Quantifying natural variability in spawning and survival of Northeast Arctic haddock

Oil companies are currently extending their search for new oil deposits to areas that have previously been sheltered from oil exploration, including the sea areas around the Lofoten Islands of northern Norway. These areas are, however, considered to be ecologically especially vulnerable, since they are spawning and larval-drift areas for several commercially important species of marine fish, including NEA cod (Gadus morhua), haddock (Melanogrammus aeglefinus) and herring (Clupea harengus). A major concern is the possible impact on the fish populations from either an accidental oil spill or chronic exposure from operational discharges of produced water.   

The effects of petroleum discharges depend on several interrelated physical and biological processes over time scales ranging from hours to years. For example, differences between years in the location and timing of spawning and in advection are likely to lead to differences in the spatiotemporal distribution of eggs and larvae. This may in turn lead to large inter-annual differences in the proportion of fish cohorts that are exposed to pollution, even if the pollution originates from the same spatiotemporal location among the years. For the NEA cod, considerable variability among years in the location of spawning has been shown, possibly caused by changes in ocean temperature or in the age structure of the spawning females. For the NEA haddock, the exact location and timing of spawning is much more uncertain. This uncertainty limits our ability to assess how large fraction of a haddock cohort is potentially exposed to pollution from a given release site, and how this fraction may vary among years. 

Figure 1 The changes in density (darker shade = higher density) of early life stages of a fish with pelagic eggs and larvae drifting in a current (indicated by arrows, from left to right) are illustrated. The changes in density are due to advection and diffusion and also spatial differentiated natural mortality. A oil-spill hitting area 2 at the egg stage will be less severe at the juvenile stage than an oil-spill hitting area 1 due to the spatial variation in natural mortality.

Furthermore, differences in survival prospects among eggs or larvae located in different geographic areas can reduce or magnify effects of local-scale pollution. Magnification will occur if the pollution (happens to) hit eggs or larvae with good survival prospects. If one erroneously assumes that the natural survival is spatially homogenous, the expected reduction in recruitment from a given pollution scenario may hypothetically be reliably estimated, but the range of possible outcomes, and, thus, the risk of extreme effects, may be underestimated. Improved knowledge about how the natural survival of fish eggs and larvae varies spatially, and which biotic and abiotic factors explain this variability, is thus of critical importance to reliably assess the risk of adverse effects of pollution. 

Using newly digitized Russian survey data from 1959-1993 (see figure 2) we will estimate the spawning time and location as well as the variations in natural mortality in space and time in the early life-stages of NEA haddock.

Figure 2 Overview of the Russian egg and larval survey stations (open circles).

Publications:

Ohlberger, J., & Langangen, Ø. (2015). Population resilience to catastrophic mortality events during early life stages. Ecological Applications, 25(5), 1348–1356. 

Stige, Langangen, Yaragina, Vikebø, Bogstad, Ottersen, Stenseth, Hjermann (2015). Combined statistical and mechanistic modelling suggests food and temperature effects on survival of early life stages of northeast arctic cod (Gadus morhua), Progress in Oceanography, 134:138-151 

Langangen, Ø., Hjermann, D. Ø., Olsen, E., Stige, L. C., Ohlberger, J.,  Yaragina, N. A., Vikebø, F. B., Bogstad, B., Stenseth, N. C.,

Implications of spatial variation in natural mortality: the effects of oil spills on marine fish, Submitted to Marine Ecology Progress Series 

Langangen, Ohlberger, Stige, Durant, Ravagnan, Stenseth, Hjermann, Cascading effects of mass mortality events in arctic marine communities,

Global Change Biology, 2017, 23, 283-292 

Langangen, Ø., Ottersen, G., Ciannelli, L., Vikebø, F. B., & Stige, L. C. Reproductive strategy of a migratory fish stock: implications of spatial variations in natural mortality. Canadian Journal of Fisheries and Aquatic Sciences, 2016, 73, 1742-1749