Large annual variation in the amount of skipped spawning for female Northeast Arctic haddock Melanogrammus aeglefinus

Although the phenomenon of skipped spawning has been described in numerous fishes, time-series are scarce. We used the presence of post-ovulatory follicles in histological gonad slides from females not developing oocytes for Northeast Arctic (NEA) haddock Melanogrammus aeglefinus from 2009 to 2012 to construct a length-based statistical model giving the probability that a non - developing female was skipping spawning, as opposed to not being sexually mature. This model was then applied on demographic winter survey data from the Barents Sea from 1989 to 2014. This indicated large annual variation in skipping numbers. Comparing these survey estimates to the total annual ICES stock numbers, we found that skipping peaked in the years 1994–1996 and 2009–2014, when the median yearly estimate of skipped spawners was 20–45 % of all females aged ≥ 3 years. In contrast, only ∼ 3 % of females at age ≥ 3 years skipped spawning in 2007. The proportional representation of skipped spawners at the stock level appeared linked to stock energy reserves with more skipping occurring when energy levels were low. Skipping also became more frequent with increasing population age, i.e. when immatures were less abundant, although the very largest/oldest fish tended to spawn. Because the proportion of NEA haddock that skips spawning is variable and can be high, understanding variation in this phenomenon and its drivers may improve population dynamic models.publishedVersio

StoX: An open source software for marine survey analyses

Scientists across the globe conduct survey programs to monitor and characterize abundance, population structure, biodiversity and geographical distributions. To assess the state of marine fish and zooplankton, population surveys are often repeated annually using standardized sampling protocols and analysis techniques to establish trustworthy stock status. However, although transparency and repeatability are recognised as important principles of this process, it is often difficult to obtain comprehensive documentation of metadata and data processing steps. This is particularly challenging for workflows that include manual processing steps. StoX was principally built to process research‐vessel survey data, and we have included several standard survey estimation models. The software was developed to be robust and versatile and aimed at the open source community, such that users could easily build their own models. StoX is fully integrated with R to utilize the large number of R‐packages and enable any StoX function and stock estimation model to be controlled using R. There has been a large need for a freely available software for research–vessel survey estimation, and StoX is tested in surveys carried out in four continents and is the official tool for many important fish stock surveys. The basic workflow and transparency principles of StoX, together with a customizable GUI, makes StoX applicable for any geographically coded surveys. Future versions of StoX will include statistical models to estimate the catch composition in commercial fisheries. In fields such as conservation management, there is also a need to document the estimation methods, and additional estimation and analyses models, including biodiversity indices are currently implemented. In parallel, we envision a closer web service integration with existing international and national data centres.publishedVersio

Spatial patterns of age-0 cod survival in the Barents Sea

Apart from human harvest, recruitment dynamics is conceivably recognized as the main source of population variability of marine fish stocks. Factors affecting recruitment dynamics can change over both temporal and spatial scales. It follows that at the same time, over the entire range of distribution of a single population, different individuals may experience different level of environmental forcing and survival, which may not be well represented by average conditions throughout the entire distribution range. In this study we focus on the spatial pattern and its relative sources of variability in the survival of the Arcto-Norwegian cod (Gadus morhua L.) from the age-0 to the age-1 stage. This is a delicate phase of the cod pre-recruitment dynamics, as individuals are confronted with a suite of survival challenges, such as settlement, pre-winter body condition, growth, and predation avoidance. During the over 20 years analyzed (1980-2004), we found that on average age-0 cod experience lower survival in the areas north of the Norwegian coastline, from about 71 to 75 degree of latitude north and about 20 to 35 degree of longitude east. However, in coastal areas, immediately north of the Norwegian coastline, age-0 cod experience greater survival. Within the studied area, the average survival of age-0 cod is significantly greater during years with low adult cod and high capelin abundance, and high Arctic Oscillation. In addition, when capelin abundance is high, age-0 cod experience better survival particularly near the Norwegian coastline. Based on these results it appears that within the sampled grid the observed geographic patterns of age-0 cod survival is affected by the predation from adult cod in relation to the availability and distribution of capelin (Mallotus villosus), the alternative and preferred prey of adult cod. Climate can affect the spatial survival of age-0 cod by both affecting the distribution of their predators (e.g., adult cod) and the distribution and availability of zooplankton prey

Spatial patterns of age-0 cod survival in the Barents Sea

Apart from human harvest, recruitment dynamics is conceivably recognized as the main source of population variability of marine fish stocks. Factors affecting recruitment dynamics can change over both temporal and spatial scales. It follows that at the same time, over the entire range of distribution of a single population, different individuals may experience different level of environmental forcing and survival, which may not be well represented by average conditions throughout the entire distribution range. In this study we focus on the spatial pattern and its relative sources of variability in the survival of the Arcto-Norwegian cod (Gadus morhua L.) from the age-0 to the age-1 stage. This is a delicate phase of the cod pre-recruitment dynamics, as individuals are confronted with a suite of survival challenges, such as settlement, pre-winter body condition, growth, and predation avoidance. During the over 20 years analyzed (1980-2004), we found that on average age-0 cod experience lower survival in the areas north of the Norwegian coastline, from about 71 to 75 degree of latitude north and about 20 to 35 degree of longitude east. However, in coastal areas, immediately north of the Norwegian coastline, age-0 cod experience greater survival. Within the studied area, the average survival of age-0 cod is significantly greater during years with low adult cod and high capelin abundance, and high Arctic Oscillation. In addition, when capelin abundance is high, age-0 cod experience better survival particularly near the Norwegian coastline. Based on these results it appears that within the sampled grid the observed geographic patterns of age-0 cod survival is affected by the predation from adult cod in relation to the availability and distribution of capelin (Mallotus villosus), the alternative and preferred prey of adult cod. Climate can affect the spatial survival of age-0 cod by both affecting the distribution of their predators (e.g., adult cod) and the distribution and availability of zooplankton prey