Are we ready to track climate-driven shifts in marine species across international boundaries? - A global survey of scientific bottom trawl data

Marine biota are redistributing at a rapid pace in response to climate change and shifting seascapes. While changes in fish populations and community structure threaten the sustainability of fisheries, our capacity to adapt by tracking and projecting marine species remains a challenge due to data discontinuities in biological observations, lack of data availability, and mismatch between data and real species distributions. To assess the extent of this challenge, we review the global status and accessibility of ongoing scientific bottom trawl surveys. In total, we gathered metadata for 283,925 samples from 95 surveys conducted regularly from 2001 to 2019. We identified that 59% of the metadata collected are not publicly available, highlighting that the availability of data is the most important challenge to assess species redistributions under global climate change. Given that the primary purpose of surveys is to provide independent data to inform stock assessment of commercially important populations, we further highlight that single surveys do not cover the full range of the main commercial demersal fish species. An average of 18 surveys is needed to cover at least 50% of species ranges, demonstrating the importance of combining multiple surveys to evaluate species range shifts. We assess the potential for combining surveys to track transboundary species redistributions and show that differences in sampling schemes and inconsistency in sampling can be overcome with spatio-temporal modeling to follow species density redistributions. In light of our global assessment, we establish a framework for improving the management and conservation of transboundary and migrating marine demersal species. We provide directions to improve data availability and encourage countries to share survey data, to assess species vulnerabilities, and to support management adaptation in a time of climate-driven ocean changes.En prensa6,86

Variation in fish condition between Atlantic cod (Gadus morhua) stocks and implications for their management

A comparative analysis of the fish condition (Fulton’s K) of 11 cod stocks in the North Atlantic in relation to the temperature of their habitat and their reproductive potential is presented. It is shown that the cod stocks in the North Atlantic display different levels of mean condition, which are partly due to the different temperature regimes of their habitats. Cod stocks living in colder waters, e.g. Southern Gulf of St Lawrence, Greenland and Grand Bank cod stocks, were more poorly-conditioned than cod stocks living in warmer waters, e.g. North Sea and Irish Sea. The a-coefficient obtained from a standardised Ricker’s recruitment-spawning stock biomass (SSB) relationship represents the function’s slope at the origin and was defined as an indicator for the recruitment potential of a given stock. The a-coefficients were found to be correlated with the mean condition factors of the stocks in 9 of the 11 cod stocks analysed. This indicates that stocks consisting of poorly-conditioned individuals appear to be very susceptible to reduced recruitment at low SSB, while the stocks which consist of well conditioned fish seem to behave more robust with a higher probability of good recruitment at low SSB. The positive effect of the cod condition on their reproductive potential generally implies that the well-conditioned stocks in the Northeast Atlantic can sustain higher exploitation rates than the poorly-conditioned stocks in the Northwest Atlantic. This implication is confirmed by a positive relationship between the estimated biological management reference points Fmed and the mean cod condition factors of the stocks

Thermal niche of Atlantic cod Gadus morhua: limits, tolerance and optima

Recent studies in the marine environment have suggested that the limited phenotypic plasticity of cold-adapted species like Atlantic cod (Gadus morhua L.) will cause distributions to shift toward the poles in response to rising sea temperatures. Some cod stocks are predicted to collapse, but this remains speculative because almost no information is available on the thermal tolerance of cod in its natural environment. We used electronic tags to measure the thermal experience of 384 adult Atlantic cod from eight different stocks found in the NE Atlantic. Over 100,000 days of data were collected in total. The data demonstrate that cod is an adaptable and tolerant species capable of surviving and growing in a wide range of temperate marine climates. Total thermal niche ranged from -1.5°C to 19°C; this range was narrower (1°C to 8°C) during the spawning season. Cod in each of the stocks studied had a thermal niche of approximately 12°C, but latitudinal differences in water temperature meant that cod in the warmer, southern regions experienced three times the degree days (~4000 DD year-1) than individuals from northern regions (~1200 DD year-1). Growth rates increased with temperature, reaching a maximum in those cod with a mean thermal history of between 8°C and 10°C. Our direct observations of habitat occupation suggest that adult cod will be able to tolerate warming seas but that cod populations may still be affected because the effects of marine climate change will impact cod at earlier life-history stages or via indirect effects on prey species