Olav Sigurd Kjesbu

Institute of Marine Research in Norway | IMR

This study explores the life‐history parameters of female Merluccius capensis off South Africa (N = 1819) during 2014–2016, including gonadosomatic index (GSI), length‐at‐maturity, length–weight relationships, and condition indices (relative condition [k] and Fulton's condition factor [K]). We detected weak indications of two peaks of spawning with...

Increasing ocean temperature will speed up physiological rates of ectotherms. In fish, this is suggested to cause earlier spawning due to faster oocyte growth rates. Over time, this could cause spawning time to become decoupled from the timing of offspring food resources, a phenomenon referred to as trophic asynchrony. We used biological data, incl...

Climate change continues to exert pressure on ocean ecosystems. The fisheries-related responses, such as altered body growth, recruitment and spatial distribution of the targeted stock(s), have generally been reasonably well investigated. Nevertheless, there are still important knowledge gaps in how biophysical drivers impact stock productivity and...

Although early embryonic protein production relies exclusively on maternal molecules such as messenger RNAs (mRNAs) incorporated into ovarian follicles, knowledge about any thermally induced, intergenerational effects is scarce in ectotherms. Here, we investigated how elevated temperatures (9°–12°C vs. 6°C) during oogenesis influenced the next gene...

Methods to reliably identify jump discontinuities in biological time series and to assess the specific contribution of various covariates are rapidly progressing. Here, we took advantage of these statistical improvements as well as those seen in complementary, down‐scaled climate and biogeochemical models to investigate causes of the substantial in...

The Northeast Atlantic mackerel is an income breeder with indeterminate fecundity, spawning in multiple batches at optimal temperatures around 11°C in the upper water column during February–July along the continental shelf from 36–62°N. Based on macroscopic staging of gonads (N ∼62000) collected in 2004–2021, we detected an on-going extension of sp...

Predicting recruitment in a reliable fashion is a great challenge within operational fisheries advice. Here, we consulted the unique but undercommunicated IMR Cod Larva Project (1975–1990), its spin-offs, placed in an international era of advancements over the last 50 years to glance into the future. Few initiatives of this kind have applied such e...

The reproductive success of marine ectotherms is especially vulnerable in warming oceans due to alterations in adult physiology, as well as embryonic and larval survival prospects. These vital responses may, however, differ considerably across the species' geographical distribution. Here we investigated the life history, focusing on reproductive ec...

The oocyte development (vitellogenesis) of individual fish is highly dependent upon their physiology which is influenced by both intrinsic and extrinsic factors. Thus, if individuals encounter poor biophysical conditions, they will likely be unable to reproduce. The photoperiod is an external factor that is constant between years but with increasin...

The present study tracked oocyte development over 9 months and noted incidences of ‘skipping’, i.e., adults terminating their upcoming reproductive cycle, in field‐caught north‐east Arctic (NEA) haddock (Melanogrammus aeglefinus), currently the largest stock of this species. Applications of advanced image and histological techniques revealed the pr...

Climate change will increase the magnitude and duration of warming events and the variability in the phenology and abundance of available prey to the early life stages of fish. These factors influence physiological, behavioral and ecological processes, impacting growth, development and survival. Using a fully factorial design with two prey-availabi...

The link between the dynamic organization of the ovary and spawning dynamics was investigated in pelagic fishes with indeterminate fecundity. Αn array of laboratory methods and statistical approaches was applied to samples of gonadal material from three commercial NE Atlantic fish species: the sardine, Sardina pilchardus, the horse mackerel, Trachu...

Impacts of climate change on ocean productivity sustaining world fisheries are predominantly negative but vary greatly among regions. We assessed how 39 fisheries resources—ranging from data-poor to data-rich stocks—in the North East Atlantic are most likely affected under the intermediate climate emission scenario RCP4.5 towards 2050. This region...

The understanding of teleost fecundity type (determinate or indeterminate) is essential when deciding which egg production method should be applied to ultimately estimate spawning stock biomass. The fecundity type is, however, unknown or controversial for several commercial stocks, including the Northeast Atlantic mackerel (Scomber scombrus). Aimin...

Maintaining healthy, productive ecosystems in the face of pervasive and accelerating human impacts including climate change requires globally coordinated and sustained observations of marine biodiversity. Global coordination is predicated on an understanding of the scope and capacity of existing monitoring programs, and the extent to which they use...

This investigation commenced by constructing principal maturation schedule equations as a function of fishing mortality (F), key biophysical factors and a term attributed to fisheries-induced adaptive change (FIAC). Following the onset of industrial trawl fishery on the model stock, Northeast Arctic cod (NEAC; Gadus morhua) (1934–2020), F on immatu...

Life-history traits of Pacific (Clupea pallasii) and Atlantic (Clupea harengus) herring, comprising both local and oceanic stocks subdivided into summer-autumn and spring spawners, were extensively reviewed. The main parameters investigated were body growth, condition, and reproductive investment. Body size of Pacific herring increased with increas...

Egg surveys are used worldwide for the estimation of spawning stock biomass (SSB) of small pelagic fish species, requiring detailed knowledge about their reproductive biology. In the present study, we revisit the current conceptual framework of teleost fecundity types using Northeast Atlantic (NEA) mackerel (Scomber scombrus) as case study due to c...

Larval drift is a key process for successful fish recruitment. We used Norwegian spring-spawning herring (Clupea harengus) as model species to investigate the relationship between larval drift and recruitment. Larval drift indices were derived from simulations based on survey observations between 1993 and 2016. We show that forward simulated larval...

Significance Both theory and experiments suggest that fishing can drive the evolution of an earlier maturation age. However, determining whether changes in the wild are the result of fisheries-induced evolution has been difficult. Temporal, genome-wide datasets can directly reveal responses to selection. Here, we investigate the genomes of two wild...

Mortality rates in the early life-history stages of fishes are generally high yet identifying the causes remain unclear. Faltering recruitment rates of Atlantic herring (Clupea harengus) in the Norwegian Sea indicate a need to identify which mortality factors influence larval herring survival. Previous research suggests that increased predation pre...

The 150th anniversary of Johan Hjort’s birth was celebrated by a symposium held in Bergen on 12–14 June 2019 to take a broad perspective on the origins of, and developments in, fisheries science and thereby examine current issues in fisheries science from different perspectives. To establish this type of non-traditional forum, historians of marine...

The assessment of postovulatory follicles (POFs) is of considerable importance when applying the Daily Egg Production Method (DEPM) since it is used to estimate both spawning frequency (S) and batch fecundity (FB), provided that daily cohorts of POFs are discernible. Atlantic sardine (Sardina pilchardus) and Atlantic mackerel (Scomber scombrus), tw...

Ambient temperature modulates reproductive processes, especially in poikilotherms such as teleosts. Consequently, global warming is expected to impact the reproductive function of fish, which has implications for wild population dynamics, fisheries and aquaculture. In this extensive review spanning tropical and cold‐water environments, we examine t...

The introduction of 200 n.m. exclusive economic zones (EEZs) in the late 1970s required increased collaboration among neighbouring coastal states to manage transboundary and straddling fish stocks. The established agreements ranged from bilateral to multilateral, including high‐seas components, as appropriate. However, the 1982 United Nations Conve...

The collection and presentation of accurate reproductive data from wild fish has historically been somewhat problematic, especially for serially spawning species. Therefore, the aim of the current study was to develop a novel method of assessing female spawning status that is robust to variation in oocyte dynamics between specimens. Atlantic cod (B...

Environmental influences on Norwegian spring-spawning herring (Clupea harengus L.) larvae reveal recent constraints in recruitment success. The lack of any abundant recruiting year class of Norwegian spring-spawning (NSS) herring between 2005 and 2015 contributed to an approximate reduction of 40% in the spawning-stock biomass since 2009, i.e. from...

Information on temporal variations in stock reproductive potential (SRP) is essential in fisheries management. Despite this relevance, fundamental understanding of egg production variability remains largely unclear due to difficulties in tracking the underlying complex fluctuations in early oocyte recruitment that determines fecundity. We applied a...

Here we challenge traditional views on the direction of change in teleost body condition and reproductive traits in response to abiotic and biotic factors by studying the data-rich, planktivorous Norwegian spring-spawning herring (NSSH), a member of the abundant Atlantic herring (Clupea harengus) stock complex. To test potential influential factors...

The temperature is one of the key parameters of climate change influencing teleost physiology and population dynamics. In addition, the thermal windows for spawners and early life stages (eggs and larvae) appear to be the narrowest during the life of the fish. The maternal contribution to fish embryogenesis is clearly established as this latter dep...

Introduction Estimation of individual egg production is a key step to understand the relationship between stock and recruitment or to assess spawning stock biomass using egg production. Here we demonstrate a fecundity method that uses less toxic fixative and is less labour intensive whilst automating the work and improving the accuracy of populatio...

Specific impacts of somatic growth, sexual maturation, and spawning events on otolith zone formation in Atlantic cod (Gadus morhua) were assessed in a 33-month tank experiment, using Barents Sea cod and Norwegian coastal cod. High and low feeding ration combinations were used to mimic environmental stressors in the field. For both stocks, apparent...

It is well known that marine fish dynamics relate with climate variability, and predicting future population developments have become increasingly urgent with on-going climate change. One approach in widespread populations is to study how individuals from different parts of the distribution area respond to climate, thereby testing for potential res...

Understanding the controls and basis of biological processes such as oogenesis and fecundity is crucial to forecast productivity changes (Morgan 2017). The selection of the method to estimate egg production is based on the fecundity type which remains uncertain for many stocks . Moreover, early oocyte recruitment, which is in the bottom of year-cla...

This paper examines variations in gender-specific body growth, morphology and reproduction of the bearded goby (Sufflogobius bibarbatus) across the Namibian shelf, built on previous work on male reproductive modes. The results indicate a spatial variation in the size composition, condition factor and maturation of gobies across the shelf area. Low...

The European hake (Merluccius merluccius) is an indeterminate spawner that shows a protracted reproductive season. While the Northern stock displays a single spawning peak in spring, the southern stock shows two peaks, in spring and summer. Under the hypothesis that these seasonal components correspond to different spawning populations, we would ex...

This study documents how settlement of juvenile Atlantic cod (Gadus morhua) in the Barents Sea affects otolith growth and morphology. A simple method to objectively discriminate between age 0 and age 1 cod sampled in late summer was demonstrated by using only two otolith morphometric descriptors: area and perimeter. In the pre-settled 0-group cod,...

Significance Fish stock advice and management have a focus on protecting the reproductive capacity of a stock. Central to the associated research undertaken is whether spawning stock biomass is a proxy for total egg production. Here we demonstrate for the planktivorous Atlantic herring that the standard use of season-independent potential fecundity...

Wild caught North Sea saithe Pollachius virens were monitored for growth, sex steroid profiles and oocyte development pre-spawning and measured for egg size and group fecundity during the spawning season in the laboratory. Vitellogenesis commenced in late October–early November, at a leading cohort size (CL) of c. 250 µm, after which oocytes grew r...

Repetitive microsatellite DNA forms a universal component of eukaryote genomes and specific biochemical properties of such repeat regions may influence the outcome of laboratory protocols. The Atlantic cod (Gadus morhua) genome contains an order of magnitude more dinucleotide repeats than the majority of vertebrates, with over eight percent of its...

A range of methods can be applied to estimate the batch fecundity of species with an indeterminate reproductive strategy. The traditional Hydrated Oocyte (HO) method based on direct counts of hydrated oocytes is the easiest and most accurate method but the main problem with this method is the shortage of hydrated ovaries in sampled fish such as tun...

This chapter considers reproductive information used or having the potential to be used in the assessment of fish stocks in order to improve fisheries management advice, aslo known as applied fisheries reproductive biology (AFRB). The focus is on stock reproductive potential (SRP), viewed at the cellular and individual level. The central concepts c...

The North Atlantic with its spring-bloom ecosystem has its particular responses to climate change, many of them different from the other parts of the world's oceans. The system is strongly influenced by anthropogenic climate change as well as to strong decadal to multidecadal natural climate variability. In particular, the northernmost part of the...

The bearded goby (Sufflogobius bibarbatus), a key species in the northern Benguela Upwelling Ecosystem, tolerates extremely low levels of oxygen. Yet little is known about how its reproduction is affected by these harsh living conditions. The distribution patterns of alternative reproductive tactics of male bearded goby across the continental shelf...

Certain recent advances in statistical methodology have promising potential for fruitful use in general biology and the fisheries sciences. This paper reviews and discusses some of the relevant themes, including accurate modelling via focused model selection techniques, dynamic goodness-of-fit testing of processes evolving over time, finding break...

Large interannual fluctuations in the numbers of offspring joining a teleost population are common, yet factors affecting offspring production, a key driver of fish population size and demography, are often poorly understood. For some iteroparous teleosts, spawning omission ('skipping') following sexual maturation may occur, but this is typically d...

Traditional histological protocols in marine fish reproductive laboratories using paraffin as the embedding medium are now increasingly being replaced with protocols using resin instead. These procedures entail different degrees of tissue shrinkage complicating direct comparisons of measurement results across laboratories or articles. In this work...

In the cascade, internal variability is represented by the range between different realizations from the same climate model (Fig. 4) and for the 2046–2065 period this range is 0.5 million km 2 on average across models and scenarios (0.6 million km 2 across the full CMIP5 ensemble; also see Supplementary Information). Internal variability on even sh...

Fish stock productivity, and thereby sensitivity to harvesting, depends on physical (e.g. ocean climate) and biological (e.g. prey availability, competition and preda-tion) processes in the ecosystem. The combined impacts of such ecosystem pro-cesses and fisheries have lead to stock collapses across the world. While traditional fisheries management...

Hidden within the seminal 1914 publication by Johan Hjort, we find what is probably one of the first comprehensive teleost time-series ever published. The series is liver size and fat content of northeast Arctic (NEA) cod measured during the traditional winter fishery in Lofoten, Northern Norway, in 1880-1912 and 1883-1913, respectively. The data w...

It is generally accepted that the high buoyancy of pelagic marine eggs is due to substantial influx of water across the cell membrane just before ovulation. Here we further develop the theoretical basis by applying laboratory observations of the various components of the fertilized egg in first-principle equations for egg specific gravity (ρegg) fo...

Knowledge of growth, age and size at the onset of maturation is important for fish stock assessment. So-called spawning checks or “spawning zones” in cod otoliths, first described by Rollefsen (1933), have subsequently been used to determine age at maturation and to construct maturity ogives for individual cohorts of Northeast Arctic cod (NEAC). Sp...

Early life stages may on average gain a survival benefit from the regular return of parent fish to the same spawning grounds. Such areas may have a considerable spatial extent, occupation of which varies between spawning seasons. Northeast Arctic cod (Gadus morhua) is an ideal candidate to pinpoint the most influential biophysical factors in these...

Significance Currently many exploited fish populations, including many of the Atlantic cod stocks, are at historically low levels with widespread concern about whether contemporary management is capable of facilitating population recovery. In contrast, the spawning stock biomass of Barents Sea cod is now at an historic high. Here we demonstrate tha...

Harvest control measures for Namibia and Angola are defined using reference points for spawning biomass, which requires knowledge of spawning potential and dynamics of fishery stocks. The reproductive biology of two species of horse mackerel, Trachurus capensis and Trachurus trecae, in these waters was investigated for spawning distribution in time...

Skagen, D. W., Skern-Mauritzen, M., Dankel, D., Enberg, K., Kjesbu, O. S., and Nash, R. D. M. 2013. A simulation framework for evaluating fisheries management decisions using environmental information. – ICES Journal of Marine Science, 70: 743–754. The population dynamics of marine fish stocks are influenced by both physical and biological conditio...

The following two hypotheses, using several years of data collected for Barents Sea and Irish Sea cod (Gadus morhua), are scrutinized: (1) potential fecundity closely reflects realised fecundity, and (2) that realised fecundity or associated properties such as spawning duration or egg weight are not dependent on maternal size or condition. Pre-spaw...

The Northeast Arctic (NEA) haddock (Melanogrammus aeglefinus) population size has fluctuated greatly over the last few decades. Such fluctuations may be influenced by changes in reproductive investment, yet no fecundity study on this population has been undertaken since 1974 with which to address such a concept. We therefore estimated potential fec...