of the commitments. There was a high degree of fulfilment of the commitments: three quarters of the commitments had a 50% or higher degree of fulfilment and 50% of the commitments have been finalised. Some recent commitments (made in 2017 and 2018) have not been initiated. Combatting of illegal, unreported and unregulated fisheries and support to the port state measures process are key issues addressed by many of the commitments. We also recognise that important components such as science, advice and laws have less support in the Our Ocean commitments and should receive more attention in the future. Regional fisheries management organizations (RFMOs) are important instruments for sustainable fisheries management and was addressed by some commitments. For RFMOs to be effective, we emphasize that they should be empowered to have legal authority to devise fisheries regulations. There are quite a few commitments in our analysis that were hard to evaluate. To increase transparency in pledging of commitments, more emphasis should be put on documenting and evaluating their impact. We consider that the Our Ocean commitments in sustainable fisheries overall have been successful in terms of generating attention to the issue and providing funding of projects that are supportive of sustainable fisheries. To achieve effective fisheries management and sustainable fisheries, it is important that all the components of the fisheries management system are in operation at the appropriate spatial scale (local, national, regional) over time. A gap analysis on requirements for achieving sustainable fisheries at the appropriate scale, is a good starting point for a systematic approach to providing commitments. We suggest that this is considered in future Our Ocean conferences.publishedVersio