Status and progress in WP5 by month 36

Summary

This work-package has produced a publicly available review of population dynamic parameters for each of the two target lantern-fish species in the Report on Initial Demographic Parameters (Review, Sampling and Estimation of Key Demographic Parameters for Pearlside Maurolicus muelleri & Glacier Lantern Fish Benthosema glaciale). The report presents a review of existing information on key demographic parameters from published literature as well as current outputs so far collated from MEESO. Additionally, the TropFishR length-based and data-limited stock assessment methodology has been used to determine spatio-temporal variability in growth parameters and mortality rates required for the estimation of MSY. The outputs from this work have been prepared as a scientific publication currently in submission with a peer-reviewed scientific journal. 

WP5 has continued to focus on producing a functional ensemble of models ready for use in assessment of harvest strategy and climate change scenarios. The models are the spatial population model StrathSPACE, the NORWECOM.E2E end-to-end ecosystem model, and the global mid-trophic-level SEAPODYM-LMTL model, developed by project partners STRATH, IMR, and CLS respectively. Current work is focussing on model parameterisation using new-available data. StrathSPACE is a single-species discrete time and space closed life-cycle population mode implemented for both target species. Under a repeating year we can drive the model to a stationary yearly cycle and calculate a fisheries yield under a range of (constant) fishing mortalities to generate yield curves. Carrying this out for selected years across the 100-year NEMO run generates a family of yield curves which change as the physical drivers change with climate change. The initial results from the Benthosema model indicate forecasted declining yield as a result of ocean warming in relation to the stock thermal preference. The NORWECOM.E2E model is an end-to-end coupled 3 dimensional physical, chemical, and biological model of the Nordic Seas at a resolution is 10-20 km grid horizontally and 21 vertical layers with Individual Based Models of target species. The Benthosema glaciale IBM module involves approximately 20000 super-individuals, horizontal movement by drift, vertical movement driven by light, foraging and growth based on visual range and bioenergetics, and reproduction as a function of surplus acquired energy. Results shows that there are large spatial and seasonal variations in both biomass and growth rates of adults over the model domain, and strong latitudinal and seasonal changes in diel vertical migration. CLS is implementing two configurations of SEAPODYM-LMTL to model the two target mesopelagic species. Model development has included, firstly, implementing modules for the two target species. Secondly, progressing from a sequential code to a parallel one for computational efficiency. And, finally, improvement to the numerical scheme used to implement the model.

Two public e-learning webinars have been produced under work package 5. The first of these from the Technical University of Denmark is on the TropFishR package which includes an introduction to the model estimation of growth, mortality and gear/fishery selectivity and its application to mesopelagic fish species. The second, from the University of Strathclyde, is an outline of the StrathSPACE Model on modelling Mesopelagic fish with the “StrathSpace” approach.

Highlights

• Data analysis of growth and mortality data shows substantial variation between species and substantial variation in space within species.
• The sources of the observed spatial variability are undetermined and are confounded by different sampling protocols in different regions. 
• The spatial variability in these demographic rates may indicate regionally differences in the potential for sustainable exploitation. 
• Currently there is little evidence of distinct stocks in the North-East Atlantic, and more standardized monitoring data is recommended. 
• Results from the population models indicate patchiness in space and time (seasonally and inter-annually) and stock sensitivity to moderate to high exploitation rates (StrathSapce and NORWECOM), whereas the third model (SEAPODYM) shows higher resilience. 
• The forward runs driven by climate change scenarios, available for StrathSPACE, predict an overall decline in abundance of these species in the northeast Atlantic even in the absence of fishing. Moreover, sustainable yields from modelled fisheries of both species are highly variable inter-annually but also show a declining overall trend.